Title: Geochemical characteristics and sedimentary environments of Devonian low metamorphic clastic sedimentary rocks in the southern margin of the Chinese Altai,North Xinjiang.
Abstract: Devonian is a key period for the tectonic evolution of the Chinese Altai and several competitive models,e.g.active continental margins and passive continental margins,have been suggested for this region.These models were mainly based on studies of the Devonian volcanic rocks in the southern margin of the Chinese Altai,and geochemical research for the sedimentary rocks is still rare.In this paper,systematic geochemical study for the Devonian low-grade metamorphosed clastic rocks was conducted to constrain the tectonic background of this orogen.The major element data show that protoliths for the metaclastic rocks are dominated by argillaceous and arenaceous sedimentary rocks.Although differing in major element contents among rocks of various types,their low Chemical Index of Alteration(CIA75),Plagioclase Index of Alteration(mean PIA=70)and Index of Compositional Variability (ICV≤1.0)indicate relatively low maturity and weak chemical weathering for their source.The samples are moderately enriched in light REE(La_N/Yb_N=2.88~9.90)and show flat heavy REE with strong negative Eu anomalies(Eu/Eu~*=0.45~0.89).Most samples have high La/Sc(1~3),La/Y(0.5~1),Ti/Zr(10~35)and low Sc/Cr(0.1~0.3)ratios,which are similar to clastic rocks deposited in continental arc settings.In both La-Th-Sc and Th-Sc-Zr/10 discriminate diagrams,almost all of the clastic rocks plot in the continental arc field.These geochemical characteristics are different from those of sedimentary rocks deposited in oceanic island arcs or passive continental margins and suggest a sedimentary environment related to continental island arcs for the Devonian clatic rocks in the southern margin of the Chinese Altai.
Publication Year: 2008
Publication Date: 2008-01-01
Language: en
Type: article
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Cited By Count: 16
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