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首页> 外文期刊>Contributions to Mineralogy and Petrology >Timescales of partial melting in the Himalayan middle crust: insight from the Leo Pargil dome, northwest India
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Timescales of partial melting in the Himalayan middle crust: insight from the Leo Pargil dome, northwest India

机译：喜马拉雅中地壳部分融化的时间尺度：印度西北部狮子山的圆顶的见解

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摘要

The Leo Pargil dome (LPD) in northwest India exposes an interconnected network of pre-, syn-, and post-kinematic leucogranite dikes and sills that pervasively intrude amphibolite-facies metapelites of the mid-crustal Greater Himalayan sequence. Leucogranite bodies range from thin (5-cm-wide) locally derived sills to thick (2-m-wide) crosscutting dikes extending at least 100 m. Three-dimensional exposures elucidate crosscutting relations between different phases of melt injection and crystallization. Combined laser ablation inductively coupled plasma mass spectrometry U–Th/Pb geochronology and trace element analysis on well-characterized monazite grains from nineteen representative leucogranites yields a large, internally consistent data set of approximately 700 U–Th/Pb and 400 trace element analyses. Grain-scale variations in age correlate with trace element distributions and indicate semi-continuous crystallization of monazite from 30 to 18 Ma. The youngest U–Th/Pb ages in a given sample are consistent with the outcrop-scale crosscutting relations, whereas older ages within individual samples record inheritance from partially crystallized melt and source metapelites. U–Th/Pb isotopic and trace element data are incorporated into a model of melting within the LPD that involves (1) steady-state equilibrium batch melting of compositionally homogeneous metapelitic sources; (2) pulses of increased melt mobility lasting 1–2 m.y. resulting in segregation of melt from its source and amalgamation into mixed magmas; and (3) rapid emplacement and final crystallization of leucogranite bodies. Melt systems in the LPD evolved from locally derived, in situ melt in migmatitic source rocks into a vast network of dikes and sills in the overlying non-migmatitic host rocks.
机译：印度西北部的Leo Pargil穹顶（LPD）暴露出运动前，同速和后运动的白云石堤和窗台的相互连接的网络，这些网络普遍侵入中地壳大喜马拉雅山序列的角闪岩相变质岩。白云石体的范围从薄的（5厘米宽）局部衍生的门槛到延伸至少100 m的厚的横切堤坝（2米宽）。三维曝光阐明了熔体注入和结晶不同阶段之间的横切关系。结合激光烧蚀-电感耦合等离子体质谱U-Th / Pb年代学和痕量元素分析，对19个代表性白云母的特征明确的独居石晶粒进行了约700 U-Th / Pb和400个痕量元素分析的内部一致性数据集。年龄的晶粒度变化与微量元素分布有关，并表明30-18 Ma的独居石半连续结晶。给定样品中最年轻的U-Th / Pb年龄与露头尺度横切关系一致，而单个样品中的最高年龄记录了部分结晶的熔体和源变质岩的遗传。 U–Th / Pb同位素和痕量元素数据被整合到LPD内的熔融模型中，该模型涉及（1）组成均质的异生源的稳态平衡批量熔融； （2）增加熔体流动性的脉冲持续1-2 m.y.导致熔体从其来源中分离出来，并融合成混合岩浆； （3）无色花岗岩体的快速定位和最终结晶。 LPD中的熔体系统从局部生源的原岩熔岩演化为上覆非非原岩宿主岩中的堤坝和基石的庞大网络。

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