青藏东缘马关地幔岩包体的岩石学与矿物学研究

Study on petrology and mineral chemical compositions of pyrolite xenoliths from Cenozoic high-K igneous rocks in Maguan area, eastern Tibet showed that the pyrolite xenolith belonged to spinel-phase lherzolite. The rock type was mainly spinel-lherzolite, with mineral assemblages of Ol + Opx + Cpx + Spl, and minor phlogolite and hornblende. Olivine was mainly chrysolite, and a little of forsterite, Fo value ranged from 89.72 to 90.47, and Mg^# from 89.75 to 90.51. En numerator in orthopyroxene ranged from 88.00 to 89.59, Mg^# value from 90.21 to 91.16 and Cr^# from 3.31 to 6.23. Clinopyroxene, mainly belonged to diopside with enstatite diopside, was characterized by high Ca (w_CaO from 18.71% to 20.78%), high Al (w_Al2O3 6.00% to 7.30%, high Mg^# value (89.93 to 91.57), and low Cr^# value (5.13 to 8.74). Spinel belonged to chromspinell. w(Cr₂O₃) in spinel from 7.62% to 12.88%. Mineral chemical composition from pyrolite xenolith in Maguan area indicated that spinel-lherzolite xenoliths belonged to type-A peridotite enclaves and the lower melted continental mantle. The equilibrium temperature and pressure conditions of the xenoliths in Maguan area ranged from 900 °C to 1 105 °C and 1.29 MPa to 2.20 GPa (equivalent to 45 km - 71 km depth), respectively. A geothermal curve of the upper mantle in the Maguan area was consistent with the ocean-type upper-mantle geothermal curve. It revealed that the lithosphere mantle in Maguan area had a high value of thermal flow, indicating that the hot asthenosphere upwelled in the period of 0 - 16 Ma in eastern Asia and resulting in the east-west lithospheric extension in eastern Tibet and the whole eastern Asia.