The Archean-Paleoproterozoic crustal evolution in the Dunhuang region, NW China: Constraints from zircon U-Pb geochronology and in situ Hf isotopes

The Dunhuang region is located on the eastern margin of the Tarim Craton and eastward to the Alxa block. The Archean-Paleoproterozoic TTG gneisses, potassic granites and supracrustal rocks (the Dunhuang Complex), and the Paleozoic magmatic and metamorphic complexes are exposed in this region. Here we report U-Pb geochronology and Hf isotope analyses on zircons from TTG gneisses in the Dunhuang Complex to probe the Archean-Paleoproterozoic tectono-thermal events and crustal formation and evolution in the Dunhuang region and to provide new insights in understanding the affinity of the Dunhuang Complex. LA-ICP-MS zircon U-Pb dating results in this study, together with previous data reveal that the Dunhuang Complex document six stages magmatic events at similar to 3.06 Ga, similar to 2.7-2.6 Ga, similar to 2.56-2.45 Ga, similar to 2.3 Ga, similar to 2.0-1.9 Ga and 1.9-1.8 Ga. However, the regional metamorphism only occurred at similar to 2.5 Ga, similar to 2.0-1.9 Ga and 1.9-1.8 Ga. Thus, the Archean-Paleoproterozoic tectono-thermal events in the Dunhuang region can be divided into three stages at 3.1-2.5 Ga, similar to 2.0-1.9 Ga and 1.9-1.8 Ga. Zircon Hf isotope compositions reveal that continental crust in the Dunhuang region was mainly formed by similar to 2.7-2.6 Ga and similar to 2.56-2.45 Ga magmatic events and reworked at similar to 2.0-1.9 Ga and 1.9-1.8 Ga. In addition, small volume of continental crust was formed before similar to 2.7 Ga. The Archean TTG rocks in the region extensively underwent the global Paleoproterozoic (ca. 2.0-1.8 Ga) orogenic event associated with the assembly of the Columbia supercontinent, and the Dunhuang Complex generally underwent the Paleozoic (ca. 440-400 Ma) orogeny-related metamorphism. TTG rocks emplaced at similar to 3.06 Ga and similar to 2.7-2.6 Ga in the central part of the Dunhuang region underwent regional metamorphism at similar to 2.0-1.9 Ga. Whereas, TTG rocks formed at similar to 2.56-2.45 Ga and similar to 2.3 Ga in the northeast of the central part (the Yulinhe area) and the southern part of the Dunhuang region underwent regional metamorphism at 1.9-1.8 Ga. Thus, the Precambrian basement rocks in the region underwent different geological evolutionary history. Compare with other cratons in China, they exhibit similarities not only with those in the Tarim Craton, but also with those in the North China Craton. Therefore, we infer that the Tarim Craton and North China Craton might have been a whole during Archean-Paleoproterozoic, and the Precambrian basement rocks in the Dunhuang region may be different parts of Tarim-North China Craton aggregated together by the Paleozoic (ca. 440-400 Ma) orogenic event. (C) 2015 Elsevier B.V. All rights reserved.