藏南萨迦拉轨岗日淡色花岗岩特征及与变质核杂岩的关系

Laguigangri Leucogranites and Its Relation with Laguigangri Metamorphic Core Complex in Sajia, South Tibet

藏南拉轨岗日带展布着串珠状变质核杂岩,其内出露的淡色花岗岩体构成北喜马拉雅淡色花岗岩带.岩体既有在变质核杂岩内核中分布的,亦有在滑脱系分布的,岩体均表现出强力主动侵位的特征.淡色花岗岩可分为两期:早期黑云母淡色花岗岩和晚期白云母淡色花岗岩.岩石高硅富铝,含白云母±电气石±石榴石特征富铝矿物,为S型花岗岩.北喜马拉雅淡色花岗岩结晶年龄为17～10Ma,源岩为MCT上部基底副变质岩.当挤压体制与伸展体制转换时,降压作用导致了岩浆的生成,同时,由于压力骤减,年轻造山带更为塑性的下地壳物质与软层隆起导致上地壳伸展,从而形成变质核杂岩,岩浆对内核的上隆起到促进作用.

Laguigangri metamorphic core complexes (MCC) occurred in paternoster shape in south Tibet. Leucogranites, distributed in the core or detachment of the MCC, form the famous northern Himalayan leucogranites belt. They actively emplaced and occurred in two periods: early biotite leucogranites and late muscovite leucogranites. With high SiO2 and Al2O3, the leucogranites have muscovite±tourmaline±garnet aluminous minerals and so do S-type granites. The crystalline of the northern Himalayan leucogranites is dated 17-10 Ma, whose source is the para-metamorphical rocks in the high Himalayan crystalline basement on top of the MCT. The magma resulted from decompression during the conversion of the structural mechanism. Simultaneously, the pressure decompression caused more plastic lower crust and the liquid layer in younger orogen to rise to the upper crust and formed the MCC. It is found that the magma speeds the formation of the MCC.