Geochemistry, geochronology and Sr–Nd–Hf isotopes of Paleozoic granitoids in the Chinese Altai, NW China: constraints on the conversion from subduction–accretion to syn-/post-collision

Abstract

The Altai region of China features abundant granitoids, which can be used to reconstruct the tectonic evolution of the orogen. We conducted petrological, geochronological, geochemical and isotopic analyses on several representative granitoids from the Altai region. U‒Pb dating revealed ages of 444 ± 3 Ma for gneissic granites, 406 ± 8 Ma for syenogranites, 280 ± 6 Ma for diorites, 278 ± 3 Ma for two-mica monzonitic granites and 269 ± 3 Ma for muscovite granites. The Ordovician gneissic granites have I-type arc-related element characteristics and are derived from volcanic magmas extracted from the mantle wedge and then metasomatized by subducted sediment in a continental arc. The Devonian syenogranites show dual I-type arc and within-plate granite geochemical signatures, suggesting derivation from volcanic magmas extracted from the lithospheric mantle metasomatized by subducted fluid/melt in a back-arc basin. The Permian diorites are Mg-diorites derived from a mixed-magma source involving residual subducted basaltic oceanic crust and lithospheric mantle. The two-mica monzonitic granites are S-type granites originating from the crustal recycling of sedimentary rocks, whereas the muscovite granites are leucogranites resulting from the anatexis of ancient metasedimentary rocks. Their tectonic setting is syn-/post-collisional. By combining these results with previously published data, we propose that the Chinese Altai region experienced mid- to late Ordovician continental arc magmatism, early to mid-Devonian back-arc extension and early to mid-Permian arc–arc syn-/post-collision. Supplementary material: Supplementary Tables S1–S3 are available at https://doi.org/10.6084/m9.figshare.c.6420236