Minerals In Sedimentary Rocks Research Articles

Temperature sensitivity of the mineral permafrost feedback at the continental scale.

Oxidative weathering of sulfide minerals in sedimentary rocks releases carbon dioxide (CO2) into the atmosphere. In permafrost zones, this could be a positive feedback on climate change if it increases with warming, yet sulfide oxidation rates and their temperature response remain unknown over large spatial and temporal scales. We analyze a 60-year sulfate concentration dataset from catchments across the Mackenzie River Basin. Sulfate fluxes increased by 45% in the mainstem with 2.3°C of warming, and the temperature sensitivity suggests that continental-scale CO2 fluxes could double by 2100. The largest increases occur in catchments with geomorphic settings which act to rapidly expose rocks through physical weathering and thermokarst processes. Comparisons with a weathering model suggest that warming can increase reaction rates, and changes in the exposure of minerals with warming are also required. Future warming across vast Arctic landscapes could further increase sulfide oxidation rates and affect regional carbon cycle budgets.

IMAGE-BASED YOLOV4 ARCHITECTURE FOR DETECTING MINERAL IN SEDIMENTARY ROCKS THIN SECTION

Thin section analysis of sedimentary rocks is the basis for identifying minerals and textures. In general, quantitative analysis of thin sections of rock often requires many hours of work when done manually. In today's era, mineralogical interpretation and percentage calculations must be carried out automatically using more practical applications. The research method begins with the identification of 44 thin section samples in parallel plane polarized (PPL) and crossed polarized (XPL) conditions with thin section analysis then mineralogy detection is carried out using a computational approach, namely the use of image-based Deep Learning YoloV4 architecture with 2D RGB image objects from the thin section of sedimentary rock. The results of this study show the best values of Average Precision in Quartz, Feldspar, and lithic are 39.21% in the XPL model, 26.53% in the XPL model, and 15.75% in combined mode, according to the training and testing of YoloV4 Models for the identification of rock minerals in thin sections. Based on the complexity of the mineral types, the granularity of the detection, and the specific geological objectives, establishing a meaningful benchmark or baseline for comparison is always challenging. Additionally, consider discussing the trade-offs between precision and recall, as a higher precision may be more critical in some geological applications. It is expected that the application of this research can produce practical, fast and accurate interpretation of the determination of minerals in sedimentary rocks from all thin-section images of rocks and thus provide a complete understanding of geological views automatically.

Rapid switch in geodynamic setting revealed by episodic granitoid magmatism in the Lynn Lake greenstone belt of Paleoproterozoic Trans-Hudson Orogen, Manitoba, Canada

Bedrock geological mapping indicates that diverse granitoid intrusions occur closely in space and time in the Paleoproterozoic Lynn Lake greenstone belt of the Trans-Hudson Orogen, Manitoba, Canada. These intrusions display distinct geochemical characteristics of I-type, A-type and adakite-like granitoids as revealed by their respective alkalinity, alumina saturation state, and trace element concentrations and ratios. The ca. 1879 Ma I-type granitoid pluton intruded the 1892 to 1884 Ma supracrustal package of volcanic, volcaniclastic and minor sedimentary rocks that constitute the greenstone belt, which was cut by 1873 Ma A-type granite and then by 1854 Ma adakite-like quartz diorite intrusions. Why the geochemical affinities of these granitoids change so rapidly (within ∼25 Myr) in orogenic belts, however, is not as well understood. Here we propose using SmNd isotope data and trace element modeling that the compositional variety of the granitoid intrusions likely reflects the mineral assemblages of their source rocks rather than magmatic fractionation. They may have been formed by partial melting of the disparate sources at different depths to respond to the change in tectonic regimes. The timing of the granitoid intrusions tracks a rapid geodynamic transition from subduction to intra-arc extension and to slab break-off due to terrane accretion and collision. This records a crucial piece of history in geodynamic evolution of the Trans-Hudson Orogen, which to date has been overlooked largely in many other orogens.

Osteohistological analysis and preservation stage of Coendou magnus Lund, 1839 (Rodentia, Erethizontidae) fossils recovered at Toca da Barriguda Cave, Northeastern Brazil

Studies on taxonomy, taphonomy, and paleoecology have been conducted on fossils from carbonate caves, however, surveys detailing the fossilization processes and bone microstructure of specimens from caves are still scarce. Our paper provides an osteohistological analysis and X-ray diffraction of a fossil rib from the extinct South American porcupine Coendou magnus Lund. Our results allowed us to interpret that there was microstructural preservation and low replacement of the organic part of the bone by minerals present in the surrounding sediments, such as apatite and abundant non-silicate minerals in sedimentary rocks, characterizing preservation in an environment with poor weathering. Keywords: cave, X-ray diffraction, late Pleistocene, histology, porcupine.

Scorched minerals in sedimentary rocks

Scorched minerals in sedimentary rocks

Building YoloV4 models for identification of rock minerals in thin section

Rock mineral identification is a costly and time-consuming task using conventional methods of testing physical and chemical properties, especially in the petrographic laboratory. A comprehensive identification model for three rock minerals in sedimentary rocks based on the YoloV4 model is available as a solution. The models predict rock minerals by calculating the pixels and the weights that have been trained previously. First, the YoloV4 models and framework were built. Then, a total of 44 manually labelled thin section images (sedimentary rocks thin section) were used to create the model to detect minerals accurately. The MAP and loss results showed that the parameters of the minerals detection model in PPL are 11% and 1.19, respectively. Meanwhile, The MAP and loss results of XPL are 19% and 1.18, respectively. Finally, Identification of rock minerals using deep learning algorithms is a very promising idea especially the YoloV4 model can build a comprehensive detection of rock samples in thin sections effectively.

Kinetics of glauconite dissolution in anoxic conditions as a function of pH and temperature

Because it is an abundant, divalent cation-bearing mineral in sedimentary rocks and hydrocarbon reservoirs worldwide, glauconite has likely played a role in Earth’s carbon cycle over geologic time and may be important for ongoing efforts to geologically store anthropogenic CO2. Yet, due to its complex chemistry and redox sensitivity, glauconite dissolution kinetics have so far been difficult to constrain. To fill this significant knowledge gap, we have undertaken a study to quantify the far-from-equilibrium rates of glauconite dissolution using a novel experimental apparatus specifically designed to explore mineral dissolution kinetics under strictly anoxic conditions. Steady-state glauconite dissolution rates were measured at varying pH from 1.7 to 11.2 and temperature from 24 to 80 °C. Temporal evolution of the differences between cation concentrations in the inlet and outlet solutions exhibits stoichiometric or close-to-stoichiometric glauconite dissolution for Fe, Mg, and Si. Fitting the rates calculated from Si release during the experiments to a standard Transition State Theory-derived, far-from-equilibrium rate law yields:k=2.18×10-12·exp-32.2R·1T-1Tr·aH+0.37+2.95×10-14·exp-37.5R·1T-1Tr,where k is the rate constant (mol m−2 s−1) at the temperature (T, Kelvin) and H+ activity (aH+) of interest, Tr is the reference temperature (298.15 K), and R is the ideal gas constant (8.314 × 10−3 kJ mol-1 K−1). Our experimental results show that the mechanism of glauconite dissolution is highly dependent on temperature and on pH in acidic solutions. Geochemical calculations based on the fitted rate equation predict that complete carbonation of glauconite in a system with a 10:1 water–rock ratio and 50 bar of CO2 fugacity can be expected after 17.5, 11.9, 7.1, and 3.8 kyr at 35 °C, 45 °C, 60 °C and 80 °C, respectively. While the lower-temperature simulations generally agree with previously published modelling efforts, the higher temperature reactions are significantly faster than previously predicted. These results highlight the importance of reservoir temperature for glauconite diagenesis and suggest that, when appropriate attention is paid to reservoir temperature during site selection, glauconite carbonation may present significant opportunities for CO2 mineralization.

Genesis and Distribution of Pyrite in the Lacustrine Shale: Evidence from the Es3x Shale of the Eocene Shahejie Formation, Zhanhua Sag, East China.

Pyrite is a common mineral in sedimentary rocks and is widely distributed in a variety of different morphologies and sizes. Pyrite is also widely distributed in the Es3x shale of the Eocene Shahejie Formation in the Zhanhua Sag, Bohai Bay Basin. A combination of geochemical and petrographic studies has been applied to address the formation and distribution of pyrite in the Es3x shale. The methods include thin section analysis to identify the representative samples of the shale-containing pyrite, total organic carbon (TOC) content analysis, X-ray fluorescence, X-ray diffraction, electron probe micro-analysis, and field emission scanning electron microscopy (FE-SEM) coupled with the energy dispersive spectrometer, to observe the characteristics, morphology, and distribution of pyrite in the lacustrine shale. The content of pyrite in the Es3x shale ranges from 1.4 to 11.2% with an average content of 3.42%. The average contents of TOC and total organic sulfur (TS) are 3.48 and 2.53 wt %, respectively. Various types of pyrites are observed during the detailed FE-SEM investigations including pyrite framboids, euhedral pyrite, welded pyrite, pyrite microcrystals, and framework pyrite. Pyrite framboids are densely packed sphere-shaped masses of submicron-scale pyrite crystals with subordinate large-sized euhedral crystals of pyrite. Welded pyrite forms due to the overgrowth and alteration of pyrite crystals within the larger pyrite framboids. Pyrite microcrystals are the euhedral-shaped microcrystals of pyrite. The framework pyrite is also observed and is formed due to the pyritization of plant/algal tissues. Based on the growth mechanism, the pyrites can be divided into syngenetic pyrites, early diagenetic pyrites, and late diagenetic pyrites. The presence of pyrite, especially the abundance of pyrite framboids, suggests that the environment during the Es3x shale deposition in the lacustrine basin was anoxic. Their dominant smaller size suggests the presence of an euxinic water column, which is consistent with the lack of in-place biota and high TOC contents. This research work not only helps to understand the pyrite mineralization, role of organic matter, and reactive iron in pyrite formation in the shale but also helps to interpret the paleoredox conditions during the deposition of shale. This research work can also be helpful to other researchers who can apply these methods and conclusions to studying shale in other similar basins worldwide.

Study on the Use of CTAB-Treated Illite as an Alternative Filler for Natural Rubber

Fillers are indispensable for rubber composites. Carbon black as an efficient reinforcing filler is most widely used in the rubber industry. However, the utilization of nonrenewable feedstock, energy consumption, and footprint for making carbon black lead to the seeking of alternative substitutes for carbon black, which is of great significance. Here in this work, the possibility of illite, a most common mineral in sedimentary rocks, as an alternative filler for natural rubber (NR) is determined. It is found that pristine illite slows the curing rate and decreases the cross-linking density of NR, which results in the inferior performance of NR. This is associated with the weak filler–rubber interaction, which is a vital factor in deciding the performance of rubber composites. Therefore, illite has been modified using hexadecyl trimethyl ammonium bromide (CTAB), a commonly used cation surfactant, for improving the filler–rubber interaction. The thus obtained C-illite is confirmed to be efficient for (i) enhancing the illite–NR interaction, (ii) improving the dispersion of illite in the NR matrix, and (iii) accelerating the curing process of NR with increased cross-linking density. All of these lead to significantly improved mechanical properties and wear resistance of the C-illite/NR composites, e.g., a 71.88% increase of the modulus at 300% strain compared to the pure NR and a 23.79% reduction of the DIN abrasion volume compared to the NR filled with 40 phr pristine illite. This illustrates the high possibility of CTAB-modified illite with an optimal particle size as a promising alternative filler of carbon black for reinforcing rubbers.

Гидрохимическая характеристика и качество подземных вод Сосновского района Челябинской области для целей орошения

Abstract. The purpose of the study was to assess the quality of groundwater used for irrigation of individual plots of land, belonging to the residents of the Sosnovskiy district of the Chelyabinsk region. Material: 73 samples taken in wells and boreholes on the territory of private land plots, villages, villa communities and garden non-profit partnerships. Methods: 30 indicators of water composition were determined (common indicators – 6, major ions and carbonate ion – 8, compounds of nitrogen, phosphorus and organic matter – 5, heavy metals and silicon – 11) using capillary electrophoresis, atomic absorption, potentiometry, spectrophotometry and conductometry. Statistical analysis included: estimation of means with 95 % confidence intervals (95 % CI) calculated by bootstrap (Kaplan – Meier method was used for censored observations), relative frequencies (in percent) with 95 % CI (Jeffreys method and simultaneous CI by Wilson). Data was visualized using Piper’s and Gibbs’ diagrams. Software: PAST, Scout 2008, R, DescTool, GW_Chart, KyPlot, QGIS. Results. On the territory of the Sosnovsky district of the Chelyabinsk region, (Ca2+–Mg2+ and HCO3––CO32–) type groundwater prevails with a pH 7.39 (95 % CI: from 7.30 to 7.48) and a TDS 651 mg/dm3 (95 % CI: from 598 to 720). Using Piper and Gibbs diagrams, it was established that the leading processes of the water chemical composition formation are: 1) the dissolution of the calcite-dolomite series’ minerals of sedimentary rocks, 2) the dissolution and the ion exchange of feldspars in the composition of granites with calcite. For mineralization and risks of chloride salinization, sodium salinization, magnesium salinization and soda formation, the proportion of samples with quality for irrigation purposes I and II category is 65.7 %. There are excesses of standards in the concentration of NO3- (24.7 % of samples), Ba (68.3 %), Cd (30.4 %), Fe (15.3 %), Mn (12.9 %), Pb (6.3 %).

Deconvolution of the composition of fine-grained pyrite in sedimentary matrix by regression of time-resolved LA-ICP-MS data

Abstract Pyrite is a common mineral in sedimentary rocks and is the major host for many chalcophile trace elements utilized as important tracers of the evolution of the ancient hydrosphere. Measurement of trace element composition of pyrite in sedimentary rocks is challenging due to fine-grain size and intergrowth with silicate matrix and other sulfide minerals. In this contribution, we describe a method for calculation of trace element composition of sedimentary pyrite from time-resolved LA-ICP-MS data. The method involves an analysis of both pyrite and pyrite-free sediment matrix, segmentation of LA-ICP-MS spectra, normalization to total, regression analysis of dependencies between the elements, and calculation of normalized composition of the mineral. Sulfur is chosen as an explanatory variable, relative to which all regressions are calculated. The S content value used for calculation of element concentrations from the regressions is calculated from the total, eliminating the need for independent constraints. The algorithm allows efficient measurement of concentrations of multiple chalcophile trace elements in pyrite in a wide range of samples, including quantification of detection limits and uncertainties while excluding operator bias. The data suggest that the main sources of uncertainties in pyrite composition are sample heterogeneity and counting statistics for elements of low abundance. The analysis of regression data of time-resolved LA-ICP-MS measurements could provide new insights into the geochemistry of the sedimentary rocks and minerals. It allows quantification of ratios of elements that do not have reference material available (such as Hg) and provides estimates on the content of non-sulfidic Fe in the silicate matrix. Regression analysis of the mixed LA-ICP-MS signal could be a powerful technique for deconvolution of phase compositions in complex multicomponent samples.

Clay mineral signatures of fault-related fluid flows in a sandstone reservoir: A case study from the Teloua Formation, Tim Mersoї Basin, Niger

During the evolution of sedimentary basins, clay minerals may record changes in their mineralogy, chemistry, and texture as a response to diagenesis, fluid flows, and tectonic activities. Therefore, studying clay minerals in sedimentary rocks provides important information that may assist to decipher the basin history. The focus of the present study is the Teloua Sandstone Formation (Fm) which belongs to the Tim Mersoï Basin located in the NE of Niger republic (West Africa). The formation is cut by the major Arlit fault which is the largest tectonic structure impacting the Tim Mersoï Basin. The aim of the present work is to use the texture, mineralogy, and chemistry of clay minerals in the Teloua Fm as geochemical markers for burial diagenesis history and fluids flows (i.e., attributed mainly to the Arlit fault). Therefore, three drill holes (DH1, DH2, and DH3) were investigated as a function of their distance from the fault and samples have been collected all along the Teloua Fm (Upper Triassic-Lower Jurassic), at the unconformity surface with the underlaying Moradi Fm (Upper Permian), and at the top of the Moradi Formation.Petrographic observations demonstrate that the sediments of the Teloua Fm have undergone transformations induced by burial diagenesis, brittle deformation, and multiple stages of fluid flows. These transformations are marked by grain compaction, fragmentation, dissolution of detrital minerals, recrystallization of authigenic clay minerals, and modifications in the primary porosity. XRD and SEM results indicate no significant variation in the detrital mineralogy of the three drill holes; Teloua Fm samples are composed of quartz, feldspars (microcline and albite), micas (biotite and muscovite), minor heavy minerals such as hematite, anatase, phosphates (apatite and monazite), and zircon. The authigenic clay minerals observed in the three drill holes are rosette-like tosudite (i.e., a regular interstratified chlorite/smectite), saponite, montmorillonite, and kaolinite/smectite mixed layer. Regarding their vertical distribution, tosudite occurs throughout the Teloua Fm, whereas montmorillonite is mainly present at the top of the formation, and saponite is only observed at the unconformity between Teloua and Moradi formations. The Mg content of tosudite tends to decrease with increasing vertical distance from the basal unconformity and the lateral distance from the Arlit fault. This is interpreted as an evidence of Mg-rich fluid circulations related to the Arlit fault activity that penetrated the formation through the unconformity surface and fractures. This is also evidenced by the enrichment of dolomite at the unconformity when moving closer to the Arlit fault. In addition, the occurrence of both authigenic saponite (at the unconformity) and montmorillonite (upper part of the Teloua Fm) that post-dated tosudite is attributed to another stage of Mg-rich fluid circulation during late diagenesis. Furthermore, late downward circulation of meteoric fluids of low pH are evidenced by the partial alteration and replacement of montmorillonite by kaolinite/smectite mixed layer in the Teloua Fm (at shallow depth of the DH3). These results demonstrate the validity of clay minerals as reliable tools to provide information about fluid/rock interaction in complex geological and tectonic setting.

Thermal analysis and FT-IR spectroscopy of synthetic clay mineral mixtures

Common clays and especially mixed-layered or interstratified clay minerals are generally mixtures of predominantly clay mineral along with minor quantity of another clay mineral, wherein the ratio of the components will determine the resulting properties of these clay materials. This study focuses on IR spectroscopy and TG/DTA analysis and their contribution to the identification of clay minerals in two-component mixtures. Identifying clay minerals in such mixtures by means of thermal analysis is often complicated by the similarity of the thermal effects of the individual clay components. Similarity in thermal behavior is mainly connected with the origin, chemical variability and crystal structure of phyllosilicates. The main problem is overlapping thermal effects of clay minerals or thermal effects related to accessory minerals (calcite, quartz, etc.) on DTA curve. A similar problem also appears in the identification of mixed clay mineral structures by infrared spectroscopy. There are also more or less overlapping absorption bands in the infrared spectra for the mixtures of clay minerals. In this paper, the prepared clay mixtures were supposed to partially simulate the natural mixed clay structures and a minimum content of detectable minerals in clay mixtures were determined according to characteristic peaks on the DTA curves and absorption bands in FT-IR spectra. The results of both methods showed that kaolinite is the most reliable detectable mineral. The detection limit for thermal analysis corresponds to 3% mass kaolinite in admixture with chlorite or montmorillonite, and 1% mass kaolinite for both of these mixtures is based on IR spectroscopy. In case of montmorillonite and chlorite, the identification by FT-IR spectroscopy shows detection limit only 30% mass in contrast to TG/DTA with the detection limit of 5% mass for montmorillonite and 5% mass or 10% mass for chlorite. The obtained results can be effectively used to solve problems in identification of clay minerals in sedimentary rocks, which is very important for subsequent applications in geotechnical, geothermal, and mining activities.

A review of structural patterns and melting processes in the Archean craton of West Greenland: Evidence for crustal growth at convergent plate margins as opposed to non-uniformitarian models

The Archean craton of West Greenland consists of many fault-bounded Eoarchean to Neoarchean tectonic terranes (crustal blocks). These tectonic terranes are composed mainly of tonalite–trondhjemite–granodiorite (TTG) gneisses, granitic gneisses, metavolcanic-dominated supracrustal belts, layered anorthositic complexes, and late- to post-tectonic granites. Rock assemblages and geochemical signatures in these terranes suggest that they represent fragments of dismembered oceanic island arcs, consisting mainly of TTG plutons, tholeiitic to calc-alkaline basalts, boninites, picrites, and cumulate layers of ultramafic rocks, gabbros, leucogabbros and anorthosites, with minor sedimentary rocks. The structural characteristics of the terrane boundaries are consistent with the assembly of these island arcs through modern style of horizontal tectonics, suggesting that the Archean craton of West Greenland grew at convergent plate margins. Several supracrustal belts that occur at or near the terrane boundaries are interpreted as relict accretionary prisms. The terranes display fold and thrust structures and contain numerous 10cm to 20m wide bifurcating, ductile shear zones that are characterized by a variety of structures including transposed and redistributed isoclinal folds. Geometrically these structures are similar to those occurring on regional scales, suggesting that the Archean craton of West Greenland can be interpreted as a continental scale accretionary complex, such as the Paleozoic Altaids. Melting of metavolcanic rocks during tectonic thickening in the arcs played an important role in the generation of TTGs. Non-uniformitarian models proposed for the origin of Archean terranes have no analogs in the geologic record and are inconsistent with structural, lithological, petrological and geochemical data collected from Archean terranes over the last four decades. The style of deformation and generation of felsic rocks on outcrop scales in the Archean craton of West Greenland and the Mesozoic Sulu orogenic belt of eastern China are similar, consistent with the formation of Archean continental crust by subduction zone processes.

Determination of the Predominant Minerals in Sedimentary Rocks by Chemometric Analysis of Infrared Spectra

AbstractThe objective of the present study was to determine the predominant minerals in sedimentary rocks using Fourier-transform infrared (FTIR) spectroscopy and chemometric analysis. The chemometric analysis was performed on three types of sedimentary rock samples (claystones, clay slates, and sandstones), each with different predominant mineral components. Chemometric models were created to determine the major minerals of the rock samples studied — chlorite, muscovite, albite, and quartz. The FTIR spectra were obtained in transmission mode from pressed pellets of KBr-sample mixtures or by diffuse reflectance from hand-packed mixtures of samples with KBr. Spectral regions measured were 4000-3000 and 1300–400 cm-1, which contained important spectral information for the creation of the chemometric models. Principal component analysis was used in the chemometric method, with calibration models being created by a partial least-squares regression method. The mean relative error, standard error of prediction, and relative standard deviation were calculated for the assessment of accuracy, precision, and reproducibility. The value of the mean relative error was 15–20% for most of the calibration models; the value of the standard error of prediction was up to 6 w/w % for most of the calibration models. The values of the standard relative deviation ranged from ~2 to 8% for calibration models based on diffuse reflectance spectra whereas calibration models based on transmission spectra had values of relative standard deviation of ~15-20%.

In situ U–Pb rutile dating by LA-ICP-MS: 208Pb correction and prospects for geological applications

Rutile is a common accessory mineral that occurs in a wide spectrum of metamorphic rocks, such as in blueschists, eclogites, and granulites and as one of the most stable detrital heavy minerals in sedimentary rocks. The advent of rutile trace element thermometry has generated increased interest in a better understanding of rutile formation. This study documents important analytical advances in in situ LA-ICP-MS U/Pb geochronology of rutile: (1) Matrix matching, necessary for robust in situ dating is fulfilled by calibrating and testing several rutile standards (R10, R19, WH-1), including the presentation of new TIMS ages for the rutile standard R19 (489.5 ± 0.9 Ma; errors always stated as 2 s). (2) Initial common lead correction is routinely applied via 208Pb, which is possible due to extremely low Th/U ratios (usually <0.003) in most rutiles. Employing a 213 nm Nd:YAG laser coupled to a quadrupole ICP-MS and using R10 as a primary standard, rutile U/Pb concordia ages for the two other rutile standards (493 ± 10 Ma for R19; 2640 ± 50 Ma for WH-1) and four rutile-bearing metamorphic rocks (181 ± 4 Ma for Ivrea metapelitic granulite; 339 ± 7 Ma for Saidenbach coesite eclogite; 386 ± 8 Ma for Fjortoft UHP metapelite; 606 ± 12 Ma for Andrelandia metepelitic granulite) always agree within 2% with the reported TIMS ages and other dating studies from the same localities. The power of in situ U/Pb rutile dating is illustrated by comparing ages of detrital rutile and zircon from a recent sediment from the Christie Domain of the Gawler Craton, Australia. While the U/Pb age spectrum from zircons show several pronounced peaks that are correlated with magmatic episodes, rutile U/Pb ages are marked by only one pronounced peak (at ca 1,675 Ma) interpreted to represent cooling ages of this part of the craton. Rutile thermometry of the same detrital grains indicates former granulite-facies conditions. The methods outlined in this paper should find wide application in studies that require age information of single spots, e.g., provenance studies, single-crystal zoning and texturally controlled dating.

Sulfuric acid as an agent of carbonate weathering constrained by δ13C DIC: Examples from Southwest China

Abstract Rock weathering by carbonic acid is thought to play an important role in the global carbon cycle because it can geologically sequestrate atmospheric CO 2. Current model of carbon cycle evolution usually assumes that carbonic acid is the major weathering agent and that other acids are not important. Here, we use carbon isotopic evidence and water chemistry of springs and rivers from the Beipanjiang River basin (Guizhou Province, Southwest China) to demonstrate that sulfuric acid is also an important agent of rock weathering. The δ 13C of dissolved inorganic carbon (DIC) in the water samples ranges from − 13.1‰ to − 2.4‰, and correlates negatively to [HCO 3 −]/([Ca 2+] + [Mg 2+]) ratios and positively to [SO 4 2−]/([Ca 2+] + [Mg 2+]) ratios. These relationships are interpreted as mixing diagrams between two reactions of carbonate weathering, using carbonic acid and sulfuric acid as a proton donor, respectively. Mixing proportions show that around 42% of the divalent cations in the spring water from Guizhou are originated from the interaction between carbonate minerals and sulfuric acid. It is shown that 40% of this sulfuric acid is derived from the atmosphere and has an anthropogenic origin. The remaining 60% are derived from the oxidative weathering of sulfide minerals in sedimentary rocks. Our results show the positive action of sulfuric acid on the chemical weathering of carbonate. Particularly, we show that sulfuric acid generated by coal combustion has increased by almost 20% the weathering rates of carbonate in Southwest China. This is a clear evidence that human activities are changing the weathering rates of rocks and demonstrates a negative feedback on the acidification of the ocean by greenhouse gases. Because of the involvement of sulfuric acid in weathering reactions, 63% of the alkalinity exported by rivers is derived from carbonate, instead of 50% when atmospheric CO 2 is the only acid involved in chemical weathering of carbonate. In the Guizhou Province, the weathering of carbonate is thus, at least transiently, a net source of CO 2 to the atmosphere. When extrapolated at global scale, sulfuric acid-induced carbonate weathering could counterbalance a significant part of the CO 2 consumed by silicate weathering. This paper highlights the competition between silicate weathering by carbonic acid and carbonate weathering by sulfuric acid for the regulation of the atmospheric CO 2 level.

U-Pb SHRIMP data for the Madibe greenstone belt: implications for crustal growth on the western margin of the Kaapvaal Craton, South Africa

Research Article| March 01, 2008 U-Pb SHRIMP data for the Madibe greenstone belt: implications for crustal growth on the western margin of the Kaapvaal Craton, South Africa M. Poujol; M. Poujol Géosciences Rennes UMR6118, Université de Rennes 1, 35042 Rennes Cedex, France, e-mail: marc.poujol@univ-rennes1.fr Search for other works by this author on: GSW Google Scholar A.J. Hirner; A.J. Hirner School of Geosciences, CAMEG, Private Bag 3, University of the Witwatersrand, WITS 2050, South Africa Current address: German Remote Sensing Data Center (DFD), German Aerospace Center (DLR), P.O. Box 1116, D-82234, Wessling, Germany, e-mail: andreas.hirner@dlr.de Search for other works by this author on: GSW Google Scholar R.A. Armstrong; R.A. Armstrong Research School for Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia, e-mail: richard.armstrong@prise.anu.edu.au Search for other works by this author on: GSW Google Scholar C.R. Anhaeusser C.R. Anhaeusser Economic Geology Research Institute, School of Geosciences, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa, e-mail: carl.anhaeusser@wits.ac.za Search for other works by this author on: GSW Google Scholar Author and Article Information M. Poujol Géosciences Rennes UMR6118, Université de Rennes 1, 35042 Rennes Cedex, France, e-mail: marc.poujol@univ-rennes1.fr A.J. Hirner School of Geosciences, CAMEG, Private Bag 3, University of the Witwatersrand, WITS 2050, South Africa Current address: German Remote Sensing Data Center (DFD), German Aerospace Center (DLR), P.O. Box 1116, D-82234, Wessling, Germany, e-mail: andreas.hirner@dlr.de R.A. Armstrong Research School for Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia, e-mail: richard.armstrong@prise.anu.edu.au C.R. Anhaeusser Economic Geology Research Institute, School of Geosciences, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa, e-mail: carl.anhaeusser@wits.ac.za Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2008, The Clay Minerals Society South African Journal of Geology (2008) 111 (1): 67–78. https://doi.org/10.2113/gssajg.111.1.67 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M. Poujol, A.J. Hirner, R.A. Armstrong, C.R. Anhaeusser; U-Pb SHRIMP data for the Madibe greenstone belt: implications for crustal growth on the western margin of the Kaapvaal Craton, South Africa. South African Journal of Geology 2008;; 111 (1): 67–78. doi: https://doi.org/10.2113/gssajg.111.1.67 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract The Madibe greenstone belt is the easternmost belt of the northern Kraaipan terrane, located in the Kimberley Block of the Kaapvaal Craton. It comprises a mature Middle to Late Archaean volcanic island arc succession that was welded onto the evolving western margin of the Kaapvaal Shield. The lithologies strike in a north-south direction and represent an assemblage of metamorphosed and strongly deformed volcanic and minor sedimentary rocks, now represented by phyllites, quartz-sericite schists, quartz-chlorite schists, amphibolites, talc-carbonate schists and banded iron formations.We report a SHRIMP U-Pb age of 3082.5 ± 5.9 Ma for an intermediate metavolcanic rock. Ages of zircon grains within a volcano-sedimentary rock define ages around 3.43, ~3.18 and, ~3.09 Ga and are as young as ~3.04 Ga, suggesting the presence of older, mature continental crust. Age relationships of rocks from the Madibe greenstone belt and the Murchison greenstone belt suggest that the Kaapvaal Shield apparently experienced an episode of rapid crustal growth at around 3090 Ma along both the northern and western margins. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geochemical study of rare earth elements in carbonate minerals in sedimentary rocks around Tono uranium deposit, central Japan –An example of natural analogue study of geological disposal of high-level nuclear waste–

Geochemical study of rare earth elements in carbonate minerals in sedimentary rocks around Tono uranium deposit, central Japan –An example of natural analogue study of geological disposal of high-level nuclear waste–

Jurassic to Early Cretaceous subduction-related magmatism in the Coastal Cordillera of northern Chile (18°30'-24°S): geochemistry and petrogenesis

Jurassic to Early Cretaceous magmatism in the Coastal Cordillera of northern Chile is represented by thick sequences of mostly basaltic-andesitic to andesitic lava flows and minor sedimentary rocks. The volcanic sucession was intruded by large plutonio bodies and smaller stocks and dikes. New geochemical data, including major and trace elements for a suite of Middle to Upper Jurassic volcanic and plutonio rocks from six localities in the Coastal Cordillera (18°30'-24°S), are presented here. The volcanic rocks are characterized by their petrological and chemical homogeneity; they are highly porphyritic basaltic-andesites and andesites with calc-alkaline to high-K calc-alkaline affinities, higher LILE than HFSE abundances, negative Nb and Ti anomalies, and LREE/HREEfractionation, which are the typical compositional features of subduction-related igneous rocks. No significant differences are observed in rocks from different areas or ages, but the plutonio rocks show subparallel, less and more enriched patterns respectively compared to volcanic rocks. The evolution and differentiation of the parental magmas is mainly due to fractional crystallization dominated by plagioclase, olivine and clinopyroxene. Assimilation of the continental crust was not important, although Th and La contents would indicate increasing sediment contribution or crustal contamination of the magmas with time. The magma source is likely to be a depleted mantle metasomatized by fluids, which originated from dehydration of the subducted oceanic crust. No evidence of slab melting was found in the studied rocks. The extensional tectonic setting that dominated the evolution of the Jurassic-Early Cretaceous arc in northern Chile would have favoured the extrusion of huge amounts of volcanic rocks during a relatively short period of time, avoiding thus a mayor interaction with the continental crust.