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

Abstract

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 εHf(t) and δ18O values range from -4.1 to +6.1 and 7.1‰ to 8.6‰. 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.U-Pb geochronology and Hf isotopic analyses of zircons from the Paleoproterozoic Heluositan intrusive complex show crustal growth episodes during 2.2-4.2 Ga with peaks at 2.3-2.5 Ga, 3.3 Ga and 3.6-3.8 Ga, distinct from the other Precambrian terranes of the Tarim Craton. A comprehensive synthesis of the records of assembly and breakup of Columbia supercontinent from different Precambrian terranes in the Tarim Craton show significant differences. The temporal distinction in tectonothermal events and the marked difference in the continental crust growth processes suggest that the early Precambrian basement of the Tarim Craton was possibly composed of discrete terranes which were fragmented from different ancient cratonic nuclei.