Petrotectonic Assemblages And Tectonic Evolution Of The East Kunlun Orogenic Belt In Qinghai Province

This paper presents a detailed study of the igneous rocks from the East Kunlun orogenic belt based on the achievements of ―National Assessment of Mineral Resources Potential, Mineralization Tectonic Setting in Qinghai Province‖ and 1:250000- 1:50000 regional geological surveys, determines the natural igneous assemblages and the petrotectonic assemblages, and creates spatial grid of igneous rocks by QAP, TAS and An-Ab-Or classification diagrams, unified geochemical analysis methods, a large number of high-precision zircon U-Pb isotope data as well as igneous mapping compilation. It also analyzes the relationship between magmatism and mineralization, and investigates magmatic-tectonic evolution of the East Kunlun orogenic belt. Through field investigation, we newly discover the Late Cambrian TTG granite, Late Silurian-Early Devonian eclogite, Late Permian continental volcanic rocks, etc., and determine mafic dykes into four assemblages: Silurian, Devonian, Early Triassic and Jurassic, reclassify the formation ages of the petrotectonic assemblages like rapakivi granite, muscovite granite and volcanic strata like Wanbaogou group, Qimantage group, Elashan group and Babaoshan group, clear about the mineralization-related rock assemblages, investigate that the East Kunlun Orogenic belt is a typical hyperplasia of subduction orogenic belt, and discuss the different phases of the tectonic units division and tectonic-magmatic evolution, which provides reliable basic data for the study of the East Kunlun Orogenic belt. We also divide igneous rock into four environment assemblages: oceanic, ocean seduction, collision and postorogenic, and 17 petrotectonic assemblages. The East Kunlun Orogenic belt has experienced hyperplasia orogen for three tectonic magmatic cycles: Jixianian-Qingbaikou Period, Cambrian-Late Devonian and Carboniferous – Jurassic, in which, two tectonic stages of Cambrian – Devonian and Carboniferous- Jurassic subduction accretion laid the basic framework of the East Kunlun orogenic belt. In Jixianian-Qingbaikou Period, the setting in the south of the Middle Kunlun fracture was MORS ophiolite and Middle Kunlun ocean composed of the sea island and mountain, north of it was the North Kunlun block mainly composed of paleoproterozoic metamorphic basement, and in Neoproterozoic, the both converged and formed the ultra-aluminum granites. In Cambrian – Devonian, this area was in the Proto-Tethys Ocean stage, the MORS ophiolite south of the Middle fracture and the two SSZ ophiolites- back-arc basin north of the Middle fracture formed a typical arc basin system. In the Cambrian – Ordovician, it developed subduction- related igneous rock assemblages, and in Silurian, the Proto-Tethys Ocean began to close, formed huge scale of south Kunlun subduction complex and the ultra-aluminum granite, and also formed S type granite- related high temperature hydrothermal- quartz vein type tungsten, while the back-arc basin in the north was in a continuous subduction stage. Early Devonian, the subduction complex belt and the high potassium continental volcanic basin in magmatic arc unconformity on both sides of the Middle Kunlun fracture marked the East Kunlun Orogenic belt shopping with overall synthesis, on both sides of the orogenic belts formed a large number of the high potassium – shoshonite granite assemblages, in the Middle, it appeared basic complex, basic dykes and highly fractionated felsic granites associated with extensional setting, and formed magmatic copper nickel deposits related to the mafic-ultramafic complex. The orogenic belt was in a continuous collision environment, ocean-land transition stage. Carboniferous – Jurassic, the area was in the Paleo-Tethys Ocean stage, Carboniferous- Permian MORS ophiolite and Xinghai- Gouli wedged SSZ ophiolites in south of the Middle Kunlun fault formed the boundary of the East Kunlun Orogenic belt, north to the Middle Kunlun fault was the fore-arc basin, north of which was continental arc, the overall composition constituted a typical back-dive hyperplasia arc basin system. From the Middle Permian- Late Triassic, it formed a series of south retreat outer arc – major arc- inner arc magmatic arc polarity, and in the Triassic it entered into the peak period of magmatic activity, formed large-scale of subduction-collision related porphyry, skarn, hydrothermal and continental volcanic type deposits. From the Jurassic, Buqingshan area turned into the collision stage, while the area in north of the Middle Kunlun fault entered into a post-collision setting, thus the tectonic magmatic activities in the East Kunlun Orogenic belt was ending. Researches show that the East Kunlun Orogenic belt has not experienced a regional stretch or widespread post-orogenic process, also not appeared complete continental- continental collision, it’s just the accretion orogenic belt formed by discontinuous northward subduction ocean in different periods in the south.