东天山博格达造山带石炭纪火山岩及其形成地质环境  

Carboniferous volcanites in the Bogda orogenic belt of eastern Tianshan: their tectonic implications

作　　者：顾连兴[1] 胡受奚[1] 于春水[1] 李宏宇[1] 肖新建[1] 严正富[1] 

机构地区：[1]南京大学地球科学系南京大学成矿作用国家重点实验室,南京210093

出　　处：《岩石学报》2000年第3期305-316,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金项目 (No.49172 0 94);国家九.五攻关 3 0 5项目 (No.96-915 -0 5 -0 3 -0 1)合作研究成果 ;南京大学现代分析中心

摘　　要：东天山博格达造山带早、中石炭世海相火山岩具有双峰式特征 ,主要岩性为富钠的玄武岩和流纹岩 ,其次是英安岩 ,安山质岩石极少出现。玄武岩的特征是 :少数岩石含有实际矿物石英 ,个别岩石含橄榄石斑晶 ;辉石主要是透辉石和次透辉石 ,其成分富含铝 (Al2 O3=4.17～ 5 .99)和钛 (Ti O2 =2 .80～ 4.78) ;基质中的长石主要是钠 -更长石 ,斑晶中有相当数量的中长石和拉长石 ;全岩化学成分 CIPW计算结果绝大部分含 Di、Ol和 Hy,少数含 Qz和 Ne,在全碱 - Si O2 图中主要投影于亚碱性区 ,并接近碱性区 ;10 0 Mg/ (Mg+ΣFe) <6 5 ;ΣREE=38.73～ 134 .48,(L a/ L u) N=2 .75～ 4.0 3,δEu=0 .93～ 1.15 ;强不相容元素适度富集 ,Nb和 Ti适度亏损 ,Ni、Cr含量低 ,εNd和 εSr均为正值。这些特征表明 ,本区的玄武岩总体上属于橄榄拉斑玄武岩 ,并具有向碱性玄武岩和石英拉斑玄武岩两个方向演化的趋势。它们是来自亏损地幔的橄榄拉斑质玄武质或苦橄质岩浆经过分异并混染少量地壳物质的产物。The Lower Middle Carboniferous marine volcanites in the Bogda Orogenic Belt of Eastern Tianshan show bimodal features and are dominated by soda rich basalts and rhyolites with minor dacites and rare andesitic rocks. The basalts are characterised by modal quartz in a few samples, occasional occurrence of olivine phenocrysts, diopsidic and salitic clinopyroxene with higher aluminum (Al2O3=4.175.99) and titanium (TiO2=2.804.78) contents, albite and oligoclase dominated matrices with considerable amounts of andesine and labradorite as phenocrysts, most wholerock CIPW norms containing Di, Ol and Hy with a few containing Qz and Ne, most of the plots on the total alkali vs. SiO2 diagram being located in the subalkaline area and close to the boundary to the alkaline area, 100Mg/(Mg+Fe)<65, REE=38.73134.48, (La/Lu)N=2.754.03, Eu=0.93~1.15, moderately enriched in highly incompatible elements, moderately depleted in Nb and Ti, low contents of Ni and Cr, positive Nd and Sr values. These characteristics indicate that basalts in the Bogda belt belong to olivine tholeiites overall, but had diverse evolution to alkaline basalts and quartz tholeiites. These basalts were produced by an olivine tholeiitic or picritic magma which originated from a depleted mantle and subsequently differentiated and was then contaminated by the crust. The bimodal volcanism represented by such basalts with accompanying dacites and rhyolites argues for the Carboniferous continental rift environment of the Bogda oregenic belt.

关 键 词：造山带 大陆裂谷 火山岩 石炭纪 地质环境 

分 类 号：P588.14[天文地球—岩石学] P534.45[天文地球—地质学]