Magmatism of mid-oceanic ridge subduction during Carboniferous in western Junggar: Evidence from Maliya ophiolite.
西准噶尔石炭纪洋中脊俯冲岩浆活动: 以玛里雅蛇绿岩为例

Maliya ophiolite occurs in a fore-arc accretionary prism, southeast of Dalabute ophiolitic belt in western Junggar. The ages of basalt and fossil indicate that it was formed during Carboniferous. Volcano and chert, the main lithologies of this ophiolite, outcropping in lenses, with non-tectonic contact, indicate they are contemporaneous products. Geochemical characteristics show their magmatic sources are complex that can be subdivided into four series: (1) A-series is dacite, with highly enriched in Th, indicating involvements of oceanic sediments, and depleted in Nb, which means they may be formed under subduction setting; (2) The REE patterns of M-series are much similar with that of N-MORB, with except of Ba, which is highly enriched because of the influence of fluids released from subducted oceanic slab; (3) E-series, locating between the mantle array of N-MORB and E-MORB, indicates it may be the mixture of mantle magmas, with no influence of other magmas; (4) The characteristics of O-series consist with that of OIB. All are located in the line of mantle sequence, except Ta, La and Th, which are slightly lower than typical OIB value. This may indicate mild mixture of other magmatic sources. The magmatic characteristics of the Maliya ophiolite mentioned above are very similar to that of the rocks formed during mid-oceanic ridge subduction in Chile. Combined with subducting at Late Paleozoic in western Junggar, we suppose the Maliya ophiolite may be generated during mid-oceanic ridge subduction.