emerging data on rodinia rifting from marathon fold-thrust belt, southern laurentia
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Emerging Data on Rodinia Rifting from Marathon Fold-Thrust Belt, Southern Laurentia. Patricia W. Dickerson, Daniel F. Stockli, Richard E. Hanson & Jonathon M. Roberts GSA – Vancouver, 2014 Birth and Death of Supercontinents. Southern Laurentia – West Texas. Ouachita-Marathon - PowerPoint PPT PresentationTRANSCRIPT
Emerging Data on Rodinia Rifting fromMarathon Fold-Thrust Belt, Southern Laurentia
Patricia W. Dickerson, Daniel F. Stockli, Richard E. Hanson & Jonathon M. Roberts
GSA – Vancouver, 2014Birth and Death of Supercontinents
Diablo PlatformAncestral Rockies-
stylebasement-cored
uplift
Deformed as Pangea was born, Marathon fold-thrust belt provides new insight into the dying
days of Rodinia
Ouachita-Marathonthin-skinned fold and thrust belt
Goetz in Goetz & Dickerson (1985)
Southern Laurentia – West Texas
L–M Ordovician Strata Bearing Igneous Clasts(Roberts et al., 2010)
Host strata: Shelf-derived fossiliferous limestone conglomerates within off-shelf deposits, western Ouachita-Cuyania Basin
Deposits spanning ~28 Ma(Intl. Subcom. Ord. Strat., 2007)
3 formations to date:Woods Hollow (Sandbian)Ft. Peña Formation (Darriwilian)Marathon Formation (Floian)
Silicified Alkali Basalt Boulder in Limestone Cobble
Conglomerate, Marathon Fm.
Rift-Related Intraplate Magmatism – Rodinia Breakup: 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
Geochronology - Marathon & Ft. Peña Basalts
U-Pb, SHRIMP (Fanning, ANU)
Marathon basalt boulder 207Pb/206Pb ages from ~1920 to ~1270 Ma Younger ages appropriate for Grenvillian basement rocksFt. Peña basalt boulder 1 - ~1230 Ma (Grenvillian)Ft. Peña basalt boulder 2 - ~720 and ~660 Ma (Neoproterozoic)
No known outcrops ofNeoproterozoic toEocambrian lavas in the region
Seismic and borehole data indicate thatGrenvillian meta- morphic rocks formfoundation for theMarathon Basin
Boulder Source(s), Marathon Basin?
PROTEROZOIC FOUNDATIONS - W. OUACHITA BASIN(modified from Karlstrom et al., 2004)
New Data from Marathon Fm:Two Magmatic Pulses during Rodinia Rifting
Tuff boulders in debris flows of the Monument Spring Mbr
Bentonitic layer in uppermost Marathon Fm
780-700 Ma – Neoproterozoic volcanism 580-520 Ma – Eocambrian volcanism U/Pb, LA-ICPMS, zircon (Stockli, UT-Austin) COEVAL WITH RIFT MAGMATIC EPISODES OF EASTERN
LAURENTIA
(Roberts, 2012)
Felsic Tuff Clasts Marathon Fm, Monument Spring Mbr
U/Pb, LA-ICPMS - zircon (Stockli, UT-Austin)
207Pb/206Pb ages: 1300-1100 Ma – Grenvillian basement source 750-700 Ma – Neoproterozoic rift volcanic source ~520 Ma – Eocambrian rift volcanic source
Bentonitic Layer Uppermost Marathon Fm
U/Pb, LA-ICPMS – zircon (Stockli, UT-Austin)
207Pb/206Pb ages: 1400-1100 Ma – Grenvillian basement source 780-750 Ma – Neoproterozoic rift volcanic source 580-520 Ma – Eocambrian rift volcanic source
South-Central Laurentia(modified from Viele, 1989)
Devils River Uplift – Prior to analyses of the Marathon (M) clasts, DRU provided the sole evidence for co-located Neoproterozoic
and Eocambrian magmatism in this span of the margin.
M
Devils River UpliftNeoproterozoic & Eocambrian Magmatism
Subsurface, 75 km ESE of Marathon fold-thrust belt exposures
Rb/Sr, whole-rock age determinations on exploration well cores:711 ± 23 Ma – metarhyolites524 ± 32 Ma and 529 ± 31 Ma – metavolcanics within metasediments
Forthcoming geochemical analyses to determine tectonic environment
(modified from Nicholas and Rozendal, 1975)
Eastern Laurentia Two-Stage Rodinia Rifting – Representative
Examples
NEWFOUNDLAND (Cawood et al., 2001) 760 – 700 Ma felsic volcanics, dike swarms 570 – 535 Ma bimodal, basalt and rhyoliteADIRONDACKS (Cawood et al., 2001; Burton and Southworth, 2010) 760 - 680 Ma felsic rocks of massif 620 - 580 Ma mafic dikes CENTRAL & SOUTHERN APPALACHIANS (McCausland et al., 2011) 750 Ma dominantly felsic 615 – 590 Ma tholeiites to alkaline basaltsAPPALACHIANS, BLUE RIDGE (Southworth et al, 2009; Tollo et al. 2012) 760 – 680 Ma felsic volcanics and plutons 565 Ma dominantly maficN. CAROLINA, GRANDFATHER MT. (Burton and Southworth, 2010) 760 – 700 Ma felsic volcanics 600 – 550 Ma basalt and rhyolite
Opening of Iapetus –Divergence of Laurentia and Gondwana
(PLATES Program, UTIG, 2011)
Two-stage rifting along E Laurentian margin at ~760 to ~700 Ma and ~570 to ~535 Ma
Intraplate extension/rift geo-chemical signature for 706 Ma volcanic boulders in L-M Ordo- vician strata of Marathon Basin
New 780 to 520 Ma ages suggest that S margin experienced coeval Neoproterozoic-Eocambrian rift magmatism
750 - 700 Ma
A fragmentary record ofNeoproterozoic - Eocambrian volcanism –
possible within-plate extensional magmatism during rifting of south-central Laurentia
Eos – the dawn of Iapetus