The generation and evolution of Archean continental crust in the Dunhuang block, northeastern Tarim craton, northwestern China

Tonalite-trondhjemite-granodiorite (TTG) preserved in Archean cratons can provide insights into the generation and evolution of the early continental crust. In this study, typical TTG gneisses from the Dunhuang block in the northeastern Tarim craton were studied in detail regarding their geochemistry and geochronology to constrain the generation and evolution of the Archean continental crust in this region. These TTG gneisses are characterized by high contents of SiO2 (68.3-71.6%), Al2O3 (15.3-16.9%), Na2O (4.43-4.85%), low K2O/Na2O ratios (0.20-0.37) and a very low HREE content (Yb < 1 ppm) and show two-stage Nd isotope model ages of similar to 3.06-2.84 Ga. Zircon U-Pb analyses reveal that these TTG gneisses were formed similar to 2.7-2.6 Ga ago, as shown by inherited magmatic zircon cores, and were later altered by Paleoproterozoic Ga) and early Paleozoic (similar to 430 Ma) high-grade metamorphic events. Two samples show positive epsilon(Hf) (t) values of 1.5-5.4 for magmatic zircons with ages of similar to 2.7-2.6 Ga and give a two-stage Hf isotope model age of similar to 2.95 Ga, while one sample exhibits negative epsilon(Hf) (t) values of -3.4 to -7.2 for magmatic zircons with ages of similar to 2.7-2.6 Ga and gives a two-stage Hf isotope model age of -3.4 Ga, suggesting that the Paleoarchean and Mesoarchean Eras were important periods for the generation of juvenile continental crust in the Dunhuang block. Lastly, based on analyses of previous studies, we speculate that the Tarim craton has been subjected to episodic crustal growths at similar to 3.4 Ga, similar to 3.2 Ga, similar to 2.95 Ga, similar to 2.8 Ga and similar to 2.6 Ga and reworking events at similar to 2.7-2.6 Ga and similar to 2.5 Ga (C) 2013 Elsevier B.V. All rights reserved.