The blueschists along the Indus Suture Zone in Ladakh, NW Himalaya
作者:
K. HONEGGER,
P. Le FORT,
G. MASCLE,
J.‐L. ZIMMERMANN,
期刊:
Journal of Metamorphic Geology
(WILEY Available online 1989)
卷期:
Volume 7,
issue 1
页码: 57-72
ISSN:0263-4929
年代: 1989
DOI:10.1111/j.1525-1314.1989.tb00575.x
出版商: Blackwell Publishing Ltd
关键词: Blueschist;Himalayan metamorphism;Indus Suture Zone;Ladakh
数据来源: WILEY
摘要:
ABSTRACTBlueschists occur along the Indus Suture Zone in Ladakh as tectonic thrust slices, as isolated blocks within mélange units and as pebbles within continental detrital series. In the Shergol‐Baltikar section high‐pressure rocks within the Mélange unit lie between the Dras‐Naktul‐Nindam nappes in the north and the Lamayuru units in the south. The blueschists are imbricated with mélange formation of probably upper Cretaceous age. They are overlain discordantly by the Shergol conglomerate of post Eocene (Oligo‐Miocene ?) age. Blueschist lithologies are dominated by volcanoclastic rock sequences of basic material with subordinate interbedding of cherts and minor carbonates. Mineral assemblages in metabasic rocks are characterized by lawsonite‐glaucophane/crossite‐Na‐pyroxene‐chlorite‐phengite‐titanite ± albite ± stilpnomelane. In the quartz bearing assemblages garnet is present but omphacite absent.P‐Testimates indicate temperatures of 350 to 420°c and pressures around 9–11 kbar. Geochemical investigations show the primary alkaline character of the blueschist, which suggests an oceanic island or a transitional MORB type primary geotectonic setting. K/Ar isotopic investigations yield middle Cretaceous ages for both whole rocks and minerals. Subduction related HP‐metamorphism affecting the Mesozoic Tethyan oceanic crust developed contemporaneously with magmatism in the Dras volcanic are and the Ladakh batholith. Subsequent collision of India with Asia obducted relics of subduction zone material which later became involved in nappe emplacement durin
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