Studies Of Precambrian Basalt And Deep Geodynamic Setting In The Northwestern Margin Of Tarim Plate

Tarim plate is one of the three important cratons in China. It had been one part of Rodinia supercontinent. In the Mesoproterozoic-Neoproterozoic, it was separated from Rodinia supercontinent. There are deficiencies and controversies on tectonic evolution in the northwestern margin of the Tarim plate, even though much previous work has been done. Two layers of basalt are intercalated in the study area. In terms of time or space, the basalt are closely linked to the breakup of Rodinia supercontinent. The chemical composition of two layers of basalt is similar and the rock-forming minerals are plagioclase, pyroxene, iron-titanium oxides. Mineral composition of clinopyroxene indicates that the crystallization temperature can be estimated to be 1420℃~ 1502℃which imply the formation temperature of magma will be higher than the 1500℃. The plagioclase mainly belong to andesine- labradorite, indicating that magma is much basaltic. The magnetite is primary in the basalt, which is besetted by the ilmenite. Based on the relationship, the crystallization temperature is calculated to be 814℃~ 1204℃, and the log(fO2) as -14.72Pa ~ -7.77 Pa, suggesting that the basalts formed at high temperature and high fO2 environment. The olivine is separated by fractional crystallization in the early experience of rifting of the magma. But the fractional crystallization of pyroxene and plagioclase is not obvious. The magma was derived from an enriched mantle source and suffered variable lithosphere mantle’s contamination but not crustal. The depth of the magma is equivalent to the garnet stability, and the degree of partial melting of the protolith is low for about 5% to 9%. The basalts formed in a continental intraplate rifting setting, on behalf of the opening of the Paleo-Asian Ocean. The basalt with Fe-rich and Mg-poor formed at the age of 784±2.3 Ma, and its geochemical characteristics are also similar to the Emeishan basalts’. Therefore, it may be resulted from a mamtle plume containing eclogite. The basalt is a line of evidence for the Neoproterozoic rifting of the Tarim plate from the Rodinia supercontinent.