江西吉泰盆地碱性玄武岩的地球化学特征及其构造意义  

Geochemical Features and Tectonic Significance of the Alkali-Basalts from Ji’an-Taihe Basin,Jiangxi Province

作　　者：余心起[1] 舒良树[2] 邓国辉 王彬[2] 祖辅平[2] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]南京大学地球科学系,江苏南京210093 [3]江西地质调查院,江西南昌330201

出　　处：《现代地质》2005年第1期133-140,共8页Geoscience

基　　金：国家自然科学基金项目(40172067);国家自然科学重点基金项目(40132010)。

摘　　要：吉泰盆地位于赣中地区, 目前尚无在该盆地中发现玄武岩的报道。新发现的玄武岩产于吉泰盆地南部泰和附近的南溪镇。玄武岩露头新鲜, 蚀变微弱, 属碱性玄武岩, 形成于板内快速拉张环境; 锆石U Pb年龄为 ( 139±0 7 ) ^(143±1 1)Ma, 表明岩石形成于早白垩世早期。玄武岩无明显的Nb、Ta负异常, Rb Sr、Sm Nd同位素组成分析结果显示[N(87Sr) /N(86Sr) ]i=0 704 1~0 704 8, εNd(t) = +3 78^+4 38, 反映玄武岩浆起源于亏损地幔, 未经地壳物质混染。结合吉泰盆地边部存在中侏罗世 (168Ma) 玄武岩的事实, 表明赣中地区在早白垩世已经处于拉张背景, 吉泰盆地的碱性玄武岩可能是在板内岩石圈伸展减薄作用下, 由北东向的赣江断裂带拉张形成的。New found basalt crop is located near the Nanxi Town, Taihe County, south of Ji'an-Taihe Basin, middle Jiangxi Province. With brown-grey and dark green color, the fresh basalt has compacted texture and some blisters and amygdules. Microscope observation reveals that the rocks have intergranular textures,more than 60% basic plagioclases, filling with olivines and augites, less than 5% almond-shaped calcites, and weak corrosion. According to its geochemical features, the basalt belongs to alkali-basalt, produced by quick regional extension within a plate. Rb-Sr and Sm-Nd isotopic composition of the basalt are as follow:(^(87)Sr/^(86)Sr)_i =(0.704 1-0.704 8) and ε_(Nd)(t)=+3.78-+4.38, indicating that the magma came from the deficit mantle and had not mixed with crust material. The zircon solution U-Pb geochronological data of(139±0.7)to(143±1.1)Ma for the alkali-basalt indicates that mantle-reached strike-slip faulting along northeast-striking Ganjiang Fault and Wuchuan-Sihui Fault was active from early period of Early Cretaceous under the extensional background of the area.

关 键 词：碱性玄武岩 亏损地幔 板内拉张环境 早白垩世早期 赣江断裂 吴川—四会断裂 吉泰盆地 

分 类 号：P588.145[天文地球—岩石学]