东南沿海地区古近纪大陆岩石圈地幔特征及成因

东南沿海地区新生代玄武岩中的橄榄岩包体来自岩石圈地幔 ,上地幔橄榄岩包体的岩石学及地球化学特征都记录了地幔演化的历史。普宁橄榄岩包体斜方辉石含量与太古宙克拉通地幔类似 ,但在矿物学、REE、痕量元素和Sr Nd同位素上又与太古宙岩石圈地幔不同。橄榄岩包体的岩相学、矿物学、REE、痕量元素特征都提供了含H2 O富Si流体交代橄榄岩的证据 ,这种流体可能主要是洋壳物质局部熔融而成。流体交代使橄榄岩富Si,同时富Sr、Pb和强不相容元素等大洋岩石圈物质。这表明普宁大陆岩石圈地幔既保留太古宙岩石圈地幔的特征 ,又具有大洋俯冲地幔的特征 ,它是古老岩石圈地幔向大洋岩石圈地幔转换的一部分 ,这种转换可能是大洋岩石圈与大陆岩石圈地幔相互作用的结果。

PETROLOGICAL RECORD OF THE PACIFIC PLATE SUBDUCTION AFFECT ON THE CONTINENTAL LITHOSPHERIC MANTLE, SOUTHEAST COAST OF CHINA-- A STUDY OF THE PERIDOTITE XENOLITHS FROM PUNING, GUANGDONG PROVINCE

The peridotite xenoliths in the Cenozoic basalts came from young lithospheric mantle in the southeastern China. There are a great number of differences in petrology, mineralogy, trace elements and Sr-Nd isotopic composition in the peridotite xenoliths. The peridotite xenoliths in volcanic rocks in Puning generated before the South China Sea spreading may reserve more information of deep process related to the Pacific Ocean Plate subduction. The peridotite xenoliths in Puning are similar to the Kaapvaal Archean continental mantle peridotite in the content of orthopyroxene, but different from the Kaapvaal Archean continental mantle peridotite in REE patterns, which show that the peridotite xenoliths underwent the enrichment after strong depletion, and that they were not affected by the host basalt magma. LREE/HREE ratios of the former are close to 1. The peridotite xenoliths from Puning is enriched in strongly incompatible elements and depleted in middle incompatible elements, which are similar to those in the sub-arc mantle from Batan, Philippine. But the peridotite xenoliths from Puning are more depleted than those from Batan, in which except positive Sr, Pb and Rb anomaly, other incompatible elements are lower than primitive mantle. The trace element patterns of the peridotite in Puning have the prominent positive Sr and Pb anomaly, but lack in negative Ta anomaly, which are different from those in Batan. These characteristics result from the reactions between the lithosphere mantle of strong depletion and the H_2O-bearing fluids rich in SiO_2. The subduction took place in the Mesozoic, while the peridotite xenoliths were brought to the surface until the Eocene. The peridotite xenoliths in Puning may have undergone a long-term homogenization, thus they are also different from the lithosphere mantle in the island arc area. The continental lithospheric mantle have both characteristics of Archean lithospheric mantle and oceanic subduction mantle, which may be product of interaction between the oceanic lithosphere and the continental lithospheric mantle.