The metasedimentary rocks from the eastern margin of the Tarim Craton: Petrology, geochemistry, zircon U–Pb dating, Hf isotopes and tectonic implications

Abstract

The Dunhuang Block, located in the eastern Tarim Craton, widely exposes Precambrian TTG gneisses and metamorphosed supracrustal rocks. A suite of metasedimentary rocks of the Dunhuang Group in the Hongliuxia area on the eastern margin of the Tarim Craton are characterized by moderate contents of quartz, plagioclase, and biotite, with minor amounts of garnet or kyanite, most of which have experienced strong deformation, resulting in well-developed amphibolite-facies foliations. The examined samples are characterized by moderate Fe2O3+MgO and TiO2 contents, and Al2O3/SiO2 and K2O/Na2O ratios with low Chemical Index of Alteration (CIA) and high Index of Compositional Variability (ICV) values, suggesting that the protolith sediments originated from continental island arc environment. The U–Pb ages of magmatic-type detrital zircons from the Hongliuxia metasedimentary rocks range between 2476Ma and 1950Ma, with a peak at 2417Ma. Detrital zircons of metamorphic origin yielded an age peak at 1832Ma, which may represent a tectono-thermal event in the Paleoproterozoic. Considering that the main age populations of the analyzed samples are consistent with the tectono-thermal events in the Tarim Craton during the early Paleoproterozoic, we propose that the Tarim Craton was possibly the major source for the protolith sediments of the metasedimentary rocks in the Hongliuxia area. Zircon Hf isotopic compositions (εHf(t)=−5.8 to +2.9) suggest voluminous addition of juvenile materials to the crust and minor reworking of old materials in the eastern Tarim Craton during the Mesoarchean (TDMC=2.8–2.9Ga). The metasedimentary rocks of the Hongliuxia area provide clear constraints to the evolution of the Tarim Craton. A possible tectonic model is that multiple thermal events (~2.4Ga, 2.2Ga, 2.0Ga and 1.8Ga) occurred in the study area, and the time period of Mesoarchean was important for crustal growth in the eastern Tarim Craton, whereas the ~1.83Ga metamorphism might represent a thermal event associated with the Tarim Craton within the supercontinent Columbia.