Bibliographic Details
| Title: |
Isolation of Primary Remanent Magnetization From Himalayan Rocks: Insights From Partially Remagnetized Upper Cretaceous Oceanic Red Beds in Southern Tibet, China. |
| Authors: |
Yuan, Jie, Jiang, Zhaoxia, Huang, Wentao, Liu, Caicai, Tsering, Thubtan, Zhang, Shuai, Qi, Kaixian, Yang, Zijuan, Shen, Zhongshan, Cai, Shuhui, Liu, Shuangchi, Qin, Huafeng, Zhang, Chunxia, Yang, Zhenyu |
| Source: |
Journal of Geophysical Research. Solid Earth; Jan2025, Vol. 130 Issue 1, p1-19, 19p |
| Subject Terms: |
RED beds, REMANENCE, TETHYS (Paleogeography), CHEMICAL processes, PALEOGEOGRAPHY, HEMATITE |
| Abstract: |
Oceanic red beds, preserving primary depositional remanent magnetization, play a key role in reconstructing the Tethyan paleogeography. However, partial remagnetization caused by chemical processes could be pervasive in these rocks, leading to flawed reconstructions, and thus, differentiating secondary and primary remanences is important. In this paper, we conduct multiple X‐ray diffraction, petrographic, diffuse reflectance spectroscopy, and rock magnetic analyses on the Upper Cretaceous oceanic red beds (CORBs) from the Cailangba section in the Gyangze region of the Tethyan Himalaya. Our results reveal that the CORBs contain coarse‐grained detrital hematite with a narrow coercivity distribution, as well as fine‐grained authigenic hematite with a broad coercivity distribution. The coarse‐grained population is mainly composed of >400 nm hematite grains and unblocks close to the Néel temperature (675°C), consistent with a detrital origin. In contrast, the fine‐grained population is mainly composed of <30−400 nm hematite grains and progressively unblocks below 650°C, consistent with a chemical (authigenic) origin. In addition to these two populations of hematite, a small amount of goethite, unblocking below 120°C, is detected. Due to the distinct unblocking temperature spectra of these two populations of hematite, isolating the primary detrital remanence of the coarse‐grained hematite from the chemical remanence of the fine‐grained hematite in the CORBs through high‐resolution thermal demagnetization treatment is feasible. This study lends confidence to the paleomagnetic studies of these oceanic red beds in Tethyan paleogeographic reconstructions. Plain Language Summary: Oceanic red beds can provide critical paleolatitude information to help restore the paleogeography of the Tethyan realm. However, acquisition of secondary remanent magnetization in these rocks is pervasive, which may introduce ambiguity in the paleogeographic reconstruction. Distinguishing primary remanence from secondary remanence is thus essential for paleomagnetic investigation of oceanic red beds. In this study, we applied a series of petrographic and rock physical experiments on the Upper Cretaceous oceanic red beds from the Himalayas. Our results reveal that magnetic carriers in these rocks are dominated by two populations of hematite and a small amount of goethite. One population of large hematite grains unblocks close to the Néel temperature (675°C), has a detrital origin, and carries stable primary detrital remanent magnetization. The other population of hematite with smaller size unblocks in a broad temperature range below 650°C and carries a secondary chemical remanent magnetization. Goethite also has a secondary origin and was precipitated together with the fine‐grained hematite. Our results confirm that oceanic red beds can carry primary remanent magnetization and provide reliable paleolatitudes for the Tethyan paleogeographic reconstructions. High‐resolution stepwise thermal demagnetization is required to isolate such a primary remanence. Key Points: Oceanic red beds contain chemical and detrital remanences held by two populations of hematite with notably different size rangesPetrographic habits and unblocking temperature spectra are two reliable indicators for distinguishing detrital remanent magnetization from chemical remanent magnetization in oceanic red bedsOceanic red beds are very promising primary remanence recorders for Tethyan paleogeographic reconstructions [ABSTRACT FROM AUTHOR] |
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