Origin and Geological Significance of the Cambrian–Permian Mafic-Felsic Magmatic Rocks in the Longshenggeng Area of the East Kunlun Orogenic Belt
摘要
A set of ultramafic-mafic-felsic rock assemblages was discovered in the Long-shenggeng area of the eastern part of the East Kunlun orogenic belt. Petrography, chronology and whole-rock geochemistry were conducted on this set of intrusive rock assemblages. U-Pb dating of apatite shows that the lherzolite formed at 492 ± 5 Ma, the granite at 473 ± 6 Ma, and the diabase at 260 ± 14 Ma, respectively. The lherzolites belong to a supra-subduction zone type (SSZ-type) ophiolite component above a subduction zone; the granites formed in an ocean-continent subduction setting; and the diabases represent products of partial melting of an asthenospheric mantle at shallow depth. The East Kunlun orogenic belt features the East Kunzhong and Buqingshan-Animaqing ophiolitic mélange belts, with the latter representing remnants of the Proto-Tethys Ocean. The Late Cambrian lherzolites and granites in the Longshenggeng area were magmatic products of the back-arc ocean basin and island arc formed during the northward subduction of the Proto-Tethys Ocean. Subsequently, extensive island arc magmatism occurred from the Late Permian to Middle Triassic, driven by the northward subduction of the Paleo-Tethys Ocean beneath the East Kunlun Block. The diabase may have formed during the transition from subduction to post-collisional extension.