Characteristics of soure region and tectonic implications of Early Indosinian Weiya gabbroic rock, eastern Tianshan mountains

Abstract

Based on the detailed petrographic study, the characteristics of source region of the Weiya gabbro and tectonic implications were studied. The results show that the gabbroic rock consists mainly of gabbro, with less amount of ultra-mafic rocks. The ultra-mafic rocks show cumulate texture and are gradually transitional contact with gabbro, indicating that they are cumulate products of parental magma. The ultra-mafic rocks consist mainly of spinel periodite and spinel clinopyroxenite. The former is mainly composed of olivine (65%–70%), spinel (10%–15%), hornblende (5%–10%) and phlogopite (5%–10%); the latter consists mainly of clinopyroxene (70%–80%), spinel (15%–20%) and phlogopite (0–10%), with minor amounts of carbonate (0–2%). No olivine or orthopyroxene is found. The gabbro is composed mainly of clinopyroxene (35%–40%), plagioclase (An 55–65, 40%–45%), hornblende (5%–15%), with variable amounts of carbonate (0–5%). Petrographic observations show that the source region of the Weiya gabbroic rock is water-rich due to intensive intra-continental A-type subduction occurring in this region during late Permian to early Triassic.