T34 Advances in Nontraditional Stable Isotope Measurements and Utility as Proxies in Modern and Paleo-Settings (Posters)

Sunday, 22 September 2024
8:00 AM - 5:30 PM
Hall D

SPATIAL DECREASE OF LITHIUM ISOTOPES ALONG THE GHEZ RIVER AT THE TECTONICALLY ACTIVE NORTHEASTERN PAMIR PLATEAU

Paper number: T34-3
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

  • Yadan Hu Presenting Author
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, Shaanxi
  • Yadan Hu Presenting Author
    University of Southern California, Los Angeles, CA
  • Fei Zhang
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, Shaanxi
  • Zhangdong Jin
    State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, Shaanxi
  • A. Joshua West
    University of Southern California, Los Angeles, CA

Abstract

The ~9‰ increase of seawater lithium isotopes (δ7Li) during the Cenozoic was proposed to reflect an enhanced continental erosion and weathering, associated with tectonic uplift. However, this interpretation contradicts with modern observations that instead showed high δ7Li values in floodplains, and low values in upstream mountains. Whether mountain uplift or the floodplain formation controlling the Cenozoic seawater δ7Li rise remains controversy. Here, we investigate spatially riverine δ7Li in the tectonically active Ghez catchment with contrasting topography and lithology in the NE Pamir Plateau. Our results show a significant decrease of δ7Li from the upper mountain to the lower floodplain, by ~15‰. The high δ7Li values (up to 20‰) in the upstream reflect relatively flat topography with long fluid residence time facilitating incongruent weathering and thus large Li isotopic fractionation, while the subsequent decline of δ7Li values to ~10‰ in the midstream is consistent with sharp topography. On the contrary, the rock-like low δ7Li values in the downstream (~5‰) reflect congruent weathering by ancient sedimentary rocks with clay dissolution at the floodplain. These observations, contrary to previous studies, indicate that weathering in floodplains associated with tectonic uplift is not necessary producing high riverine δ7Li, and thus renewed our understanding of the role of floodplains on deciding riverine δ7Li from the land to the oceans.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-402547

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