Traces of Archean Subduction in the Tarim Craton, Northwest China: Evidence from the Tuoge Complex and Implications for Basement Formation

The Tuoge Complex, the oldest basement block exposed in the northeastern Tarim Craton, northwest China, consists mainly of supracrustal rocks, tonalite-trondhjemite-granodiorite (TTG) gneisses, and gneissic granitoids. SHRIMP zircon U-Pb dating shows three episodes of TTG magmatism in the Neoarchean: approximate to 2603, approximate to 2565, and approximate to 2516 Ma. Based on geochemical characteristics, two groups of TTG gneisses are recognized. Group 1 (approximate to 2603 Ma) has relatively high Mg#, Al2O3, and Sr/Y and low rare earth element and (La/Yb)(N) compared to group 2 (approximate to 2565 and approximate to 2516 Ma). Both groups show negative Nb, Ta, and Ti anomalies. Group 1 shows a slightly negative to positive Eu anomaly, whereas group 2 has a negative Eu anomaly. Group 1 gives a Nd depleted-mantle modal age (T-DM) of approximate to 2.73 Ga, with epsilon Nd(t) ranging from +0.09 to +4.30 and (Sr-87/Sr-86)(i) between 0.701 and 0.704. The T-DM of group 2 varies from 3.04 to 2.95 Ga, and epsilon Nd(t) changes from -3.48 to -1.52. We propose that group 1 TTG gneiss is derived from deep partial melting of subducted oceanic slab with garnet and rutile as a residual assemblage, whereas group 2 TTG gneiss originated from a later partial melting of underplated lower crust with amphibolite and plagioclase in the restite. Therefore, we infer that not only a subducted slab but also a reworked continental crust contributed to the formation of the basement of the northern Tarim Craton in the late Neoarchean.