Presence and Evidence of Kuhai-Saishitang Branching Ocean in Copulae between Kunlun-Qinling Mountains

A branching ocean basin, to be known as the Kuhai-Saishitang branching ocean, has been discovered in the area between the Kunlun and Qinling Mountains, China. The Kuhai-Saishitang branching ocean was discovered by detailed mapping and analysis, which revealed an ophiolite complex in a north-north-east orientated branching basin connected to the (Buqingshan) -Animaqing ocean. The basin includes Xueqiong and Cuozama MOR-type ophiolites which indicate that spreading of the basin took place in the Late Devonian-Carboniferous. This is supported by an Ar⁴⁰/Ar³⁹ age for the ophiolite complex/compound (which compound?) of (368.6±1.4) Ma, which is contemporaneous with the formation of the Buqingshan- (Animaqing) ocean. The ophiolite present indicates that the oceanic lithosphere of the Kuhai-Saishitang basin formed in a small, immature ocean basin. One behavior of expansion is tectonic hot event heavy recorded in cracking block slice and crystal base, for instance, amphibole ⁴⁰Ar/³⁹Ar low temperature plateau age of amphibolite in Longtong area is (358.9±3.2) Ma, biotite ⁴⁰Ar/³⁹Ar plateau age of mica-quartz tectonic schist in Yangqu area is (387.3±2.3) Ma, Rb-Sr isochrone age of biotite plagioclase-gneiss in Kuhai area is (336±2.2) Ma, amphibole ⁴⁰Ar/³⁹Ar low temperature plateau age of amphibolite in Zanaheruo is (376.9±0.9) Ma, these ages reflect cracking time limit. The pyroxene ³⁹Ar/⁴⁰Ar plateau age of diabase in cracking slice in Lalongwa is 398.4 Ma which reflects that expansion began in the Devonian. There is evidence of the formation of a volcanic island arc in the Early Permian (264 Ma) and subduction occurring along the south-east edge of the (Chaidamu) minor continental block in the Early-Middle Permian (267 Ma). The subduction is marked by the presence of subduction-type granite which was altered by middle-high pressure metamorphism as the strength of the subduction increased. Also associated with the subduction zone is a hyperplasia mélange wedge. In the Late Permian, the interaction of the Chaidamu and Ruoergai minor continental blocks caused arc-continent collision which resulted in the closure of the Kuhai-Saishitang branching ocean and the formation of collision-type mica-containing granite in the Cuoka area and the deposition of syn-collision molasse sediments of the Gequ Group.