A Paleozoic gabbro–diabase–granite association in the Shangdan suture zone (SDSZ) has been studied for zircon U–Pb ages, whole-rock geochemistry, and Sr-Nd isotopic compositions to constrain their petrogenesis and reveal tectonic implications. These rocks have distinctive crystallization ages: the Guchenggou gabbro yield zircon U–Pb ages of 423 to 424 Ma; the average age of Yueritan diabase is 411 Ma; and the Danfeng granites yield zircon U–Pb ages of 411 to 414 Ma. The Guchenggou gabbro was formed by partial melting of phlogopite-bearing garnet lherzolite modified by subduction fluid in a continental arc setting. The Yueritan diabase was generated by mixing phlogopite-bearing garnet lherzolite modified by subduction melt and continental crust in a post-collision setting. The Danfeng granites are weakly peraluminous I-type, formed by mixing juvenile crust and metagreywacks under high temperature and high pressure in a tectonic transition environment from compression to extension. We suggest that the subduction of the Shangdan Ocean induces the formation of gabbro. Meanwhile, the diabases and granites are related to the continental crustal relamination in response to the collision of North Qinling Belt (NQB) and South Qinling Belt (SQB), suggesting that the closure of the Shangdan Ocean may have occurred in ca. 410 Ma.
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
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