Download Geology of the Precambrian Sangre De Cristo Range of New Mexico

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Geology of the Precambrian
Sangre De Cristo Range and
Picuris Mountains of New
Angelique Northcutt, Garrett Owen, Chris
Perdue, Bo Price, Tory Rogers
Where are we going?
-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,
-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.
-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.
-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
-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
-This Orogeny also formed many high grade
metamorphic rocks through generally pervasive
Pre-Cambrian rocks
-Isoclinal folding
-East-west strike
-Southward dips (60-70 degrees)
-2 major anticlines and 2 major synclines
-Wave lengths 1 to 2 miles
-Doubly plunging (~20-30 degrees)
Pilar Anticline
-Widely displaced by the Pilar-Vadito tear fault
-Slightly overturned to the north
-Axial plane dipping south (60 degrees)
Hondo Syncline
-Axial plane dips south (60-70 degrees)
-Eastern segment plunges 30-40W
-Western segment plunges 10-20E
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
-Abundant/wide variability in pre-Cambrian
-3 predominant sets
-N10W to N10E (almost vertical)
-N50W to N70W (dipping steeply NE)
-N20E to N40E (dipping steeply SE)
-N-S joints followed almost
exclusively by copper
quartz veins
-Mineralization after granitic
-Harding pegmatite estimated
-Indicates time of jointing
Stretched Pebbles
-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
Three Major Fault Systems
Picuris-Pecos fault
Embudo transfer fault
Sangre de Cristo fault
Picuris-Pecos Fault System
84 km long fault system consisting of five parallel fault zones:
-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
-North-striking strike slip fault
-West-down branching fault splay
Rio Grande del Rancho
-Kilometer-wide, west-down fault zone
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
Fault consists of two sections based on reversal
of throw
Strike of N60E
Sinistral net slip rate of .15 mm/year
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
Aerial View of Faults in Taos Region
Pre-Cambrian Formations:
• The Hondo Group
-The Pilar Formation
-The Riconada Formation
-The Ortega Formation
• The Vadito Formation
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
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
The Riconada Formation
Quartzite bed – Grayish white in color, contains
glassy- white and translucent quartzite
Muscovite-quartz-biotite-garnet Phyllite bedMuscovite rich phyllite containing garnet
crystals and biotite, sheen that ranges from
pearly gray to greenish
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
Vadito Formation
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
Marquenas Formation
Total thickness: ~ 2,000 feet
Composed of Quartz Conglomerate and Quartzite, Felsites and
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
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
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
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
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
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