LA-ICP-MS U-Pb zircon geochronology and Hf isotope, geochemistry and kinetics of the Daxigou anorthosite from Kuruqtagh block, NW China

Abstract

Kuruqtagh block is the best area for Precambrian geology in Xinjiang Autonomous Region, NW China, since it exposed complete Precambrian lithology units. The study of this ancient base will deepen the understanding of the Precambrian evolution of the Tarim Basin. In this paper, we studied the petrology, geochemistry, zircon LA-ICPMS U-Pb chronology and zircon Hf isotope of Daxigou anorthosite (DA) which is located at the northern margin of Tarim craton and discussed the rock formation, tectonic and geological significance. Zircons from the intrusions display oscillatory zoning and high Th/U ratios (0.39–1.35), implying their magmatic origin. Zircon LA-ICP-MS U-Pb dating results indicate that they formed during the Paleoproterozoic age with the weighted 206Pb/238U average age of 1818±9 Ma, which is significantly different from former’s Neoproterozoic age, and is coincidentally identical with its associated syenite granite age within the error range. Studies on petrogeochemistry suggest that DA belongs to medium-sodium peraluminous alkaline type, rich in Pb, La, Th and LILE, and poor in HFSE (Gd, Nd, and Ta). The chondrite-normalized REE pattern is slightly to the right form. The average ΣREE is 317.2×10−6; HREE show moderate fractionation [average LREE/HREE is 14.71, average (La/Yb)N is 24.77; average (La/Sm)N is 3.85, and average (Gd/Yb)N is 3.46]; and the δEu and δCe are not obvious. Their initial Hf isotope ratios and Hf two-stage model ages range from −6.6 to −4.43 and 2.63 to 2.74 Ga, respectively. Taken together, it is suggested that Daxigou anorthosite is a typical volcanic anorthosite and its primary magma could be contaminated by the partial melt Neoarchaean crust and mainly formed in the arc environment, which recoded the tectonic-magma activities response of the Tarim refers to the amalgamation of the supercontinent Columbia.