苏鲁造山带五莲地区岩浆岩元素和同位素地球化学研究  

Geochemistry of elements and isotopes in igneous rocks from the Wulian region in the Sulu orogen.

作　　者：黄洁[1] 郑永飞[1] 吴元保[1] 赵子福[1] 

机构地区：[1]中国科学院壳幔物质与环境重点实验室

出　　处：《岩石学报》2005年第3期545-568,共24页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40334036和40303002)资助成果

摘　　要：对苏鲁造山带五莲地区新元古代和中生代岩浆岩分别进行了主量元素、微量元素、Sr-Nd同位素和氧同位素研究。结果表明,新元古代花岗岩具有显著的LREE富集,高场强元素Nb、Ta、P和Ti负异常。εNd(t)为-12．6--6．9,可能与古元古代老地壳物质再循环有关。锆石δ18O值为-1．02-7．60‰,变化范围较大,近半数样品明显低于典型地幔锆石δ18O 值。新元古代辉长岩具有板内裂谷环境的特征,其εNd(t)在1．6-5．3之间,说明其岩浆起源于亏损地幔,但是经受了一定程度的地壳混染作用。唯一一个辉长岩样品的锆石δ18O值与部分花岗岩锆石δ18O值一样,明显高于典型地幔值,可能是基性岩浆在沿裂谷喷发过程中经历了低温热液蚀变,随后又发生破火山口垮塌,导致蚀变玄武岩在岩浆房重熔而形成高δ18O岩浆。中生代花岗岩和闪长岩表现出明显的高场强元素(Nb、Ta、P和Ti)负异常以及显著的LREE富集。εNd(t)值很低(-19．2 --15．3),同样是由古老地壳物质部分熔融形成。其锆石δ18O变化范围为3．19-6．43‰,大多数样品与典型地幔锆石一样。石英与锆石之间大都达到并保存了氧同位素平衡分馏,而其它矿物(如长石、黑云母和角闪石等)与锆石之间由于受到岩浆期后亚固相热液蚀变而大都表现出明显的氧同位素不平衡分馏。元素和氧同位素特征表明,中生代闪长岩可能是基性下地壳脱水部分熔融并经过结晶分异形成的;花岗岩则可能是由中性下地壳的脱水部分熔融形成的。新元古代花岗岩与中生代花岗岩在微量元素配分模型和Sr-Nd同位素组成上具有十分相似的特征,因此未经历强烈热液蚀变的新元古代花岗质侵入岩可能是中生代花岗岩的原岩。但这些新元古代岩浆岩的锆石δ18O变化范围较大,与中生代岩浆岩相比在流体活动性元素含量上也存在差别,这可能是由于新元古代岩浆岩侵位深�Major and trace elements, Sr-Nd and oxygen isotope compositions were determined for the Neoproterozoic and Mesozoic igneous rocks from the Wulian region in the northwestern part of the Sulu orogen. The Neoproterozoic granites are characterized by strong LREE enrichment, and negative HFSE（ Nb, Ta, P and Ti） anomalies. Zircon δ^18O values of the Neoproterozoic granites vary in a large range （ - 1.02‰ to 7.60‰） , and half of them are lower than the typical mantle zircon values. The Neoproterozoic gabbro represent the characteristics of basic rocks forming in a continental rift setting. The results of Sr-Nd isotope analyses indicate that they are derived from the depleted mantle. Hence, the formation of the Neoproterozoic gabbro is correlated with the intrusion of the juvenile crust in the late period of the Neoproterozoic syn-rift magmatism. The Mesozoic granites and diorites are characterized by strong LREE enrichment and negative anomalies of HFSE （Nb, Ta, P and Ti）. Zircon δ^18O values are from 3.19 to 6.43, and most of them are consistent with the typical mantle zircon values. Most of the granites have attained and preserved oxygen isotope equilibrium fractionations between quartz and zircon, but disequibrium fractionations also occur between zircon and the other minerals （ such as feldspar, biotite and hornblende） due to the post-magmatic hydrothermal alteration. The results of element and isotope analyses indicate that the Mesozoic diorites were derived from dehydration melting of mafic rocks in the thickened lower crust, coupled with fractional crystallization during magma emplacement; whereas the Mesozoic granites maybe formed by partial melting of intermediate middle-lower crust. The Neoproterozoic granites share the similar trace element partition pattern and Sr-Nd isotope features with the Mesozoic granites, indicating that the Neoproterozoic granitoids may be the protolith of the Mesozoic granitic rocks in material compositions. However, zircon δ^18O values of the Neoproterozoic ig

关 键 词：锆石 氧同位素 新元古代 中生代 岩浆岩 热液蚀变 

分 类 号：P597.2[天文地球—地球化学]