A Study on the mantle xenoliths in the Cenozoic volcanic rocks from Maguan Area, Yunnan Province

There is a large numbers of Cenozoic volcanic rocks in Meguan area, Eastern Yunnan province due to Indo-Asian collision and uplift of whole Tibet Plateau quickly since late-Cenozoic Era. Abundant xenoliths derived from mantle contained in the some volcanic rocks. This paper provide the analytic data of the whole rock chemistry of the Cenozoic volcanic rocks and EMB data of the garnet-Iherzolite, spinel-lherzolite, garnet-pyroxenite end garnet-websterite xenoliths in the volcanic rocks from Bazhai, Maguan area; and obtained equilibrium temperatures and pressures of the xenoliths using the mineralogical thermobarometer; and to contributed local mantle geotherm and made a compare with the geotherm of typic geotectonic units from worldwide. The studies showed that, the equilibrium T and P of the garnet-lherzolite and websterite are 1209 degrees C similar to 1230 degrees C and 2. 13 similar to 2.93GPa, 1034 degrees C similar to 1095 degrees C and 1.69 similar to 2.35GPa respectively, but the equilibrium T and P of spinel lherzolite are 944 degrees C similar to 1072 degrees C and 1.46 similar to 2.74 GPa,the depth origined the xenoliths is corresponding to 69 similar to 93 km, 55 similar to 75 km and 48 similar to 87 km respectively. Therefore, the xenoliths of spinel-lherzolite, garnet-lherzolite and garnet- websterite are coexistence and transition each other, but not boundary sharply among of them. The geotherm contributed by equilibrium T and P of the xenoliths located at between the geotherm of the eastern margin of the Australian Craton and alkanic volcanic province, similar to the geotherm of Huabei area but higher than the Huabei geotherm clearly, which consistent with the value of heat flow in Maguan area and eastern China, and demonstrate the pyroxenit and lherzolite xenoliths come from mantle. The depth inversed by equilibrium T and P of the xenoliths demonstrate the garnet lherzolite may be come from the base of lithosphere or asthenospher. This paper advanced that, according to the studies mentioned above, link the achievements about the time-space structure of the Cenozoic potassic magmatism in Tibetan Plateau and western Yunnan, the genesis of Cenozoic alkaline magmatism and mantle-derived xenoliths in Maguan area related to the activities of lateral asthenosperic mantle flow resulted by collision and subduction of India-Eurasia.