Pressure dependence of hydroxyl solubility in coesite

 The solubility of hydroxyl in coesite was investigated in multianvil experiments performed at 1200 °C over the nominal pressure range 5–10 GPa, at an f _O2 close to the Ni-NiO buffer. The starting material for each experiment was a cylinder of pure silica glass plus talc, which dehydrates at high P and T to provide a source of water and hydrogen (plus enstatite and excess SiO₂). Fourier-transform infrared (FTIR) spectra of the recovered coesite crystals show five sharp bands at 3606, 3573, 3523, 3459, and 3299 cm⁻¹, indicative of structurally bonded hydrogen (hydroxyl). The concentration of hydrogen increases with pressure from 285 H/10⁶ Si (at 5 GPa) to 1415 H/10⁶ Si (at 10 GPa). Assuming a model of incorporation by (4H)_Si defects, the data are fit well by the equation C _OH=Af ² _H2<\INF>Oexp(−PΔV/RT), with A=4.38 H/10⁶ Si/GPa, and ΔV=20.6 × 10⁻⁶ m³ mol⁻¹. An alternative model entailing association of hydrogen with cation substitution can also be used to fit the data. These results show that the solubility of hydroxyl in coesite is approximately an order of magnitude lower than in olivines and pyroxenes, but comparable to that in pyropic garnet. However, FTIR investigations on a variety of ultrahigh pressure metamorphic rocks have failed in all cases to detect the presence of water or hydrogen in coesite, indicating either that it grew in dry environments or lost its hydrogen during partial transformation to quartz. On the other hand, micro-FTIR investigations of quartz crystals replacing coesite show that they contain varying amounts of H₂O. These results support the hypothesis that preservation of coesite is not necessarily linked to fast exhumation rates but is crucially dependent on limited fluid infiltration during exhumation. Received: 23 August 1999 / Accepted: 10 April 2000     

Diamonds and eclogites of the Jericho kimberlite (Northern Canada)

We studied diamonds and barren and diamondiferous eclogite xenoliths from the Jericho kimberlite (Northern Slave craton). The majority of the diamonds are non-resorbed octahedral crystals, with moderately aggregated N (IaB < 50%, N < 300 ppm) and δ¹³C = −5 to −41‰. The diamonds belong to “eclogitic” (90% of the studied samples), “websteritic” (7%) and “peridotitic” (3%) assemblages. The Jericho diamonds differ from the majority of “eclogitic” diamonds worldwide in magnesian compositions of associated minerals and extremely light C isotopic compositions (δ¹³C = −24 to −41‰). We propose that metasomatism triggered by H₂O fluids may have been involved in the diamond formation. Multiple episodes of the metasomatism and associated melt extraction of various ages are evident in Jericho eclogite xenoliths where primary garnet and clinopyroxene have been recrystallized to more magnesian minerals with higher contents of some incompatible trace elements and to hydrous secondary phases. The model is supported by the general similarity of mineral compositions in diamondiferous eclogites to those in diamond inclusions and to secondary magnesian garnet and clinopyroxene in recrystallized barren eclogites. The ultimate products of the metasomatism could be “websteritic” diamond assemblages sourced from magnesian eclogites. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Origin of quartz clusters in Vinalhaven granite and porphyry,coastal Maine

We use the crystallographic orientations of quartz crystals, as determined with EBSD, to provide new evidence for the formation of clustered quartz crystals during magma crystallization. Vinalhaven is dominated by granite, with minor porphyry that formed when granite remelted during input of coeval basalt. CL zoning suggests that most quartz clusters in granite and porphyry formed by synneusis, the “swimming together” of preformed crystals. In granite, most quartz pairs in clusters have random orientations—only about 10% have parallel or Esterel twin orientations. Porphyry has fewer quartz clusters, and all pairs have approximately parallel or Esterel twin orientations. CL zoning of quartz pairs in porphyry indicates that they attached prior to a major remelting event. Interpretation of the Vinalhaven quartz clusters leads us to propose that oriented synneusis occurs during crystal accumulation on a magma chamber floor. During hindered settling, some quartz crystals should have come into contact along their dipyramidal faces. Once in contact, continued settling and loss of interstitial melt may have rotated some quartz crystals such that lattices on their dipyramidal faces matched—producing parallel and Esterel twin orientations and creating strong bonds between pairs. Only a small proportion of pairs with matched dipyramidal faces formed in the granite and, during rejuvenation to produce porphyry, only these oriented pairs survived. Hence, the presence of oriented synneusis in a plutonic rock may demonstrate a history of crystal accumulation.     

榴辉岩相峰期流体活动：来自东昆仑榴辉岩石英脉的证据

本文通过对东昆仑温泉地区榴辉岩中石英脉的锆石U-Pb定年和Lu-Hf同位素的综合研究,为榴辉岩相峰期变质阶段的流体活动提供了一定的证据。石英脉中的锆石晶型较好,具有振荡环带或弱分带,排除了从寄主榴辉岩中捕获锆石的可能性。石英脉和寄主榴辉岩中锆石U-Pb年龄的加权平均值分别为450±2Ma和451±2Ma,说明石英脉中锆石的形成年龄与榴辉岩相的峰期变质阶段一致。两种锆石Hf同位素组成的相似性说明形成石英脉的流体/熔体为内部来源,推测可能为榴辉岩中石英发生溶解以及绿辉石和石榴石分子结构中羟基的出溶作用形成。锆石较低的U、Th含量以及Th/U比值说明石英脉更可能是流体活动形成而非熔体。     

Hydroxyl defects in garnets from mantle xenoliths in kimberlites of the Siberian platform

A suite of more than 200 garnet single crystals, extracted from 150 xenoliths, covering the whole range of types of garnet parageneses in mantle xenoliths so far known from kimberlites of the Siberian platform and collected from nearly all the kimberlite pipes known in that tectonic unit, as well as some garnets found as inclusions in diamonds and olivine megacrysts from such kimberlites, were studied by means of electron microprobe analysis and single-crystal IR absorption spectroscopy in the v _OH vibrational range in search of the occurrence, energy and intensity of the v _OH bands of hydroxyl defects in such garnets and its potential use in an elucidation of the nature of the fluid phase in the mantle beneath the Siberian platform. The v _OH single-crystal spectra show either one or a combination of two or more of the following major v _OH bands, I 3645–3662 cm⁻¹, II 3561–3583 cm⁻¹, III 3515–3527 cm⁻¹, and minor bands, Ia 3623–3631 cm⁻¹, IIa 3593–3607 cm⁻¹. The type of combination of such bands in the spectrum of a specific garnet depends on the type of the rock series of the host xenolith, Mg, Mg-Ca, Ca, Mg-Fe, or alkremite, on the xenolith type as well as on the chemical composition of the respective garnet. Nearly all garnets contain band systems I and II. Band system III occurs in Ti-rich garnets, with wt% TiO₂ > ca. 0.4, from xenoliths of the Mg-Ca and Mg-Fe series, only. The v _OH spectra do not correspond to those of OH⁻ defects in synthetic pyropes or natural ultra-high pressure garnets from diamondiferous metamorphics. There were no indications of v _OH from inclusions of other minerals within the selected 60 × 60 μm measuring areas in the garnets. The v _OH spectra of pyrope-knorringite- and pyrope-knorringite-uvarovite-rich garnets included in diamonds do not show band systems I to III. Instead, they exhibit one weak, broad band (Δv _OH 200–460 cm⁻¹) near 3570 cm⁻¹, a result that was also obtained on pyrope-knorringite-rich garnets extracted from two olivine megacrysts. The quantitative evaluation, on the basis of relevant existing calibrational data (Bell et al. 1995), of the sum of integral intensities of all v _OH bonds of the garnets studied yielded a wide range of “water” concentrations within the set of the different garnets, between values below the detection limit of our single-crystal IR method, near 2 × 10⁻⁴ wt%, up to 163 × 10⁻⁴ wt%. The “water” contents vary in a complex manner in garnets from different xenolith types, obviously depending on a large number of constraints, inherent in the crystal chemistry as well as the formation conditions of the garnets during the crystallization of their mantle host rocks. Secondary alteration effects during uplift of the kimberlite, play, if any, only a minor role. Despite the very complex pattern of the “water” contents of the garnets, preventing an evaluation of a straightforward correlation between “water” contents of the garnets and the composition of the mantle's fluid phase during garnet formation, at least two general conclusions could be drawn: (1) the wide variation of “water” contents in garnets is not indicative of regional or local differences in the composition of the mantle's fluid phase; (2) garnets formed in the high-pressure/high-temperature diamond-pyrope facies invariably contain significantly lower amounts of “water” than garnets formed under the conditions of the graphite-pyrope facies. This latter result (2) may point to significantly lower f _H2O and f _O2 in the former as compared to the latter facies. Received: 25 November 1997 / Accepted: 9 March 1998     

Gold mineralization in the Mazowe area, Harare-Bindura-Shamva greenstone belt, Zimbabwe: II. Genetic relationships deduced from mineralogical, fluid inclusion and stable isotope studies, and the Sm-Nd isotopic composition of scheelites

In the Mazowe area some 40 km NW of Harare in Zimbabwe, gold mineralization is hosted in a variety of lithologies of the Archean Harare-Bindura-Shamva greenstone belt, in structures related to the late Archean regional D2/3 event. Conspicuous mineralzogical differences exist between the mines; the mainly granodiorite-hosted workings at Mazowe mine are on pyrite-rich reefs, mines of the Bernheim group have metabasalt host rocks and are characterized by arsenopyrite-rich ores, and Stori's Golden Shaft and Alice mine, both in metabasalts, work sulfide-poor quartz veins. In contrast to the mineralogical diversity, near-identical fluid inventories were found at the different mines. Both H₂O-CO₂-CH₄ fluids of low salinity, and highly saline fluids are present and are regarded to indicate fluid mixing during the formation of the deposits. Notably, these fluid compositions in the Mazowe gold field markedly contrast to ore fluids “typical” of Archean mesothermal gold deposits on other cratons. Stable isotope compositions of quartz from the various deposits (δ¹⁸O=10.8 to 13.2‰ SMOW), calcite (δ¹⁸O=9.5 to 11.9‰ SMOW and δ¹³C=−3.2 to −8.0‰ PDB), inclusion water (δD=−28 to −40‰ SMOW) and sulfides (δ³⁴S=1.3 to 3.2‰ CDT) are uniform within the range typical for Archean lode gold deposits worldwide. The fluid and stable isotope compositions support the statement that the mineralization in the Mazowe gold field formed from relatively reduced fluids with a “metamorphic” signature during a single event of gold mineralization. Microthermometric data further indicate that the deposits formed in the PT range of 1.65–2.3 kbar and 250–380 °C. Ages obtained by using the Sm/Nd and Rb/Sr isotope systems on scheelites are 2604 ± 84 Ma for the mineralization at Stori's Golden Shaft mine, and 2.40 ± 0.20 Ga for Mazowe mine. The Archean age at Stori's is regarded as close to the true age of gold mineralization in the area, whereas the Proterozoic age at Mazowe mine probably reflects later resetting. Received: 30 September 1998 / Accepted: 17 August 1999     

“Hot” particles of the Yenisei River: Radioisotope composition,structure, and behavior in natural conditions

The radioisotope compositions, structure, and behavior of “hot” particles under the natural conditions of the Yenisei River in the nearby influence zone of Krasnoyarsk mining and chemical combine were examined in this study. By the composition of gamma-radiating isotopes, all particles are divided into three groups: mono-isotopic, bi-isotopic and poly-isotopic. Mono-isotopic “hot” particles, containing only ⁶⁰Co were discovered for the first time. Transuranium elements (²⁴¹Am and ²⁴³Cm) were revealed in poly-isotopic particles. Investigation of poly-isotopic particles by means of a scan electron microscope showed that the presence of UO₂ together with the lack of activation of ¹⁵²Eu testifies to the reactor origin of this particle. Experiments showed that in natural conditions “hot” particles under the influence of filtrating water and moisture of pore solutions are gradually dissolved and radionuclides are repeatedly drawn into migration.     

A crystallographic and m?ssbauer spectroscopy study of Fe

The crystal chemistry of garnet solid solutions on the Fe ₃ ²⁺ Al₂Si₃O₁₂-Fe ₃ ²⁺ Fe ₂ ³⁺ Si₃O₁₂ (almandine-“skiagite”) and Ca₃Fe ₂ ³⁺ Si₃O₁₂-Fe ₃ ²⁺ Fe ₂ ³⁺ Si₃O₁₂ (andradite-“skiagite”) joins have been investigated by single-crystal X-ray structure refinements and M?ssbauer spectroscopy. Together, these two solid solution series encompass the complete range in Fe³⁺/ΣFe from 0.0 to 1.0. All garnets are isotropic and were re0fined in the Ia d space group. Small excess volumes of mixing are observed in andradite-“skiagite” solid solutions (W _v =1.0±0.2 cm³ mol^-1) and along the almandine-“skiagite” join (W _v =-0.77±0.17cm³ mol^-1). The octahedral (Al, Fe³⁺)-O bond lengths show a much greater variation across the almandine-skiagite join compared to the andradite-skiagite garnets. The dodecahedral (X)-O bond lengths show the opposite behaviour. In andradite-“skiagite” solid solutions, the octahedral site passes from being flattened to elongated parallel to the 3 axis of symmetry with increasing “skiagite” content. A perfect octahedron occurs in a composition of ≈35 mol% “skiagite”. The occupancy of the neighboring dodecahedral sites has the greatest effect on octahedral distortion and vice versa. The M?ssbauer hyperfine parameters of Fe²⁺remain constant in both solid solutions. The hyperfine parameters of Fe³⁺ (at room temperature: centre shift=0.32–0.40 mm/sec, quadrupole splitting (QS)≈0.21–0.55 mm/ sec) indicate that all Fe³⁺ is in octahedral coordination. The Fe³⁺ parameters are nearly constant in almandine-“skiagite” solid solutions, but vary significantly across the andradite-“skiagite” join. The structural unit that contributes to the electric field gradient of the octahedral site is different from that of the coordinating oxygen polyhedron, probably involving the neighboring dodeca-hedral sites.     

Implications from inclusions in topaz for greisenisation and mineralisation in the Hensbarrow topaz granite, Cornwall, England

Textural and geochemical studies of inclusions in topaz from greisens in the Hensbarrow topaz granite stock (St. Austell, Cornwall) are used to constrain the composition of fluids responsible for late stage greisening and mineralisation. The topaz contains an abundant and varied suite of inclusions including aqueous liquid + vapour (L + V), quartz, zinnwaldite, albite, K-feldspar, muscovite, ilmenorutile, apatite, columbite, zircon, varlamoffite [(Sn, Fe)(O, OH)₂] and qitianlingite [(Fe⁺²,Mn⁺²)₂(Nb,Ta)₂W⁺⁶O₁₀]. Primary L + V inclusions in topaz show relatively high T _h (mainly 300 to >500 °C) and a narrow range of salinities (23–30 wt % NaCl equivalent) compared with those in greisen quartz (150–450 °C, 0–50 wt % NaCl equivalent). Textures indicate that topaz formed earlier than quartz and the fluid inclusion data are interpreted as indicating a cooling of the hydrothermal fluids during greisenisation, mixing with meteoric waters and a decrease in pressure causing intermittent boiling. The presence of early-formed albite and K-feldspar as inclusions in the topaz is likely to indicate that the greisen-forming fluid became progressively more acid during greisenisation. The most distinctive inclusions in the topaz are wisp- and bleb-shaped quartz, < 50 μm in size, which show textural characteristics indicating former high degrees of plasticity. They often have multiple shrinkage bubbles at their margins rich in Sn, Fe, Mn, S and Cl and, more rarely, contain euhedral albite, K-feldspar, stannite or pyrrhotite crystals up to 40 μm in size. The quartz inclusions show similar morphologies to inclusions in topaz from quartz-topaz rocks elsewhere which have been interpreted as trapped “silicate melt”. Their compositions are, however, very different to those expected for late stage topaz-normative granitic melts. From their textural and chemical characteristics they are interpreted as representing crystallised silica colloid, probably trapped as a hydro gel during greisenisation. There is also evidence for the colloidal origin of inclusions of varlamoffite in the topaz. These occurrences offer the first reported evidence in natural systems for the formation of colloids in high temperature hydrothermal fluids. Their high ore carrying potential is suggested by the presence of varlamoffite and the occurrence of stannite, pyrrhotite and SnCl within the quartz inclusions. Received: 9 April 1996 / Accepted: 12 November 1996     

Mobility and H2O loss from fluid inclusions in natural quartz crystals

Petrographic observations on quartz crystals from the Mole Granite (Australia) and other localities shed new light on the mechanisms of post-entrapment modification of fluid inclusions. These modifications include migration away from pseudosecondary trails, changes in fluid salinity and density, shape distortion and the formation of “sweat-haloes” around strongly deformed inclusions. Increases in fluid salinity, which usually are associated with inclusion migration, indicate water-losses of up to 50%. However, LA-ICP-MS-analysis of unmobilized and mobilized inclusions of the same trail reveals basically unchanged ratios of major – and trace element cations, with the exception of Li, which seems to be incorporated into the crystal lattice during migration. Despite the fact that all these modifications are closely related to deformation processes, they occur not only in mechanically deformed quartz, but also in free-standing crystals. In the latter samples, stress has been generated internally as a result of brazil-twinned growth and compositional zonation. These observations and their interpretation leads to a list of practical criteria that should help in differentiating between reliable and suspect fluid inclusions in other samples. Received: 17 November 1998 / Accepted: 16 April 1999     

Tourmaline in the Vetka porphyry copper-molybdenum deposit of the Chukchi Peninsula of Russia

Three generations of tourmaline have been identified in propylite in the Vetka porphyry copper-molybdenum deposit of the Chukchi Peninsula of Russia. Tourmaline-I is characterized by its Fe_tot/(Fe_tot + Mg) value, which ranges from 0.33 to 0.49. Tourmaline-II, which crystallizes at a lower temperature, overgrowing tourmaline-I or occurring as isolated crystals, is distinguished by a higher Fe_tot/(Fe_tot + Mg), which varies from 0.46 to 0.72. The Fe_tot/(Fe_tot + Mg) ratio in tourmaline-III, which overgrows tourmaline-II is lower (0.35–0.49), and is identical to that of the first tourmaline generation. This is probably caused by the beginning of sulfide deposition. Tourmalines in the deposit characterized by complex isomorphic substitutions can be attributed to the intermediate members of the dravite—“hydroxy-uvite”-“oxy-uvite” and schorl-“hydroxy-feruvite”-“oxy-feruvite” series. Tourmaline starts to crystallize at temperatures above 340°C. The fluid responsible for the tourmaline deposition was magmatic, with a significant admixture of meteoric water (δ¹⁸O_{H 2}O = −0.85 to −0.75‰). The high Fe³⁺/Fe_tot ratio (0.50) indicates high oxygen activity when the tourmaline precipitated. It has been established that the isomorphic substitution Fe_tot → Al is typomorphic of tourmalines from porphyry copper deposits worldwide.     

Ultrahigh-pressure metamorphic rocks from the Chinese Continental Scientific Drilling Project: II Oxygen isotope and fluid inclusion distributions through vertical sections

In order to reconstruct the formation and exhumation mechanisms of UHP metamorphic terrains, the Chinese Continental Scientific Drilling Program (CCSD) has been carried out in Donghai of the Dabie-Sulu ultrahigh-pressure (UHP) metamorphic belt, East China. Eclogite, gneiss, amphibolite (retrograded from eclogite), ultramafic rocks, and minor schist and quartzite have been drilled. Aiming to reveal the fluid behaviour in a vertical sequence of an UHP slab, we investigated fluid inclusion and oxygen isotope characteristics of selected drillcores from the main hole and the pilot-holes PP2 and ZK 703 of the CCSD. More than 540 laser-ablation oxygen isotope analyses on garnet, omphacite, quartz, kyanite, amphibole, phengite, rutile, epidote, amphibole, plagioclase, and biotite from various rocks in the depth range of 0–3,000 m (mainly eclogite and gneiss) show that the investigated rocks can be divided into two groups: ¹⁸O-depleted rocks (as low as δ¹⁸O = −7.4‰ for garnet) indicate interaction with cold climate meteoric waters, whereas ¹⁸O-normal rocks (with bulk δ¹⁸O > +5.6‰) have preserved the O-isotopic compositions of their protoliths. Meteoric water/rock interaction has reached depths of at least 2,700 m. Oxygen isotope equilibrium has generally been achieved. Isotopic compositions of mineral phases are homogeneous on a mm to cm scale regardless of lithology, but heterogeneous on the scale of a few metres. Oxygen isotope distributions in the vertical sections favour an “in situ” origin of the UHP metamorphic rocks. The very negative δ¹⁸O eclogites usually have higher hydroxyl-mineral contents than the normal δ¹⁸O rocks, indicating higher water content during UHP metamorphism. Fluid inclusion data suggest that rocks with depleted ¹⁸O compositions have had different fluid histories compared to those with normal δ¹⁸O values. Rocks with depleted ¹⁸O mainly have primary medium-to-high salinity inclusions in omphacite, kyanite and quartz, and abundant secondary low-salinity or pure water inclusions in quartz, indicating a high-salinity-brine-dominated fluid system during peak UHP metamorphism; no carbonic inclusions have been identified in these rocks. By contrast, primary very high-density CO₂ inclusions are commonly found in the rocks with normal δ¹⁸O values. These observations suggest that fluid and oxygen isotope composition of minerals are related and reflect variable degrees of alterations of the Dabie-Sulu UHP metamorphic rocks.     

Survival of the thinnest: rediscovery of Bauer’s (1898) ichthyosaur tooth sections from Upper Jurassic lithographic limestone quarries,south Germany

During the late Early Cretaceous, the shallow-water domains of the western Tethys are characterized by the widespread deposition of Urgonian-type carbonates rich in rudists, corals and other oligotrophic, shallow-marine organisms. In the Helvetic Alps, the Urgonian occurrences have been dated by ammonite biostratigraphy as Late Barremian and Early Aptian. For the more proximal occurrences in the western Swiss Jura, a recent age model based on bio-, chemo- and sequence stratigraphy has been proposed, which allows for an improved correlation with the Helvetic counterparts. In order to corroborate the recently proposed age model for the Jura, a set of well-preserved rhynchonellids collected from five different lithostratigraphical formations and members (“Marnes bleues d’Hauterive”, “Marnes d’Uttins”, basal marly layers within the “Urgonien Jaune”, “Marnes de la Russille”, “Urgonien Blanc”) has been analysed for its strontium–isotope ratios (⁸⁷Sr/⁸⁶Sr). In addition, K–Ar dating was performed on well-preserved glauconite grains from two different levels (“Marnes d’Uttins” and a basal layer within the “Urgonien Jaune”). The correlation of the Sr–isotope data set with a belemnite-based, ammonite-calibrated reference curve provides an age model which is coherent with recently published ages based on calcareous nannofossil biostratigraphy and the correlation of trends in chemo- and sequence stratigraphy. K–Ar dating on well-preserved glauconite grains from the “Marnes d’Uttins” and lowermost part of the “Urgonien Jaune” delivered ages of 127.5 ± 2.3 and 130.7 ± 2.6 Ma, respectively. Whereas the age of the glauconitic level near the base of the “Urgonien Jaune” is chronostratigraphically meaningful, the K–Ar age of the “Marnes d’Uttins” appears too young relative to the presently used time scale. This may be related to rejuvenation of the K–Ar chronometer due to post-depositional Ar loss, most likely during hardground formation. The ages obtained here confirm the Late Barremian age for the onset of the Urgonian platform, an age which is conform with ages obtained in the Helvetic Alps and elsewhere along the northern Tethyan margin.     

Origin, spectral characteristics and practical applications of the cathodoluminescence (CL) of quartz – a review

Summary Investigations of natural and synthetic quartz specimens by cathodoluminescence (CL) microscopy and spectroscopy, electron paramagnetic resonance (EPR) and trace-element analysis showed that various luminescence colours and emission bands can be ascribed to different intrinsic and extrinsic defects. The perceived visible luminescence colours in quartz depend on the relative intensities of the dominant emission bands between 380 and 700 nm. Some of the CL emissions of quartz from the UV to the yellow spectral region (175 nm, 290 nm, 340 nm, 420 nm, 450 nm, 580 nm) can be related to intrinsic lattice defects. Extrinsic defects such as the alkali (or hydrogen)-compensated [AlO₄/M⁺] centre have been suggested as being responsible for the transient emission band at 380–390 nm and the short-lived blue-green CL centered around 500 nm. CL emissions between 620 and 650 nm in the red spectral region are attributed to the nonbridging oxygen hole centre (NBOHC) with several precursors. The weak but highly variable CL colours and emission spectra of quartz can be related to genetic conditions of quartz formation. Hence, both luminescence microscopy and spectroscopy can be used widely in various applications in geosciences and techniques. One of the most important fields of application of quartz CL is the ability to reveal internal structures, growth zoning and lattice defects in quartz crystals not discernible by means of other analytical techniques. Other fields of investigations are the modal analysis of rocks, the provenance evaluation of clastic sediments, diagenetic studies, the reconstruction of alteration processes and fluid flow, the detection of radiation damage or investigations of ultra-pure quartz and silica glass in technical applications. Zusammenfassung Ursachen, spektrale Charakteristika und praktische Anwendungen der Kathodolumineszenz (KL) von Quarz – eine Revision Untersuchungen von natürlichen und synthetischen Quarzproben mittels Kathodolumineszenz (KL) Mikroskopie und -spektroskopie, Elektron Paramagnetischer Resonanz (EPR) und Spurenelementanalysen zeigen verschiedene Lumineszenzfarben und Emissionsbanden, die unterschiedlichen intrinsischen und extrinsischen Defekten zugeordnet werden k?nnen. Die sichtbaren Lumineszenzfarben von Quarz werden durch unterschiedliche Intensit?tsverh?ltnisse der dominierenden Emissionsbanden zwischen 380 und 700 nm verursacht. Einige der KL Emissionen vom UV bis zum gelben Spektralbereich (175 nm, 290 nm, 340 nm, 420 nm, 450 nm, 580 nm) stehen im Zusammenhang mit intrinsischen Defekten. Die kurzlebigen Lumineszenzemissionen bei 380–390 nm sowie 500 nm werden mit kompensierten [AlO₄/M⁺]-Zentren in Verbindung gebracht. Die KL-Emissionen im roten Spektralbereich bei 620 bis 650 nm haben ihre Ursache im “nonbridging oxygen hole centre” (NBOHC) mit verschiedenen Vorl?uferzentren. Die unterschiedlichen KL-Farben und Emissionsspektren von Quarz k?nnen oft bestimmten genetischen Bildungsbedingungen zugeordnet werden und erm?glichen deshalb vielf?ltige Anwendungen in den Geowissenschaften und in der Technik. Eine der gravierendsten Einsatzm?glichkeiten ist die Sichtbarmachung von Internstrukturen, Wachstumszonierungen und Defekten im Quarz, die mit anderen Analysenmethoden nicht oder nur schwer nachweisbar sind. Weitere wesentliche Untersuchungsschwerpunkte sind die Modalanalyse von Gesteinen, die Eduktanalyse klastischer Sedimente, Diageneseuntersuchungen, die Rekonstruktion von Alterationsprozessen und Fluidmigrationen, der Nachweis von Strahlungssch?den oder die Untersuchung von ultrareinem Quarz und Silikaglas für technische Anwendungen. Received March 29, 2000 Accepted October 27, 2000     

The hydro geochemical characterization of ground waters in Tunisian Chott’s region.

Tunisian Chott’s region is one of the most productive artesian basins in Tunisia. It is located in the southwestern part of the country, and its groundwater resources are developed for water supply and irrigation. The chemical composition of the water is strongly influenced by the interaction with the basinal sediments and by hydrologic characteristics such as the flow pattern and time of residence. The system is composed of an upper unconfined “Plio-Quaternary” aquifer with a varying thickness of 20–200 m, an intermediate confined/unconfined “Complex Terminal” aquifer about 100 m in thickness and a deeper “Continental Intercalaire” aquifer about 150 m in thickness separated by thick clay and marl layers. The dissolution of evaporites and carbonates explains part of the contained Na⁺, Ca²⁺, Mg²⁺, K⁺, SO₄²⁻ and Cl^-, but other processes, such carbonate precipitation, also contributes to the water composition. The stable isotope composition of waters establishes that the deep groundwater (depleted as compared to present corresponding local rainfall) is ancient water recharged probably during the late Pleistocene and the early Holocene periods. The relatively recent water in the Plio-Quaternary aquifer is composed of mixed waters resulting presumably from upward leakage from the deeper groundwater.     

Strontium and oxygen isotopic variations in Mesozoic and Tertiary plutons of central Idaho

Regional variations in initial ⁸⁷Sr/⁸⁶Sr ratios (r _i) of Mesozoic plutons in central Idaho locate the edge of Precambrian continental crust at the boundary between the late Paleozoic-Mesozoic accreted terranes and Precambrian sialic crust in western Idaho. The r _i values increase abruptly but continuously from less than 0.704 in the accreted terranes to greater than 0.708 across a narrow, 5 to 15 km zone, characterized by elongate, lens-shaped, highly deformed plutons and schistose metasedimentary and metavolcanic units. The chemical and petrologic character of the plutons changes concomitantly from ocean-arc-type, diorite-tonalite-trondhjemite units to a weakly peraluminous, calcic to calcalkalic tonalite-granodiorite-granite suite (the Idaho batholith). Plutons in both suites yield Late Cretaceous ages, but Permian through Early Cretaceous bodies are confined to the accreted terranes and early Tertiary intrusions are restricted to areas underlain by Precambrian crust. The two major terranes were juxtaposed between 75 and 130 m.y. ago, probably between 80 and 95 m.y. Oxygen and strontium isotopic ratios and Rb and Sr concentrations of the plutonic rocks document a significant upper-crustal contribution to the magmas that intrude Precambrian crust. Magmas intruding the arc terranes were derived from the upper mantle/subducted oceanic lithosphere and may have been modified by anatexis of earlier island-arc volcanic and sedimentary units. Plutons near the edge of Precambrian sialic crust represent simple mixtures of the Precambrian wall-rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r _i of 0.7035. Rb/Sr varies linearly with r _i, producing “pseudoisochrons” with apparent “ages” close to the age of the wall rocks. Measured δ ¹⁸O values of the wall rocks are less than those required for the assimilated end-member by Sr-O covariation in the plutons, however, indicating that wall-rock δ ¹⁸O was reduced significantly by exchange with circulating fluids. Metasedimentary rocks of the Belt Supergroup are similarly affected near the batholith, documenting a systematic depletion in ¹⁸O as much as 50 km from the margin of the batholith. Plutons of the Bitterroot lobe of the Idaho batholith are remote from the accreted terranes and represent mixtures of Precambrian wall-rocks with melts dominated by continental lower crust (r _i>0.708) rather than mantle. “Pseudoisochrons” resulting from these data are actually mixing lines that yield apparent “ages” less than the true age of the wall rocks and meaningless “r_i”. Assimilation/ fractional-crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region.     

Radiation-induced defects in euclase: formation of O<Superscript>−</Superscript> hole and Ti<Superscript>3+</Superscript> electron centers

Irradiation techniques are often applied to gem minerals for color enhancement purposes. Natural green, blue and colorless specimens of rare gemological quality euclase, BeAlSiO₄(OH), from Brazil were irradiated with gamma rays in the dose range from 10 to 500 kGy. Although the colors of the different specimens were not strongly influenced, two different irradiation-induced paramagnetic defect centers were found by electron paramagnetic resonance (EPR). The first one is an O⁻ hole center interacting with one Al neighbor and the second is a Ti³⁺ electron center. The EPR angular rotation patterns of both irradiation-induced defects were measured and analyzed. The results suggest that O⁻ hole centers are formed by dissociation of the hydroxyl ions, similar as in topaz crystals. In euclase the OH⁻ ions interconnect distorted Al octahedra and Be tetrahedra in O₅ positions. During irradiation, the electrons are captured by titanium ions (Ti⁴⁺ + e⁻), leading to the formation of paramagnetic Ti³⁺ ions. From the EPR rotation patterns it is clear that these ions substitute for Al ions. The spin Hamiltonian parameters of the irradiation-induced defects are analyzed and compared to similar defect centers in other mineral specimens. Thermal annealing experiments show that the O⁻ hole centers and Ti³⁺ electron centers are directly connected through the radiation process.     

Generation of a crust-mantle magma mixture: magma sources and contamination at Cerro Panizos,central Andes

 Cerro Panizos, a large caldera in the central Andes Mountains, produced two large dacitic ignimbrites at 7.9 Ma and 6.7 Ma and many andesitic and dacitic lava flows and domes. The older rhyodacitic Cienago Ignimbrite represents the most silicic magma erupted by the system. The younger, much larger volume dacitic Cerro Panizos Ignimbrite is very crystal-rich, containing up to 50% biotite, plagioclase, and quartz crystals in the pumice. It is weakly zoned, with most of the zoning apparent between two main cooling units. Major and most trace elements show little variation through the Cerro Panizos Ignimbrite, but the small range of composition is consistent with typical fractionation trends. Sr, Nd, and Pb isotopic ratios are very “crustal”, with initial ⁸⁷Sr/⁸⁶Sr values of 0.711 to 0.715, ɛ_Nd values of –7.5 to –10.2, and nearly invariant Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb=18.85, ²⁰⁷Pb/²⁰⁴Pb=15.67, and ²⁰⁸Pb/²⁰⁴Pb=38.80). The limited zonation observed in the Cerro Panizos Ignimbrite is explained by impeded crystal settling due to high crystal content. The magma body was a crystal-liquid mush before ascent to the pre-eruption crustal levels. Crystals formed, but did not separate easily from the magma. Limited fractionation of plagioclase and biotite may have occurred, but the composition was largely controlled by lower crustal MASH processes. AFC modeling shows that the Cerro Panizos magmas resulted from a mixture of roughly equal proportions of late Miocene mantle-derived basalts and melts from ∼1.0 Ga (Grenville age) lower crust. This occurred in a MASH zone in the lower crust, and set the crustal isotopic ratios observed in the Cerro Panizos magmas. The great thickening of the crust beneath the central Andes Mountains sent upper and middle crustal rock types to lower crustal (and deeper) depths, and this explains the “upper crustal” isotopic signatures of the Cerro Panizos rocks. Minor upper crustal assimilation of early Miocene volcanic or subvolcanic rocks produced much of the isotopic variation seen in the system. The nearly invariant high Pb isotopic values and high Pb concentrations indicate that Pb came almost entirely from the crustal source, and was little altered by any subsequent upper crustal assimilation. This Pb signature is isotopically similar to that of the southern Bolivian Tin Belt, suggesting a widely distributed Pb source. The great difference between compositions of Miocene and Quaternary central Andean volcanic rocks is explained by crustal thickening in early Miocene time leading to abundant lower crustal water and associated fluxed melting during the time of the earlier eruptions. The lower crust dried out considerably by Quaternary time, so less crustal component is present. Received: 22 December 1994 / Accepted: 13 September 1995     

Using ALSM to map sinkholes in the urbanized covered karst of Pinellas County,Florida—2. Accuracy statistics

We apply the logic of clinical epidemiological studies to quantify the accuracy of mapping sinkholes by ALSM in the 750 km² Pinellas County. By such studies, a new diagnostic procedure is tested by comparing the diagnoses in a clinical trial to diagnoses on the same patients from a more reliable, but more elaborate and expensive procedure (“gold standard” in epidemiological context). A relatively undeveloped, 65 km² focus area where we have aerial photographs that are effectively contemporaneous with the ALSM flights serves as the “clinical trial”. The xy-locations in the focus area are the “patients” in the trial. The “diagnostic test” for having “sinkhole disease” is inclusion in a database of sinkhole polygons delimited by ALSM contours (“ALSM-alone”), as detailed in Part 1. The standard of comparison (“gold standard” would be an overstatement in the absence of geophysical testing) is inclusion in a database of sinkhole outlines derived by best judgment of conjunctive interpretation of ALSM and aerial photography. GIS intersections that indicate the sensitivity and specificity of the test (ALSM-alone) are 43 and 98.3%, respectively, and, in the focus area where the prevalence of “sinkhole disease” is 4.7%, the positive and negative predictive values are 55.5 and 97.2%, respectively. Over much of the rest of the county, where only the test can be applied, the prevalence of sinkholes is sufficiently small that it cannot be determined to be any different from zero given the paucity of interpreted sinkholes (positive diagnoses) and the low specificity of the test method. The conclusion, therefore, is that contemporaneous aerial photography is essential to compile an ALSM-derived database that aims to state that the given xy-points lay inside or outside of topographic depressions in the covered karst of west-central Florida.     

Occurrence and distribution of “moganite” in agate/chalcedony: a combined micro-Raman, Rietveld, and cathodoluminescence study

Agate/chalcedony samples of different origin were investigated by performing Raman, X-ray diffraction (using Rietveld refinement), and cathodoluminescence measurements. These analyses were performed to measure the content and spatial distribution of the silica polymorph moganite, which is considered to represent periodic Brazil-law twinning of α-quartz at the unit-cell scale in agate/chalcedonies. Homogeneous standard samples including the nearly α-quartz free moganite type material from Gran Canaria were analysed in order to compare results of the X-ray diffractometry and Raman spectroscopy techniques and to provide a calibration curve for the Raman results. However, due to the different length scales analysed by the two techniques, the “moganite content” in microcrystalline SiO₂ samples measured by Raman spectroscopy (short-range order) was found to be considerably higher than the “moganite content” measured by X-ray diffractometry (long-range order). The difference is explained by the presence of moganite nanocrystals, nano-range moganite lamellae, and single Brazil-law twin-planes that are detected by vibrational spectroscopy but that are not large enough (in the sense of coherently scattering lattice domains) to be detected by X-ray diffractometry. High resolution Raman analysis provides a measure of the moganite content and its spatial variation in microcrystalline silica samples with a lateral resolution in the μm-range. Variations in the moganite-to-quartz ratio are revealed by varying intensity ratios of the main symmetric stretching-bending vibrations (A₁ modes) of α-quartz (465 cm⁻¹) and moganite (502 cm⁻¹), respectively. Traces of Raman microprobe analyses perpendicular to the rhythmic zoning of agates revealed that the moganite-to-quartz ratio is often not uniform but shows a cyclic pattern that correlates with the observed cathodoluminescence pattern (colour and intensity). Data obtained from an agate sample from a fluorite deposit near Okorusu, Namibia and from a volcanic agate from Los Indios, Cuba were selected for detailed presentation. Variations of cathodoluminescence and Raman data between single bands in agates suggest alternating formation of fine-grained, highly defective chalcedony intergrown with moganite, and coarse-grained low-defect quartz. Multiple zones indicate dynamic internal growth during a self-organizational crystallization process from silica-rich fluids. Received: 4 December 1997 / Accepted 19 June 1998