Source provenance
Khan, M.A., Jan, M.Q., Windley, B.F., Tarney, J. & Thirlwall, M.F. (1989). The Chilas mafic-ultramafic igneous complex; the root of the Kohistan island arc in the Himalaya of northern Pakistan. In: Malinconico, L.L. & Lillie, R.J. (eds) Tectonics of the Western Himalayas. Geological Society of America Special Paper 232, 75-94.
Cited by 2 units (2 published) · 0 field-level citations · 2 revision notes.
The Chilas Complex as the root/deepest level of the Kohistan island arc: a >300 km long, up to 40 km wide mafic-ultramafic body of massive to layered gabbro-norite with a dunite-peridotite-troctolite-pyroxenite-anorthosite association. Not an ophiolite; trace-element chemistry (negative Nb, positive Sr-Ba-P) indicates a hornblende-bearing sub-arc mantle source. Interpreted as the arc root-zone magma chamber or intra-arc rift diapir. Kohistan-Ladakh arc formed by northward neo-Tethyan subduction (Late Jurassic-mid Cretaceous), bounded by the MKT (north) and MMT (south); tonalite-diorite plutons 110-95 Ma.
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Units citing this source
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- Geological significance: Khan et al. (1989): the Chilas Complex is the root (deepest exposed level) of the Kohistan island arc — a mafic-ultramafic body >300 km long and up to 40 km wide at the base of the arc. It is dominantly massive to locally layered gabbro-norite, with a central near-base association of layered dunite-peridotite-troctolite-gabbronorite-pyroxenite-anorthosite (graded bedding, slump breccias, syn-depositional faults) representing a more primitive magma batch. It is NOT an ophiolite: trace-element patterns (marked negative Nb, positive Sr-Ba-P, high K/Rb) indicate melting of a hornblende-bearing sub-arc mantle, and the complex is interpreted as the arc root-zone magma chamber or a diapir formed during early intra-arc (back-arc) rifting.
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- Geological significance: Khan et al. (1989): the Kohistan–Ladakh island arc formed by northward subduction of neo-Tethyan oceanic lithosphere in Late Jurassic to Cretaceous time and extends for at least 1,000 km across the western Himalaya, southern Karakoram and eastern Hindu Kush. It is juxtaposed against the Asian plate to the north along the Main Karakoram Thrust (MKT) and against the Indian plate to the south along the Main Mantle Thrust (MMT), and comprises calc-alkaline volcanics, intra-arc sediments (with Aptian–Albian fossils) and diorite–tonalite–granite plutons; the earliest tonalite–diorite plutons have isotopic ages of 110–95 Ma.