Petrogenetic and dynamic links between felsic and mafic magmas: Insights from the Devonian post-collisional magmatism in the North Qaidam terrane, western China

Abstract

Felsic-mafic magmatism in post-collisional settings provides valuable insights into the growth and evolution of continental crust, but the interaction processes between felsic and mafic magmatism and their implications for the diversity of igneous rocks remain controversial. This study presents petrological, geochronological, geochemical, and Sr-Nd-Hf isotopic analyses of the Mohe felsic-mafic complex, a rare post-collisional composite pluton in the North Qaidam terrane (western China), to investigate the petrogenetic and dynamic links between felsic and mafic magmas. The results reveal that the Mohe complex, consisting of granite, granodiorite, diorite, and appinites, is genetically related and formed between ca. 408–400 Ma. The granites and granodiorites are classified as I-type and are characterized by enriched isotopic signatures, including whole-rock (⁸⁷Sr/⁸⁶Sr)ᵢ values of 0.714584–0.728765, εNd_{(400 Ma)} values of −7.75 to −5.56, and zircon εHf(t) values of −3.04 to −0.28. These rocks were primarily derived from partial melting of Mesoproterozoic to Paleoproterozoic crustal materials, with minor input from a mantle source. The appinites display depleted zircon Hf isotopic compositions (εHf(t) = +4.10 to +5.71), indicating derivation from an OIB-like depleted mantle source that was metasomatized by subducted slab-derived melts. The diorites show weakly enriched isotopes ((⁸⁷Sr/⁸⁶Sr)_i = 0.709358–0.713210, εNd_{(400 Ma)} = −2.99 to −2.73, εHf(t) = −1.35 to +3.54), and were formed by the mixing of 80–90 % appinitic magma with 10–20 % crustal-derived granitic magma. Our findings suggest that the Early Devonian magmatism in the North Qaidam terrane was likely driven by slab break-off-related geodynamic processes, where crust-mantle magma mixing, along with mineral accumulation and fractional crystallization, played a key role in the petrological diversity of the continental crust in a post-collisional extensional setting.