Re-Os Geochronology of the Liuchapo Formation across the Ediacaran-Cambrian Boundary of the Yangtze Block (South China)

• 作者: Yong Fu Fuliang Wang Chuan Guo Chao Li Peng Xia
• 来源期刊: 地球科学学刊（英文版）
• 年，卷（期）: 2022,（1）
• 所属期刊栏目: Special Issue on Isotope Geochronology and Isotope Geochemistry
• 页码范围: 25-35
• 页数: 11页
• 语种: 英文

摘要

The Ediacaran-Cambrian (E-C) succession in South China records remarkable oceanic, biological and geochemical variations, but it was not well defined geochronologically, which hinders the interpretation of the spatio-temporal seawater chemical architecture during the time E-C interval. This study presents two Re-Os isochron ages of 520.2 ± 6.1 and 561.7 ± 8.5 Ma for the barite-rich black shales from the top Liuchapo and Doushantuo formations respectively in Tianzhu County, Guizhou Province. In combination with existing age data, the two new Re-Os isochron ages suggest that the Liuchapo Formation was deposited between 550 and 520 Ma. Moreover, like the polymetallic Ni-Mo- PGE layers of shelf margin (or platform) facies and V-rich horizons of transitional (or shelf slope) to deep-water facies, the barite deposits were likely formed due to differential mineralization. The timing offset likely resulted from differential elemental concentration related to certain local factors (i. e., hy- drothermal fluids, seawater redox and biological activity). The isochron-derived initial 187Os/188Os ratios of the top Liuchapo Formation (0.902 ± 0.048) and the Doushantuo Formation (0.740 ± 0.042) fall with- in the range of continental weathering flux (1.54) and oceanic crust (0.126), implying the involvement of marine hydrothermal fluids. Moreover, their difference of initial 187Os/188Os ratios may reflect varia- tions of continental weathering intensity and uplift magnitude.