Compositions, Proportions, and Equilibrium Temperature of Coexisting Two-feldspar in Crystalline Rocks

Compositions, proportions, and equilibrium temperature of coexisting two-feldspar in crystalline rocks are of great importance to classification in petrography and interpretation of petrogenesis. Crystalline rocks are usually composed of 4-6 minerals (phases), depending on their independent chemical components and the equilibrium temperature of crystallizations. In general, number of mineral phases can be determined by the “Phase Rule”. According to the mass balance principle, bulk composition of coexisting two-feldspar could be evaluated from the bulk chemistry of a rock, provided that the compositions of the coexisting mafic mineral phases containing calcium, sodium, and potassium oxides are determined, e.g., by microprobe analysis. The compositions, proportions, and temperature of two-feldspar in equilibrium can thus be simultaneously resolved numerically from bulk composition of the rock, by incorporating the activity/composition relations of the ternary feldspars with the mass balance constraints. Upon the numerical approximation method presented in this paper, better-quality, internally consistent data on feldspar group could usually be obtained, which would be expected more realistic and accurate in consideration of thermodynamic equilibria in the system of crystalline rocks, as well as bulk chemistry of a rock and the composing minerals.     

Polymetamorphism of the Variscan Basement of the Moldanubian Black Forest （Germany） Documented in Zircon and Garnet Minerals from Gneisses

High-grade metamorphic Variscan basement is exposed in the Moldanubian zone of the Black Forest (BF), being the internal zone of the European Variscan belt. Zircon grains from K-rich felsic orthogneisses and an anatectic paragneiss in the Moldanubian Black Forest demonstrate a multi-stage crystallization at ～ 600 Ma, ～ 480 Ma, ～ 400 - 380 Ma, and ～350 Ma. The last three stages of crystallization probably represent metamorphic overprint during pre-Variscan and Variscan metamorphism.Using stepwise leaching procedures, garnet minerals from felsic orthogneisses as well as paragneisses in the Moldanubian Black Forest yielded Early Carboniferous Sm-Nd ages (～ 330- 340 Ma), which are consistent with the well-constrained Variscan HT metamorphic event,and Early Palaeozoic ( ～480 Ma) to Devonian ( ～400 - 370 Ma) Pb-Pb ages. The coincidence of growth time for zircon and garnet minerals at Early Palaeozoic is interpreted as dating a metamorphic event. These garnet data demonstrate that the Moldanubian BF basement underwent at least two metamorphic events during the Early Palaeozoic and Early Carboniferous.During the Variscan HT metamorphism, the Sm-Nd system of garnet was disturbed, but not the U-Pb system, implying the peak metamorphic temperature was lower than ～800℃.     

Post-collisional Variscan lamprophyres (Black Forest, Germany): Ar/Ar phlogopite dating, Nd, Pb, Sr isotope, and trace element characteristics

Subsequent to high-pressure and temperature metamorphism of the axial zone of the Variscan foldbelt in central Europe at ca. 340 to 330 Ma, formation of lamprophyre dikes during transtensional tectonics may be viewed as the beginning of the post-collisional stage of the orogeny. We report the results of ⁴⁰Ar/³⁹Ar mica dating, major and trace element data, and isotope compositions for lamprophyre and rhyodacite samples from the southern Black Forest. The chemical compositions of these rocks shed light on the upper mantle and crust at the end of the Variscan orogeny. ⁴⁰Ar/³⁹Ar plateau ages for four phlogopite–biotite separates from lamprophyres indicate emplacement at 332 to 314 Ma. This event coincides with melting of the crust as indicated by ⁴⁰Ar/³⁹Ar biotite plateau ages of ca. 332 Ma for rhyodacite dikes which are probably related to coeval undeformed granites. Incompatible trace element patterns of the lamprophyre samples reveal the characteristics of evolved continental crust and are interpreted as evidence for melting of sediment in a subduction-modified mantle. Nd, Sr, and Pb isotope compositions indicate an enriched mantle source with _Nd-values of −1.5 to −6.8 which is similar to Variscan crust. Significant contamination of the lamprophyric melts by Variscan crust can be ruled out as mantle-derived phlogopite phenocrysts have similar _Nd-values as in the whole-rock samples. We propose that the isotope compositions and incompatible trace element characteristics of the lamprophyres were predominantly inherited from melted sediment. The isotope compositions of Variscan lamprophyres from western Europe suggest that enriched upper mantle was only partly delaminated when ascending hot mantle triggered melting of the lower crust, as has been invoked for the origin of post-collisional granites. The isotope compositions of Tertiary basalts and mantle xenoliths indicate a depleted upper mantle under western Europe, implying that the enriched Variscan material was efficiently removed and mixed into the convecting mantle.     

Quantitative temperature-time information from retrograde diffusion zoning in garnet: constraints for the P–T–t history of the Central Black Forest, Germany

Garnet from a kinzigite, a high-grade gneiss from the central Black Forest (Germany), displays a prominent and regular retrograde diffusion zoning in Fe, Mn and particularly Mg. The Mg diffusion profiles are suitable to derive cooling rates using recent datasets for cation diffusion in garnet. This information, together with textural relationships, thermobarometry and thermochronology, is used to constrain the pressure–temperature–time history of the high-grade gneisses. The garnet–biotite thermometer indicates peak metamorphic temperatures for the garnet cores of 730–810  °C. The temperatures for the outer rims are 600–650  °C. Garnet–Al₂SiO₅–plagioclase–quartz (GASP) barometry, garnet–rutile–Al₂SiO₅–ilmenite (GRAIL) and garnet–rutile–ilmenite–plagioclase–quartz (GRIPS) barometry yield pressures from 6–9  kbar. U–Pb ages of monazite of 341±2  Ma date the low- P high- T metamorphism in the central Black Forest. A Rb/Sr biotite–whole rock pair defines a cooling age of 321±2  Ma. The two mineral ages yield a cooling rate of about 15±2  °C Ma⁻¹. The petrologic cooling rates, with particular consideration of the f O₂ conditions for modelling retrograde diffusion profiles, agree with the geochronological cooling rate. The oldest sediments overlying the crystalline basement indicate a minimum cooling rate of 10  °C Ma⁻¹.     

黑色翡翠的宝石学及矿物学特征

翡翠热的兴起引起了市场对翡翠需求量的急剧增加，加速引发了对翡翠新品种的开发与研究。翡翠新品种之一——绿辉石玉(即黑色翡翠)与传统意义上的翡翠在光学性质、结构、成分等方面有一定的差异，有观点认为不应称其为翡翠。通过对黑色翡翠样品进行的一般宝石学特征观察、薄片鉴定、红外光谱分析、粉晶X射线分析、X荧光光谱分析，确认其宝石学特征和矿物学特征与翡翠基本一致。     

Zircon ages and Nd isotopic and chemical compositions of orthogneisses from the Black Forest, Germany: evidence for a Cambrian magmatic arc

 Single zircon U–Pb dating combined with ²⁰⁷Pb/²⁰⁶Pb ages obtained by the evaporation method constrains the emplacement of tonalitic, trondhjemitic, and granodioritic orthogneisses of the Moldanubian zone in the Black Forest between 500 and 510 Ma. Two detrital zircon populations of 1.9 and 1.6 Ga indicate Early-Middle Proterozoic material in the former setting of the basement. The initial e_Nd values range from –0.1 to –3.4 and mean crustal residence ages of 1.0–1.4 Ga are consistent with involvement of Early-Middle Proterozoic crust, and a subordinate juvenile component probably originating from subduction-related melting of the mantle. The orthogneisses have fractionated REE patterns and slightly higher K₂O/Na₂O ratios than typical low-K tonalite–trondhjemite–granite suites. The chemical data are interpreted as evidence for melting of amphibolite and contributions from evolved crust. The emplacement of the orthogneisses was superceded by a high-temperature metamorphic event at ∼480 Ma which we interpret as a result of lithospheric thinning in a marginal basin behind a Cambrian magmatic arc. Received: 29 March 1999 / Accepted: 25 August 1999     

姚桥矿地下水化学特征及在矿井水源判别中的意义

姚桥矿地下水系统包含四个子系统：新生界孔隙含水层组，煤系砂岩裂隙含水层组，太原群石灰岩溶隙含水层组及奥陶系灰岩岩溶含水层组。通过对这四个子系统水文地球化学特征的系统研究，提出了各子系统所特有的水质模型，并确定出能作为矿井水源判别依据的水溶组分，为矿井防治水提供水化学特征依据。     

Authigenic sericite record of a fossil geothermal system: the Offenburg trough,central Black Forest,Germany

A fossil geothermal area is hosted by the Carboniferous, Permian and Bunter sandstones of the Offenburg intramontane trough in the central Black Forest. The hydrothermal alteration is identified on the basis of newly formed sericites, which appear as pseudomorphs after feldspar and filling of pore spaces. According to K–Ar dating of sericite, serititization occurred about 145 Ma ago (Jurassic). On the basis of ¹⁸O analyses of sericite, sericite composition and vitrinite reflectance, the hydrothermal fluids had temperatures of 150–210 °C. Because their electrolyte content was low, these fluids are assumed to have derived from meteoric water. A second pulse of electrolyte-rich hydrothermal fluids resulted in quartz overgrowths. Fluid mobilization seems to be linked to the disintegration of Pangaea and to reactivated fault systems extending from the crystalline basement into the intramontane sediments.     

Elastic and Seismic Properties of Dabie-Sulu Ultrahigh Pressure Metamorphic Rocks

Lamé modulus (λ) and shear modulus (μ) are among the most important,intrinsic,elastic constants of rocks.Using λ and μ could be much more advantageous than using P- and S-wave velocities (Vp and Vs).He...     

烃源岩不同性质有机酸的分离及其检测方法

烃源岩中的有机酸来源于有机质,但有机质具有不同的赋存形式,有机酸具有不同性质,这将影响有机酸与不同赋存有机质的关系,进而影响分离和检测方法。文章在总结前人对有机质赋存形式和有机酸性质等特征的基础上,提出烃源岩中的有机酸并以非单一的形式存在,具有水溶性、脂溶性和难溶性有机酸三种类型,游离有机质中存在水溶性和脂溶性有机酸,而结合有机质中存在水溶性、脂溶性和难溶性有机酸。因此在检测方法上需采取分步分离的方法,且根据有机酸的性质选取合适的检测方法,即水溶性有机酸利用离子色谱检测,索氏抽提得到的脂溶性有机酸利用气相色谱—质谱检测,通过酸解抽提残渣得到的难溶性有机酸利用红外光谱检测,全面系统地认识烃源岩中有机酸含量和类型等特征。这对进一步探讨烃源岩各种类型有机酸特征和演化规律,深化烃源岩有机质生烃以及有机—无机相互作用等机理都具有重要意义。     

地下侵蚀对结晶片岩滑坡活动的影响——以日本善德滑坡为例

为了研究和评价降雨对滑坡活动的影响过程及其作用,利用地表伸缩计、三维地表位移观测计以及地下水流量和地下侵蚀观测计等现场监测仪器,对一典型的日本结晶片岩滑坡--善德滑坡内部的地下侵蚀特征以及地下侵蚀与该滑坡活动之间的关系进行了定量的分析和研究。研究结果表明,季节性集中强降雨是导致地下侵蚀发生的主要原因。善德滑坡地下侵蚀主要有连续土砂排泄和集中土砂排泄2种侵蚀类型,而结晶片岩滑坡的异常活动主要与暴雨引起的集中土砂排泄型地下侵蚀作用有关。通过对地下侵蚀和滑坡活动之间关系的分析发现,地下侵蚀对善德滑坡不同滑体活动的影响作用表现出不同的特征。其中,厚度为10～20 m的浅层滑体,地下侵蚀的影响作用最为显著,而对于具有深层滑动面的滑体（>20 m）其影响作用并不明显。     

韩城矿区奥灰水化学特征及形成机制探讨

以岩石化学成分、水质分析、同位素组分以及水质动态长期监测等资料为基础，分析了矿区岩溶水介质的赋存与分布等水文地质背景，重点研究了水化学组分特征及其形成机制。结果表明：由矿区边部至中深部，水化学类型由重碳酸硫酸钙镁型向硫酸盐氯化钠钙型过渡，TDS随含水层埋深升高而水质变差，水化学组分主要由溶滤作用经去膏盐化和脱白云岩化过程形成，开采井群水质变劣的主因是矿区中深部高矿化水的混合作用所致。     

鲁西平原地热水的化学特征及开发利用

鲁西平原地热水资源较丰富,属中低温地热,埋藏分布广,温度适中,开采潜力大。通过对鲁西平原地热水的水化学和冷水、海水的水化学进行对比分析,研究地热水的形成及水化学特征,根据地热水的水化学特征对地热水进行有针对性地开发利用。     

Groundwater in fractured crystalline rocks, the Clara mine, Black Forest (Germany)

The chemical composition of water sampled in a 700 m deep underground barite-fluorite mine in the crystalline basement of the Black Forest area (SW Germany) varies systematically with depth and the length of flow paths trough, the fracture porosity of the gneiss matrix. Calcium and sulfate increase as a result of a combined sulfide oxidation and plagioclase alteration reaction. The gneiss contains andesine–plagioclase (An₂₀–An₄₀) and is rich in primary sulfide. As an effect of Ca and SO₄ release by the prime water–rock reaction, dissolved oxygen decreases and the waters become more reduced. The waters have Cl/Br mass ratios of about 50, which is very close to that of experimentally leached gneiss powders indicating that the rock matrix is the source of the halogens. The waters are undersaturated with respect to calcite in the upper parts of the mine. With increasing reaction progress, calcite saturation is reached and carbonate forms as a reaction product of the prime reaction that also controls the partial pressure of CO₂ to progressively lower values. The chemical evolution of groundwater in fractured basement of the Clara mine suggests that the partial pressure of CO₂ is an internally buffered parameter rather than a controlling external variable.     

Radiocarbon dating of dissolved inorganic carbon in groundwater from confined parts of the Upper Floridan aquifer, Florida, USA

Geochemical reaction models were evaluated to improve radiocarbon dating of dissolved inorganic carbon (DIC) in groundwater from confined parts of the Upper Floridan aquifer in central and northeastern Florida, USA. The predominant geochemical reactions affecting the ¹⁴C activity of DIC include (1) dissolution of dolomite and anhydrite with calcite precipitation (dedolomitization), (2) sulfate reduction accompanying microbial degradation of organic carbon, (3) recrystallization of calcite (isotopic exchange), and (4) mixing of fresh water with as much as 7% saline water in some coastal areas. The calculated cumulative net mineral transfers are negligibly small in upgradient parts of the aquifer and increase significantly in downgradient parts of the aquifer, reflecting, at least in part, upward leakage from the Lower Floridan aquifer and circulation that contacted middle confining units in the Floridan aquifer system. The adjusted radiocarbon ages are independent of flow path and represent travel times of water from the recharge area to the sample point in the aquifer. Downgradient from Polk City (adjusted age 1.7 ka) and Keystone Heights (adjusted age 0.4 ka), 14 of the 22 waters have adjusted ¹⁴C ages of 20–30 ka, indicating that most of the fresh-water resource in the Upper Floridan aquifer today was recharged during the last glacial period. All of the paleowaters are enriched in ¹⁸O and ²H relative to modern infiltration, with maximum enrichment in δ¹⁸O of approximately 2.0‰. Electronic Publication     

苏鲁超高压变质岩中地震波速随围压的变化规律

我们在10~800MPa的静水压力下测量了中国大陆科学钻探(CCSD)主孔岩心和采自苏鲁地区地表露头上的共68块典型超高压变质岩试样的地震波速,并建立了波速和围压的定量关系,成功地解释了描述这一定量关系方程中4个参数的物理意义。笔者相信,本文将为超高压变质岩地区以及新老俯冲带地震波资料的解释提供必不可少的理论和实验支撑。     

新疆阿克纳瓦山晚泥盆世火山岩及其构造环境

新疆北部阿克纳瓦山晚泥盆世中基性火山岩以全碱含量较高为其最突出的特点。岩相学、矿物学、岩石化学、稀土元素和微量元素地球化学的研究表明,火山岩属于碱性玄武岩系列,以碱性玄武岩组岩石为主,同时有少量橄榄玄粗岩组岩石,表现为碱性玄武岩演化的肯尼迪趋势。火山岩是地幔部分熔融作用的产物,但在岩浆上升过程中发生过橄榄石和(或)辉石的分离结晶作用。火山岩产出的构造环境为具有陆壳基底的岛弧或活动大陆边缘火山弧,不可能是洋中脊。岛弧或活动大陆边缘火山弧的产生是以阿尔曼泰—扎河坝蛇绿混杂岩带为代表的次生洋盆,自晚泥盆世起向北东方向(现代方向)俯冲作用的结果。     

Association of Late Paleozoic Adakitic Rocks and Shoshonitic Volcanic Rocks in the Western Tianshan, China

The late Paleozoic adakitic rocks are closely associated with the shoshonitic volcanic rocks in the western Tianshan Mountains, China, both spatially and temporally. The magmatic rocks were formed during the period from the middle to the late Permian with isotopic ages of 248-268 Ma. The 87Sr/86Sr initial ratios of the rocks are low in a narrow variation range (-0.7050). The 143Nd/144Nd initial ratios are high (-0.51240) with positive εND(t) values (+1.28-+4.92). In the εNd(t)-(87Sr/86Sr)i diagram they fall in the first quadrant. The association of the shoshonitic and adakitic rocks can be interpreted by a two-stage model: the shoshonitic volcanic rocks were formed through long-term fractional crystallization of underplated basaltic magma, while the following partial melting of the residual phases formed the adakitic rocks.     

四川盐源盐泉水水化学特征分析

通过对四川盐源盐井河、盐塘周围盐泉水水化学特征及其与云南勐野井钾盐矿周围盐泉水、浓缩海水、盐源卤水的相互比较,结合盐源盐井河盐矿底辟构造及前人所做工作以及近年来EH-4连续电导率剖面的探测结果,推断可能存在大量的盐类矿物沉积、聚集于盐盆中;盐源洼陷属于特提斯深海槽的边缘洼陷,故盐盆中的易溶矿物(盐岩、钾镁盐等)有可能向凹陷中迁移、蒸发而形成钾盐;盐源盆地盐泉水及溶滤卤水对钾盐的显示具有一定指示意义,认为所采集的盐泉水样可能是深部钾镁盐矿的外围盐泉水;深部盐类物质来源可能为寒武系岩盐层。