Geology of the Precambrian Sangre De Cristo Range of New Mexico

Report
Geology of the Precambrian
Sangre De Cristo Range and
Picuris Mountains of New
Mexico

Angelique Northcutt, Garrett Owen, Chris
Perdue, Bo Price, Tory Rogers
Where are we going?
Background
-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
-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.
History
-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
-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
-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.
Pre-Cambrian rocks
-Isoclinal folding
-East-west strike
-Southward dips (60-70 degrees)
Folds
-2 major anticlines and 2 major synclines
-Wave lengths 1 to 2 miles
-Doubly plunging (~20-30 degrees)
Folds
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
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
Jointing
-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
-N-S joints followed almost
exclusively by copper
ore-bearing
quartz veins
-Mineralization after granitic
intrusion
-Harding pegmatite estimated
800myo
-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
shape
Three Major Fault Systems
•
Picuris-Pecos fault
system
•
Embudo transfer fault
•
Sangre de Cristo fault
zone
Picuris-Pecos Fault System
84 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
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
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:
Staurolite
• 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
Andalusite
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
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
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
composition
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
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
Questions?

similar documents