塔里木盆地寒武系层状硅质岩与硅化岩的元素、δ^(30)Si、δ^(18)O地球化学研究  

δ^(30)Si,δ^(18)O and elements geochemistry on the bedded siliceous rocks and cherts in dolostones from Cambrian strata,Tarim Basin

作　　者：陈永权[1,2] 蒋少涌[2] 周新源[1] 杨文静[1] 韩利军[1] 

机构地区：[1]中国石油塔里木油田分公司勘探开发研究院,新疆库尔勒841000 [2]南京大学地球科学系内生金属矿床成矿机制研究国家重点实验室,江苏南京210093

出　　处：《地球化学》2010年第2期159-170,共12页Geochimica

基　　金：中国石油塔里木油田分公司2006年博士后科研项目基金资助课题

摘　　要：塔里木盆地寒武系发育层状硅质岩和硅化岩,层状硅质岩主要发育于塔东下寒武统深水沉积相区;硅化岩发育于塔东上寒武统斜坡沉积区与西部台地区寒武系白云岩中。根据显微结构特征,可将硅化岩分为放射状硅化岩与交代残余结构硅化岩两种。分析结果表明,层状硅质岩在Al-Fe-Mn三元图中位于正常海水沉积硅质岩区内,在微量元素平均地壳标准化图解上显示平缓右倾的特征;层状硅质岩Si同位素组成δ30Si为0.9‰～1.4‰,O同位素组成δ18O为21.4‰～24.4‰,与沉积型硅质岩相吻合,指示了正常海水沉积成因。硅化岩区别于层状硅质岩的典型特征是具有高U异常的特征;罗西斜坡放射状硅化岩具有较高的微量元素和稀土元素含量(∑REE为18.8～96.9μg/g)与较低的Si、O同位素值(δ18O和δ30Si值分别为15.8‰和1.7‰);西部台地区交代残余结构硅化岩具有较低微量元素和稀土元素含量(∑REE为0.58～2.61μg/g)与较高的δ30Si(1.0‰～3.8‰)、δ18O(21.6‰～27.0‰)值特征。盆地东西部硅化岩的地球化学差异可能与硅化流体的温度差异有关,罗西斜坡放射状硅化岩硅化温度相对更高;另一方面,硅化过程对H430SiO4选择性较高,因而形成的交代石英具有较高的δ30Si值。根据古城4井硅化岩包裹体均一温度与交代石英的O同位素值计算得到交代流体的δ18O值为9.1‰,该值与酸性岩浆水的δ18O值相似,指示了硅化流体可能来自于岩浆或变质水;以δ18O值(9.1‰)作为西部台地区硅化流体的O同位素值,计算得到西部台地区硅化岩硅化流体温度为101.3～158.5℃。根据石英O同位素温度计计算的硅化流体温度呈东高西低的趋势,指示了硅化流体可能来自台地东部。Bedded siliceous rocks and cherts-bearing dolostone are widely distributed in Cambrian strata in Tarim Basin. The bedded siliceous rocks occur mainly as deep water sediments in the eastern Tarim Basin, and have been sampled from the Yingdong 2 well. The chert-bearing dolostones show a wide distribution in Cambrian dolostones of the whole Tarim Basin. In A1-Fe-Mn diagram, data for the bedded siliceous rocks fall within the normal seawater sedimentary field. In the crust-normalized trace element spider diagram, the bedded siliceous rocks show relatively smooth right-inclined curves, indicating sedimentary origin. Their silicon and oxygen isotope compositions are 0.9‰ - 1.4‰, and 21.4‰ - 24.4‰, respectively, coincident with those of the sedimentary siliceous rocks. The cherts in dolostone demonstrate higher U content in comparison with the bedded siliceous rocks. The stelliform cherts in Luoxi slope show high content of trace dements and low oxygen （15.8‰） and silicon （1.7‰） isotope compositions, as a result of high reaction temperature; on the contrary, the original texture remained cnerts in the western platform demonstrate low trace and rare earth elements concentrations and high oxygen （21.6‰ - 27.0‰） and silicon （ 1.0‰ - 3.8‰） isotope compositions, resulting from relatively low reaction temperature. Compared to other types of siliceous rocks, the cherts show relatively high δ30Si value, maybe as a result of the selectivity of H430SIO4 during the silicatization process. Based on the homogeneous temperatures of fluid inclusions in quartz in Gucheng 4 well and the δ18O values of cherts, the δ18O value of silicatized fluid is calculated to be 9. 1‰. Therefore, We can calculate the temperatures of silicatized fluid in western basin, and the temperatures range in 101.3 - 158.5 ℃. The temperatures show a decreasing trend from east to west in western platform, indicating that the hydrothermal fluids might have come from some eastern faults of the western platform.

关 键 词：硅质岩 硅化岩 Si同位素 O同位素 微量元素 稀土元素 塔里木盆地 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]