Field and petrographic data of 1.90 to 1.88 Ga I- and A ...

Revista Brasileira de Geociências 42(4): 690-712, dezembro de 2012

690 Arquivo digital disponível on-line no site www.sbgeo.org.br

ABSTRACT The SW Presidente Figueiredo district, which is located in the northeastern Amazonas State of the central Amazonian Craton, Brazil, consists of 1890 to 1898 Ma I-type granitoids (Terra Preta Granite, Água Branca Suite), A-type hornblende-bearing syenogranites (Canoas Syenogranite, Mapuera Suite), felsic to intermediate volcanic rocks (Iricoumé Group), and 1883 to 1889 Ma rapakivi granites (São Gabriel Granite, Mapuera Suite) and related rocks (quartz-gabbro-anorthosite and diorite), in addition to Castanhal quartz-monzonite, mylonites, and hornfels. The quartz-diorite facies of Terra Preta Granite were formed by mingling processes between a synplutonic quartz-gabbro dike and a hornblende granodiorite. Partially assimilated globules of Canoas hornblende-bearing syenogranite and their clear contacts with Terra Preta hornblende granodiorite suggest that Canoas Syenogranite is slightly younger than Terra Preta Granite. Canoas Syenogranite xenoliths inside São Gabriel Granite show that the granite is younger than the Canoas Syenogranite. New geologic and petrographic evidence improve the petrological understanding of these rocks and suggest that, in addition to fractional crystallization, assimilation and magma mingling played a role, at least at the local scale, in the evolution and compositional variation of the plutons. Such evidence is found in Terra Preta Granite mingled quartz-diorite, felsic material associated with the Canoas Syenogranite and in the intermediate microgranular enclaves, which exhibit primary biotite in hornblende-bearing rocks, plagioclase dissolution, corrosion of feldspars rims, alkali feldspar mantles, second apatite generation, and high xenocrystal contents in intermediate enclaves formed from the fragmentation of mafic intrusions. Petrographic analyses show that a deformational event recorded in the western part of the study area (with progressive deformation from E to W) is dated between the 1.90 Ga postcollisional magmatism and the intrusions of the São Gabriel Granite and related mafic/intermediate rocks (intra-plate). However, it is extremely necessary to obtain absolute ages for this metamorphic event.

Keywords: field data; petrography; I- and A- type granitoids; lithostratigraphy; NE Amazonas State.

RESUMO Dados de campo e petrográficos de granitoides dos tipos I e A de 1,90 a 1,88 Ga da região central do Cráton amazônico, NE do Estado do Amazonas, Brasil. O SW do município de Presidente Figueiredo, localizado no Estado do Amazonas, Nordeste do Cráton Amazônico Central, Brasil, hospeda granitoides do tipo I de idade entre 1890 a 1898 Ma (Terra Preta Granito, Suíte Água Branca), hornblenda-sienogranitos do tipo A (Sienogranito Canoas da Suíte Mapuera), rochas vulcânicas ácidas à intermediárias (Grupo Iricoumé) e granitos rapakivi de idades entre 1883 a 1889 Ma (Granito São Gabriel da Suíte Mapuera), e rochas afins (quartzo-gabro-anortosito e diorito), além de quartzo-monzonito Castanhal, milonitos e hornfels. A fácies quartzo-diorito do granito Terra Preta foi formada por processos de mistura entre um dique quartzo-gabro sinplutônico e um granodiorito hornblenda. Glóbulos parcialmente assimilados de sienogranitos hornblenda Canoas e seus contatos com o granodiorito hornblenda Terra Preta sugerem que o sienogranito Canoas é um pouco mais jovem do que o Granito Terra Preta. Xenólitos do sienogranito Canoas no interior do Granito São Gabriel mostram que o granito é mais jovem do que o sienogranito Canoas. Novas evidências geológicas e petrográficas avançam na compreensão petrológica destas rochas e sugerem que, além de cristalização fracionada, assimilação e mistura de magma, desempenharam um papel importante, pelo menos em escala local, na evolução e variação composicionais dos plutons. Tal evidência é encontrada no Granito Terra Preta misturado com materiais quartzo-diorito, félsico associado ao sienogranito Canoas e nos enclaves microgranulares intermediários, que apresentam biotita e hornblenda primárias, além de dissolução plagioclásio, corrosão de feldspatos, mantos feldspatos alcalinos, segunda geração de apatita, e elevados teores xenocristais em enclaves intermediários formados a partir da fragmentação de intrusões máficas. Análises petrográficas mostram que um evento deformacional registrado na parte Ocidental da área de estudo (com deformação progressiva de E para W) é estimado entre o magmatismo pós-colisional de 1,90 Ga e as invasões do Granito São Gabriel e rochas afins máficas/intermediárias (intraplaca). No entanto, torna-se extremamente necessário obter idades absolutas para este evento metamórfico.

Palavras-chave: dados de campo; petrografia; granitoides dos tipos I e A; litoestratigrafia; NE do Estado do Amazonas.

1Geosciences Institute, Federal University of Roraima, Boa Vista (RR), Brazil. E-mail: [email protected] of Isotope Geology, Geosciences Institute, Federal University of Pará, Belém (PA), Brazil. E-mail: [email protected] Institute, University of Brasília, Brasília (DF), Brazil. E-mail: [email protected]*Corresponding author

Field and petrographic data of 1.90 to 1.88 Ga I- and A-type granitoids from the central region of the Amazonian Craton,

NE Amazonas State, Brazil

Cristóvão da Silva Valério1*, Moacir José Buenano Macambira2, Valmir da Silva Souza3

Cristóvão da Silva Valério et al.

Revista Brasileira de Geociências, volume 42(4), 2012 691

INTRODUCTION The igneous associations in the northeastern Amazonas State, southern Uatumã-Anauá domain, are generically included in regional units based on limited knowledge of their field re-lationships and petrography. Recently, new outcrops of granitoids and related rocks, in addition to gran-itoids that recorded subsolidus deformation, were found. These rocks and their contact relationships re-vealed important information that allowed updating the lithostratigraphy of the southern Uatumã-Anauá domain. Moreover, detailed field and petrographic studies showed the first insights on the dynamic pro-cesses involved in the generation of the granitoid fa-cies, and a new tectonic interpretation based on mi-cro-deformational analysis was proposed.

In spite of modern methodologies advance, classic methods still supply enough information for understanding of the geology of remote areas. These methods are fundamental in areas in which the geo-logical history is poorly understood, such as in the central Amazonian craton.

The objectives of this study were: present-ing an integrated geological map, proposing a new lithostratigraphy for rocks of the southern region of the Uatumã-Anauá domain, discussing petrological and deformational features, and summarizing new data on the field of relationships and petrography of the 1.90 to 1.88 Ga I- and A-type granitoids and relat-ed rocks from the south portion of the Uatumã-Anauá domain in the central Amazonian craton, Brazil.

GEOLOGICAL SETTING Tassinari & Macambira (1999 and 2004) and Tassinari et al. (2000) subdivided the Amazonian Craton into Central Amazon (> 2.3 Ga), Maroni-Itacaiunas (2.2 – 1.95 Ga), Ventuari-Tapajós (1.95 – 1.8 Ga), Rio Negro-Juruena (1.8 – 1.55 Ga), Rondoniana-San Ignácio (1.5 – 1.3 Ga), and Sunsás (1.25 – 1.0 Ga) geotectonic provinces (Fig. 1A). Based on this mod-el, this study was carried out in the central portion of the Ventuari-Tapajós Province, central Amazonian Craton, in the Uatumã-Anauá domain (CPRM 2006, Almeida 2006, Almeida et al. 2008).

The Uatumã-Anauá domain has rocks from the entire Orosirian period, mainly composed of igneous units, in addition to Paleoproterozoic and Phanerozoic sedimentary cover that filled the Amazonas basin, as seen in Fig. 1B (CPRM 2000 & 2006, Faria et al. 2003, Ferron 2006, Valério 2006, Almeida 2006). Early regional mapping carried out

in this region identified several felsic and mafic igne-ous rocks (Santos et al. 1974, Araújo Neto & Moreira 1976, Veiga Jr. et al. 1979, Costi et al. 1984). Later studies have focused on the petrography, geochemis-try, and geochronology of felsic to intermediate gran-itoids and volcanic rocks (Valério et al. 2005, 2006 A & B 2009, & 2010, Souza et al. 2006, Marques et al. 2007, Souza et al. 2007, Freitas et al. 2007, Souza & Nogueira 2009, Costi et al. 2009).

The country rock of the Uatumã-Anauá do-main consists of tonalite-trondhjemite-granodio-rite (TTG)-like calc-alkaline meta-granitoids of the Anauá Complex (2.03 Ga) in association with meta-volcanic sedimentary rocks of the Uai-Uai Group (1.97 Ga?), both representing volcanic arc and back-arc basin settings (Faria et al. 2002 & 2003). According to Almeida (2006) and Almeida & Macambira (2007), the Anauá basement was intruded by S- (Serra Dourada, 1.96 Ga) and I-types (Matins Pereira, 1.97 Ga), and calc-alkaline granitoids in a collisional setting.

The youngest igneous rocks of the Uatumã-Anauá domain are 1.89 to 1.90 Ga I-type, high-K calc-alkaline granitoids of the Água Branca Suite, felsic to intermediate volcanic rocks of the Iricoumé Group, A-type granites of the Mapuera Suite (1.87 to 1.89 Ga, Abonari and São Gabriel granites), and re-lated rocks (quartz-gabbro, diorite and minor anor-thosite), in addition to quartz-monzonites, mylonites and hornfels (Valério et al. 2009 & 2010 and Costi et al. 2009). According to Santos et al. (2001 and 2006), the Mapuera granites are also associated with 1.87 Ga charnockites. After the first generation of the Mapuera A-type granites and a gap of ca. 60 Ma, a second generation of tin-bearing, A-type, anorogen-ic granites (1.81 Ga) of the Madeira Suite intruded in the Pitinga region (Costi et al. 2000). These latter have a similar age to the Moderna Granite in north-ernmost Brazil (Santos et al. 1997). In addition to the youngest units, metagranites, metamafics and gneiss in the southern portion of the Guyana Shield have been grouped into Jauaperi complex (CPRM 2006).

IGNEOUS ASSOCIATIONS The study area con-sists of I-type, high-K calc-alkaline granitoids of the Terra Preta Granite (Água Branca Suite), volca-nic and pyroclastic rocks (Iricoumé Group), A-type hornblende-bearing syenogranites of the Canoas Syenogranite (Mapuera Suite), rapakivi granites of the São Gabriel Granite (Mapuera Suite), and

1.90 to 1.88 Ga I- and A-type granitoids from NE Amazonas State

692 Revista Brasileira de Geociências, volume 42(4), 2012

Solimões BasinAmazon Basin

Atlantic Ocean

500 kmFigura 1b

Neoproterozoic mobile beltSunsás (1.25-1.0 Ga)Rondonian-San Ignácio (1.5-1.3 Ga)Rio Negro-Juruen (1.80-1.55 Ga)

Ventuari-Tapajós (1.95-1.80 Ga)Maroni-Itacaiunas (2.2-1.95 Ga)Central Amazonian (.2.5 Ga)

Undated mafic

Cenozoic deposit

Alter do Chão Formation

Trombetas Group

BR-174 roadLineamentsPitinga Sn Province

Fig. 2

Prosperança Formation

Seringa Formation (1.18 Ga) continental flood basalts

Quarentena Ilhas Formation (1.79 Ga) Continental flood basalts

Urupi Formation (1.79-1.90 Ga)sedimentary and volcaniclastic rocks

Madeira Suite (1.79-1.82 Ga)A-type granites

Iricoumé volcanics (1.86-1.88 Ga)rhyolitic-andestic lava and mass flows deposits

Jauaperi Complex1.89-1.90 Ga? metagranitoidsÁgua Branca Suite (1.89-1.90 Ga)I-type high-K calk-alkaline granitoids

Phanerozoic

Neoproterozoic

Mesoproterozoic

Paleoproterozoic

A

B

Figure 1 – (A) Tectonic provinces of the Amazonian Craton (Tassinari and Macambira 1999, modified by Macambira et al. 2009); (B) simplified geological map of the central Amazonian Craton, NE Amazonas State (modified from CPRM 2006, Ferron et al. 2006, and Valério et al. 2006b and 2009).

Castanhal quartz-monzonite. The area also includes mafic dikes associated with granitoids, younger mafic

stocks and dikes likely belonging to the Seringa and/or Quarenta Ilhas formations. Some of the granitoids



display features of dynamo-static crystallization and static re-crystallization (thermal metamorphism), probably linked to shear zones and mafic intrusions, which have not yet been well characterized (Fig. 2).

Terra Preta Granite The size and shape of the Terra Preta Granite remain undefined due to rework-ing of its western and southern borders caused by a poorly defined deformational event, and the cover of the Amazon basin. Its compositional variation con-sists on quartz-diorite (mingled), hornblende monzo-diorite, hornblende tonalite, hornblende granodiorite, biotite-hornblende granodiorite, hornblende mon-zogranite, biotite-hornblende monzogranite, biotite monzogranite, and biotite syenogranite.

Terra Preta Granite hosts aplite, mafic and in-termediate dikes, and enclaves. The contacts of the aplite dikes with the wall rock are sharp and have no chilled borders. The granite has two types of en-claves: volcanic xenoliths and mafic and intermedi-ate microgranular enclaves. The xenoliths of glome-roporphyritic andesite have sub-rounded shapes and their contacts with the wall rock are abrupt, irregular and lack chilled borders. The mafic enclaves are cir-cular to ellipsoidal, with 5 to 40 cm in diameter or length and display a mesocratic color-index, irregular transitional contacts and a high content of wall rock crystals (feldspars and quartz xenocrysts). Another important feature is a NE-striking gabbro dike that intruded into the contact between the Terra Preta

Granite and Canoas Syenogranite (Fig. 3A). Radar imagery shows that the southern part of the dike was inflected to strike NW-SE. The contact of the dike with the Terra Preta hornblende granodiorite is char-acterized by the formation of a transitional zone con-taining features of magma mingling (Fig. 3B), as well as dike fragmentation and formation of sub-angular to rounded microgranular enclaves and a mingled rock (quartz-diorite), as observed in Fig. 3C. Such aspects indicate a synplutonic dike that was partially fragmented and that physically and chemically inter-acted with the granodioritic magma before complete-ly chilling.

Iricoumé Group The rocks of the Iricoumé Group include pyroclastic flows (eutaxitic ignim-brite, ignimbrite, and co-ignimbrite), lava flow (an-desite/traquiandesite and rhyolite/rhyodacite) de-posits, and intrusions of autoclastic breccias. The lithostratigraphic sequence shows alternations of lava flow deposits above fiamme-rich ignimbrites, followed by ignimbrites and co-ignimbrites.

The basis of the mass flow deposits is formed by ignimbrites with highly flattened pumices (fi-ammes), and crystal and lithic fragments character-ized by eutaxitic textures. Its origin, at least in the ignimbrites, was the welding compaction of pumice clasts (Bull & McPhie 2007). The ignimbrites/co-ignimbrites display fragmentary textures and a fine matrix, layers with gradational fining upward cycles

Nhamundá FormationProsperança FormationGabbo-diorite±anorthositeMuscovite-actinolite hornfels,Actionlite hornfels

Mafic dike

Hornblend±biotiteHornblende monzogranite

Hornblend quartz-monzonite

Hornblend-bearing syenogranite, horn-bearing alkai feldspar granite

Piroclastic flow depositLava flow deposit

Biotite syenograniteBiotite monzograniteBiotite-hornblende monzograniteMingled quartz-dioriteHornbçende granodioriteHornblende tonaliteHornblende quartz-monzodiorite

BR-174 roadacess dirty roadPermanent drainageFault (zones)

São Gabriel Granite1883-1889 Ma, low-quartz rapakivi granite mapuera Suite (A-type)

Castanhal quartz-monzoniteMapuera Suite

Canoas Syenogranite (A-type)Mapuera Suite

Terra Preta Granite1890-1898 Ma high-K calc-alkalineÁgua Branca (I-type

Iricoumé volcanics (~1.88 Ga)

Lithostraigraphy

Mafic dike

Mafic dike

Figure 2 – Geological map of the southwestern Presidente Figueiredo district, NE Amazonas State, central Amazonian Craton. The boundaries of the granitoid and volcanic facies and main fault zones have been estimated from the integration of field data, SAR/SIPAM remote sensing products, and airborne geophysical data.



containing ≤ 20 cm ejected fragments (bombs), and gas escape-related vesicular cavities between the lay-er boundaries.

The andesites/traquiandesites display several amygdaloidal cavities related to gas release. The pres-ence of autoclastic breccias suggests an emplacement similar to cauldron collapse. The breccias have a rhyo-lite-rhyodacite matrix and are composed of highly var-ied rock fragments of andesite, rhyolite, and pumice.

Canoas Syenogranite The Canoas Syenogranite consists of a group of ellipsoidal NW-SE stocks with 5 to 15 km length, mainly composed of red-dish syenogranite and minor alkali feldspar-gran-ite (Fig. 2). It has two types of contacts with the Terra Preta Granite. The intrusions measuring less than 5 km in diameter generated outward and in-ward aureoles. The outward aureole is characterized by a thick alteration zone (> 1 m) marked by a color change likely caused by low temperature of aqueous fluids. The narrow inward aureole (< 20 cm) is char-acterized by increasing grain size and quartz con-tent, and it is likely recrystallized. The fine-grained stock borders reflect rapid heat loss to the wall rock that characterizes chilled borders. The contact be-tween a large stock (> 15 km length) and the wall rock (Terra Preta hornblende granodiorite) is in-terdigited, and chilled borders were not observed. The presence of rounded globules of syenogranite assimilated by granodioritic magma and the con-tact type suggest physical interaction between both magmas before complete crystallization. Therefore, it is plausible that the Canoas Syenogranite is slight-ly younger than the Terra Preta Granite. The maf-ic enclaves of the Canoas Syenogranite are circu-lar, with part of their ellipsoidal shape preserved, and the contacts with the wall rock are irregular and show strong assimilation.

Quartz-gabbro dikes oriented WNW-ESE/70ºSW are the main features that indicate mag-ma mingling processes. The features include fractur-ing and fragmentation of the dike borders (8 to 15 cm angular and < 5 cm rounded fragments), with the formation of mingled material among the maf-ic fragments. The irregular and interdigited contact with the wall rock is marked by a narrow transition-al zone (~ 5 cm) containing < 1 cm rounded mafic enclaves (Fig. 3D). The contact presents evidence of thermal contrast and interaction between the dike and the wall rock, whereas the small rounded enclaves

reveal extensive interaction between both felsic and mafic systems.

São Gabriel Granite Rapakivi-type hornblende monzogranite, hornblende syenogranite, and bio-tite-hornblende syenogranite are the major petro-graphic variations observed in São Gabriel Granite. Microgranite porphyry and microdiorite occur infre-quently as dikes near the boundaries of the batholith.

The São Gabriel Granite is an irregular, NW-SE striking, sub-ellipsoidal-shaped pluton (Fig. 2). Its main field features include volcanic, granitic and mafic enclaves, in addition to mafic and intermediate dikes. The volcanic xenoliths are sub-rounded and present dacitic compositions. The borders of the en-claves are irregular, sharp, and composed of imbri-cated quartz and feldspars crystals. The eastern and southeastern borders of the granite are characterized by sub-angular xenoliths of recrystallized alkali feld-spar-rich syenogranites (muscovite-actinolite horn-fels), likely from the Canoas Syenogranite, whose contacts with the wall rock vary from straight and abrupt to irregular ones (Fig. 3E).

The presence of these xenoliths demonstrates that the Canoas stocks are slightly older than the São Gabriel Granite. The textural dissimilarity between the preserved Canoas plutons (granoblastic) and the sub-angular xenoliths (granolepidoblastic) suggests that these fragments, which are partially assimilat-ed by São Gabriel magma, preserved the effects of a dynamo-thermal deformation event, which was fol-lowed by a mafic intrusion-related thermal event. Alternatively, the foliation of xenoliths could have been caused by the increasing turbulent flux close to the borders of the São Gabriel magma chamber.

The contact between the biotite-hornblende syenogranite and the microgranite porphyry is clear (Fig. 3F). In general, the São Gabriel mafic enclaves are sub-rounded and include high contents of xeno-crystals from the host rock. Along the granite pluton boundaries, they are stretched according to the igne-ous foliation. Mafic dikes that fill fractures in the São Gabriel Granite do not have features that support a genetic correlation. However, the intermediate dikes were frequently linked to all petrographic types.

Mafic and intermediate intrusions The dikes and stocks of the gabbros, diorites and anorthosites are associated with each other according to geograph-ic criteria and petrographic similarities (segregation



and fractionation) as it was elsewhere observed (Campbell 1996). In the field, the intrusions did not display clear relationships with the wall rocks, and

the outcrops are restricted to blocks and flagstones located along tracks and small creeks. The rocks are often very weathered.

Figure 3 – Field features of the Terra Preta, Canoas and São Gabriel granitoids and related rocks. (A) Quartz-gabbro dike emplacement into the contact zone between Terra Preta hornblende granodiorite and Canoas syenogranite; (B) zone of transitional contact between a quartz-gabbro dike and Terra Preta hornblende granodiorite, showing fragmentation and mingling of the dike, and subangular to rounded mafic enclaves without visible xenocrystals (dropped crystals); (C) Terra Preta mingled quartz-diorite with variable feldspar xenocrystals; (D) contact between a mafic dike and wallrock (muscovite-actinolite hornfels). Arrows show the formation of mingled material among the incompletely crystallized mafic fragments and a narrow (~ 5 cm) transitional zone. (E) Sub-angular xenoliths of recrystallized syenogranite (muscovite-actinolite hornfels) of Canoas Syenogranite inside São Gabriel Granite; (F) regular contact between biotite-hornblende syenogranite and microgranite porphyry dike.

A

C

E

B

D

F



PETROGRAPHY Material and methods The petrographic analy-sis consisted on the microscopic characterization of 165 polished thin sections that represent the composi-tional variations and geographical distribution of the rocks from the study area. The classification of granit-oid varieties and enclaves, totalizing 62 samples, was based on the modal parameters obtained by count-ing 1,500 points for medium- and fine-grained rocks and 1,800 for coarse-grained types. The composition of plagioclase zones was obtained from the Michel-Lèvy conventional method and, when possible, from the 010 cleavage-Albite Law twining and Albite Law-Carlsbad twining methods (variations of the Michel-Lèvy method), as described by Hibbard (1995).

Terra Preta Granite According to their mineral-ogical compositions, the main facies observed in the Terra Preta Granite are hornblende monzodiorite, horn-blende tonalite, hornblende granodiorite, hornblende-biotite granodiorite, hornblende monzogranite, horn-blende-biotite monzogranite, and biotite syenogranite, besides the mingled quartz-diorite (Tab. 1, Fig. 4A). The main texture is seriate but it varies to porphyritic, fine-grained equigranular and, locally, to granophyric.

Two types of plagioclase, both euhedral, were identified. Plagioclase-1 measures 1.5 to 4.0 mm and varies from An22–21 in the core to An25–22 in the rims. Progressive oscillatory zoning is common, whereas sudden oscillatory zoning is rare. Apatite and zircon inclusions are common in the core and rims, where-as Fe-Ti oxides inclusions only happen in the rims. Plagioclase-2 (< 0.5 mm) is usually zoned, and its composition varies from An28 in the core to An22–25 in

the rim. In both types, the contacts with all other min-erals are straight (Tab. 2).

Three types of quartz were identified. Quartz-1 is sub-hedral – anhedral (≤ 1 mm) and has opaque ti-tanite and hornblende inclusions. Quartz-2 is associ-ated with alkali feldspar-2 to form magmatic grano-phyric textures in the granodiorites. Quartz-3 is a hydrothermal phase that was precipitated on the al-kali feldspar-1.

Three types of alkali feldspar were identified: alkali feldspar-1 is euhedral and measures from 2 to 8 mm in length. Film-, strings- and interlocking-type perthites are common. In the monzogranite, the insular perthite surrounds perthitic alkali feldspar, whereas the albite chessboard is developed in the syenogranites. A second-generation of perthite (flames-type) is linked

to subsequent deformation processes. In the contacts with alkali feldspar, it developed a swapped rim struc-ture related to albite intergranular migration caused by Na-K exchange (Smith & Brown 1988). Alkali feld-spar-2 represents those portions of the granophyric textures of the granodiorites. The anhedral alkali feld-spar-3 (0.5 – 2.0 mm) has planar contacts with quartz 1 and -2 and interpenetrative contacts with quartz 3. Interlocking and flame perthites are frequent, whereas the beads-type one occurs locally. Apatite and zircon inclusions are common in this mineral. In the porphyry portion of the granodiorite, alkali feldspar-3 exhibits strings, veins, microfilms and recrystallization-linked flame perthites.

The hornblende is euhedral and sub-hedral and displays planar contacts with the quartz and al-kali feldspar and interpenetrative contacts with the ti-tanite. Fe-Ti oxides, zircon and apatite inclusions are very common. In the alkali feldspar-poor petrograph-ic types, hornblende also occurs as a product of an early reaction between the liquidus and clinopyrox-enes, forming clinopyroxene pseudomorphs.

Sub-hedral biotite-1 has hornblende, Fe-Ti ox-ides and titanite inclusions, while biotite-2 occurs as anhedral interstitial crystals associated with titanite.

The Fe-Ti oxides occur both associated with varietal minerals and as inclusions. The titanite is euhedral and is commonly associated with varietals. The apatite needles are euhedral–sub-hedral and measure < 0.1 mm. In the granodiorites, apatite crys-tals grew up to 2 mm (type-2 apatite). The zircons are euhedral–sub-hedral and zoned, and they always happen in association with apatite.

The epidote is originated from more calcic portions of plagioclase and hornblende. The seric-ite-muscovite and argilic minerals commonly occur on alkali feldspar and less commonly on plagioclase. The intergranular albite and individual crystals are associated with exsolution of the sodic phase from alkali feldspar to form perthites. The actinolite ap-pears as individual crystals and rims of hornblende and clinopyroxene pseudomorphs.

MAFIC DIKES AND ENCLAVES The gab-bro dikes and related mafic enclaves (sub-angular) possess intergranular textures and high clinopyrox-ene pseudomorph contents. Despite being intensely decalcified, some measurements of plagioclase re-vealed calcic andesine compositions (An41–48). The sub-hedral calcic andesine contains inclusions of



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02.

02.

11.

00.

10.

50.

01.

33.

50.

5Ti

tani

te

1.0

1.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

Apa

tite

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

Zirc

on

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

Mos

covi

te0.

00.

00.

00.

00.

00.

00.

01.

01.

01.

01.

5Fe

lsic

95.8

94.8

96.8

95.7

96.8

96.5

97.4

98.3

95.6

93.7

97.2

Mafi

c3.

04.

03.

04.

13.

03.

20.

50.

53.

25.

11.

1

Tabl

e 1

– M

odal

com

posi

tion

of st

udie

d gr

anito

ids.

The

amph

ibol

e an

d m

usco

vite

from

stat

ical

ly re

crys

talli

zed

rock

s are

met

amor

phic

min

eral

sA

ssoc

iatio

nTE

RR

A P

RET

A G

RA

NIT

EFa

cies

mQ

Dm

QD

mQ

D H

QM

DH

QM

DH

QM

DH

TH

GH

GH

GH

G(p

)H

GH

GB

HG

(f)

HM

BH

MB

HM

HB

M(f

)B

MB

MB

MB

M(f

)B

M(f

g)B

SB

SB

SB

SB

SS(

f)S(

fg)

Sam

ples

CC

-13

9HCC

-49

HCC

-14

3HCC

-13

2aCC

-13

2bCC

-65

CC-1

7CC

-14

C-38

04CC

-16

CC-4

7C-

6504

CC-5

0C-

6304

C-40

04C-

1504

CC-6

4C-

3504

C-09

04a

C-21

04b

C-21

04a

C-29

04C-

1804

C-08

04V

S-08

bV

S-08

aC-

0404

bC-

5004

C-04

04a

C-05

04

Qua

rtz

7.9

9.3

7,1

12,1

14,4

11.5

13.7

25.7

22.5

22.4

20.5

21.5

37.5

24.0

26.3

28.8

34.6

45.9

29.1

29.9

32.9

37.3

26.2

28.2

33.6

24.4

28.2

22,2

31.9

37,5

Alk

ali f

elds

par

0.1

0.8

0,5

15,0

17,3

21.6

1.0

22.3

16.4

7.4

22.9

15.7

13.7

17.7

23.9

31.7

39.9

21.9

35.3

35.9

35.0

25.9

44.4

45.4

48.9

47.7

43.3

60,5

48.9

21,0

Plag

iocl

ase

59.5

36.9

31,9

54,0

54,7

42.4

38.0

43.3

39.7

53.7

50.5

43.7

33.1

49.0

34.1

28.8

18.9

10.5

24.9

27.9

24.7

27.0

22.2

16.1

16.3

17.7

18.1

11,1

15.0

37,7

Pyro

xene

0.

40.

00,

30,

00,

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00,

00.

00,

0A

mph

ibol

e 31

.652

.659

,617

,312

,122

.246

.98.

419

.415

.65.

415

.412

.54.

714

.03.

83.

12.

20.

00.

00.

00.

00.

00.

00.

00.

00.

00,

00.

00,

2B

iotit

e0.

00.

00,

00,

00,

10.

00.

00.

00.

60.

00.

20.

40.

82.

10.

02.

92.

111

.56.

24.

05.

19.

35.

08.

10.

07.

86.

03,

00.

01,

0O

paqu

es0.

10.

10,

30,

11,

11.

60.

10.

20.

50.

30.

31.

60.

91.

51.

21.

90.

17.

72.

11.

01.

00.

11.

00.

10.

10.

10.

11,

00.

12,

2Ti

tani

te

0.1

0.1

0,1

1,3

0,1

0.6

0.1

0.0

0.7

0.4

0.1

1.4

0.8

0.9

0.3

1.9

1.0

0.1

2.1

1.0

1.0

0.1

1.0

0.1

0.1

0.1

0.1

2,0

0.1

0,2

Apa

tite

0.1

0.1

0,1

0,1

0,1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.6

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0,1

0.1

0,1

Zirc

on

0.1

0.1

0,1

0,1

0,1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0.1

0,1

0.1

0,1

Alla

nite

0.0

0.0

0,0

0,0

0,0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0,0

0.0

0,0

Fels

ic67

.647

.039

,581

,186

,475

.452

.791

.278

.683

.593

.881

.084

.390

.684

.389

.393

.478

.389

.493

.892

.690

.292

.789

.798

.889

.889

.793

,895

.896

,2M

afic

32.1

52.7

59,9

17,3

12,2

23.8

47.3

8.6

20.5

15.9

5.9

17.4

14.2

8.3

15.2

8.6

5.4

21.4

8.3

5.0

6.2

9.4

6.0

8.2

0.1

7.9

6.1

3,0

0.1

1,2

Ass

ocia

tion

SÃO

GA

BR

IEL

GR

AN

ITE

Faci

esH

MH

M(s

r)H

MH

MH

M(f

)H

MH

MH

MH

BM

HS(

sr)

HS(

sr)

HS

HS(

f)H

SH

BS

HB

SH

BS

BS(

f)Sa

mpl

es

CC

-46

CC

-83

CC

-95

CC

-01

CC

-80

CC

-55

CC

-02

C-4

404

CC

-61

CC

-86

CC

-88

CC

-45

CC

-72

C-1

704

C-5

204

C-5

104

C-5

404

C-2

004

Qua

rtz

27.5

41.0

31.9

19.4

27.6

29.3

21.8

18.5

20.9

37.5

48.1

18.3

31.2

21.6

26.7

32.3

34.6

52.8

Alk

ali f

elds

par

23.6

16.9

26.5

33.5

30.0

26.7

22.4

27.1

25.7

38.1

33.1

58.9

47.8

60.2

39.0

47.0

48.8

35.9

Plag

iocl

ase

44.6

32.5

29.8

31.2

30.0

36.9

35.1

31.8

44.8

18.8

14.2

14.4

16.7

10.9

28.0

15.7

12.0

9.0

Am

phib

ole

1.9

5.9

6.0

12.1

9.7

5.8

19.2

17.9

2.5

4.0

3.3

5.1

2.3

3.8

2.8

2.1

1.7

0.5

Bio

tite

0.4

1.5

0.7

0.0

0.0

0.4

0.0

1.3

2.7

0.0

0.3

1.2

0.3

1.3

3.1

2.6

2.5

1.5

Opa

ques

1.5

0.3

2.4

3.6

2.2

0.3

1.2

3.2

1.2

0.6

0.5

1.5

1.4

1.9

0.1

0.1

0.1

0.1

Tita

nite

0.

30.

82.

50.

00.

20.

50.

00.

01.

80.

80.

30.

20.

00.

10.

10.

10.

10.

1A

patit

e 0.

11.

00.

10.

10.

10.

10.

10.

10.

10.

10.

10.

20.

10.

10.

10.

10.

10.

1Zi

rcon

0.

10.

10.

10.

10.

10.

10.

10.

10.

20.

10.

10.

20.

10.

10.

10.

10.

10.

1A

llani

te0.

00.

00.

00.

00.

00.

00.

00.

00.

10.

00.

00.

00.

00.

00.

00.

00.

00.

0Fe

lsic

95.7

90.4

88.2

84.1

87.7

92.8

79.4

77.4

91.4

94.4

95.4

91.6

95.8

92.7

93.7

94.9

95.4

97.6

Mafi

c3.

87.

79.

115

.711

.96.

520

.422

.46.

44.

64.

17.

84.

07.

06.

04.

84.

32.

1

QD

: qua

rtz-d

iorit

e; Q

MD

: qua

rtz-m

onzo

dior

ite; T

: ton

alite

; G: g

rano

dior

ite; M

: mon

zogr

anite

; S: s

yeno

gran

ite; A

FG: a

lkal

i-fel

dspa

r gr

anite

; H: h

ornb

lend

e; B

: bio

tite;

f: f

olia

ted;

fg:

fine

-gra

ined

; g:

gra

noph

iric;

p: p

orph

yriti

c; sr

: sta

tic re

-cry

stal

lizat

ion;

m: m

ingl

ed



Fe-Ti oxides and displays interpenetrative contacts with hornblende. Actinolite and chlorite are the prod-ucts for the substitution of clinopyroxene and horn-blende, respectively. They are usually fibrous and include Fe-Ti oxide inclusions when altered to bio-tite (Tab. 3). The dikes have rounded clasts filled by fine-grained tremolite-actinolite and subordinate pla-gioclase. Their rims are formed by fibrous crystals (≤ 1 mm) of tremolite-actinolite that display sutured contacts with the host rock (Fig. 5A). The absence of inclusions, granulation, and contact type suggest that the mineral clasts are a late crystallized vesicular

phase filled by secondary minerals (amygdales), sug-gesting near-surface chilling.

MINGLED QUARTZ-DIORITE AND RELATED EN-CLAVES The mingled quartz-diorite displays intergranular textures and a mineralogical assemblage formed by poikilitic crystals of quartz and alkali feld-spar (string and flames perthites), xenocrystals of quartz, plagioclase and alkali feldspar, plagioclase, hornblende, high titanite content Fe-Ti oxides, apatite, zircon, and actinolite. The poikilitic crystals include hornblende, plagioclase, and titanite inclusions. All xenocrystals from the wallrock exhibit re-absorption/re-equilibrium features (engulfing, corroded core and patchy zones) (Fig. 5B). The preserved mafic phase possesses two types of plagioclase, both of which are intensely altered. The 1-type (from 2 to 3 mm) has a euhedral habit and oscillatory zoning with preserved sodic rims. It contains Fe-Ti oxides, apatite and zircon inclusions in the core and hornblende in the rims, andsharp contacts with oth-er minerals except hornblende, which have interpenetra-tive contacts. Plagioclase-2 is sub-hedral (< 1 mm) and is frequently associated with hornblende. Hornblende-1 is euhedral–sub-hedral with Fe-Ti oxides and titanite in-clusions. This hornblende has interpenetrative contacts with plagioclase-1 and straight contacts with quartz and alkali feldspar. Hornblende-2, quartz and alkali feldspar are interstitials. Two types of apatite were also identified: a long/narrow (20:1) and a short/wide (5:1).

Iricoumé GroupPYROCLASTIC FLOW DEPOSITS Lithic frag-ments and bent fiamme lenses make up the eutaxitic or fiamme-rich ignimbrite. The lithic clasts are angu-lar and very fragmented. The fiammes show wrinkled rims and are locally smooth. The ash matrix has an accentuated orientation and high degree of welding by compaction. The ignimbrite exhibits a microlith-ic texture and strong mineral foliation or orientation from pyroclastic flow. The ignimbrite is composed of fragments of quartz, alkali feldspar, plagioclase, bi-otite and Fe-Ti oxides, pumice fragments, and fine-grained ash matrix. The co-ignimbrite consists of similar proportions of clasts of quartz, alkali feldspar, plagioclase and opaques, as well as ash matrix.

LAVA FLOW DEPOSITS The andesite has a glomeroporphyritic amygdaloidal texture and consists of phenocrystals of quartz, calcic oligoclase (An22–25), pyroxene and hornblende in a trachytic matrix, with

A Q60

20

5A 10 35 65 90 P

mingled rockmicrogranularenclave

qz-monzodiorite

monzo-granitemonzo-diorite

syen

ogra

nite

Tonalite

qz-diorite

QTerra Preta Granite

10 35 65 90 P

B Canoas Syenogranite

muscovite-actinolitehornfels

qz-richgranitoid

monzo-granite

syeno-granite

alkali

feld

spar

gran

ite

60

Q

20

5

A

20

5

rapakivi-typeSão Gabriel Granite QQ

10 35 65 90 P

monzo-granite

monzo-diorite

actinolite hornfels

syen

ogra

nite

C

A

60

Figure 4 – QAP modal composition of the studied plutons (Streckeisen 1976). Granitic series according to Lameyre and Bowden (1982). (A–C) calc-alkaline granodioritic subseries (A – Corsica, Sardinia; B – Chile, C – Peru). The dashed field corresponds to granites generated from crustal melting, according to Lameyre & Bowden (1982).



Plut

on, U

nit

Terr

a Pr

eta

Gra

nite

, Águ

a Br

anca

Sui

teC

anoa

s Sye

nogr

anite

, Map

uera

Sui

teSã

o G

abrie

l Gra

nite

, Map

uera

Sui

te

Petro

grap

hic

varia

tion

(Hor

nble

nde)

quar

tz-d

iorit

e, m

onzo

dior

ite,

tona

lite,

gra

nodi

orite

, and

(bio

tite)

mon

zogr

anite

an

d -s

yeno

gran

ite.

Hor

nble

nde-

bear

ing

syen

ogra

nite

and

alk

ali

feld

spar

gra

nite

.H

ornb

lend

e m

onzo

gran

ite, h

ornb

lend

e sy

enog

rani

te, b

iotit

e-ho

rnbl

ende

syen

ogra

nite

.

Text

ural

var

iatio

n Th

e se

riate

text

ure

varie

s to

porp

hyrit

ic, fi

ne-

grai

ned

equi

gran

ular

and

loca

lized

gra

noph

yric

te

xtur

es.

Med

ium

- to

fine-

grai

ned

seria

te te

xtur

e.M

ediu

m- t

o co

arse

-gra

ined

seria

te te

xtur

e.

Esse

ntia

l min

eral

s

Plag

iocl

ase-

1

Leng

th 1

.5–4

.0 m

m, c

alci

c ol

igoc

lase

(An 22

–21 i

n co

re),

(An 25

–22 i

n rim

s), p

rogr

essi

ve o

scill

ator

y zo

ning

, apa

tite

and

zirc

on in

clus

ions

are

co

mm

on in

cor

e an

d rim

s, Fe

-Ti o

xide

s in

clus

ions

onl

y in

rim

s, co

ntac

ts w

ith a

ll ot

hers

m

iner

als a

re re

ctili

near

.

Euhe

dral

, 0.5

–3.0

mm

, unz

onin

g, so

dic

olig

ocla

se (A

n 10-1

2), tw

inin

g A

lbite

and

Alb

ite-

Car

lsba

d La

ws.

Its c

onta

ct w

ith th

e al

kali

feld

spar

and

qua

rtz is

rect

iline

ar a

nd w

ith

horn

blen

de is

inte

rdig

ited.

Euhe

dral

(2–6

.5 m

m),

An 22

–An 28

in c

ore,

An 22

–17 in

rim

s, co

ntac

t is

rect

iline

ar w

ith th

e ho

rnbl

ende

-1 a

nd in

terp

enet

rativ

e w

ith th

e qu

artz

-1, c

onta

ins h

ornb

lend

e-Fe

-Ti o

xide

s, ap

atite

and

zirc

on

incl

usio

ns. T

win

ning

Alb

ite a

nd A

lbite

-Car

lsba

d La

ws a

nd m

ajor

no

rmal

zon

ings

, and

abr

upt a

nd se

ctor

ed o

scill

ator

y zo

ning

s.

Plag

iocl

ase-

2<

0.5

mm

, ind

efini

te z

onin

g, A

n 28 in

cor

e an

d A

n 22–2

5 in

rim

s, co

ntac

ts w

ith a

ll ot

hers

min

eral

s ar

e re

ctili

near

.ab

sent

pha

se

0.5–

1.5

mm

, anh

edra

l–su

bhed

ral,

abru

pt o

scill

ator

y zo

ning

. Occ

urs

fillin

g in

inte

rstic

es a

mon

g gr

ains

and

con

tain

s inc

lusi

ons o

f qua

rtz-1

an

d bi

otite

-2. A

n 27–2

5 in

core

and

An 21

–17 i

n rim

s, al

tera

tion

to e

pido

te

and

seric

ite in

cal

cic

zone

.

Alk

ali f

elds

par-1

Eued

ral,

leng

th 2

–8 m

m. F

ilm-,

strin

gs- a

nd

inte

rlock

ing-

type

per

thite

are

com

mon

. In

mon

zogr

anite

s, th

e in

sula

r per

thite

occ

urs

surr

ound

ing

perth

itic

alka

li fe

ldsp

ar, a

lbite

-ch

essb

oard

dev

elop

ed in

syen

ogra

nite

s. A

pe

rthite

seco

nd-g

ener

atio

n (fl

ames

-type

) is

linke

d to

subs

eque

nt d

efor

mat

ion

proc

esse

s. In

co

ntac

ts w

ith o

ther

s alk

ali f

elds

par d

evel

oped

sw

appe

d rim

s.

Subh

edra

l, st

rong

ly p

erth

itic

(stri

ngle

ts, s

tring

s, in

terlo

ckin

g an

d ch

essb

oard

alb

ite) w

ith

gene

ratio

n of

subh

edra

l cry

stal

s of a

lbite

. It

poss

esse

s sev

eral

pla

gioc

lase

incl

usio

ns a

nd it

s co

ntac

t with

the

plag

iocl

ase

and

quar

tz is

fain

tly

inte

rdig

ited.

Subh

edra

l, 2.

5–6.

0 m

m, c

omm

only

occ

urs a

ssoc

iate

d to

the

quar

tz-1

, lo

cal i

nter

lock

ing

and

bead

s per

thite

s, al

bite

inte

rgra

nula

r occ

ur,

corr

oded

rim

s for

m o

void

shap

e (r

apak

ivi t

extu

re).

Bot

h al

kali

feld

spar

pre

sent

Alb

ite-P

eric

line

Law

twin

ing,

slig

htly

tra

nsfo

rmed

to se

ricite

and

arg

ilic

min

eral

s, co

ntai

n pl

agio

clas

e-2,

ho

rnbl

ende

-1, z

ircon

and

apa

tite

as in

clus

ions

and

alb

ite m

icro

film

s an

d st

ring

perth

ite a

re v

ery

com

mon

.

Alk

ali f

elds

par-2

Ane

dral

, 0.5

–2.0

mm

, rec

tilin

ear c

onta

ct w

ith

the

quar

tz-1

and

-2 a

nd in

terp

enet

rativ

e w

ith th

e qu

artz

-3.

abse

nt p

hase

It is

subh

edra

l–an

hedr

al, m

easu

res 0

.5–2

.5 m

m.

Qua

rtz-1

Sube

dral

–ane

dral

(≤ 1

mm

), tit

anite

, opa

ques

an

d ho

rnbl

ende

incl

usio

ns.

Ane

dral

and

con

tain

s tita

nite

and

opa

ques

in

clus

ions

Anh

edra

l–su

bhed

ral,

1–1.

5 m

m.

Qua

rtz-2

Alk

ali f

elds

par-2

-ass

ocia

ted

to fo

rm a

mag

mat

ic

gran

ophy

ric te

xtur

e.ab

sent

pha

seIn

ters

titia

l, oc

curs

ass

ocia

ted

to th

e bi

otite

-2.

Qua

rtz-3

Rep

rese

nts a

hyd

roth

erm

al p

hase

pre

cipi

tate

d on

th

e al

kali

feld

spar

-1.

abse

nt p

hase

It sh

ows s

trong

ly u

ndul

ator

y ex

tinct

ion,

typi

cally

occ

urs i

nclu

ded

in

the

alka

li fe

ldsp

ar-1

.

Tabl

e 2

– Pe

trogr

aphi

c ch

arac

teri

stic

s of s

tudi

ed g

rani

tic p

luto

ns

Con

tinua

...



Tabl

e 2

– C

ontin

uatio

nVa

riet

al m

iner

als

Hor

nble

nde-

1

Euhe

dral

–sub

hedr

al, r

ectu

m c

onta

ct w

ith q

uartz

an

d al

kali

feld

spar

and

inte

rpen

etra

tive

with

th

e tit

anite

. Fe-

Ti o

xide

s, zi

rcon

and

apa

tite

incl

usio

ns a

re v

ery

freq

uent

. It a

lso

occu

rs a

s cl

inop

yrox

ene

pseu

dom

orph

s.

Stro

ngly

alte

red

to c

hlor

ite, o

ccur

s com

mon

ly

as in

ters

titia

ls c

ryst

als c

onta

inin

g in

clus

ions

of

Fe-T

i oxi

des.

Subh

edra

l to

euhe

dral

. It i

s ass

ocia

ted

to F

-Ti o

xide

s tita

nite

, al

tera

tion

to c

hlor

ite, e

pido

te a

nd b

iotit

e. T

he c

onta

ct w

ith th

e pl

agio

clas

e-1

is re

ctili

near

and

with

the

quar

tz-1

and

alk

ali f

elds

par-1

is

inte

rdig

ited.

Con

tain

s inc

lusi

ons o

f Fe-

Ti o

xide

s.

Hor

nble

nde-

2 ab

sent

pha

seab

sent

pha

seas

soci

ated

to q

uartz

-2, o

ccur

s filli

ng in

inte

rstit

ials

and

mai

nly

clea

vage

s of p

lagi

ocla

ses

Bio

tite-

1Su

bedr

al, c

onta

ins h

ornb

lend

e, F

e-Ti

oxi

des a

nd

titan

ite a

s inc

lusi

ons.

abse

nt p

hase

Subh

edra

l, co

ntai

ns se

vera

l cor

rode

d m

agne

tite

and

ilmen

ita

incl

usio

ns.

Bio

tite-

2O

ccur

s as a

nhed

ral i

nter

stiti

al c

ryst

als a

nd

titan

ite-a

ssoc

iate

d.ab

sent

pha

seO

ccur

s as p

rodu

ct o

f tra

nsfo

rmat

ion

of h

ornb

lend

es a

nd a

s filli

ng in

in

ters

tices

.

Acce

ssor

y m

iner

als

Fe-T

i oxi

des

Occ

ur a

ssoc

iate

d to

var

ieta

ls a

nd a

s inc

lusi

ons.

mis

char

acte

rized

They

com

bine

with

Fe-

Mg

hydr

ated

min

eral

s and

tita

nite

.

Tita

nite

Eued

ral,

occu

rs c

omm

only

ass

ocia

ted

to

varie

tals

.So

me

crys

tals

hav

e be

en a

ltere

d to

epi

dote

Occ

urs a

s euh

edra

l cry

stal

s of u

p to

2 m

m a

nd is

ass

ocia

ted

to th

e ho

rnbl

ende

and

Fe-

Ti o

xide

s. So

me

crys

tals

con

tain

flui

d in

clus

ions

in

bub

ble

shap

e.

Apa

tite-

1A

patit

e ne

edle

s are

euh

edra

l–su

bhed

ral a

nd

mea

sure

< 0

.1 m

m.

mis

char

acte

rized

Euhe

dral

, aci

cula

r and

hex

agon

al, a

nd e

xhib

its in

timat

e re

latio

ns

with

the

horn

blen

de-2

and

pla

gioc

lase

s.

Apa

tite-

2C

ryst

als g

rew

up

to 2

mm

.ab

sent

pha

seab

sent

pha

se

Zirc

onEu

hedr

al–s

ubhe

dral

, zon

ed, a

lway

s occ

urs

asso

ciat

ed to

apa

tite.

Euhe

dral

, mea

sure

s up

to 0

.2 m

m a

nd so

me

crys

tals

hav

e be

en h

ugel

y al

tere

d to

epi

dote

.Eu

hedr

al–s

ubhe

dral

and

shar

ply

zone

d.

Gar

net

abse

nt p

hase

Ve

ry fi

ne c

ryst

als i

n ev

olve

d te

rms

abse

nt p

hase

Seco

ndar

y m

iner

als

Epito

deO

rigin

ated

from

mor

e ca

lcic

por

tions

of

plag

iocl

ase

and

horn

blen

de.

From

cal

cic

porti

on o

f pla

gioc

lase

s. It

stan

ds o

ut b

y fo

rmin

g eu

hedr

al c

ryst

als.

Seric

ite-m

usco

vite

M

ajor

ly o

ccur

on

alka

li fe

ldsp

ar a

nd p

lagi

ocla

se.

From

alk

ali f

elds

par a

nd p

lagi

ocla

se.

Occ

urs a

ssoc

iate

d to

cal

cic

porti

ons o

f pla

gioc

lase

s.

Arg

ilic

min

eral

sO

ccur

on

alka

li fe

ldsp

ar a

nd p

lagi

ocla

se.

From

alk

ali f

elds

par.

The

argi

lizat

ion

occu

rred

with

smal

l int

ensi

ty in

alk

ali f

elds

pars

.

Inte

rgra

nula

r alb

iteA

re a

ssoc

iate

d to

sepa

ratio

n of

the

sodi

c ph

ase

from

alk

ali f

elds

par t

o fo

rm p

erth

ites.

From

per

thite

and

alb

ite c

hess

boar

d.

It is

pro

duct

from

the

perth

ite.

Act

inol

iteO

ccur

s as i

ndiv

idua

l cry

stal

s and

rim

s of

horn

blen

de a

nd c

linop

yrox

ene

pseu

dom

orph

s.Fr

om h

ornb

lend

e.ab

sent

pha

se

Chl

orite

Occ

urs f

aint

ly fr

om b

iotit

es.

From

hor

nble

nde.

Fr

om h

ornb

lend

e an

d bi

otite

.

Hem

atite

abse

nt p

hase

Occ

urs a

s im

preg

natio

n on

alk

ali f

elds

par,

as

fillin

g in

to m

icro

frac

ture

s.

Com

mon

in th

e al

kali

feld

spar

-ric

h gr

anite

s, as

impr

egna

tion

in so

dic

lam

ella

s of p

erth

ites,

inte

rstit

ial p

ortio

ns a

nd m

icro

frac

ture

s and

as

esph

erul

itic

crys

tals

.



Plut

onTe

rra

Pret

a G

rani

teC

anoa

s Sye

nogr

anite

São

Gab

riel G

rani

te

Fels

ic d

ike

Mic

rosy

enog

rani

te, r

hyol

ite w

ith in

equi

gran

ular

and

mic

ropo

rphy

ritic

te

xtur

es. A

lkal

i fel

dspa

r phe

nocr

ysta

ls a

re p

erth

itic

and

pres

ents

A

lbite

-Per

iclin

e La

w tw

inni

ng.

Xen

olith

s

Glo

mer

opor

phyr

itic

ande

site

with

a v

ery

fine-

grai

ned

mat

rix fo

rmed

by

clu

ster

s of a

mph

ibol

es, f

elds

pars

and

qua

rtz. T

wo

phen

ocry

stal

s ty

pes o

f pla

gioc

lase

:1-ty

pe h

as 2

–8 m

m, A

n 24 in

cor

e an

d A

n 21 in

rim

; 2-

type

has

< 0

.5 m

m, A

n 28 in

cor

e an

d A

n 26 in

rim

.

1. M

usco

vite

-act

inol

ite-h

orfe

ls (C

anoa

s Sy

enog

rani

te) w

ith in

terlo

bate

gra

nobl

astic

text

ure.

2.

Hor

nble

nde-

rhyo

daci

te.

Mafi

c di

ke

Inte

rgra

nula

r tex

ture

gab

bros

and

hig

h cl

inop

yrox

ene

pseu

dom

orph

s co

nten

t em

phas

ize

the

gabb

ro d

ike

and

encl

aves

ass

ocia

ted.

subh

edra

l ca

lcic

and

esin

e (A

n 41–4

8). It

als

o is

form

ed b

y ci

rcul

ar fi

ne-g

rain

ed

trem

olite

-act

inol

ite c

rust

s and

subo

rdin

ated

pla

gioc

lase

, who

se ri

ms

are

form

ed b

y fib

rous

cry

stal

s of t

rem

olite

-act

inol

ite.

Show

s int

ergr

anul

ar a

nd su

b-op

hitic

te

xtur

es, h

igh

amph

ibol

es c

onte

nts

and

plag

iocl

ase

xeno

crys

tals

. The

xe

nocr

ysta

ls h

ave

been

par

tially

di

ssol

ved

in th

eir c

ore

and

rims.

Mafi

c en

clav

eId

em to

mafi

c di

ke.

Inte

rmed

iate

enc

lave

Qua

rtz-d

iorit

e, in

terg

ranu

lar t

extu

re, a

min

eral

ogic

al a

ssem

bly

form

ed

by p

oiki

litic

cry

stal

s of q

uartz

and

alk

ali f

elds

par (

strin

g an

d fla

mes

pe

rthite

s), x

enoc

ryst

als o

f qua

rtz, p

lagi

ocla

se a

nd a

lkal

i fel

dspa

r, an

d,

high

tita

nite

con

tent

. Xen

ocry

stal

s exh

ibit

engu

lfing

, cor

rode

d co

re

and

patc

hy z

one,

and

als

o po

sses

ses a

mafi

c ph

ase

pres

erve

d an

d tw

o ap

atite

type

s, a

long

/nar

row

(20:

1) a

nd a

noth

er sh

ort/w

ide

(5:1

).

Qua

rtz-d

iorit

e ke

pt p

etro

grap

hic

feat

ures

sim

ilar t

o Te

rra

Pret

a m

afic

encl

aves

. Exc

eptio

ns in

clud

e th

e bi

otite

pre

senc

e, a

mph

ibol

e ps

eudo

mor

phs a

nd p

lagi

ocla

ses

light

ly m

ore

calc

ic (A

n 27-3

0).

Met

agra

nito

ids

Dyn

amo-

stat

ic d

efor

mat

ion

prog

ress

ivel

y in

crea

sing

from

E to

W in

to th

e W

sect

or o

f stu

died

are

a. It

s in

tens

ity e

mbr

aces

low,

low

–med

ium

and

med

ium

–hig

h te

mpe

ratu

re d

egre

es.

Iric

oum

é ig

nim

brite

Lith

ic fr

agm

ents

and

ben

t fiam

mes

con

stitu

te th

e fia

mm

e-ric

h ig

nim

brite

. It i

s for

med

by

cry

stal

s fra

gmen

ts o

f qua

rtz, a

lkal

i fel

dspa

r, pl

agio

clas

e, b

iotit

e an

d Fe

-Ti o

xide

s, an

d pu

mic

e fr

agm

ents

and

fine

-gra

ined

ash

mat

rix. T

he c

o-ig

nim

brite

con

sist

s of s

imila

r pr

opor

tions

of c

last

s of q

uartz

, alk

ali f

elds

par,

plag

iocl

ase

and

opaq

ues,

besi

des a

sh m

atrix

.

Iric

oum

é an

desi

te/tr

achy

ande

site

Glo

mer

opor

phyr

itic

amyg

dalo

idal

text

ure

and

cons

ists

of p

heno

crys

tals

of q

uartz

, cal

cic

olig

ocla

se (A

n 22–2

5), p

yrox

ene

and

amph

ibol

e in

a tr

achy

tic m

atrix

.

Iric

oum

é rh

yolit

e/rh

yoda

cite

The

horn

blen

de-rh

yolit

e/rh

yoda

cite

con

sists

of p

heno

crys

tals

of fe

ldsp

ars,

horn

blen

de a

nd

Fe-T

i oxi

des i

n m

atrix

of q

uartz

, fel

dspa

rs a

nd h

ornb

lend

e. S

mal

l clu

sters

of h

ornb

lend

e fo

rm

radi

al a

rrang

emen

t. Tw

o ph

enoc

rysta

ls ty

pes o

f pla

gioc

lase

. 1-ty

pe is

subh

edra

l–eu

hedr

al

(1–2

mm

), an

d ha

s cal

cic

olig

ocla

se (A

n 29) i

n co

mpo

sitio

n. T

he p

lagi

ocla

se-2

(< 0

.5 m

m) i

s eu

hedr

al, h

as A

n 26 in

com

posit

ion.

The

alk

ali f

elds

par (

1–2

mm

) phe

nocr

ysta

l is s

ubhe

dral

an

d co

ntai

ns in

clus

ions

of p

lagi

ocla

se-2

. The

bul

bous

-type

myr

mek

ite is

ver

y fre

quen

t.

Mic

rogr

anite

por

phyr

y di

keTh

e po

rphy

ritic

text

ure

cont

aini

ng fe

ldsp

ars c

ryst

als

of u

p to

2 c

m, m

ediu

m- t

o fin

e-gr

aine

d m

atrix

and

lo

caliz

ed g

rano

phyr

ic in

terg

row

ths.

Hor

nfel

s

Into

the

NE

sect

or, m

afic

rock

s and

gra

nito

ids,

abov

e al

l, C

anoa

s Sye

nogr

anite

, wer

e st

atic

ally

recr

ysta

llize

d. P

rese

nt in

terlo

bate

gra

nobl

astic

text

ure

and

less

recr

ysta

llize

d ro

cks p

osse

ss ig

neou

s loc

ally

pre

serv

ed te

xtur

e, w

here

is p

ossi

ble

desc

ribe

fibro

us v

eins

, cr

ysta

lpla

stic

def

orm

atio

n of

qua

rtz a

nd fr

agile

def

orm

atio

n of

feld

spar

s.

Tabl

e 3

– M

ain

petro

grap

hic

and

min

eral

ogic

al c

hara

cter

istic

s of r

ocks

ass

ocia

ted

to a

ppra

ised

gra

nitic

plu

tons

.



both being slightly following the magmatic flow. The quartz is usually anhedral and occurs as phenocrys-tals, as strings in amygdales rims and partially filling amygdales. The euhedral calcic oligoclase displays twinning according to the Albite-Carlsbad law. The pyroxene is scattered and is commonly associated with andesine and Fe-Ti oxides. The actinolite-tremo-lite, generated from the alteration of hornblende, is as fibrous crystals filling amygdales.

The hornblende rhyolite/rhyodacite consists of phenocrystals of feldspars, hornblende and Fe-Ti ox-ides in a matrix of quartz, feldspars and hornblende. Zircon and apatite are the most common accessory minerals. The hornblende phenocrystals are sub-hedral and commonly associated with the Fe-Ti oxides. They present inclusions of Fe-Ti oxides, and their contacts with the matrix are gradual. Clusters of small horn-blende crystals in radial arrangements are common.

Two types of plagioclase phenocrystals have been recorded. Plagioclase-1 is sub-hedral–euhedral (from 1 to 2 mm) and has a calcic oligoclase (An29) composition. Plagioclase-2 (< 0.5 mm) is euhedral, has An26 composition, and also occurs as inclusion in the alkali feldspar. Both types of plagioclase exhibit Albite and Albite-Carlsbad law twinning. Their calcic cores break up into muscovite, sericite, and clay minerals.

The alkali feldspar phenocrystals (from 1 to 2 mm) are sub-hedral with inclusions of plagio-clase-2. The bulbous-type myrmekite is very com-mon and mainly occurs in the rims of larger crystals. Feldspars show strong wavy extinction and deforma-tion lamellas. Such aspects are only observed in the phenocrystals and are absent in the matrix compo-nents. This suggests synvolcanic deformation associ-ated with the attrition of crystals at the eruption vent, which only affected the phenocrystals that had already been formed. Among some feldspar crystals, there are clusters of intermediate size quartz-feldspar between the matrix and the phenocrystals. Some of the crystals in the clusters have the same optical orientation as the phenocrystals (Fig. 5C), which indicate the variations of mineral nucleation and growth rates involved in the formation of these volcanic rocks.

Canoas Syenogranite The hornblende-bearing sy-enogranites and minor hornblende-bearing alkali feld-spar granites have a medium-grained seriate texture (Tab. 1, Fig. 4B). The alkali feldspar is sub-hedral and strongly perthitic (stringlets, strings, interlocking and chessboard albite) with generation of sub-hedral

albite crystals. It contains plagioclase inclusions, and its contacts with the plagioclase and quartz are faintly interdigited. The euhedral, normal-zoned plagioclase measures between 0.5 and 3.0 mm. It is a sodic oligo-clase (An10-12) and displays Albite and Albite-Carlsbad Laws twining. Its contacts with the alkali feldspar and quartz are rectilinear, and those with hornblende are interdigited. The hornblende, strongly altered to chlo-rite, commonly occurs as interstitial crystals contain-ing Fe-Ti oxide inclusions. The zircon is euhedral and measures up to 0.2 mm. Some sub-hedral titanite crys-tals have been greatly altered to epidote. According to geologist Desaix Silva (Brazilian Geological Service, personal communication), the garnet happens only in more evolved rocks as very fine crystals. The relat-ed mafic dikes are represented by quartz-gabbro and have intergranular and sub-ophitic textures, high am-phibole contents, and plagioclase xenocrystals. The xenocrystals have been partially dissolved in their cores and rims.

São Gabriel Granite Hornblende monzogran-ite, hornblende syenogranite and biotite-hornblende syenogranite are the major petrographic variations observed in São Gabriel Granite (Tab. 1, Fig. 4C). Microgranite porphyry and microdiorite occur infre-quently as dikes near the boundaries of the batholith. Medium-grained rapakivi-type textures predominate in all litho-types. Albite and Albite-Carlsbad Law twinning and major normal zoning, as well as mi-nor abrupt and sectored oscillatory zoning, are in two plagioclase types (Tab. 2).

Plagioclase-1 is euhedral (from 2 to 6.5 mm), has an An22–An28 composition in the core (seen in different hydrothermal transformation zones) and an An22–17 one in the rims. The contacts are rectilin-ear with the hornblende-1 and are interpenetrative with the quartz-1. This plagioclase contains amphi-bole, Fe-Ti oxides, apatite, and zircon inclusions. The amphibole and Fe-Ti oxides inclusions are fre-quently located in the core of the plagioclase crys-tals. Plagioclase-1 and -2 form clusters similar to the Synneusis. Plagioclase-2 (0.5 – 1.5 mm) is anhedral–sub-hedral, unzoned and zoned (oscillatory). It is in the interstices between grains and contains inclusions of quartz-1 and biotite-2. In composition, it is An27–25 in the core and An21–17 in the rims. The alteration of the zoned plagioclase-2 resulted in anhedral crystals of epidote and sericite, whereas in the unzoned pla-gioclase-2, only sericite was formed.



Albite-Pericline law twining is common in two alkali feldspar types. Manebach twining is only ob-served in the alkali feldspar-2. The alkali feldspar-1 is sub-hedral (from 2.5 to 6 mm) and commonly oc-curs associated with quartz-1. The alkali feldspar-2 is sub-hedral–anhedral and measures 0.5 – 2.5 mm in length. Both alkali feldspars are slightly changed to sericite and clay minerals. Inclusions of plagio-clase-2, hornblende-1, zircon, apatite, and perthite are very common. Albite microfilms grew along con-tacts and shift to a string-type arrangement coin-ciding with 001 cleavage. Locally interlocking and beaded perthites developed in the alkali feldspar-1 of the biotite-hornblende syenogranite. Intergranular al-bite is in all facies, however it is very abundant in the syenogranites. Some mantled alkali feldspar crys-tals (1-type) have ovoid shapes due to corroded rims (Fig. 5D). The product of alkali feldspar-1 exsolution seems to have grown on plagioclase-2 with corroded rims (anti-rapakivi-like) and on plagioclase-mantled alkali feldspar-1 (double mantle rapakivi-like).

Quartz-1 is anhedral–sub-hedral and measures 1 – 1.5 mm length. Quartz-2 is interstitial and is as-sociated with biotite-2. Quartz-3 shows strong undu-latory extinction and is typically precipitated on the alkali feldspar-1.

Hornblende-1 is sub-hedral to euhedral and is associated with Fe-Ti oxides and titanite. Alteration to chlorite is very common, but epidote and biotite are also observed. The contacts with the plagioclase-1 are rectilinear, whereas those with the quartz-1 and alka-li feldspar-1 display re-entrances. The hornblende-1 has inclusions of Fe-Ti oxides. Hornblende-2 is as-sociated with quartz-2 and fills interstices and cleav-ages of the plagioclase.

Sub-hedral crystals of biotite-1 display sev-eral apically corroded magnetite and ilmenite inclu-sions. The biotite-2 is a product of breaking-up horn-blende-1 and -2, filling the interstices between grains.

The Fe-Ti oxides are coupled with hydrat-ed Fe-Mg minerals and titanite. The latter happens as euhedral crystals up to 2 mm long and is asso-ciated with hornblende-1 and Fe-Ti oxides. Some titanite crystals have fluid inclusions with bubble shapes. The apatite is euhedral, acicular and hex-agonal, and exhibits intimate relationships with hornblende-2 and plagioclases with simultaneous extinctions that suggest contemporaneous phases (Hibbard 1995). The zircon is euhedral to sub-he-dral and sharply zoned.

The sericite-muscovite is associated with cal-cic portions of plagioclase. Low intensity argilization also occurred in the alkali feldspar. The epidote stands out by forming euhedral crystals, reflecting the high decalcification rates of calcic plagioclase. The albite is formed from the perthite. Hematite is common in alkali feldspar-rich granites. It is in sodic lamellas of perthite, interstitial among other minerals, filling microfractures, and as espherulitic crystals. Most of the hematite must have originated from magnetite-il-menite alteration or substitution, precipitation on the feldspars by hydrothermal aqueous fluids.

The microgranite porphyry dikes contain feld-spar crystals up to 2 cm in length (Fig. 5E), medi-um- to fine-grained matrix and local granophyric intergrowths, which mark the intrusive stage. The re-lationship between the phenocrystals and the matrix is similar to lava flow rhyolite, suggesting correlation.

The mingled microgranular enclaves (quartz-diorite, Fig. 5F) of São Gabriel Granite present tex-tural and mineralogical features similar to those de-scribed for the mafic enclaves of Terra Preta Granite. Exceptions include the presence of biotite, amphi-bole pseudomorphs, and slightly more calcic plagio-clases (An27-30).

Crystallization sequences The crystallization sequence of Terra Preta Granite (Fig. 6A) involves the stabilization of precocious minerals (apatite and zircon), followed by nucleation of plagioclase-1 (core) and stabilization of the Fe-Ti oxides. The high integrity of the oxides suggests slight participation in the formation of titanite. The synneusis relation-ship indicates that the plagioclase-2 grew concomi-tantly with some plagioclase-1 crystals. The presence of clinopyroxene pseudomorphs indicates a crystal-lization sequence, which includes deuteric reactions between varietal minerals and liquid.

The crystallization sequence of Canoas Syenogranite starts with the crystallization of zircon and apatite, followed by the consecutive crystalliza-tion of Fe-Ti oxides, plagioclase, quartz, hornblende, alkali feldspar, and titanite (Fig. 6B).

In São Gabriel Granite, the crystallization of the Fe-Ti oxides, Fe-Mg minerals, plagioclase, alkali feldspars and quartz were in a similar way as in the analyzed facies. The crystallization order (Fig. 6C) consisted of the stabilization of oxides, titanite, horn-blende-1, biotite-1, plagioclase-1 core, apatite-zir-con, plagioclase-1 rims, plagioclase-2 core, quartz-1,



and alkali feldspar-1. After the crystallization of the first phase, destabilization of the lower minerals tem-perature occurred, which resulted in the partial or to-tal corrosion of the rims and congruent dissolution of the calcic core of the plagioclase-1 by forming plagioclase-3. The alkali feldspar-1 had their rims

corroded to form ovoid crystals, whereas part of the quartz-1 was solubilized. Stabilization of the crystals of hornblende-2 and quartz-2, alkali feldspar-2 and plagioclase-2 rims happened soon after. Some of the alkali feldspar-2 and plagioclase-2 appears to have only epitaxially grown on the plagioclases, corroded

Figure 5 – Microtextural features of the studied plutons and related rocks. (A) Tremolite-actinolite and minor plagioclase in amygdaloidal structures in the Terra Preta Granite-related synplutonic quartz-gabbro. (B) Re-absorption features in xenocrystals of Terra Preta Granite hybrid quartz-diorite. (C) Intermediate-size crystal clusters between matrix and phenocrystals, displaying the same optical orientation as the phenocrystals. (D) Ovoid plagioclase mantled by perthitic alkali feldspars crystal (rapakivi texture). (E) Alkali feldspar crystal in microgranite porphyry dike. (F) Microgranular enclave of São Gabriel Granite. pl: plagioclase, af: alkali feldspar and qz: quartz.

A

C

E

B

D

F



post-magmatic crystalizationmagmatic crystalizationFe-Ti oxides

titaniteplagioclasse-1 core pl-1 rim, plagioclase-2

quartz-1 quartz-2

alkali feldspar-1

hornblende

apatite, zircon

biotite-1 biotite-2

af-2 af-3

hematiteepidoteepidote, sericite, argilic minerals,muscovite, carbonate

actinolite, chlorite, biotite,epitode, titanite?

argilic minerals, albite intergranular,perthite, albite chessboard

quartz-3

A


titaniteplagioclase

quartz-1

alkali feldspar

hornblende

apatite, zircon

hematiteepidoteepidote, sericite, argilic minerals,muscovite, carbonate

chlorite

argilic minerals, albite intergranular,perthite, albite chessboard, albite

quartz-3

B


titanite

plag-1 core plagioclase-2 rimplag-1 rim, plag2 core

quartz-1 quartz-2

alkali feldspar-1 alkali feldspar-2

hornblende-1 hornblende-2, biotite-1 bt-2

apatite, zircon

hematiteepidote

epidote, sericite, argilic minerals,muscovite, carbonate

chlorite, biotite

perthites, albite intergranular,argilic minerals, myrmekite

quartz-3

C

Figure 6 – Magmatic crystallization sequence and the postmagmatic minerals of Terra Preta Granite (A), Canoas Syenogranite (B), and São Gabriel Granite (C). The crystallization sequence was suggested from mineral inclusions and contacted relationships between crystals.

alkali feldspar rims, and the mantled alkali feldspar. These features are named stricto sensu anti-rapaki-vi and rapakivi and double-mantle rapakivi textures, respectively (Rämö 1991, Hibbard 1995, Rämö & Haapala 1995, Haapala & Rämö 1999).

Dynamostatic rocks The field and microdefor-mational features revealed increasingly intense de-formation from E to W, recorded mainly in Terra Preta granitoids and minor Canoas syenogranites in the western sector of the study area. According to Paschier and Trouw’s (1998) criteria, the deformed rocks registered low, low-medium, and medium-high temperatures.

The less deformed rocks have medium-grained granular texture. The quartz is ellipsoidal and moder-ately flattened, with rims that present undulatory ex-tinction and sutured contacts. Mantles composed of small new-grains surround slightly deformed or un-deformed porphyrclasts of quartz and feldspars. The quartz with strong undulatory extinction developed

deformation bands, whereas trails of neoblasts of quartz were formed in the boundaries of subgrains (Fig. 7A). The fragile structure of the alkali feldspar crystals allowed the local development of fractures filled by quartz, and it formed curved and rarely sig-moidal, antitaxial and fibrous quartz veins (Fig. 7B). The foliation is spaced and disjunctive and composes about 20% of the cleavage domain and 70% of the microlithes. The cleavage domain is irregular and its spatial relationship and transitions to the microlithe domains are anastomosed and gradual.

In the low-medium deformed rocks, recov-ery rate involves strong undulatory extinction and deformation bands and subgrains. Subgrain rotation is common and grain boundary migration is local. Some feldspar porphyroclasts have mantles of quartz neoblasts and trails, and fluid inclusions. Alkali feld-spar porphyroclasts are surrounded by new grains of quartz and feldspar (mantle-core structure). Plagioclase inclusions, flame perthite and bulbous myrmekite rims are also common (Fig. 7C). The fo-liation is spaced, irregular disjunctive in about 30% of the cleavage domain, anastomosed, and gradual.

In the medium-high degree zone, the rocks are formed of a matrix of quartz and feldspars that are broadly recrystallized, in addition to quartz and feld-spar porphyroclasts, biotite, and Fe-Ti-oxide trails. The quartz porphyroclasts occur as trail-shaped poly-crystalline crystals due to accentuated stretching and formation/rotation of subgrains. Interdigited subgrain contacts are associated with grain boundary migration of denser grains onto less dense ones. The feldspar porphyroclasts exhibit prominent mantle-core struc-ture (Fig. 7D). The bulbous myrmekite is very com-mon on alkali feldspars. Locally, the perthitic alka-li feldspar displays antitaxial fibrous veins of quartz, suggesting that the pressure solution remained active during deformation. The alkali feldspar cores were preserved and myrmekites were formed on border-core boundaries. The foliation is spaced disjunctive, regular in about 80% of the cleavage domain and the contacts with microlithes are abrupt.

Static metamorphic rocks In the NE sector of the studied area, intermediate rocks and granit-oids of São Gabriel Granite, and especially Canoas Syenogranite, have been statically recrystallized by a thermal event likely linked to intrusions of mafic dikes/stocks. The metagranites contain diabase dikes and pods displaying fractures that were filled by the



same material provided by one of the host rocks (Canoas Syenogranite).

DIABASE The recrystallized diabase (nemato-blastic texture) displays schistose textures due to the emplacement structures (dikes) and spaced, disjunc-tive and irregular foliation with a cleavage domain of about 80% (Fig. 7E). It locally happens as lenses (augen) composed of actinolite inclusions in escapo-lite porphyroblasts. The augen seems to have been composed of amphibole, escapolite (meionite?) and epidote (clinozoisite) probably generated from py-roxene + H2O → hornblende and plagioclase + H2O → escapolite + epidote reactions. Hydrothermal re-actions are observed in hornblende rims formed by actinolite. Escapolite occurs as < 0.1 mm crystals and 3 to 5 mm plagioclase pseudomorphs. The sub-he-dral–euhedral (up to 0.2 mm) epidote is usually asso-ciated with escapolite and actinolite.

GRANITOIDS The predominant texture of the re-crystallized granitoids is interlobate granoblastic, ranging from seriate to equigranular. Minor recrys-tallized rocks locally preserve igneous textures, in-cluding fibrous veins, crystal-plastic deformation of quartz, and fragile deformation of feldspars (Fig. 7F). With the exception of mafic dikes, all rocks contain muscovite associated with deformation, which is more abundant in the rocks that have no preserved igneous textures. The muscovite may have been gen-erated by the hydration reaction of alkali feldspar + H2O → muscovite + quartz. The granolepidoblastic texture of Canoas muscovite hornfels xenoliths con-trast with the equigranular interlobate granoblastic texture of São Gabriel Granite wall rock. This oc-curs by virtue of the decreasing thermal contrast be-tween the partially assimilated wall rock fragments (sub-angular) and the host magma, preserving pre-vious characteristics of a dynamo-thermal deforma-tion event. These features and the presence of a dyna-mo-thermal event suggest a different deformational event between 1.88 Ga and younger mafic intrusions. Alternatively, the textural orientation of the enclaves may have happened due to increasing turbulent flux near the borders of São Gabriel magma chamber.

DISCUSSIONLithostratigraphic units The main 1.90 to 1.89 Ga calc-alkaline rocks of the central portion of Amazonian Craton are associated with Água

Branca Suite (CPRM 2006, Ferron 2006, Almeida 2006, Valério et al. 2006b). The more thoroughly studied pluton (Caroebe Granite) consists of a gran-itoid association of Peru- or Sierra Nevada-type granodiorite of the calc-alkaline series (Almeida 2006, Almeida & Macambira 2007). The Terra Preta Granite is classified in this study as an I-type, high-K calk-alkaline pluton, whose size and shape re-main undefined due to reworking of its western and southern borders caused by a poorly defined defor-mational event and the cover of the Amazon basin (Valério et al. 2009 & 2010).

The Jauaperi Complex term was applied by CPRM (2006) to characterize gneiss and metagran-ites occurring in the southern region of the Guyana Shield. Our study showed that this region is domi-nated by Água Branca group and Mapuera granitoids and undivided mafic rocks, which recorded the ef-fects of a supposed regional metamorphism whose age, amplitude, and magnitude were not delimited.

Based on their geochemical signatures and plutonic association types, the volcanic rocks from the NE Amazonas (1.89 – 1.87 Ga) were classified into a high-K calc-alkaline group associated with Água Branca granitoids (Jatapu volcanics) and an alkaline potassic-type related to the Mapuera gran-ites (Almeida 2006, CPRM 2006, Valério et al. 2006A & B, Ferron et al. 2006 & 2010, Almeida & Macambira 2007, Marques et al. 2007). Ferron et al. (2006) proposed separating the volcanic rocks of Iricoumé Group into formations, and argued that Pitinga Province‘s volcanism is associated with the generation of alkaline-K, high-Sr, A-type gran-ites. Part of this volcano-plutonic event was de-veloped from preserved caldera structures (Ferron et al. 2006, Souza et al. 2007). Due to the high ero-sion rates that are characteristic of the area near the northern border of the Amazon basin, the supposed caldera structure of the study region was only faint-ly preserved.

However, the structural features are similar to classic models of eroded calderas (cauldrons) with-out sedimentary events (Lipman 1984 & 1997, Cole et al. 2005, Acocella 2007), such as the presence of effusive andesite, explosive eruptions caused by un-der-pressure (Acocella 2007), and presence of sev-eral ignimbrite deposits, intrusions of autoclastic breccias and microgranite porphyry, and lava flow deposits (hornblende rhyolite/rhyodacite) associated with the postcollapse phase.



Figure 7 – Microtextural features of studied pluton-related metamorphic rocks. (A) Less deformed rocks of the study area. The quartz crystals present strong undulatory extinction and development of deformation bands, subgrains and trails of quartz neoblasts. (B) Antitaxial, fibrous quartz veins in fractured alkali feldspar crystals. (C) Rims of bulbous myrmekite and new grains on the plagioclase. (D) Prominent mantle-core structure in an alkali feldspar porphyroclast. (E) Detail of lenses composed of actinolite inclusions in an escapolite porphyroblast in diabase linked to statically recrystallized Canoas hornblende-bearing syenogranite (muscovite-actinolite hornfels). (F) Details of muscovite crystals in muscovite-actinolite hornfels. pl: plagioclase; af: alkali feldspar; qz: quartz; bt: biotite; ms: muscovite.

A

C

E F

B

D

The Mapuera Suite is made up of several large A-type granite plutons emplaced at 1.89 to 1.86 Ga (CPRM 2006, Almeida 2006). Several stocks

of reddish syenogranites and minor alkali feldspar-granite associations were generically grouped into the Mapuera Suite, mainly based on geochemistry



and absolute ages, but without taking into consid-eration problems such as geochemical convergence and absence of field evidence. Valério et al. (2006a) showed that there are petrographic and geochemi-cal similarities between biotite-hornblende syeno-granite from the south/southeastern borders of São Gabriel Granite and other large granitic bodies of the Mapuera Suite, however this is not conclusive for Canoas Syenogranite. In addition, the major re-lationship of Canoas Syenogranite with Terra Preta granitoids has driven to classify some of these syeno-granitic bodies as the São Gabriel Granite. Another aspect that supports this stratigraphic arrangement is the textural dissimilarity between the hornfels xe-noliths (granolepidoblastic) and São Gabriel Granite wall rock (granoblastic).

Some of the mafic rocks from the southwest sector of the study area, described along the Pardo River (e.g., olivine-gabbro), have been includ-ed in the Seringa Formation, with 1.20 to 1.07 Ga (CPRM 2000). According to its original definition (Veiga Jr. et al. 1979), the Seringa Formation is characterized by mafic dikes and lava flow depos-its. Differentiated diorites and quartz-diorites, not associated with calcic-alkaline granitoids, are only mentioned in the Quarenta Ilhas Formation (1.79 Ga) (CPRM 2006) and are never cited as rocks re-lated to the studied granitoids.

Petrological considerations In the central-southern Guyana Shield (SE Roraima State, Brazil), Almeida et al. (2002) and Almeida & Macambira (2003) described important field and petrographic features that demonstrated the evolutionary pro-cesses of Água Branca magma, including the local assimilation of wall rocks. Ague & Brimhall (1987) observed similar aspects in calc-alkaline granit-oids from Sierra Nevada. They showed that granit-oid magmas were variably contaminated at region-al and local scales by crustal igneous, metamorphic and sedimentary rocks. Chappell (1996) conclud-ed that the assimilation processes and hybridization between mafic and felsic magmas do not result in great compositional variations and argued that the partial melting of the lower crust alone would ex-plain such variations. Other authors have proposed that homogeneous petrographic types of granitoids could be formed by hybridization of crustal liquids with mafic magma (Frost & Mahood 1987, Huppert & Sparks 1988, Rämö 1991, Haapala & Rämö 1992

& 1999, Rämö & Haapala 1995) or with dioritic and tonalitic magmas derived, by fractional crystal-lization, from mantle basaltic liquids (Castro et al. 1990 & 1991).

Based only on the F, Zr, Nb and rare earth ele-ments contents of the Mapuera magma, Ferron et al. (2010) advocated a mantle origin before being modi-fied by subduction in a post-collision tectonic setting. However, they have also considered a bimodal origin in and extensional environment, as previously argued by Almeida (2006).

The present evaluation, based on field and pe-trographic data, suggest that, in addition to fraction-al crystallization, processes of wall rock assimilation and magma mingling had played a role, at least at the local scale, in the evolution of granitoids from the NE Amazonas State.

Texture and deformation of Terra Preta and Canoas granitoids Barker (1970) showed that granophyric intergrowths could be formed in re-sponse to the simultaneous/rapid crystallization of alkali feldspar and quartz from liquid or vapor. The origin of intergrowths would involve volatile-rich liquids in the final processes of crystallization in epi-zonal environments (Hibbard 1979, & 1987, Hughes 1982). These magmatic conditions are compatible with underformed granitoids with restricted grano-phyric textures that are likely related to the presence of aplite dikes formed from sudden replacement of H2O-saturated phases, due to pressure loss that ac-celerated the nucleation rates (Hibbard 1995). In re-crystallized granitoids, however, the granophyric textures must be associated with dynamo-thermal deformation.

The bulbous and intergranular myrmekites that were developed along alkali feldspar boundaries showed different crystallographic orientations. For Phillips (1974, 1980), and Smith & Brown (1988), the myrmekite is formed by the exsolution of alka-li feldspar accompanied of pressure-induced disso-lution and reprecipitation in a subsolidus state with some participation of primary quartz and K-feldspar. Smith & Brown (1988) suggested that subsequent processes could partially or completely modify the myrmekite by recrystallizing it. This points out myr-mekites as petrogenetic indicators and suggests that myrmekites in the dynamically crystallized studied granitoids must have been originated from subsolidus deformational processes.



The origin theories of the deformation pro-cess proposed for rocks of the area study are con-troversial, not only due to limited geochronological data, but also because of the incomplete knowledge of structural features at the field level. The reconsti-tution of events shows that Terra Preta Granite was emplaced during the postcollisional uplift, followed by deformation induced by the effects of oceanic plate subduction under the Vantuari-Tapajós paleo-continent at the beginning of Rio Negro Province building (Valério et al. 2009). This model can be valid if we consider the different crustal levels be-tween the undeformed São Gabriel Granite (and related rock) and Terra Preta Granite and Canoas Syenogranite (deformed). In contrast, CPRM (2000) and Valério et al. (2006b) presented a collisional model that is incompatible with the small differ-ence in age (~ 10 Ma) and petrographic dissimilari-ties between the syncollisional and anorogenic bod-ies. Therefore, based on petrographic analysis, it is simpler to think that this deformation and metamor-phism must be linked to an event slightly younger than the Terra Preta magmatism, which was likely associated with strike-slip faults in an extension-al setting, whose effects were not registered by the subvolcanic, shallower São Gabriel Granite and re-lated rocks.

CONCLUSION REMARKS Field and petro-graphic features supported by previous works raised in this study lead to the following conclusions:• Transitional contact zones between par-

tially fragmented mafic dikes and wall rocks (Terra Preta hornblende granodiorite), where mafic and intermediate enclaves with low and high xenocrystals contents, respective-ly, and mingled quartz-diorite, have been formed. These features indicate that at least one generation of mafic dikes was emplaced before the complete crystallization of Terra Preta Granite.

• The diffuse contact and recrystallized xeno-liths suggests that Canoas Syenogranite is slightly younger than Terra Preta Granite and older than São Gabriel Granite. We considered that the Canoas hornblende-bearing syeno-granites were generated from Mapuera mag-ma. However, the intimate field relationships with the Terra Preta granitoids and differenti-ated mineral paragenesis point to a divergent

evolution, and therefore its association with Mapuera magma is not conclusive.

• Interaction features and petrographic evi-dence suggest that, in addition to fraction-al crystallization, assimilation and magma mingling processes played a role at least in the local scale, in the evolution of the Terra Preta Granite, Canoas Syenogranite and São Gabriel Granite. Microfeatures of magma mingling have been found in all granitoid plutons at variable rates, such as plagioclase dissolution, feldspar rim corrosion, alkali feldspar and plagioclase mantles, a second generation of apatite and high xenocrystals contents in mafic enclaves.

• The crystallization sequences support frac-tional crystallization as a dominant differ-entiation process of Terra Preta Granite and Canoas Syenogranite, while in São Gabriel Granite, magma mingling seems to have been in harmony with all phases of fractional crystallization.

• Undeformed gabbros, diorites and minor anor-thosite likely are linked to the rapakivi-type São Gabriel Granite. Except near these un-deformed rocks, all granitoids in the western sector of the study area recorded apprecia-ble and progressive dynamostatic deforma-tion from E to W. Such event must have oc-curred between 1.90 Ga (Terra Preta Granite) and the intrusions of the São Gabriel Granite (1.89 Ga) and related rocks. We point to an alternative origin, which is associated with an event slightly younger than the postcollision-al uplift. However, it is extremely necessary to obtain absolute ages for this metamorphic event, which is the purpose of these authors’ next paper.

ACKNOWLEDGEMENTS This research was financed by the Institute of Geosciences, Federal University of Pará and the CT-Amazonia proj-ect (MCT-CNPq 575520/2008-6). We thank the Brazilian National Council of Technological and Scientific Development (CNPq) scholarship (140758/2007-0) granted for funding the first au-thor, and the Department of Geosciences, Federal University of Amazonas, for storing the sam-ples gathered in the field and for partial sample preparation.



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Field and petrographic data of 1.90 to 1.88 Ga I- and A ...

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