Title: Late Paleozoic Adakite and Nb-enriched Basalt from Northern Xinjiang: Evidence for the Southward Subduction of the Paleo-Asian Ocean
Abstract:An adakite and Nb-enriched basalt association is found in early Devonian Group in north Junggar, Xinjiang, northwest China. This association is very important not only for studying the southward subdu...An adakite and Nb-enriched basalt association is found in early Devonian Group in north Junggar, Xinjiang, northwest China. This association is very important not only for studying the southward subducsion of the Paleo-Asian Ocean, but also provides an ideal research project for evolution of northern margin of the Kazakhstan-Junggar Plate in Late Paleozoic. The geochemical results show that the geochemical characteristics of the andesitic rocks in this area are consistent with those of adakites. They have high Al_2O_3, Na_2O and Sr contents, and high Sr/Y ratio. HREE and Y in the samples are obviously depleted. MORB-normalized trace element spider diagram shows negative Nb, Ta anomalies and remarkably positive Sr anomaly with very strong HFSE depletion. Their chrondrite-normalized REE patterns show no Eu anomaly and HREE depletion. The geochemical features of the associated Nb-enriched basalts are very similar to those of typical Nb-enriched basalts. They are SiO_2 overstraturated and Na-enriched,and are distinguishable from the typical arc basalts which are characteristic of high Nb, Ti, P contents, and HSFE enrichment. The projections of the adakites fall into the mantle array area that is defined by oceanic basalt in the ~ (87) Sr/~(86)Sr vs ~(143) Nd/~(144)Nd diagram. It means that the adakite was derived from the partial melting of the Palaeo-Asian oceanic crust, and the Nb-enriched basalt was originated by the partial melting of the mantle wedge which was slightly contaminated by the continental crust. Because the adakite and Nb-enriched basalt are related with ocean plate subduction, the distribution of the association in northern Junggar indicates that the Palaeo-Asian oceanic crust subducted southwards beneath the Kazakhstan-Junggar Plate in Early Devonian.Read More
Publication Year: 2004
Publication Date: 2004-03-20
Language: en
Type: article
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Cited By Count: 36
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