Angelique Northcutt, Garrett Owen, Chris Perdue, Bo Price, Tory Rogers Geology of the Precambrian...
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![Page 1: Angelique Northcutt, Garrett Owen, Chris Perdue, Bo Price, Tory Rogers Geology of the Precambrian Sangre De Cristo Range and Picuris Mountains of New.](https://reader038.fdocuments.net/reader038/viewer/2022102818/56649cbb5503460f949834ec/html5/thumbnails/1.jpg)
Angelique Northcutt, Garrett Owen, Chris Perdue, Bo Price, Tory Rogers
Geology of the Precambrian Sangre De Cristo Range and Picuris Mountains of
New Mexico
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Where are we going?
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-The Sangre de Cristo fault is a west dipping fault in New Mexico -It forms the border between the Sangre de Cristo Mountains and the San Luis Basin.
-The Sangre de Cristo fault extends from poncho Pass, Colorado to near where we’ll be in Taos, NM.
Background
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-The section we will be focused on extends from the San Pedro Mesa creek south to the intersection with the Embudo Fault at Rio del Rancho which is about 8 km south of Taos.
-The Sangre de Cristo is part of the more recent Rio Grande Rift.
-It is a normal fault that moves less than 0.2 mm/year.
Background
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-The Basement rocks in this location are Precambrian in age.
-The rocks of Colorado and Northern New Mexico are juvenile Volcanic- Plutonic, Ocean Arc rocks that are approximately 1.78 to 1.65 billion years old.
-In New Mexico these rocks have been assigned to the Yavapi and Mazatzal provinces.
- These Rocks were deformed during 2 major Proterozoic orogenies.
History
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-First the Colorado Orogeny has a U-Pb date that goes through 1.78-1.75 Ga.
-It was a prolonged thermotectonic episode resulting from collision, subduction, and continued convergence.
-This occurred along the paleosuture known as the Cheyenne Belt along the Archean Wyoming Province.
History
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-Second the Berthoud Orogeny has a U-Pb date that started 1.45 Ga and went through 1.40 Ga.
-This was a thermo tectonic episode that produced NE trending ductile shear zones and related folds.
-The mechanism powering this Orogeny was granitic plutonism.
-This Orogeny also formed many high grade metamorphic rocks through generally pervasive metamorphism.
History
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-Isoclinal folding
-East-west strike
-Southward dips (60-70 degrees)
Pre-Cambrian rocks
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-2 major anticlines and 2 major synclines
-Wave lengths 1 to 2 miles
-Doubly plunging (~20-30 degrees)
Folds
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Pilar Anticline
-Widely displaced by the Pilar-Vadito tear fault
-Slightly overturned to the north
-Axial plane dipping south (60 degrees) Hondo Syncline
-Overturned
-Axial plane dips south (60-70 degrees)
-Eastern segment plunges 30-40W -Western segment plunges 10-20E
Folds
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Copper Hill Anticline
-Axial plane plunges 30-35W
-N85W, 50W
-Can be traced 9 miles east of Copper Hill
Harding Syncline
-Structural detail is obscure
-Strikes E-W
-Plunge ranges 25-17NE
Folds
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-Abundant/wide variability in pre-Cambrian rocks
-3 predominant sets
-N10W to N10E (almost vertical)
-N50W to N70W (dipping steeply NE)
-N20E to N40E (dipping steeply SE)
Jointing
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-N-S joints followed almost exclusively by copper ore-bearingquartz veins
-Mineralization after granitic intrusion
-Harding pegmatite estimated 800myo
-Indicates time of jointing
Jointing
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-Conglomerate of the Vadito -Pebbles have average axial ratio of 1:2:3
-Shortest axis perpendicular to foliation
-Some wedge-like shaped with apex oriented down the lineation
-Pebbles in close contact have greater impacted shape
Stretched Pebbles
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Three Major Fault Systems
• Picuris-Pecos fault system
• Embudo transfer fault
• Sangre de Cristo fault zone
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Picuris-Pecos Fault System84 km long fault system consisting of five parallel fault zones:
• Picuris-Pecos-Major crustal boundary juxtaposing two Proterozoic rock sequences: the Hondo Group and the Miranda Granite
• La Serna-East-down fault separating Miranda Granite and Picuris Formation
• Miranda-North-striking strike slip fault
• McGaffey-West-down branching fault splay
• Rio Grande del Rancho-Kilometer-wide, west-down fault zone
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Embudo Fault Zone• Sinistral, antithetic transfer zone which
forms border between the Española Basin and the San Luis Basin
• 64 km long fault thought to be part of Jemez lineament
• Fault consists of two sections based on reversal of throw
• Strike of N60E
• Sinistral net slip rate of .15 mm/year
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Sangre de Cristo Fault Zone• West-dipping normal fault that forms border between the Sangre de
Cristo Mountains and the San Luis Basin
• Beginning of Sangre de Cristo Fault forms the terminus of the Embudo fault
• The southern area of the fault is divided into five sections. From north to south, the sections are: - San Pedro Mesa - Urraca - Questa
The northern three strike north-south - Hondo
Strikes N30W - Cañon
Strikes N20E
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Aerial View of Faults in Taos Region
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• The Hondo Group
-The Pilar Formation
-The Riconada Formation
-The Ortega Formation
• The Vadito Formation
Pre-Cambrian Formations:
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The Ortega Formation
• Estimated 2,500 ft. thick
• Gray to very light gray in color
• Mostly Quartzite
• Thin beds of sillmanite - kyanite gneiss
• Bands of schistose with muscovite
• Tourmaline
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Riconada Formation
-Richly micaceous foliated rocks
-Consists of four distinct beds:
• Andalusite-biotite Hornfels bed- Muscovite and quartz matrix that contains biotite, nodular masses of quartz and andalusite
• Staurolite Schist and Gneiss Bed- Soft and
light gray in color micaceous matrix speckled with biotite, contains staurolite crystals
Staurolite
Andalusite
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The Riconada Formation
• Quartzite bed – Grayish white in color, contains glassy- white and translucent quartzite
• Muscovite-quartz-biotite-garnet Phyllite bed- Muscovite rich phyllite containing garnet crystals and biotite, sheen that ranges from pearly gray to greenish
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Pilar Phyllite Formation
• Estimated 2,300 ft. thick
• Black to gray-black in color with a gray sheen
• Contains muscovite flakes
• Quartz veins
• Limonite masses
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• Occupies the southern 1/3 of the Picuris Range
-Named after the village of Vadito
• Best outcrops come from within a one-mile radius of the Harding Mine
-Total thickness: 4,500 feet
• Comprised of a Lower Conglomerate Member and an Upper Schist Member
Vadito Formation
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Marquenas Formation• Total thickness: ~ 2,000 feet
• Composed of Quartz Conglomerate and Quartzite, Felsites and Meta-andesites
• Quartz conglomerate outcrops in a quarter-mile wide east-west belt near Picuris Canyon but grow sparser farther east
• Composed of gray coarse to pebbly Quartzite with fine-grained micaceous quartzite matrix
• Thickness of the Quartz Conglomerate: 500 - 1,000 feet
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Marquenas Formation
• Felsites occur to the east and west of the canyon but appear to pinch out to the west along the Ortega-Vadito contact
• Composed of meta-rhyolite that grades into coarser granite representing partial replacement by granite
• Gray-white to pink-white and has a dense felsitic texture with micas and feldspars present
• Thickness of the Felsites: 50-100 feet
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Marquenas Formation
• Meta-andesites occur abundantly to the south and east of the Harding mine
• Greenish-gray to gray-black in color
• Hornblende occurs in all of these rocks as prisms and give the variable darkness in color to them
• Rocks show strong pleochroism in thin-section.
• Represent thin-layered volcanic material of dacitic and andesitic composition
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Schist Member• Consists of a schist and phyllite composed of quartz-
muscovite and a quartz-biotite granulite
• The schist is similar to the underlying conglomerate quartzite with more densely disseminated flakes of muscovite
• Phyllite is a lustrous, silvery-gray rock with stubby biotite porphyroblasts
• Granulite is fine-grained, sandy, and crudely foliated with micaceous surfaces with flakes of biotite
• Thickness: At least 1,250 feet and no more than 2,500 feet
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Amphibolites• The amphibolites found in the Vadito Formation are split
into two zones based on lithology: -One of the zones occurs in the Lower Conglomerate and one occurs in the Upper Schist
• These amphibolites show effects of intrusion by granitic and pegmatitic magma
• Thickness: 750 feet in Lower Conglomerate, and 1,250 feet in Upper Schist
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Questions?