Metamorphic Schists Research Articles

Tectono-Metamorphic Evolution of the Cretaceous Kluane Schist, Southwest Yukon

Abstract A wealth of information regarding the Mesozoic evolution of the Northern Canadian and Alaskan Cordillera is held within a series of variably metamorphosed and deformed rocks that formed in Jura-Cretaceous basins. Located at the interface between the pericratonic Intermontane and exotic Insular terranes, these basinal rocks are key to understanding the timing and tectonic style of Insular terrane accretion, a topic of longstanding debate. This study unravels the structural and metamorphic evolution of one of these basins, the Kluane Basin, within southwest Yukon Territory. The Kluane Schist is the primary assemblage of the Kluane Basin. It consists of metamorphosed and deformed low-Al pelites that were intruded by granodioritic plutons of the Paleocene Ruby Range batholith. Previous workers have suggested the variable metamorphic character of the Kluane Schist represents an extensive and static thermal aureole related to Ruby Range batholith emplacement. Our work, however, indicates that the Kluane Schist experienced Buchan-style metamorphism coeval with protracted deformation and can be divided into seven distinct petrologic zones, which, based on their unique combination of mineral assemblage and structure, are incompatible with static thermal metamorphism. Instead, we propose the Kluane Schist experienced two distinct metamorphic phases: (1) an early greenschist-facies phase that resulted in the development of a bedding-parallel chlorite-muscovite-titanite fabric, preserved by its lowest-grade units, and (2) a later amphibolite-facies phase that manifests as the progressive transposition of the earlier chlorite-muscovite-titanite fabric into a penetrative biotite-rich schistosity that transitions upgrade into a segregated gneissic fabric comprised of biotite-cordierite and plagioclase-quartz (± sillimanite-K-feldspar-melt). By integrating the results of detailed petrography and petrological modeling, we demonstrate that the second main metamorphic phase experienced by the Kluane Schist preserves a record of pressures and temperatures that align with other Buchan-style terranes worldwide. Our data defines a field gradient across the Kluane Schist ranging from 3.0–3.5 kbar at 375–400 °C to 4–4.5 kbar at 700–750 °C. This record of a coupled Buchan-style metamorphic-deformational evolution and tops-to-the SW non-coaxial shear structures is consistent with the override of the thermally mature Yukon-Tanana terrane as the principal driver of Kluane Schist metamorphism, with some limited heat likely contributed by the late-syn- to post-tectonic intrusion of the Ruby Range batholith.

Age and generation conditions of quartz crystal deposits in the Subpolar Urals

Research subject. The Dodo and Puiva quartz crystal deposits in the Neroiskiy mineral province (Subpolar Urals) were studied. Although these deposits have received sufficient research attention, a number of issues remain to be elucidated, including the age of crystal-bearing mineralization and the age of host rocks. Aim. In this work, we aim to determine the age of the metasomatites that bear quartz crystal mineralization and to develop a model of the formation of the Dodo and Puiva deposits. Materials and Methods. 40Ar/39Ar dating was carried out according to the method described by A.V. Travin et al. The argon isotope composition was measured on a Micromass 5400 mass spectrometer (IGM SB RAS). Results. Microprobe studies of the mineralogy of the Dodo and Puiva quartz crystal deposits were carried out. The temperatures of meta-somtaite formation were determined to range within 339–364°C. Six main structural and morphological types of quartz veins were identified and described. The 40Ar/39Ar ages of mica of quartz crystal deposits and host metamorphic schists were determined. Reliable plateaus were obtained, the values of which ranged within 251–257 Ma and agreed with each other within the deviation (average for 4 dates is 255 ± 2 Ma). Conclusion. A new model for the formation of quartz crystal deposits in the Subpolar Urals is proposed. The obtained 40Ar/39Ar ages correspond to the period of the post-orogenic extension of the Urals. At that time, a system of meridional grabens and rifts was formed in the Urals and in the West Siberian Plate. At the same time, and as a result of the same stretching impulse, large blocks of the middle crust (granite, schist, etc.) were brought to the Earth’s surface in the Urals. During the rise of deep blocks, at a depth of 10 km, a sharp, approximately 3-fold drop in fluid pressures (from lithostatic to hydrostatic) and a strong decrease in temperatures due to adiabatic expansion and the throttling effect occurred. The obtained 40Ar/39Ar ages (255 Ma) reflect not only the age of the quartz crystal deposits of the Subpolar Urals, but also place the moment of rise of the entire Central Ural uplift above a depth of 10 km, i.e., to the level of the upper cortex.

Update for reactive transport modeling of the Kızıldere geothermal field to reduce uncertainties in the early inspections

The development of carbon capture and storage techniques has become essential to reduce and mitigating CO2 emissions to the atmosphere. CarbFix1 and CarbFix2 projects carried out in Iceland demonstrated that the emissions of waste CO2 gas from geothermal power plants can be captured and mixed with the effluent geofluid and subsequently injected back into the geothermal reservoir. This experience gained in the CarbFix projects expanded into other geothermal fields around Europe, and one of the demonstration sites is the geothermal field in Turkey, Kızıldere. This paper focuses on the results of an updated study on early field evaluations with reactive transport simulations. In the new three-dimensional numerical model, the geological formations and fault zones were updated according to the well-logs data. Based on the tracer tests performed in the field, the anisotropic permeabilities between the wells were evaluated and imposed into the model. Geofluid chemistry, mineral components, and the volume fractions used as input in the simulations are modified depending on the performed laboratory experiments on the metamorphic schists taken from the geothermal site (i.e. X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning-electron microscope (SEM), and batch reactor tests). Different thermodynamic databases such as Lawrance Livermore National Laboratory (LLNL) and Thermoddem databases were tested using PHREEQC and TOUGHREACT programs for consistency with experiments. The thermodynamic conditions and the geofluid-rock-CO2 interactions prevent the mineralization of CO2 in the reservoir. This outcome differs from CarbFix projects in terms of the carbonization process, but the CO2 injection is still reliable with solubility-trapping in a geothermal reservoir to partially mitigate the emission. Roughly, 200 kt of CO2 in 10 years can be safely injected into the geothermal reservoir. According to the new analysis, the ratio of magnesium, sodium, and potassium varies in solid solution series of feldspars and clay minerals as albite end-member and montmorillonite/illite end-members, respectively. The evaluations of solid solution reactions are relatively limited in the law of mass action approach used by PHREEQC and TOUGHREACT.

Gold potential of the upper devonian basal conglomerates of the Kanin peninsula (Nenets autonomous district, Russia)

Native gold and garnets are described for the frst time in heavy concentrates from coarse-grained sediments of the Upper Devonian Tayaokuyakha Formation, which occurs on the eroded Upper Riphean schists with angular and azimuthal unconformity (middle reaches of the Murseyakha River, Kanin Peninsula, Nenets autonomous district, Russia). Particular attention was paid to indicators of primary source of native gold for the Upper Devonian conglomerates. The composition of weakly rounded almandine-spessartine garnets indicates their metamorphic origin and allows us to relate the primary source of native gold in conglomerates (D3tk) with underlying metamorphosed Riphean strata or intrusive rocks in them. Native gold is mainly characterized by a heterogeneous composition and contains Ag, Cu and Hg. The poorly rounded native gold grains, the absence of supergene rims and preservation of mineral inclusions in the margins indicate its proximal primary source. The presence of Cu suggests a link of native gold with mafc/ultramafc rocks: metamorphosed dikes of dolerites of the Nekhaiteyakha metagabbroid complex (m??RF3) or dolerite dikes of the Kanin-Timan complex (?D3kt), which intrude the Precambrian metamorphic schists. It is established that the Devonian conglomerates are intermediate reservoirs for the possible present-day placer formation.

УЛАМКИ ЕКЗОТИЧНИХ МЕТАМОРФІЧНИХ СЛАНЦІВ В ОЛІГОЦЕНОВИХ ВІДКЛАДАХ СІЛЕЗЬКОГО ПОКРИВУ (УКРАЇНСЬКІ КАРПАТИ)

The study aims at analyzing the petrographic composition of exotic metamorphic schist clasts in the Oligocene deposits filling the Silesian Nappe in the south-western part of the Ukrainian Carpathians and reconstructing their possible source area. The methodology includes petrographic, sedimentological and comparative geological methods. To achieve this goal, field research was carried out along the first right tributary of the Hysnyi Stream (the village of Uzhok, Velykobereznyanskyi district, Transcarpathian region) and petrographic analysis of the selected samples of the exotic metamorphic schist clasts included in the Oligocene debris-flow deposits was performed. The results of microscopic studies showed that these exotic rocks are represented by mica-quartz schist and garnet-muscovitebiotite-plagioclase-quartz schist with a low content of chlorite, carbonate and epidote. Mineral composition and structure/texture features suggest the rocks were metamorphosed under green schist and epidote-amphibolite facies. Similar exotic rock fragments were identified by Polish scientists in the south-eastern part of the Polish Carpathians in the Silesian Nappe, where possible source area of the exotic rocks is related to the Bukowiec Paleo-Ridge, which had been located between the Dukla and Silesian basins of the Carpathian sedimentary realm. Scientific novelty. For the first time, the petrographic composition and textural and structural features of the exotic schists fragments included in the Oligocene deposits of the Silesian Nappe in the Ukrainian Carpathians (area of the village of Uzhok, Ukrainian Carpathians) are described. These schists are similar to the exotic rocks included in the Oligocene deposits of the Silesian Nappe in the Polish Carpathians, which may indicate the same source area.

Compositional Evolution of REE- and Ti-Bearing Accessory Minerals in Metamorphic Schists of Atomfjella Series, Western Ny Friesland, Svalbard and Its Petrogenetic Significance

Compositional Evolution of REE- and Ti-Bearing Accessory Minerals in Metamorphic Schists of Atomfjella Series, Western Ny Friesland, Svalbard and Its Petrogenetic Significance

Акцессорная и рудная минерализация сланцев из фундамента полуострова Ямал (Западно-Яротинский участок, Западная Сибирь)

The results of studying the mineralogy of metamorphic schists from the Pre-Jurassic base of the Arctic part of the West Siberian plate are presented. The accessory and ore mineralization of schists from the Zapadno-Yarotinsky license area located in the southern part of the Yamal Peninsula is studied. The schists was uncovered by the Zapadno-Yarotinskaya No. 300 well at a depth of 2762 m. Above the section, the metamorphic rocks are overlain by a young Meso-Cenozoic cover. The schists are mainly composed of quartz, plagioclase (albite), carbonates (dolomite and siderite), mica (muscovite) and chlorite (donbassite). The discovered accessory and ore minerals in the metamorphic schists of the Zapadno-Yarotinsky area can be divided into two groups. The first group includes minerals that were formed during the metamorphism of schists, or were preserved as detrital matter. These minerals include zircon, fluorapatite, and rutile as the most stable compounds. The remaining mineralization (pyrite, sphalerite, chalcopyrite, cubanite, galena, cobaltite, barite, xenotime-(Y), goyazite, synchysite-(Nd), native silver and copper) is clearly secondary and was formed as a result of superimposed metasomatic processes. Judging from the described mineralogy, the schists underwent changes as a result of superimposed propyllitization. The temperature range of this process is determined by the formation of cubanite in association with chalcopyrite at a temperature of 200-210 оС.

Features of the composition of metapelites from the basement of the Arctic part of the West Siberian megabasin (Verkhnerechenskaya exploration area, Yamal Peninsula)

Relevance of the work. Comprehensive studies of the geology of the Arctic part of Western Siberia are very important for the search for oil and gas in this vast but understudied territory. At present, unfortunately, we know little about the geological structure of the Arctic in the region of Western Siberia, where the sedimentary cover is mainly investigated (the thickness of which is about 3–4 km) and only a few wells are drilled to the foundation. Therefore, a comprehensive study of core samples from this little-studied territory seems extremely relevant. The purpose of the work is a detailed description of the mineralogy and petro-geochemical features of garnetquartz-chlorite-muscovite schists from the well Verkhnerechenskaya no. 2 from the foundation Arctic part of the West Siberian megasbasin. Scope of application of work. This work can be useful in constructing geological maps of the pre-Jurassic foundation of the Yamal Peninsula. Results of work and conclusions. Mineralogy has been studied in detail and the trace element composition of garnetquartz-chlorite-muscovite schists is obtained. The mineral composition of the rocks is as follows: almandine, muscovite, quartz, chamosite, calcite, albite, rutile, titanite, fluorapatite, zircon, xenotime-(Y) and pyrite. The progressive zonality in the almandine is determined, which is confirmed by the calculated data of metapelite formation temperature, progressive metamorphism. Distribution of rare, scattered and REE in the studied rocks is characteristic of metamorphic schists from the foundation of the Urals part of the West Siberian megasbasin, which compel the framing of monzodiorite-granite massifs of Shaimsko-Kuznetsov meganticlinorium of Western Siberia. Probably, the metapelites studied are the result of warming up the thickness of sedimentary rocks with granite intrusion located in the vicinity of Verkhnerechenskaya area. Later, the rocks underwent propylitization with the formation of secondary carbonate and pyrite.

GEOLOGICAL AND GEOMORPHOLOGICAL ANALYSIS AND HYDROGEOCHEMICAL ENVIRONMENT OF AQUIFERS OF THE SOUTHERN WEST COAST OF KARNATAKA, INDIA

Dakshina kannada district is situated in peninsular region. The peninsula is composed of geologically ancient rocks of diverse original and most of them have undergone metamorphism. The early Precambrian tonalitic gneisses invaded by granites, granulites and dolerite dykes. Granulites are mostly restricted to areas south of Mangalore. High grade alumina rich (corundum bearing) metamorphic schists have been encountered and younger alkaline intrusive rocks like Aegerine syenites have been reported. There are ve rivers and estuaries. Number of lineaments cut across each other and some lineaments are parallel to each other. The Arabian sea class is the largest among other land cover features in the study area. The river/tidal creek land cover appear as long irregular and sinous in outline. Mulki river, Netravati river, Gurupur river at southern terrain. The qualities of groundwater at sandy aquifer are good, lateritic/weathered gneissic rocks it is sweet.

Experimental research on the effect of water-rock interaction in filling media of fault structure

Water damage is one of the five disasters that affect the safety of coal mine production. The erosion of rocks by water is a very important link in the process of water inrush induced by fault activation. Through the observation and experiment of fault filling samples, according to the existing rock classification standards, fault sediments are divided into breccia, dynamic metamorphic schist and mudstone. Similar materials are developed with the characteristics of particle size distribution, cementation strength and water rationality, and then relevant tests and analyses are carried out. The experimental results show that the water-rock interaction mainly reduces the compressive strength, mechanical strength, cohesion and friction Angle of similar materials, and cracks or deformations are easy to occur under uniaxial load, which may be an important process of water inrush induced by fault activation. Mechanical experiment of similar material specimen can not only save time and cost of large scale experiment, but also master the direction and method of the experiment. The research provides a new idea for the failure process of rock structure in fault activation water inrush.

High-Grade Flake Graphite Deposits in Metamorphic Schist Belt, Central Finland—Mineralogy and Beneficiation of Graphite for Lithium-Ion Battery Applications

More than 40 m length of drill cores were collected from four boreholes drilled by Geological Survey of Finland (GTK) and Outokumpu Oy in high-grade metamorphic rocks of Rautalampi and Käypysuo, Central Finland. The hosted rocks of the graphite mineralization were mica–quartz schist and biotite gneiss. The graphite-bearing rocks and final concentrated graphite powder were studied with petrographic microscope, scanning electron microscope (SEM-EDS), Raman spectroscopy, and X-ray analysis (XRD and XRF). A majority of the studied graphite had a distinctly flakey (0.2–1 mm in length) or platy morphology with a well-ordered crystal lattice. Beneficiation studies were performed to produce high-purity graphite concentrate, where rod milling and froth flotation produced a final concentrate of 90% fixed carbon with recoveries between 67% and 83%. Particle size reduction was tested by a ball and an attritor mill. Graphite purification by alkaline roasting process with 35% NaOH at 250 °C and leached by 10% H2SO4 solution at room temperature could reach the graphite purity level of 99.4%. Our analysis suggested that purifying by multistage flotation processes, followed by alkaline roasting and acid leaching, is a considerable example to obtain high-grade graphite required for lithium-ion battery production.

First Data on the Age of Metamorphic Schists from the Taz Peninsula (Arctic, Western Siberia)

The 40Ar/39Ar dating of metamorphic schists from the basement of the West Siberian Platform exposed by Lenzitskaya well no. 77 on the Taz Peninsula was performed. The samples collected at depths of 3503 and 3515 m yielded age dates of 251.6 ± 3.5 and 271.2 ± 3.5 Ma. The age of ~271 Ma reflects the age of metamorphism of schists, which was induced by a strong tectonomagmatic event, associated with the onset of emplacement of rift zones and outflow of basalts in the Permian–Triassic. The age of ~252 Ma coincides with the period of the most intense emplacement of submeridional rifts in the basement of the West Siberian Platform. This process was accompanied by extension and thinning of the Earth’s crust in this region, which resulted in the exhumation of rocks from the mid-crystal level. The age boundary of ~250 Ma was established in the metamorphic and intrusive complexes of western Siberia and the Urals. This age is fixed almost everywhere and is correlated with the age of formation of the Siberian Trap Province.

Lattice preferred orientation of talc and implications for seismic anisotropy in subduction zones

Strong seismic anisotropy is generally observed in subduction zones. Lattice preferred orientation (LPO) of olivine and elastically anisotropic hydrous minerals has been considered to be an important factor causing anomalous seismic anisotropy. For the first time, we report on measured LPOs of polycrystalline talc. The study comprises subduction-related ultrahigh-pressure metamorphic schists from the Makbal Complex in Kyrgyzstan-Kazakhstan and amphibolite-facies metasomatic schists from the Valla Field Block in Unst, Scotland. The here studied talc revealed a strong alignment of (001) planes (sub)parallel to the foliation and a girdle distribution of [100] axes and (010) poles (sub)parallel to the foliation. The LPOs of polycrystalline talc produced a significant P-wave anisotropy (AVp = 72%) and a high maximum S-wave anisotropy (max AVs = 24%). The results imply that the LPO of talc influence both the strong trench-parallel azimuthal anisotropy and positive/negative radial anisotropy of P-waves, and the trench-parallel seismic anisotropy of S-waves in subduction zones.

Development of a fluid-dynamical model (DFM) of the Yamal Novoportovsky oiland gas-condensing deposit (based on DFM seismic data interpretation)

Research subject. The idea of forecasting fluid-dynamical parameters is based on the views connecting the processes of sedimentation, tectonogenesis and fluid flows into an active fluid-dynamical model of the “sedimentary cover–basement” system. In such models, main fluid-dynamical parameters of oil and gas collectors, i.e. penetration and the vector of the fluid flow, are functionally connected with the components of the current state of the rock massif having a discrete (block) structure. These parameters can be calculated using DFM-interpretation technology developed by the authors in their previous works.Materials and methods. For the first time, DFM results are provided for the Yamal Novoportovsky oiland gas-condensing deposit. Here, the paleozoic basement stripped at a depth of 2700–3200 m is largely represented by metamorphic schists and marbled limestones. The basement has been covered by sediments and a platform cover since the early Jurassic age. The forecast of parameters describing modern geodynamical processes was performed on the basis of a comprehensive tectonophysical analysis of major geological and geophysical data.Results. The main axes of the neo-tectonic activity of the plate complex break the area under study into a quite regular block system that reflects a right-sided shift of fundamental blocks, that, in its turn predetermines the block shift in plate complex with the turn of the shift axis by 30 degrees. The most significant oil and gas holes in terms of influx demonstrate a connection with the described scheme of block activity. Thus, practically all high-debit boreholes were drilled in active axial zones.Conclusion. The proposed scheme of block activity satisfies the general principles of geodynamics. The developed model of abnormal pressure estimations by main productive intervals shows a good agreement with the distribution oiland gas boreholes in terms of productivity. Contact zones of active blocks present a particular interest from the standpoint of selecting the location of high-debit boreholes. These zones should be taken into account when developing new oil and gas deposits.

Detrital zircon ages and Hf isotopic compositions of metasedimentary rocks in the Wuqia area of Southwest Tianshan, NW China: implications for the early Paleozoic tectonic evolution of the Tianshan orogenic belt

ABSTRACTThe Chinese Southwest Tianshan Orogenic Belt is located along the boundary between the Central Asian Orogenic Belt (CAOB) and the Tarim Block (TB), NW China. It records the convergence of the Tarim Block and the Middle Tianshan, and is, therefore, a crucial region for understanding the Eurasia continental growth and evolution. The Wulagen (geographical name) metasedimentary rocks of the Wuqia area (mainly metamorphic sandstones and mica schists) form one of the metamorphic terranes in the Southwestern Tianshan Orogenic Belt. The geochronology of these rocks is poorly known, which hampers our understanding of the tectonic evolution of the belt. We analyzed 517 zircon grains for detrital zircon U–Pb dating and 93 zircon grains for in situ Lu–Hf isotopic compositions from the Wulagen metasedimentary rocks. The analyzed zircon grains yield Neoarchean to late Paleozoic U–Pb ages with major age peaks at ~2543 Ma, 1814 Ma, 830 Ma, 460 Ma, and the youngest cluster of zircon (magmatogene) ages is 395 Ma. The zircon U–Pb data show that the late Paleozoic (Early Devonian) is the maximum depositional age of the Wulagen metasedimentary rocks, rather than the previously considered Precambrian period. The zircons with Paleozoic ages yield εHf(t) values of −22.0 to +11.3 and two-stage model ages (TDM2) of 3.95 to 1.30 Ga, suggesting that the parental magmas were formed from partial melting of pre-existing crustal rocks. Our zircon U–Pb geochronology and Hf isotopic data indicate the major source regions for the Wulagen metasedimentary rocks was the Kyrgyzstan North Tianshan. The zircon age population of 600–400 Ma (peak at ~460 Ma) has negative εHf(t) values (−15.0 to −0.6) and Mesoproterozoic two-stage model ages, suggesting that the early Paleozoic magmatism resulted mainly from the melting of ancient crust, which played an important role in crustal evolution in the southern CAOB.

Petrography of garnet-containing rocks of the Ufalei block, the Southern Urals

Object of study. The article presents of the petrographic study results of the garnet-containing rocks from the Ufaleiskii complex, located on the border of the Ufaleyskii metamorphic gneiss-amphibolite block with the Main Ural Fault (GUR). Methods. Petrographic studies were conducted using a polarizing microscope Axiolab ZS и Olimpus BX 51. Chemical composition of garnets is performed on the raster electron microscope of the РЭММА-202М with an energy dispersive spectrometer LZ-5. Results. Investigations made it possible to distinguish two types of garnet-containing rocks. One type, in which garnet was formed after amphibole (amphibolites and gornbendites), and the second one, in which garnet is the primary mineral (metamorphic schists). Zoisite and chlorite are formed in rocks of the first type together with granate. CaO, MgO, FeO and Al2O3 were extracted from amphibole, in the process of crystallization of garnet, some of these components went to form zoisite and chlorite, and the released silica formed quartz. Garnet grains in these rocks are 64–68% composed of almandine. In the rocks of the second type, represented by biotite-hornblende, biotite-chlorite-quartz and double-mica schists, garnet is the primary mineral formed from the original rocks in the process of progressive metamorphism. The composition of the garnet in these rocks correlates with the composition of the original rock. Conclusion. A complex of garnet-containing rocks with a high content of granulated quartz may be of interest as a raw material for obtaining pure quartz concentrates. The paper presents the results of a detailed petrographic study of all types of rocks of the complex and discusses possible options for their genesis.

Precambrian Complexes of the West Siberian Plate: Problem and Solution

The heterogeneous assemblage of zircons was identified in metamorphic schists of the Karabash site of the West Siberian Plate. Based on the U–Pb (SHRIMP II) isotope data, zircon varies in age from the Archean–Paleoproterozoic boundary to the early Permian. The Precambrian age data obtained for the study area reflect the erosion of the Precambrian complexes in the framework of West Siberian Plate (with subsequent redeposition of the ancient detrital material within the West Siberian megabasin). Our results make it possible to clarify the history of the formation and evolution of metamorphic rocks in the basement of the West Siberian Plate.

Groundwater isoscapes in a montane headwater catchment show dominance of well‐mixed storage

AbstractWe conducted an integrated groundwater–surface water monitoring programme in a 3.2‐km2experimental catchment in the Scottish Highlands by sampling all springs, seepages, and wells in six, spatially extensive synoptic surveys over a 2‐year period. The catchment has been glaciated, with steep hillslopes and a flat valley bottom. There is around 70% glacial drift cover in lower areas. The solid geology, which outcrops at higher elevations, is granite and metamorphic schist. The springs and seepages generally occur at the contact between the solid geology and drift or at breaks of slopes in the valley bottom. Samples were analysed for stable isotopes, Gran alkalinity and electrical conductivity. Despite the surveys encompassing markedly different antecedent conditions, the isotopic composition of groundwater at each location exhibited limited temporal variability, resulting in a remarkable persistence of spatial patterns indicating well‐mixed shallow, groundwater stores. Moreover, line‐conditioned excess values derived from the isotope data indicated no evidence of fractionation affecting the groundwater, which suggests that most recharge occurs in winter. The alkalinity and electrical conductivity of groundwater reflected geological differences in the catchment, being highest where more weatherable calcareous rocks outcrop at higher altitudes in the catchment. Springs draining these areas also had the most variable isotope composition, which indicated that they have shorter residence times than the drift covered part of the catchment. The study showed that even in geologically heterogeneous upland catchments, groundwater can be characterized by a consistent isotopic composition, reflecting rapid mixing in the recharge zone. Our work, thus, emphasizes the critical role of groundwater in upland catchments and provides tracer data that can help constrain quantitative groundwater models.

The Origin of A New Pargasite-Schist Hosted Ruby Deposit From Paranesti, Northern Greece

Gem-quality (cabochon) ruby-bearing occurrences (here termed PAR-1 and PAR-5) located near Paranesti, north eastern Greece have been systematically studied for the first time in this paper. Tectonically, the occurrences are located within the Nestos Shear Zone (NSZ). The NSZ separates two distinct geological units. The Rhodope Terrane is a heterogeneous unit of gneisses, mafic, ultramafic, and meta-sedimentary rocks in the hanging wall. The footwall Pangaion-Pirin Complex consists of marbles and acid gneisses of a Mesozoic carbonate platform on pre-Mesozoic continental basement. In this paper, a range of petrographic and geochemical techniques were used to determine (1) any similarities and differences to other mafic-ultramafic hosted ruby deposits worldwide; (2) distinctive geochemical fingerprints for Paranesti; and (3) the likely P-T conditions of formation. Detailed petrographic and whole-rock analyses utilizing ICP-MS, XRF, and XRD have found the Paranesti corundum to be of a mafic/ultramafic protolith with approximately 40 wt.% SiO2, 16 wt.% Mg, 11000 ppm Cr, and 440 ppm Ni. EMPA major element analysis determined the mineral inclusions within the corundum grains to be picotite and hercynite spinels. Pargasite is the dominant amphibole within the corundum-bearing amphibole schist host. The surrounding non-corundum bearing chlorite schist mainly comprises clinochlore. Petrographic examination of the mineral assemblages within the corundum-bearing schists revealed strong fracturing and alignment (parallel to the main regional foliation) of the corundum grains and margarite reaction rims around the corundum. The surrounding non-corundum amphibolites also contain anorthite, along with relict sillimanite, kyanite, and chlorite/muscovite/epidote overprinting. Detailed LA-ICP-MS trace element analysis of the color range of corundum from the two occurrences showed the corundum to be mainly of metamorphic origin, though pale rubies from PAR-5 suggest some metasomatic influence. The corundum displays distinctive geochemical locality signatures, with a combination of high Cr (average 2300 ppm with 15% sample points on core positions >5000 ppm and maximum 8600 ppm); high Si (average 1400 ppm with 40% over 1500 ppm and maximum 2500 ppm), low Mg (average 30 ppm), and very low V, Ti, and Ga. Based on the literature for similar occurrences, and the mineral assemblages observed at Paranesti, the estimated P-T conditions of corundum formation are <7 kbar and <750 °C, similar to the mafic African amphibolite-hosted rubies. This study has found the Paranesti occurrences to be most similar to the Winza, Tanzania ruby deposit, whilst there are some similarities to other high-Cr ruby deposits, primarily the Fiskenaesset, Greenland and metamorphic amphibolitic schist hosted African deposits. The Paranesti corundum most likely formed during regional amphibolite facies metamorphism which created the Nestos Shear Zone, along with a lesser influence (primarily observed in the PAR-5 occurrence) of more localized metasomatism. Subsequent multiple greenschist facies retrogression of the occurrences resulted in the current-day host amphibole-chlorite schist assemblages.

Early medieval seascapes in Western Ireland and the geochemistry of ecclesiastical cross stones

Select early medieval period (400–1100CE) Irish people pursued lifestyles of ascetic devotion leading to the establishment of ecclesiastical communities on small islands along Ireland's western coastline. These communities were separated by rough ocean waters, unpredictable Atlantic storms and rocky coastlines. Nevertheless, contemporary textual evidence and shared patterns of architecture, technology, and artisanship, including carved cross stones indicate that these communities were nodes in regional networks of institutional affiliation, shared religious practice, and material procurement or exchange.This study uses geochemical characterization of rock lithologies by hand-held, portable x-ray fluorescence (HHpXRF) in conjunction with routine petrographic analysis to assess the inter-island distribution of rock types used to produce early medieval cross stones in an effort to better define this integrated seascape. The cross stones were produced from a wide range of different geologic materials, including sedimentary limestones to high-grade metamorphic schists. The goal of this study was to determine what proportion of the cross stones were produced from materials locally available on each of the individual islands, and what proportion were produced from imported, non-local lithologies. This study demonstrates that in-field use of portable HHpXRF instrumentation provides semi-quantitative chemical data that can be used in conjunction with visually obtained petrographic data to broadly discriminate and identify different bedrock lithologies. Our results indicate that approximately 25% of the 41 cross stones analyzed were produced from non-local lithologies.Results of this study suggest that early medieval inhabitants primarily used locally procured (on-island) material for cross stone production; non-locally obtained (off-island) rock was used less frequently. These results are consistent with other recent archaeological interpretations that highlight western Ireland seascapes as a connective network between members of early medieval communities who used open-water seafaring and raw material procurement/exchange as a means to maintain regional connections.