Abstract The Himalayan leucogranites, which were derived from crustal anatexis during the India-Asia continental collision, have recorded the tectono-magmatic evolution process of the Himalayan orogenic belt. In the Gurla Mandhata area of the western Himalaya, tourmaline leucogranites accompanied by variable deformation are observed along the Gurla Mandhata detachment fault. Whole-rock compositions show that these leucogranites have high SiO2, alkaline elements and low CaO, MgO, FeO, TiO2 contents, and are strongly peraluminous with A/CNK value of 1.13–1.27. For trace elements, these leucogranites are characterized by low Ba Sr, Nb, Nd concentrations and relatively high Rb, U concentrations with significant negative Eu anomalies. Zircon U Pb dating on the tourmaline leucogranites reveals a crystallization age of 11–12 Ma. Field observations, mineral assemblage, and geochemical features indicate that the Gurla Mandhata tourmaline leucogranites experienced high-degree fractional crystallization, which mainly induced by the long-distance migration from generation to emplacement, and the enrichment of volatile component (B, F, Cl, and H2O) facilitates the transportation ability of the leucogranite magma. Two types of tourmaline, Tur I and Tur II, are identified in the tourmaline leucogranites, enclosing relationships and mineral compositions suggest that these tourmalines should have formed at late and early stage in terms of magma evolution, respectively. The occurrence of early-stage tourmaline suggests that the primitive magma of the Gurla Mandhata tourmaline leucogranites is enriched in boron and H2O, which is most likely derived from fluid-flux melting of metasedimentary rocks from the Greater Himalayan Crystalline. The existence of the inherited zircon with ages of Paleoproterozoic and Neoproterozoic in combination with previous whole-rock Sr Nd isotopic study implies that the source region of the Gurla Mandhata tourmaline leucogranites is a two-component mixture between the Greater Himalayan Crystalline and the Lesser Himalayan Sequence.

中文翻译：

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藏西南Gurla Mandhata变质核杂岩中变形碧玺白花岗岩成因

摘要 喜马拉雅白质花岗岩是印亚大陆碰撞过程中地壳深熔岩的产物，记录了喜马拉雅造山带的构造-岩浆演化过程。在喜马拉雅西部的 Gurla Mandhata 地区，沿 Gurla Mandhata 拆离断层观察到伴有可变变形的碧玺白花岗岩。全岩成分表明，这些白质花岗岩具有高 SiO2、碱性元素和低 CaO、MgO、FeO、TiO2 含量，并且是强过铝质，A/CNK 值为 1.13-1.27。对于微量元素，这些淡色花岗岩的特点是 Ba Sr、Nb、Nd 浓度低，Rb、U 浓度相对较高，具有显着的负 Eu 异常。碧玺白花岗岩上的锆石 U Pb 定年显示结晶年龄为 11-12 Ma。实地观察，矿物组合和地球化学特征表明，Gurla Mandhata碧玺白花岗岩经历了高度分异结晶，其主要是由生成到就位的长距离迁移以及挥发性成分（B、F、Cl和H2O）的富集引起的有利于白花岗岩岩浆的输送能力。在白光花岗岩中发现了两种碧玺，Tur I 和 Tur II，封闭关系和矿物成分表明这些电气石应该分别形成于岩浆演化的晚期和早期阶段。早期碧玺的赋存表明，Gurla Mandhata 碧玺的原始岩浆富含硼和 H2O，这很可能来自大喜马拉雅结晶的变沉积岩的流体通量熔化。古元古代和新元古代的继承锆石的存在，结合前期全岩Sr Nd同位素研究，表明Gurla Mandhata碧玺白花岗岩的源区是大喜马拉雅结晶和小喜马拉雅层序的双组分混合物.