Stable isotopic and trace element evidence for restricted fluid migration in 2 GPa eclogites

Mineral stable isotopic and trace element studies in 2 GPa banded eclogites of the Tauern Window, eastern Alps, record mm- to cm-scale heterogeneities that reflect compositional variations in the accompanying metamorphic fluids. A close correlation between dolomite mode and dolomite δ¹⁸O is consistent with equilibrium partitioning among coexisting minerals and fluids. Small variations in dolomite δ¹³C values correspond with δ¹⁸O variations, but an overall decrease in dolomite δ¹³C by c. 1%o across a 12-cm sample is a relict feature that pre-dates eclogite equilibration. Garnet, omphacite, and clinozoisite rims show little systematic mineral-mineral partitioning behaviour for Ti, V, Cr, Y, Sr, or Zr; major elements, however, are well equilibrated among these same minerals. Despite the apparent lack of mineral-mineral trace element equilibration, most of the trace elements vary systematically with water activity calculated in each layer. Trace element behaviour during the eclogite metamorphism thus appears to have been controlled largely by mineral-fluid interactions along grain boundaries. Shallow structural levels in other subduction complexes (c. 10-45 km) typically exhibit fracture-controlled permeability and extensive metasomatism, but there is no field or geochemical evidence for extensive fluid advection during high-pressure metamorphism in the Tauern eclogites. Because most dewatering and devolatilization during tectonic burial occurs prior to eclogite conditions, the volumetric fluid/rock ratio in eclogites should generally be low. Low fluid/rock ratios, coupled with the possible non-wetting nature of the fluids, permits the production and preservation of fine-scale chemical heterogeneities in deeply subducted eclogites and associated fluids. However, the eventual breakdown at greater depth of volatile-bearing dolomite, phengite, clinozoisite, zoisite, or amphibole could lead to renewed fracture-controlled fluid release from the subducted rocks to regions appropriate for arc magma generation.     

Evidence for pre-regional metamorphic fluid infiltration of the Lower Calcsilicate Unit, Reynolds Range Group (central Australia)

Grandite garnet-rich calcsilicate rocks from the Lower Calcsilicate Unit of the regionally metamorphosed Reynolds Range Group (central Australia) crop out along a strike-parallel section in which a transition zone from M2₂ amphibolite to granulite facies rocks is exposed. Across this transition the grandite-rich layers do not show systematic changes in mineral assemblages, compositions and modes, or stable isotope compositions. These layers are deformed by F2₂ folds that are associated with the peak of regional low-pressure/high-temperature metamorphism. Therefore, the grandite-rich layers appear to pre-date regional metamorphism and to have acted as closed chemical systems during prograde M2₂ metamorphism. Mineral assemblages in the grandite-rich layers are consistent with their formation through the infiltration of oxidized, water-rich fluids (X_co2 < 0.1–0.3; log f_o2 -16 to -14). The stable isotope values of calcite (Δ¹³C=-4.2 to -0.8%₀ PDB; Δ¹⁸O = 10.5–14.0%⁰ V-SMOW) and bulk-silicate fractions (Δ¹⁸O = 6.1 to 10.8%) of the grandite-rich layers are most consistent with the infiltrating fluid being from a magmatic source. It is most likely that fluid infiltration occurred during the pre-M2₂ contact metamorphism (M2₁) that affected much of the Reynolds Range Group. The preservation of these assemblages is probably due to their high variance and little pervasive fluid-rock interaction having occurred during M2₂. The clinopyroxene- and feldspar-rich calcsilicate rocks that host the grandite-rich layers contain poikiloblastic grandite garnet that formed during prograde M2₂ metamorphism. Thin marbles that locally occur with the grandite-rich layers contain a third garnet generation that is post- or late M2₂. This grossular-rich garnet occurs in coronas around calcite, plagioclase, clinopyroxene, wollastonite and scapolite. These coronas are consistent with cooling and/or compression. However, because the marble assemblages are themselves overprinted by M2₁ grandite-rich layers the development of coronal garnet does not reflect a continuous P-T-t path. Rather, it more probably reflects the partial re-equilibration of M2₁ contact metamorphic assemblages to post-M2₂ conditions.     

The chemical anomalous behaviors of water-marble rock system under action of ultrasound

By the experiment, it is confirmed that water-marble rock system shows obviously chemical anomalous behaviors: the relevant minerals which formed marble rock are resolved fast, water becomes alkaline, meanwhile H₂ emission appears under action of ultrasound; based on rock identification by microscope and chemical analysis of water and rock, the mechanism of above chemical reaction is analyzed and discussed. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15 498–507, 1993. This study was supported by the Chinese Joint Seismological Science Foundation.     

地震地电阻率前兆异常特征及其机理研究

本文在全面整理我国大陆二十余年来的地电阻率观测资料的基础上,分析了地电阻率前兆异常特征及其与地震三要素之间的关系,给出地震强度(震级)与异常时间和震中距乘积的对数呈线性关系的实用结果,研究了不同类型地震地电阻率短临前兆特征及其在地震预报中的应用,探讨了地电阻率前兆变化的机理。     

东天山黄土坡铜锌矿床成矿流体的氦-氩同位素示踪

黄土坡铜锌矿床是东天山卡拉塔格地区一中型海相火山岩型块状硫化物（VHMS）矿床,赋存于早志留世海相火山-沉积岩系中。矿体产于酸性火山角砾岩与凝灰岩之间,主矿体呈厚大的扁豆状,矿石主要呈块状、浸染状、条带状和网脉状构造。本文报道了黄土坡铜锌矿床成矿流体的氦和氩同位素组成,黄铁矿流体包裹体的³He 含量低,介于0.039×10^-12 cm³ STP/g～0.64×10^-12 cm³ STP/g,n（³He）/n（⁴He）值为 0.11～0.94 Ra,介于壳源He与幔源He之间。⁴⁰Ar 含量变化于 3.49×10^-8cm³ STP/g～34.25×10^-8 cm³ STP/g 之间,n（⁴⁰Ar）/n（³⁶Ar）介于301.40～425.98 之间。成矿流体中有幔源 He（1.71%～10.97%）和放射性成因 Ar（⁴⁰Ar*含量为1.96%～30.63%）。结合矿床包裹体及 H-O-S 同位素特征,认为幔源流体和富放射性成因He 和Ar 的海水参与了成矿。     

Sulfur isotope and fluid inclusion geochemistry of metamorphic Cu–Au vein deposits,central Cobar area,NSW, Australia

Vein-type, structurally controlled Cu–Au mineralisation hosted by turbidites of late Silurian to earliest Devonian age, forms an important resource close to the eastern margin of the Cobar Basin. Here we report 103 new sulfur isotope analyses, together with homogenisation temperatures and salinity data for 545 primary two-phase fluid inclusions for the mineralised zones from the central area of the Cobar mining district. A range in δ³⁴S values from 3.8 to 11.2‰ (average 7.9‰) is present. Sulfur is likely to have been derived from rock sulfur/sulfide in basin and basement rocks, but there may be an additional connate-derived component. Homogenisation temperatures (T_h) for inclusion fluids trapped in quartz and minor calcite veins range from near 150°C to 397°C. Fluid inclusions are characterised by a low CO₂ content and low, but variable salinities (2.1–9.1 wt% NaCl equivalent). Generations of inclusion fluids correspond to six paragenetic stages of vein quartz deposition and recrystallisation at the Chesney mine. Primary fluid inclusions in the first two stages were subjected to re-equilibration resulting from increased confining pressure. Their T_h range (151–317°C) is considered a minimum for the temperature of these fluids. Sulfide and gold deposition at Chesney appears to be related to fluids of moderately high T_h (range 270–397°C) associated with the final paragenetic stage. T_h for the ore-related fluids may be close to the solvus of the H₂O–NaCl–CO₂ system and hence near trapping temperatures. Late-stage entry of a hot, moderately saline ore-forming fluid is implicated as the origin of the Cu–Au mineralisation. However, comparison with geochemical data for the vein-style Zn–Pb–Ag deposits at Cobar demonstrates that differences in metal content for individual zones cannot be attributed to major differences in fluid temperature or salinity. Rather, these differences are probably due to variations in source-rock reservoirs and structural pathways along which the ore-forming fluids moved.     

特提斯域的密西西比河谷型(MVT)铅锌矿床

特提斯域是全球最重要的密西西比河谷型(MVT)铅锌矿床富集区,矿床广泛地分布在陆-陆碰撞造山带两侧的陆块上,就位于碰撞形成的褶皱-逆冲带和前陆带内,成矿通常发生在碰撞挤压作用晚期或之后、区域处于走滑或伸展的阶段。矿床、矿体的就位与张性断裂密切相关,主要控矿因素有蒸发盐底辟构造、碳酸盐岩溶蚀垮塌构造、蒸发盐溶蚀垮塌构造、高孔隙度白云岩、含重晶石地层等。油气流体在许多矿床和矿集区出现,其主要通过与硫酸盐发生反应为铅锌成矿提供还原硫。陆-陆碰撞的大地构造环境、大量的蒸发盐、丰富的油气流体是特提斯域富集MVT矿床的重要原因,域内寻找MVT矿床的潜力巨大。     

Interactions between tectonics and fluid circulations in an inverted hyper-extended basin: Example of mesozoic carbonate rocks of the western North Pyrenean Zone (Chaînons Béarnais,France)

Interactions between fracturing, fluid circulations and fluid chemistry in hyper-extended margins are still poorly described as most of them are located offshore, buried underneath post-rift sediments. The southern Aquitaine basin and the northern Pyrenees constitute an appropriate case study to investigate these interactions since a model of hyper extended margin with mantle exhumation during the Lower Cretaceous subsequently inverted was recently proposed. From a field study, we here describe three main sets of fractures (set 1 to set 3). They are correlated with main stages of the geodynamic evolution of the basin corresponding to the Liassic rifting, the Aptian-Cenomanian hyper-extension, and the Pyrenean compression. Petrographic observations, Raman and micro-thermometry analysis on fluid inclusions, ICP-MS, and isotope analysis permitted to determine chemistries, temperatures, redox conditions, gas compositions, oxygen and carbon isotopic signatures, and REE contents of parent fluids for cements precipitated during each episode. In particular saddle dolomite and chlorite precipitated in set 2 fractures during the hyper-extension corresponding to the thermal peak at temperatures higher than 300 °C. The isotopic signature, the high CO₂ content, the occurrence of H₂S and the high salinity of parent fluids suggest ascending magmatic fluids percolating across Triassic evaporites. The late and post hyper-extensional phase is characterized by hydraulic brecciation in dolomitic formations, a decrease in temperature and salinity, a decrease in magmatic contribution in parent fluids, a closing of the diagenetic system during burial and a switch to reducing conditions during the precipitation of quartz, pyrite and calcite. The Pyrenean compressive phase associated with the third fracturing stage induced a reopening of the diagenetic system and favored a return to oxidizing conditions and infiltrations of meteoric fluids.     

The impact of organic fluids on the carbon isotopic compositions of carbonate-rich reservoirs: Case study of the Lucaogou Formation in the Jimusaer Sag,Junggar Basin,NW China

The processes involved in the interaction between organic fluids and carbonates, and the resulting effect on reservoir quality during the evolution and maturation of organic matter remain unclear despite the fact that these processes influence the carbon and oxygen isotopic compositions of carbonates. Here, we provide new insights into these processes using data obtained from a detailed analysis of a mixed dolomitic–clastic and organic-rich sedimentary sequence within the middle Permian Lucaogou Formation in the Junggar Basin of NW China. The techniques used during this study include drillcore observations, thin section petrography, scanning electron microscopy (SEM) and electron probe microanalysis, and carbon and oxygen isotope analyses. Oil grades and total organic carbon (TOC) contents represent the amount of oil charging and the abundance of organic fluids within a reservoir, respectively, and both negatively correlate with the whole-rock δ¹³C and δ¹⁸O of the carbonates in the study area, indicating that organic fluids have affected the reservoir rocks. Secondary carbonates, including sparry calcite and dolomite overgrowths and cements, are common within the Lucaogou Formation. Well-developed sparry calcite is present within dark mudstone whereas the other two forms of secondary carbonates are present within the dolomite-rich reservoir rocks in this formation. Comparing thin section petrology with δ¹³C compositions suggests that the carbon isotopic composition of matrix carbonates varies little over small distances within a given horizon but varies significantly with stratigraphic height as a result of the development of secondary carbonates. The net change in whole-rock δ¹³C as a result of these secondary carbonates ranges from 1.8‰ to 4.6‰, with the secondary carbonates having calculated δ¹³C compositions from −18.6‰ to −8.5‰ that are indicative of an organic origin. The positive correlation between the concentration of Fe within matrix and secondary carbonates within one of the samples suggests that the diagenetic system within the Lucaogou Formation was relatively closed. The correlation between δ¹³C and δ¹⁸O in carbonates is commonly thought to be strengthened by the influence of meteoric water as well as organic fluids. However, good initial correlation between δ¹³C and δ¹⁸O of whole rock carbonates within the Lucaogou Formation (resulted from the evaporitic sedimentary environment) was reduced by organic fluids to some extent. Consequently, the δ¹³C–δ¹⁸O covariations within these sediments are not always reliable indicators of diagenetic alteration by organic fluids or meteoric water.The characteristics and δ¹³C compositions of the sparry calcite within the formation is indicative of a genetic relationship with organic acids as a result of the addition of organic CO₂ to the reservoir. Further analysis suggests that both carbonate and feldspar were dissolved by interaction with organic CO₂. However, dissolved carbonate reprecipitated as secondary carbonates, meaning that the interaction between organic fluids and dolomites did not directly improve reservoir quality, although this process did enhance the dissolution of feldspar and increase porosity. This indicates that the δ¹³C and δ¹⁸O of secondary carbonates and their influence on whole-rock carbonate isotopic values can be used to geochemically identify the effect of organic fluids on closed carbonate-rich reservoir systems.     

晶体中的空位测量

夫伦克尔［１］提出晶体中的一些原子会自发地离开它们的晶格的格点位置,从而形成一部分空着的晶格位置,即空位,将保持在平衡态。这一观点,首次解释了物质如何在晶体中输运的问题,因为邻近的原子会掉进空位中,使空位本身迁移了。有一类叫快离子导体的导电性是由离子的运动产生的。假如所有的离子都是按照理想状态规规矩矩地处于晶格点阵的位置上,就不可能理解离子怎样通过格点而运动。只有假设晶格点阵中存在空位和原子可能处于点阵中的间隙位置上,才能解释固体中的离子的运动。此后,晶体的空位成为固体物理、固体化学、冶金学乃至…