Multiple episodes of early Precambrian magmatism and tectonism in the Tarim Craton: A North China connection

The accretion and recycling of Archean-Paleoproterozoic continental crust is the key to understanding the for-mation and evolution of early continental crust. Early Precambrian metamorphic basement is well developed in the Aktashtagh area, southeastern margin of the Tarim Craton, northwestern China. We report zircon SHRIMP U-Pb dating, LA-MC-ICP-MS Lu-Hf isotopic analysis and whole-rock geochemical analysis on 16 samples (mainly TTG, tonalite-trondhjemite-granodiorite) from Aktashtagh. Multiple episodes of early Precambrain magmatism, including 3.72 Ga, 3.63 Ga, 3.10 Ga, 2.83-2.69 Ga, 2.55-2.50 Ga, 2.05-2.02 Ga and 1.93-1.82 Ga events, have been identified in the Aktashtagh region. The most intense magmatism occurred in the late Mes-oarchean to early Neoarchean. Significantly, 3.63 Ga and 3.10 Ga TTG rocks are identified, together with more extensive 2.8-2.7 Ga and -2.5 Ga TTG rocks. The TTG suites are dominated by tonalitic, with some trondh-jemitic and grandioritic rocks. They show large variations in REE contents, are mainly distributed in the high-and medium-pressure fields in the Sr/Y-Y and La/Yb-Yb diagrams, and the 2.7 Ga TTG rocks commonly show higher and more variable Sr/Y and La/Yb ratios. The 3.63-3.10 Ga TTG rocks have magmatic zircon epsilon Hf(t) values of-3.9 to +3.1 and tDM1(Hf) model ages of 3.9-3.6 Ga, whereas the-2.7-2.51 Ga TTG rocks have magmatic zircon epsilon Hf(t) values of-13.4 to +2.1 and tDM1(Hf) model ages of 3.3-3.0 Ga. The-2.7 to-2.0 Ga meta-gabbroic-dioritic rocks have magmatic zircon epsilon Hf(t) values of-19.7 to +0.6 and tDM1(Hf) model ages of 3.2-2.4 Ga. Metamorphic zircon ages of 3.56 Ga, 2.75-2.73 Ga, 2.53-2.51 Ga, 2.03-1.96 Ga and -1.85 Ga are also recorded, whereas-2.83 Ga, 2.53-2.40 Ga, 2.05-2.02 Ga and 1.86-1.83 Ga crustally-derived K-rich granites are identified, with the most important occurring in the late Neoarchean and late Paleoproterozoic. In this regard, the Tarim Craton is similar to the North China Craton in its early Precambrian geological evolution. The main difference is that the Paleoproterozoic tectonothermal event in the Tarim Craton started as early as 2.00 Ga, whereas in the North China Craton it occurred between 1.95 and 1.80 Ga.

Automated summary

By studying the Aktashtagh area in the southeastern margin of the Tarim Craton, northwestern China, multiple episodes of early Precambrian magmatism have been identified, which are important for understanding the formation and evolution of early continental crust.