Archean–Paleoproterozoic tectonothermal events in the central Tarim Block: Constraints from granitic gneisses revealed by deep drilling wells

Abstract

The Tarim Block is one of the oldest continental fragments in China. However, its Precambrian framework and basement are insufficiently studied because it is mainly covered by desert in its center. We report new zircon U-Pb-Hf isotopic, zircon rare earth elements (REEs), hornblende, and biotite Ar-Ar dating, and whole-rock geochemical data for granitic gneisses collected from three drilling wells in the central area of the Tarim Basin. Zircons from three granitic gneisses yielded different crystallization ages of 2.8, 2.4 and 2.2 Ga, but a similar metamorphic age of 2.0–1.9 Ga. Two samples yielded Ar-Ar plateau ages of 1.85–1.79 Ga. Combined with previous studies, our data provide Archean–Paleoproterozoic tectonic implications for the Tarim Block: (1) The varied εHf (t) values of the zircon cores suggest that the magmatism of 2.8, 2.4 and 2.2 Ga in the central Tarim Block involved synchronous crustal growth and reworking, respectively; (2) The 2.0–1.9 Ga metamorphic rocks, widely distributed in the Tarim Block, are most likely associated with the assembly of the Tarim Block to the Columbia supercontinent; (3) The Ar-Ar ages of 1.85 –1.79 Ga might be related to a post-orogenic extension.