藏南洛扎地区淡色花岗岩锆石U-Pb年龄、Hf同位素、地球化学与岩石成因

The Luozha Miocene leucogranite intrusive whose zircon U-Pb age is 17. 7Ma is located in the eastern part of high Himalayan leucogranite belt. Luozha leucogranites are high-K calc-alkaline and strongly peraluminous (A/CNK >1.1), including tourmaline bearing muscovite leucogranites and tourmaline bearing two-mica leucogranites. The SiO₂ and Al₂O ₃ of these rocks range from72. 75% to 74. 62% , 14.45% to 15.48% , respectively. These leucogranites are slight right incline, showing the fractionation between LREE and HREE, and display strongly negative Eu anomalies (Eu/Eu* =0. 57) , enrichments in LILE, and lack of HFSE. The high Rb/Sr ( >4) and low CaO/Na₂O (0. 19 ∼0. 26) indicate the source of the Luozha leucogranite is pelite. The (87Sr/86Sr) t, sNd(t) and £Hf(t) are 0. 725802 ∼0. 727276, - 13. 4 12. 9 and - 13. 9 ∼ -7. 5 respectively, which imply the crustal origin. But the large variation range of £Hf(t) suggest the magma source of leucogranite is complex. Luozha leucogranites are generated during the STDS activity that resulting in the decompression dehydration melting of muscovite in metapelite. Therefore, these melts intruded up along the weakened part of STDS and located around STDS under settings of crust extension and rapid plateau uplift.