THE MAYA-CHORTÍS BOUNDARY: A TECTONOSTRATIGRAPHIC APPROACH

Fernando Ortega-Gutiérrez1, Luigi A. Solari1, Carlos Ortega-Obregón1, Mariano Elías-

Herrera1, Uve Martens2, Sergio Morán-Icál3, Mauricio Chiquín3, John Duncan Keppie1,

Rafael Torres de León1, Peter Schaaf4

1 Instituto de Geología, Universidad Nacional Autónoma de México

2 Department of Geological and Environmental Sciences, Stanford University, USA

3 Universidad de San Carlos, Cobán, Guatemala

4 Instituto de Geofísica, Universidad Nacional Autónoma de México

Corresponding author: Fernando Ortega Gutiérrez

fortega@servidor.unam.mx

Tel. +5255-56224300, ext. 106

Fax +5255-564289

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ABSTRACT

This work presents an updated revision of the complex stratigraphic and tectonic

relationships that characterize the geologic boundary between the Chortís and Maya

continental blocks of the Caribbean region. Based on field, petrologic, structural and

geochronological work in key areas of central Guatemala, we propose a new

tectonostratigraphic structure that appraises more fully the fundamental tectonic role of

the multiple major faults that cut across the continental isthmus between the Americas,

and bounds separate stratigraphic packages that may well qualify as

tectonostratigraphic terranes (or fault blocks according to JDK). Accordingly, we

subdivide the area into seven of theses units, which from south to north are as follows:

1. Chortís, 2. Yoro, 3. Sula, 4. El Tambor, 5. Jacalteco, 6. Achí, and 7. Maya, bounded

respectively by the Agúan-La Ceiba, Jocotán-Chamelecón, Motagua, Baja Verapaz,

and Chixoy-Polochic fault zones. Unfortunately, the extreme paucity of modern geologic

data bearing on the pre-Cretaceous cover and basement units in the entire region,

constitutes a major obstacle for building up convincing paleogeographic models that

may explain the complex tectonic evolution of the area from Precambrian to Cenozoic

times. Consequently, this work should be taken as a valuable line to understand more

clearly the nature and contact relationships between deep crustal blocks in the Nuclear

Central America area, and as a contribution to the ultimate endeavor of restoring their

geologic evolution in the modern paradigm of plate tectonics.

1. INTRODUCTION

The integral geology of the Central America-Caribbean region was first presented in the

monumental work of Schuchert (1935), followed by the opus magnus of Sapper

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(1937), then well described in relation to its mineral deposits (Roberts and Irving,

1957), subsequently comprehensively treated by Butterlin (1977) and Weyl (1980),

and most thoroughly reviewed on occasion of the Centennial Decade celebration of the

Geological Society of America by Donnelly and others (1990). Subsequently, geologic

research in the area has been mainly directed toward fundamental questions about the

Mesozoic and Cenozoic tectonic evolution of the Caribbean realm (e.g. Pindell and

Barret, 1990; Heubeck and Mann, 1991; Beccaluva et al., 1995; Meshede and

Frisch, 1998; Rogers, 2003), including a complete volume of the Geologica Acta

dedicated to plate tectonics implications of the Caribbean (Iturralde-Vinent and Lidiak,

2006), and yet very little has been published about the metamorphic basement

complexes, or the pre-Jurassic cover of the Central America subcontinent, which

constitutes a critical element bridging the North American and South American cratons.

Complex geological conditions require careful assessment of the local and regional

stratigraphy before meaningful reconstructions of past geological history are attempted.

In this regard, the pre-Mesozoic stratigraphic composition of the Chortís and Maya

blocks (Dengo, 1969), as well as the intervening old crustal slices, have to be

considered as completely as possible before establishing robust correlations with the

pre-Mesozoic rocks of continental areas of Mexico, northern South America, and the

United States. In this paper, we use well established tectonostratigraphic criteria (e.g.

Coney et al., 1980; Howell, 1985) to differentiate fault-bounded geologic entities in the

region and to group them in three major domains: 1) Chortís block (Dengo, 1969), 2)

Maya block (Dengo, 1969), and 3) intervening fault-bounded crystalline complexes

(note that JDK prefers the term “fault blocks” rather than terranes for these fault-

bounded blocks because the age of many of the units is too uncertain to be sure if one

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is comparing rocks of the same age: see Keppie, 2004). The latter group is herein

defined as a series of crustal slices formed by metamorphic basement complexes

located between the Polochic-Cuilco-Chixoy fault system in the north, and the Jocotán-

Chamelecón-La Ceiba in the south (Figure 1). With this approach, the main purpose of

the study is to present a new regional stratigraphic framework that may serve to better

accommodate and understand the abundant data that is presently produced by a

growing international community working in the area.

2. NORTH WESTERN BOUNDARY OF THE NORTH AMERICA-CARIBBEAN

PLATES

The boundary between the Caribbean and North America plates in the Central

American region is marked (Figure 1) by a diffuse arcuate system of roughly E-W

trending faults, concave northwards with a mean radius of about 300 km centered at the

northern Mexico-Guatemala border near the town of Paxbán. From south to north, the

Jocotán-Chamelecón, San Agustín-Motagua-Cabañas, and Cuilco-Chixoy-Polochic fault

systems, subsequently referred respectively as Jocotán, Motagua, and Polochic faults

for simplicity, currently define this composite structural boundary. On the other hand,

Guzmán-Speziale, (1989, 1998) extended the active part of the plate boundary as far

north as the Chiapas fold-thrust belt in southeastern Mexico (see Figure 1), and

proposed left lateral displacements of about 70 km accumulated on 9 major faults. We

think, from field work in the area and the analysis of satellite imagery, that the Polochic

fault splays into two main branches: a) the Cuilco-Motozintla fault that intersects the

Mexican border near Amatenango de la Frontera, following from there about 20 km up

to the Motozintla River headwaters where it seems to end, contrary to other models (i.e.

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Burkart et al., 1987) that continue the fault westwards gradually bending it northward to

follow the southern limit of the Soconusco batholith, and b) a structural lineament

complex that departing from just west of Huehuetenango in Guatemala follows the

Selegua River and continues across the Mexican border along an arcuate fault, which in

turn joins at Mapastepec with a major shear zone defining the southern margin of the

Chiapas batholith (Figure 1). This major fault was named as the Tonalá shear zone

(Wawrzyniec et al., 2005) and is marked by vertical mylonites dated (Ar-Ar) at 8.0 ± 0.1

Ma with left lateral kinematics (Tovar-Cortés et al., 2005). The Motagua fault, on the

other hand, although apparently interrupted or buried in central Guatemala by the most

recent volcanic deposits, may be traced into Mexico following the E-trending Belisario

Domínguez mylonitic shear zone that intersects the Mexico-Guatemala border near the

Tacaná volcano (Figure 1), and it may continue from there eastward under the

Guatemalan volcanic cover, to merge with the westernmost exposed trace of the

Motagua fault south of Huehuetenango.

Present activity along these faults (Malfait and Dinkelman, 1972; Dengo, 1985;

Donnelly et al., 1990; Cáceres et al., 2005), is recorded along the Motagua-Polochic

fault system (Figure 2), as dramatically demonstrated by the 1976 earthquake (Ms =

7.5, Plafker, 1976; Kanamori and Stewart, 1978) with measured sinistral

displacements up to 2 meters along the Motagua-Cabañas fault, and the by the large

Guatemalan earthquake of 1816 (MW = 7.5-7.75) with epicenter at the Polochic fault

(White, 1985). The present displacement rate of the Caribbean plate relative to the

North America plate is around 2 cm/year (e.g. De Mets et al., 2000). Other authors (e.g.

Burkart, 1983) proposed that the northern Caribbean limit was successively occupied

since Miocene times by one of the three main faults: Polochic, Motagua, and Jocotán.

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Cumulative displacements proposed across these faults vary from more than 1100 km

(Mann and Burke, 1984; Rosencrantz and Sclater, 1986; Rosencrantz et al., 1988)

to only a few hundred kilometers, with a maximum displacement of 130 km taken by the

Polochic fault, as documented by Burkart (1978, 1983), and Deaton and Burkart

(1984). The remaining offset (>1000 km), if true, should be recorded by the Motagua-

Jocotán and other undocumented faults south of the Polochic. However, total

displacements based alone on geologic relations of these faults are essentially

unknown (Gordon and Muehlberger 1994), or up to 300 km (Manton, 1987). The

Polochic fault extends westward across central Guatemala and constitutes the

northernmost and distinct structural element of the inferred northwestern Caribbean

Plate boundary. To the west, and just before entering Mexico, it appears to develop a

horsetail pattern that does not reach the Pacific Ocean, whereas other authors have

advocated continuity of the Polochic fault to the west where it either intersects the

Acapulco trench at a putative triple junction in the Gulf of Tehuantepec area (e.g. De

Cserna, 1958; Muehlberger and Ritchie, 1975; Burkart and Self, 1985), or along the

southern margin of the Chiapas batholith (Lapierre et al., 2000). An eastward 45º

deflection of the NW-trending Chiapas-Petén fold-and-thrust belt (from NW to E-W) as it

approaches the E-W-trending Polochic fault indicates a minimum left-lateral

displacement of about 150 km (assuming the bending is linked with faulting). The

continuity of the present Cayman Trough and main Guatemalan fault systems, with the

ancestral Middle America trench in the past, is implicit in models that advocate up to

1400 km of Eocene-Miocene, left-lateral displacements of the Chortís block off the

margin of southwestern Mexico. This order-of-magnitude difference and uncertainty in

possible Cenozoic displacements between the Chortís and Maya blocks places severe

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constraints to robust paleogeographic reconstructions of the region as discussed below.

On the other hand, Keppie and Morán-Zenteno (2005) propose that the Eocene

boundary between the North America and Caribbean plates may be projected

southwestward along the strike of the Cayman faults beneath the Central America arc

and coinciding with a gravity anomaly, allowing the Chortís block to move 1100 km

about a pole of rotation located near Santiago de Chile northeastward from the Pacific

Ocean to its present position.

3. STRATIGRAPHY

The region of Central America has been naturally subdivided into blocks or terranes

with contrasting stratigraphic columns (Figure 3) separated by major faults (e.g. Dengo,

1969; Horne et al., 1976; Case et al., 1984). Each block contains a distinctive

crystalline basement with poorly known ages exposed under a cover of sedimentary

and volcanic rocks, the age of which may be as old as early Paleozoic (this work), to as

young as Neogene. Unfortunately, stratigraphic correlations among the blocks (e.g.

Figure 2 of Horne et al., 1976), have been plagued by the paucity of fossiliferous rocks

in the pre-Cretaceous cover, as well as by the lack of reliable isotopic ages for their

crystalline basements; consequently, the relative mobility and magnitude of offsets

across the major faults in the studied area still remain as principal subjects of study and

debate. From south to north we now describe the crystalline basement components

(Figure 4) of three tectonostratigraphic domains: a) Chortís block, b) fault-bounded

crystalline terranes, and c) Maya block, followed by a general description of the pre-

Cretaceous volcanic and sedimentary cover across the area

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3.1. Pre-Mesozoic crystalline basement units of Chortís and Maya blocks

3.1.1. Chortís Block

Nelson et al., (1997) stated that U/Pb zircon crystallization ages and Sm-Nd data

indicate that the Chortís crust in Guatemala and Honduras “is mainly of Grenville age or

has an inherited Grenville component.” If the Chortís block indeed extends to the

Motagua fault zone, the oldest rocks reported (Grenvillian) from the Chortís block crop

out south of the Jocotán-La Ceiba fault between the El Progreso and Yoro (Figure 1) in

NW Honduras (Manton, 1996). Mesozoic sedimentary rocks cover this basement

terrane and it is in fault contact with low-grade units of the undated San Diego Phyllite.

Unfortunately, the data are in abstract form and the full appraisal of geologic

relationships and precision of the study cannot be assessed, particularly in the apparent

absence of supracrustal rocks of Paleozoic age throughout the Chortís block. These

metamorphic rocks were included in his more recent work (Manton and Manton, 1999).

Along the northern limit of the Chortís block in Guatemala, between the Motagua and

Jocotán faults, orthogneissic units of Las Ovejas Complex in southeastern Guatemala,

and equivalent lithologies of Sierra de Omoa in northwestern Honduras (Bañaderos

complex) were also dated by Rb-Sr as possibly Precambrian (Horne et al., 1976).

However, although these rocks are commonly included in the Chortís block, their fault-

bounded nature casts some doubts on their inclusion within the Chortís block, and thus,

we choose to describe them under the intervening domain of fault-bounded crystalline

terranes.

Well within the Chortís block, crystalline basement units crop out in central Honduras

(Fakundiny and Everett, 1976), and northwestern Nicaragua (Nueva Segovia District).

The oldest sedimentary packages overlying this basement consist of low grade, Late

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Triassic (?) to Middle Jurassic marine and continental metasediments of the Agua Fría

Formation (Ritchie and Finch, 1985) that, in turn, underlie with strong angular

unconformity Lower Cretaceous clastic and carbonate platform marine sequences

(Tepemechin Formation and Yojoa Group), followed by red beds of the Upper

Cretaceous Valle de Angeles Group. Detailed descriptions of these basement

complexes of the Chortís and Maya blocks are given below proceeding from the

southeast (Nicaragua) to the northwest (Guatemala, Belize, and southeastern Mexico).

3.1.1.1. Cacaguapa Group (Fakundiny, 1970) and equivalent formations in Nicaragua:

(Palacaguina of Zoppis, 1957), and Petén Formation in Honduras (Carpenter, 1954)

Extensive outcrop areas in northwestern Nicaragua and northeastern Honduras contain

low and very rarely high-grade metamorphic rocks of volcanic and sedimentary origin.

They are considered of Paleozoic age because limited radiometric dating (Pushkar et

al., in Horne et al., 1976) suggest a maximum Silurian age (412 Ma), and apparently

rest unconformably beneath Middle Jurassic rocks of the Agua Fría Formation (Viland

et al., 1996), or Late Triassic-Jurassic sedimentary rocks of the El Plan Formation

(Carpenter, 1954; Maldonado-Koerdell, 1953). The Cacaguapa Group or Schist

(locally called Petén and Palacaguina formations) is described more generally as a

sequence of phyllitic micaceous and graphitic rocks with abundant concordant quartz

veins and pyrite casts, locally grading to garnet schist, metaconglomerate, quartzite,

metavolcanics (meta-andesite and meta-rhyolite), and including a distinctive

augenschist characterized by intersecting foliations. In the El Porvenir quadrangle (not

shown in Figure 1) of Honduras, Simonson (1981) described epidote-amphibolite

facies rocks beneath Jurassic beds that consist of garnet-chloritoid-biotite-albite-chlorite

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schists, marble, and mylonitic augengneisses with up to three phases of deformation. A

few kilometers northeast of La Chacra, in central Honduras, Fakundiny and Everett

(1976) report “Paleozoic” quartz-muscovite schists unconformably overlain by Jurassic

“shales” of the Agua Fría Formation. Particularly intriguing are the antigorite

serpentinites and related mafic and ultramafic rocks reported by Emmet (1988) from the

Guanaja Quadrangle of central Honduras, as these, possibly ophiolitic tectonites, would

suggest the presence of major sutures of unknown age well within the Chortís block. It

should be kept in mind that local contact relationships of these higher grade crystalline

rocks with the pre-Jurassic phyllitic units have been described as unconformable,

tectonic or gradational, and the generally assumed Paleozoic age for the more strongly

metamorphosed rocks must be verified before considering them as true pre-Mesozoic

basement.

3.1.1.2. Nueva Segovia Schist (Del Giudice, 1960)

Most outcrops of this metamorphic complex occur in the alto Río Coco area of Nueva

Segovia District in northwestern Nicaragua (see Figure 4a). They are described as

phyllites, quartzites and mica schists, some of which still preserve primary sedimentary

features (Paz-Rivera, 1962). However, a small outcrop of these rocks described at

Macuelizo, Nueva Segovia by Echávarri-Pérez and Rueda-Gaxiola (1962) consists of

quartz, muscovite, biotite, sericite, rutile, hematite, chlorite, tourmaline, and opaques.

Furthermore, in another local report (Piñeiro and Romero, 1962), the metamorphic

rocks exposed in a nearby area are described as consisting of schists, phyllites,

marbles, quartzites and gneisses, thus indicating the possible presence of basement

formations with different ages and exposure depths. The lower grade metamorphic

rocks are intensely folded and intruded by abundant veins and pods of quartz. A

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gneissic rock that crops out near the Carao village over the Mosonte River consists of

quartz, biotite and muscovite. The rocks are intruded by batholithic bodies of granitic to

dioritic composition, and covered nonconformably by coarse continental clastics of

Tertiary age known as Totogalpa Formation (Del Giudice, 1960). According to Rogers

(2003) the Middle Jurassic Agua Fría Formation, east of the Guayape fault, shows a

transition to low-grade metasediments, which elsewhere have been considered part of

the Paleozoic Cacaguapa Schist. On the other hand, the common presence in the

Quebrada Santa Ana, and Mosonte River areas of schists and gneisses with biotite,

pyroxene, graphite, oligoclase and cordierite, suggests the existence of high-grade

rocks.

3.2. Intervening fault-bounded crystalline complexes or terranes

Between the Polochic fault in the north and the Jocotán fault in the south, several

crustal slices tens of kilometers wide and composed essentially of high-grade crystalline

rocks, crop out defining the main mountain ranges of Central Guatemala and

northwestern Honduras. The Motagua Valley, on the other hand, is mainly occupied by

volcano-sedimentary and low-grade metamorphic rocks of oceanic affinity constituting a

composite tectonostratigraphic terrane with its Cenozoic cover: the Late Jurassic-

Cretaceous El Tambor Group (McBirney, 1963; McBirney and Bass, 1969; Wilson,

1974; Beccaluva et al., 1995; Giunta et al., 2002. This composite terrane, however,

will not be considered in detail here, as it consists of a late Mesozoic accretionary

wedge of tectonic slices and melange that rest above, or abut against older basement

and pre-Cenozoic units of the Maya and Chortís blocks. At many places most rocks of

this Jurassic-Cretaceous sequence appear to form rootless allochthons derived from

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Late Jurassic-Early Cretaceous arc-ocean complexes associated with the evolution of

the Caribbean area (Dengo, 1972; Williams, 1975; Rosenfeld, 1981; Lewis et al.,

2006). Further descriptions and discussion of tectonic and paleogeographic models

constitute a complex subject far beyond the purposes of this paper, which mostly

focuses on pre-Mesozoic history of the Chortís-Maya region.

3.2.1. Precambrian Yoro complex

South of the Jocotán fault and north of the inferred southern continuation of the Aguán-

Esperanza fault, between the towns of El Progreso and Yoro in northwestern Honduras,

high-grade metamorphic and crystalline basement rocks, here named as Yoro Complex,

are exposed (Manton, 1996; Manton and Manton, 1999). They extend 60 km along a

WNW-trending strip with a maximum width of 10 km, and consist of massive and

banded granitic gneisses, together with minor greenschist-lower amphibolite facies

micaceous to garnetiferous metapelites, that are intruded by lineated granites. The

granites were dated (Manton, 1996) and yielded concordant U-Pb data on zircon at

1000 Ma, with a Sm-Nd model age of 1400 Ma. Low-grade metasedimentary rocks

occur in the same area, but their contact relationships are undetermined. Because the

age and nature of these high grade rocks differ from adjacent basement units (Las

Ovejas Complex on the north, and Cacaguapa Schist on the south), and they lie

between the Jocotán fault to the north and Aguán-Esperanza faults to the south (see

Figures 1 and 10), the Sula-Yoro block may be considered as the southernmost

tectonostratigraphic slice interposed between the less deformed Maya and Chortís

blocks.

3.2.2. Las Ovejas-Omoa Complex

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The high-grade metamorphic rocks exposed between the Motagua and the Jocotán

faults structurally overlain by ultramafic late Campanian allochthons of El Tambor

sequence, were grouped under the name of Las Ovejas Complex (Schwartz, 1977) in

Guatemala, and Omoa complex in Honduras (Horne et al., 1976). The former

sequence was described in detail at El Progreso quadrangle as consisting of gneiss,

schist and migmatite, with sporadic thin beds of white marble, and defining a strip

parallel to the E-W trend of the Motagua fault with a maximum width of 22 km. The best

outcrops occur between the El Tambor and Las Ovejas rivers, and in the Zacapa-

Gualán area of east-central Guatemala (see Figure 4b). Structurally, Las Ovejas

Complex consists of an upper part formed by granitic gneisses and intercalated marble,

and a lower sequence of dioritic gneisses and amphibolites. However, common

migmatitic aluminous metapelites with garnet, sillimanite, staurolite and potassium

feldspar indicate abundant sedimentary protoliths affected by middle to upper

amphibolite facies metamorphism that was accompanied by migmatization. Las Ovejas

Complex is intruded by the 50 ± 5 Ma (K-Ar) Chiquimula pluton and covered tectonically

by the late Campanian to Aptian ophiolitic nappes. Eastwards, Las Ovejas Complex

eventually merges with the Omoa Complex in the Sierra de Omoa, of northwestern

Honduras. Here, metamorphic rocks near San Pedro Sula are remarkably similar to

those of Las Ovejas Complex, except that marbles are poorly represented, whereas

kyanite is common along with garnet and staurolite. Poorly defined early Paleozoic to

Late Precambrian Rb-Sr ages (980-460 Ma) were reported (Horne et al., 1976) for

some of the Omoa orthogneisses (Bañaderos Complex) intruding the metasedimentary

units. More specifically, these authors dated a granitic pluton at 305 ± 12 Ma (Rb-Sr

whole-rock isochron) that crosscuts infolded medium-grade calcareous to silicic and

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metavolcanic units in the eastern part of Sierra de Omoa. On the other hand, similar

low-grade metavolcanic rocks dated as Mesozoic (Ave-Lallemant and Gordon, 1999)

occur further east in the Roatán Island. The only “well" dated intrusion into the Omoa

Complex is an undeformed adamellite-granodiorite pluton yielding an age (Rb-Sr) of

150 Ma. Early Cretaceous sedimentary rocks rest unconformably on the low- and high-

grade units in the area, indicating a minimum Jurassic age for the metamorphic

basement of this fault-bounded crystalline unit extending between the Motagua and

Jocotán faults.

3.2.3. Chuacús Complex

Although this metamorphic complex is commonly considered the basement of the Maya

block in Guatemala, it is, in fact, bounded by large-scale faults (Baja Verapaz and

Motagua), and true unconformable stratigraphic relationships with neighboring late

Paleozoic sedimentary rocks of the Santa Rosa Group have not been demonstrated.

For this reason, we prefer to group the unit within the fault-bounded tectonostratigraphic

domains of Nuclear Central America separating the more stable Maya and Chortís

continental blocks.

The Chuacús Complex was originally referred to as Chuacús Series (McBirney, 1963)

and then changed to Chuacús Group by Kesler et al. (1970). In a more recent

publication (Ortega-Gutiérrez et al. (2004) proposed the name Chuacús Complex, in

conformity with current stratigraphic nomenclature for high-grade metamorphic or

structural terranes where primary stratigraphic relations have been essentially

destroyed (Whitaker et al., 1991; International Subcommission on Stratigraphic

Classification, 1994). Ortega-Gutiérrez et al. (2004) reported a pervasive eclogite

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facies event that conveyed a fundamentally new tectonic significance to the entire unit

because of the strong possibility that pressure conditions occurred in the coesite or

diamond fields of ultra-high pressure metamorphism.

The type locality lies at the Sierra de Chuacús of central Guatemala, where the first

systematic study and definition of the metamorphic unit was published (McBirney,

1963). Later, the sequence was extended and mapped as the Western Chuacús by

Kesler et al. (1970), and subdivided into several lithostratigraphic units in areas

adjacent to the Motagua fault zone of east central Guatemala (Newcomb, 1978; Roper,

1978). Previous and more detailed studies exist in several unpublished thesis (Bosc,

1971; van den Boom, 1972; Schwartz, 1976). The ages determined for the Chuacús

Complex are poorly known, as they range from the Precambrian (e.g. Gomberg et al.,

1968), late Paleozoic (Ortega-Gutiérrez et al., 2004), to as young as the Late

Cretaceous. The metamorphic complex consists throughout of banded, highly

aluminous gneisses and schists formed originally in the eclogite and amphibolite facies

(see Figures 4c-d) that later underwent several events of retrogression and

mylonitization (Figures 4e-f) related to continued orogeny since its formation probably

in the Paleozoic (Ortega-Gutiérrez et al., 2004). Non-conformable relationships

between the upper Paleozoic Santa Rosa Group and the Chuacús Complex, as

proposed by McBirney (1963), have been generally considered proof of its pre-

Pennsylvanian age (McBirney and Bass, 1969; Carfantan, 1985, p. 196; Donnelly et

al., 1990). However, detailed studies carried out by us in the same area (Figure 5),

have failed to support this contention and demonstrate instead that the northern limit of

the Chuacús Complex is located tens of kilometers south of the Polochic fault, where it

is abruptly faulted against a low-grade siliciclastic sequence (the Salamá schist of van

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den Boom, 1972), which in turn was intruded by the Rabinal granite, recently dated as

early Paleozoic (Ortega-Obregón, 2005). This relationship may be extended

westwards to the Huehuetenango area, where a thin band of low grade metasediments

similar to those formerly included in the Salamá schist and intruded by muscovite

leucogranites strongly resembling certain facies of the Rabinal pluton, separates the

Western Chuacús retrograde gneisses to the south, from the Maya block located north

of the Polochic fault where the upper Paleozoic Santa Rosa Group is widely exposed.

Therefore, in our opinion, the age of the Chuacús Complex is still unconstrained by

stratigraphic relations, whilst radiometric ages are also scarce and controversial. The U-

Pb age of 305 ± 5 Ma recently published (Ortega-Gutiérrez et al., 2004) for the

migmatization event represented in the El Chol area (about 15 km south of Rabinal)

within the Chuacús Complex should presently be considered the best evidence for its

pre-Mesozoic age. Previously, Gomberg and others (1968) obtained a mixed age from

rocks of the Rabinal granite and Chuacús Complex at 1075 ± 25 Ma, but warned about

the possibility of zircon inheritance from unknown Precambrian sources. Other Rb-Sr

data assigned an age of 395 Ma to one Chuacús gneiss (Pushkar, 1968), whereas

most K-Ar data obtained from different minerals (white mica, biotite, and hornblende)

across all of the Chuacús Complex and published by several authors (Gomberg et al.,

1968; Ortega-Gutiérrez et al., 2004), fall in a narrow interval between about 70-60 Ma,

indicating a pervasive, Late Cretaceous event superposed on the Chuacús Complex

that reset all relatively low temperature “geoclocks”. However, provided there is no

excess argon, a previous event may be recorded in some hornblendes from Chuacús

amphibolites that yielded a 40Ar/39Ar age of 238 Ma (Donnelly et al., 1990), and several

16

Paleozoic hornblende and mica dates that we have measured (unpublished data) in

migmatitic gneisses at El Chol area.

3.2.4. San Gabriel-Rabinal suite

Low-grade clastic rocks, here referred to as the San Gabriel sequence after a small

town between the cities of Salamá and Rabinal (see Figure 5), crop out in close

intrusive relationship with the Rabinal granite of the Baja Verapaz area. This unit was

formerly considered part of the Chuacús Complex and named the Salamá schist (van

den Boom, 1972). It constitutes a critical and independent sequence separating high-

grade gneisses of the Chuacús Complex to the south, from typical Paleozoic

sedimentary and probably Precambrian basement rocks of the Maya block to the north.

The newly-defined Baja Verapaz shear zone (Ortega-Obregón et al., 2004) (Figure 5)

defines a wide (ca.10 km), moderately south-dipping, left-lateral oblique thrust that

places retrograde gneisses of the Chuacús Complex above the low-grade granite-

metasedimentary terrane to the north. Whereas intrusive relationships of the Rabinal

granite and the San Gabriel sequence are clearly exposed between the towns of

Salamá and Rabinal, similar granites at Huehuetenango intruding the Chuacús

Complex and low-grade units comparable to the San Gabriel sequence may or may not

correspond with the Rabinal granite. At Chixolop (Figure 5), a small village east of

Salamá, deformed limestone and shales with conodonts of Early Mississippian age, and

thus older than the Sacapulas Formation of the Maya block, rest unconformably on the

San Gabriel sequence and the Rabinal granite (Ortega-Obregón et al., 2004, Ortega-

Obregón, 2005) indicating a pre-Mississippian stratigraphic age for both units. On the

other hand, near the village of San Francisco (see Figure 5) and at the eastern road

17

entrance to Salamá, coarse-grained sedimentary units, including basal

metaconglomerates with abundant pebbles of deformed (mylonitized) and undeformed

granites similar to Rabinal granite, may represent strata equivalent to the Sacapulas

Formation. These granitic pebbles in the basal conglomerates at San Francisco and

Salamá support an important nonconformity between the late Paleozoic rocks above,

and the Rabinal granite-San Gabriel sequence below. The observed stratigraphic

relationships are consistent with K-Ar ages recently obtained by us for igneous

muscovite books in pegmatites of the Rabinal Granite intruding the San Gabriel

sequence, which dated the granite between 440 and 429 Ma (Ortega-Obregón, 2005).

3.3 Maya block

The Maya block is currently extended westward across the Isthmus of Tehuantepec into

the Mixtequita area, where Grenvillian basement granulite facies rocks are intruded by

late Paleozoic to Jurassic plutons (Weber and Köhler, 2001; Restrepo-Pace et al.,

2002). However, east of the Tehuantepec Isthmus, the Maya block is extensively

covered by Mesozoic and Cenozoic formations, and only in the Chicomuselo area, the

Maya Mountains of Belize (Dixon, 1955; Steiner and Walker, 1996; Steiner, 2006),

the Chiapas batholith (Schaaf et al., 2002; Weber et al., 2005), and in the core of the

Altos Cuchumatanes in Guatemala (Anderson et al., 1973; this work) pre-Mesozoic

crystalline rocks and late Paleozoic sedimentary units are well exposed. On the other

hand, east of the Isthmus of Tehuantepec exposed Grenvillian crust is essentially

absent, thus making the Grenvillian integrity of the Maya block across the isthmus

suspect.

3.3.1. The Chiapas batholith

18

The Pacific coast along the entire state of Chiapas in southeastern Mexico is formed by

a continuous crystalline complex known as the Chiapas batholith because most of its

rocks are intrusive granitoids dated as late Paleozoic to Triassic (Schaaf et al., 2002;

Weber et al., 2005), with only a few younger (Jurassic) and possibly older (early

Paleozoic and Neoproterozoic) outliers. In fact, only a few pre-batholithic rocks were

previously known (Pantoja-Alor et al., 1974; Damon et al., in Salas, 1975), until

Weber et al., (2005) recently documented an extensive orogenic event 250-254 Ma old,

including abundant high-grade metamorphic rocks in the Chiapas batholith. These rocks

are represented by migmatites, ortho-, and para-gneisses intruded by undeformed

plutons with ages around 250 Ma. This deep orogenic event is not registered in the

Pennsylvanian-Permian sedimentary rocks exposed in the Chicomuselo area, which

extend along the strike to meet the upper Paleozoic Santa Rosa Group of west central

Guatemalan. Direct contact relationships of the Paleozoic-earliest Mesozoic granitoids

and the older sedimentary units are mostly buried beneath a thick blanket (> 2000 m) of

Middle Jurassic red beds of the Todos Santos Formation. However, the presence of

chiastolite (andalusite) and granitic dikes within sedimentary rocks closely bordering the

granitoids in the Chicomuselo area (Carfantan, 1985), and clearly exposed in the Valle

de Obregón-Amatenango de la Frontera area, demonstrate intrusive relationships, in

accord with the younger radiometric ages obtained from the granites and the

paleontologic evidence of possible Mississippian to Early Permian age of the

sedimentary rocks at Chicomuselo (Hernández-García, 1973).

Although inherited Grenvillian zircons are commonly found in the granitoids (Weber et

al., 2005), no pre-late Paleozoic crystalline rocks of any kind have been satisfactorily

identified in the entire massif. Stratigraphic relationships in the southeastern sector of

19

the batholith show pre-Middle Jurassic marine sedimentary rocks overlying high-grade

gneisses in the Honduras-Pablo Galeana area north of Motozintla. At Barranca Honda,

near the villages of Honduras and Paisthal (not shown in map), crystalline basement

rocks for the late Paleozoic sequence of Chicomuselo are probably exposed

(Carfantan, 1985, p. 116). The sedimentary sequence is represented either by basal

conglomerates, followed by black metapelites and intruded by granites, or

unconformably covered by the Jurassic red beds with basal units containing abundant

pebbles of gneisses, schists, and vein quartz. Additional possible basement rocks found

in our study consist of retrograde, high-grade, quartzo-feldspathic gneisses including

wide bands of garnet amphibolite that suggest minimum formation pressures of 8-12

kbar (e.g. Liu et al., 1996). These pressures stand in contrast with the relatively low

pressures (up to 5.8 kbar at 730-780 ºC) of metamorphism (Hiller et al., 2004) and the

post-Early Permian ages that characterize the paragneissic rocks elsewhere in the

Chiapas batholith.

3.3.2. Maya Mountains

Pre-Mesozoic crystalline, sedimentary and volcanic rocks crop out in the Maya

Mountains of Belize in the heart of the Maya block (Hall and Bateson, 1972; Kesler et

al., 1973; Bateson and Hall, 1977; Steiner and Walker, 1996). Most of the area

(about 8000 km2) consists of upper Paleozoic fossiliferous sedimentary rocks of the

Santa Rosa Group, with the remainder occupied by several plutons, the age of which

range from Silurian to Permian or Triassic (Bateson and Hall, 1977; Steiner and

Walker, 1996). On the other hand, high-grade metamorphic rocks have not been

encountered in the region, and intrusive relationships between some of the plutons and

the Santa Rosa Group rocks are inconclusive. Steiner and Walker (1996) offered a

20

detailed description of the igneous bodies, which in general consist of undeformed, two-

mica granitoids that range in composition from granite to diorite. Three main bodies

were studied, Mountain Ridge, Cockscomb-Sapote, and Hummingbird. The two former

are similar and consisting of leucocratic, unfoliated muscovite-biotite-perthite-oligoclase-

tourmaline granite rich in alkalis (up to 8.32 wt %) and silica (75.58 wt %), whereas the

latter is a granodiorite with 65-66 SiO2 wt %. The zircon U-Pb Devonian-latest Silurian

ages (404-418 Ma) obtained by Steiner and Walker (1996) for three of the Maya

Mountains plutons unfortunately are not well constrained because of strong isotopic

disturbance and paucity of data. Monazite in one of these granites yielded similar Late

Silurian ages, but the data are highly (14-30 %) discordant. Moreover, some of the

conglomerates in the upper Paleozoic sequence include pebbles of contact

metamorphic sedimentary rocks, and one of the plutons dated as Silurian is surrounded

by andalusite-bearing pelites, locally with abundant biotite, sillimanite, garnet, and

staurolite probably of the Pennsylvanian Santa Rosa Group, indicating, in this case, a

younger age for the intrusion. Steiner and Walker (1996) explained this apparent

inconsistency in terms of a hypothetical hydrothermal event triggered by the breakup of

Pangea in the Late Triassic. The common presence in the pelitic rocks of the Santa

Rosa Group of chiastolite (a variety of andalusite) demonstrates that some of these

plutons intruded the upper Pennsylvanian-Lower Permian sequence, and consequently

that they may be of latest Paleozoic to Triassic age. Older formations in the basement

of the Maya block are represented by zircon populations ejected in the Cretaceous from

the Chicxulub crater (Krogh et al., 1993). They yielded a dominant basement

component of 544 ± 5 and 559 ± 5 Ma, and minor populations at 418 ± 6, 320 ± 31, and

286 ± 14 Ma.

21

3.3.3. Altos Cuchumatanes

The metamorphic rocks of the Altos Cuchumatanes uplift are only poorly known. As

described by Anderson et al., (1973), they consist chiefly of “gneiss, schist,

amphibolite, and metavolcanic and metaplutonic rocks”. Based on relict textures and

intense superposed retrogression and cataclasis, these authors considered that the

original rocks were in the upper greenschist and lower amphibolite facies. However,

most of the rocks described in the area lie south of, or at the Polochic fault in the

Huehuetenango District (e.g. Colotenango, Santa Barbara, San Sebastián, and Selegua

river areas), and thus they may or may not belong to the Maya block, but instead could

be part of the fault-bounded Chuacús Complex, or of the structurally underlying Rabinal

granite and San Gabriel sequence (Ortega-Obregón et al., 2004).

Within the dissected part of the Altos Cuchumatanes uplift, 30-40 km north of the

Polochic fault trace and near the town of Barillas (see Figure 1), metamorphic rocks

were described to consist of low-grade metasedimentary rocks (slate and phyllite)

correlative with the lower Santa Rosa Group, as well as limited outcrops of underlying

biotite gneiss, and amphibolite. Abundant granites probably intruded the phyllites

because they contain andalusite. Anderson et al., (1973) described the core of the

Altos Cuchumatanes as consisting mainly of biotite gneiss, mica schist, and amphibolite

correlative with the metamorphic units exposed at or south the Polochic fault in the

Huehuetenango area (Western Chuacús Group of Kesler and others, 1970). However,

along the Amelco River near the town of Barillas, we found well-exposed high-grade

crystalline rocks of metamorphic and igneous origin, including probable high-pressure

lithologies consisting of strongly retrogressed kyanite schists and garnet amphibolites.

22

These rocks are comparable with certain facies of the Chuacús Complex, but differ from

it by the lack of muscovite, which characterizes everywhere the latter unit.

4. PRE-JURASSIC COVER

4.1. Chortís block

No sedimentary or volcanic rocks of proved Paleozoic age are known anywhere in the

Chortís block, even if it is extended to the Motagua fault. However, in Honduras (San

Juancito area), phyllitic rocks (Agua Fría Formation?) as old as Late Triassic were

reported (Maldonado-Koerdell, 1953) based on the presence of Palaeoneilo sp. and

Tropites Mojsisovics, which are similar to marine fossils from the well-known Upper

Triassic Zacatecas Formation of north central Mexico. The underlying Cacaguapa or

Nueva Segovia schists, on the other hand, are considered of Paleozoic age, but this

age has not been proven either. In fact, Rogers (2003) has suggested that there may be

a transitional contact between the Agua Fría Formation of Middle Jurassic age and

these “basement” units. It is clear that this conundrum in the stratigraphy of the Chortís

block deserves the priority attention of researchers interested in finding a home place

for the Chortís block.

4.2. Fault-bounded complexes

The fault-bounded crustal slice situated between Jocotán and Motagua faults, whose

crystalline basement is considered to be Las Ovejas and Bañaderos complexes,

includes sedimentary (San Diego Phyllite) and igneous rocks (granitoids) of possible

Paleozoic age, overlain by marine Cretaceous strata. Because the San Diego Phyllite

has been correlated with the late Paleozoic Santa Rosa Group of the Maya block and is

23

intruded by granitoids as old as Early Jurassic (Hirshman, 1963; Lawrence, 1975;

Horne et al., 1976), it is currently considered of possible Paleozoic age. However, the

San Diego Phyllite lacks any fossils and its contact relationships with Las Ovejas

Complex is either faulted or unexposed (e.g., Lawrence, 1975). Apart from this

intriguing and extensive unit, which crops out on both sides of the Jocotán fault, not

other sedimentary or volcanic units of presumed Paleozoic age have been found south

of the Motagua fault. The San Diego Phyllite is lithologically similar to both, the low-

grade phyllites of the pre-Jurassic Palacaguina and Cacaguapa formations, and to the

slightly metamorphosed phyllites of the Middle Jurassic Agua Fría Formation, and thus

it cannot be specifically correlated on this basis with any of these units that characterize

the metamorphic basement of the Chortís block. The sequence in the San Diego-La

Union region located between the Motagua and Jocotán faults consists of very low

grade (subgreenschist facies) carbonate-free, siliciclastic laminated units varying from

dark metapelite to feldspathic schist and fine grained conglomerates with clasts of chert,

quartzose rocks, vein quartz and pyrite cubes reminiscent of those abundantly found in

the Cacaguapa Schist. Locally, it contains a marked fine-grained tuffaceous component

of felsic and intermediate composition mixed with the carbonaceous phyllites. It shows a

single penetrative foliation with local crenulation folding.

The crystalline basement rocks exposed between the Motagua and Polochic faults are

covered by sedimentary and volcanic rocks deposits of Cenozoic age. The Chuacús

Complex situated between the Motagua and Baja Verapaz faults is unconformably

overlain only by upper Cenozoic volcanics. On the other hand, ophiolitic units of the

Upper Jurassic-Cretaceous El Tambor sequence were thrust over the Chuacús

Complex during the Campanian (e. g. Fourcade et al., 1994) thus implying a minimum

24

Cretaceous age for the overridden basement. Although sedimentary and volcanic rocks

assigned to the late Paleozoic Santa Rosa Group crop out south of the Polochic fault in

the San Sebastián Huehuetenango and Sacapulas areas (Bohnemberger, 1966;

Anderson et al., 1973; Clemons et al., 1974), as well as in the Baja Verapaz area,

direct contact relationships with the Chuacús Complex are not clearly exposed and may

be tectonic, as documented further east in the Salamá area (Ortega-Obregón et al.,

2005). Moreover, no rocks of Jurassic age that commonly blanket the Chortís and Maya

blocks have been reported in the cover of any of the fault-bounded complexes, possibly

due to either non-deposition or profound erosion.

Finally, the mountainous, west-trending strip located between the Baja Verapaz shear

zone to the south and the Polochic fault to the north contains the Silurian Rabinal

granite and the intruded San Gabriel sedimentary sequence covered by a sedimentary

sequence correlated with the Sacapulas Formation of Pennsylvanian age. The Early

Mississippian strata reported from this unit, however, is older than the Santa Rosa

Group typical of the Maya terrane Paleozoic cover, and thus cast some doubts about

their continuity across the Polochic fault.

4.3. Maya block

Mississippian (?) to Early Permian marine sedimentary rocks crop out abundantly in SE

Mexico along the NE flank of the Chiapas batholith near the Guatemalan border

(Hernández-García, 1973), in the Maya Mountains of Belize (Dixon, 1955; Batson,

1972; Batson and Hall, 1977) and in dispersed small outcrops along west central

Guatemala north, and probably south of the Polochic fault (Bohnenberger, 1966;

Anderson et al., 1973; Clemons et al., 1974; Vachard et al., 1997).

25

4.3.1. West central Guatemala

Chicol Formation

The type locality was defined 2-5 km southeast of San Sebastián Huehuetenango,

where rocks exposed along the Chicol and Selegua Rivers on both sides of the Polochic

fault consist of 1000 m of coarse clastics and volcanic rocks affected by deformation

and low-grade regional and contact metamorphism. Granitic sills and dikes intruding the

conglomeratic units (Anderson et al., 1973) may have been fed by the large intrusive

bodies that crop out in the Huehuetenango area, south of the Polochic fault. Moreover,

the abundance of conglomerates in the unit suggested to Anderson et al. (1973)

tectonic and volcanic activity as old as late Paleozoic associated with a precursor or

ancestral Polochic fault. Unfortunately, the formation is bounded by faults associated

with the splayed termination of the Polochic fault in Mexico, and neither its Paleozoic

age nor its presence south of the main trace of the Polochic fault are certain.

Nevertheless, the Chicol Formation was correlated by Anderson et al. (1973) with the

late Paleozoic Sacapulas Formation defined by Bohnemberger (1966) about 60 km

east of Huehuetenango, but based only on their lithologic similarities.

Sacapulas Formation (Bohnemberger, 1966)

According to Donnelly et al. (1990) this unit may be up to 1200 m thick and is similar in

lithology (volcanosedimentary) to the Chicol Formation, although topped by distinctive

limestone beds. It is locally considered to form the base of the upper Paleozoic Santa

Rosa Group and has been be extended to the Salamá area, about 30 km south of the

Polochic fault, where it unconformably overlies pre-Devonian, low grade metasediments

of the San Gabriel sequence and the Rabinal granite.

Tactic Formation (Anderson et al., 1973)

26

This unit consists of interbedded black shale, quartzite and rare beds of limestone and

dolomite. It crops out at or north of Polochic fault and may be more than 800 m thick,

locally converted to slate and phyllite by incipient metamorphism and strong

deformation.

Esperanza Formation (Anderson et al., 1973)

This unit is a fossiliferous, 470 m thick sequence of dark shales and siltstones that

grades into the underlying Tactic Formation, but is distinguished from the latter by the

abundance of >5 m thick limestone beds. The Esperanza Formation grades upwards

into more massive Leonardian carbonates of the Chóchal Formation.

Chóchal Formation (Roberts and Irving, 1957)

This unit and equivalent carbonates in Mexico cap the late Paleozoic sedimentary

column of the Maya terrane. It consists of 500-1000 m of fossiliferous, massive

limestone and dolomite with shale intervals that locally grade into the underlying Tactic

Formation. The abundance and preservation of fossils indicate an age as young as

Roadian (Vachard et al., 2004) at the base of the middle Permian.

4.3.2. Maya Mountains (Belize)

This area exposes by far the majority of late Paleozoic sedimentary rocks in the entire

Maya block. Dixon (1955) first described and named the sedimentary and metamorphic

rocks widely exposed in the Maya Mountains of Belize. He subdivided the sequence

into two separate Series, the Maya (graywackes, phyllites, shales, quartzite, shales, and

some schists and gneisses), and the Macal (conglomerate, sandstone and shales with

Late Pennsylvanian to Middle Permian fossils). Kesler et al. (1971) questioned this

subdivision as they found neither a regional unconformity within the sequence, nor

schists or gneisses, and only one penetrative folding phase affecting both units.

27

Therefore, those authors proposed the Macal Group be extended to the entire

sequence and be considered equivalent to the Santa Rosa Group. The Santa Rosa

Group in the Maya Mountains of Belize (Maya and Macal series) consists of slightly

metamorphosed shale, graywacke, quartzite, conglomerate and some limestone with

late Pennsylvanian to middle Permian fusulinids, and includes some “schists and

gneisses” (Dixon, 1955). Distinctive felsic volcanic rocks in the sequence were mapped

as the Bladen Volcanic Member, which together with the plutonic rocks yielded K-Ar and

Rb apparent Triassic ages between 205 and 237 Ma (Steiner and Walker, 1996). The

volcanic rocks include alkalic rhyolite breccias and andesitic lavas exposed along an

ENE-trending band 25 long and 7 km wide (Bateson and Hall, 1971). Unfortunately,

contact relationships with neighboring plutonic units are poorly known and for the most

part faulted. Although a plethora of local names were assigned to this sequence of

slightly metamorphosed rocks, they may be included in the Santa Rosa Group, which in

Guatemala consists of the Chicol and Sacapulas formations of Pennsylvanian age at

the base, and capped by the Chóchal Limestone of Leonardian age (Figure 6).

Bateson (1972) and Bateson and Hall (1977) described a large area about 4200 km2

(70 x 60 km) trending N60E in the Maya Mountains, where the late Paleozoic rocks are

better exposed. Intrusive granitoids compose about 500 km2 of the outcrop area, and a

thick volcanic unit named the Bladen Volcanic Member formed by mixed rhyolitic, tuffs

and lavas within the sedimentary rocks was separately mapped as a member of the

Group. The Late Pennsylvanian age assigned to part of the sequence on the basis of its

fossils is consistent with the Rb-Sr whole-rock isochron age of 300 Ma for one of the

intrusive granitoids (Bateson, 1972). Intrusive relationships are supported by the growth

of andalusite porphyroblasts as large as 15 cm and small grains of sillimanite in the

28

contact with the surrounding sedimentary rocks. Garnet, biotite and staurolite also occur

locally indicating a considerable depth of intrusion.

4.3.3. Chicomuselo area (SE Mexico)

Late Paleozoic, shallow sedimentary and low-grade metamorphic marine rocks are

continuously exposed within an anticlinorium trending WNW in southeastern Chiapas,

Mexico. The outcrops extend from Comalapa at the border of Guatemala to the

Concordia area for nearly 100 km along the strike and are about 30 km wide. They

contain fossiliferous Middle Pennsylvanian-Early Permian and probably Mississippian,

clastic units in the core, and Permian shales and carbonates in the limbs of the structure

(Hernández-García, 1973). These rocks are poorly studied and their total thickness

estimates vary from about 2700 m (Gutiérrez-Gil, 1956) to more than 7500 m

(Hernández-García, 1973); they have been correlated with the Santa Rosa Group of

Guatemala, and formally subdivided into a lower, weakly metamorphic section (slate-

metaquartzite) of apparent Late Mississippian age, and an upper, unmetamorphosed

section where carbonates rich in fusulinids indicate an Early Permian age for the

youngest carbonates. The contact between the two sequences is an angular

unconformity, which indicates important Carboniferous orogenic perturbations in this

region before the Middle Pennsylvanian.

5. ULTRAMAFIC BODIES

The area between the Jocotán and Polochic fault systems and a few kilometers south of

Siuna in northwestern Nicaragua (Baumgartner, 2004), contain allochthonous bodies

of partly to completely serpentinized peridotites, varying in size from a few hundred

meters up to 80 x 10 km associated with other members of an ophiolitic complex. Main

outcrops of this suite occur in the Sierra Santa Cruz of east central Guatemala

29

(Rosenfeld, 1981). Because mantle rocks in orogenic systems commonly mark the site

of fundamental faults (sutures), establishing the crystallization and emplacement ages

of these bodies would be germane to the tectonic interpretation of the Maya-Chortís

connections in the past. Although the ultramafic units in Guatemala are now considered

part of the Late Jurassic-Cretaceous El Tambor Group, in his pioneer work on the

basement rocks of the Sierra de Chuacús, McBirney (1963) considered the

serpentinites as the main Paleozoic or Precambrian basement for the rest of the rock

column, including the highly metamorphosed units of the Chuacús Complex. Indeed, the

reported presence of serpentinite within the Chuacús Complex west of Rabinal (van

den Boom, 1972), and as cobbles in basal conglomerates of the Middle Jurassic Todos

Santos Formation (cf. Anderson et al., 1973, p. 809), as well as the serpentinite

mélange tectonically beneath the Santa Rosa Group just north of Huehuetenango

(Anderson et al., 1973), indicate the existence of pre-Jurassic serpentinites associated

with a protracted history for some of these major tectonic boundaries.

6. INTRUSIVE POST-PALEOZOIC BODIES

Mesozoic and Cenozoic plutonic igneous rocks of granitic to gabbroic composition are

mainly found in the Chortís block, but are present in all tectonostratigraphic domains

(see Weyl, 1980, Table 9, p. 192-193 for a comprehensive compilation up to that year).

In the interior of the Maya block, several Cretaceous to Tertiary intrusions are exposed

in the Chiapas batholith and adjacent to the Polochic fault. In the Altos Cuchumatanes

generally undated deformed and undeformed granitic intrusions are common. The only

one for which a radiometric age exists in this latter area is a deformed granitoid exposed

in the Poxlac area, with a K-Ar date of 196 Ma reported by Donnelly et al. (1990). Las

30

Ovejas Complex, south of the Motagua fault, is intruded by the Chiquimula pluton dated

(K-Ar) at 50 ± 5 Ma (Clemons and Long, 1971), and the Palacaguina Formation in the

Chortís block is intruded by a pluton with a four-point Rb-Sr isochron age (Horne et al.,

1976) of 140 ± 15 Ma. Several large intrusive granitoids are known from central

Honduras, with K-Ar hornblendes ages ranging from 55 ± 1.1 to 123 ± 2 Ma, and from

59 ± 1 to 118 ± 2 Ma on biotites (McDowell, in Gose, 1985). At San Marcos, Honduras

a granitic pluton dated at 149 ± 7 Ma (Rb-Sr) intrudes the metamorphic basemement

(Horne et al., 1976).

The Chuacús Complex contains scarce granitic intrusions, of which the largest one is

the Matanzas granite that intrudes biotite gneisses of the Chuacús Complex in the

northern slopes of Sierra Chuacús (McBirney, 1963). A Rb-Sr whole rock-mineral

analyses performed on this body yielded ages of 250 and 280 Ma, assuming 86Sr/87Sr

initial ratios of 0.707 and 0.703 respectively (McBirney and Bass, 1969), whereas

biotite and muscovite separates yielded Ar-Ar ages ranging from 161 to 213 Ma (cf.

Donnelly et al., 1990, p. 44). These data, if true, reinforce the pre-Mesozoic age

generally assigned to the Chuacús Complex. Other intrusive rocks in the Chortís block,

mostly dated as Late Cretaceous-Paleogene, form voluminous batholiths, which are

commonly associated with skarn metallic deposits at contact zones with the massive

Cretaceous carbonates (i.e., Drobe and Crane, 2001). Along the Motagua valley and

south of Motagua fault, several intrusive bodies stitching the Las Ovejas Complex

(Omoa Complex of Horne et al., 1976) and the San Diego Phyllite, yielded apparent

Rb/Sr and 39Ar/Ar40 ages from 104 to 35 Ma (Donnelly et al., 1990).

31

7. TECTONOSTRATIGRAPHIC APPROACH

Although the golden age for the terrane paradigm born in the early eighties and

successfully used across the world and into the present century (e. g. Coney et al.,

1980; Jones et al. 1983; Howell et al., 1985; Dickinson and Lawton, 2001) appears

to have passed, there are areas such as Central America where the concept has not

been systematically applied despite the obvious complexity of its rock units and the

hefty faults that characterize the area. As described above, the land extending more

than a thousand kilometers from the Isthmus of Tehuantepec in the Maya block to

central Nicaragua in the Chortís block, includes major displaced pieces of past and

present orogens that have to be considered separately because each package is

characterized by fault-bounded geologic entities that comply fully with the canonical

definition of a terrane (Coney et al., 1980).

7.1. Southern boundary of the Maya block and formerly proposed tectonostratigraphic

terranes in Nuclear Central America

The Maya block is currently considered to abut the Chortís block at the Motagua fault

system (e.g. Dengo, 1969; Avé-Lallemant and Gordon, 1999) without consideration of

the different crystalline complexes that characterize the intervening region between the

two continental platforms. Furthermore, the very presence along the Motagua valley of

the widespread El Tambor Group, composed of ocean-kindred successions that are

tectonically emplaced on all high-grade crystalline terranes from the Chortís to the Maya

blocks, indicate considerable displacements and plate interactions in the region that

render the Chortís-Maya connection a rather complex suture zone.

32

Using the late Paleozoic sedimentary cover (Santa Rosa Group) of the Chicomuselo

basin in southeastern Mexico, north-central Guatemala (Altos Cuchumatanes), and

widely exposed in central Belize (Maya Mountains) as a critical stratigraphic reference

for the identification of the Maya block, the main trace of the Polochic fault could not

represent such limit if clastic and calcareous rocks of Paleozoic age (Bonis, 1967;

Vachard et al., 2000) are proved to stratigraphically overlie crystalline basement (e.g.

Chuacús Complex) south of the fault. In their detailed geologic map Anderson et al.

(1973) show the Chicol Formation of Pennsylvanian age cropping out on both sides of

the Polochic fault, implying little or no post-Paleozoic displacement there. However, the

very small exposure of Chicol Formation (3 km2) mapped south of the fault, may

constitute a rootless allochthonous mass displaced from the north across the Polochic

fault, which probably exposes pre-Middle Jurassic serpentinite at the foot of the scarp

just of north of Huehuetenango; this age is suggested by the presence of pebbles of

serpentinite in the overlying Middle Jurassic red beds of the Todos Santos Formation.

Our current studies in that area, demonstrate that tens of kilometers south of Polochic

fault, at the Rabinal-Salamá region, late Paleozoic fossiliferous sedimentary rocks as

old as Early Mississippian (van den Boom, 1972; Ortega-Obregón, 2005) were

deposited on low-grade metasediments (San Gabriel sequence) intruded by the Rabinal

granite, the igneous micas of which yield K-Ar ages between 429 and 440 Ma (Ortega-

Obregón, 2005). However, these late Paleozoic fossiliferous rocks may or may not be

continuous with Santa Rosa Group of the Maya block because its age is Late

Pennsylvanian to Early Permian, and lack Early Mississippian strata. Thus, the crustal

slice in the Baja Verapaz district of Guatemala, bounded by the Polochic fault to the

north and by the Baja Verapaz fault to the south, is stratigraphically suspect and may or

33

may not constitute a new tectonostratigraphic terrane accreted to the Maya block in the

Carboniferous. Because rocks equivalent to San Gabriel or Rabinal units have not been

found intruding or covering the Chuacús Complex, but they are tectonically juxtaposed

along the Baja Verapaz shear zone (Figure 5), we prefer to define the true northern

boundary of the Chuacús Complex along this newly defined shear zone (Ortega-

Obregón et al., 2004). However, the absence of ophiolitic units occupying the Baja

Verapaz fault zone and its dominant left lateral component, may also suggest that the

Chuacús Complex and San Gabriel-Rabinal units belong to the Maya continental

margin, which were later sliced off from that margin during the Late Cretaceous left

oblique collisional orogeny, and then again displaced in the Cenozoic by left lateral

movements associated with the active Polochic-Motagua fault system.

Reconnaissance studies recently performed in the core of the Cuchumatanes uplift by

us, revealed garnet-rich banded gneiss, garnet amphibolites and kyanite schist

(suggesting former eclogite facies rocks), intruded by deformed and undeformed pre-

Jurassic plutons of possible Permian-Triassic age. This high grade crystalline basement

is best exposed along the Amelco and Ixbal rivers between the villages of Barillas in the

north, and Soloma in the south (see Figure 1), where it seems to be covered by

sedimentary rocks of the Santa Rosa Group, indicating an early Paleozoic or

Precambrian age for the basement of the Maya block in this area.

7.2. Current terrane subdivisions in the study area

Case et al., (1984) distinguished over 100 geologic provinces in the Caribbean-Central

America region, including tectonostratigraphic terranes if bounded by major faults. In the

area of our study, they distinguished about 10 of these geologic provinces, but did not

34

explain which of them were tectonostratigraphic terranes, nor which specific faults

defined the respective boundaries. Nevertheless, they referred to the Chortís block and

the Motagua zone as superterranes.

Based mainly on Pb isotopes of mineral deposits distributed across most of the Central

American region (Figure 7) and magnetic anomalies, Rogers (2003) proposed five

major “terranes” forming the Chortís block in Honduras dubbed as Northern, Central,

and Eastern Chortís continental “terranes”, together with the Mesozoic Southern Chortís

arc and Siuna oceanic terranes (Venable, 1994). Note that this usage does not conform

to the standard definition of tectonostratigraphic terranes that is based on stratigraphy:

Pb isotopes and magnetic anomalies may reflect such terrane boundaries, but the initial

definition requires a stratigraphic basis. On the other hand, the oceanic stratigraphy of

Siuna terrane, in contrast with the continental nature of the Chortis block, does qualify it

as a tectonostratigraphic terrane. Probably the most striking fact in this subdivision is

the similarity of the Pb isotopes of the Central Chortís and Maya terranes in spite of the

intervening ophiolitic complexes and the Motagua, Baja Verapaz, and Polochic fault

zones, as well as their different basement and cover stratigraphies. The Eastern Chortís

(floored by Jurassic sedimentary rocks), and Siuna “terranes”, on the other hand, plot

well outside the Maya lead isotopes, possibly indicating their younger origins. It should

be pointed out that the Central and Northern Chortís “terranes” of Rogers (2003)

contain the highest grade metamorphic complexes so far described from Central

America, namely Las Ovejas Complex of unknown, possibly Paleozoic age, and yet

correlated with the Yoro Complex, dated as Grenvillian. The Southern Chortís arc

“terrane” is shown by Rogers (2003, his Figure 5.8) as a Late Cretaceous (80 Ma)

tectonic accretion to the Pacific margin of the Chortís block synchronously with the

35

emplacement of the Guerrero terrane onto the western margin of Mexico, whereas the

Siuna oceanic “terrane” was accreted to the Chortís block later by Cretaceous-

Paleogene times during the full collision of the Caribbean plate onto the southern edge

of the Maya block. Implicit in this subdivision is the direct connection between the

Chortís and the Maya blocks, with the latter extending south of the Polochic fault as far

south as the Motagua fault, thus comprising within the same block the fault-bounded

Chuacús and San Gabriel-Rabinal crystalline complexes. The 300 km long

transcontinental Guayape fault (Finch and Ritchie, 1991; Gordon and Muehelberger,

1994) juxtaposing blocks with exposed pre-Mesozoic crust and younger Mesozoic

formations, may represent another major terrane boundary within the Chortís block,

thus making this region a truly composite superterrane. However, the Agua Fría

Formation of Middle Jurassic age was deposited synchronously with dextral

displacements along the fault and lays on either side of it (Gordon, 1993); therefore, the

accretion of terranes along this fault, if at all real, occurred before the Jurassic.

However, a full discussion on the nature and evolution of possible terranes within the

Chortís block is again beyond the scope of the present study.

On the other hand, Keppie (2004) divided the region into three blocks: Chortís,

Motagua and Maya based on the occurrence of ophiolites in the Motagua terrane

between two continental terranes.

7.3. Proposed terrane subdivision

The former and more recent terrane subdivision (Rogers, 2003) followed geophysical

and geochemical criteria based mainly on buried properties of the crust beneath the

Chortís block. We prefer to follow more specific stratigraphic and structural criteria that

are visible in the geology of each packet for the definition of terranes in the wider

36

Central America area (Figure 8). Based on our field work on the crystalline complexes

exposed from the Maya to the Chortís blocks as described above, and a review of the

literature that document the presence of major tectonic boundaries truncating their

stratigraphic packages, our terrane names were chosen following the traditional usage

for Central America established by Dengo, (1969), and Anderson and Schmidt

(1983), who named major tectonic blocks in Mesoamerica after the dominant pre-

Hispanic cultures in each region as Maya, Chortís, and Chorotega. From south to

north, we have recognized in the Nuclear Central American region seven fault-bounded

geologic entities (Figure 8) characterized by notable contrasts in their basement

complexes (shown between parentheses), and supracrustal cover as follows: 1. Chortís

(Cacaguapa Group of unknown age, possibly Paleozoic). 2. Yoro (Grenvillian complex).

3. Sula (Las Ovejas Complex of unknown, possibly Paleozoic age). 4. Motagua

(Jurassic oceanic crust). 5. Jacalteco (Chuacús Complex of apparent Paleozoic age). 6.

Achí (early Paleozoic San Gabriel-Rabinal suite). 7. Maya (Barillas complex of

unknown, possibly Paleozoic or Precambrian age). The poor age constraints for many

of these units led one of us (JDK) to prefer the term, fault blocks for most of the

terranes, as contrasts could merely reflect different aged units. These blocks are

separated from south to north by the Aguán-La Ceiba, Jocotán, Motagua, Baja Verapaz

(this work), and Polochic faults. The eastern limit of the Chortís block is currently

defined by the Hess Escarpment and its projection across Nicaragua; however, the

recent discovery of mafic and ultramafic rocks in northeastern Nicaragua (Baumgartner

et al., 2004), which have been associated with the western boundary of an oceanic

terrane in Nicaragua (Siuna) have major implications about the true extension of the

Chortís block as a pre-Mesozoic continental block.

37

Most probably the Chortís and Yoro terranes, although they preserve different

basement units (Paleozoic and Grenvillian outcrops respectively), belong to the same

block, considering that the Aguán fault is not a conspicuous structure as the other

terrane-boundary faults are. However, marked differences in basement age and

lithology, make the Yoro a tectonostratigraphic unit until better dating and geologic

mapping is done in the area. Also, the apparent presence of the Santa Rosa and

Chochal formations south of the Polochic and, if fully documented, would extend the

Maya block down to the northern edge of the Baja Verapaz shear zone, thus deleting

the Achí terrane (Rabinal-San Gabriel suite) to include it in the Maya terrane or block.

8. PAST POSITIONS OF CHORTÍS BLOCK

The origin of the Chortís block has been a matter of debate ever since the first

publication on the reconstruction of Pangea (Bullard et al., 1965) placed the entire

region overlapping with the South American Plate. Several models have considered the

pre-Cenozoic position of the Chortís block in contrasting paleogeographic scenarios: In

Pangean reconstructions (Triassic-Jurassic) the Chortis block has been placed a) filling

the Gulf of Mexico (Freeland and Dietz, 1971), b) attached to southern Mexico in the

Pacific (Karig et al., 1978; Pindell and Dewey, 1982; Anderson and Schmidt, 1983;

Wadge and Burke, 1983; Pindell, 1982, 1985, 2006; Pindell et al., 1988; Ross and

Scotese, 1990; Meshede and Frisch, 1998; Dickinson and Lawton, 2001; Harlow et

al., 2004). In pre-Pangean times (Paleozoic and Precambrian) the Chortís block has

been attached to northwestern South America (Keppie, 1977; Keppie and Ramos,

1999; Keppie, 2004)). In Cenozoic times the Chortis block has been placed adjacent to

the southern part of the North American Cordillera (Sedlock et al., 1983; and within the

38

Pacific ocean (MacDonald, 1976; Vachard et al., 2000; Giunta et al., 2002, 2006;

Keppie and Morán-Zenteno, 2004), as an autochthonous microplate (Dillon and

Vedder, 1973), or simply ignored (Montgomery et al., 1994). Because the geologic

history of the Chortís block extends to the Mesoproterozoic (Manton 1996; Nelson et

al., 1997) and many authors have used regional stratigraphic correlations with

Precambrian to Mesozoic terranes in southern Mexico (see Figure 9), it is convenient to

discuss its past positions in these three major stages: Pre-Pangean, Pangean and post-

Pangean.

8.1 Pre-Pangean

Unfortunately, the paucity of stratigraphically proven pre-Mesozoic rocks and precise

paleomagnetic and age data for well described Mesozoic and pre-Mesozoic basement

rocks in the Chortís block severely limit inferences about its paleogeographic positions

before the assembly of Pangea. The Mesoproterozoic (1,075 Ma) gneisses briefly

described by Manton (1996), may have counterparts in the Oaxaquia superterrane of

southern and eastern Mexico (Ortega-Gutiérrez et al., 1995), which at southern Mexico

it is composed of ca. 990-1,150 Ma granulite facies banded ortho and paragneisses

intruded by pre- to synkinematic anorthositic complexes (Solari et al., 2003; Keppie et

al., 2003). Accreted and autochthonous belts with Grenvillian gneisses along northern

and western Amazonia, also exist in northwestern and west central South America

(Colombia, Ecuador, and Perú) forming the cratonic margin of Amazonia

(Kroonemberg, 1982; Sadowski and Betancourt, 1996; Restrepo-Pace et al., 1997;

Loewy et al., 2004), and Grenvillian granitoids of Laurentian affinity intruded into

greenschist to amphibolite facies formations are common in northwestern Mexico and

39

southwestern U.S.A. (e.g. Anderson et al., 1979; Condie et al., 1992, Iriondo et al.,

2004). These areas, that once formed part of the supercontinent Rodinia, may be

considered as other possible paleogeographic connections for the Grenvillian units of

the Chortís block exposed in Honduras. Current models analyzing the evolution of the

pre-Mesozoic oceans of the pre-Atlantic paleogeographic domain (i.e. Murphy et al.,

2006) locate the Chortís block by the end of the Proterozoic on the eastern side of the

Iapetus Ocean adjacent to NW Amazonia and next to Oaxaquia and Yucatán blocks.

Evidently, in the absence of precise data regarding all aspects of the pre-Mesozoic

geology including the basement and cover units of the Central American region, the pre-

Pangean position of the Chortís block cannot be constrained by geologic correlations,

and any pre-Mesozoic paleogeographic model linking the Chortís block with any of

those areas on these bases should be considered with extreme caution. Nonetheless,

considering the apparent absence of Paleozoic sedimentary rocks in the cover of the

crystalline basement in the Chortís block, precise connections for this time with

southwestern Mexico and the Maya blocks, which contain a thick blanket of late

Paleozoic marine and continental fossiliferous units resting on crystalline basement

rocks, cannot be established.

8.2 Pangean

The final accretion of Pangea in the Mesoamerican region occurred in latest Paleozoic

times, involving collision of the southern margin of Laurentia onto the northern leading

edge of Gondwana, amalgamating major continental areas such as Oaxaquia, Yucatán,

Florida, and possibly the Chortís block. A continental collision of this magnitude

imprinted a strong sedimentological and tectonothermal record in the local geology of

the Oaxaquia and Maya blocks, represented by thick sedimentary prisms, massive

40

batholiths, and tectonothermal events of late Paleozoic to earliest Mesozoic age. On the

other hand, the Chortís block does not show a similar geologic history, which may be

explained by two possible scenarios: (i) that orogenic rocks of late Paleozoic age exist

in the block but are not exposed, or have not been dated nor discovered; for example,

the high-grade metamorphic rocks of Las Ovejas Complex and San Diego Phyllite

intruded by Middle Jurassic plutons may be of Paleozoic age and thus form an integral

part of the Chortís block; (ii) that the Chortís block arrived at its present position in

Mesozoic or Cenozoic times traveling from exposed cratonic masses facing the Pacific

Ocean, which were not affected by the terminal Pangean collisional orogenic fronts.

This latter possibility would preclude the Chortís block from being part of the suture

zone between Gondwana and Laurentia that formed Pangea (Ortega-Gutiérrez, et al.,

1995; Grajales-Nishimura et al., 1999; Elías-Herrera and Ortega-Gutiérrez, 2002).

On the other hand, if confirmed, the Mississippian age of intense deformation and high-

grade metamorphism of the Chuacús Complex measured at El Chol (Ortega-Gutiérrez

et al., 2004) would imply collisional orogenic activity and terrane accretion associated

with the integration of Pangea in the Chortís-Maya suture zone. However, the

ambiguous tectonic setting of the Chuacús Complex as part of the Maya, Chortís or

other blocks requires further studies to evaluate its role in the context of Alleghenian-

Variscan tectonism and formation of Pangea in this region.

8.3. Post-Pangean

The position of the Chortís block during Mesozoic and early Cenozoic times, although

better constrained by stratigraphic successions (see Figure 9), is still controversial;

some Jurassic plate tectonic models place it outboard in the Pacific (e.g. Giunta et al.,

2006), whereas most other models show the entire block attached to southern Mexico

41

until the Jurassic (e.g. Anderson and Schmidt, 1983, Keppie, 2004), or remaining

fixed there until the Eocene (e.g. Pindell and Dewey, 1982; Gose, 1985; Ross and

Scotese, 1988; Pindell and Barret, 1990; Meshede and Frish, 1998; Kerr et al.,

1999; Harlow et al., 2004; Pindell, 2006). More elaborate models (Rogers, 2003)

include an Early Cretaceous rifting event of the Chortís block off southern Mexico and

its orogenic collision in the Albian in order to explain certain Cretaceous stratigraphic

and tectonic events that southern Mexico and the Chortís block seem to share. The

ubiquitous presence of Middle Jurassic to Early Cretaceous marine and continental

facies containing similar taxa of ammonites and plants that extend from southern

Mexico to Nicaragua, Cuba (Figure 9), and the northwestern South American Andes

(Ritchie and Finch 1985; Azema et al., 1985; Westerman et al., 1992; Rodríguez,

1995, Viland, 1996) suggests close paleogerographic connections at this time.

Moreover, the subsequent Cretaceous stratigraphic succession is similar across the

entire Central America area and southern Mexico (see Figure 3), and composed of

Early to middle Cretaceous massive carbonates followed by Late Cretaceous

terrigenous sedimentary rocks of marine as well as continental and volcanic origin. This

similarity of sedimentary, volcanic, and faunal facies for the middle and late Mesozoic

stratigraphic record of Mesoamerican terranes, and also for some of the Andean

terranes in northwestern South America, constitutes a fundamental geologic framework

that constrains relative displacements between terranes to at most a few hundred

kilometers since the Jurassic. A little known but intriguing correlation model between

Nuclear Central America and southern Mexico (de Cserna, 1990) was based upon

similarities in the nature and age of mineral deposits along the Cordilleran margins of

those regions, implying close connections of both blocks during the Mesozoic.

42

The comparative analysis of the Cretaceous and Eocene-Miocene stratigraphy of

Chortís block and southern México blocks is thus germane for the paleogeographic

reconstruction and timing of the latest movements of these blocks. Mills (1998) also

proposed a close Cretaceous connection between southern Mexico and the Chortís

block based on structural, stratigraphic, and sedimentological correlations between the

Early Cretaceous Morelos Formation of southern Mexico, and deformed equivalent

Cretaceous carbonates of the Atima Formation in northern Honduras. However, the

units underlying the Morelos Formation in Mexico, namely the Chapolapa

volcanosedimentary formation and the polymetamorphic Acatlán Complex, are different

in age (Early Cretaceous and Ordovician-Permian respectively), and their lithologies are

vastly different than the rocks shown by Mills (1998) beneath the Yojoa Group of

Honduras (Agua Fría Formation of Middle Jurassic age, and Las Ovejas Complex of

unknown age). Therefore, the direct continuity between Chortís and southern Mexico

blocks during the Cretaceous is not clear. The thick (up to 3,000 m) Subinal Formation

of Eocene-Miocene? of central Guatemala (Hirshman, 1963; Donnelly et al., 1990, p.

52-53) is virtually restricted to the Motagua valley. Its sediments include serpentinite

and blueschist pebbles, indicating post- Cretaceous tectonic disturbances and uplift

along the fault that may be related to displacements of the Chortís block in the

Paleogene. Similar, but somewhat older (Paleocene-Eocene) thick continental red beds

in southern Mexico are well represented in the Balsas Formation (Fries, 1960). The

younger age of the Subinal Formation could be explained by a southeasterly migrating

depocenter associated with the alleged displacement of the Chortís block off Mexico

during the Cenozoic. However, a fatal argument against all models depicting the Chortís

block adjacent to southwestern Mexico during the Paleogene may be that the

43

Caribbean ophiolitic nappes were emplaced in the Late Cretaceous onto both the Maya

and Chortís blocks, implying juxtaposition of the two blocks by that time (e.g. Pindell,

1985; Mauffret et al., 2001; Keppie, 2004). Another fatal argument is the presence of

an undeformed Cretaceous to Holocene sedimentary basin in the Gulf of Tehuantepec

that straddles the Motagua fault zone (Keppie and Morán-Zenteno, 2005). Other

similar models depict the extinction of El Tambor basin (proto-Caribbean sea) and

compressional orogeny by late Campanian time at the southern edge of the Maya block,

but caused by collision of the Greater Antilles arc and the Caribbean oceanic plateau

migrating eastward from the Pacific (Stockhert et al., 1995; Bralower and Iturralde-

Vinent, 1997; Hutson et al., 1998; Kerr and Tarney, 2005). However, as proposed by

Harlow et al. (2004) and supported by detailed structural analysis (Francis, 2005), the

Chortís block may have traveled more than a thousand kilometers between 120 and 80

Ma ago along the paleo-Motagua fault, with their southern ophiolitic slabs emplaced

during the Aptian collision with southern Mexico, to clash again in the Maastrichtian

against the southern margin of the Maya block, closing a segment of the Caribbean

ocean and producing the northern ophiolitic nappes.

The present position of the Chortís block has generally been linked to the tectonic

history of the Motagua and Polochic fault zones that have moved since the Paleogene,

as the Cayman Trough was formed (McBirney and Bass, 1969). Current models link

the two active faults to the early Cenozoic opening of the Cayman Trough in the

Caribbean and the Middle America trench in the Pacific, thereby restoring a minimum of

1,100 km of sinistral movement of the Chortís and thus placing it adjacent to

southwestern Mexico in theA

Eocene. However, while it is evident that the Motagua and

44

Polochic faults are still moving, the newly defined Baja Verapaz shear zone that outlines

the northern limit of the Chuacús Complex (Jacalteco terrane) appears to be inactive. If

by Cretaceous times this terrane had been amalgamated with the Maya block, during

the Cenozoic it probably moved no more than about 200 kilometers to its present

position along the Baja Verapaz transpressional and Polochic-Motagua left lateral

structures. Evidently, and as thoroughly discussed by James (2006), the Cretaceous

location of the Chortís block near its present position would make it impossible for the

Caribbean plate to have a Pacific origin.

The few paleomagnetic data available from the rigid blocks, Maya (see Steiner, 2006

for a recent synthesis), and Chortís (Gose, 1985) unfortunately have not been

conclusive, although for the latter block the results suggest latitudinal displacements of

up to 1,500 km, and counterclockwise rotations up to 60° consistent with a past position

in front of southern Mexico.

In conclusion, models that propose the emplacement of the Chortís block near its actual

position by the end of the Paleogene would be more in accord with left lateral

transpressional orogenic interactions of the Maya and Chortís blocks in Eocene-

Holocene times associated with activity of the Cayman Trough, but those that advocate

a Cretaceous arrival are more consistent with geologic studies produced at the southern

edge of the Maya block. In this regard, it should be reckoned that the Chuacús

Complex, located between the Maya and Chortís blocks, was affected by very high-

pressure metamorphism and covered by far-travelled ophiolitic nappes of El Tambor

Group during the Late Cretaceous, arguing for some sort of full continental collision

rather than the oblique interaction of the Maya margin with passing Caribbean arcs.

45

As a inevitable concluding remark it should be mentioned again that the virtually

unknown nature of the pre-Mesozoic Chortís block basement, and the apparent

absence of Paleozoic supracrustal units south of the Baja Verapaz fault, seriously

hamper the Precambrian and Paleozoic paleogeographic reconstructions of the area in

relation the adjacent continents. Younger paleogeographic scenarios may be easier to

develop, however, but they should be based on close geologic comparisons between

the known Mesozoic and Cenozoic stratigraphic units of southern Mexico and Central

America, and their possible counterparts of the Circum-Caribbean region, particularly

including large segments of Andean terranes in northwestern South America.

10. ACKNOWLEDGEMENTS

This paper benefited from funds from the Universidad Nacional Autónoma de México

(PAPIIT-DGAPA Grant IN100002 to LAS), and from internal funds of the Instituto de

Geología, UNAM. We want to thank the CUNOR, Universidad de San Carlos, for

logistical support during fieldwork. Diego Aparicio at UNAM, Instituto de Geología, made

more than 300 thin sections for petrography and microprobe of selected studied areas

in Central America, which were used to elucidate petrographic conditions of some of the

outcrops.

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64

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FIGURE CAPTIONS

Figure 1. Main geographic localities and major tectonic features of the Maya-Chortís

continental region referred in the text.

Figure 2. Panoramic views of the major physiographic units that characterize the

tectonic boundary between the Chortís block to the south, and the Maya block to the

north. a) Northern mountainous front (Sierra de Las Minas) of the Motagua fault zone.

65

b) Rugged interior of the Sierra de Chuacús. c) Northern front of the Sierra de Chuacús

and the northern limit of the Chuacús Complex defined by the Baja Verapaz fault zone.

d) Altos Cuchumatanes, an impressive plateau uplift of almost 4000 m at the southern

edge the Maya block, facing the Polochic fault zone to the south.

Figure 3. Tectonostratigraphic correlation chart for the study area as discussed in this

work.

Figure 4. a) High-Al metapelite of the Cacaguapa schist (Nueva Segovia, Nicaragua) a

basement outcrop of the Chortís block. b). Las Ovejas Complex, Gualán area. c) Garnet

amphibolites (meta-eclogite) of the Chuacús Complex interlayered with banded quartzo-

feldspathic high-pressure gneisses (Sierra de Las Minas). d) Retrograde, refolded

gneisses of Chuacús Complex in tectonic contact with low-grade metasediments of

unknown age (Rio Hondo). e) Typical outcrop of the low-grade arkosic psammite San

Gabriel sequence, route Rabinal-Salamá, near the town of San Miguel Chicaj. f)

Weathered outcrop of the Rabinal granite about 3 km northwest of Rabinal city. g) Block

of garnet amphibolite (metaeclogite?), Barillas town area, along the Amelco River,

representing local outcrops of the Barillas metamorphic complex. h) Ophiolitic tectonites

of El Tambor Group at the trace of the Motagua fault zone.

Figure 5. Detailed geologic map and cross section of the Baja Verapaz shear zone, as

exposed between the cities of Rabinal and Salamá (modified from Ortega-Obregón,

2005).

66

Figure 6. Correlation table for units of the late Paleozoic Maya block (modified from

Clemons et al. (1973).

Figure 7. Tectonostratigraphic correlation chart for terranes located in southern Mexico

and in the Maya-Chortís blocks.

Figure 8. Terrane subdivision as proposed by Rogers (2003) on the bases of Pb

isotope and magnetometric geophysical data. Inset: Pb isotopes for selected

tectonostratigraphic provinces of the Central America region (data from Rogers, 2003).

Figure 9. A) Schematic map of proposed terrane subdivision for the Chortís-Maya

region, based on terrane analysis principles, namely, the presence of distinctive

stratigraphic packages bounded by major faults. PF, Polochic fault; BVZ, Baja Verapaz

fault; MFZ, Motagua fault; JchF, Jocotán-Chamelecón-La Ceiba fault; AF, Aguán fault.

B) Schematic tectonostratigraphic cross-section from the Maya to the Chortís block.

67

Caribbean Plate

Cocos Plate

MAYA

CHORTIS

NICARAGUA

HONDURAS

EL SALVADOR

MEXICO

Pacific Ocean

0 100 200 km

BELIZE

PFZ

ZMF

JChFZLCF

GF

BVF

Guatemala

Paxban

Salama’

Tegucigalpa

San Pedro Sula

Tuxtla Gutiérrez

A

I

CHIAPS BATHOL TH

B

CHIAPAS-PETÉN FOLD ELT

GJ

V BAS

RI ALA

INChicomuselo

Motozintla

Tapachula

TOSALCU UMCH ATANES

Barillas

Huehuetenango

Sacapulas

QuetzaltenangoL. Atitlán

MAYA MOUNTAINS

Cd. Belize

SIERRA S. CRUZ

SI RRA LA MINA

E S

S

S E RA E CH A ÚSI R D U C

Gualán

Jocotán

Chiquimula

87°90°93°

18°

16°

14°

Progreso

AF

La Ceiba

Roa Isla d

tánn

Util I landa s

NUE A V

SEGOVIA

CAYMAN TROUGH

Zacapa

Rabinal

YUCATAN PLATFORM

CI

AS - PETÉN

HAPFOLD BELT

Caribbean Sea

YUCATAN BASIN

North American Plate

GUATEMALA

NUCLEAR CENTRAL AMERICA

CIFF

SRE B

IN

PAIC O

FHO

AS

ACIFI BASIN

PC

Figure 1, Ortega et al., 2006

Tacaná volcano

a b

c d

AGE

CE

NO

ZO

IC

EARLY

LATE

T

J

KL

E

E

E

L

L

M

M

Q

Pl

Mi

Ol

Eo

Pal

C

O

S

D

Ms

Ps

P

MAYA FAULT BOUNDED TERRANES CHORTIS

BARILLAS

COMPLEX

S. GABRIEL sequence

RABINALCACAGUAPA

SCHIST

PALACAGUINA

CHIXOLOP FM

YOROJACALTECOACHIGUATEMALA

SACAPULASCHICOL

TACTIC

CHOCHAL

TODOSSANTOS

COBAN

SEPUR

TEPEMECHIN

AGUA FRIA

EL PLAN

CAMPUR-

SUBINAL

VOLCANICS ALLUVIUM TUFF ALLUVIUM TUFFALLUVIUM

ME

SO

ZO

ICP

AL

EO

ZO

IC

?

?

?

?

SAN RICARDO

SA

NTA

RO

SA

GR

OU

P

TUILÁN

MOTAGUA SULA

SACAPULAS

?

PO

LO

CH

IC F

AU

LT

ZO

NE

BA

JA

VE

RA

PA

Z F

AU

LT

ZO

NE

TU

NC

AJ

TH

RU

ST

JO

CO

TÁ

N-C

HA

ME

LE

CÓ

N-L

A C

EIB

A F

AU

LT

AG

UÁ

N F

AU

LT

?

?

?

CHUACÚSCOMPLEX

SUBINAL

?

?

TUFFALLUVIUM

GUASTATOYA

EL TAMBORGROUP

GUASTATOYA

PADRE MIGUEL

VALLE DE ANGELES

ATIMACANTARRANAS

SAN DIEGOPHYLLITE

?

?

? ?

?

LAS OVEJASCOMPLEX

LAS OVEJASCOMPLEX

(?)

1.075 GaGRANITES

&GNEISSES

PADRE MIGUEL PADRE MIGUEL

VALLE DE ANGELESVALLE DE ANGELES

ATIMACANTARRANAS

ATIMACANTARRANAS

NUEVA SEGOVIA

?

?

?

Figure 3, Ortega et al., 2006

HONDURAS/NICARAGUA

COYOL

P

MO

TA

GU

A F

AU

LT

ZO

NE

PUNTA GORDA PUNTA GORDA

CHORTÍSAND

MAYABLOCKS

c d

e f

g h

a b

ío La Ei

R

tancs

a

ío La Ei

R

tancs

a

R

amá

ío Sal

R

amá

ío Sal

r

R oan J

ó

í

ni

S

emo

r

R oan J

ó

í

ni

S

emo

am áRío Salam áRío Sal

au

Pyá

e

o

q

Rí au

Pyá

e

o

q

Rí

ba O

a

ura

r tán

ed

Qb

a Oa

ura

r tán

ed

Q

90°30’15°10’

15°05’

Cerro Camperez

Cerro El Jocotillo

Cerro Mumús

Cerro El Cimiento

Cerro La Cruz Cerro El Portezuelo

Montaña Chiquihuital

Cumbre Balamche

15°00’90°30’ 90°20’90°25’ 90°15’

15°00’

90°20’90°25’

SALAMÁ

San MiguelChichaj

San Francisco

El Tempisque

RABINAL

San Gabriel

Chixolop

Las Minas

El Durazno

5

5458

40

4033

5532

4140 55

77

78

34

3235

21

51

32

46

40

648056

66

6026

52

70

15

53

6465

5442

59

64

53

8047

7383

73

58

5144

44

4747

54

6885

72

63

46

34

49

34

46

77

37

5342

79

85

75

44

22 34

45

7148

48 4082 64

67

5266

53

45

19

3645

32 48

4047

50

45

50

26

151048

4754

52

55

43

34

22

1410

28

06

15

05

38

10

18 2507

15

35

38

3420 10

7066 80

34

0 1 5 Km

S1 foliation

LEGEND

Towns

Secondary roads

Main roads

52

Rabinal granite

Metalimestones

Conglomeratic metasandstonephylites, shales Metaconglomerate

(metasandstone, phylites and deformedgranite clasts )S

AN

TA R

OS

A

GR

OU

P

Lineation46

Orthogneiss

Augen gneiss, Bt-Pl gneiss

Muscovite and garnet schistCH

UA

CÚ

S

CO

MP

LE

X

Volcanic and fluvial depositsundifferenciated

Metasediments, meta-arkoses, undifferentiated

Main faults

Inferred contacts

?

?

??

Section line

Main metasedimentary bands intruded by granites

Main trace of the“Baja Verapaz Shear zone”

B3

B2

B1

SA

N M

IGU

EL

SE

QU

EN

CE

1000

1500

2000

0 m

500

S10°WN30°WS30°E N10°E

B2 1B3B

Figure 5, Ortega et al., 2006

AGEMAYA BLOCK

GUADALUPAN PASOHONDO

LEONARDIAN

WOLFCAMP

PRE-WOLFCAMP

Chiapas Central Guatemala Maya Mts.S Chuacús

Thompson & Miller 1944

Bohnenberger1966

Van der Boomet al.1971

Mc Birney1963

Bateson& Hall1971

CHUACÚS CHUACÚSCHUACÚS

GANIT

OI

R

DS

VAINILLA

GRUPERA

SANTAROSA

Cuchumatanes

Andersonet al. 1973

CHUACÚS

CHOCHAL

ESER

ANZA

P

SA

NTA

RO

SA

GR

OU

P

TACTIC

CHICOL

SA

NTA

RO

SA

GR

OU

P

SA

NTA

RO

SA

GR

OU

PCHOCHAL

TACTIC UPPERTACTIC

L. TACTIC

SACAPULAS SACAPULASSACAPULAS

TACTIC Bladen Volc.

Figure 6, Ortega et al., 2006

AGETerrane CHATINO JUCHATECO MIXTECO ZAPOTECO MAYA CHORTÍS

MIOCENE

OLIGOCENE

PAL-EOCENE

LATE K

EARLY K

LATE J

MIDDLE J

EARLY J

TRIASSIC

LATE PZ

EARLY PZ

NEOPROT

MESOPROT

?

?

?

?

?

?

?

Limestone Continental clastic Marine clastic Volcanic Intrusive Metamorphic

Figure 7, Ortega et al., 2006

15.00

15.50

16.00

16.50

17.00

17.50

18.00

18.50

19.00

19.50

20.00

MAYA CCT ECT SIUNA CLIPSCT

207/204 Minumum

207/204 Maximum

206/204 Minimum

206/204 Maximum

CLIP

SIUNA

SCT

ECT

CCT

Northern NicaraguanRise

Southern NicaraguanRise

MAYA

94° 89° 84°

15°

20°

Figure 8, Ortega et al., 2006

Hess escar mentp

C y n ouga ma tr h