Late Mesozoic subduction‐induced hydrothermal gold deposits along the eastern Asian and northern Californian margins: Oceanic versus continental lithospheric underflow |
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| Authors: | Wallace Gary Ernst |
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| Institution: | Department of Geological and Environmental Sciences, Stanford University, Geological & Environmental Sciences Building 320, Room 118, Stanford, CA 94305‐2115, USA (email: wernst@standford.edu) |
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| Abstract: | During late Mesozoic subduction of paleo‐Pacific lithospheric plates, numerous gold vein deposits formed in the Dabie–Sulu Belt of east‐central China plus its east‐Asian extensions, and in the Klamath Mountains plus Sierran Foothills of northern California. In eastern Asia, earlier transpression and continental collision at about 305–210 Ma generated a high pressure–ultrahigh pressure orogen, but failed to produce widespread intermediate to felsic magmatism or abundant hydrothermal gold deposits. Similarly in northern California, strike‐slip ± minor transtension–transpression over the interval of about 380–160 Ma resulted in the episodic stranding of oceanic terranes, but generated few granitoid magmas or Au ore bodies. However, for both continental margin realms, nearly head‐on Cretaceous destruction of oceanic lithosphere involved sustained underflow; reaching magmagenic depths of about 100 km, the descending mafic‐ultramafic plates dewatered, producing voluminous calc‐alkaline arc magmas. Ascent of these plutons into the middle and upper crust released CO2 ± S‐bearing aqueous fluids and/or devolatilized the contact‐metamorphosed wall rocks. Such hydrothermal fluids transported gold along fractures and fault zones, precipitating it locally in response to cooling, fluid mixing, and/or reactions with wall rocks of contrasting compositions (e.g. serpentinite, marble). In contrast, where sialic crust was subducted to depths of about 100 km, only minor production of granitoid melts occurred, and few major coeval Au vein deposits formed. The mobilization of precious metal‐bearing fluids in continental margin and island arc environments apparently requires long‐continued, nearly orthogonal descent of oceanic, not continental, lithosphere. |
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| Keywords: | Continental plate subduction hydrothermal gold deposits oceanic plate subduction |
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