Chronology, geochemistry and pedogenesis of monzonitic granite and quartz diorite in Mangai area: Its inspiration to Early Paleozoic tectonic-magma tic evolution of the southern Altyn Tagh. Acta Petrologica Sinica, 32 (6) : 1731 - 1748
Kang, L; Xiao, P; Gao, X; Xi, R; Yang, Z
Early Paleozoic monzonitic granite and quartz diorite, outcropped in Mangai area of the southern Altyn Tagh, its' ages are each 322.8 ±2. 2Ma and 319 ± 1. 7Ma with the method of LA-ICP-MS zircon U-Pb dating. According to geochemical data, the former is ascribed to shoshonitic with peraluminous S-type granite which he characterized by high (La/Yb)N and Sr/Y and low contents of HREE, Yb and Y, and the latter is ascribed to high K calc-alkaline series with metaluminous to slightly peraluminous I-type granite which has the characteristic of low (La/Yb)N and Sr/Y and high contents of HREE, Yb and Y. Moreover, in view of its' pedogenesis and tectonic setting, we considered that monzonitic granite in Mangai area was most likely derived from upper crust (sandstone and a little mudstones) which had be subducted into 50 ∼ 80 km depth, and partial melted on the environment of high pressure ( > 1. 5GPa) and low temperature ( 779. 8 ∼ 792. 0°C ) by the dehydration from biotite with the residual mineral of garnet + rutile ( without amphibole) , and subsequently underwent the fractional crystallization of plagioclase, meanwhile quartz diorite in Mangai area should be likely derived from metabasalt in upper cmst which had be lifted to < 30km depth, and partial melted on the environment of low pressure ( <0. 8GPa ) and high temperature ( 811. 0 ∼ 821. 0°C ) with the residual mineral of amphibole + plagioclase ( without garnet) during the stage of crustal uplifting after continent-continent collision, and subsequently underwent the fractional crystallization of pyroxene, rutile and apatite (without amphibole and plagioclase). Consequently, we consider that Early Paleozoic tectonic-magmatic evolution of southern Altyn Tagh should be subdivided into three stages; 1 ) 505 ∼472Ma, the dominating event during the period of continent-continent collision was continental crust deep subduction which was characterized by high pressure magma, with the slab breaking; 2) 467 ∼450Ma, break-off of deep subducted continental slab caused strong buoyancy, which mainly leaded to exhumation and lifting of the upper crust, and magmatic activity on the environment of high temperature and low pressure displays characteristics of syn-exhumation magmatism with mantle magma underplating; 3 ) 424 ∼ 385. 2Ma, tectonic stress had transformed from vertical uplifting to lateral extending in the stage of the post-collisional extension, meanwhile magma was characterized by A-stye granitic magma on high temperature and low pressure which be relative to mantle magma upwelling.
Chronology; Monzonitic granite and quartz diorite; Pedogenesis; Southern A ltyn Tagh; Tectonic-magmatic evolution; diorite; fractional crystallization; geochronology; granite; I-type rock; igneous geochemistry; magmatism; Paleozoic; plagioclase; tectonic evolution; uranium-lead dating; Altun Mountains; Cook Islands; Mangaia