Hydromechanical coupling in response to earthquakes: on the possible consequences for aftershocks   总被引：1，自引：0，他引：1  

Pierre Gavrilenko 《Geophysical Journal International》2005,161(1):113-129

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Zebra dolomitization as a result of focused fluid flow in the Rocky Mountains Fold and Thrust Belt, Canada   总被引：4，自引：0，他引：4  

VEERLE VANDEGINSTE  RUDY SWENNEN  SARAH A. GLEESON†  ROB M. ELLAM‡  KIRK OSADETZ§  FRANÇOIS ROURE¶ 《Sedimentology》2005,52(5):1067-1095

Discordant zebra dolomite bodies occur locally in the Middle Cambrian Cathedral and Eldon Formations of the Main Ranges of the Canadian Rocky Mountains Fold and Thrust Belt. They are characterized by alternating dark grey (a) and white (b) bands, forming an ‘abba’ diagenetic cyclicity. These bands developed parallel to both bedding and cleavage. Dark grey (a) bands consist of fine (< 300 μm) non-planar crystalline impure dolomite. The white (b) bands are composed of coarse (up to several millimetres) milky-white pure saddle dolomites (b1) which are often covered by pore-lining zoned dolomite (b2). The b phases often possess a saddle-shaped morphology. In contrast to the replacement origin of the a dolomite, the zoned b2 dolomite rims are interpreted as a cement formed in open cavities. The b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non-carbonate components. All the zebra dolomites studied are (nearly) stoichiometric and are characterized by enriched Na and depleted Sr concentrations. Fe and Mn concentrations in these dolomites differ depending on the sample locality. Fluid inclusion data indicate that the dolomites formed from relatively hot (T_H = 130–200 °C), saline (20–23 wt% CaCl₂ eq.) fluids. A diagenetic high temperature origin is also supported by depleted δ¹⁸O values (−20 to −14‰ VPDB). A contribution of ⁸⁷Sr-enriched fluids is reflected in the ⁸⁷Sr/⁸⁶Sr values (0·7091–0·7123). Zebra dolomite development is explained by focused fluid flow, which exploited areas of structural weaknesses (e.g. basin-platform, rim areas, faults, etc.). Expulsion of hot basinal brines in a tectonically active regime generated overpressures, which explains the development of secondary porosity during zebra dolomitization as well as the intra-zebra fracturing at decimetre to micrometre scale.  相似文献   

Preferential embrittlement of graphitic schists during extensional unroofing in the Alps: the effect of fluid composition on rheology in low-permeability rocks   总被引：3，自引：0，他引：3  

J. SELVERSTONE 《Journal of Metamorphic Geology》2005,23(6):461-470

Interlayered graphitic and non‐graphitic schists from the Tauern Window, Eastern Alps, record contrasting mechanical behaviour during extensional exhumation. Graphitic schists contain mesoscale extension fractures, pervasive microcracks in garnet, and abundant secondary fluid inclusion planes; all three types of structures are oriented perpendicular to the stretching lineation. Crack spacings in garnet from graphitic samples are tightly clustered around a mean of 180 μm. Non‐graphitic schists have fewer and more randomly oriented microcracks and fluid inclusion planes and maintained strain compatibility via crystal plasticity. The presence or absence of graphite appears to have exerted a fundamental control on rheology during unroofing. Calculations for a model graphitic rock at 500 °C and f_O2 = 10^?24 MPa show that the equilibrium metamorphic fluid evolves from X_CO2 = 0.07 to 0.38 during decompression from 700 to 400 MPa, in agreement with microcrack fluid inclusion data that show a change from X_CO2 < 0.1 to 0.45 in graphitic samples over the same pressure interval. This compositional shift results in >60% expansion of the pore fluid during decompression. H₂O‐rich fluid in non‐graphitic rocks expands <15% over the same pressure interval. The greater pore fluid expansion in low‐permeability graphitic horizons likely promoted tensile failure during unroofing. These results suggest that microcracking should be an inevitable consequence of decompression in many graphitic schists, whereas rocks that lack graphite are less likely to undergo microcracking. Microseismicity is predicted to be more common in graphitic than non‐graphitic rocks during unroofing of mountain belts.  相似文献   

Hydrothermal Quartz Vein Formation, Revealed by Coupled SEM-CL Imaging and Fluid Inclusion Microthermometry: Shuteen Complex, South Gobi, Mongolia     

Bayaraa Batkhishig    Greg Bignall  Noriyoshi Tsuchiya 《Resource Geology》2005,55(1):1-8

Abstract. Scanning electron microscopy-cathodoluminescence (SEM-CL) imaging of vein quartz in the Cu-mineralised, Shuteen Complex (South Gobi, Mongolia) has revealed a complex history of crystal growth, dissolution and microfracture healing, associated with several hydrothermal events that could not be detected using other observational techniques (e.g. transmitted/reflected light microscopy, back-scattered electron imaging, or secondary electron imaging).
The quartz initially grew as CL-bright/grey crystals in a 345±30C liquid reservoir, as inferred by the analysis of primary liquid fluid inclusions (average Th of 343C; 6.6∼7.7 wt% NaCl_eq). Quartz precipitation occurred at the edge of the crystals as reservoir fluids cooled to 260±25C, as indicated by micron-scale CL-dark/CL-bright quartz growth bands containing abundant fluid inclusions (with an average T_h values of 261C). Pressure fluctuations were the likely cause of dissolution, as SEM-CL imaging reveals the quartz have corroded or rounded crystal edges, and precipitation of later quartz into open space. SEM-CL imaging shows the quartz contains healed microfractures that trapped low salinity fluids (3.9 wt% NaC1_eq) with Th values of 173±15C.
SEM-CL imaging provides a means of deciphering the thermal and chemical evolution of the fossil Shuteen hydrothermal system, and the nature of hydrothermal quartz vein-forming processes, by facilitating the correlation of distinct fluid inclusion populations and their relative chronology, with specific hydrothermal events.  相似文献   

Primary Ore Mineral Assemblage and Fluid Inclusion Study of the Batu Hijau Porphyry Cu-Au Deposit, Sumbawa, Indonesia   总被引：3，自引：0，他引：3  

Akira Imai  Satoshi Ohno 《Resource Geology》2005,55(3):239-248

Abstract. The Batu Hijau porphyry Cu‐Au deposit, Sumbawa Island, Indonesia, is associated with a tonalitic intrusive complex. The temperature‐pressure condition of mineralization at the Batu Hijau deposit is discussed on the basis of fluid inclusion microthermometry. Then, the initial Cu‐Fe sulfide mineral assemblage is discussed. Bornite and chalcopyrite are major copper ore minerals associated with quartz veinlets. The quartz veinlets have been classified into ‘A’ veinlets associated with bornite, digenite, chalcocite and chalcopyrite, ‘B’ veinlets having chalcopyrite bornite along vuggy center‐line, rare ‘C’ chalcopyrite‐quartz veinlets, and late ‘D’ veinlets consisting of massive pyrite and quartz (Clode et al., 1999). Copper and gold mineralization is associated with abundant ‘A’ quartz veinlets. Abundant fluid inclusions are found in veinlet quartz consisting mainly of gas‐rich inclusions and polyphase inclusions throughout the veinlet types. The hydrothermal activity occurred in temperature‐pressure conditions of aqueous fluid immiscibility into hypersaline brine and dilute vapor. The halite dissolution (Tm[halite]) and liquid‐vapor homogenization (Th) temperatures of the polyphase inclusions in veinlet quartz range from 270 to 472d?C and from 280 to 454d?C, respectively. The estimated salinity ranges from 36 to 47 wt% (NaCl equiv.). The apparent pressures lower than 300 bars are estimated to have been along the liquid‐vapor‐halite curve for the fluid inclusions having the Th lower than the Tm that trapped the brine saturated with halite, or at slightly higher pressure relative to liquid‐vapor‐halite curve for the fluid inclusions having the Th higher than the Tm that trapped the brine unsaturated with halite. The actual temperature and pressure during the hydrothermal activity at the Batu Hijau deposit are estimated to have been around 300d?C and 50 bars. At such temperature‐pressure conditions, the principal and initial Cu‐Fe sulfide mineral assemblages are thought to be chalcopyrite + bornite solid solution (bnss) for the chalcopyrite‐bearing assemblage, and chalcocite‐digenite solid solution and bnss for the chalcopyrite‐free assemblage.  相似文献   

Evolution of Hydrothermal System at the Dizon Porphyry Cu-Au Deposit, Zambales, Philippines     

Akira Imai 《Resource Geology》2005,55(2):73-90

Abstract. Evolution of hydrothermal system from initial porphyry Cu mineralization to overlapping epithermal system at the Dizon porphyry Cu‐Au deposit in western central Luzon, Zambales, Philippines, is documented in terms of mineral paragen‐esis, fluid inclusion petrography and microthermometry, and sulfur isotope systematics. The paragenetic stages throughout the deposit are summarized as follows; 1) stockwork amethystic quartz veinlets associated with chalcopyrite, bornite, magnetite and Au enveloped by chlorite alteration overprinting biotite alteration, 2) stockwork quartz veinlets with chalcopyrite and pyrite associated with Au and chalcopyrite and pyrite stringers in sericite alteration, 3) stringer quartz veinlets associated with molybdenite in sericite alteration, and 4) WNW‐trending quartz veins associated with sphalerite and galena at deeper part, while enargite and stibnite at shallower levels associated with advanced argillic alteration. Chalcopyrite and bornite associated with magnetite in quartz veinlet stockwork (stage 1) have precipitated initially as intermediate solid solution (iss) and bornite solid solution (bnss), respectively. Fluid inclusions in the stockwork veinlet quartz consist of gas‐rich inclusions and polyphase inclusions. Halite in polyphase inclusions dissolves at temperatures ranging from 360d?C to >500d?C but liquid (brine) and gas (vapor) do not homogenize at <500d?C. The maximum pressure and minimum temperature during the deposition of iss and bnss with stockwork quartz veinlets are estimated to be 460 bars and 500d?C. Fluid inclusions in veinlet stockwork quartz enveloped in sericite alteration (stage 2) consist mainly of gas‐rich inclusions and polyphase inclusions. In addition to the possible presence of saturated NaCl crystals at the time of entrapment of fluid inclusions that exhibit the liquid‐vapor homogenization temperatures lower than the halite dissolution temperatures in some samples, wide range of temperatures of halite dissolution and liquid‐vapor homogenization of polyphase inclusions from 230d?C to >500d?C and from 270d?C to >500d?C, respectively, suggests heterogeneous entrapment of gaseous vapor and hypersaline brine. The minimum pressure and temperature are estimated to be about 25 bars and 245d?C. Fluid inclusions in veinlet quartz associated with molybdenite (stage 3) are dominated by gas‐rich inclusions accompanied with minor liquid‐rich inclusions that homogenize at temperatures between 350d?C and 490d?C. Fluid inclusions in vuggy veinlet quartz associated with stibnite (stage 4) consist mainly of gas‐rich inclusions with subordinate polyphase inclusions that do not homogenize below 500d?C. Fluid inclusions in veinlet quartz associated with galena and sphalerite (stage 4) are composed of liquid‐rich two‐phase inclusions, and they homogenize into liquid phase at temperatures ranging widely from 190d?C to 300d?C (suggesting boiling) and the salinity ranges from 1.0 wt% to 3.4 wt% NaCl equivalent. A pressure of about 15 bars is estimated for the dilute aqueous solution of 190d?C from which veinlet quartz associated with galena and sphalerite precipitated. In addition to a change in temperature‐pressure regime from lithostatic pressure during the deposition of iss and bnss with stockwork quartz veinlets to hydrostatic pressure during fracture‐controlled quartz veinlet associated with galena and sphalerite, a decrease in pressure is supposed to have occurred due to unroofing or removal of the overlying piles during the temperature decrease in the evolution of hydrothermal system. The majority of the sulfur isotopic composition of sulfides ranges from ±0 % to +5 %. Sulfur originated from an iso‐topically uniform and homogeneous source, and the mineralization occurred in a single hydrothermal system.  相似文献   

金龙——丘岭金矿床成矿流体的储运规律及区域找金方向     

刘新会 刘爽李渊  魏宽义 《地质找矿论丛》2005,20(8):10-14

金龙山——丘岭金矿区含金矿源为层上泥盆统南羊山组和下石炭统袁家沟组。组成含金矿源层岩石为高频互层的细碎屑岩-碳酸盐岩，其中细砂岩、粉砂岩、碳酸盐岩含成矿流体物性较好．页岩、板岩含成矿流体物性较差，构成屏蔽层。金鸡岭Ⅰ级复式向斜控制着金、砷、锑等异常范围；松枣Ⅱ级复式背斜控制着金的矿化带；金龙山-丘岭金矿Ⅲ级背斜控制着金的矿（化）体；镇安——板岩镇断裂的次级断裂是金矿化体的容矿有利位置。在成矿过程中，构造变形与成矿流体的形成、运移及储集密切相关。其规律是：①原生构造导致成矿流体的初次聚集。②第一期构造变形导致成矿流体的聚集。③第二期构造变形导致成矿流体运移及金矿床形成。此期变形是金的主要成矿期。④第三期构造变形使成矿流体进一步聚集和金矿体的富集。⑤第四期构造变形是石英方解石脉的形成时期。总结出矿床形成模式。据此提出了在4种不同的构造部位找金的方向。  相似文献   

雅满苏铁矿床地质特征及成因浅析     

王兴保 《地质找矿论丛》2005,20(8):125-128

雅满苏铁矿矿体的空间分布受成矿期断裂构造的控制，呈透镜状、舒缓波状延伸，分3个层位产出。铁矿的形成与火山热液活动关系密切，矿体中既有热液活动的特征又有矿质流体贯入的特征，早期热液活动形成交代充填型矿石，后期富铁流体贯入充填后形成品位较高的磁铁矿体。  相似文献   

新型充气钻井液在新疆严重漏失地层的应用          下载免费PDF全文

夏建国  乌效鸣  胡郁乐 《探矿工程》2005,32(9):46-48,51

利用特殊植物纤维KWS作为泥浆处理剂的新型充气钻井液，不仅具有常规充气钻井液低密度、排粉能力强、节约用水等优点，还可以不受钠、钙离子的影响，提高钻井泡沫稳定性和钻井液抗盐能力。通过采用此种新型充气钻井液，利用其低密度特性、特殊泥饼、泡沫的群体封堵作用和泡沫的疏水屏蔽作用，成功解决了裂隙地层的漏失问题，恢复了钻探生产。在我国西部干旱缺水漏失地区具有良好的应用前景。  相似文献   

浙江江山石鼓水库除险加固工程技术措施          下载免费PDF全文

龚新晖  郐开富  刘席军 《探矿工程》2005,32(4):31-34

根据浙江江山石鼓水库大坝的结构构造特点、水库地质条件以及水库病险原因与状况，制定出一套科学完善的病险水库除险加固工程技术措施和施工操作规程，对病险水库进行了全面彻底治理，并取得良好效果。详细介绍了工程病险状况，除险加固方案设计，施工工艺及操作规程，加固效果检测及评价等。  相似文献