Petrogenesis and geodynamic significance of Kayinde gabbro in the Ashele Basin, Altay Orogenic Belt, Xinjiang, Northwest China: Constraints from geochronological and geochemical data

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Mafic‐ultramafic intrusions occur sporadically but are pivotal to constrain the tectonic evolution of the Chinese Altay, a key part of the Central Asian Orogenic Belt. The tectonic setting of the Early‐Middle Devonian is well documented, but that of the Late Devonian remains a matter of ongoing debate. The Kayinde gabbro occurs in the Ashele Basin of the South Altay. This paper reports petrologic, zircon U‐Pb geochronological, geochemical, and Sr‐Nd isotopic data of the Kayinde gabbro, with the aims to investigate its formation time, petrogenesis, and geodynamic significance. Zircons separated from the gabbro yield a cluster of concordant data points and a weighted mean age of 373.1 ± 4.1 Ma, representing a Late Devonian emplacement. Geochemically, the Kayinde gabbro is subalkaline, tholeiitic, and characterized by high Mg# values (68–73), enrichment in large‐ion lithophile elements (including Ba, Sr, Rb, and U), depletion in high‐field‐strength elements (including Nb, Ta, Zr, and Hf), fairly flat REE patterns, low (87Sr/86Sr)i (0.70366–0.70440) and positive εNd(t) (3.4–5.4) values. The geochemical characteristics collectively suggest that the Kayinde gabbro was derived from a spinel‐stable lithospheric mantle source, which was depleted by previous magma extraction and metasomatized by later slab‐derived fluids or melts in an island arc setting. The geochemical similarities between the Kayinde gabbro and other contemporary mafic‐ultramafic intrusions reveal that the subduction continued during the Late Devonian in the Chinese Altay. In combination with the published research, we favour a two‐unit arc system composed of a continental arc and an island arc, spanning across the Early to Late Devonian. The Ashele Basin can be considered to be an oceanward setting in this model.