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The blueschists along the Indus Suture Zone in Ladakh, NW Himalaya
Author(s) -
HONEGGER K.,
Le FORT P.,
MASCLE G.,
ZIMMERMANN J.L.
Publication year - 1989
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1989.tb00575.x
Subject(s) - geology , blueschist , geochemistry , glaucophane , metamorphism , nappe , lawsonite , mafic , orogeny , volcanic rock , subduction , petrology , eclogite , paleontology , tectonics , volcano
Blueschists 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‐T estimates 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 during the Himalayan mountain building.