Timing and conditions of peak metamorphism and cooling across the Zimithang Thrust, Arunachal Pradesh, India
Timing and conditions of peak metamorphism and cooling across the Zimithang Thrust, Arunachal Pradesh, India
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DOI：
10.1016/j.lithos.2014.04.005
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发表时间：
2014-07
期刊：
影响因子：
3.5
通讯作者：
C. Warren;A. K. Singh;N. Roberts;D. Regis;A. Halton;R. B. Singh
中科院分区：
文献类型：
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作者：
C. Warren;A. K. Singh;N. Roberts;D. Regis;A. Halton;R. B. Singh
在印度东北部的阿鲁纳恰尔邦，子米塘逆冲推覆构造与大喜马拉雅序列的两个岩石构造单元并列。独居石U-Pb、白云母40Ar/39Ar和来自上盘和下盘岩石的温压测量数据限制了它们在整个结构中并置的时间和条件，以及随后的冷却。采空区黑云母-硅线片麻岩中的独居石颗粒LA-ICPMS U-Pb年龄为16~12.7×10~(-4)Ma。高应变带内片麻岩的独居岩年龄为14.9 Ma±60.3 Ma~11.5 Ma±60.3 Ma。紧邻下盘的石榴石-十字石-云母片岩产生的独居石年龄为27.3 Ma±20.6 Ma至17.1 Ma±60.2 Ma。黑云母钛测温和石榴石黑云母测温表明，在悬壁和脚壁(约525-650°C)也达到了类似的峰值温度。在高应变区本身和距离逆冲更远的下盘，似乎达到了约700摄氏度的高温。来自逆冲断层两侧样品的40Ar/39Ar白云母单颗粒熔融数据获得了~8.7 Ma的年龄，表明在达到白云母中Ar扩散的闭合温度时，沿逆冲断层的运动使两个单元并列在一起。这些数据证实了以前的观点，即主要造山带平行的无序结构在喜马拉雅演化过程中的不同时间扰乱了大喜马拉雅序列，并突出了沿喜马拉雅走向在同等构造水平上40Ar/39Ar白云母冷却年龄的东移-年轻趋势。
The Zimithang Thrust juxtaposes two lithotectonic units of the Greater Himalayan Sequence in Arunachal Pradesh, NE India. Monazite U–Pb, muscovite40Ar/39Ar and thermobarometric data from rocks in the hanging and footwall constrain the timing and conditions of their juxtaposition across the structure, and their subsequent cooling. Monazite grains in biotite–sillimanite gneiss in the hanging wall yield LA-ICP-MS U–Pb ages of 16 ± 0.2 to 12.7 ± 0.4 Ma. A schistose gneiss within the high strain zone yields overlapping-to-younger monazite ages of 14.9 ± 0.3 to 11.5 ± 0.3 Ma. Garnet–staurolite–mica schists in the immediate footwall yield older monazite ages of 27.3 ± 0.6 to 17.1 ± 0.2 Ma. Temperature estimates from Ti-in-biotite and garnet–biotite thermometry suggest similar peak temperatures were achieved in the hanging and footwalls (~ 525–650 °C). Elevated temperatures of ~ 700 °C appear to have been reached in the high strain zone itself and in the footwall further from the thrust. Single grain fusion40Ar/39Ar muscovite data from samples either side of the thrust yield ages of ~ 7 Ma, suggesting that movement along the thrust juxtaposed the two units by the time the closure temperature of Ar diffusion in muscovite had been reached. These data confirm previous suggestions that major orogen-parallel out-of-sequence structures disrupt the Greater Himalayan Sequence at different times during Himalayan evolution, and highlight an eastwards-younging trend in40Ar/39Ar muscovite cooling ages at equivalent structural levels along Himalayan strike.