High-resolution petrographic evidence confirming detrital and biogenic magnetites as remanence carriers in Zongpu carbonates, South Tibet

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Authors

Qian Zhao, Baochun Huang, Zhiyu Yi, Pengfei Xue

Abstract

Paleocene carbonates from the Gamba area of South Tibet provide the largest paleomagnetic dataset for constraining the paleogeography of the India-Asia collision in the early stage. The characteristic remanences (ChRMs) obtained from this unit were, however, argued for a chemical remagnetization via orogenic fluids. This study carries out a high-resolution petrographic study on the Paleocene carbonates from Gamba aiming to test the nature of the ChRMs. Electron microscopic observation on magnetic extracts identified a large amount of detrital magnetite that are multi- to single domain in sizes and biogenic magnetite in nanoscale. Minor framboidal iron oxides were also identified, which were previously interpreted as authigenic magnetite that substitutes pyrite. However, our scanning and transmission electron microscopic (SEM/TEM) observations, along with optical microscope and Raman spectrum investigations further suggest that these magnetic minerals are pigment hematite and goethite that are incapable of carrying a stable remanence. We therefore argue that the ChRMs of the limestones from the Zongpu Formation in the Gamba area are carried by detrital and biogenic magnetites rather than authigenic magnetite. The paleomagnetic data from the Gamba area are interpreted as primary origin and can thus be used for tectonic reconstructions. We emphasize that magnetic extraction, integrated with advanced mineralogic studies (e.g., electron backscatter diffraction and electron diffraction) are effective approaches for investigating the origin of magnetic carriers in carbonate rocks.

DOI

https://doi.org/10.31223/X52S5V

Subjects

Earth Sciences

Keywords

Magnetic extraction, Carbonates, Tethyan Himalaya, Paleocene

Dates

Published: 2021-05-26 04:42

Last Updated: 2021-05-26 11:42

License

CC BY Attribution 4.0 International

Additional Metadata

Conflict of interest statement:
None

Data Availability (Reason not available):
Data from this manuscript are available from the corresponding author upon reasonable request.

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