Archean crustal evolution of the northern Tarim craton, NW China: Zircon U-Pb and Hf isotopic constraints

Abstract

Tarim craton is one of the major cratons in Central Asia. Basement rocks of the craton, such as TTG gneisses, are dominantly exposed in the northern (Kuluketage area) and the Eastern (Altyn Tagh Mountain). Recent years, only a few reliable Archean ages have been obtained for the basement rocks in the Altyn Tagh Mountain. Geochronological and geochemical studies have been conducted on the orthogneisses exposed in the Kuluketage area in order to unravel complex history of the Tarim craton. Zircon U-Pb dating of the rocks yielded three weighted mean 207Pb/ 206Pb ages of 2516 ± 6, 2575 ± 13 and 2460 ± 3 Ma, indicating that their protoliths were formed in the late Neoarchean to early Paleoproterozoic. The late Neoarchean orthogneisses exhibit low Sr/Y ratios (4-19) and Mg # values (35-44), with depleted Sr contents, negative Nb, Ta and Ti anomalies and strongly fractionated REE patterns ((La/Yb) N = 13-62), displaying typical geochemical features of arc igneous rocks. In contrast, the early Paleoproterozoic orthogneisses are characterized by high-SiO 2 contents, Sr/Y ratios (37-67) and Mg # values (46-67), with variably fractionated REE patterns ((La/Yb) N = 9-89), slight Sr enrichment and positive Eu anomalies, resembling high-SiO 2 adakites derived from subducted basaltic slab-melts. The late Neoarchean TTGs have low ε Hf(t) values (-5 to +1) and initial Hf compositions (0.280987-0.281160) with Mesoarchean two-stage model ages (T DM2 = 2.9-3.3 Ga), suggesting that the crustal materials of the basement rocks in this area were initially extracted from a depleted mantle in the late Paleo- to Mesoarchean and were reworked in the late Neoarchean. The history of crustal growth is different from that of the North China and Yangtze cratons and thus implies relatively younger cratonization than the North China and Yangtze cratons. Zircons in the early Paleoproterozoic orthogneisses have high ε Hf(t) values (+4 to +10) and young Neoarchean two-stage model ages (2.5-2.7 Ga), revealing a juvenile crustal growth event in the late Neoarchean. Because there is no record of coeval juvenile crustal growth in the other two cratons, we suggest a separate crustal evolution for the northern Tarim craton which was stayed far from the other two cratons before the early Paleoproterozoic. © 2010 Elsevier B.V. All rights reserved.