Pat Dickerson, Ph.D
Pat is a Visiting Research Fellow with the Jackson School of Geosciences and the American Geosciences Institute
Reconstructing the tectonic history of southwestern Laurentia is Dickerson’s research focus: seeking the diagnostic evidence for Rodinia assembly and fragmentation (West Texas, Argentine Precordillera), Pangaea amalgamation (Marathon/Solitario fold-thrust belt, Ancestral Rocky Mts.), Laramide foreland deformation (Big Bend), and Rio Grande riftng/transform faulting. Research sponsors include NPS and NASA. She draws from those investigations in leading geological and natural history field seminars for students and professional scientists, as well as for Smithsonian groups. Pat has also served on task forces to develop scientific strategies for exploring the Moon and Mars. Based in the UT Walter Geology Library, her current professional service work is with the GeoRef geosciences database project of the American Geosciences Institute.
ABSTRACT
An essential tectonostratigraphic complex for assessing the timing and mode of Rodinia breakup in central southern Laurentia is the Devils River Uplift, a Laurentian Grenville basement-cored block in the subsurface of west Texas, which was severed during Cryogenian-early Cambrian rifting, then thrust back onto the southern margin during late Paleozoic collisional orogenesis. Zircon U/Pb geochronological data from Mesoproterozoic to upper Cambrian metamorphic and sedimentary strata cored in the uplift significantly extend the record of Cryogenian onset of intraplate extensional magmatism, as well as early Cambrian igneous activity, in the region.
Results of LA-ICP-MS analyses place formation of the basement orthogneisses at 1230 Ma. Younger Grenvillian detritus (~1070 Ma) is common in lower to middle Cambrian metasediments and predominates in upper Cambrian sandstones. Lower to middle Cambrian units yielded abundant Cryogenian grains (780 to 700 Ma) reflecting early-phase rifting. Also recovered from those intervals were plentiful zircons indicative of late Neoproterozoic to early Cambrian (580 to 520 Ma) rift magmatism. Volcanic clasts and detritus of like ages have been dated from Cambrian and Ordovician sedimentary rocks in the Marathon/Solitario basin, ~75 km farther west. Episodic Neoproterozoic to early Paleozoic rifting is thus increasingly documented on the central southern Laurentian margin.
Devils River Uplift geochronologic data enable direct comparison with potential counterparts in the Cuyania terrane, which rifted away from the Marathon-Ouachita Embayment of southern Laurentia and is now an element of the Andes of western Argentina. Clear correlatives confirm the shared pre-rift and rift history of DRU and the conjugate Cuyania block from Mesoproterozoic through mid-Cambrian time.