Deciphering Magma Mingling Processes in the Zouzan Pluton, Eastern Iran: Multi-Method Constraints From Zircon Geochronology, Nd-Sr Isotopes and Amphibole-Apatite Chemistry on Mafic Enclave Formation

Abstract

The Zouzan pluton in the Lut Block (eastern Iran) comprises coeval gabbro–diorite and felsic intrusions that contain abundant mafic enclaves (MEs). Integrated zircon U-Pb dating, whole-rock Sr-Nd isotopes and amphibole-apatite chemistry are used to investigate ME formation. Zircon ages indicate synchronous emplacement of the gabbro–diorite, MEs, and granodiorite ca. 40 Ma. The MEs plot along a Sr-Nd isotopic mixing line between mantle-derived gabbro–diorite and more crustally contaminated granodiorite, supporting a magma-mixing origin. Mineral chemistry, however, reveals more complex interactions. Apatite in MEs is acicular with trace element compositions intermediate between those of mafic and felsic magmas, indicating rapid crystallisation from a hybrid melt. Amphiboles display two distinct compositional groups: one matching gabbro–diorite amphiboles and the other resembling those in the granodiorite. This bimodality suggests that ME formation involved incomplete mixing, crystal transfer between magmas and variable re-equilibration rather than simple hybridisation. A dynamic model is proposed in which mafic magma globules were injected into a partly crystallised felsic chamber, producing mingling, quenching and crystal exchange that ultimately shaped the petrographic and geochemical features of the Zouzan pluton.

Keywords

eastern Iran / enclaves / gabbro–diorite / granodiorite / magma mixing / Zouzan pluton

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2026 Geological Society of China.