Metamorphic evolution of the High Himalayan Crystallines in SE Zanskar, India
作者:
U. POGNANTE,
B. LOMBARDO,
期刊:
Journal of Metamorphic Geology
(WILEY Available online 1989)
卷期:
Volume 7,
issue 1
页码: 9-17
ISSN:0263-4929
年代: 1989
DOI:10.1111/j.1525-1314.1989.tb00571.x
出版商: Blackwell Publishing Ltd
关键词: High Himalayan Crystallines;Himalayan metamorphism;polymetamorphism;Zanskar
数据来源: WILEY
摘要:
ABSTRACTThe High Himalayan Crystallines (HHC) of SE Zanskar consist of biotite paragneisses, of orthogneisses that derive from early‐Palaeozoic granitoids, of minor metabasics and of post‐metamorphic leucogranites of Miocene age.Two main metamorphic events have been documented in the HHC. The first event occurred atP= 12.0 ± 0.5 kbar andT= 750 ± 50° C in rare metabasics intruded by early‐Palaeozoic granitoids. In the biotite paragneisses, thermobarometric estimates of the first event point to comparableTatP4–5 kbar lower. The first event is followed by a pervasive syn‐tectonic crystallization characterized by lowerPandT. On the basis of the cooling ages of the metamorphic minerals and on the geological evidence, the second event is referred to the Tertiary Himalayan crystallization. Further petrological and geochronological studies are necessary to prove whether a few mineral relics ascribed to the first event define a polyphase Himalayan evolution or if they record the incomplete obliteration of an older history during the Himalayan event.The HHC of SE Zanskar show a decrease in metamorphic grade from the middle structural levels upward, close to the Kade unit, and downward, close to the Lesser Himalaya (from sillimanite‐K‐feldspar‐biotite‐bearing assemblages to kyanite‐staurolite‐muscovite‐bearing assemblages). This metamorphic zonation is probably a consequence of the polyphase history of intracontinental thrusts and of the tectonic emplacement of hot crustal slabs within shallower and colder thrust sheets at relatively late stages of the continental collision
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