Microfabric of folded quartz veins in metagreywackes: dislocation creep and subgrain rotation at high stress

The microfabrics of folded quartz veins in fine‐grained high pressure–low temperature metamorphic greywackes of the Franciscan Subduction Complex at Pacheco Pass, California, were investigated by optical microscopy, scanning electron microscopy including electron backscatter diffraction, and transmission electron microscopy. The foliated host metagreywacke is deformed by dissolution–precipitation creep, as indicated by the shape preferred orientation of mica and clastic quartz without any signs of crystal‐plastic deformation. The absence of crystal‐plastic deformation of clastic quartz suggests that the flow stress in the host metagreywacke remained below a few tens of MPa at temperatures of 250–300 °C. In contrast, the microfabric of the folded quartz veins indicates deformation by dislocation creep accompanied by subgrain rotation recrystallization. For the small recrystallized grain size of ～8 ± 6 μm, paleopiezometers indicate differential stresses of a few hundred MPa. The stress concentration in the single phase quartz vein is interpreted to be due to its higher effective viscosity compared to the fine‐grained host metagreywacke deforming by dissolution–precipitation creep. The fold shape suggests a viscosity contrast of one to two orders of magnitude. Deformation by dissolution–precipitation creep is expected to be a continuous process. The same must hold for folding of the vein and deformation of the vein quartz by dislocation creep. The microfabric suggests dynamic recrystallization predominantly by subgrain rotation and only minor strain‐induced grain boundary migration, which requires low contrasts in dislocation density across high‐angle grain boundaries to be maintained during climb‐controlled creep at high differential stress. The record of quartz in these continuously deformed veins is characteristic and different from the record in metamorphic rocks exhumed in seismically active regions, where high‐stress deformation at similar temperatures is episodic and related to the seismic cycle.     

Discontinuous grain growth of quartz in metacherts: the influence of mica on a microstructural transition

Abstract The microstructure of quartz in metacherts of the Ryoke metamorphic belt in central Japan develops from polygonal, through duplex to irregular with increasing metamorphic grade. The polygonal microstructure is composed of small (mostly 90–160 μm), equant, equigranular, polygonal quartz grains, whereas the irregular microstructure is characterized by large (>300 μm) grains with irregular grain boundaries. The duplex microstructure is a mixture of small polygonal and large irregular grains. The development of these microstructures is interpreted as being due to secondary recrystallization. The size of polygonal grains is greatly influenced by the presence of second-phase minerals, such as mica, whereas that of large irregular grains is unaffected by second-phase minerals. There seems to be a critical grain size for quartz to occur as polygonal aggregates: no polygonal aggregates occur in rocks with larger than the critical grain size. The size (about 140 μm) decreases slightly with increasing volume fraction of mica. The mean grain sizes of polygonal quartz ( D ) and coexisting mica ( d ) in the duplex microstructure are systematically related to the volume fraction of mica ( f ) by D = 0.728 d (1/ f )^0.629.     

石英显微变形机制及流变学特征研究进展

石英是组成地壳的主要矿物之一,其物理性质与地壳的变形行为及流变学属性密切相关,因此石英的显微变形机制及流变学特征研究意义重大。随着石英显微变形机制及流变学属性实验学研究的深入,我们对石英在地壳变形过程中重要作用的认识也随之提升。本文从石英结构入手,对升温过程中石英主滑移系的转换进行了总结,并且升温过程中显微变形机制也发生了改变,对流变学内涵也不同,所以分述了石英的主要变形机制,及其流变学参数;由于应变局部化为地壳变形的研究热点,并且石英对应变局部化具有一定的指示意义,所以本文对石英在应变局部化过程中的表现进行了深入讨论。考虑到地壳变形的研究过程中,石英不常作为单矿物发生变形,所以本文对多相矿物的变形表现也进行了讨论。最后我们将简单介绍一些现今主流的石英显微变形机制的研究手段。     

The (Na–Ca)amphibole–albite–chlorite–epidote–quartz geothermobarometer in the system S–A–F–M–C–N–H2O. 1. An empirical calibration

The proposed geothermobarometer is based on an empirical calibration which takes account of two equilibria involving the tremolite, edenite, pargasite and hastingsite components in amphiboles. It has applications to assemblages found in metabasic rocks of widely different chemical compositions (magnesian to Fe-rich metabasalts), and for metamorphism ranging from lower greenschist to highest amphibolite facies. Knowing the Si_(T1), Al^iv, Al^vi, Fe³⁺, Fe²⁺, Mg, Ca, Na_M4, Na_A and A vacancy in an amphibole, and the Al³⁺ and X _Mg in coexisting epidote and chlorite, it is possible to calculate two values of In K _d for this assemblage. These equilibria involve edenite-tremolite and (pargasite/hastingsite)-tremolite end-members in amphibole (the calculation program is given). For these equilibria, the isopleths (iso-values of K _d) have been calculated for 0.27 < X _Mg < 0.75 and 0 < X _Fe3+= Fe³⁺/(Fe³⁺+ Al^vi) < 0.8. It is then possible to determine pressure and temperature directly when X _Mg, X _Fe3+, In K _d for tremoliteedenite and In K _d for (pargasite/hastingsite)-tremolite are known. Application of this geothermobarometer is limited to Ca-free plagioclase assemblages, and complete P–T paths can be drawn only if all the minerals are considered together. Phase relations at successive stages of crystallization can be constrained by studying the relationships between the coexisting minerals, their zoning and the metamorphic fabrics.     

鄂东南付家山脉石英矿杂质特征及其用作高纯石英原料的潜力

作为战略性矿产资源之一,高纯石英已广泛应用于集成电路、半导体芯片、太阳能等高新技术产业中,但是能够生产高纯石英的原料矿床极为稀缺,我国尤为紧缺高纯石英原料矿。鄂东南地区是湖北省脉石英矿床的主要分布区。本文针对鄂东南付家山脉石英矿床,通过光学显微镜、扫描电子显微镜观察了脉石英的脉石矿物类型和包裹体特征,采用电感耦合等离子发射光谱法(ICP-OES)对原矿进行了微量元素分析,旨在获得付家山脉石英矿床的杂质元素特征,进而评价矿床用作高纯石英原料的潜力。结果表明,付家山脉石英矿石SiO₂含量大于99.95%,杂质元素主要为Al、K、Fe、Ti、Ca等,脉石矿物主要有白云母、钾长石、铁氧化物等,流体包裹体较为发育。杂质元素分析结果表明,付家山脉石英原矿质量达到低端高纯石英标准,经传统工艺提纯后,可能具有生产中高端高纯石英的潜力。     

钙长辉长无球粒陨石中普通石英与鳞石英成因研究

钙长辉长无球粒陨石(Eucrite)是 Howardite-Eucrite-Diogenite(HED)族陨石的重要成员,也是研究灶神星壳演化历史的重要对象.本文研究了多个玄武质Eucrite样品中主要的SiO2相——普通石英和鳞石英的成因,进而讨论其对Eucrite陨石热演化的启示.研究对象包括不同冲击程度样品,以探...     

Cathodoluminescence imaging and titanium thermometry in metamorphic quartz

Cathodoluminescence (CL) of quartz from metamorphic rocks representing a range of conditions from the garnet grade to the migmatite grade reveals a variety of textures, that is, a function of metamorphic grade and deformation history. Ti concentrations, determined by electron microprobe and ion microprobe, generally correlate with CL intensity (blue wavelengths), and application of the Ti‐in‐quartz thermometer (TitaniQ) reflects the temperature of quartz growth or recrystallization, and, in some settings, modification by diffusion. Quartz from garnet grade samples is not visibly zoned, records temperatures of 425–475 °C, and is interpreted to have recrystallized during fabric formation. Quartz grains from staurolite grade samples are zoned in CL with markedly darker cores and brighter rims, some of which are interpreted to have been produced by the dominant staurolite‐producing reaction, whereas others are interpreted as having formed by diffusion of Ti into quartz rims. Quartz from the matrix of kyanite and sillimanite grade samples are generally unzoned, although locally displays slightly brighter rims (higher Ti); quartz inclusions within garnet and staurolite have distinctly brighter rims, which are interpreted as having been produced by diffusive exchange with the host mineral. Quartz from migmatite grade samples displays highly variable CL intensity, which is dependent on the location of the grain. Matrix grains in melanosomes are largely unzoned or rarely zoned with darker cores. Leucosome quartz is strongly zoned with bright cores and dark rims and is interpreted as having formed during crystallization of the melt. Locally within the leucosome is observed oscillatory‐zoned quartz, which is interpreted as a subsolidus recrystallization to achieve strain relaxation. Quartz inclusions within garnet or plagioclase crystals often show bright domains separated by zones of dark CL. These enigmatic textures possibly reflect local melting fluxed by fluid inclusions. Temperatures calculated from the Ti–in–quartz thermometer are a function of the metamorphic grade of the sample, the textural setting of the quartz, the reaction history and the deformation history of the rock. The TitaniQ temperatures can be used to constrain the conditions at which various metamorphic processes have occurred.     

In-situ IR measurements of OH species in quartz at high temperatures

The nature of OH species in natural clear quartz was investigated by means of in-situ IR measurements over the temperature range –185 to 1000 °C. Reversible thermal behavior of OH species was examined for a sample pre-heated to 1000 °C for 1 hour. At room temperature, the IR spectrum of the quartz sample examined includes an intense absorption peak at 3379 cm^–1 which has been assigned to an OH stretching vibration associated with Al substituting for Si (OH(Al)). The major spectral changes of the OH(Al) bond involve a systematic shift of its peak position and a decrease in its integral absorbance with temperature. A quasi-linear increase of the peak position from –185 to 400 °C is interpreted to be due to the change in the vibrational frequency of OH(Al) with hydrogen bond (H bond) distance. At higher temperatures, the IR frequency shows only a slight change, indicating a small influence of the H bond. On the other hand, the gradual decrease of the integral absorbance of OH(Al) with temperature indicates a decrease of this defect’s molar absorptivity without any reduction in defect concentration. This is interpreted to result from a decrease in dipole moment of OH(Al) with temperature. A sudden shift of the vibrational frequency from 3396 to 3386 cm^–1 between 550 and 560 °C and a constant value of the integral absorbance from 535 to 570 °C were considered to be related to the change in H bond distance during the structural transformation of α-quartz to its β-form. The local environment of OH(Al) begins to change at temperatures below 570 °C, where the crystallographic α–β transition occurs. Received: 18 February 1998/ Accepted: 10 July 1998     

全球高纯石英原料矿的资源分布与开发现状

高纯石英是集成电路、半导体芯片、光伏、光纤、新型玻璃等产业必不可少的关键原料,但是能够生产高纯石英的矿床极为稀缺。梳理全球高纯石英原料矿床的资源分布和开发现状,发现矿床分布于美国、澳大利亚、挪威、俄罗斯、中国、毛里塔尼亚、加拿大等国家,除中国外,共有14处矿床,美国和澳大利亚的资源量最大。矿床类型包括白岗岩型、伟晶岩型、热液脉石英型、风化残积型、尾矿型,其中热液脉石英型分布最广。优质矿石多产于太古宙-元古宙黑云母片麻岩、花岗片麻岩、片岩等古老变质岩系中,受古生代-中生代花岗质岩浆活动控制,经历了长期而缓慢的变质过程。我国高纯石英原料矿床尤为紧缺,在当前国际政治经济环境下,作为战略性矿产资源,高纯石英的资源安全形势尤其严峻。一方面,我国应立足国内石英资源,大力加强境内太古宙-元古宙变质岩系中纯度较高的玻璃用脉石英、伟晶岩、白岗岩的地质调查和质量评价,关注花岗闪长岩、伟晶岩和高岭土矿开采后残留尾矿中的石英,开展选矿实验,评估资源潜力;另一方面,应打破高纯石英砂进口渠道多年来依赖美国的境况,加大挪威、俄罗斯、毛里塔尼亚等国的进口力度,拓展高纯石英的来源渠道,维护国家战略安全。     

Boundaries and transborder relations,or the hole in the prison wall: On the necessity of superfluous limits and boundaries

Boundaries can be seen as barriers or as places of contact. It has been suggested that we are “prisoners of borders”, of all kinds of borders (political, religious, social, cultural, linguistic etc.). While this statement appears to be somewhat exaggerated, it holds some truth. Boundaries are elements in spatial organization, and they influence daily life in many ways (not only for people living right along them). The paper addresses the question if we must call ourselves “prisoners” or if we simply have to live with all kinds of borders. Departing from theoretical observations, the paper discusses the various aspects boundaries assume in the European context before looking at a few concrete Swiss examples. They reveal that even regions at a certain distance of the state border will feel its effects (the case of Zurich airport), but the most important benefit can been drawn by people living in the border area itself (through price differences between the two countries, as exemplified by the Swiss-Italian border). There may be asymmetry on state borders, but this asymmetry can also swing around: the advantages often lie on both sides. The paper concludes by pointing to the persistence of the boundary concept. They are a necessity for the organization of space and society, but they are not absolute. There are always holes in these prison walls, and the examples where boundaries were impermeable are probably rare.     

石英包体拉曼偏移压力计——一种变质压力计算方法

矿物或流体包体可以有效保存寄主矿物生长过程中的化学环境、温度、压力等信息。在高压变质过程中,石榴子石中石英包体的分子振动与环境压力之间具有良好的相关性。根据这一特性,前人提出了石英包体拉曼偏移压力计,其原理是利用显微激光拉曼光谱仪分析石英包体在室温常压下保留的残余压力,再结合石英与寄主矿物的弹性物理特性,恢复石英包体被捕获时的压力,属于矿物物理光谱学压力计,本文介绍了利用石英包体的拉曼位移计算变质压力的基本原理和方法,并对不同方法的适用条件和使用局限做了简要分析。石英包体拉曼偏移压力计是恢复变质岩石形成温度和压力条件的有效方法,具有广泛的应用前景。     

夏杖子金矿载金矿物石英的标型特征及成因探讨

石英是夏杖子金矿床主要脉石矿物及载金矿物之一,通过对石英的化学成分、流体包裹体、稀土元素特征、红外吸收光谱和同位素组成等的分析研究,结果表明,夏杖子金矿床的石英流体包裹体主要为单相液体H2O包裹体为主,气液包裹体较少,占5%～10%,另还有一种更少见的富HO4包裹体。液相成分和氢氧同位素揭示成矿流体为岩浆热液和大气降水的混合流体。包裹体的均一温度90℃～210℃,盐度7.0%～11%,为中—低温、低盐度成矿流体。石英稀土元素组成与岩浆岩一致,说明石英与岩浆岩有着渊源关系。夏杖子金矿为燕山晚期浅成中低温岩浆热液金矿床。     

龙首山地区中深构造层次及岩石变形特征研究

龙首山韧性剪切带运动学及动力学特征在加里东运动早期以自下而上的张应力作用为主,加里东运动中期为北西南东向的右行纯剪切作用,加里东运动后期以北东南西向的正压力作用伴有局部的压扭作用。其中,右行剪切变形最大主应力方向为北西南东向,后期压应力的主应力方向为北东南西向。研究区韧性剪切带主要分布在蓟县系、震旦系中,在其后地层中未发现,可以确定剪切带的形成应在震旦纪之后。并认为发生于震旦纪末至志留纪末的加里东造山运动导致了研究区韧性剪切带的形成,并在加里东造山运动的不同阶段有所叠加。结合金川超基性岩体的形成年龄,认为该韧性剪切带对成矿没有贡献。但是,对深部超基性岩体向浅部带动可能会有帮助。根据石英亚颗粒的直径估算,其古差应力值为282.9 MPa。     

四川省沐川地区石英砂岩特征及利用途径探讨

四川省沐川地区石英砂岩储量巨大,开采技术条件好。通过采集沐川地区矿区坑道的原矿样品和精选厂的工业品,开展地球化学、薄片鉴定和导流能力实验等测试分析,研究了沐川地区石英砂岩的特征并探讨其开发利用途径。结果显示: 矿石主要为中粒岩屑石英砂岩,矿物成分以石英和硅质岩屑等陆源碎屑为主,含少量黏土杂基和石英胶结物等填隙物; 40/70目工业级石英砂样品在闭合压力28 MPa条件下的破碎率为9.05%,在70 MPa 闭合压力下的导流能力为1.12 µm2·cm,满足四川盆地页岩气井主裂缝的导流能力要求。沐川地区石英砂岩的矿石产品有磷化工、玻璃制品、铸造用型砂以及压裂支撑剂4种应用途径,建议加强石英砂岩压裂支撑剂用途的评价,综合开发利用石英砂岩矿资源,保障服务于支撑剂产业的砂源本地化。     

Crystallographic orientations of high-angle grain boundaries in dynamically recrystallized quartz: First results

The crystallography and geometry of high-angle grain boundaries from dynamically recrystallized quartz have been studied. On the basis of combined electron backscatter diffraction and universal stage measurements, the complete crystallographic orientation of the grain boundaries could be calculated. The u-stage rotation of the grain boundaries to a vertical position reveals that they are never curved but always consist of straight segments. Our results show that these segments preferentially occupy rhombohedral, trapezohedral and bipyramidal orientations, i.e., orientations in a  25–50° girdle to the c-axis. A specific, albeit low, number of segments with special crystallographic orientation, with respect to a neighbouring quartz grain, often shows another special orientation with respect to the other neighbouring grain. Preferred combinations of grain boundary orientations related to both neighbouring grains are (i) low-index rhombohedral and high index trapezohedral, (ii) low-index bipyramidal and low-index trapezohedral or high-index rhombohedral, and (iii) low-index trapezohedral and low or high index trapezohedral. In certain cases, such as at triple junctions, the boundaries occupy specific trapezohedral orientations with a constant angle to the c-axis. This argues for energy isotropy of trapezohedral planes with the same angle to the quartz c-axis. In general, good match coincidence site lattice (CSL) orientations are not preferentially occupied so that most of the studied grain boundaries represent general boundaries. The formation of straight segments in special crystallographic orientations indicates the crystallographic control and implies an energy reduction of certain general boundaries.     

西藏甲玛铜多金属矿区成矿斑岩的岩浆混合作用:石英及长石斑晶新证据

西藏甲玛矿区斑岩内石英和长石斑晶的阴极发光(CL)特征及元素含量变化有效记录了岩浆演化、混合及补给事件.石英斑晶的显微生长结构表明,原始岩浆经历过2次铁镁质岩浆混合作用.根据石英斑晶中Ti含量的变化可知,在2次溶蚀前后,石英结晶温度分别增高了约110℃和80℃.此外,斜长石斑晶的反环带及其Ba、Sr、Fe等元素的浓度梯...     

云南南洞地下河系统边界及性质研究

地下河系统具有固定补给范围和资源要素,是岩溶地下水进行独立循环的基本单元,控制了岩溶水的运移富集、水化学演化特征、资源构成以及环境地质问题。开展地下河系统研究首要任务是确定系统边界位置及其水文地质性质。以南洞地下河系统为研究对象,据野外调查、勘探、试验资料,以地球系统科学理论为指导,运用现代岩溶学、地质学及水文地质学的分析方法,确定南洞地下河系统是由1号暗河和2号暗河系统组成的,其中2号暗河还有叠置于其上的平石板和黑龙潭两个全排型暗河子系统;其含水岩层主要为三叠系个旧组（T2g）灰岩、灰质白云岩、白云质灰岩;根据边界的水文地质性质可以划分为地表分水岭边界、地下分水岭边界、隔水边界、岩溶含水层深埋滞留型边界。      

Quartz and zircon decoupling in sandstone: Petrography and quartz cathodoluminescence of the Early Triassic continental Buntsandstein Group in Germany

This study illustrates how decoupling of quartz and zircon can be used advantageously in provenance research. Thirty‐eight fine‐grained to coarse‐grained arkose samples of the Early Triassic intracontinental Buntsandstein Group from the Central European Basin in Germany were analysed for their petrography and 1200 grains in 23 of these for their detrital quartz cathodoluminescence characteristics. The samples represent the Hessian and Thuringian sub‐basins and the Eichsfeld–Altmark Swell separating them. The Hessian Sub‐basin includes more metamorphic lithoclasts with a larger content of plutonic grains than are found further east in the Thuringian Sub‐basin. More than 90% of the detrital quartz from the eastern Thuringian Sub‐basin produce medium to bright blue cathodoluminescence colours and corresponding spectra that are typical for igneous or high‐temperature metamorphic origin. Differently, the quartz from the Hessian Sub‐basin mostly luminesces brown and dark to medium blue, typical for a low‐temperature metamorphic origin. Quartz from the Eichsfeld–Altmark Swell and the western Thuringian Sub‐basin is a mixture between these origins. The quartz indicates different catchments for the sub‐basins, possibly the Bohemian Massif and the Massif Central, with converging transport routes on and close to the eastern fringe of the swell. Taking published zircon data from the same samples into account, light mineral‐zircon grain‐size shifts are up to 2 Φ units. That can be explained by mineral decoupling due to different transport modes for quartz and zircon and different zircon‐size availability in the source areas, exaggerated by combined aqueous–aeolian transport, as well as sample preparation‐induced sorting. This study concludes that submerged highs significantly can influence continental sediment transport. Hence, vast, flat continental areas with submerged morphological highs and a seemingly straightforward transportation pattern may be more complex than expected. The results also illustrate that analysis of detritus that has been affected by different dominating transport modes, and further sorting during sampling and preparation can reveal additional source information.     

湘西龙山江家垭铅锌矿床石英Rb-Sr同位素测年与示踪研究

江家垭铅锌矿床位于扬子地台东南缘,红岩溪背斜轴部,是湘西—鄂西铅锌成矿带重要的铅锌矿床之一,铅锌矿体呈似层状和脉状,受地层与构造的控制,主要产于下奥陶统南津关组砂屑灰岩中。文章首次采用超低本底石英Rb-Sr同位素测年方法,对湘西龙山江家垭铅锌矿床主成矿期形成的富铅锌石英脉进行了等时线年龄测定,获得成矿年龄为(372±9.8)Ma,n(87Sr)/n(86Sr)=(0.709409±0.000058)。通过成矿地质背景探讨,认为该矿床的形成与晚泥盆世华南地区发生的拉张断陷导致的盆地流体大规模运动有关。锶同位素初始比值测试结果表明江家垭铅锌矿床成矿物质来源可能主要源自围岩碳酸盐岩,成矿过程中陆壳的影响较为明显。