Growth and evolution of Precambrian continental crust in the southwestern Tarim terrane: New evidence from the ca. 1.4 Ga A-type granites and Paleoproterozoic intrusive complex

摘要

The Precambrian tectonic evolution and growth of continental crust in the southwestern Tarim Craton in NW China remain enigmatic. In this contribution, we report petrography, zircon U-Pb ages, geochemistry and Nd-Hf-O isotope data on the ca. 1.4 Ga granitic pluton in southwestern Tarim Terrane. We also present zircon U-Pb ages and Hf isotope data on the Paleoproterozoic intrusive complex from this area, and use the combined data to evaluate Precambrian tectonic evolution of the region in relation to the Columbia supercontinent. The ca. 1.4 Ga Azibailedi pluton is mainly composed of biotite monzogranite with contents SiO2 (72.8-75.1 wt.%). The major element chemistry of the pluton reveals alkali-calcic and ferroan affinities and metaluminous to peraluminous feature with A/CNK ranging from 0.86 to 1.15. The granite shows high total REE contents with variable enrichment in LREE ((La/Yb)(N) = 8.5-12.2). Both REE and other incompatible elements features define A-type affinities. The initial epsilon Nd values vary from -3.5 to -2.2 and zircon epsilon(Hf)(t) and delta O-18 values range from -4.1 to +6.1 and 7.1 parts per thousand to 8.6 parts per thousand. Integrating geological, geochemical and Nd-Hf-O isotope data, we suggest that the Azibailedi A-type granites were derived from pre-existing early Paleoproterozoic mafic lower crust with involvement of variable amount of Paleoproterozoic juvenile crust, possibly trigged by basaltic magma upwelling, during the breakup of the Columbia supercontinent.