【摘要】 拿日雍错片麻岩穹窿位于特提斯喜马拉雅带的东部,穹窿边部淡色花岗岩脉形成于21.8±0.3Ma,穹窿核部主体淡色花岗岩的结晶年龄为20.1±0.1Ma,其中1件样品记录了~17.3Ma热液蚀变事件。大部分淡色花岗岩具有以下特征:(1)较高的Si O2(>72.9%),Al2O3(>14.7%)和A/CNK(>1.1),较低的Fe O、Mg O、Mn O和Ti O2;(2)高度变化的大离子亲石元素(如Rb、Sr、Ba)和高场强元素(如Nb、Ta、Hf、Th)和Rb/Sr、Nb/Ta、Zr/Hf比值;(3)富集轻稀土元素,亏损重稀土元素,Eu和Nd都显示负异常(Eu/Eu*<0.7,Nd/Nd*=0.5~0.8);(4)Sr同位素比值变化范围较大(87Sr/86Sr(t)=0.7132~0.7330),但Nd同位素比值一致(εNd(t)=-12.4~-10.9)。这些特征表明:拿日雍错淡色花岗岩形成于20Ma,是变泥质岩部分熔融作用的产物,经历了不同程度的斜长石、锆石、独居石、磷灰石、富Ti矿物等的分离结晶作用。更多还原

【Abstract】 The Nariyongcuo Gneiss Dome is located to eastern Tethyan Himalaya. New zircon U-Pb data show that the main leucogranite pluton in the core formed at 20. 0 ± 0. 1Ma,whereas the leucogranitic dike in the margin at 21. 8 ± 0. 3Ma,respectively.Some zircon grains also record a hydrothermal event at ~ 17. 3Ma. The Nariyongcuo leucogranites are characterized by:(1) high Si O2( > 72. 9%),Al2O3( > 14. 7%) and A/CNK( > 1. 1),but low Fe O,Mg O,Mn O and Ti O2;(2) large variations in concentrations of large ion lithophile elements( e. g.,Rb,Sr,Ba) and high field strength element( e. g.,Nb,Ta,Hf,Th),as well as ratios of Rb/Sr,Nb/Ta,Zr/Hf;(3) enrichment in LREE,depletion in HREE,and negative Eu and Nd anomalies( Eu/Eu*< 0. 7,Nd/Nd*= 0. 5 ~ 0. 8);( 4) large variations in initial87Sr/86 Sr ratios( 0. 7132 ~ 0. 7330) but relatively uniform unradiogenic Nd isotope compositions( εNd(t) =-12. 4 ~-10. 9). These data indicate that the Nariyongcuo leucogranite was derived from partial melting of metapelite at 20 Ma and experienced various degrees of fractional crystallization of plagioclase,zircon,monazite,apatite and Ti-rich mineral phases.更多还原