Monazite geochronology unravels the timing of crustal thickening in NW Himalaya
Monazite geochronology unravels the timing of crustal thickening in NW Himalaya
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DOI：
10.1016/j.lithos.2014.09.024
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发表时间：
2014-12
期刊：
影响因子：
3.5
通讯作者：
K. Stübner;D. Grujic;R. Parrish;N. Roberts;A. Kronz;J. Wooden;T. Ahmad
中科院分区：
文献类型：
--
作者：
K. Stübner;D. Grujic;R. Parrish;N. Roberts;A. Kronz;J. Wooden;T. Ahmad
喜马拉雅西北部的绿片岩至角闪岩级别的海曼塔变质岩保存了大部分爱奥喜马拉雅地壳增厚的进行性变质历史，这一历史已被喜马拉雅其他地区的渐新世-中新世混合岩化所抹去。我们的锆石和独居石U/Th-Pb数据揭示了一个多阶段的进退变质演化过程。前进型巴罗型变质独居石生长的最早证据约为41M a。高峰期变质条件(约8-8.5kbar，约600-700℃)出现在37-36 Ma，随后经历了漫长的高温演化，独居石至少经历了3次明显的生长，这可能与北喜马拉雅推覆构造(如锡喀尔推覆构造、尼马岭推覆构造)的形成有关。晶体的快速折返开始于约226亿Ma，并导致通过Muscovite40Ar/39Ar闭合温度冷却21.8亿Ma。尽管在喜马拉雅邦中部不能明确地确定藏南支队的局部延续，但晚渐新世/早中新世几个较小的从顶到北到北向北的剪切带系统可能促进了挤压。与赞斯卡和东喜马恰尔邦的结晶不同，挤压没有伴随着广泛的减压熔融。
Greenschist to amphibolite grade Haimanta metasediments of the NW Himalaya preserve much of the prograde metamorphic history of Eohimalayan crustal thickening, which has been erased by Oligo-/Miocene migmatization elsewhere in the Himalaya. Our zircon and monazite U/Th–Pb data unravel a multi-stage prograde metamorphic evolution. The earliest evidence of prograde Barrovian metamorphic monazite growth is ~ 41 Ma. Peak metamorphic conditions (~ 8–8.5 kbar, ~ 600–700 °C) were attained at 37–36 Ma and followed by a prolonged evolution at high temperatures with at least three distinct episodes of monazite growth, which may be related to the formation of the northern Himalayan nappes (e.g., Shikar Beh nappe, Nyimaling nappe). Rapid exhumation of the crystalline started at ~ 26 Ma and resulted in cooling through the muscovite40Ar/39Ar closure temperature by 21.8 Ma. Although a local continuation of the South Tibetan detachment is not unambiguously identified in central Himachal Pradesh extrusion was likely facilitated by a system of several minor late Oligocene/early Miocene top-to-the-N to NE shear zones. In contrast to the crystalline of Zanskar and eastern Himachal Pradesh, extrusion was not accompanied by widespread decompression melting.