Burial and exhumation history of a Lesser Himalayan schist: Recording the formation of an inverted metamorphic sequence in NW India

被引:92
作者
Caddick, M. J. [1 ]
Bickle, M. J. [1 ]
Harris, N. B. W. [2 ]
Holland, T. J. B. [1 ]
Horstwood, M. S. A. [3 ]
Parrish, R. R. [3 ,4 ]
Ahmad, T. [5 ]
机构
[1] Univ Cambridge, Dept Earth Sci, Cambridge CB2 3EQ, England
[2] Open Univ, Dept Earth Sci, Milton Keynes MK7 6AA, Bucks, England
[3] NERC, Isotope Geosci Lab, Kingsley Dunhan Ctr, Keyworth NG12 5GG, Notts, England
[4] Univ Leicester, Dept Geol, Leicester LE1 7RH, Leics, England
[5] Univ Delhi, Dept Geol, Delhi 110007, India
基金
英国自然环境研究理事会;
关键词
PTt evolution; monazite chronometry; Lesser Himalaya; western Himalaya; inverted metamorphism;
D O I
10.1016/j.epsl.2007.09.011
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 [地球物理学]; 070902 [地球化学];
摘要
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 degrees C followed burial to approximately 25 km depth. Laser-ablation monazite geochronology yields a weighted mean Pb-206*/U-238 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 excess Pb-206 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 infer-red 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. (c) 2007 Elsevier B.V. All rights reserved.
引用
收藏
页码:375 / 390
页数:16
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