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The area studied had developed into an inactive continental margin on the western edge of the Yangtzeplate during the Jinning period in Proterozoic time.The Yangtze plate drifted from the south northwards inPaleozoic time and reached about 9 °S between Late Cambrian and Early Ordovician.The alkalic olivinebasalt magma,which was produced via 2—5% partial melting of a fractionated mantle and was accumu-lated in a deep-seated magma chamber near the Moho,found its way upward along the reviving bounda-ry faults into the upper crust.Two types of layered intrusions,basic and ultrabasic-basic,crystallized fromthe magma at different pressures.The high initial oxygen fugacity of the magma provides a favorabie condi-tion for the deposition of Fe-Ti oxides in the early stage of magma evoletion,resulting in large-sized ear-ly magmatic deposits.Magma crystallization may have been interrupted and repealed as a result of pulsativemagma influx,giving rise to rhythmic cycles (including the corresponding V-Ti-magnetite ore beds).Themagma was stratified owing to double diffusion at the crystallization front and convection was thusoccassioned by the density gradient.This has greatly complicated the sequence as would be expected fromnormal crystallization.
The area studied had developed into an inactive continental margin on the western edge of the Yangtzeplate during the Jinning period in Proterozoic time. The Yangtze plate drifted from the south northwards in Paleozoic time and reached about 9 ° S between Late Cambrian and Early Ordovician. The alkalic olivinebasalt magma, which was produced via 2-5% partial melting of a fractionated mantle and was accumu-lated in a deep-seated magma chamber near the Moho, found its way upward along the reviving bounda-ry faults into the upper crust.Two types of layered intrusions, basic and ultrabasic-basic, crystallized from the magma at different pressures. high on oxygen fugacity of the magma provides a favorabie condi-tion for the deposition of Fe-Ti oxides in the early stage of magma evoletion, resulting in Large-sized ear-ly magmatic deposits. Magma crystallization may have been interrupted and repealed as a result of pulsative magma influx, giving rise to rhythmic cycles (including the corresponding ing V-Ti-magnetite ore beds. The magma was stratified due to double diffusion at the crystallization front and convection was thus induced by the density gradient. This has greatly complicated the sequence as would be expected from normal crystallization.