云南金宝山含铂钯超镁铁质侵入体中铬铁矿的成因研究

位于扬子地台西缘的金宝山岩体赋存我国最大的独立铂族元素矿床,岩体为似层状产出的小型超镁铁岩,在时间和空间上与晚二叠纪(260 Ma)峨眉山大火成岩省相关.该岩体由单辉橄榄岩、辉橄岩及橄辉岩、辉石岩异离体组成.铬铁矿以副矿物形式出现,从形态上可以分为三类:包嵌于橄榄石中的自形铬铁矿、以自形或半自形体存在于辉石中铬铁矿以及环绕结构铬铁矿.其中环绕结构铬铁矿外壁浑圆,内为棱角状,其中心为橄榄石、辉石.本文在薄片观察的基础上,结合电子探针研究,认为包嵌于橄榄石中的自形铬铁矿是在岩浆早期深部岩浆房中结晶形成的;存在于辉石中的铬铁矿则是岩浆进一步结晶演化的结果,主要为就地结晶的产物;在岩体形成的过程中,作为岩体赋存空间的堆晶相与后续岩浆持续反应,使铬铁矿不断聚集和生长,最终形成了环绕橄榄石晶体的形态.铬铁矿的生成模式进一步说明了金宝山侵入体为一岩浆通道,并且经历深部结晶分异演化.     

云南金宝山镁铁-超镁铁岩的地球化学特征及成因

金宝山超镁铁侵入岩赋存有超大型硫化物铂族元素矿床。单辉橄榄岩是岩区员主要的含矿岩石类型。根据单辉橄榄岩的矿物学、岩石学、岩石化学及微量元素地球化学特征，探讨岩浆的结晶分异演化过程，提出岩体的形成与岩浆结品分异有关，母岩浆成分为拉斑质玄武质岩浆。岩体高镁、高稀土总量，以及橄榄石与辉石的结构特征显示岩体是橄揽石、铬尖晶石等矿物与残留岩浆混合形成。     

阿尔泰南缘中泥盆统北塔山组火山岩的矿物学研究

阿尔泰山南缘中泥盆统北塔山组火山岩极为发育。本文对富辉橄玄岩和玄武岩中的单斜辉石和橄榄石斑晶进行了矿物化学分析,并结合矿物的地质温压计和岩浆结晶模拟,约束了两种岩石中矿物的形成过程,推测了原始岩浆的演化过程。提出富辉橄玄岩和玄武岩的原始岩浆属于拉斑玄武系列,富辉橄玄岩中的高压单斜辉石来源于深部（40～50 km）,其结晶早于橄榄石;玄武岩中单斜辉石大多属于岩浆房结晶产物（30～40km）,其结晶晚于橄榄石;两种岩石中橄榄石均属于岩浆房结晶产物（30～40 km）。     

新疆北山地区罗东镁铁质-超镁铁质层状岩体岩石成因

罗东镁铁质-超镁铁质岩体位于塔里木板块东北部的新疆北山地区,岩体平面形态为眼球状,出露面积约2.1 km2.由纯橄岩、单辉橄榄岩、斜长二辉橄榄岩、橄榄二辉岩、方辉辉石岩、橄长岩、橄榄辉长岩、辉长岩、苏长辉长岩和淡色辉长岩组成,堆晶结构和堆晶韵律发育,属于层状岩体.岩浆演化过程中主要分离结晶/堆晶相是橄榄石和单斜辉石,此...     

应用电子探针技术研究北京密云放马峪铬铁矿床成因——来自含铬尖晶石矿物化学的证据

似层状铬铁矿床长期以来被认为是岩浆分异成因,但近年来有学者提出其中个别产在蛇绿岩中。本文选择北京放马峪似层状铬铁矿床中纯橄岩、辉橄岩和辉石岩中不同类型的含铬尖晶石进行了电子探针分析。研究表明,岩浆早期的纯橄岩和辉橄岩中的铬尖晶石富铬(Cr2O3平均43.32%),而岩浆晚期辉石的结晶消耗了大量Cr3+,由于氧逸度的升高,在辉石岩的单斜辉石中出溶贫铬的铬磁铁矿(Cr2O3平均10.32%)和富铝尖晶石(Cr2O3平均15.77%)。与世界上不同类型铬尖晶石的矿物化学特征进行对比,可以认为放马峪铬铁矿床是产在阿拉斯加型岩体中的早期岩浆矿床,而与蛇绿岩无关。本文对放马峪铬铁矿床成因和成矿专属性的限定,为这类镁铁-超镁铁岩体的铬、铜镍、铂族元素的找矿勘查提供了依据。     

新疆北山地区漩涡岭镁铁质—超镁铁质层状岩体岩石学与矿物学研究

位于新疆北山地区的漩涡岭岩体是一堆晶层理发育的镁铁质-超镁铁质层状岩体。岩石类型主要有纯橄岩、橄长岩、橄榄辉长岩和辉长岩等。主要的造岩矿物有橄榄石、辉石、斜长石、铬尖晶石,岩相学特征表明岩浆在演化过程中经历了橄榄石、尖晶石、斜长石、斜方辉石和单斜辉石的分离结晶,结晶次序依次为橄榄石+尖晶石→斜长石→辉石,表明结晶时压力较低。漩涡岭岩体的纯橄岩中橄榄石的Fo高达90.1,这不同于新疆北部黄山岩带、喀拉通克岩体群以及甘肃金川岩体的橄榄石Fo组成,利用橄榄石最高Fo值估算得到漩涡岭岩体的母岩浆的Mg#为0.73~0.75,岩浆的液相线温度高达1330~1350℃,其岩浆为高温高Mg的苦橄质岩浆,这为塔里木东北部二叠纪地幔柱活动提供了新的证据。     

甘肃金川Ⅱ号岩体橄榄石成因探讨

金川是世界第三大在采岩浆铜镍硫化物矿床,其成因备受中外地质学家的关注。金川岩体被一系列北东-东向左行平移断层自西向东依次划分为Ⅲ、Ⅰ、Ⅱ、Ⅳ等4个岩体。金川岩体主要由硫化物纯橄岩、二辉橄榄岩、橄榄辉石岩组成,边缘断续分布少量斜长石二辉橄榄岩和辉石岩。金川最大的1号矿体产于Ⅱ号岩体的中心,呈现出由中间硫化物纯橄岩向两侧浸染状的二辉橄榄岩和橄榄辉石岩过渡的对称式岩相分布。电子探针分析结果显示,金川Ⅱ号岩体橄榄石Fo值在79.7%～83.9%之间变化,w（Ni）为959×10^-6～2060×10^-6,大多低于从硫不饱和玄武岩浆中结晶出的橄榄石Ni含量。模拟计算表明金川岩体母岩浆为高MgO玄武岩浆(w（MgO）=10%～13%,w（FeO）=11.5%～12.5%)。橄榄石Ni含量偏低的原因是橄榄石结晶的同时发生了硫化物熔离,橄榄石与硫化物的质量比值约为40﹕1。硫化物纯橄岩和二辉橄榄岩中橄榄石的Ni含量及其与Fo值的相关性都存在显著的区别,暗示它们可能是从Ni含量不同的母岩浆中结晶出来的。同时,硫化物纯橄岩中橄榄岩经历了与硫化物熔体的Fe-Ni交换...     

东昆仑石头坑德镁铁-超镁铁质岩体矿物学特征及成矿指示

石头坑德镁铁-超镁铁质岩体位于东昆仑造山带东段五龙沟地区,邻近昆中大断裂,主要岩性为辉石岩、橄辉岩、橄榄岩、辉长岩等,铜镍矿体主要赋存于Ⅰ号岩体的辉石岩、橄辉岩和橄榄岩中。岩石地球化学特征表明,其镁铁比值(m/f)变化范围在2.77~6.01之间,属铁质系列的镁铁-超镁铁岩,有利于成铜镍矿。稀土总量总体较低,轻稀土元素之间分馏强,重稀土元素之间分馏弱。岩石总体富集LILE(Rb、Ba、Th、U),贫HFSE(Nb、Ta、Zr、Y),具有明显的Rb、U正异常及Nb、Ta的负异常。超镁铁岩类橄榄石中的Ni普遍亏损,指示深部存在硫化物的熔离作用,在橄榄石结晶之前,大量的Ni进入到硫化物中,极有利于形成富矿岩浆或矿浆。可见,伴随同化混染作用的发生,岩浆中S达到过饱和,进而硫化物发生不混溶作用,富含硫化物的岩浆运移至东昆仑造山带邻近昆中断裂构造薄弱的部位成岩成矿。铜镍矿体多赋存在含橄榄石的超镁铁质岩体内,指示石头坑德岩体深部存在高度富集铜镍的部位,是下一步的找矿方向。     

新疆萨尔托海超基性岩体及铬铁矿床的地质特征和成因

萨尔托海铬铁矿是我国大型铬矿床之一。本文论述了该区超基性岩与地表、浅部和深部铬铁矿床的地质特征。根据岩体产状、内部构造、岩石矿物学、岩石组构及通过稀土元素和锶同位素的分析对比、矿物包裹体的研究结果等,提出萨尔托海超基性岩体是岩浆成因的,是在造山带区域应力场作用下成岩、成矿与变形、变质的。该区铬铁矿主要产于纯橄岩申,其次为斜辉辉橄岩,而橄榄岩仅有少量矿化。主要成矿地段的岩相均有自上而下由偏酸性到偏基性的垂直分带现象,工业矿体赋存于中下部纯橄岩—辉橄岩杂岩带的纯橄岩内或偏基性的辉橄岩中,其构造位置处在岩体基底凹槽之上;地表矿体则多是由形成浅部或中深部矿床的矿浆派生、沿裂隙贯入的脉状矿体。在造矿铬尖晶石中发现了原生硅酸盐熔体包裹体;肯定了褪色岩石富含Cl、B、S等挥发组分,岩石发生蚀变褪色在空间上和成因上与铬矿成矿作用有关;并从岩相、构造、地球化学及矿床特征等方面探讨了岩浆分异及铬矿床的形成作用。超基性岩及铬铁矿结晶温度介于1300—700℃之间。     

新疆北山地区坡一岩体橄榄石成分特征及其对地幔源区的制约

坡一超镁铁质岩体位于塔里木板块东北缘与中亚造山带南缘拼贴处的北山地区,主要由纯橄岩、异剥橄榄岩、方辉橄榄岩、橄榄辉石岩和少量橄长岩组成,其中方辉橄榄岩和橄榄辉石岩赋含铜镍硫化物矿化。不同类型岩石中橄榄石的Fo值介于84%～89%之间,其中纯橄岩中橄榄石的Fo值最高可达89%,与幔源原生岩浆结晶橄榄石的Fo值(88%～91%)相当。岩体中异剥橄榄岩和纯橄岩中Fo大于86%的橄榄石结晶于硫化物熔体熔离之前,相比与饱满地幔熔体平衡的橄榄石,其具有更高的Ni和更低的Mn含量,指示坡一岩体母岩浆可能不是饱满地幔部分熔融形成的。利用坡一岩体纯橄岩全岩成分和其中Fo值最高的橄榄石成分估算出的母岩浆成分与夏威夷玄武岩的母岩浆成分类似,均表现为富Si和富Ni,显示其地幔源区可能存在辉石岩组分。利用橄榄石的Ni/(Mg/Fe)和Mn/Fe比值估算出地幔源区部分熔融时辉石岩组分贡献的熔体比例约为49%。     

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)

Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.     

The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts

The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H₂O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H₂O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species.     

Quaternary stresses revealed by calcite twinning inversion: insights from observations in the Savonnières underground quarry (eastern France)

Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ₁ roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003).     

HYDROGEOLOGY

正20141756 Chen Ruige(Mathematical College,China University of Geosciences,Beijing100083,China);Zhou Xun Numerical Simulation of Groundwater Level Fluctuation in a Coastal Confined Aquifer with Sloping Initial Groundwater Level Induced by the Tide(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.1099-1104,6 illus.,16 refs.) Key words:confined water,groundwater level     

METAMORPHIC PETROLOGY

正20141408 Cai Jia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China);Liu Fulai Petrogenesis and Metamorphic P-T Conditions of Garnet-Spinel-Biotitebearing Paragneiss in Danangou Area,Daqingshan-Wulashan Metamorphic Complex Belt(Acta Petrologica Sinica,ISSN1000-0569,CN11-1922/P,29(7),     

SERIALS

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GEOPHYSICAL EXPLORATION

正20142386An Guoying(China Aero Geophysical Survey and Remote Sensing Center for Land and Resources,Beijing 100083,China)Application of Satellite Remote Sensing in Regional Hydrogeological Investigation:Taking Cenozoic Strata in Wenquan Sheet(1∶250 000)of Karakoram Range as an Example(Geosci-     

QUATERNARY GEOLOGY & GEOMORPHOLOGY

正20141016An Chengbang(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,Lanzhou University,Lanzhou 730000,China);Zhao Yongtao Lake Records during the Last Glacial Maximum from Xinjiang,NW China and Their Climatic Impli-     

PETROLEUM GEOLOGY

正20141538 Cao Qing(School of Earth Sciences and Engineering,Xi’an Petroleum University,Xi’an 710065,China);Zhao Jingzhou Characteristics and Significance of Fluid Inclusions from Majiagou Formation,Yichuan Huangling Area,Ordos Basin(Advances in Earth Science,ISSN1001-8166,CN62-1091/P,28(7),2013,p.819-828,7 illus.,3 tables,43 refs.)     

GEOCHEMISTRY

正20142002 Wei Hualing(Institute of Geophysical and Geochemical Exploration,Chinese Academy of Geological Sciences,Langfang065000,China);Zhou Guohua Element Content and Mineral Compositions in Different Sizes of Soil in Tongling Area,Anhui Province(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(11),2013,p.1861