Burial and exhumation history of a Lesser Himalayan schist: Recording the formation of an inverted metamorphic sequence in NW India
Burial and exhumation history of a Lesser Himalayan schist: Recording the formation of an inverted metamorphic sequence in NW India
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小喜马拉雅片岩的埋藏和挖掘历史：记录印度西北部倒变质层序的形成
DOI：
10.1016/j.epsl.2007.09.011
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发表时间：
2007
影响因子：
5.3
通讯作者：
T. Ahmad
中科院分区：
文献类型：
--
作者：
M. Caddick;M. Bickle;N. Harris;T. Holland;M. Horstwood;R. Parrish;T. Ahmad
通过对单个样品的压力-温度演化和副相年代学的耦合分析，揭示了小喜马拉雅部分地区中中新世的埋藏-隆升历史。相平衡计算表明，埋藏至约25公里深处后，温度峰值为600-640 °C。激光烧蚀独居石年代学获得的206 Pb年龄为11.1±2.0 Ma，Tera-Wasserburg Concordia截距年龄为10.6±0.9 Ma，基质和包裹体颗粒之间没有明显的年龄差异。考虑到过量~（206）Pb的可能性，进一步表明结晶年龄在9-10 Ma之间。结构分析表明独居石是在逆冲变质作用中生长的。峰变质条件之后折返和冷却，形成了一个独特的紧密PT路径关闭。这条路径的形状和它相对年轻的逆冲阶段区分小喜马拉雅的演化，通常推断为高喜马拉雅，并允许探索的热机制，在西喜马拉雅期间的间隔约。23-6 MA. PTT历史的特点是下盘加热，由于快速逆冲热岩（高喜马拉雅），随后纳入一个逆冲岩席，挖出的序列足够迅速，以保持倒置的变质梯度。
Coupled analysis of the pressure–temperature (PT) evolution and accessory phase geochronology of a single sample reveals the burial-uplift history of part of the Lesser Himalaya during the Middle Miocene. Phase-equilibria calculations indicate that a peak temperature of 600–640 °C followed burial to approximately 25 km depth. Laser-ablation monazite geochronology yields a weighted mean206Pb⁎/238U age of 11.1±2.0 Ma and a Tera-Wasserburg Concordia intercept age of 10.6±0.9 Ma, with no distinguishable age difference between matrix and inclusion grains. Considerations of the likelihood of excess206Pb further suggest that the crystallization age lies in the range 9–10 Ma. Textural analysis suggests that monazite grew during prograde metamorphism. Peak metamorphic conditions were followed by exhumation and cooling, forming a distinctively tight PT path closure. Both the shape of this path and its relatively young prograde phase distinguish Lesser Himalayan evolution from that typically inferred for the High Himalaya, and allow exploration of the thermal mechanisms that operated in the western Himalaya during the interval ca. 23–6 Ma. The PTt history is characteristic of footwall heating due to rapid overthrusting of hot rock (the Higher Himalaya), followed by incorporation into a thrust sheet that exhumed the sequence rapidly enough to preserve an inverted metamorphic gradient.