T223 Radiogenic Isotopes as Tracers of Geologic Processes: Dates, Rates, and Proxies I

Wednesday, 12 October 2022
8:00 AM - 12:00 PM
502

SOURCE-TO-SINK TANDEM GEOCHRONOLOGY PROVIDES NEW OPPORTUNITIES FOR RECONSTRUCTING ANCIENT PALEOGEOGRAPHY AND PALEOTOPOGRAPHY: AN EXAMPLE FROM THE TRANSCONTINENTAL ARCH OF LAURENTIA

Paper number: T223-15
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Abstract

A fundamental goal of detrital zircon geochronology is to link changing sedimentary provenance to geologic processes. Here, we apply tandem in situ (LA-ICP-MS) and isotope dilution (CA-ID-TIMS) U-Pb geochronology paired with trace and rare earth element (TREE) geochemical and Hf-isotope tracers to source-to-sink detrital zircon provenance analysis to test competing hypotheses that attribute a regional loss of ca. 1.2-1.0 Ga detrital zircon from the Cambrian Sauk Sequence in southwestern North America to differing plate tectonic controls on surface topography. Three hypotheses explaining this provenance shift are: 1) faulting, epeirogenic uplift, and unroofing of local sources during the transition from mechanical rifting to thermal subsidence and rapid marine transgression, 2) drowning Stenian bedrock sources by passive margin subsidence and transgression of the Iapetus Ocean with no epeirogenic uplift, and 3) diachronous (ca. 600-510 Ma) flexural uplift of a structurally segmented Transcontinental Arch between the subsiding Iapetan and Cordilleran margins. Existing tandem U-Pb geochronology links ca. 530 detrital zircon in the Sixtymile Formation to the Wichita igneous province, and quantitative comparison of εHf(t) values from ca. 1.1 detrital zircon in the Sixtymile Formation with potential basement sources in southern Laurentia suggest derivation from the Llano Uplift of central Texas. In contrast, TREE geochemistry and new high-precision dates from syenite (511.44 ± 0.51 Ma) and granite (510.83 ± 0.20 Ma) of the Florida Mountains intrusive complex in southern New Mexico links these sources to the Tapeats Formation, with additional contributions from proximal ca. 1.4 and 1.7 Ga basement. These data allow us to reconcile competing hypotheses into a refined tectonic model. We attribute a regional provenance shift to plume-lithosphere interactions on the Iapetan margin, tectonism along “leaky” intracratonic transverse fault zones, and the rift-to-drift transition on the Cordilleran margin. This example demonstrates how the improved temporal resolution of tandem U-Pb geochronology provides new opportunities for understanding the interplay between tectonics, magmatism, sedimentation, and surface topography in ancient landscapes.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-379523

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