水对硅酸盐岩体系部分熔融行为的影响：第二临界端点的重要意义

水对硅酸盐岩体系的许多物理-化学行为有着非常重大的影响.具体对部分熔融过程来说,水可以显著地降低熔融温度、改变熔体性质、影响微量元素在固-液相之间的分配.近年来,科学家们就大量水对硅酸盐岩体系的部分熔融过程的影响进行了许多的高压实验,他们主要关注第二临界端点对熔融过程的重要作用:第二临界端点的出现极大地改变着部分熔融过程中的基本相关系.本文主要针对这些高压实验研究做一总结,并对未来研究方向做一初步探讨.     

深层搅拌桩高压旋喷桩及静压注浆联合式挡墙在深基坑中的应用

本文以广东省花都市花都宾馆大厦为例，介绍了深层搅拌桩，高压旋喷桩及静压注浆联合式挡土防渗墙在大砂砾层深基坑中的作用，简述了其设计方案，施工工艺及效果。     

东南极格罗夫山镁铁质麻粒岩的变质作用

东南极内陆－格罗夫山存在一套经历了麻粒岩相变质作用的镁铁质麻粒岩和斜长角闪岩。变质反应结构显示该区多为单一的区域性麻粒岩相变质作用。但是，对含石榴石的镁铁质麻粒岩的详细工作则显示了包括3个阶段的近等温降压（ITD）的顺时针PT演化轨迹，M1：0．93GPa＞800℃：M2:0.65GPa,733-850℃;M3:0.46-0.61GPa，并有着与拉斯曼丘陵相似的演化历史。根据矿物组合和成分、变质反应结构及温压计算结果，格罗夫山镁铁质麻粒岩可能为高压麻粒岩。     

Methane and CO2 sorption and desorption measurements on dry Argonne premium coals: pure components and mixtures

Sorption and desorption behaviour of methane, carbon dioxide, and mixtures of the two gases has been studied on a set of well-characterised coals from the Argonne Premium Coal Programme. The coal samples cover a maturity range from 0.25% to 1.68% vitrinite reflectance. The maceral compositions were dominated by vitrinite (85% to 91%). Inertinite contents ranged from 8% to 11% and liptinite contents around 1% with one exception (Illinois coal, 5%). All sorption experiments were performed on powdered (−100 mesh), dry coal samples.Single component sorption/desorption measurements were carried out at 22 °C up to final pressures around 51 bar (5.1 MPa) for CO₂ (subcritical state) and 110 bar (11 MPa) for methane.The ratios of the final sorption capacities for pure CO₂ and methane (in molar units) on the five coal samples vary between 1.15 and 3.16. The lowest ratio (1.15) was found for the North Dakota Beulah-Zap lignite (VR_r=0.25%) and the highest ratios (2.7 and 3.16) were encountered for the low-rank coals (VR_r 0.32% and 0.48%) while the ratio decreases to 1.6–1.7 for the highest rank coals in this series.Desorption isotherms for CH₄ and CO₂ were measured immediately after the corresponding sorption isotherms. They generally lie above the sorption isotherms. The degree of hysteresis, i.e. deviation of sorption and desorption isotherms, varies and shows no dependence on coal rank.Adsorption tests with CH₄/CO₂ mixtures were conducted to study the degree of preferential sorption of these two gases on coals of different rank. These experiments were performed on dry coals at 45 °C and pressures up to 180 bar (18 MPa). For the highest rank samples of this sequence preferential sorption behaviour was “as expected”, i.e. preferential adsorption of CO₂ and preferential desorption of CH₄ were observed. For the low rank samples, however, preferential adsorption of CH₄ was found in the low pressure range and preferential desorption of CO₂ over the entire pressure range.Follow-up tests for single gas CO₂ sorption measurements consistently showed a significant increase in sorption capacity for re-runs on the same sample. This phenomenon could be due to extraction of volatile coal components by CO₂ in the first experiment. Reproducibility tests with methane and CO₂ using fresh sample material in each experiment did not show this effect.     

Metamorphic path constrained by metapelitic rocks from the inner Aiuruoca-Andrelândia nappe, south of the São Francisco craton, SE Brazil

A Nappe system south to southwest of the São Francisco Craton represents the southern extension of the Brasília belt and describes an inverted metamorphic pile of greenschist facies toward amphibolite facies. The Aiuruoca-Andrelândia nappe is one of the nappes of this system. The hind portion of the Aiuruoca-Andrelândia nappe, south of Caxambu and Aiuruoca (MG), consists of a structural-metamorphic domain transported toward the E-NE. There is a metamorphic transition, from the kyanite zone to kyanite and sillimanite coexistence, until the sillimanite zone. Metapelitic rocks preserve high-pressure parageneses (Rt–Ky–Grt–Ms–Bt–Pl–Qtz) and contain retrograde eclogitic rocks. Sil–Pl–Qtz coronitic intergrowths around garnets are common decompressive textures. Kyanite schists register the P_max of 11 kbar at 660 °C and define a decompressive path until 6–7.5 kbar at 650 °C. These P–T conditions represent the equilibrium in S₂ schistosity (amphibolite facies) and the beginning of the cooling path in the Ky–Sil transition. The decompressive path suggests an extrusional process, immediately after burying at about 60 km. Exhumation controlled by convergent events, related to the São Francisco Plate subduction and tectonic erosion, took these units, isothermally, to higher levels (20–33 km). Later, the metamorphic path shifted toward near-isobaric cooling.     

Evolution of the REE mineralogy in HP–LT metapelites of the Sebtide complex, Rif, Morocco: Monazite stability and geochronology

REE mineralogy was characterized at the micrometer scale (using scanning electron microscopy) in the four tectono-metamorphic units of the Beni Mzala window, Sebtide Complex, Internal Rif, Morocco, which sample a HP-LT metamorphic gradient from subgreenschist to blueschist/eclogite facies. These tectonic units are composed of garnet-free metapelites (and associated synmetamorphic veins) from the same homogeneous aluminium-rich and calcium-poor protolith. In that context, mineralogical differences between units are assumed to result from contrasted pressure and temperature histories. Light REE-bearing Al-phosphates of the crandallite group with florencite-rich composition and variable goyazite content are the dominant LREE minerals in the lowest-grade units, Tizgarine (300 °C, 3 kbar as peak conditions) and Boquete de Anjera (350 °C, 10 kbar). In the latter unit, metamorphic florencite is associated with MREE-rich monazite. In the schist of the highest-grade units, Beni Mzala 2 (420–450 °C, 12 kbar) and Beni Mzala 1 (550 °C, 16 kbar), associations of allanite-rich epidote and synchisite (a LREE-fluorocarbonate) are found whereas florencite and monazite are no longer observed. At the wall of the quartz–kyanite veins, retrograde monazite-(Ce) with grain size of 20 to 50 μm is the only LREE-bearing mineral. Th–Pb and U–Pb SIMS data on some of these grains yield ages of 21.3 ± 1.7 Ma and 20.9 ± 2.1 Ma, respectively, consistent with previous K–Ar ages obtained on retrograde clay–mica mixtures in rocks from the same locality. The identification of a stability field for monazite in high-pressure aluminous metapelites with an upper thermal-limit below 450 °C as well as the derivation of meaningful U–Pb and Th–Pb SIMS ages demonstrates the monazite potential for dating HP-LT metapelites. However, since, under these conditions, monazite growth occurs below its admitted closure-temperature, these ages must be interpreted on the basis of monazite textural relationships.     

俯冲洋岛玄武岩脱水释放的水流体成分：来自西天山榴辉岩相高压脉的约束

俯冲洋壳的脱水作用对于岛弧火山岩的成因具有重要意义。西天山高压低温变质带中切割主岩蓝片岩/榴辉岩的榴辉岩相脉体记录了古生代俯冲带中的脱水过程。脉体具有典型高压矿物组合：石榴石(＞8%)+绿辉石(15%)+石英(＞55%)+蓝闪石(5%)+冻蓝闪石(10%)±黝帘石±方解石。高压脉及其主岩的岩相学与矿物化学研究表明流体是在俯冲过程中蓝片岩向榴辉岩进变质条件下释放。脉的主量元素成分显示流体富Si。主岩的稀土元素和微量元素表明其原岩为洋岛玄武岩(OIB)。脉和主岩具有相似的微量元素配分模式,并且相对N-MORB都显示富Li、Be、Cs、Rb、Ba、Pb、La的特点。通过模拟计算,在高压脉、与脉平衡的流体以及模拟的原生流体中都富集流体活动性元素(Li、Be、Pb)和LILE(Cs、Rb、Ba),贫HFSE(Nb)和REE(Nd、Sm)。证实了在古生代南天山洋俯冲时洋岛玄武岩脱水释放出富Li、Be、LILE、La和Pb,贫HFSE和HREE的流体。     

喜马拉雅中段哲古拉花岗岩中高压麻粒岩包体及其主岩的^40Ar／^39Ar年代学研究

为了深入了解喜马拉雅构造带的地质演化历史,同时为了探讨作为建立高压变质条件下的同位素年代学方法的重要前提的同位素体系特征,对出露于喜马拉雅中段西藏哲古拉地区的高压麻粒岩包体中的峰期矿物和退变质矿物及其主岩花岗岩中的富钾矿物进行了常规~(40)Ar/~(39) Ar 年代学研究。花岗岩中的黑云母坪年龄为11.48±0.18Ma,钾长石坪年龄为12.63±0.19Ma,二者的等时线年龄与之相当,分别为11.63Ma 和12.58Ma。高压麻粒岩峰期矿物黑云母的坪年龄为48.5±0.54Ma,等时线年龄为48.95±0.83Ma,(~(40)Ar/~(36)Ar)_i 为285;退变质矿物角闪石的坪年龄谱呈马鞍形,坪区数据对应的等时线年龄为31.1±5.4Ma,(~(40)Ar/~(36)Ar)_i 为394,显示有过剩~(40)Ar 的存在。结合前人的研究,推定高压麻粒岩经历了一个快速的退变质作用过程,不仅变质作用没有达到平衡,早期与晚期变质矿物之间也没有达成氩同位素交换平衡,在标本尺度上或高压麻粒岩包体与主岩花岗岩之间均是如此。根据~(40)Ar/~(39)Ar 年代学结果也可以了解到,在高压麻粒岩的退变质过程中,早期与晚期变质矿物之间的氩同位素体系有明显不同,这种氩同位素体系在不同变质阶段的不平衡记录为帮助建立不同变质地质事件的年代学序列提供了研究途径。依照获得的~(40)Ar/~(39)Ar 年代学数据,可以建立喜马拉雅中段高压麻粒岩包体形成和演化的动力学过程:推定高压麻粒岩经受了两期变质作用的叠加,峰期变质老于48.5Ma,晚期变质发生在31Ma 前后;大约在17Ma 前后为其主岩花岗岩捕虏,并在11Ma～12Ma 之间被带至地表。文中对前人锆石 U-Pb 年龄进行了再分析,认为在高压变质作用条件下,由于熔体或流体从变质岩石中被抽提出去而限制了变质锆石的生长,因此,高压麻粒岩包体中的锆石 U-Pb 年龄没有能够记录高压变质事件。     

Effect of high-pressures on the electrical resistivity of natural zeolites from Deccan Trap, Maharashtra, India

We report here the electrical resistivity measurements on two natural zeolites–natrolite and scolecite (from the Killari borehole, Maharashtra, India) as a function of pressure up to 8 GPa at room temperature. High-pressure electrical resistivity studies on hydrous alumino-silicate minerals are very helpful in understanding the role of water in deep crustal conductivities obtained from geophysical models. The results obtained by magneto-telluric (MT) soundings and direct current resistivity surveys, along with the laboratory data on the electrical resistivity of minerals and rocks at high-pressure–temperature are used to determine the electrical conductivity distribution in continental lithosphere. The electrical resistivity of natural natrolite decreases continuously from 2.9 × 10⁹ Ω cm at ambient condition to 7.64 × 10² Ω cm at 8 GPa, at room temperature. There is no pressure-induced first order structural phase transitions in natrolite, when it is compressed in non-penetrating pressure transmitting medium up to 8 GPa. On the other hand scolecite exhibits a pressure-induced transition, with a discontinuous decrease of the electrical resistivity from 2.6 × 10⁶ to 4.79 × 10⁵ Ω cm at 4.2 to 4.3 GPa. The observed phase transition in scolecite is found to be irreversible. Vibrational spectroscopic and X-ray diffraction studies confirm the amorphous nature of the high-pressure phase. The results of the present high-pressure studies on scolecite are in good agreement with the high-pressure Raman spectroscopic data on scolecite. The thermo gravimetric studies on the pressure-quenched samples show that the samples underwent a pressure-induced partial dehydration. Such a pressure-induced partial dehydration, which has been observed in natural scolecite could explain the presence of high conductive layers in the earth's deep-crust.     

高压旋喷桩与倾斜锚固桩在加固岩溶强烈发育地基中的应用

以中国人民银行怀化分行营业大楼为例,探讨高压旋喷注浆技术和倾斜锚固技术在加固岩溶强烈发育地基中应用的基本工艺,该工程基础原设计为冲击成孔嵌岩灌注桩,因岩基中溶洞发育,在中南部还存在一个深度超过100m的大型溶槽,岩面起伏极大,施工和成桩困难、进度极慢,造价较高,针对上述实际情况,为减小施工难度,加快施工进度,降低造价,改用高压旋喷桩加固土体地基及倾斜锚固桩处理大型溶槽,并取得了良好的效果.