Petrogenetic implications of mineral crystallization trends of Troodos cumulates, Cyprus

1987 ◽  
Vol 124 (1) ◽  
pp. 1-11 ◽  
Author(s):  
P. Thy
Keyword(s):  
Magma Chamber ◽  
High Water ◽  
Coarse Grained ◽  
High Water Content ◽  
Drill Core ◽  
Troodos Ophiolite ◽  
Fine Grained ◽  
Intermediate Group ◽  
Rock Types ◽  
Ultramafic Cumulates

AbstractHole number CY-4 of the Cyprus Crustal Study Project penetrated the lower sheeted dyke complex, gabbros and ultramafic cumulates of the Troodos ophiolite. The lower part of the drill core sampled a coarse-grained plutonic complex revealing phase and cryptic layering and one major magma chamber replenishment. This magma chamber intruded medium-grained gabbroic rocks showing intricate chemical evolution trends reflecting several magma replenishments. In the upper part of the core, the gabbroic cumulates are intruded by fine-grained dykes, which grade into the sheeted dyke complex and chemically can be correlated with the lavas of the lower pillow sequence. The upper pillow lavas are best correlated with the ultramafic cumulates. A study of coexisting plagioclase (An) and mafic mineral (opx Mg #) compositions in the drill core revealed three main rock types: (1) a primitive group (An95–98, Mg #75–85) represented by the lower, coarse-grained gabbroic and ultramafic cumulates. (2) an intermediate group (An86–95 and Mg #70–78) represented by the upper level gabbroic cumulates, and (3) the lower part of the sheeted dyke complex (An60–80 and Mg #60–70). The plagioclase of the gabbros and ultramafic cumulates have an unusually high An content. Numerical simulation of the expected anhydrous, one atmosphere, crystallization trends show that the Troodos trends cannot be reproduced from known spreading or subduction related glasses. Mineralogical evidence indicates that the extrusives and the cumulate sequences of the Troodos ophiolite are genetically related. Glasses from the extrusives, nevertheless, also fail to reproduce the mineral crystallization trends observed in the plutonics. Attempts to model high PH2O crystallization produced trends more consistent with those observed in the cumulates. The very sodium-poor nature of the plagioclase may therefore mainly reflect high PH2O crystallization. High water content is consistent with the inferred subduction zone basin origin for the Troodos ophiolite.

scholarly journals Effects of Separated Fractions of Fbc Bottom Ash on Selected Properties of Cement Mortars

2020 ◽  
Vol 30 (4) ◽  
pp. 1-20
Author(s):  
Zbigniew Kledyński ◽  
Łukasz Krysiak
Keyword(s):  
Power Plants ◽  
Activity Index ◽  
Bottom Ash ◽  
High Water ◽  
Coarse Grained ◽  
Partial Replacement ◽  
Fine Grained ◽  
Cement Mortars ◽  
Inert Additive ◽  
High Silica

Abstract This paper discusses the effects of partial replacement of cement with fluidized bed bottom ash on the properties of mortars. The analyzed ash samples originating from four Polish power plants were separated by grain size selection into fine and coarse-grained fractions. This process leads to a creation of derivative samples of differing physical properties and, partially, phase compositions, as tested in XRD and TG analyses. Despite its high water demand, the obtained fine-grained fraction has the potential for application in cementbased composites as a reactive, pozzolanic additive. An acceptable activity index may be reached when the sulfate content is limited, implying benefits of combining the ash with low gypsum cements. The coarse-grained fraction is significantly less reactive, while a high silica and aluminate content is related to improved mechanical properties of the composite. It can, therefore, potentially be used as a quasi-inert additive or a substitute for sand.

Formation of the hour-glass structure in augite

1969 ◽  
Vol 37 (288) ◽  
pp. 472-479 ◽  
Author(s):  
D. F. Strong
Keyword(s):  
Glass Structure ◽  
Coarse Grained ◽  
Crystal Face ◽  
Thin Sections ◽  
Rapid Crystallization ◽  
Fine Grained ◽  
Rock Types ◽  
The Common

SummaryA study of augite in over three hundred thin sections of mainly alkalic rocks permits the distinction of two main types of hour-glass structure. The common ‘swallow-tailed’, sometimes skeletal augite crystals are found in the fine-grained groundmass of many rock types, and it is suggested that rapid crystallization alone accounts for their formation. Hence, this type of hour-glass structure has been called ‘quench hour-glass’. The hour-glass structures of larger augite crystals of porphyritic and coarse-grained rocks are commonly described as hour-glass ‘zoning’, as they result primarily from compositional differences between the different sectors. These were formed under conditions of relatively slower cooling than the ‘quench hour-glass’, and thus cannot be explained in the same way. They are thought to have formed by a process involving adsorption of impurities on a particular crystal face so as to impede growth of these faces, producing an initial skeleton of hour-glass form, which is completed by later crystallization of augite richer in FeO, Na2O, TiO2, and Al2O3. This hypothesis also explains the patchy zoning of other augite crystals, casting doubt on some petrogenetic interpretations of such zones as core zones.

scholarly journals Crack-enhanced weathering in inscribed marble: a possible application in epigraphy

2021 ◽  
Vol 33 (2) ◽  
pp. 189-202
Author(s):  
Stylianos Aspiotis ◽  
Jochen Schlüter ◽  
Kaja Harter-Uibopuu ◽  
Boriana Mihailova
Keyword(s):  
Raman Spectroscopy ◽  
Penetration Depth ◽  
Environmental Conditions ◽  
Coarse Grained ◽  
Asia Minor ◽  
X Ray Diffraction ◽  
Western Turkey ◽  
Fine Grained ◽  
Rock Types ◽  
Micro Cracks

Abstract. Raman spectroscopy has been applied to check if there are detectible material differences beneath the inscribed and non-inscribed areas of marble-based written artefacts, which could be further used to visualize lost or hardly readable text via suitable mapping. As a case study, marble segments with ∼ 2000-year-old inscribed letters from Asia Minor (western Turkey) and marble gravestones with 66 ± 14-year-old inscriptions from the cemetery of Ohlsdorf (Hamburg, Germany) have been subjected to Raman spectroscopy, as well as to complementary X-ray diffraction, wavelength-dispersive electron probe microanalysis, and Fourier-transform infrared spectroscopy, to thoroughly study the effect of different environmental conditions, grain size, and inscription age on the nature and penetration depth of marble alteration. The results demonstrate that environmental conditions rule over the type of dominant weathering changes, which are carotenoid molecular inclusions produced by lichen and amorphous carbon for marbles from Hamburg and Asia Minor, respectively. The alteration is much stronger in medium- and coarse-grained than in fine-grained marble, but it is suppressed by letter colouring. In the absence of letter colouring, the weathering-related products in both ancient and modern engraved marbles are more abundant beneath than away from the engraved areas, and the penetration depth is larger due to the enhancement of fissures and micro-cracks around the inscribed areas. We show that the Raman intensity ratio between the strongest peak of the weathering-related product (ν(C=C) ∼ 1520 cm−1 for carotenoids or the G peak ∼ 1595 cm−1 for soot-like carbon) and the strongest peak of marble (CO3 stretching near 1087 cm−1) can serve as a quantitative marker to indirectly map the lateral distribution of cracks induced during the inscribing process and hence can potentially be used to trace lost text on vanished marble inscriptions. This approach can be applied to other rock types, but further studies are required to identify the corresponding autochthonous weathering-related products.

Cumulate mush hybridization by melt invasion: Evidence from compositionally-diverse amphiboles in ultramafic-mafic arc cumulates within the eastern Gangdese Batholith, southern Tibet

2021 ◽  
Author(s):  
Wei Xu ◽  
Di-Cheng Zhu ◽  
Qing Wang ◽  
Roberto F Weinberg ◽  
Rui Wang ◽  
...  
Keyword(s):  
Mineral Assemblage ◽  
Large Body ◽  
The Body ◽  
Coarse Grained ◽  
Southern Tibet ◽  
Fine Grained ◽  
Arc Magmas ◽  
Rock Types ◽  
Geochemical Study ◽  
Host Rocks

Abstract Amphibole plays an important role in the petrogenesis and evolution of arc magmas, but its role is not completely understood yet. Here, a field, petrological, geochronological and geochemical study is carried out on ultramafic-mafic arc cumulates with textural and chemical heterogeneities and on associated host diorites from the eastern Gangdese Batholith, southern Tibet to explore the problem. The cumulates occur as a large body in diorite host-rocks. The core of the body consists of coarse-grained Cpx hornblendite with a porphyritic texture. Towards the contact with the host diorite, the coarse-grained Cpx hornblendite grades to relatively homogeneous fine-grained melagabbro. Zircon U–Pb dating indicates they all crystallized at 200 ± 1 Ma. Textural features and whole-rock and mineral chemical data reveal that both the Cpx hornblendite and the melagabbro are mixtures of two different mineral assemblages that are not in equilibrium: (1) brown amphibole and its clinopyroxene inclusions; (2) matrix clinopyroxene + green amphibole + plagioclase + quartz + accessory phases. Clinopyroxene and brown amphibole from the first assemblage are enriched in middle rare earth elements (MREE) relative to light REE (LREE) and heavy REE (HREE), and are weakly depleted in Ti, whereas clinopyroxene and green amphibole from the second assemblage are characterized by LREE enrichment over MREE-HREE and more marked Sr and Ti depletion. The higher Mg#, MgO and Cr of the late-formed green amphibole than the early-formed brown amphibole suggest that the two assemblages are not on the same liquid line of descent. Given the close relations of the three rock types in the exposed crustal section, the cumulates are interpreted to have formed in an open system, in which an ultramafic cumulate body consisting of the first assemblage reacted with the host dioritic melt to form new clinopyroxene and amphibole of the second assemblage. The melt calculated to be in equilibrium with the first mineral assemblage resembles an average continental arc basalt, that is less evolved than the host dioritic melt, responsible for the second mineral assemblage. On the basis of whole-rock Sr–Nd–Hf isotopic similarity of the cumulates and a host diorite sample, we argue that the host diorites were formed through crystal fractionation from the parent melt of the first assemblage. Results of least-squares mass-balance calculations suggest the quantities of the host dioritic melts, involved in the generation of these modified cumulates, vary from ~25% to ~44%. The presence of magmatic epidote in the host diorites and Al-in-Hb geobarometry indicate the reaction that occurred when the dioritic melts percolated through the cumulate body was at ~6 kbar. Both the brown and green amphiboles are enriched in MREE relative to HREE, and can impart residual melts with a strong geochemical signature of amphibole fractionation (low Dy/Yb). Thus, we conclude that fractional crystallization and melt-rock reaction are two mechanisms by which amphibole controls arc magma petrogenesis and evolution.

Global occurrence, geology and characteristics of tubular halloysite deposits

Clay Minerals ◽  
2016 ◽  
Vol 51 (3) ◽  
pp. 309-324 ◽  
Author(s):  
Ian Wilson ◽  
John Keeling
Keyword(s):  
Hydrothermal Fluid ◽  
Coarse Grained ◽  
Bone China ◽  
Fine Grained ◽  
Rock Types ◽  
Wide Range ◽  
The Usa ◽  
Low Levels ◽  
Paper Filler ◽  
Tubular Morphology

AbstractHalloysite with tubular morphology is formed in a wide range of geological environments from the alteration of various rock types. Intrusive acidic coarse-grained rocks, such as granites, pegmatites and anorthosite, with large potash and sodic feldspars contents, are subsequently altered to kaolinite, halloysite and other clay minerals by weathering or shallow hydrothermal fluid activity. Processing to separate the halloysite-kaolinite fraction from the altered host rock provides a product which can be used as a paper filler and in ceramics and fibreglass, among other uses, with various deposits in Brazil, China, Thailand and elsewhere. In the Kerikeri-Matauri Bay district of Northland, North Island, New Zealand, volcanic alkali rhyolite was extruded as domes and cooled rapidly with fine-grained feldspar subsequently altered to halloysite. The IMERYS plant in Matauri Bay separates the clay from the quartz-cristobalite matrix with an ∼20% yield of halloysite. The principal market is for high-quality porcelain and bone china that require low levels of Fe2O3 and TiO2. Deposits with high levels of halloysite occur in China, Turkey and the USA. The Dragon mine in Utah, USAwas recently reopened by Applied Minerals Inc. and now produces halloysite from zones of up to 100% white halloysite. Smaller occurrences of tubular halloysite are mined in China, Turkey and elsewhere from masses of comparatively pure clay that appear to have crystallized directly from solutions in which Al and Si were soluble.

Electrical conductivity of dry lower crustal rocks

Geophysics ◽  
1983 ◽  
Vol 48 (1) ◽  
pp. 52-61 ◽  
Author(s):  
K. A. Kariya ◽  
T. J. Shankland
Keyword(s):  
Electrical Conductivity ◽  
Coarse Grained ◽  
Mean Values ◽  
Crustal Rocks ◽  
Fine Grained ◽  
Rock Types ◽  
Order Of Magnitude ◽  
Temperature Ranges ◽  
Best Fitting ◽  
Lower Crustal

This study provides values of electrical conductivity of possible lower crustal materials to assist interpretation of lower crustal magnetotelluric soundings. We present mean values of conductivity measurements collected from the literature for dry mafic and silicic rocks in the temperature range of 500°C to 1000°C. We observe statistically significant differences between rock types: mafic rocks are better conductors than granites by about half an order of magnitude and within the mafic group, aphanitic (fine‐grained) rocks have higher conductivity than phaneritic (coarse‐grained) ones. “Best‐fitting” curves of log conductivity versus temperature are presented for each rock type to show mean log conductivity values together with standard deviations so that most probable temperature ranges can be inferred from conductivity. Because the laboratory rocks are dry, their conductivities are lower at a given temperature than they would be if fluids or volatiles were present; hence any temperatures inferred from magnetotelluric (MT) contivities are upper bounds.

scholarly journals The Growth of Sodic Amphibole at the Greenschist- to Blueschist-facies Transition (Dent Blanche, Western Alps): Bulk-rock Chemical Control and Thermodynamic Modelling

2020 ◽  
Vol 61 (4) ◽  
Author(s):  
Paola Manzotti ◽  
Michel Ballèvre ◽  
Pavel Pitra ◽  
Benita Putlitz ◽  
Martin Robyr ◽  
...  
Keyword(s):  
Western Alps ◽  
Thermodynamic Modelling ◽  
Geochemical Data ◽  
Chemical Compositions ◽  
Bulk Rock ◽  
Rock Composition ◽  
Fine Grained ◽  
Rock Types ◽  
Sodic Amphibole ◽  
Ultramafic Cumulates

Abstract The sodic amphibole glaucophane is generally considered as indicative of blueschist-facies metamorphism. However, sodic amphiboles display a large range in chemical compositions, owing principally to the Fe2+Mg–1 and Fe3+Al–1 substitutions. Therefore, the whole-rock composition (namely its Na2O and FeO* content, and the Fe2+–Fe3+ ratio), strongly controls the stability field of the sodic amphiboles at the transition from greenschist- to blueschist-facies conditions. Neglecting these variables can lead to erroneous estimates of the metamorphic conditions and consequently the tectonic framework of the rocks. This paper explores the mechanisms that control the development of sodic amphibole and sodic pyroxene within the basement of the Dent Blanche Tectonic System (Western Alps), as a result of the Alpine metamorphic history. Field, petrographic and geochemical data indicate that sodic amphibole and sodic pyroxene form in different rock types: (1) in undeformed pods of ultramafic cumulates (hornblendite), sodic amphibole (magnesioriebeckite) forms coronas around magmatic pargasite; (2) metatonalite displays patches of radiating sodic (magnesioriebeckite) and calcic (actinolite) amphiboles; (3) sodic amphibole (magnesioriebeckite–glaucophane) occurs with high-Si potassic white mica (phengitic muscovite) in fine-grained (blue) schists; (4) in mylonitized granitoids (amphibole-gneiss) metasomatized along the contact with ultramafic cumulates, sodic amphibole (magnesioriebeckite–winchite) mainly forms rosettes or sheaves, generally without a shape-preferred orientation. Only locally are the needles aligned parallel to the stretching lineation. Pale green aegirine–augite is dispersed in an albite–quartz matrix or forms layers of fine-grained fibrous aggregates. The bulk-rock chemical composition of the different lithologies indicates that sodic amphibole and sodic pyroxene developed in Na- and Fe-rich systems or in a system with high Fe3+/Fe*. Thermodynamic modelling performed for different rock types (taking into account the measured Fe2O3 contents) reveals that sodic amphibole appears at ∼8 ± 1 kbar and 400–450 °C (i.e. at the transition between the greenschist- and blueschist-facies conditions) about 5 kbar lower than previous estimates. To test the robustness of our conclusion, we performed a review of sodic amphibole compositions from a variety of terranes and P–T conditions. This shows (1) systematic variations of composition with P–T conditions and bulk-rock chemistry, and (2) that the amphibole compositions reported from the studied area are consistent with those reported from other greenschist- to blueschist-facies transitions.

scholarly journals Fabrics, geothermometry, and geochronology of the Songshugou ophiolite: Insights into the tectonic evolution of the Shangdan suture, Qinling orogen, China

Lithosphere ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 784-803
Author(s):  
Shengsi Sun ◽  
Yunpeng Dong ◽  
Xiaoming Liu ◽  
Dengfeng He ◽  
Chao Cheng
Keyword(s):  
Tectonic Evolution ◽  
Electron Backscatter Diffraction ◽  
High Water ◽  
Coarse Grained ◽  
Spreading Center ◽  
Heavy Rare Earth Element ◽  
Fine Grained ◽  
Suprasubduction Zone ◽  
Backscatter Diffraction ◽  
Water Contents

Abstract The Songshugou ophiolite, located in the northern Qinling belt, consists mainly of metamorphosed mafic and ultramafic rocks recording details of deformation and metamorphism that occurred during subduction, accretion, and collision along the Shangdan suture in the Qinling orogenic belt. Electron backscatter diffraction measurements revealed that the harzburgites are dominated by olivine C-type crystal preferred orientations (CPOs), which were possibly induced by high pressure during slab subduction. Olivine A-type CPOs were also observed in some harzburgites, representing the remnants of the original fabric in oceanic mantle rocks formed in the spreading center of the Shangdan ocean. Coarse-grained dunites are characterized by B-type CPOs, which may have been caused by melt-rock reactions and/or high water contents in a suprasubduction-zone setting during exhumation. Fine-grained dunites are also dominated by B-type CPOs, suggesting that grain-size reduction related to mylonitization did not result in fabric variations. Combined with the mineral assemblages, application of geothermometry suggested that the Songshugou ophiolite has experienced metamorphism and deformation under amphibolite-facies conditions. Zircons from garnet-bearing amphibole schist are characterized by flat heavy rare earth element (HREE) patterns and low Th/U ratios and yielded a mass spectrometry U-Pb age of 500.5 ± 8.8 Ma, representing the peak metamorphic age of the metamafic rocks. Other zircons displayed relative HREE enrichment and a clearly negative Eu anomaly and gave an age of 492.5 ± 3.0 Ma, constraining the time of the exhumation of the ophiolite. Integrated with all the available regional geology, our new fabric, geochemical, and geochronological data suggest that the tectonic evolution of the Songshugou ophiolite can be proximately constrained as subduction at ca. 500 Ma and exhumation at ca. 492 Ma.

Sulfur Isotope Constraints on the Conditions of Pyrite Formation in the Paleoproterozoic Urquhart Shale Formation and George Fisher Zn-Pb-Ag Deposit, Northern Australia

2020 ◽  
Vol 115 (5) ◽  
pp. 1003-1020
Author(s):  
Philip Rieger ◽  
Joseph M. Magnall ◽  
Sarah A. Gleeson ◽  
Richard Lilly ◽  
Alexander Rocholl ◽  
...  
Keyword(s):  
Sulfate Reduction ◽  
Sulfur Isotope ◽  
Coarse Grained ◽  
Drill Core ◽  
Northern Australia ◽  
Fine Grained ◽  
Mount Isa ◽  
History Of ◽  
Shale Formation ◽  
Stage 1

Abstract The Carpentaria province (McArthur basin and Mount Isa inlier) in northern Australia is one of the most important districts for clastic-dominated (CD-type) massive sulfide deposits. The George Fisher Zn-Pb-Ag deposit, located in this province, is hosted by the carbonaceous Urquhart Shale Formation (ca. 1654 Ma) in a region that has an active history of metamorphism and tectonism. In this study, paragenetically constrained pyrite in samples from the George Fisher deposit and unmineralized Urquhart Shale have been analyzed in situ using secondary ion mass spectrometry (SIMS) of sulfur isotopes (δ34S values). Samples were taken from four drill cores through the main orebodies at George Fisher and one drill core through correlative, unmineralized Urquhart Shale (Shovel Flats area). Five generations of pyrite were identified at George Fisher and record a protracted history of sulfate reduction under diagenetic and subsequent hydrothermal conditions: (1) fine-grained, subhedral-spheroidal pyrite (Py-0), (2) coarse-grained, anhedral pyrite (Py-1) associated with ore-stage 1 sphalerite and galena, (3) coarse-grained, euhedral pyrite (Py-2) associated with ore-stage 2 sphalerite, galena, and pyrrhotite, (4) massive subhedral to euhedral pyrite (Py-3) associated with ore-stage 3 chalcopyrite, pyrrhotite, galena, and sphalerite, and (5) coarse-grained euhedral pyrite (Py-euh), which occurs only in unmineralized rocks. In the unmineralized Shovel Flats drill core, only Py-0 and Py-euh are present. Whereas pre-ore pyrite (Py-0) preserves negative δ34S values (–8.1 to 11.8‰), the ore-stage pyrites (Py-1, Py-2, and Py-3) have higher δ34S values (7.8–33.3, 1.9–12.7, and 23.4–28.2‰, respectively). The highest δ34S values (7.2–33.9‰) are preserved in Py-euh. In combination with petrographic observations, the δ34S values of pyrite provide evidence of three different processes responsible for the reduction of sulfate at George Fisher. Reduced sulfur in fine-grained pyrite (Py-0) formed via microbial sulfate reduction (MSR) under open-system conditions prior to the first generation of hydrothermal pyrite (Py-1) in ore-stage 1, which most likely formed via thermochemical sulfate reduction (TSR). During deformation, previously formed sulfide phases were then recycled and replaced during a second hydrothermal event (ore-stage 2), resulting in intermediate sulfur isotope values. Another syndeformational hydrothermal Cu event, involving a sulfate-bearing fluid, formed ore-stage 3 via TSR. This study demonstrates that the fine-grained pyrite formed pre-ore under conditions open to sulfate and outlines the role of multiple stages of sulfide formation in producing high-grade Zn-Pb-Ag orebodies in the Mount Isa inlier.

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