鄂尔多斯地块西南缘中元古代玄武安山岩地球化学特征及其构造意义  

Geochemical characteristics of Mesoproterozoic basaltic andesite in southwestern margin of Ordos Block and its tectonic implication

作　　者：高山林 刘士林 张仲培[2] GAO Shanlin;LIU Shilin;ZHANG Zhongpei(Petroleum Exploration and Production Branch of SINOPEC,Beijing,100728;Petroleum Exploration and Production Research Institute of SINOPEC,Beijing,100083)

机构地区：[1]中国石油化工股份有限公司油田事业部,北京100728 [2]中国石化石油勘探开发研究院,北京100083

出　　处：《地质论评》2023年第1期164-178,共15页Geological Review

基　　金：国家油气专项(编号:2017ZX05005-002)的成果。

摘　　要：铁马河玄武安山岩位于鄂尔多斯地块西南缘,沿六盘山东麓断裂带出露。岩石发育气孔和杏仁状构造,具有斑状结构—间隐结构,斑晶主要为长条状斜长石和少量蚀变暗色矿物。岩石地球化学呈现富Na2O、Fe OT、Al2O3,贫Mg O、TiO2、K2O的特点,稀土配分曲线为右倾轻稀土富集型,LREE/HREE=6.50~7.01,(La/Yb)N为5.620.69~0.91。样品[n(87Sr)/n(86Sr)]i为~7.14,富集Ba、Th、U、K等大离子亲石元素,Nb、Sr和Ti相对亏损,δEu=0.70587~0.70934,εNd(t)介于-6.9-4.8,TDM为2562~2730~Ma,Nb/Ta(6.60~8.25)低于大陆地壳的平均值,指示了受俯冲流体改造的古老富集地幔参与了岩浆形成。SHRIMP锆石U-Pb定年结果显示铁马河玄武安山岩形成于中元古代早期(~1740Ma),其形成与研究区中元古代早期陆内伸展作用引起的古老岩石圈地幔减压熔融有关,是华北克拉通陆内裂谷发育过程在鄂尔多斯地块西南缘的体现。Southwestern margin of the Ordos Block in the Paleo—Mesoproterozoic is a part of the rifts of the southern margin of the North China Craton, previous studies mainly focus on the 1.85~1.75 Ga granites exposed in the research area, but later than 1.85 Ga intermediate—basic eruptive rock in the Proterozoic has not been reported. Basaltic andesite at the Tiemahe section is exposed in the Liupanshan faults zone in the southwestern margin of the Ordos Block with amygdaloid structure and porphyritic texture. The phenocrysts are mainly composed of plagioclase and small amount of mafic minerals. SHRIMP zircon U-Pb dating results show that the Tiemahe basaltic andesite was erupted in the early Mesoproterozoic(ca. 1740±14 Ma). Geochemically, the rock samples show low SiO2, TiO2, K2O, and high Na2O, FeOTand Al2O3. and display LREE-enrichment patterns, with LREE/HREE ratios of 6.50~7.00,(La/Yb)Nof 5.62~7.14, and δEu of 0.69~0.91. In the spider diagrams, they are enriched in large ion lithophile elements(e.g., Ba, Th, U, K) and relatively depleted in Nb, Sr and Ti. The values of(87Sr/86Sr)i(0.70587~0.70934),εNd(t)(-6.9 ~-4.8), Nb/Ta(6.6~8.3) and TDM(2562~2730 Ma) suggest that the Tiemahe basaltic andesite was originated from enriched lithospheric mantle that had been metasomatized by subducted slab derived fluids, which may be related with late Paleoproterozoic orogeny in the western margin of the Ordos Block. This paper suggests that the Tiemahe volcanic rocks were generated by decompression melting under intracontinental extension, which reverify that the western Ordos Block was involved in tectonic processes of the intracontinental extension of the NCC in the Mesoproterozoic.

关 键 词：鄂尔多斯地块西南缘 铁马河玄武安山岩 中元古代 地球化学特征 陆内伸展 

分 类 号：P548[天文地球—构造地质学] P588.14[天文地球—地质学]