The Kumaun and Garwhal Lesser Himalaya, India: Part 2. Thermal and deformation histories
The Kumaun and Garwhal Lesser Himalaya, India: Part 2. Thermal and deformation histories
复制标题
DOI：
10.1130/b26343.1
复制
发表时间：
2009-09
影响因子：
4.9
通讯作者：
J. Célérier;T. Harrison;O. Beyssac;F. Herman;W. Dunlap;A. Webb
中科院分区：
文献类型：
--
作者：
J. Célérier;T. Harrison;O. Beyssac;F. Herman;W. Dunlap;A. Webb
综合岩石学，热年代学和数值模拟研究约束印度Kumaun和Garwhal地区的小喜马拉雅序列的热演化。在Tons逆冲断层以南，最高变质温度不超过330 °C。在北方一侧，记录了主中央逆冲断层上盘附近向高温的过渡。在主中央逆冲断层的直接下盘，峰值温度平均约为550 °C。根据计算，Vaikrita逆冲断层下方的逆热场梯度约为30 °C/km。在Vaikrita逆冲断层以南约25 km处的主中央逆冲断层上盘的飞来峰下方也记录到了约20 °C/km的反向热场梯度，在飞来峰底部剪切带附近记录到了530 °C的最高下盘温度。小喜马拉雅序列热变质作用的机制被解释为从主中央逆冲断层和（或）上盘到下盘的热传导。一个局部的热场梯度也与吨推力。^（40）Ar/^（39）Ar热年代学研究表明，在晚第三纪，Kumaun和Garwhal小喜马拉雅地区的出露岩石在不同时期经历了低于白色云母闭合温度（Tc）的冷却过程。Munsiari逆冲断层的近端下盘在约100 ℃时经历了低于白色云母Tc的冷却。8.5 MA.在Munsiari逆冲断层以南，Chaukori和Askot klippen的近端下盘，白云母年龄约为2000年。11.5 Ma，比北部样品老约3 Ma。从北方和南方曝光的样品中的年龄差异被解释为文件冷却相关的热松弛以下通过的主要中央逆冲上盘顶部的小喜马拉雅序列。热模拟的结果实现了良好的拟合的数据时，场景涉及到一个热的上盘逆冲推覆在下行下盘的早中新世阶段，其次是小喜马拉雅层序岩石内的双相启动。
An integrated petrologic, thermochronologic, and numerical modeling study constrains the thermal evolution of the Lesser Himalayan Sequence in the Kumaun and Garwhal regions of India. South of the Tons thrust, peak metamorphic temperatures do not exceed 330 °C. On the northern side, a transition toward higher temperatures adjacent to the Main Central thrust hanging wall is documented. In the immediate footwall of the Main Central thrust, peak temperatures average ~550 °C. An inverted thermal field gradient of ~30 °C/km beneath the Vaikrita thrust is calculated. An inverted thermal field gradient of ~20 °C/km is also documented beneath a klippe of the Main Central thrust hanging wall ~25 km south of the Vaikrita thrust, and a peak footwall temperature of 530 °C is recorded close to the shear zone at the base of the klippe. The mechanism for thermal metamorphism in the Lesser Himalayan Sequence is interpreted to be conduction of heat from the Main Central thrust fault and/or hanging wall to the footwall. A localized thermal field gradient is also associated with the Tons thrust. The ^(40)Ar/^(39)Ar thermochronology reveals that the exposed rock in the Kumaun and Garwhal Lesser Himalaya underwent cooling below the closure temperature (Tc) for white mica at different times in the late Tertiary. The proximal footwall of the Munsiari thrust experienced cooling below the white mica Tc at ca. 8.5 Ma. South of the Munsiari thrust, in the proximal footwalls of the Chaukori and Askot klippen, muscovites ages are ca. 11.5 Ma, ~3 Ma older than samples to the north. The age differences in samples from northern and southern exposures are interpreted to document cooling related to thermal relaxation following passage of the Main Central thrust hanging wall atop the Lesser Himalayan Sequence. Results of thermal modeling achieve good fits to the data when scenarios involve an early Miocene phase of overthrusting of a hot hanging wall over a downgoing footwall, followed by the initiation of a duplex within Lesser Himalayan Sequence rocks.