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 Chinese Altai features abundant granitoids, which can be used to reconstruct the tectonic evolution of the orogen. Here, petrological, geochronological, geochemical and isotopic analyses have been conducted 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. Ordovician gneissic granites have I-type arc-related element characteristics and are derived from volcanic magmas extracted from the mantle wedge metasomatized by subducted sediment in a continental arc. Devonian syenogranites show I-type arc and within-plate granite dual geochemical signatures, suggesting derivation from volcanic magmas extracted from the lithospheric mantle metasomatized by subducted fluid/melt in a back-arc basin. Permian diorites are Mg-diorites derived from a mixed magma source involving residual subducted basaltic oceanic crust and lithospheric mantle; two-mica monzonitic granites are S-type granites originating from crustal recycling of sedimentary rocks; muscovite granites are leucogranites resulting from the anatexis of ancient metasedimentary rocks. Their tectonic setting is syn/postcollision. Combining with previous data, we propose that the Chinese Altai experienced middle–late Ordovician continental arc magmatism, early–middle Devonian back-arc extension, and early–middle Permian arc–arc syn/postcollision. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6420236