西藏丁青地区与玻镁安山岩类有关的蛇绿岩的矿物学特征

西藏丁青蛇绿岩的东杂岩体是一种与玻镁安山岩(Boninite)有关的特殊的蛇绿岩类型。其 堆晶斜方辉石岩、辉长岩和辉绿岩的岩石化学、微量元素以及稀土元素的地球化学特征均与西太平洋诸岛(伊豆—马利亚纳、巴布亚新几内亚、新喀里多尼亚等)的玻镁安山岩相似。此外,超镁铁质构造岩中的橄榄石和顽火辉石富镁,指示残余地幔具强烈亏损的性质。尖晶石的Cr含量中等至较高,与深海橄榄岩及大洋中脊玄武岩中的尖晶石不同。堆晶岩和辉长岩中的古铜辉石富镁,斜长石富钙,也明显不同于典型大洋中脊环境的特征,表明丁青东蛇绿岩形成的环境不像大洋中脊或弧后盆地,而可能是在洋内俯冲带之上的岛弧底部。     

西藏蛇绿岩中硅铁合金组合及成因探讨

在雅鲁藏布江蛇绿岩带的东端罗布莎蛇绿岩的铬铁矿中发现不寻常的硅铁合金组合。4种硅铁合金的理论分子式分别为Fe0.84Si2.00(Fe3Si7)、Fe7Si3、Fe6Si4以及Fe4Ti3Si2P。这些合金均选自铬铁矿石的人工重砂中，在少数颗粒中见到由3种硅铁合金组成的交生结构，明显表明这些合金的同生和同成因性。推测它们为化学反应成因,来自于核幔边界地带。     

东南极格罗夫山泛非期麻粒岩相变质作用

东南极格罗夫山主要由麻粒岩相高级变质岩和花岗岩类组成，其中变质岩以浅色和暗色含斜方辉石长英质片麻岩占主导地位，夹有少量镁铁质麻粒岩、变沉积岩和含方柱石钙硅酸盐岩。这些岩石一般都展示了平衡的矿物共生结构，但在镁铁质麻粒岩的单斜辉石中普遍发育斜方辉石(易变辉石)的出溶片晶。根据出溶辉石的重组分析获得麻粒岩相变质作用的峰期温度约为850℃，而浅色片麻岩中的石榴子石—斜方辉石—斜长石—石英组合给出的变质压力为0．61～0．67GPa。镁铁质麻粒岩中火成亚钙质普通辉石斑晶的保存表明格罗夫山地区可能只发育单一的泛非期高温麻粒岩相变质事件，岩石在高温变质之后经历了缓慢冷却过程，这主要归因于花岗质岩浆的板底垫托作用。     

河南嵩县香春沟石英脉型钼矿的矿石及地球化学特征

香春沟钼矿床是河南省新发现的唯一中型石英脉型钼矿床.主要矿石类型为石英脉型钼矿石,具有超酸高钾的特点,矿石构造结构简单,矿区有用矿物主要是辉钼矿,其粒度细小,不易与脉石分离.文章通过分析区内元素的地球化学特征,为寻找该类型钼矿床提供参考.     

Petrography and textural development of inorganic and biogenic lithotypes in a relict barite tufa deposit at Flybye Springs, NT, Canada

A relict mound of Holocene barite (BaSO₄) tufa underlies the Flybye Springs, a small, barium‐rich, cold sulphur spring system in the Northwest Territories of Canada. The tufa is composed of relatively pure barite with ≤0·34 wt% Ca²⁺ and ≤0·77 wt% Sr²⁺. The mound is made up of coated bubble, raft, undulatory sheet, stromatolitic, coated grain and detrital conglomerate barite tufa. Although previously unreported in barite, these lithotypes are akin to facies found in many carbonate spring deposits. Raft and ooid‐coated grain tufa was formed via ‘inorganic’ barite precipitation in spring water ponds and tributaries where rapid oxidation of sulphide to sulphate established barite supersaturation. Undulatory sheet tufa may have formed by the reaction of dissolved barium with sulphate derived from the oxidation of extracellular polysaccharide‐rich colloidal sulphur films floating in oxygenated, barite‐saturated spring water ponds. Coated bubble, oncoid‐coated grain and stromatolitic tufa with filamentous microfossils was formed in close association with sulphur‐tolerant microbes inhabiting dysoxic and oxygenated spring water tributaries and ponds. Adsorption of dissolved barium to microbial extracellular polysaccharide probably facilitated the development of these ‘biogenic’ lithotypes. Detrital conglomerate tufa was formed by barite cementation of microdetrital tufa, allochthonous lithoclasts and organic detritus, including caribou hair. Biogenic textures, organic artefacts and microfossils in the Flybye barite tufa have survived diagenetic aggradational recrystallization and precipitation of secondary cements, indicating the potential for palaeoecological information to be preserved in barite in the geological record. Similarities between the Flybye barite tufa and carbonate spring deposits demonstrate that analogous textures can develop in chemical sedimentary systems with distinct mineralogy, biology and physiochemistry.     

Melting of the subcontinental lithospheric mantle by the Emeishan mantle plume; evidence from the basal alkaline basalts in Dongchuan, Yunnan, Southwestern China

The Emeishan continental flood basalt (ECFB) sequence in Dongchuan, SW China comprises a basal tephrite unit overlain by an upper tholeiitic basalt unit. The upper basalts have high TiO₂ contents (3.2–5.2 wt.%), relatively high rare-earth element (REE) concentrations (40 to 60 ppm La, 12.5 to 16.5 ppm Sm, and 3 to 4 ppm Yb), moderate Zr/Nb and Nb/La ratios (9.3–10.2 and 0.6–0.9, respectively) and relatively high _{Nd (t)} values, ranging from − 0.94 to 2.3, and are comparable to the high-Ti ECFB elsewhere. The tephrites have relatively high P₂O₅ (1.3–2.0 wt.%), low REE concentrations (e.g., 17 to 23 ppm La, 4 to 5.3 ppm Sm, and 2 to 3 ppm Yb), high Nb/La (2.0–3.9) ratios, low Zr/Nb ratios (2.3–4.2), and extremely low _{Nd (t)} values (mostly ranging from − 10.6 to − 11.1). The distinct compositional differences between the tephrites and the overlying tholeiitic basalts cannot be explained by either fractional crystallization or crustal contamination of a common parental magma. The tholeiitic basalts formed by partial melting of the Emeishan plume head at a depth where garnet was stable, perhaps > 80 km. We propose that the tephrites were derived from magmas formed when the base of the previously metasomatized, volatile-mineral bearing subcontinental lithospheric mantle was heated by the upwelling mantle plume.     

陕西洛南绿松石的结构构造特征研究

采用偏光显微镜观察、扫描电镜、X射线粉晶衍射分析,对产于绿松石遗址陕西洛南的绿松石进行了详细的结构构造研究。结果表明,陕西洛南绿松石的结构多呈隐晶质结构,部分可见环带状结构、结核状结构;可见块状构造、致密块状构造,部分见葡萄状构造;扫描电镜下观察陕西洛南绿松石多呈鳞片状结构、不规则团块状分布,可见板状绿松石微晶不规则分布,部分见孔隙分布;绿松石微晶越接近它形,孔隙越少,排列越均匀,则结构越紧密,呈现致密块状构造;反之则呈葡萄状构造;XRD实验结果表明,样品中均含有绿松石和石英,部分样品中含有少量的伊利石和高岭石。     

川口油田长6储层成岩作用

详细分析了川口油田长6储层的成岩作用类型、储层物性演化及影响因素。通过岩石学、铸体薄片、电镜扫描等研究方法说明川口油田长6储层主要成岩作用包括压实-压溶作用、胶结作用、交代蚀变作用及溶蚀作用等,成岩阶段属晚成岩A期。其中,机械压实作用、化学胶结作用是导致砂岩孔隙度降低、储集性能变差的主要因素。机械压实作用主要表现为软碎屑的塑性变形、颗粒间由点接触向凹凸接触演变;胶结作用表现为浊沸石、绿泥石、粘土矿物、碳酸盐胶结;石英和长石的次生加大、溶蚀作用特别是浊沸石的溶蚀在一定程度上提高和改善了砂岩储集性能。结果表明,影响储层物性的主要因素为沉积作用和成岩作用。     

Metamorphic reactions in dry and aluminous granulites: a Perple_X <Emphasis Type="Italic">P–T</Emphasis> pseudosection analysis of the influence of effective reaction volume

In high-Mg, Al metapelites, monophase sapphirine corona occur around spinel–corundum aggregates in monomineralic cordierite layers, and bi-phase orthopyroxene–sillimanite aggregates replace locally warped sapphirine in polygonized cordierite aggregates. P–T phase topologies computed (Perple_X software) using compositions of cordierite-rich layers that host the reaction textures did not match the assemblages for the discontinuous reactions spinel + corundum + cordierite → sapphirine and sapphirine + cordierite → orthopyroxene + sillimanite. Instead, the reaction assemblages were reproduced using P–T pseudosection analysis for micro-domain reaction volumes estimated from compositions of product phases in the volume proportion they occur. The results are consistent with known phase relations deduced using Schreinmakers P–T grids. Apparently, the compositions of cordierite-rich layers that hosted the reaction textures were inadequate chemical proxies for determining P–T–X relations of phase-boundary controlled reactions influenced by compositions of the nearest-neighbor minerals in the proportion they react (effective composition), and not in the proportion they existed in the layer/bulk rock. In other words, P–T–X phase topologies and reconstructed P–T paths in dry and aluminous rocks may be best understood by thermodynamic modeling of reactions using effective reaction volume compositions rather than the bulk composition of the rock or the mineralogical layer that host the reaction textures.     

云南香格里拉红山铜矿石硫化物环带及地质意义

云南香格里拉县红山铜矿是三江义敦岛弧带南端重要铜矿床,颇受关注,成因认识分歧大.矿区出露上三叠统板岩、变碎屑岩和灰岩夹中基性火山岩、火山碎屑岩以及少量侵入其中的中酸性和超基性岩脉、岩株,透镜状铜硫化物矿体产在顺层状矽卡岩体内或边部,成矿后断裂明显.矿石中普遍发育以黄铁矿为核部、黄铜矿为中间带、磁黄铁矿为边部带的硫化物环带,其中核部黄铁矿呈立方体自形-半自形晶,黄铜矿呈他形晶围绕黄铁矿沉淀,磁黄铁矿呈他形分布在黄铜矿外围,内带常被外带硫化物溶蚀交代.环带从内到外硫化物先后沉淀,矿物生成顺序为黄铁矿-黄铜矿-磁黄铁矿.环带中三种硫化物矿物的REE配分曲线和微量元素蛛网图极为相似,负Eu异常显著,富集U、Th、Zr、Hf,亏损Rb、Sr、Ba,与矿区超基性岩表现出较高相似性;环带从内到外,∑REE(0.17371×10-6、1.22626×10-6、5.25925×10-6)和微量元素含量依次升高,Co/Ni和Se/Te比值降低,指示矿石硫化物沉淀过程中,可能伴随热液体系内地壳物质不断增加.环带中硫化物矿物δ34SV-CDT=3.81‰～5.23‰,具有岩浆硫源特征,δ34SV-CDT边部带磁黄铁矿 (4.47‰)＜δ34SV-CDT中间带黄铜矿(4.58‰)＜ δ34SV-CDT核部黄铁矿(4.65‰),三种硫化物间没有达到同位素平衡分馏.红山铜矿石环带结构是岩浆热液为主成矿流体中黄铁矿、黄铜矿、磁黄铁矿先后晶出成因,伴随硫化物环带的形成,热液系统从早到晚H2S和O2逸度降低或pH升高过程.