石英显微构造阴极发光特征研究——以西藏甲玛岩体为例

根据石英在阴极射线下显示的生长结构差异,可以区分不同世代的石英斑晶,揭示岩浆演化过程。本次研究以西藏甲玛岩体中石英斑晶为例,采用光学显微镜阴极发光仪(OM-CL)和扫描电镜阴极发光仪(SEM-CL)。研究表明甲玛矿区中基性岩体有5个世代的石英斑晶。早期石英斑晶至少经历了两次岩浆混合作用:第一次基性岩浆的混入,石英斑晶核部形成了浑圆状重熔表面,然后石英经历了较稳定的生长阶段,形成均匀的生长环带;随着岩浆的快速上升侵位,岩浆储层中压力减小,导致第二次基性岩浆混入,形成富Ti的波状、港湾状重熔表面和石英钾长石外壳。     

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...     

西藏甲玛铜钼多金属矿区花岗岩石英斑晶阴极发光特征与岩浆混合研究初探

阴极发光是一种研究火成岩石英显微生长结构的有效技术方法.本次研究分析了西藏甲玛铜钼多金属矿区四个不同岩体中石英斑晶阴极发光(CL)特征,并用电子探针(EPMA)得到了相应斑晶中不同环带微量元素含量.     

岩浆演化对成矿作用的控制——以西藏冈底斯北缘铅锌矿带为例

与岩浆-热液或热液矿床有关的岩浆,大都经历了不同程度的演化(如结晶分异、同化混染等),其岩石学和地球化学特征只是岩浆演化终态的反映,针对这些岩浆岩本身的研究有时很难刻画出其详细的演化过程及该过程中关键成矿元素的地球化学行为。已有研究显示,同时代同区域大面积分布的火成岩可能记录着含矿岩浆演化早期或演化不同阶段的岩石学和地球化学信息,为解决上述难题提供了可能。基于此,本文以发育于大陆碰撞初期(即主碰撞)的西藏冈底斯北缘铅锌矿带为例,通过对主碰撞阶段冈底斯带大量火成岩地球化学数据的统计学研究,初步展示了岩浆演化过程及其对成矿的控制作用。研究结果表明,除了自身体系的分离结晶,陆壳混染作用是大陆碰撞早期岩浆由基性向中酸性演化的另一关键控制因素,主碰撞岩浆中普遍不具有高的含水量和氧逸度,但演化到中后期,岩浆的氧逸度会逐渐升高;富S和H2O的幔源岩浆底侵,诱发具有较高Zn含量的陆壳物质熔融,产生的岩浆再经历高度的演化(以达到Pb的富集),最终浅成就位形成岩浆-热液成矿系统。这是形成冈底斯北缘铅锌矿带的成矿动力学机制。     

东昆仑造山带家琪式斑岩型Cu-Mo矿床中花岗闪长岩的斜长石晶体群及其成矿意义

近年来,越来越多的作者接受火成岩由多种晶体群组成的新概念。本文以东昆仑造山带家琪式斑岩型Cu-Mo矿床中花岗闪长岩为例,试图阐明火成岩晶体群的涵义及其研究方法和意义。显微镜观察表明,花岗闪长岩的斜长石按其结晶习性可划分为5种不同类型,阴极发光图像分析证实了这一观察,并揭示了它们的生长过程。电子探针剖面分析揭示了横跨晶体切面的化学变化,进一步表明这些晶体具有不同的生长环境和生长过程,属于不同的晶体群。基于平衡热力学原理,推测晶体群来自5个不同的岩浆子系统,暗示形成花岗闪长岩的岩浆为多重岩浆房系统岩浆混合作用的产物,且混合岩浆经历了快速固结过程。这些认识对于探讨斑岩型矿床成因具有重要意义。     

江西大岭上钨矿含斑细粒花岗岩锆石成因及成岩成矿启示

锆石成因研究成果是锆石定年、源区性质示踪和岩浆演化过程分析的基础。本文利用阴极发光和LA-ICP-MS技术发现研究区含斑细粒花岗岩包含了无继承核锆石和有继承核锆石。无继承核锆石阴极发光暗黑,其Th/U值低,LREE相对富集,Ce弱正异常,Ti温度计得到地质温度为801℃,是形成于富含热液的岩浆环境的锆石。有继承核锆石残留核具有均匀的灰白阴极发光,边缘阴极发光暗黑,其Th/U值较高,LREE相对较低、Ce正异常明显,Ti温度计得到地质温度为771℃,是形成于正常岩浆环境的中、深成岩浆岩中的锆石。结合区域地质情况,推断残留核锆石很可能是晋宁期花岗闪长岩中的锆石,说明矿区晋宁期花岗闪长岩可能是含斑细粒花岗岩的一种源岩。无继承核锆石的结晶环境反映了当时岩浆已经演化到晚期,而且其结晶时的富含热液的岩浆可能是一种良好的成矿物质的载体,值得进一步研究。     

山东文登金矿成矿条件及成矿过程——阴极发光技术在包裹体研究中的应用

使用阴极发光技术可取得一般岩石显微镜无法得到的地质信息,并可将包裹体的研究从原来的“群分析”统计规律研究水平提高到“单包体分析”水平,获得更小时间单位成矿流体的演化特征,因而能更准确地模拟和恢复地质作用过程。运用阴极发光对石英等矿物的研究,发现蚀变带中的石英按不同的形态特征和发光性可以分为三期,和成矿关系密切为第一、二期石英。根据阴极发光下显示的生长微形态,系统地测试三期石英不同生长时期的包裹体物相,从而获取了整个成矿过程流体的p-t-v-x参数,确定构造作用加热大气降水形成成矿流体,体系开放流体两次减压沸腾导致金矿沉淀的矿体定位机理和成矿动力学机制。     

山东文登金矿成矿条件及成矿过程─—阴极发光技术在包裹体研究中的应用

使用阴极发光技术可取得一般岩石显微镜无法得到的地质信息，并可将包裹体的研究从原来的“群分析”统计规律研究水平提高到“单包体分析”水平，获得更小时间单位成矿流体的演化特征，因而能更准确地模拟和恢复地质作用过程。运用阴极发光对石英等矿物的研究，发现蚀变带中的石英按不同的形态特征和发光性可以分为三期，和成矿关系密切为第一、二期石英。根据阴极发光下显示的生长微形态，系统地测试三期石英不同生长时期的包裹体物相，从而获取了整个成矿过程流体的ｐ—ｔ—υ—ｘ参数，确定构造作用加热大气降水形成成矿流体，体系开放流体两次减压沸腾导致金矿沉淀的矿体定位机理和成矿动力学机制。     

石英的结构和微量元素特征研究进展及其在岩浆-热液矿床中的应用

石英(SiO₂)具有稳定的化学性质和晶格结构,因此在地质演化过程中可以保存成岩成矿的基本信息。本文系统总结了国内外关于石英中微量元素的种类、分布、含量变化等诸多研究,详细论述了石英中微量元素的赋存状态和进入石英晶格中的机制,以及控制这些微量元素进入石英中的因素:如温度、压力、pH值和流体/熔体成分等;介绍了岩浆-热液矿床中石英复杂多样的结构,包括:单向固结结构(UST结构)、石英眼、晶洞以及雪球结构;评述了石英中微量元素的具体应用:石英的Ti温度计(TitaniQ)、Ti的扩散计时器、石英中Al温度计、Al的pH计,以及石英微量元素比值对岩浆-热液过程的指示作用;最后总结了阴极发光(CL)在揭示石英中微量元素的扩散过程、石英的世代关系等方面的应用,及相关的分析测试方法。据此,利用石英的特性可了解寄主岩石的成因,并分析岩浆-热液矿床中成矿流体的演化过程及石英中微量元素的沉淀机制,为找矿勘查提供依据。     

海南岛海西-印支期花岗岩的地球化学特征及成因

海南岛海西-印支期花岗岩具有一个较完整的演化系列。花岗质岩浆由混合岩进一步重熔而形成。岩浆演化过程中具有一定程度的分离结晶作用。花岗岩的原岩主要为上地壳的岩石,但混有来自下地壳的火成岩。     

Quartz zoning and the pre-eruptive evolution of the ~340-ka Whakamaru magma systems,New Zealand

Cathodoluminescence (CL) zoning in quartz crystals from rhyolitic pumices in two ignimbrite members of the ~340-ka Whakamaru super-eruption deposits, Taupo Volcanic Zone, New Zealand, is investigated in conjunction with the analysis of Ti concentration in quartz to reconstruct the history of changing magma chamber conditions and to elucidate the eruption-triggering processes. CL intensity images are taken as a proxy for Ti concentration and thus temperature and/or pressure and/or compositional variations during crystal growth history. Estimates of the maximum temperature changes (i.e., assuming other factors influencing Ti uptake remain constant) are made using the TitaniQ geothermometer based on the Ti concentration in quartz. These results are reviewed in comparison with Fe–Ti oxide, feldspar-melt and amphibole geothermometry. Core-to-rim quartz Ti profiles record a marked change in conditions (temperature increase and/or pressure decrease and/or change in melt composition) causing and then following a significant resorption horizon in the outer parts of the crystals. Two alternative models that could explain the quartz Ti zonation invoke a temperature increase caused by mafic recharge and/or a pressure decrease due to magma ponding and re-equilibration at shallow crustal levels. Concomitant changes in melt composition and Ti activity may, however, also have strongly influenced Ti uptake into the quartz. Some crystals also show other marked increases in CL brightness internally, but any accompanying magmatic changes did not result in eruption. Diffusion modelling indicates that this significant change in conditions occurred over ~10–85 years prior to caldera-forming eruption. This rapid thermal pulse or pressure change is interpreted as evidence for open-system processes, and appears to record a magma chamber recharge event that rejuvenated the Whakamaru magma system (melt-dominant magma plus crystal mush), and potentially acted as a trigger for processes that led to eruption.     

Quartz chemistry – A step to understanding magmatic-hydrothermal processes in ore-bearing granites: Cínovec/Zinnwald Sn-W-Li deposit,Central Europe

Quartz from granites, greisens and quartz veins from a 1596 m long vertical section through the Cínovec/Zinnwald Li-Sn-W deposit (Czech Republic) was studied using cathodoluminescence (CL) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP MS). The trace contents of Al, Ti, Li and the Ge/Ti and Al/Ti values in quartz reflect the degree of fractionation of parental melt from which primary quartz crystallized. From the biotite granite to the younger zinnwaldite granite, quartz is characterized by increasing contents of Al (from 136–176 to 240–280 ppm) and decreasing Ti (from 16–54 to 6–14 ppm), while the contents of Li and Ge are similar (15–36 and 0.8–1.7 ppm, respectively). Quartz of the greisen stage and vein stage is poor in all measured elements (26–59 ppm Al, 0.5–1.6 ppm Ti, 2–13 ppm Li, 0.8–1.6 ppm Ge). The youngest low-temperature quartz forming thin coatings in vugs in greisen and veins differs in its extreme enrichment in Al (>1000 ppm) and Li (∼100 ppm) and very low Ti (<1 ppm). Within the greisen, remnants of primary magmatic quartz should be distinguished from metasomatic greisen-stage quartz in their higher intensity of CL and relatively higher Ti contents. A part of primary magmatic quartz may by secondarily purified via infiltration of hydrothermal fluids and dissolution–reprecipitation processes. Such quartz parallels newly formed greisen-stage quartz in its chemical and CL properties; the share of greisen-stage quartz may by therefore overestimated.     

Insights from quartz cathodoluminescence zoning into crystallization of the Vinalhaven granite,coastal Maine

The Vinalhaven intrusive complex provides field and petrographic evidence for multiple replenishments of mafic and silicic magmas, mingling and limited mixing, and rejuvenation of granite. Quartz in granitic rocks preserves a record of those processes, in the form of cathodoluminescence (CL) zoning, which is related to concentration of titanium, and to temperature of crystallization using the new TitaniQ (Ti in quartz) geothermometer. Injection of mafic melts into partly crystalline Vinalhaven granite resulted in partial quartz resorption followed by higher-temperature growth from H₂O-undersaturated melt. This is shown by steep, rimward increases in CL intensity and Ti content across discordant boundaries that truncate older growth zones. Quartz zoning in granite affected by mafic magmas displays large rimward jumps in Ti content, whereas quartz in granitic feeders and in granite far from mafic rocks typically displays broad rims with decreasing Ti contents, consistent with slow cooling without thermal disruptions due to mafic recharge.     

Cathodoluminescence and micro-structural evidence for crystallisation and deformation processes of granites in the Eastern Lachlan Fold Belt (SE Australia)

Trace elements (Al, K, Ti, Fe), growth and deformation pattern in quartz of the multiple deformed Carcoar, Barry and Sunset Hills granites were investigated by electron micro probe and cathodoluminescence. Zoned quartz phenocrysts with high Ti concentrations (>70 ppm) that show blue cathodoluminescence originated from the early stage of magma crystallisation. Multiple deformation of quartz causes the redistribution of Al and K in the quartz lattice, which results in the accumulation of these elements in submicroscopic inclusions (<0.5 µm) of muscovite-like composition. In contrast, structural Ti in quartz is mostly kept in the lattice. Common halos of defect-poor, secondary quartz around fluid inclusions result from re-equilibration of fluid inclusions because of differences between fluid pressure and lithostatic pressure, e.g. during uplift (isothermal decompression) and/or !/#-transition of quartz. During healing, defect-poor secondary quartz grows at the cost of the host quartz and releases or replaces defect centres. The results of micro-structural investigations combined with Al-in-hornblende thermobarometry allow the reconstruction of regional processes. Carcoar and Barry granodiorites and Sunset Hills granite were intruded in the Late Ordovician-Early Silurian at depths of 4-8.6 and 10-12 km, respectively. In contrast to the continuous crystallisation of the granodiorite magmas, the magma of the Sunset Hills granite ascended in a stepwise fashion, causing multiple quartz nucleation. The two granodiorites were multiple, post-magmatically deformed, first, during Early Devonian under more brittle conditions at temperatures of 350-400 °C, whereas the Sunset Hills granite experienced more ductile deformation at temperatures of around 550 °C.     

Trace elements and cathodoluminescence of igneous quartz in topaz granites from the Hub Stock (Slavkovský Les Mts., Czech Republic)

Summary ¶Igneous quartz of the late-Variscan topaz-bearing granites from the Hub Stock (Slavkovský Les, Czech Republic) was investigated by cathodoluminescence (CL) and electron probe micro-analysis (EPMA) to demonstrate the intra-granular heterogeneity of growth patterns and trace element distribution in quartz. We show that EPMA is well suited for the in situ study of Al and Ti in zoned quartz, because of its high spatial resolution down to 5µm in conjunction with the ability to combine spot analyses with CL imaging. In the quartz phenocrysts of the topaz granites high Ti is associated with blue luminescent growth zones. High Ti (>40ppm) in quartz indicates a high crystallisation temperature and pressure. The groundmass quartz of the granites which is almost free of Ti, has higher Al than the phenocrysts which may reflect an increase of lithophile elements and water content in melt during the late magmatic stage. The occurrence of similar quartz phenocrysts in most of the late-Variscan granites and rhyolites of the Kruné Hory/Erzgebirge which intruded over a period of about 40Ma points to a similar crystallisation environment and origin of the quartz phenocrysts in the lower to middle crust.Received November 6, 2001; revised version accepted January 30, 2003 Published online June 2, 2003     

Application of cathodoluminescence to magmatic quartz in a tin granite – case study from the Schellerhau Granite Complex, Eastern Erzgebirge, Germany

A model of the cooling history of tin-bearing granitic magma forming the Schellerhau granites (Eastern Erzgebirge, Germany) is shown on the basis of quartz textures. Similar grain size, similar grain habit and correlatable growth textures of phenocrysts in different granite varieties give proof of a common crystallization history before the melts of the Schellerhau granite varieties were intruded. Four nucleation events occurred during crystallization in different crustal levels between about 20 and 1 km depth. The parental melt of the Schellerhau granites is interpreted to have contained<2.5 wt% H₂O originally. The water content of the melt during the subvolcanic intrusion stage amounted to more than 5 wt% and characterizes highly evolved residual melts that enable the formation of tin deposits. This study contributes to a better understanding of the development and behaviour of fractionated tin-bearing granitic melts, and links quartz cathodoluminescence (CL) with microanalytical studies. Received: 28 October 1998 / Accepted: 18 August 1999     

Diversity of primary CL textures in quartz from porphyry environments: implication for origin of quartz eyes

Porphyry-style mineralization is related to the intrusion and crystallization of small stocks, which can be of different compositions (from intermediate to felsic) and can intrude into different host rocks (from magmatic to sedimentary). We used cathodoluminescence and electron probe microanalysis to study the internal textures of more than 300 quartz eyes from six porphyry deposits, Panguna (Papua New Guinea), Far Southeast porphyry (Philippines), Batu Hijau (Indonesia), Antapaccay (Peru), Rio Blanco (Chile) and Climax (USA). Significant diversity of the internal textures in quartz eyes was revealed, sometimes even within a single sample. Quartz grains with Ti-rich cores surrounded by Ti-poor mantles were found next to the grains showing the opposite Ti distribution or only slight Ti fluctuations.We propose that diversity of the internal patterns in quartz eyes can actually reflect in situ crystallization history, and that prolonged crystallization after magma emplacement under conditions of continuous cooling can account for the observed features of internal textures. Formation of quartz eyes begins at high temperatures with crystallization of high titanium Quartz 1, which as the melt becomes more and more evolved and cooler, is overgrown by low Ti Quartz 2. Subsequent fluid exsolution brings about dramatic change in the melt composition: OH ^? , alkalis and other Cl-complexed elements partition into the fluid phase, whereas Ti stays in the melt, contributing to a rapid increase in Ti activity. Separation of the fluid and its further cooling causes disequilibrium in the system, and the Quartz 2 becomes partially resorbed. Exsolution of the fluid gradually builds up the pressure until it exceeds the yield strength of the host rocks and they then fracture. This pressure release most likely triggers crystallization of Quartz 3, which is higher in Ti than Quartz 2 because Ti activity in the melt is higher and pressure of crystallization is lower. As a result of the reaction between the exsolved fluid and quartz a new phase, a so called ‘heavy fluid’ forms. From this phase Quartz 4 crystallizes. This phase has extremely high metal-carrying capacity, and may give a rise to mineralizing fluids. Finally, on the brink of the subsolidus stage, groundmass quartz crystallizes. Prolonged crystallization under conditions of continuous cooling accounts better for the diversity of CL textures than crystallization in different parts of a deep magma chamber. It is also in a better agreement with the existing model for formation of porphyry-style deposits.     

Textural and Chemical Evolution of Unidirectional Solidification Textures in Highly Differentiated Granitic Rocks at Kharaatyagaan,Central Mongolia

Unidirectional solidification texture (UST) in an aplite body is recognized in the Neoproterozoic highly differentiated granitic rocks at Kharaatyagaan, central Mongolia. On the basis of crystal morphology, two main types of UST were identified in the aplite body: (i) thin crenulate UST layers; and (ii) thick intergrowth UST layers. Bulk geochemistry indicates that the Kharaatyagaan UST‐bearing aplite and aplite dike are alkaline, and are enriched in light rare‐earth elements. Scanning electron microscopy and cathadoluminescence imaging of UST quartz from Kharaatyagaan show four types of quartz: euhedral quartz phenocrysts with well‐developed concentric growth zoning (Qa1) in the aplite; euhedral quartz with weak growth zoning in the aplite (Qa2); UST quartz exhibiting distinct growth zones (Qu1); and UST quartz showing mosaic texture (Qu2). Crystallization temperatures determined by the Ti‐in‐quartz geothermometer of Qa1 and Qu1 quartz range between around 500°C and 780°C and Qa2 and Qu2 range between about 490° and 630°C. The cathodoluminescence textures of quartz are predominantly caused by variations in the trace elements contents of quartz. The Qa1 and Qu1 quartz crystals are characterized by high Ti and Al concentrations in the quartz lattice, and are observed in the bottom of the Kharaatyagaan hill, which formed in the early, less evolved magmatic stage. The Qa2 and Qu2 UST quartz characterized by low Ti and variable Al concentrations are found at the top. The UST layers crystallized along the upper part of the magma chamber in the presence of fluid phases exsolved from felsic magma.     

Quartz and feldspar zoning in the eastern Erzgebirge volcano-plutonic complex (Germany, Czech Republic): evidence of multiple magma mixing

Zoned quartz and feldspar phenocrysts of the Upper Carboniferous eastern Erzgebirge volcano-plutonic complex were studied by cathodoluminescence and minor and trace element profiling. The results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends, magma mixing and recharge events, and suggest that much heterogeneity in plutonic systems may be overlooked on a whole-rock scale. Multiple resorption surfaces and zones, element concentration steps in zoned quartz (Ti) and feldspar phenocrysts (anorthite content, Ba, Sr), and plagioclase-mantled K-feldspars etc. indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern Erzgebirge volcano-plutonic complex. Generally, feldspar appears to be sensitive to the physicochemical changes of the melt, whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas. The regional distribution of mixing-compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late-Variscan granites and associated volcanic rocks.

Quartz phenocrysts from 14 magmatic phases of the eastern Erzgebirge volcano-plutonic complex provide information on the relative timing of different mixing processes, storage and recharge, allowing a model for the distribution of magma reservoirs in space and time. At least two levels of magma storage are envisioned: deep reservoirs between 24 and 17 km (the crystallisation level of quartz phenocrysts) and subvolcanic reservoirs between 13 and 6 km. Deflation of the shallow reservoirs during the extrusion of the Teplice rhyolites triggered the formation of the Altenberg-Teplice caldera above the eastern Erzgebirge volcano-plutonic complex. The deep magma reservoir of the Teplice rhyolite also has a genetic relationship to the younger mineralised A-type granites, as indicated by quartz phenocryst populations. The pre-caldera biotite granites and the rhyodacitic Schönfeld volcanic rocks represent temporally and spatially separate magma sources. However, the deep magma reservoir of both is assumed to have been at a depth of 24–17 km. The drastic chemical contrast between the pre-caldera Schönfeld (Westfalian B–C) and the syn-caldera Teplice (Westfalian C–D) volcanic rocks is related to the change from late-orogenic geotectonic environment to post-orogenic faulting, and is considered an important chronostratigraphic marker.