Age and Provenance of the Nindam Formation, Ladakh, NW Himalaya: Evolution of the Intraoceanic Dras Arc Before Collision With India
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Abstract The Dras Arc in NW India Himalaya is a belt of basaltic‐andesites intercalated with arkose‐dominated volcaniclastic rocks of the Nindam Formation situated along the Indus Suture between India and Eurasia. Debates exist as to whether these rocks developed in a forearc basin to the Eurasian margin or as part of an intraoceanic island arc system that collided with either India or Eurasia before final continental collision. Detrital zircons from the Nindam Formation yield U‐Pb age spectra with dominant youngest age populations of ~84–125 Ma, corresponding with arc magmatism. Sandstone provenance analysis from the Nindam Formation indicates that the Dras Arc evolved from an undissected arc to dissected arc over a period of ~41 Myr. Slightly older, smaller populations occur at ~135–185 Ma, corresponding with reported ages of Neotethyan ophiolites (e.g., Spongtang). The basal section of the Nindam Formation reveals the presence of arc‐derived basaltic‐andesite and tonalite clasts, plus ophiolitic components sourced from an adjacent accretionary complex. There is a distinct absence of quartz or felsic granitic clasts, suggesting that the Nindam Formation did not develop as a forearc basin to the Ladakh Batholith of southern Eurasia but rather as separate intraoceanic island arc. A distinct “Gondwanan” signature occurs in all samples, with zircon age peaks at ~514–988, ~1000–1588, ~1627–2444, and ~2500 Ma. We suggest that the Dras and Spong arcs are the same intraoceanic island arc system that developed as a result of subduction initiation along NNE‐SSW transform faults perpendicular to the Indian and Eurasia continents.Keywords:
Forearc
Island arc
Fractional crystallization (geology)
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The late Mesozoic Marum and Papuan ophiolites of Papua New Guinea
dip from the continental margin towards accreted Paleogene island-arcs and
appear to represent frontal-arc basement emplaced as a result of mid-
Tertiary continent/arc collision. Both ophiolites comprise thick sequences
of layered ultramafic and mafic cumulates overlying tectonite peridotite
and have associated basaltic pillow lavas. The petrology and geochemistry
of the cumulate sequences are not consistent with an origin from common
mid-ocean ridge basalts (MORE). Discrimination between mid-ocean ridge or
marginal basin origins for the Papua New Guinea ophiolites is more dependent
on accurate dating of the rocks rather than geochemical characteristics.
Island arc
Petrogenesis
Peridotite
Pillow lava
Ultramafic rock
Paleogene
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Emplacement of ophiolitic rocks in forearc areas: Examples from central Japan and Izu-Mariana-Yap island arc system
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Volcanic arc
Back-arc basin
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Abstract The Shyok Suture in western Himalaya preserves a record of the opening and closure of the Mesotethys Ocean between the Shyok ophiolite and Karakoram terrane prior to the India–Eurasia collision. The formation age of the Shyok ophiolite was unknown, which impeded correlation with similar rocks along the Shyok Suture in Pakistan and corresponding sutures in Tibet. We report the first zircon U–Pb ages of a newly documented suite, here named the Changmar Complex. The Changmar Complex gabbronorite and plagiogranite yielded SHRIMP U–Pb zircon Late Jurassic ages of 159.4 ± 0.9 Ma and 151.9 ± 1.5 Ma. Their highly positive initial ε Hf values (+14.9 to +16.9) indicate a juvenile mantle origin, without continental crust influence on the magma source. The Shyok ophiolite represents either: (1) a separate island arc that preceded formation of the Cretaceous–Eocene Ladakh Arc; or (2) the oldest magmatism and early stage of the Ladakh Arc. Intrusive and extrusive mafic rocks from the Shyok Suture analysed in this study have typical supra-subduction zone enrichment characteristics in their geochemistry and are classified as part of the volcanic-arc ophiolite. The U–Pb age and Hf isotopic signatures for the Shyok ophiolite are similar to the Late Jurassic Matum Das tonalite within the Kohistan Arc; we therefore suggest that they are part of the same intra-oceanic island-arc system that formed in the Mesotethys Ocean prior to Late Jurassic time.
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The sand and gravel within the Waipaoa River system of North Island, New Zealand, elucidate the provenance and sedimentary delivery system of an actively deforming continental forearc. In this region, Mesozoic to Cenozoic forearc basin sedimentary successions are being uplifted, eroded, and recycled into younger deposits. The identification of specific characteristics of the drainage basin bedrock can be linked to sediment composition, which in turn can document the processes of provenance mixing and dilution.
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Abstract New whole‐rock major and trace element geochemistry from the Leka Ophiolite Complex in Norway is presented and compared to the geochemical evolution and proposed tectonomagmatic processes recorded in the Izu‐Bonin‐Mariana system. These data demonstrate that the Leka Ophiolite Complex formed as forearc lithosphere during subduction initiation. A new high‐precision zircon U‐Pb date on forearc basalt constrains the timing of subduction initiation in the “Leka sector” of the Iapetus Ocean to 491.36 ± 0.17 Ma. The tectonomagmatic record of the Leka Ophiolite Complex captures only the earliest stages of subduction initiation and is thereby distinct from some other Appalachian–Caledonian ophiolites of similar age. The diversity of Appalachian–Caledonian ophiolite records may represent differing preservation and exposure of a variable forearc lithosphere.
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