【作者】 文华国；

【导师】 郑荣才；

【作者基本信息】 成都理工大学 ， 沉积学， 2008， 博士

【摘要】 热水沉积岩为当前地质学研究领域最前沿的热点之一,其中涉及湖相热水沉积岩的研究成果甚少,酒泉盆地青西凹陷下白垩统下沟组发育的湖相暗色“白云质泥岩”和“泥质白云岩”已被证实为罕见的湖相“白烟型”热水沉积岩而成为本文独一无二的经典研究素材。本论文受国家自然科学基金（编号:40672073）和教育部高校博士点专项科研基金（编号:20060616014）共同资助,在总结对比国内外热水沉积岩最新研究成果基础上,采用岩相、矿相鉴定技术以及碳氧同位素、锶同位素、微量元素、稀土元素和流体包裹体等测试手段,对这套特殊的湖相“白烟型”热水沉积岩进行了系统研究,获得以下结论和成果:1)从湖相“白烟型”热水沉积岩中识别出的热水矿物以钠长石和铁白云石为主,其次有石英、方沸石、重晶石、地开石、萤石等,还有少量黄铁矿、方铅矿、黄铜矿、闪锌矿等热水金属矿物,且具有7种不同热水矿物共生组合类型。以铁白云石和钠长石为代表的热水矿物具有半自形—自形晶结构的镶嵌状或堆晶状,显示以结晶沉淀为主的化学沉积特征。确定了典型的岩石组构以具微—隐晶结构和纹层状构造为主,其次可见特征的热水碎屑结构、热水角砾结构和网脉状、旋涡状构造和同生变形层理。其中的热水碎屑和热水角砾结构可根据不同矿物类型各可识别出7种类型,部分岩石组构类型十分罕见,具有特殊成因意义。2)碳、氧同位素研究结果证实,泥晶铁白云石沉淀时湖泊相对封闭,且成矿流体温度较高,热流体在循环和上升过程中,可能与围岩进行了碳、氧同位素交换,吸收了深部重碳而导致流体δ¹³C值较高;分散的碳、氧同位素组成特征应该与地壳浅部下渗湖水对上地壳各类岩石淋滤萃取演化而成的热流体有关。3)锶同位素研究发现,纹层状泥微晶热水沉积岩锶同位素比值变化范围较小,可代表均一化的热卤水池流体锶同位素组成特征,发育于同一位置的水爆角砾与其胶结物锶同位素组成基本一致,说明两者属具相同成因意义的同期热水喷流沉积产物。总体上湖相热水沉积岩⁸⁷Sr/⁸⁶Sr比值远高于同期海水和下沟组玄武岩,略高于代表早白垩世湖水锶同位素组成的藻灰岩,但低于基底壳源硅铝质岩,反映热流体与海水无关,也不可能为单纯的湖水或幔源岩浆水,推测为富集硅铝质基岩高放射性成因Sr的下渗湖水与少量上升幔源岩浆水的混合热流体。4)稀土元素地球化学特征具备LREE＞HREE的热水沉积建造特点,其高丰度的∑REE、稀土配分模式、正δCe异常和负δEu异常,虽有悖于海相热水沉积岩,但与同层位的碱性拉斑玄武岩非常一致,说明下沟组热水沉积岩与同层位的玄武岩有很强的亲缘关系,热流体/湖水混合过程的Eu/Sm—La/Ce模拟反映了下沟组湖底的热水沉积作用发生在具备还原、偏碱性条件的深源热卤水池环境中。5)流体包裹体分析并结合C-O-Sr同位素、微量元素地球化学和稀土元素特征,认为青西凹陷早白垩世湖底热流体应与火山喷发有关,整体上应属于深循环下渗湖水与岩浆水混合形成的中低温（90～200℃）、中等盐度（8～22wt%NaCl）、中等密度（0.97～1.2g/cm³）)的NaCl-H₂O体系高碱性热卤水,并具有贫金属硫化物,富CO₃^2-、SO₄^2-、Cl^-、F^-和Ca²⁺、Mg²⁺、Fe²⁺、Ba²⁺、Si⁴⁺、Al³⁺、Na⁺等常量元素和络阴离子,以及Zn、Rb、Mo、As、Ni、Co、Sb、Ba和Ag等深源气液型和深部幔源型微量元素组合。整体显示,不同类型热水沉积岩的成矿热流体自主喷流通道、分支喷流通道经喷流口至附近及远端的盆地热卤水区存在温度、盐度、密度和压力等物理化学参数逐渐降低的规律性变化。6)提出热流体运移驱动力主要有三种:重力驱动力、压实驱动力和岩浆热能驱动力,这三种驱动力共同作用使热流体循环流动,并不断萃取岩层中的成矿化学物质,并可能存在四种超压热流体失衡回返运移机制,其中构造抬升泵吸作用、断裂搓动浅部构造减压和阵发性火山岩浆热液水热增压作用这三种机制在研究区占主导,并促使热流体沿断裂回返上升并突破上覆沉积物发生沸腾爆炸,低温低盐度湖水迅速混入冷却,并破坏了热流体的化学平衡,使得氯络合物解离,热水矿物化学沉淀聚集形成一系列不同成因类型的湖相“白烟型”热水沉积岩。7)青西凹陷下沟组湖相“白烟型”热水沉积岩可划分出4种成因类型,其中的热水沉积白云岩据国内外资料检索,属极其罕见的湖相原生白云岩中的特殊成因类型,具有特定的成因特征和识别标志。8)建立了青西凹陷湖相“白烟型”热水沉积岩分带性热水沉积模式:主喷流口内主要发育水爆角砾型热水沉积岩（铝硅酸盐矿物+硫酸盐矿物+微量金属硫化物矿物组合）→与主喷流通道连通的分支喷流口内主要发育脉状充填型热水沉积岩（碳酸盐矿物+铝硅酸盐矿物+硫酸盐矿物组合）→主喷流口附近发育碎屑状热水沉积岩（碳酸盐矿物+铝硅酸盐矿物+硫酸盐矿物组合）→分支喷流口附近或相对远的卤水池内发育盆地沉积型热水沉积岩（碳酸盐矿物+铝硅酸盐矿物组合）→远端发育区域扩散型热水沉积岩（单一碳酸盐矿物组合）。更多还原

【Abstract】 Hydrothermal sedimentary rock is becoming one of the research hot spots in the geoscience field.However,little achievement has been done with the hydrothermal sedimentary rock formed in the lacustrine basin.The dark argillaceous dolomite and dolomitic mudstone in the Xiagou Formation of Lower Cretaceous in Qingxi sag, Jiuxi basin have been identified as infrequent lacustrine white smoke type hydrothermal sedimentary rocks.This is the particular subject dissertation.The subject is supported by Natural Science Foundation（NO.40672073）and Ministry of Education university special scientific research fund for doctor （NO.20060616014）.Based on rock-mine identify,carbon and oxygen isotope,Sr isotopic,trace elements,rare earth elements,solution inclusion and other experimental tests,combining with the latest research achievements home and abroad,some results of the lacustrine white smoke type hydrothermal sedimentary rock are got as follow:1)The hot water minerals in the lacustrine white smoke type hydrothermal sedimentary rock of Xiagou Formation are mainly albite and ankerite,quartz,analcite, barite,dickite and fluorite are its secondary mineral components,and pyrite,galena, chalcopyrite,zinc blende occur in the rock occasionally.Seven paragenetic associations of hot water minerals in the hydrothermal sedimentary rocks of the Xiagou Formation are recognized.The hot water minerals represented as albite and ankerite are cyclopean and cumulate of hypautomorphic-automorphic structure.It shows that crystallization and precipitation are the mainly chemical sedimentation of the hydrothermal sedimentary rock of Xiagou Formation.The hydrothermal sedimentary rock is of micritic-aphanitic texture,and shows laminated structure mainly,with hot water clastic texture,hot water breccia texture,network vein structure,vortex structure and deformation bedding only partially in the rocks.The hot water clastic and hot water breccia texture can be identified seven types as different minerals associations,some of which are rare and of special significance.2)It is proved that the micrite ankerite of Xiagou Formation is precipitated in a relatively closed environment with a high temperature mineralizing solution from the carbon and oxygen isotopes analyses.The solution interchanges carbon and oxygen isotopes with the surrounding rocks in the rising and circulating,as a result the hot solution gets heavy carbon as to has a higher value ofδ¹³C.The characteristic of carbon and oxygen isotopes of Xiagou Formation may be caused by the hot solution, which is formed in the process that supracrustal rocks are leached and extracted by descending lacustrine water in the surface crust.3)Through Strontium isotope test,the ⁸⁷Sr/⁸⁶Sr ratio of the laminated hot water sedimentary rock only has minor changes.It can represent homogenization ⁸⁷Sr/⁸⁶Sr ratio in the hot brine pool.The composition of Sr-isotope of hydrothermal breccia and cementation are almost consistent,which shows that both of them are the same period and the same resource eruptive flow sediments.The ⁸⁷Sr/⁸⁶Sr ratio of hydrothermal sedimentary rock in the study area is much higher than the ⁸⁷Sr/⁸⁶Sr ratio of seawater and basalt of corresponding period and a little higher than the ⁸⁷Sr/⁸⁶Sr ratio of the algal limestone,which represents the strontium isotopes composition of lake water in early cretaceous,but lower than the ⁸⁷Sr/⁸⁶Sr ratio of underlying silicon-aluminum rock.It shows that the thermal solution is neither related with seawater nor simplex lake water or mantle magmatic water.It is primarily speculated that early Cretaceous sublacustrine hydrothermal solution in the area is the mixed hydrothermal solution which is constituted of deep circulating lake water and a little of mantle-derived magmatic water and full of high radiogenic Strontium of underlying silicon-aluminum basement rock.4)It was shown that the hydrothermal sedimentary rock of Xiagou Formation has basal characteristics of hydrothermal depositional formation of LREE>HREE, with high abundance∑REE,exceptional distribution pattern of REE,positiveδCe and negativeδEu,which is different from characteristics of marine exhalative rock,but is highly similar to the characters of alkalescent tholeiitic basalt in the same layer,the hydrothermal sedimentary rock of Xiagou Formation was considered to be closely related to the origin of basalt in the same horizon.The Eu/Sm-La/Ce simulation in the mixing process of hot solution and lacustrine water shows that the deep hot water sedimentation of Xiagou Formation is in hot brine pool which is in the condition of reducing and alkalescence.5)It is concluded that the hot solution of Lower Cretaceous in Qingxi sag is relevant with volcanic eruption from solution inclusion,C-O-Sr isotope,trace elements geochemistry and rare earth elements tests.The hot solution,which is descending lacustrine water mixed with magmatic water,is moderate-to-low temperature（90～200℃）,moderate-to-low salinity（8～22wt%NaCl）,and moderate density（0.97～1.2g/cm³）strongly alkaline hot brine water.It is short of metal sulfides, rich in CO₃^2-,SO₄^2-,Cl^-,F^-,Ca²⁺,Mg²⁺,Fe²⁺,Ba²⁺,Si⁴⁺,Al³⁺,Na⁺ and other major elements and anionic complexes,and contains Zn,Rb,Mo,As,Ni,Co,Sb,Ba,Ag and other deep source gas-liquid or mantle source trace elements associations.The temperature,salinity,density and pressure of the mineralizing hot solution of hydrothermal sedimentary rocks in different location decreases outwards by the order: main exhalative-channel—branch exhalative-channel—exhalative mouth—near exhalative mouth—distal basin.6)There are three driving forces for hot solution movement:gravity driving force,compaction driving force and magma heat driving force.The three forces cause the circulation of hot solution together,and extract metallogenetic chemistry materials from surrounding rocks.There may be four kinds of mechanisms of overpressure hot solution overbalance returning movement,three of the mechanisms are structural uplift pump,decompression in the shallow fault and supercharge of surging volcanic magma hot water,and they cause hot solution moving upward to breakout against overlying sediments with boiling and bursting along faults.It is mixed with the lower tempreture and salinity lacustrine water,and cooled suddenly.Then the chemical balance of the hot solution is broken and chlorine complex compounds are liberated. As a result,hydrothermal minerals are precipitated forming a series of lacustrine white smoke type hydrothermal sedimentary rock of different kinds.7)The lacustrine white smoke type hydrothermal sedimentary rock of Xiagou Formation of Lower Cretaceous in Qingxi sag,Jiuxi basin can be divided into four genetic types.By consulting available data about hydrothermal sedimentary rock published in China and abroad,this kind hydrothermal sedimentary rock belongs to rare lacustrine orthodolomite,which has particular genetic features and identification signs.8)The sedimentary model of the lacustrine white smoke type hydrothermal sedimentary rock of Xiagou Formation of Lower Cretaceous in Qingxi sag is founded: main exhalative mouth→branch exhalative-channel connecting to the main exhalative-channel→near main exhalative mouth→near branch exhalative mouth or further brine pool→distal basin.In the main exhalative mouth,hot water breccia hydrothermal sedimentary rock（aluminum silicate minerals + sulfate minerals + trace metal sulfide minerals association）develops;In the branch exhalative mouth,network vein hydrothermal sedimentary rock（carbonate minerals + aluminum silicate minerals + sulfate minerals）develops;Near main exhalative mouth,clastic hydrothermal sedimentary rock（carbonate minerals + aluminum silicate minerals + sulfate minerals） develops;Near branch exhalative mouth or in further brine pool,sedimentary type hydrothermal sedimentary rock（carbonate minerals + aluminum silicate minerals association）develops;At distal basin diffuse type hydrothermal sedimentary rock （only carbonate minerals association）develops.更多还原