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Tectonic Evolution of South-Central
Laurentia – The West Texas Nexus
Big Bend Landsat Mosaic
OR
K Sullivan N view of W. TX. & Rift
Patricia Wood Dickerson
University of Texas at Austin
April 2013
South-Central GSA, Austin
Mesoproterozoic – Eocambrian(?)
(Mosher, 2010; Grimes, 2013)
Tumbledown Mt., Van Horn area
Franklin Mountains
1) Intraplate rifting (1380-1327 Ma) – Granite-Rhyolite terrane
Carrizo Mt. Group metaigneous and metasedimentary rocks
2) Continental margin basin development (~1250 Ma)
3) Grenvillian collision, transpression (1057-1035 Ma)
Streeruwitz thrust (1000-980 Ma)
4) Franklin Mts. – Metamorphic rocks (1250 Ma) intruded by granite (1120 Ma)
Granites in part coeval with Pecos Mafic Complex (1163-1073 Ma), 400 km east
5) Van Horn Ss – Synrift fan delta complex (~555 Ma?) related to Rodinia breakup
and opening of Iapetus (Elston & Clough, 1993)
Rift-Related Intraplate Magmatism – Iapetus Opening:
Basalt & Trachyandesite Clasts in Fort Peña Fm Conglomerate
~706 Ma
U/Pb, zircon
(Hanson,
Roberts,
Dickerson,
& Fanning,
2012, 2013)
Basalt, open blue circle
Trachyandesite, blue X
Trachyandesite, polarized light
Opening of Iapetus –
Divergence of Laurentia and Gondwana
(PLATES Program, UTIG, 2011)
Rifting along Laurentian margins
from ~750 to ~550 Ma
Intraplate extension/rift geochemical signature for volcanic
boulders in L-M Ordovician strata
of Marathon Basin
720 to 660 Ma ages consistent
with Neoproterozoic-Eocambrian
magmatism at source(s) of clasts
750 - 700 Ma
Shared History
Cuyania – the Departed Laurentian Terrane
Parting of the Ways − Terrane Transfer
(Dickerson, 2012)
Late Carboniferous
Ancestral Rockies & Ouachita-Marathon Belt
(Blakey, 2003)
Late Paleozoic Deformation
in West Texas
Ouachita-Marathon
thin-skinned fold and
thrust belt
Goetz in Goetz & Dickerson (1985)
Diablo Platform
Ancestral Rockies-style
basement-cored uplift
Cretaceous-Paleogene Magmatism
Red Hills intrusion(s)
Presidio Co., TX
Quartz monzonite
Laramide, ~64 Ma
(Gilmer, 2001)
(Barnes et al., 1979)
Basaltic phreatomagmatic volcanism, 77 Ma,
Big Bend National Park −
westward extension of LK
Balcones intraplate
igneous province
(from Befus, 2008)
Cretaceous-Paleogene Deformation
Laramide basement-cored uplifts (Sierra del
Carmen) and evaporite-cored folds
(Chihuahua Tectonic Belt)
L-L fault, striae rake 40° SE
Left transpressive
component on
major NNWtrending structures,
as at Mariscal Mt.
Thrust Fault in Mariscal Canyon
(Dickerson, Muehlberger and Collins, 2010)
North riverbank – revealed by 2008 flood
Ksp and Kse are thrust, overturned to E
Thrust is cut by N-striking normal fault;
thin-bedded, overturned Ksp against
massive, near-horizontal Kse
Paleogene Magmatism – Newly Exhumed Ignimbrite
(gray, foreground)
• Densely welded rhyolite tuff
• Dips 25° SSW
• Discordant with respect to
deformed Cretaceous strata
• N contact buried beneath sand
and gravel; E, S & W contacts
submerged
• Probable remnant of more
extensive deposit, preserved
in depression in K rocks
• Did it founder into a solutioncollapse cavity? (common on
Mariscal Mt.)
• Was it let down due to undercutting
by the river and removal of
fractured, less resistant K rock?
Paleogene Magmatism – Intrusions
(Collins, Dickerson & Muehlberger, 2008)
Glenn Spring
porphyritic
microgranite sill
~30.5 Ma
(Ar-40/Ar-39,
feldspar; Miggins
in Collins et al.,
2008)
Xenoliths
Northern & Eastern Glenn Spring Sill - 4 Survey Areas
(Dickerson, Muehlberger & Collins, 2007)
Compositions: Quartzite
Schist
Marble
Rare metachert
Fabrics:
Sheared, isoclinally folded,
dynamically recrystallized
Sizes:
Maximum
~1 m
Minimum
~1 mm
Majority
1 – 15 cm
Morphology:
Subangular to subrounded
Distribution:
From 3 or 4/sq m (3+ cm)
to 9 or 10/sq m
Present throughout sill, down to at least 13 m
Increase in size and number toward sill center
Mica schist rinds in voids – initially more numerous
Marble more common away from sill margins
Exposed
Analogues
Sierra del Carmen
(Coahuila, MX)
GS & SdC on margin of
Laurentia during
Ouachita orogenesis
277 ± 2 Ma
Greenschist-facies
metamorphism
(Carpenter, 1997)
Neogene-Quaternary
Rio Grande Rift – Transform Complex
Rift grabens (N) – Sunken Block
Bimodal magmatism (olivine basalt dominant)
Border Corridor Transform Zone basins & faults (NW)
Transfer zones (W-WNW) – Tascotal Mesa TZ
Rift-transform junctions – Terlingua, mafic intrusions
with mantle, lower crustal xenoliths
Quaternary faulting, present seismicity
EARTHQUAKES:
Valentine
1931 (M 6.4)
Alpine
1995 (M 5.7)
2012 (M 3.6)
Extension with
right slip
(Dickerson & Muehlberger,
1994; Dickerson, 2013)