Isotope Geochronologic and Geochemical Constraints on the Magmatic Associations of the Collisional Orogenic Zone in the West Kunlun Orogen, China

摘要

The Jiajiwaxi pluton in the southern portion of the West Kunlun Range can be divided into two collision-related intrusive rock series,i.e.,a gabbro-quartz diorite-granodiorite series that formed at 224+2.0 Ma and a monzonitic granite-syenogranite series that formed at 222±2.0 Ma.The systematic analysis of zircon U-Pb geochronology and bulk geochemistry is used to discuss the magmatic origin (material source and thermal source),tectonic setting,genesis and geotectonic implications of these rocks.The results of this analysis indicate that the parent magma of the first series,representing a transition from I-type to S-type granites,formed from thermally triggered partial melting of deep crustal components in an early island-arc-type igneous complex,similar to an I-type granite,during the continental collision orogenic stage.The parent magma of the second series,corresponding to an S-type granite,formed from the partial melting of forearc accretionary wedge sediments in a subduction zone in the late Palaeozoic-Triassic.During continued collision,the second series magma was emplaced into the first series pluton along a central fault zone in the original island arc region,forming an immiscible puncture-type complex.The deep tectonothermal events associated with the continent-continent collision during the orogenic cycle are constrained by the compositions and origins of the two series.The new information provided by this paper will aid in future research into the dynamic mechanisms affecting magmatic evolution in the West Kunlun orogenic belt.