Tectonic Evolution of South-Central Laurentia – The West Texas Nexus

Patricia Wood DickersonUniversity of Texas at Austin

April 2013South-Central GSA, Austin

Big Bend Landsat MosaicORK Sullivan N view of W. TX. & Rift

Mesoproterozoic – Eocambrian(?)(Mosher, 2010; Grimes, 2013)

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 east5) Van Horn Ss – Synrift fan delta complex (~555 Ma?) related to Rodinia breakup and opening of Iapetus (Elston & Clough, 1993)

Franklin Mountains

Tumbledown Mt., Van Horn area

Rift-Related Intraplate Magmatism – Iapetus Opening: Basalt & Trachyandesite Clasts in Fort Peña Fm

Conglomerate

Basalt, open blue circle Trachyandesite, blue X Trachyandesite, polarized light

(Hanson, Roberts,Dickerson, & Fanning, 2012, 2013)

~706 MaU/Pb, zircon

Opening of Iapetus –Divergence of Laurentia and Gondwana

(PLATES Program, UTIG, 2011)

Rifting along Laurentian marginsfrom ~750 to ~550 Ma

Intraplate extension/rift geo-chemical signature for volcanicboulders in L-M Ordovician strataof Marathon Basin

720 to 660 Ma ages consistentwith Neoproterozoic-Eocambrianmagmatism at source(s) of clasts

750 - 700 Ma

Shared HistoryCuyania – the Departed Laurentian

Terrane

Parting of the Ways − Terrane Transfer (Dickerson, 2012)

Late CarboniferousAncestral Rockies & Ouachita-Marathon

Belt(Blakey, 2003)

Diablo PlatformAncestral Rockies-

stylebasement-cored

uplift

Late Paleozoic Deformation

in West Texas

Ouachita-Marathonthin-skinned fold and thrust belt

Goetz in Goetz & Dickerson (1985)

Basaltic phreatomag-matic volcanism, 77 Ma,Big Bend National Park − westward extension of LK Balcones intraplateigneous province(from Befus, 2008)

Cretaceous-Paleogene Magmatism

Red Hills intrusion(s) Presidio Co., TXQuartz monzonite Laramide, ~64 Ma (Gilmer, 2001)

(Barnes et al., 1979)

Cretaceous-Paleogene Deformation

Laramide basement-cored uplifts (Sierra del Carmen) and evaporite-cored folds (Chihuahua Tectonic Belt)

Left transpressive component on major NNW-trending structures, as at Mariscal Mt.

L-L fault, striae rake 40° SE

Thrust Fault in Mariscal Canyon

(Dickerson, Muehlberger and Collins, 2010)

North riverbank – revealed by 2008 floodKsp and Kse are thrust, overturned to EThrust 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 solution- collapse 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 Springporphyriticmicrogranite sill

~30.5 Ma(Ar-40/Ar-39,feldspar; Miggins in Collins et al., 2008)

XenolithsNorthern & Eastern Glenn Spring Sill - 4 Survey

Areas(Dickerson, Muehlberger & Collins, 2007)

Compositions: QuartziteSchistMarbleRare metachert

Fabrics: Sheared, isoclinally folded,dynamically recrystallized

Sizes: Maximum ~1 mMinimum ~1 mmMajority 1 – 15

cmMorphology: Subangular to subroundedDistribution: 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 centerMica schist rinds in voids – initially more

numerousMarble more common away from sill margins

Sierra del Carmen(Coahuila, MX)

GS & SdC on

margin of Laurentia during Ouachita

orogenesis277 ± 2 Ma

Greenschist-faciesmetamorphism (Carpenter, 1997)

ExposedAnalogues

Neogene-QuaternaryRio Grande Rift – Transform Complex

EARTHQUAKES:

Valentine 1931 (M 6.4)Alpine 1995 (M 5.7) 2012 (M 3.6)

Extension withright slip

(Dickerson & Muehlberger, 1994; Dickerson, 2013)

Rift grabens (N) – Sunken BlockBimodal magmatism (olivine basalt dominant)Border Corridor Transform Zone basins & faults (NW)Transfer zones (W-WNW) – Tascotal Mesa TZRift-transform junctions – Terlingua, mafic intrusions with mantle, lower crustal xenolithsQuaternary faulting, present seismicity