新疆乌苏泥火山地球化学特征及其泥浆源

Geochemical characteristics of Wusu mud volcanoes in Xinjiang and their mud sources

泥火山是地质流体活动的结果,喷发需具备泥浆源、泥浆运移通道和水补给3个条件。对乌苏泥火山8个喷口泥浆进行岩石地球化学分析,轻稀土元素富集,重稀土元素亏损,轻、重稀土元素平均比值为6.81,泥浆中富集大离子亲石元素Ba、Rb等,高场强元素Nb、Ta强烈亏损,Th弱亏损,(La/Yb)_N值为5.47,Ce/La值为2.22,球粒陨石标准异常值δEu显示中等负异常(0.760~0.805);Sr/Ba值为0.33~1.01(平均值0.60),表明源岩为陆相沉积且古盐度较低,Ce/La(2.22)、Ce_(anom)(-0.007)、V/(V+Ni)(0.78)值均指示源岩形成于还原环境。稀土、微量元素分析及地层对比分析表明,乌苏泥火山源岩来自于下侏罗统八道湾组、三工河组,为河流沼泽相-半深湖相含煤地层代表的弱还原-还原沉积环境,源岩的最大埋藏深度为7~8km。泥火山源岩的研究为指示油页岩、烃类物质的位置提供了证据。

The mud volcano results from magmatic eruption formed by geological fluid activity.The formation of mud volcano requires three conditions,i.e.,mud source,mud migration channel and water supply.Geochemical data of8samples from Wusu mud volcanoes are characterized by enrichment of LREEs relative to HREEs.Chondrite standard abnormalδEu values are0.760~0.805,(La/Yb)N is5.47,and Ce/La is2.22.The mud is enriched in large ion stone elements(LILE)such as Ba and Rb,whereas the high field strength elements(HFSE)Nb,Ta are strongly depleted.Sr/Ba ratios(0.33~1.01)suggest a lower paleo-salinity,Ce/La(2.22),Ceanom(-0.007),and V/(V+Ni)(0.78)ratios indicate that the source rocks were formed in a reducing environment.REE and trace elements analyse show that the source rocks of Wusu mud volcanoes were derived from lower Jurassic Dadaowan Formation and San gonghe Formation,suggesting a river swamp-semi-deep lake sedimentary facies of coal-bearing strata which represent a kind of weak reducing environment.The mud volcano geochemical data and stratigraphic section of Wusu imply that the maximum depth of mud source strata is about7~8km.