T15 The Dynamics of Tectono-Sedimentary Systems During Basin Formation and Fill I

Sunday, 22 October 2017
8:00 AM - 12:00 PM
Ballroom 6C

COMMON MINERALS AND COMMON PB ISOTOPES: UNCOMMON APPLICATIONS AND NEW METHOD DEVELOPMENT FOR DETRITAL K-FELDSPAR PROVENANCE ANALYSIS

Paper number: T15-15
Program: Technical Sessions
Time: 11:30 AM – 11:45 AM

Authors

Abstract

Geochemical provenance studies use a combination of traditional and new analytical methods to characterize complex sediment source dynamics. One emerging provenance tool is the use of common-Pb isotopes in detrital K-feldspar grains. K-feldspars are less susceptible to extensive recycling than more durable mineral types such as zircon; they also are relatively abundant in clastic rocks, an advantage when working with limited sample material (e.g. core, well-cuttings). Lead isotope ratios in whole rocks and K-feldspar vary proportionally through time and by U/Th, and therefore are useful for fingerprinting gross crustal structure. The relationship between 207Pb/204Pb and 206Pb/204Pb falls along a somewhat predictable curve, depending on the system’s 238U/204Pb ratio through time.

New work presented here tests the use of detrital K-feldspar common-Pb isotopic ratios as a provenance indicator in sandstones from southern Utah. The well-studied Late Cretaceous Cordilleran foreland basin provides a robust detrital zircon U-Pb geochronology dataset, already integrated with stratigraphy, paleocurrent data, and sandstone petrography; however, some ambiguity regarding provenance interpretations remains, specifically the relative input of sediment from the more distal Mogollon Highlands and Cordilleran Magmatic Arc, versus the more proximal Sevier fold-thrust belt. Building on previous work (e.g. Tyrrell et al. 2012), we spot-analyzed ~30 detrital K-feldspar grains for each of four pilot samples. Preliminary data demonstrate analytical viability of the common-Pb isotope method, indicating a dominant population of Proterozoic-aged K-feldspars and a mixed Cretaceous arc signal. This supports previous interpretations suggesting sediment source terranes were located to the southwest, such as the Mogollon Highlands (1250-1900 Ma) and the Cordilleran Magmatic Arc (86-260 Ma). This work adds new insights for the development of Cretaceous Kaiparowits plateau deposits of southern Utah and promises new potential applications to other enigmatic basins.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-297330

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