The major element compositions of glass inclusions in plagioclase and pyroxene phenocrysts of basalt and pumice in the Okinawa Trough back-arc basin are determined by electron microprobe. The results indicate that bas...The major element compositions of glass inclusions in plagioclase and pyroxene phenocrysts of basalt and pumice in the Okinawa Trough back-arc basin are determined by electron microprobe. The results indicate that basalt and pumice are cognate and respectively represent the products at early stages of magmatism and at late stage of crystal fractionation. The initial magma in the trough is rich in H2O. The variation of H2O content in magma may play an important role in the magma evolution. Plagioclase is the mineral crystallized throughout the whole magmatic process and accumulates in the zoned magma chamber. From these features it can be inferred that the initial magma in the Okinawa Trough, whose opening began in recent years, is seriously affected by fluid or other materials carried by subducting slab and the geochemical feature of volcanic rocks is in some degree similar to that of lavas in island-arc environments.展开更多
The Mesozoic volcanic rocks in the coastal region of southeastern China were superimposed on some different basement tectonic elements. The volcanic rocks developed in these different basement tectonic elements have g...The Mesozoic volcanic rocks in the coastal region of southeastern China were superimposed on some different basement tectonic elements. The volcanic rocks developed in these different basement tectonic elements have great differences in Sr and Nd isotopic compositions. The rocks in western Zhejiang and northeastern Jiangxi Provinces which belong to the Lower Yangtze subplate have lower initial 87Sr/ 86Sr ratios, but are higher in initial Nd isotopic ratios. The initial 143Nd / 144Nd values of the volcanic rocks developed in the Cathaysian subplate increase clearly from early to late in time, and from the core of the Wuyishan uplift coastwards constantly, but the initial 87Sr/86Sr values tend to decrease. The isotopic characteristics and their spatial variations in Mesozoic volcanic rocks in the study region are, to a great extent, manifestations of the isotopic characteristics in basement metamorphic complexes, and the generation of the Mesozoic acid magma in this region is attributed to the recycling of pre-existing crustal materials.展开更多
基金The study was supported by the National Natural Science Foundation of China under contract Nos 49625609 and 49673194.
文摘The major element compositions of glass inclusions in plagioclase and pyroxene phenocrysts of basalt and pumice in the Okinawa Trough back-arc basin are determined by electron microprobe. The results indicate that basalt and pumice are cognate and respectively represent the products at early stages of magmatism and at late stage of crystal fractionation. The initial magma in the trough is rich in H2O. The variation of H2O content in magma may play an important role in the magma evolution. Plagioclase is the mineral crystallized throughout the whole magmatic process and accumulates in the zoned magma chamber. From these features it can be inferred that the initial magma in the Okinawa Trough, whose opening began in recent years, is seriously affected by fluid or other materials carried by subducting slab and the geochemical feature of volcanic rocks is in some degree similar to that of lavas in island-arc environments.
基金This paper resulted from the joint support of the National Natural Science Foundation of China (Grant No. 49070162)a key project of the Ministry of Geology and Mineral Resources for the Seventh Five-Year Plan period (Project No. 86017)
文摘The Mesozoic volcanic rocks in the coastal region of southeastern China were superimposed on some different basement tectonic elements. The volcanic rocks developed in these different basement tectonic elements have great differences in Sr and Nd isotopic compositions. The rocks in western Zhejiang and northeastern Jiangxi Provinces which belong to the Lower Yangtze subplate have lower initial 87Sr/ 86Sr ratios, but are higher in initial Nd isotopic ratios. The initial 143Nd / 144Nd values of the volcanic rocks developed in the Cathaysian subplate increase clearly from early to late in time, and from the core of the Wuyishan uplift coastwards constantly, but the initial 87Sr/86Sr values tend to decrease. The isotopic characteristics and their spatial variations in Mesozoic volcanic rocks in the study region are, to a great extent, manifestations of the isotopic characteristics in basement metamorphic complexes, and the generation of the Mesozoic acid magma in this region is attributed to the recycling of pre-existing crustal materials.
