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1.
We present a structural analysis of serpentine-bearing faults and shear zones in the Koniambo Massif, one of the klippes of the Peridotite Nappe of New Caledonia. Three structural levels are recognized. The upper level is characterized by a dense network of fractures. Antigorite and polygonal serpentine form slickenfibers along fault planes with distinct kinematics. As a result, the upper level keeps the record of at least two deformation events, the first associated with the growth of antigorite (WNW-ESE extension), the second with the growth of polygonal serpentine (NW–SE compression). The lower level coincides with the ‘serpentine sole’ of the nappe, which consists of massive tectonic breccias overlying a layer of mylonitic serpentinites. The sole records pervasive tangential shear with top-to-SW kinematics and represents a décollement at the base of the nappe. The intermediate level is characterized by the presence of several meters-thick conjugate shear zones accommodating NE–SW shortening. Like the sole, these shear zones involve polygonal serpentine and magnesite as the main syn-kinematic mineral phases. The shear zones likely root into the basal décollement, either along its roof or, occasionally, around its base. Compared to top-to-SW shearing along the sole, the two deformation events recorded in the upper level are older.The three structural levels correlate well with previously recognized spatial variations in the degree of serpentinization. It is therefore tempting to consider that the intensity of serpentinization played a major role in the way deformation has been distributed across the Peridotite Nappe. However, even the least altered peridotites, in the upper level, contain so much serpentine that, according to theoretical and experimental work, they should be nearly as weak as pure serpentinite. Hence, no strong vertical gradient in strength due to variations in the degree of serpentinization is expected within the exposed part of the nappe. Our proposal is that strain localization along the serpentine sole results from the juxtaposition of the nappe, made of weak serpentinized peridotites, against the strong mafic rocks of its substratum. This interpretation is at odds with the intuitive view that would consider the nappe, made of peridotites, as stronger than its basement. 相似文献
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Konstantin D. Litasov Yingwei Fei Eiji Ohtani Takahiro Kuribayashi Kenichi Funakoshi 《Physics of the Earth and Planetary Interiors》2008,168(3-4):191-203
Pressure–volume–temperature relations have been measured to 32 GPa and 2073 K for natural magnesite (Mg0.975Fe0.015Mn0.006Ca0.004CO3) using synchrotron X-ray diffraction with a multianvil apparatus at the SPring-8 facility. A least-squares fit of the room-temperature compression data to a third-order Birch–Murnaghan equation of state (EOS) yielded K0 = 97.1 ± 0.5 GPa and K′ = 5.44 ± 0.07, with fixed V0 = 279.55 ± 0.02 Å3. Further analysis of the high-temperature compression data yielded the temperature derivative of the bulk modulus (∂KT/∂T)P = −0.013 ± 0.001 GPa/K and zero-pressure thermal expansion α = a0 + a1T with a0 = 4.03 (7) × 10−5 K−1 and a1 = 0.49 (10) × 10−8 K−2. The Anderson–Grüneisen parameter is estimated to be δT = 3.3. The analysis of axial compressibility and thermal expansivity indicates that the c-axis is over three times more compressible (KTc = 47 ± 1 GPa) than the a-axis (KTc = 157 ± 1 GPa), whereas the thermal expansion of the c-axis (a0 = 6.8 (2) × 10−5 K−1 and a1 = 2.2 (4) × 10−8 K−2) is greater than that of the a-axis (a0 = 2.7 (4) × 10−5 K−1 and a1 = −0.2 (2) × 10−8 K−2). The present thermal EOS enables us to accurately calculate the density of magnesite to the deep mantle conditions. Decarbonation of a subducting oceanic crust containing 2 wt.% magnesite would result in a 0.6% density reduction at 30 GPa and 1273 K. Using the new EOS parameters we performed thermodynamic calculations for magnesite decarbonation reactions at pressures to 20 GPa. We also estimated stability of magnesite-bearing assemblages in the lower mantle. 相似文献
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V. Sedlák 《Geotechnical and Geological Engineering》1993,11(1):25-35
Summary Geophysical principles have a very extensive and important application in borehole technologies. A special form of magnetometry for borehole deviation measurement in certain special cases of tunnelling and driving other underground workings is presented. The mutual position of boreholes arranged in groups, used for driving underground workings in water-bearing layers by freezing and grouting methods, is determined. 相似文献
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Ian M. Power Siobhan A. Wilson James M. Thom Gregory M. Dipple Janet E. Gabites Gordon Southam 《Chemical Geology》2009,260(3-4):286-300
Anthropogenic greenhouse gas emissions may be offset by sequestering carbon dioxide (CO2) through the carbonation of magnesium silicate minerals to form magnesium carbonate minerals. The hydromagnesite [Mg5(CO3)4(OH)2·4H2O] playas of Atlin, British Columbia, Canada provide a natural model to examine mineral carbonation on a watershed scale. At near surface conditions, CO2 is biogeochemically sequestered by microorganisms that are involved in weathering of bedrock and precipitation of carbonate minerals. The purpose of this study was to characterize the weathering regime in a groundwater recharge zone and the depositional environments in the playas in the context of a biogeochemical model for CO2 sequestration with emphasis on microbial processes that accelerate mineral carbonation.Regions with ultramafic bedrock, such as Atlin, represent the best potential sources of feedstocks for mineral carbonation. Elemental compositions of a soil profile show significant depletion of MgO and enrichment of SiO2 in comparison to underlying ultramafic parent material. Polished serpentinite cubes were placed in the organic horizon of a coniferous forest soil in a groundwater recharge zone for three years. Upon retrieval, the cube surfaces, as seen using scanning electron microscopy, had been colonized by bacteria that were associated with surface pitting. Degradation of organic matter in the soil produced chelating agents and acids that contributed to the chemical weathering of the serpentinite and would be expected to have a similar effect on the magnesium-rich bedrock at Atlin. Stable carbon isotopes of groundwater from a well, situated near a wetland in the southeastern playa, indicate that 12% of the dissolved inorganic carbon has a modern origin from soil CO2.The mineralogy and isotope geochemistry of the hydromagnesite playas suggest that there are three distinct depositional environments: (1) the wetland, characterized by biologically-aided precipitation of carbonate minerals from waters concentrated by evaporation, (2) isolated wetland sections that lead to the formation of consolidated aragonite sediments, and (3) the emerged grassland environment where evaporation produces mounds of hydromagnesite. Examination of sediments within the southeastern playa–wetland suggests that cyanobacteria, sulphate reducing bacteria, and diatoms aid in producing favourable geochemical conditions for precipitation of carbonate minerals.The Atlin site, as a biogeochemical model, has implications for creating carbon sinks that utilize passive microbial, geochemical and physical processes that aid in mineral carbonation of magnesium silicates. These processes could be exploited for the purposes of CO2 sequestration by creating conditions similar to those of the Atlin site in environments, artificial or natural, where the precipitation of magnesium carbonates would be suitable. Given the vast quantities of Mg-rich bedrock that exist throughout the world, this study has significant implications for reducing atmospheric CO2 concentrations and combating global climate change. 相似文献
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中国辽东地区超大型菱镁矿矿床的地球化学特征和成因模式 总被引：4，自引：1，他引：4
我国辽东地区早元古代大石桥组镁质碳酸盐-泥质岩建造中赋存有多个超大型菱镁矿矿床。在这些矿床中,菱铁矿矿体均只限定在大石桥组三段岩层中。该层岩石主要由白云质大理岩、菱镁质大理岩、菱镁矿和少量泥质板岩薄层组成。赋矿层位之下地层为大石桥组二段的云母片岩;其下为大石桥组一段的白云质大理岩与云母片岩夹层。在大石桥组一段中未见菱铁矿体产出。研究表明,菱铁矿的δ18O值为5.2‰~13.8‰,低于围岩大理岩的δ18O值(11.2‰~22.8‰)。但两音的δ13C值大多接近零值,其中菱镁矿δ13C值变化为-1.4‰~1.2‰,大理岩δ13C值变化为-4.5‰~4 4‰。在菱镁矿层位中发现有石膏成层和脉状产出,其δ34S值为23.9‰~26.5‰,显示海相蒸发沉积特征。菱镁矿的稀土元素分析表明存在三种不同页岩标准化配分模式。类型Ⅰ显示中稀土富集特征,类型Ⅲ显示重稀土富集和正铕异常特征,它们可能反映了不同时期成矿热液的特征。而类型Ⅱ显示与围岩大理岩相同的平坦型,反映继承了原岩沉积碳酸盐岩的特征。本文认为,辽东地区的镁质碳酸盐岩(镁方解石和白云石)可能是从蒸发的泻湖盆地中沉积的,而菱镁矿石则主要是沉积后富镁卤水下渗交代原岩碳酸盐岩形成的。由于大石桥组二段云母片岩渗透率低隔水性强,因此菱铁矿的矿化交代作用只发 相似文献
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Peter Bajto 《岩石学报》2004,20(4)
Dubravsky Massif菱镁矿体的开采产生了部分局限在石炭纪低裂缝渗透变质岩中的喀斯特型裂缝含水层。大量的开矿过程对含水层中的地下水循环和化学成分都造成了可观的变化。本文研究了在这种复杂条件下地下水化学成分变化成因模型。根据化学配位模型,计算出所选矿物的饱和指数,从而指示所有喀斯特裂缝含水层饱和带中的地下水对菱镁矿、白云石、方解石的过饱和度和石膏的不饱和度。假设地下水未受人类活动的污染,而白云石中黄铁矿的氧化对成矿影响甚微,则水化学数据的统计描述代表了含水层中的水文地球化学背景。矿山中矿石焙烧释放的富氮气体凝聚产生的醋酸,能促进菱镁矿和白云石的溶解。这样产生的地下水相对背景值来说则富集NO3,Mg,和TIC。因此,由于地下开矿,岩溶作用估计将是原来的1.5倍。尽管有污染,这些所测参数并没有超过斯洛伐克卫生保健部颁发的No.29／2002 Z.z.饮用水标准临界值。因此采矿后含水层的开采也是可行的。 相似文献
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当前我国尚无菱镁矿、蛇纹岩、高品位碲金矿化学成分标准物质,国外相应标准样品存在定值元素少,且主成分含量不成系列,不能满足地质行业对菱镁矿、蛇纹岩、碲金矿标准物质的迫切需求。该文研制了菱镁矿、蛇纹岩、碲金矿化学成分标准物质共12个,将采自典型矿区的样品按照常规球磨方式粉碎混匀,采用电感耦合等离子体发射光谱法(ICP-AES)和电感耦合等离子体质谱法(ICP-MS)进行均匀性和稳定性检验,选择11家有资质的实验室,采取经典分析方法与现代仪器分析方法相结合的方式,选用2种以上不同原理的准确度高的可靠方法对该标准物质联合定值,依照JJF 1343—2012和一级标准物质技术规范,12个化学成分标准物质给出了30项主、微量元素的认定值和不确定度。其中,菱镁矿Mg O的含量范围为43.64%~81.26%,蛇纹岩Mg O的含量范围为23.73%~43.09%,高品位碲金矿Au的含量范围为19.6×10~(-6)~32.1×10~(-6)、Te的含量范围为51×10~(-6)~83×10~(-6),基本涵盖我国菱镁矿、蛇纹岩、高品位碲金矿的矿物类型,能够满足菱镁矿、蛇纹岩、碲金矿勘查、评价和开发的需求。 相似文献
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Mine
zdemir Dilek ak&#x;r &#x;lker K&#x;pak 《International Journal of Mineral Processing》2009,93(2):209-212
The recovery of magnesium from magnesite tailings in aqueous hydrochloric acid solutions by acid leaching was studied in a batch reactor using hydrochloric acid solutions. Subsequent, production of magnesium chloride hexahydrate (MgCl2.6H2O) from leaching solution was also investigated. The effects of temperature, acid concentration, solid-to-liquid ratio, particle size and stirring speed on the leaching process were investigated. The pseudo-second-order reaction model seemed to be appropriate for the magnesium leaching. The activation energy of the leaching process was estimated to be 62.4 kJ mol− 1. Finally, MgCl2.6H2O in a purity of 91% was produced by evaporation of leaching solution obtained at a temperature of 40 °C, 1.0 M acid, solid-to-liquid ratio of 10 g/L, particle size of 100 µm, stirring speed of 1250 rpm and leaching time of 60 min. 相似文献
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