Paleoproterozoic multiphase magmatism and metamorphism recorded in metamorphic basement rocks of the northern Altyn Tagh, southeastern Tarim Craton

Abstract

The Paleoproterozoic is a pivotal time for understanding the geochronological framework of the Tarim Craton. Located at the southeastern margin of the Tarim Craton, the northern Altyn Tagh is the main region of exposed Paleoproterozoic magmatic and metamorphic rocks. These rocks are diverse, diachronous, and modified by multiphase tectonothermal events. In this study, we performed systematic analyses on the amphibolite, felsic gneisses, and metasedimentary rocks in the Aketashitage area, southeastern Tarim Craton, including petrography, mineral chemistry, and whole-rock geochemistry, as well as in-situ zircon U-Pb ages and Hf isotopes, to examine the Paleoproterozoic magmatic-metamorphic events in the northern Altyn Tagh. Results from our study indicate that geochemically, the amphibolite and felsic gneisses in the Aketashitage area resemble the typical bimodal associations of mafic and acidic volcanic rocks. In addition, felsic gneisses are characterized by high Sr and low Y contents, high Sr/Y and (La/Yb) N ratios, and indistinctive Eu anomalies, closely resembling high-SiO2 adakites derived from subducted basaltic slab-melt. The palimpsest textures and geochemical features of the Aketashitage metasedimentary rocks suggest that their protoliths are argillaceous rocks. The amphibolite from the study area has a metamorphic age of 1.96 Ga, and the felsic gneisses yield crystallization ages of 2.54–2.52 Ga. The major age peaks of metasedimentary rocks in the Aketashitage area, namely 2.72 Ga, 2.05 Ga, and 1.97 Ga, are remarkably consistent with the magmatic and/or metamorphic events in the same area. Furthermore, the minimum age peak of the studied metasedimentary rocks suggests a depositional age no earlier than 1.97 Ga. Geochemical and geochronological evidence from the exposed rock associations in the Aketashitage area suggest a subduction-related tectonic setting during the Paleoproterozoic. Our new data combined with the findings of previous studies indicate that Paleoproterozoic magmatism and metamorphism in the northern Altyn Tagh area are nearly synchronous, and that both are likely related to oceanic subduction.