山西吕梁袁家村条带状铁建造沉积相与沉积环境分析

山西吕梁作为华北克拉通上条带状铁建造(BIF)的重要产区之一,位于华北中央构造带中。袁家村BIF分布于吕梁岚县袁家村一带,极有可能是华北克拉通内最为典型的Superior型BIF。与华北克拉通其他大多数BIF相比,袁家村BIF具有明显的差异性,其中包括它的形成时代(2.3~2.1Ga)、铁建造类型和低级变质程度(低绿片岩相)等。因此,研究袁家村BIF具有特殊的研究意义,可为探讨大氧化事件之后古海洋氧化还原状态以及国内Superior型BIF的成因提供研究基础。袁家村BIF产于吕梁群袁家村组变沉积岩系的下部,前人根据上覆和下伏含火山岩地层的时代,推测袁家村组的形成时代为2.3~2.1Ga。BIF整体产状陡倾,沿北北东-北东东向呈L形带状分布。依据原生矿物的共生组合及产出特征,可将BIF沉积相划分为氧化物相(60%)、硅酸盐相(30%)和碳酸盐相(10%)。氧化物相是本区BIF最主要的沉积相,主要矿物为赤铁矿、磁铁矿和石英,从而可进一步划分为赤铁矿(24%)和磁铁矿(36%)亚相;硅酸盐相BIF以大量硅酸盐矿物出现为特征,散布于研究区,主要矿物组成除了石英和磁铁矿之外,还有铁黑硬绿泥石、绿泥石、铁滑石、镁铁闪石和阳起石等。在与碳酸盐相BIF构成过渡相的BIF中,还可发现大量的铁白云石。而碳酸盐相主要矿物为菱铁矿、铁白云石和石英等,主要发育于研究区的南部。依据含铁岩系构造格局特点复原获得了原始沉积相分布略图,沉积相主要呈南北向延展,自东向西显示出相变规律,西边为碳酸盐相,东边为氧化物相,其间是过渡的硅酸盐相。通过袁家村BIF的岩相学和含铁矿物化学成分的研究,可大致推测原始沉积的矿物组成为无定形硅胶、水铁矿、与铁蛇纹石和黑硬绿泥石组成类似的铁硅酸盐凝胶、富Al的粘土碎屑和含铁、镁、钙的碳酸盐软泥。这些沉积物在随后的成岩期和绿片岩相的区域变质作用下发生矿物之间的相互转变。BIF中主要含铁矿物的PO-P-Eh 2CO2和pH相关图解说明除了赤铁矿之外,其他矿物均是在较低氧逸度环境中形成的,且所有矿物共存的水体系为中性到弱碱性。袁家村BIF氧化物相中发育豆粒、内碎屑结构和板状交错层理等原始沉积构造,指示氧化相部分是在相对高能的浅水环境下沉积的。但BIF大部分应该形成于浪基面以下(200m)较为深水的环境中,沉淀可能同时发生于上部氧化和下部还原的水体之中,由于还原弱酸性的深部富铁海水在海侵的过程中上升到浅部相对氧化和弱碱性的浅水环境中,因为Eh、pH及氧逸度等物化条件的骤然变化,最终导致铁质的沉淀和沉积相自上而下的变化。     

冀东迁滦地区沉积变质型铁矿床变质作用程度：来自石榴子石的制约

石榴子石是冀东地区沉积变质铁矿中常见的变质矿物之一。本文采集迁安-滦县地区代表性铁矿中含有石榴子石的岩石样品,对其石榴子石进行电子探针和X-射线粉晶衍射分析,得出司马地区为角闪岩相,杏山-黄柏峪一带为角闪岩-麻粒岩相,水厂-大石河地区为麻粒岩相,这与前人对迁滦地区用主要矿物共生组合等来研究变质相的结论相一致;同时迁滦地区沉积变质铁矿中石榴子石的端元组分和晶胞参数a0随变质程度的增加呈规律性变化: 司马地区的铁铝榴石+钙铝榴石→杏山-黄柏峪一带的铁铝榴石→水厂-大石河一带铁铝榴石+镁铝榴石,其晶胞参数a0值逐渐减小。因此在沉积变质型铁矿床中,变质矿物石榴子石的化学成分及晶胞参数特征对不同地区的变质程度具有示踪意义。     

晋北娄烦吕梁群变质相带的划分及其成因研究

晋北娄烦吕梁群由一套经受过两期不同性质变质作用的泥砂质岩、基性火山岩和酸性流纹岩组成。早期为吕梁期变质作用,其结果使该区地层构造形迹总体上呈NE走向;晚期为西川河韧性剪切断裂所产生的区域变质作用,其结果使该区地层走向由早期的NE向扭转为近SN向,且使地层层序发生倒转,并与递增变质带的形成关系密切。选取该区中对变质温度和压力变化反映较敏感的原岩为泥砂质岩石的袁家村组和裴家庄组地层为研究对象,采用电子探针微区分析(EPMA)对沿地层走向上连续分布的特征变质矿物及矿物共生组合特征进行研究,并利用矿物对地质温度计估算该区不同采样点的变质温度和压力条件,对研究区进行变质相带的划分,确定各变质相带的变质温、压条件,并探讨其成因。研究结果表明,袁家村组和裴家庄组为等化学系列地层。沿该地层走向上:西川河断裂以北地区,从北向南,特征变质矿物绿泥石、黑云母、石榴石、十字石和蓝晶石依次规律出现;西川河断裂以南地区,红柱石和夕线石依次规律出现。根据特征变质矿物的空间分布规律、首次出现的地点及矿物共生组合特征,划分出5个变质带:绿泥石带、黑云母带、石榴石带、十字石-蓝晶石带和红柱石-夕线石带。这一完整的递增变质带可与苏格兰高地的巴罗型相媲美。矿物对地质温度计估算结果。     

羌塘盆地查郎拉地区中-新生代充填序列及沉积旋回研究

以实测剖面和路线剖面为基础,采用旋回沉积学理论和地层优势相(亚相)法首次系统地研究了羌塘盆地查郎拉地区中-新生代的充填序列和沉积旋回特征.指出该区充填序列自下而上由上三叠统肖查卡组-上第三系石平顶组构成,根据各种相标志将其划分出7大沉积相、18个亚相及若干个微相,并从老至新划分出6个沉积体系,相应组成5个沉积旋回层.着重阐述了充填序列中各个沉积体系及沉积旋回层特征,并对沉积演化过程中的沉积旋回曲线特征、水位变化和抬升-沉降历史作了讨论.     

娄烦尖山铁矿矿石特征及矿物相

娄烦尖山铁矿赋存于品梁群袁家村组中部地层中。矿石矿物组成及矿石类型简单，常见矿物为石英，磁铁矿及铁闪石，以前两者为主。相应的矿石类型为石英型磁铁矿及闪石型磁铁矿。矿物相为石英磁铁矿氧化物相及闪石型磁铁矿硅酸盐相，后者因含在原生菱铁矿，更可能是碳酸盐－硅酸盐相。     

浙江长兴二叠系—三叠系界线剖面层序地层研究

本文是在详细研究了国际二叠系—三叠系界线展型侯选剖面——中国长兴煤山剖面生物事件面、生态地层事件、高分辨率异旋回驱动机制事件、微相及沉积体系的基础上,将晚二叠世长兴期和早三叠世Griesbachian期划分出三个三级层序及百余个高频旋回层或米兰科维奇旋回层,建立了以煤山剖面为主干的,下扬子区跨越不同相区沉积体系、在等时地层格架内的空间配置和层序地层格架。本文还应用生物群生境型,进行了古水深半定量测定和相对海平面变化研究。     

东准噶尔塔克札勒蛇绿混杂岩带变质作用特征

塔克札勒蛇绿混杂岩带的变质作用 ,具大洋水热变质、俯冲变质和区域低温动力变质作用的特征 ,其中以大洋水热变质作用为主。中志留世末洋盆扩张阶段 ,形成葡萄石、绿纤石相→低绿片岩相→角闪岩相的递增变质特征 ;早石炭世初洋壳向陆壳之下俯冲 ,俯冲变质作用不显著 ,仅见超镁铁岩具叶蛇纹石、纤维蛇纹石及绢石蚀变矿物 ;早石炭世中期塔克札勒有限洋盆开始粘连闭合 ,于晚石炭世早期褶皱造山 ,使蛇绿混杂岩带产生角闪岩相→高绿片岩相→低绿片岩相的退变质特征 ,使蛇绿岩带在辉长岩中由棕色角闪石退变为透闪石、阳起石和绿泥石、绢云母及绿帘石等变质矿物 ,是区域低温动力变质作用的产物 ,属低绿片岩相     

贵州及邻区中奥陶世早期沉积物中鲕绿泥石鲕和海绿石的时序位置和环境意义

贵州及邻区中奥陶世早期沉积物中普遍含有鲕绿泥石鲕和海绿石矿物，过去一直不曾有人研究过。本文在野外观察研究３５个中奥陶世地层剖面的基础上，选择了其中的六个剖面进行详细的微相研究和相序重塑，对鲕绿泥石鲕和海绿石的形态特征、结构、成份等以及包含它们的岩石的岩性特征、两种矿物颗粒的分布和时序位置进行了论述和总结，讨论了两种矿物颗粒在当时的古环境意义。     

斯洛伐克西喀尔巴阡山脉Gemerská Poloma滑石-菱镁矿矿床中镁的交代作用

Gemerská Poloma矿床是个重要的滑石矿床(储量20万吨),位于西喀尔巴阡山脉Germeric地区。部分滑石化的镁质碳酸盐体赋存在早古生代火山沉积杂岩体中(黑色片岩,变质泥岩),在Variscan变质作用(M1)过程中受到了绿泥石-黑云母带区域变质相的改造。这种原岩是石灰岩的矿体由白色-灰白或者灰色-黑色的菱镁矿与白云石1组成,被次生的白云石2和滑石脉切割。本次研究考察了两次变质事件(M1和M2)的几个连续的矿物组合,最早的组合包括铁白云石,镁菱铁矿与菱铁矿,(并与黑电气石,铁绿泥石,磷灰石,与伊利石-白云母伴生),它们以微小残留物形式产出在菱镁矿和白云石1中,其形成可能早于M1变质作用高峰期。M1变质事件的高峰期以富铁金云母,镁绿泥石1,镁电气石(黑电气石的边缘)和石英的组合为代表。在M1退变质作用过程中,发生了镁交代作用,开始是白云石1结晶,接下来形成菱镁矿,最后是以铁菱镁矿沿裂隙的形成而终。根据碳酸盐地质测温原理,M1变质事件的高峰期温度为460~490℃,变质矿物组合特征也支持这一测温结果。滑石,白云石2,与镁绿泥石2沿着镁碳酸盐岩石裂隙的发育,主要受到M2变质事件的影响,这个变质事件与较年青的Alpine造山事件有关。 菱镁矿流体包裹体的研究表明,成矿流体具有复杂的组成,可能以MgCl2组分为主,主要来     

新疆阿克陶县苏巴什一带磁铁矿地质特征及成因浅析

新疆阿克陶县苏巴什一带具有优越的成矿地质条件,带内相继发现了多个铁矿床,并具有一定的空间连续性。本文通过总结对比带内不同铁矿床的地质特征、赋矿地层、构造变质变形等特征,并以带内典型的磁铁矿床为例,深入分析矿体地质特征、矿体形态、矿物组合及矿石结构构造特征,认为该地区的磁铁矿具有相似的矿床成因及成矿演化史,经历了原始沉积期、区域变质改造期和热液叠加改造期3个阶段,属于沉积变质型磁铁矿。通过物探磁测,明确了区内磁异常主要由磁铁矿（化）引起,并总结了带内磁铁矿找矿标志,为该区铁矿进一步勘探调查指明方向。     

Low-grade regional metamorphism in the Mesozoic-Cenozoic volcanic sequences of the Central Andes

ABSTRACT All the Mesozoic and Cenozoic volcanic rocks of the Central Andes (from southern Ecuador to central Chile), except Recent ones, have been affected by episodes of regional metamorphism, without change in texture and structure. The metamorphism, which ranges from low zeolite to greenschist facies, can be classified as burial metamorphism because there is an overall increase in metamorphic grade with stratigraphic depth in the individual volcanic sequences separated by regional unconformities. Some sequences display metamorphic patterns transitional to ocean-floor and to geothermal field types, reflecting variations along and across the Andes in tectonic setting and thermal gradients. Volcanism was closely followed by metamorphism during each cycle characterizing the geological history of the Central Andes. The episodic nature of the metamorphism has led to breaks in metamorphic grade at regional unconformities and repetition of facies series, where strata of higher grade may even overlie those of lower grade. The existence of permeability-controlled distribution patterns of secondary minerals within individual flows shows that gradients of chemical activity, rate of reaction and P_fluid were acting, in addition to temperature and P,_tot overall gradients, during the regional metamorphism. The alteration is accompanied by chemical changes and disturbances of the K-Ar and Rb-Sr isotope systems. Similarities between Mesozoic facies series in the western and eastern flanks of the Andes are consistent with a mechanism of ensialic spreading-subsidence.     

Tectonic Setting of the Late Proterozoic Lavalleja Group (Dom Feliciano Belt), Uruguay

The Lavalleja Group exposed along the Dom Feliciano orogenic belt is located in the southeast of Uruguay. This group consists of volcano-sedimentary rocks, developed during the Neoproterozoic Brasiliano cycle. The geochemical signature of the igneous rocks of the Lavalleja Group, mainly metagabbros and basic and acidic metavolcanic rocks, indicates a back-arc basin tectonic setting. The metamorphic grade increases to the southeast, from very low grade, lower green-schist facies, in the Minas Formation, to a medium grade, amphibolite facies, in Fuente del Puma and Zanja del Tigre Formations. The metamorphic mineral assemblages correspond to a low-pressure regional metamorphism associated with a high thermal gradient. A compressive deformational event that probably corresponds to the closure of the Lavalleja basin during a continental collision, was recognized. The petrology, geochemistry, metamorphic grade, and tectonic setting are consistent with a back-arc basin setting for the Lavalleja Group.     

The geochemistry of Precambrian granulite facies rocks from the Lewisian complex of Tiree,Inner Hebrides,Scotland

The metamorphism and geochemistry of the major components of a small area of granulite facies rock are described and discussed, and a chemical model for the evolution of anomalous trace element distributions in such materials is suggested. The local complex was subjected to medium to high pressure granulite facies metamorphism between 2,900 and 2,600 m.y. All the analysed granulite facies rocks from Tiree; acid to intermediate gneisses, basic metamorphic rocks, and granitic rocks, have anomalous chemistries, being depleted in K, Rb, Nb, Y and Th, and have high K/Rb, Ba/Rb and Ca/Y ratios, and very low K/Ba and Rb/Sr ratios relative to normal portions of the upper continental crust. The gneisses seem to have been enriched in Ba and Sr.The chemical features of the rocks are considered to reflect their stable mineral assemblages in the granulite facies, and to be representative of deep-level crustal materials. The geochemical peculiarities of the complex may have been largely controlled by an upward intergranular diffusion, or “degassing” caused by high-grade metamorphism. It is suggested that such diffusion may have been active at the crust/upper mantle interface, some diffused material of mantle origin accounting for certain chemical oddities typical of Lewisian and some other Precambrian granulite facies rocks.     

Multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks

Pyritized plant tissues with well-preserved morphology were studied in rocks from Vanoise (western Alps, France) that experienced high-pressure, low-temperature metamorphic conditions in the blueschist facies during the Alpine orogeny. Organic and inorganic phases composing these fossils were characterized down to the nanometer scale by Raman microspectroscopy, scanning transmission X-ray microscopy and transmission electron microscopy. The graphitic but disordered organic matter composing these fossils is chemically and structurally homogeneous and mostly contains aromatic functional groups. Its original chemistry remains undefined likely because it was significantly transformed by diagenetic processes and/or thermal degradation during metamorphism. Various mineral phases are closely associated with this organic matter, including sulphides such as pyrite and pyrrhotite, carbonates such as ankerite and calcite, and iron oxides. A tentative time sequence of formation of these diverse mineral phases relative to organic matter decay is proposed. The absence of traces of organic matter sulphurization, the pervasive pyritization of the vascular tissues and the presence of ankerite suggest that the depositional/diagenetic environment of these metasediments was likely rich in reactive iron. Fe-sulphides and ankerite likely precipitated early and might have promoted the preservation of the fossilized biological soft tissues by providing mechanical resistance to compaction during diagenesis and subsequent metamorphism. In contrast, iron oxides which form rims of 100-nm in thickness at the interface between organic matter and Fe-sulphides may result from metamorphic processes. This study illustrates that it may be possible in some instances to deconvolve metamorphic from diagenetic imprints and opens new avenues to better constrain processes that may allow the preservation of organic fossils during diagenesis and metamorphism.     

Burial metamorphism in rocks of the Western Andes of Peru

An unconformity bound, episodic pattern of burial metamorphism is preserved in marine and terrestrial volcanic and sedimentary rocks which were deposited in the West Peruvian Trough during the Mesozoic and Cenozoic Eras. A particular metamorphic facies series is developed in each of the stratigraphic-structural units bounded by unconformities. In each unit, grade increases with stratigraphic depth and covers part or all of the range from zeolite to greenschist facies. At every unconformity a mineralogic break occurs where higher grade assemblages on top of the unconformity plane overlie lower grade assemblages. The presence of wairakite and the development of a wide range of metamorphic facies in thin sequences suggest high geothermal gradients, possibly related to generation of magma at depth.     

繁昌桃冲铁矿成因探讨

The problems of the formation conditions for stratiform skarns and the genesis of the Taochong iron deposits are dealt with in this paper. Following is a summary of this discussion: 1. Stratiform skarns in this area occur in carbonate rocks of the Upper and Middle Carboniferous Period and the lower part of the Permian Qixia Group. No outcropping or concealed igneous bodies have ever been found, let alone any indications of an igneous contact zone or a corresponding zonality from "dry" skarn to "wet" skarn. The mineral facies and zonation of the skarns depend predominantly on the properties of the initial host rocks, and the development of skarns seems to have had much to do with chemical potential of silicon in these host rocks. As a result of the reaction of iron-bearing carbonates with siliceous materials in the rocks, iron-bearing silicates were formed, which in turn were transformed by pneumato-hydrothermal processes of the later stage. The stratiform skarns of this area, therefore, probably fall into the category of stratabound skarns subjected to transformation of thermometamorphism. 2. The iron deposits bear undisputable stratabound characteristics. The positions of ore-bearing beds and the petrological features as well as the mineral associations all point to a sedimentary ore-forming process of iron-carbonate (siderite). The presumption of siderite ore source is supported by the following facts: (l) Remnants of sedimentary siderite which survived the metamorphism have recently been observed in magnetite ore from neighbouring Xinqiao mining area. Siderite can have as many as 12.07% Fe⁺⁺ and, after corrosion, shows oolitic texture. (2) The ore is mainly of calcite/ dolomite- magnetite type. Mineral associations are quite simple and sulfides are rarely seen. (3) A comparison of the analytical data suggests that the content of organic carbon in iron ore decreases due to oxidation caused by metamorphism but is still higher than that in magnetite of contact- metasomatic skarn. (4) The paleogeographic reconstruction shows that this area was once an ancient underwater uplift favorable for the precipitation of iron carbonates. After its formation, the siderate bed underwent thermodynamic metamorphism and was hence decomposed into magnetite, which was then subjected to the superimposed transformation by subsequent hydrothermal fluids, leading to the partial activation and migration of iron matter and thus the formation of such ore as hematite (specularite) at shallow depth of the Changlongshan mining area. In brief, this deposit has a complex genesis: it experienced sedimentation, thermal metamorphism and transformation by hydrothermal fluids.     

繁昌桃冲铁矿成因探讨

桃冲铁矿,开采历史悠久,由于其品位富,以平炉富矿为主要矿石类型,受到了重视。有关矿床的成因也一直被人们所注意。自三十年代提出火成接触变质——热液成因的观点以来(谢家荣、程裕淇1935),人们习惯于将矿床划归于矽卡岩型。作者通过野外调查和初步研究之后,对本区铁矿的成因产生了疑问。本文就现有资料的分析,对层状矽卡岩的形成条件和铁矿的成因,做如下讨论。     

A reappraisal of episodic burial metamorphism in the Andes of central Chile

The Jurassic to Miocene sequences of the central Andes, east of Santiago, reputedly show repeated cycles of episodic sub-greenschist facies, burial metamorphism that are identified by sharp breaks in metamorphic grade at major stratigraphic boundaries. This paper presents the first detailed petrochemical analysis of these low-grade metamorphic sequences by examining the progressive development of secondary minerals, reaction progress in mafic phyllosilicates, and topological variations in the low-grade assemblages as a means of testing this model. The results indicate a progressive increase from zeolite facies through to close to the onset of greenschist facies from Miocene to Jurassic rocks. Combined analysis of reaction progress in mafic phyllosilicates and petrochemical relationships of chlorite–pumpellyite–actinolite in metabasites provides no evidence for sharp metamorphic breaks at major stratigraphic boundaries. Integrating the results presented here with the most recent models of stratigraphic/tectonic development of the central Andes shows that the metamorphism took place in two episodes, and was not episodic on a 40-million-year cycle. An absence of sharp breaks in metamorphic grade in any part of the succession, as demonstrated here, shows that the original petrographic establishment of low-grade facies provided insufficient resolution of changes in metamorphic conditions to establish definitive evidence of such breaks. Accordingly, this study suggests that re-assessment of metamorphic breaks reputedly developed in other areas of the Andean Cordillera is imperative in order to resolve the questions raised here about the origin of the low-grade metamorphism.Editorial responsibility: B. Collins     

Petrochemical characterization of mafic rocks from the Ligurian ophiolites,southern Apennines

New mineralogical and chemical data for ophiolitic rocks from the southwesternmost Liguride Units are presented in order to constrain their ocean-floor origin and subsequent emplacement in an accretionary wedge. Their complete petrochemical evolution is particularly well preserved in the southern Apennine metabasites. Metadolerites show amphibolite and greenschist facies mineral assemblages of ocean-floor metamorphism. Metabasalts display greenschist facies ocean-floor metamorphism and spilitic alteration. Veins cutting the mafic rocks show mineral assemblage of the prehnite–pumpellyite metamorphic facies. HP/LT orogenic metamorphism, reflecting underplating of the ophiolitic suite at the base of the Liguride accretionary wedge during subduction of the western Tethys oceanic lithosphere produced a mineral assemblage typical of the lawsonite–glaucophane facies. Bulk-rock chemistry suggests that the mafic protoliths had a MORB-type affinity, and were affected by ocean-floor rodingitic and/or spilitic alteration. Hydrothermal alteration-induced LREE mobility and LREE enrichment may be correlated with the ocean-floor metamorphism.     

鞍本太古代绿岩盆地铁矿的成矿特征

辽宁省鞍山本溪地区是我国著名的铁矿产区。对于本区鞍山式铁矿的成矿特征,作者在前人工作的基础上,经过三年多的调查研究,认为本区鞍山式铁矿不是一种单一的矿床类型,而是赋存在不同时代、不同大地构造环境的两种矿床系列,即属于阿尔戈马型铁矿系列和苏必利尔型铁矿系列。并在划分成矿系列的基础上提出了本区的成矿模式。