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Emerging Data on Rodinia Rifting from Marathon Fold-Thrust Belt, Southern Laurentia

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

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Emerging Data on Rodinia Rifting from Marathon Fold-Thrust Belt, Southern Laurentia

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  1. 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

  2. Southern Laurentia – West Texas Ouachita-Marathon thin-skinned fold and thrust belt Goetz in Goetz & Dickerson (1985) Deformed as Pangea was born, Marathon fold-thrust belt provides new insight into the dying days of Rodinia Diablo Platform Ancestral Rockies-style basement-cored uplift

  3. 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)

  4. Silicified Alkali Basalt Boulder in Limestone CobbleConglomerate, Marathon Fm.

  5. Rift-Related Intraplate Magmatism – Rodinia Breakup: 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

  6. Geochronology - Marathon & Ft. Peña BasaltsU-Pb, SHRIMP (Fanning, ANU) Marathon basalt boulder 207Pb/206Pb ages from ~1920 to ~1270 Ma Younger ages appropriate for Grenvillian basement rocks Ft. Peña basalt boulder 1 - ~1230 Ma (Grenvillian) Ft. Peña basalt boulder 2 - ~720 and ~660 Ma (Neoproterozoic)

  7. Boulder Source(s), Marathon Basin? No known outcrops of Neoproterozoic to Eocambrian lavas in the region Seismic and borehole data indicate that Grenvillian meta- morphic rocks form foundation for the Marathon Basin PROTEROZOIC FOUNDATIONS - W. OUACHITA BASIN (modified from Karlstrom et al., 2004)

  8. 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 (Roberts, 2012) 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

  9. 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

  10. Bentonitic Layer Uppermost Marathon FmU/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

  11. South-Central Laurentia (modified from Viele, 1989) M Devils River Uplift – Prior to analyses of the Marathon (M) clasts, DRUprovided the sole evidence for co-located Neoproterozoic and Eocambrian magmatism in this span of the margin.

  12. 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 – metarhyolites 524 ± 32 Ma and 529 ± 31 Ma – metavolcanics within metasediments Forthcoming geochemical analyses to determine tectonic environment (modified from Nicholas and Rozendal, 1975)

  13. 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 rhyolite ADIRONDACKS (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 basalts APPALACHIANS, BLUE RIDGE (Southworth et al, 2009; Tollo et al. 2012) 760 – 680 Ma felsic volcanics and plutons 565 Ma dominantly mafic N. CAROLINA, GRANDFATHER MT. (Burton and Southworth, 2010) 760 – 700 Ma felsic volcanics 600 – 550 Ma basalt and rhyolite

  14. 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

  15. Eos – the dawn of Iapetus A fragmentary record of Neoproterozoic - Eocambrian volcanism – possible within-plate extensional magmatism during rifting of south-central Laurentia

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