Remagnetization of Upper Triassic Limestone From the Central Lhasa Terrane (Tibet): Identification, Mechanisms, and Implications for Diagnosing Secondary Remanent Magnetization in Carbonate Rocks

作者：Yong Yao, Wentao Huang, Huafeng Qin, Weiwei Bian, Zhenhua Jia, Chenglong Deng · 发表于：Journal of Geophysical Research Solid Earth · 年份：2024 · DOI：10.1029/2024jb029316 · 被引用次数：8 · 研究领域：Geomagnetism and Paleomagnetism Studies、Geological and Geochemical Analysis、High-pressure geophysics and materials

Abstract Carbonate rocks, widely used for quantifying paleolatitude of the Gondwana‐derived terranes on the Tibetan Plateau and the geodynamic evolution of the Tethyan Oceans, are prone to remagnetization. However, diagnosing such secondary remanent magnetization is difficult and the mistakes have induced confusion in paleogeographic reconstructions. To evaluate if the Upper Triassic limestones of the Duoburi Formation from the Lhasa terrane carry a primary remanence, we report comprehensive rock magnetic, diffuse reflectance spectroscopic, and petrographic results of these rocks. We discover that magnetic carriers vary systematically from magnetite to magnetite plus minor hematite/goethite to hematite/goethite plus minor magnetite with change of rock color and demagnetization behavior of the specimens. Most magnetite and all hematite/goethite grains have clear authigenic origin and were possibly formed during oxidation of early diagenetic pyrite. Such a process was likely assisted by oxic fluid circulation as shown by omnipresent calcite veins within the rocks. These authigenic iron oxides have widely distributed grain sizes with most of them being superparamagnetic at room temperature. Detrital (titano)magnetite is also recognized in some specimens, but its concentration is much lower than that of the authigenic magnetic grains. Based on these results, we conclude that limestone from the Duoburi Formation was remagnetized due to fluid circulation during late diagenesis. We ...