北京西山髫髻山组火山岩的地球化学特征与岩浆起源
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P588.14 P595

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国土资源部“九五”重大基础项目(9501111);国家自然科学基金资助项目(49602037)及国家杰出青年科学基金项目(49725300)


Geochemical Features and Origin of Volcanic Rocks of Tiaojishan Formation inWestern Hills of Beijing
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    摘要:

    对北京西山髫髻山组粗安岩斜长石Ar-Ar年龄测定获得全坪年龄和等时线年龄分别为148.91Ma±2.98Ma和146.60Ma±2.93Ma(相关系数r=0.9997),本文将其时代划为晚侏罗世.元素-同位素地球化学显示,西山髫髻山组火山岩主要为高钾钙碱性系列,低Ti\K,高Al\Ca和Na,轻稀土元素富集,Eu异常不明显,大离子亲石元素Rb\Sr\Ba等相对富集,高场强元素Nb\Ta\Ti\Zr\Hf相对亏损,Nd\Sr和Pb同位素比值较低,反映出火山岩形成于岛弧或活动大陆边缘,其源岩为富集地幔.据此认为髫髻山组火山岩形成于陆内挤压环境,由中生代玄武质岩浆底侵于下地壳-壳幔过渡带诱发古老(太古宙)的玄武质岩石部分熔融形成的.

    Abstract:

    Tiaojishan Formation in Western Hills of Beijing was dated at Late Jurassic based on the Ar-Ar ages for tachyandesites (all plateau ages and isochrone ages of plagioclase are respectively 148.91±2.98 Ma and 146.60±2.93 Ma). Geochemistry of elements and isotopes shothat volcanic rocks of Tiaojishan Formation are mainly of high-K calc-alkaline series characterized by indistinct Eu anomaly, relative enrichment of large-ion lithophile elements such as.Rb,Sr and Ba, relative depletion of high field-strength elements (e.g. Nb, Ta, Ti, Zr, Hf ), and low Nd, Sr and Pb ratios, suggesting the features of island -arc and active continental margin and enriched mantle. The authors think that volcanic rocks of Tiaojishan Formation were derived from partial melting of old-age (Archean) basaltic rocks of the lower crust and the crustmantle transitive zone by the underplating of basaltic magma during intrcontinental orogeny

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李伍平,路凤香,李献华,等, 2001. 北京西山髫髻山组火山岩的地球化学特征与岩浆起源[J]. 岩石矿物学杂志, 20(2):123~133.
LI Wu-ping, LU Feng-xiang, et al, 2001. Geochemical Features and Origin of Volcanic Rocks of Tiaojishan Formation inWestern Hills of Beijing[J]. Acta Petrologica et Mineralogica, 20(2): 123~133.

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  • 最后修改日期:2000-10-11
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