| 西昆仑黑伞顶新近纪次火山岩地球化学特征及成因 |
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| 引用本文：张祥信,陈必河.2009.西昆仑黑伞顶新近纪次火山岩地球化学特征及成因[J].地球学报,30(3):354-362. |
| DOI：10.3975/cagsb.2009.03.09 |
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| 基金项目:中国地质调查局地质大调查项目(编号：19991300009051) |
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| 中文摘要:黑伞顶次火山岩分布于西昆仑东段华北板块与华南板块的结合部位, 主要由花岗斑岩体组成, 侵入于石炭系托库孜达坂群、二叠系树维门科组及古近系阿克塔什组地层中。花岗斑岩黑云母K-Ar同位素年龄值13.2 Ma, 为新近纪中新世的产物。黑伞顶次火山岩具有低硅镁、高铝钾的特点, SiO2含量介于65.19%~67.21%之间, MgO含量为0.83%~1.47%, Al2O3在14.53%~16.5%之间变化, K2O含量为4.44%~4.93%。K2O/Na2O为1.49~1.52, A/CNK为1.08~1.14, 里特曼指数σ为2.22~3.03, 为过铝质高钾钙碱性岩石。富集大离子亲石元素K、Rb、Th、U, 高场强元素Nb、Ta、Ti明显亏损。高Sr(528×10?6~707×10?6)及Sr/Y(38.2~63), 低Y(8.38×10?6~18.24×10?6)和Yb(0.73×10?6~1.64×10?6)。稀土元素总量较高, 介于307.87×10?6~458.20×10?6之间, 稀土元素配分曲线为右倾斜型。LREE/HREE为24.19~34.47, 属轻稀土元素富集型。具有弱至中等的负铕异常。地球化学特征表明, 黑伞顶次火山岩为高钾钙碱性C型埃达克质岩, 形成于青藏高原隆升和板内地壳加厚的背景下, 是青藏高原北部在中新世因陆壳加厚引起下地壳部分熔融的产物。 |
| 中文关键词:次火山岩 新近纪 C型埃达克质岩 地球化学 黑伞顶 西昆仑 |
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| Geochemistry and Petrogenesis of the Neogene Subvolcanic Rocks in Heisanding Area of West Kunlun Mountains |
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| Abstract:Located at the juncture between the North China plate, the eastern section of west Kunlun and the South China plate, the subvolcanic rocks in Heisanding area are mainly composed of granite porphyry and have intruded into such strata as the Carboniferous Tuokuzidaban Group, the Permian Shuweimenke Formation and the Paleogene Aketashi Formation. The K-Ar age of the granite porphyry is 13.2Ma, suggesting that it was formed in Miocene. The subvolcanic rocks are characterized by low SiO2 (65.19% to 67.21%), MgO (0.83% to 1.47%), Y (8.38×10?6~18.24×10?6) and Yb (0.73×10?6~1.64×10?6), and high Al2O3 (14.53% to 16.5%), K2O (4.44% to 4.93%), Sr (528×10?6~707×10?6) and Sr/Y (38.2~63) values. K2O/Na2O=1.49~1.69, A/CNK=1.08~1.14, and σ= 2.22~3.03, implying that these rocks belong to the peraluminous high-K calc-alkalic type. The rocks are obviously enriched in LILE such as K, Rb, Th, U, and depleted in HFSE such as Nb, Ta, and Ti, with obvious negative anomalies. The total REE contents range from 307.87×10?6 to 458.20×10?6, and the LREE/HREE ratios range from 24.19 to 34.47, with the enrichment of LREE and weak to medium negative Eu anomalies. These geochemical characteristics show that the Heisanding subvolcanic rocks are high-K calc-alkaline and C-type adakitic rocks, which resulted from partial melting of the thickened continental crust in northern Tibetan plateau and were formed in an intraplate post-collision tectonic setting during Miocene. Fractional crystallization played an important role in magmatic evolution. |
| keywords:subvolcanic rock Neogene c-type adakitic rock geochemistry Heisanding area west Kunlun Mountains |
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