Petrology of ultrahigh-pressure eclogites from the ZK703 drillhole in the Donghai, eastern China

The 558-m-deep ZK703 drillhole located near Donghai in the southern part of the Sulu ultrahigh-pressure metamorphic belt, eastern China, penetrates alternating layers of eclogites, gneisses, jadeite quartzites, garnet peridotites, phengite–quartz schists, and kyanite quartzites. The preservation of ultrahigh-pressure metamorphic minerals and their relics, together with the contact relationship and protolith types of the various rocks indicates that these are metamorphic supracrustal rocks and mafic-ultramafic rock assemblages that have experienced in-situ ultrahigh-pressure metamorphism. The eclogites can be divided into five types based on accessory minerals: rutile eclogite, phengite eclogite, kyanite–phengite eclogite, quartz eclogite, and common eclogite with rare minor minerals. Rutile eclogite forms a thick layer in the drillhole that contains sufficient rutile for potential mining. Two retrograde assemblages are observed in the eclogites: the first stage is characterized by the formation of sodic plagioclase+amphibole symplectite or symplectitic coronas after omphacite and garnet, plagioclase+biotite after garnet or phengite, and plagioclase coronas after kyanite; the second stage involved total replacement of omphacite and garnet by amphibole+albite+epidote+quartz. Peak metamorphic P–T conditions of the eclogites were around 32 to 40 kbar and 720°C to 880°C. The retrograde P–T path of the eclogites is characterized by rapidly decreasing pressure with slightly decreasing temperature. Micro-textures and compositional variations in symplectitic minerals suggest that the decompression breakdown of ultrahigh-pressure minerals is a domainal equilibrium reaction or disequilibrium reaction. The composition of the original minerals and the diffusion rate of elements involved in these reactions controlled the symplectitic mineral compositions.     

视剖面图温压计研究进展评述

视剖面图温压计是目前定量估算变质温度和压力的主要方法之一。其理论基础为热力学平衡原理与质量守恒定律。利用内恰的热力学数据库和相应的成分-活度模型对特定成分体系进行视剖面图计算,可以正演模拟给定温度和压力条件下的矿物组合、矿物丰度及其成分,与实测岩石对比,可以准确获取岩石的形成温度和压力。在应用视剖面图温压计时,应选择受全岩成分影响小、且受退变质作用影响微弱的矿物成分;对于有成分变化的体系,应结合多种方法恢复有效全岩成分。文中通过视剖面图对KFMASH(K2O-Fe O-Mg O-Al2O3-Si O2-H2O)体系下不同矿物组合内多硅白云母硅含量及其等值线斜率的研究,认为多硅白云母硅含量及其等值线斜率主要由不同矿物组合内多硅白云母参与的契尔马克替换及纯转换端元反应中的主导反应决定,进一步深化了对变质过程中控制矿物成分变化的内部缓冲反应机制的理解,从而也可为选择和应用矿物温压计提供指导。因此,视剖面图方法是目前研究变质岩石形成条件及变质作用精细过程的最佳方法之一。     

点苍山-哀牢山变质杂岩带变沉积岩的变质演化

点苍山-哀牢山变质杂岩带位于青藏高原东南缘大理-元江-元阳-河口一带,出露规模达数百千米,是扬子板块和印支陆块之间的一条重要构造带.该变质杂岩带主要由各类正片麻岩、副片麻岩、大理岩所组成,夹有斜长角闪岩、石榴辉石岩和超镁铁质岩石的透镜体或团块.其中,变沉积岩如含夕线石和蓝晶石的片麻岩类岩石保存了多阶段的矿物组合及异常复杂的矿物相转变关系.详细的岩相学、成因矿物学以及矿物相转变关系分析表明,变沉积岩系经历了早期进变质阶段(M1)、峰期角闪-麻粒岩相变质阶段(M2)、峰后近等温减压(脱水熔融)阶段(M3)以及晚期退变质阶段(M4)的变质演化.其中,M1阶段的稳定矿物组合为石榴石+斜长石+白云母+石英+十字石±蓝晶石±黑云母±钾长石,M2阶段的稳定矿物组合为石榴石+黑云母+蓝晶石/夕线石+斜长石+石英、石榴石+黑云母+斜长石+石英±钾长石±夕线石,M3阶段的共生矿物组合为石榴石+黑云母+夕线石+斜长石+石英,M4阶段的矿物组合为黑云母+白云母+斜长石+石英±钾长石±石榴石等.通过传统GB-GASP温压计和二云母温度计的估算结果,配合P-T视剖面定量计算,确定早期进变质阶段(M1)的温压条件为T=560 ～ 590℃,P=5.5 ～6.3kb,峰期角闪-麻粒岩相阶段(M2)的温压条件为T=720～ 760℃、P=8.0～9.3kb,峰后近等温减压阶段(M3)的温度压力条件为T=640～760℃,P=5.0～7.3kb,晚期退变阶段(M4)的温压条件为T=521～648℃,P=4.0～5.0kb.上述研究结果表明,点苍山-哀牢山变沉积岩记录了典型碰撞造山带型式的顺时针P-T演化轨迹,表明点苍山-哀牢山变质杂岩带的形成与印度板块和欧亚板块之间的俯冲-碰撞存在密切的成因关系.     

Quantification of mineral matter in the Argonne Premium Coals using interactive Rietveld-based X-ray diffraction

The mineral matter in the eight reference North American coal samples of the Argonne Premium Coal series has been investigated on a quantitative basis using X-ray diffraction (XRD) techniques. X-ray diffraction data obtained from electronic low-temperature (oxygen–plasma) ash (LTA) residues, from ashes produced by heating the coals in air at 370°C, and also from the raw coals themselves, were evaluated using an interactive data processing system ( ™) based on Rietveld interpretation methods. The results from the three types of material (LTA, 370°C ash and raw coal) were compared for each sample. This allowed the components present in the raw coals in crystalline form to be recognised separately from mineral artifacts produced, particularly in the low-rank coals, from interaction of organically associated elements (Ca, S, etc.) during the two ashing processes.After the allowance for the production of any artifacts, the quantitative mineral assemblages identified from XRD of the raw coals were found to be consistent, even for coals having a relatively low ash percentage (around 5%), with the results obtained from the respective mineral concentrates prepared by the ashing methods. The effects of heating the coal to 370°C could also be distinguished, relative to the raw coal or the LTA, through changes in components such as pyrite and the clay minerals.Although some areas of uncertainty exist, particularly with magnesium in the low-rank coals, the calculated chemical compositions of the coal ash derived from the mineral mixtures identified for each coal were also found to be consistent with the results of direct chemical analysis of the respective coal ash materials.     

中国菊花石的矿物组成特征

中国菊花石产于二叠纪栖霞组碳酸盐岩层位中,菊花石经光学显微鉴定,Ｘ－射线衍射分析和ｘ－射线能谱仪测试,其原生矿物主要天青石和菱锶矿,两种含锶矿物后期广泛被方解石,白云石和石英交代,依据其菊花石原生矿物组成,将我国菊花石划分为天青石型（浏阳菊花石为典型）菱锶矿型（宣恩,来宾菊花石）和青青石－菱锶矿混合型（永丰型菊花石）菊花石三种类型。     

Metamorphic evolution of oceanic gabbros: recrystallization from subsolidus to hydrothermal conditions in the MARK area (ODP Leg 153)

The 117.38 m of gabbroic core drilled during the Ocean Drilling Program (ODP) Leg 153 at Sites 921 to 924 in the Mid-Atlantic Ridge (MAR) between 23 °N and the Kane Fracture Zone, exhibits a remarkable primary compositional heterogeneity, such as magmatic layering, intrusive contacts and late magmatic veining, which express a succession of magmatic events. Textural indicators suggest that the cooling of the crystal mush occurred in a dynamic environment, with infiltration of progressively evolved liquids. Magmatic features include random shape fabric and magmatic lamination; the subsequent deformational overprint occurred in subsolidus conditions. The ductile deformation, generally concentrated in discrete domains of the gabbro, is associated with continuous re-equilibration of the metamorphic assemblages of (1) olivine + clinopyroxene + orthopyroxene + plagioclase + ilmenite + Ti-magnetite, (2) olivine + clinopyroxene + plagioclase + ilmenite + Ti-magnetite + red hornblende. At lower temperatures brittle deformation prevails and subsequent fractures control the development of metamorphic assemblages: (3) clinopyroxene + plagioclase + red brown hornblende + Ti-magnetite + magnetite (?) + ilmenite, (4) plagioclase + brown hornblende + Ti-magnetite + magnetite + hematite + titanite ± Ti-oxide, (5) plagioclase + green hornblende + magnetite + titanite, (6) plagioclase + actinolite + chlorite + titanite + magnetite, (7) albite + actinolite + chlorite + prehnite ± epidote ± titanite and (8) albite + prehnite + chlorite ± smectite. Assemblages 1 to 8 express increasing water/rock ratios and decreasing degrees of recrystallization.

During the ductile phase, red hornblende is stable and its abundance increases with deformation intensity, possibly as an effect of the introduction of hydrous fluids. During the brittle phase, water diffusion controls the development of the fracture-filling mineral assemblages and re-equilibration of the adjacent rock; temperatures decrease further, as demonstrated by mineral zoning and incompletely re-equilibrated assemblages. The lowest temperatures correspond to the development of hydrothermal assemblages.

Compared with oceanic gabbros from fast-spreading transform environments, high-temperature ductile phases (granulite and amphibolite) are well developed, whereas brittle phases are widespread, as microcracks, prevalent on fracturing associated with discrete veins.     

腾冲-梁河地区锡铜铅锌稀有多金属成矿模式

腾冲-梁河地区Sn、Cu、Pb、Zn等元素成矿规律明显,找矿标志清楚。由东往西划分为四个次级成矿带,各具有不同矿产组合或典型矿床。根据成矿地质条件、矿产分布特征、控矿因素和找矿标志等,归纳5种成矿模式。初步建立该区矿床找矿模型,为今后矿产预测奠定基础。     

庆阳-合水地区长8油层组沉积物源分析

物源分析对砂岩储层的展布与分析预测具有重要的意义。通过对鄂尔多斯盆地西南缘庆阳-合水地区上三叠统延长组长8油层组的砂岩重矿物组合、轻矿物组合及砂岩岩屑组分的平面分布特征分析,判断了庆阳-合水地区的沉积物源方向。研究表明,庆阳-合水地区存在两大物源和古流沉积体系,即西南方向的庆阳沉积古流体系和南部方向的合水沉积古流体系;长82亚组沉积期以南部的沉积古流体系为主,而长81亚组沉积期以西南部的沉积古流体系为主;重矿物组合特征分析显示长81亚组沉积期合水区带混源现象明显。     

矿物标型六性及其在胶东金矿中的应用

目前矿物标型研究和应用已进入一个新的阶段。作者从哲学的高度,把国内外矿物标型特征的分散研究加以集中概括和总结,提出了“矿物标型六性”的普遍规律,即普遍性、特殊性、变化性、相应性、继承性和分带性,对矿物标型特征研究具重要的指导意义。这些规律在胶东金矿中得到广泛应用,并已取得良好效果。     

Tracing the protolith, UHP metamorphism, and exhumation ages of orthogneiss from the SW Sulu terrane (eastern China): SHRIMP U–Pb dating of mineral inclusion-bearing zircons

Orthogneisses are the major country rocks hosting eclogites in the Sulu UHP terrane, eastern China. All of the analyzed orthogneiss cores from the main drilling hole of the Chinese Continental Scientific Drilling Project (CCSD-MH) have similar major and trace element compositions and a granite protolith. These rocks have relatively high LREE/HREE ratios, strong negative Eu anomalies (Eu/Eu*=0.20–0.39), and negative Ba anomalies (Ba/Ba*=0.25–0.64). Coesite and coesite-bearing UHP mineral assemblages are common inclusions in zircons separated from orthogneiss, paragneiss, amphibolite, and (retrograded) eclogite of the CCSD-MH. This suggests that the eclogite, together with its country rocks, experienced in situ ultrahigh-pressure (UHP) metamorphism. Laser Raman spectroscopy and cathodoluminescence (CL) images show that zircons from the orthogneisses are zoned and that they have distinct mineral inclusions in the different zones. Most zircons retain early magmatic cores with abundant low-pressure mineral inclusions, which are mantled with metamorphic zircon-containing inclusions of coesite and other UHP minerals. The outermost rims on these grains contain low-pressure mineral inclusions, such as quartz and albite. SHRIMP U–Pb dating of the zoned zircons gives three discrete and meaningful groups of ages: Proterozoic ages for the protolith, 227±2 Ma for the coesite-bearing mantles, and 209±3 Ma for the amphibolite facies retrograde rims. The widespread occurrence of UHP mineral inclusions in zircons from the Sulu metamorphic belt dated at about 227 Ma suggests that voluminous continental crust experienced late Triassic subduction to depths of at least 120 km and perhaps more than 200 km. Eighteen million years later, the terrane was rapidly exhumed to midcrustal levels, and the UHP rocks were overprinted by amphibolite facies metamorphism. The exhumation rate deduced from the zircon age data and previously obtained metamorphic P–T data is estimated to be 5.6–11.0 km/Ma. Such rapid exhumation of the Sulu UHP terrane may be due to the buoyancy forces produced by subduction of low-density continental material into the deep mantle.