Petrogenesis and metallogenesis of the Kalatage mafic intrusions associated with Fe–Ti oxide ores in the Eastern Tianshan, Central Asian Orogenic Belt

• The Shaxi and Shaxinan Fe-Ti oxide-bearing gabbros were emplaced during Late Carboniferous. • The Shaxi and Shaxinan gabbros were likely derived from interaction between asthenospheric melts and subcontinental lithosphere. • Fractional crystallization and crustal contamination induced Fe-Ti oxide mineralization in the Shaxi and Shaxinan mafic intrusions. Small-scale layered mafic intrusions hosting Fe–Ti oxide ores within orogenic belts are unconventional, and their geodynamic background, petrogenesis and metallogenic mechanisms remain poorly understood. To address this issue, our study focuses on investigating two recently discovered layered mafic Shaxi and Shaxinan intrusions from Eastern Tianshan belt in the Central Asian Orogenic Belt (CAOB). The Shaxi and Shaxinan intrusions are characterized as layered gabbro, intricately composed of alternating strata of hornblende gabbro and gabbro. Notably, the Fe–Ti oxide ores are specifically hosted within the basal sections of the hornblende gabbro layers. The zircon U–Pb dating yields an age of 307.9 ± 4.0 Ma for the Shaxi gabbro, which is coeval with the Shaxinan intrusion and Late Carboniferous mafic magmatism in East Tianshan. Both intrusions are tholeiitic and exhibit enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE, e.g., Ba and U), and high field strength elements (HFSE, e.g., Nb and Zr) with obvious positive Eu anomalies. The Shaxi and Shaxinan intrusions have limited ranges of the εNd (t) values from 1.78 to 1.86 and 2.07 to 2.29 respectively but a relatively high ( 87 Sr/ 86 Sr) i from 0.7072 to 0.7075 and from 0.7067 to 0.7069, respectively. In combination with previous studies, our new geochemical and isotopic data suggest that the parental magmas of the Shaxi and Shaxinan intrusions likely originated from the partial melting of a metasomatized lithospheric mantle, a process that was likely initiated by the influx of hot, rising asthenospheric melts. The Shaxi and Shaxinan intrusions display highly differentiated chemical signatures, indicating their parental magmas underwent intense fractional crystallization, leading the residual melts enriched in ore-forming elements and H 2 O. During ascent and emplacement, these magmas likely assimilated country rocks of the Xingxingxia Group, introducing additional H 2 O and CO 2 into the system. This contamination elevated magmatic oxygen fugacity and played a key role in the formation of Fe–Ti oxide deposits