新疆乌苏泥火山地球化学特征及其泥浆源

摘要

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)、Ceanom(-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 of 8 samples from Wusu mud volcanoes are characterized by enrichment of LREEs relative to HREEs.Chondrite standard abnormal δ Eu values are 0.760～0.805,(La/Yb)N is 5.47,and Ce/La is 2.22.The mud is enriched in large ion stone dements (LILE) such as Ba and R.b,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),Ce (-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 Sangonghe 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 about 7～8km.