Polybaric fractional crystallization-driven magma differentiation in continental arcs: Insights from the intrusive complex in Langshan arc, southeastern Central Asian Orogenic Belt

Differentiation processes governing the transformation of the mantle-derived primitive arc melts into more evolved, intermediate to felsic compositions in continental arcs is pivotal in the formation and evolution of the continental crust. Yet the relative contribution of deep and shallow crustal differentiation during the trans-crustal evolution of primary arc magmas remains unclear. Here, we present petrographic observations, detailed geochronological, bulk-rock, and mineral geochemical investigations, and geochemical modelling for the Chaoge Carboniferous intrusive complex (Chaoge CIC) in the Langshan arc, southeastern Central Asian Orogenic Belt. Our results show that Chaoge CIC comprises cogenetic mafic to felsic rocks and ultramafic-mafic cumulates, which were formed by polybaric fractional crystallization of the primary hydrous arc melts at ca. 319–341 Ma. The ol-px-cumulate and cumulate gabbro represent the complementary residues after extraction of the evolved basaltic melts at the deep crustal level. The extracted basaltic melts further participated in different high-pressure and low-pressure differentiation paths to generate the diverse intermediate to felsic lithologies in the Chaoge CIC. These inferences are reinforced by a two-stage polybaric fractionation model constructed by stepwise subtraction of the high-pressure and low-pressure cumulate compositions. The Chaoge CIC case in the Langshan arc shows the significance of polybaric crystallization fractionation in the production of differentiated arc magmas in continental arc settings, and also highlights the relative contribution of high-pressure versus low-pressure differentiation paths in the generation of the compositional diversity of continental arc magmas. •Cogenetic mafic to felsic rocks and cumulates exist in the Chaoge CIC.•Polybaric differentiation processes govern the formation of the Chaoge CIC.•Both high- and low-pressure paths contributed to the intermediate-felsic products.