Articles de revues : « Bulk petrography »

1

Gleason, James D., David A. Kring, Dolores H. Hill et William V. Boynton. « Petrography and bulk chemistry of Martian lherzolite LEW88516 ». Geochimica et Cosmochimica Acta 61, n^o 18 (septembre 1997) : 4007–14. http://dx.doi.org/10.1016/s0016-7037(97)00196-8.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

2

Sajid, Muhammad, Muhammad Yaseen, Muhammad Zeeshan Ullah et Ghulam Murtaza. « Textural Implications in Assessment of Physico-Mechanical behaviour of Metavolcanic Rocks from Dir Upper, north western Pakistan ». International Journal of Economic and Environmental Geology 11, n^o 3 (4 décembre 2020) : 1–10. http://dx.doi.org/10.46660/ijeeg.vol11.iss3.2020.469.

Texte intégral

Résumé :

The Dir-Utror meta-volcanics from the south western portion of the Kohistan arc in northern Pakistan areanalyzed in term of their petrography, physico-mechanical properties. Field observations and petrography show thecollected representative samples to be fine-grained meta-andesites (FMA), coarse-grained meta-andesites (CMA) andagglomerate (AG). The relationship between petrography and physico-mechanical properties has been investigatedwhich inferred the grain size to be the major factor, alongside grains’ shape, arrangement and size distribution as wellas degree of mineral alteration significantly affecting the mechanical behavior of rocks. The CMA yield more strength(98 MPa) than FMA (93 MPa) due to its lesser degree of mineral alteration, inequigranular texture, lack of preferredmineral alignment, relatively low porosity and water absorption. The lower strength of agglomerate (57 MPa)corresponds to abundance of soft minerals (calcite), exotic rock fragments and coarse-grained texture. Based onphysico-mechanical properties including specific gravity, bulk density, aggregate impact value, Los Angeles abrasionvalue and unconfined compressive strength (UCS), these rocks fall within permissible range to be utilized for multipleengineering purposes including dimension stones and foundation materials for other civil structures. However,petrographic investigations reveal excessive amount of reactive silica in these rocks making them prone to alkali-silicareactivity in concrete works with ordinary Portland cement (OPC). Hence these rocks are not recommended for use assole aggregate material or low-alkali cement is recommended, if used.

Styles APA, Harvard, Vancouver, ISO, etc.

3

NISHIOKA, Yoshiharu. « Petrography and bulk chemical composition of the Miyako zoned pluton, Kitakami Mountains. » JOURNAL OF MINERALOGY, PETROLOGY AND ECONOMIC GEOLOGY 92, n^o 8 (1997) : 291–301. http://dx.doi.org/10.2465/ganko.92.291.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

4

Kim, Yoon Kyu. « Petrology of Ulreung Volcanic Island, Korea - Part2. Petrography and bulk chemical composition. » Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists 80, n^o 7 (1985) : 292–303. http://dx.doi.org/10.2465/ganko1941.80.292.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

5

Guice, George, Iain McDonald, Hannah Hughes, Denis Schlatter, Kathryn Goodenough, John MacDonald et John Faithfull. « Assessing the Validity of Negative High Field Strength-Element Anomalies as a Proxy for Archaean Subduction : Evidence from the Ben Strome Complex, NW Scotland ». Geosciences 8, n^o 9 (8 septembre 2018) : 338. http://dx.doi.org/10.3390/geosciences8090338.

Texte intégral

Résumé :

The relative depletion of high field strength elements (HFSE), such as Nb, Ta and Ti, on normalised trace-element plots is a geochemical proxy routinely used to fingerprint magmatic processes linked to Phanerozoic subduction. This proxy has increasingly been applied to ultramafic-mafic units in Archaean cratons, but as these assemblages have commonly been affected by high-grade metamorphism and hydrothermal alteration/metasomatism, the likelihood of element mobility is high relative to Phanerozoic examples. To assess the validity of HFSE anomalies as a reliable proxy for Archaean subduction, we here investigate their origin in ultramafic rocks from the Ben Strome Complex, which is a 7 km2 ultramafic-mafic complex in the Lewisian Gneiss Complex of NW Scotland. Recently interpreted as a deformed layered intrusion, the Ben Strome Complex has been subject to multiple phases of high-grade metamorphism, including separate granulite- and amphibolite-facies deformation events. Additional to bulk-rock geochemistry, we present detailed petrography, and major- and trace-element mineral chemistry for 35 ultramafic samples, of which 15 display negative HFSE anomalies. Our data indicate that the magnitude of HFSE anomalies in the Ben Strome Complex are correlated with light rare earth-element (LREE) enrichment likely generated during interaction with H2O and CO2-rich hydrothermal fluids associated with amphibolitisation, rather than primary magmatic (subduction-related) processes. Consequently, we consider bulk-rock HFSE anomalies alone to be an unreliable proxy for Archaean subduction in Archaean terranes that have experienced multiple phases of high-grade metamorphism, with a comprehensive assessment of element mobility and petrography a minimum requirement prior to assigning geodynamic interpretations to bulk-rock geochemical data.

Styles APA, Harvard, Vancouver, ISO, etc.

6

Gleason, James D., David A. Kring, Dolores H. Hill et William V. Boynton. « Petrography and bulk chemistry of Martian orthopyroxenite ALH84001 : Implications for the origin of secondary carbonates ». Geochimica et Cosmochimica Acta 61, n^o 16 (août 1997) : 3503–12. http://dx.doi.org/10.1016/s0016-7037(97)00173-7.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

7

Sato, Daisuke, Ichiro Matsumoto et Atsushi Kamei. « Petrography and bulk rock composition of the Wakurayama Dacite from Matsue City, Shimane Prefecture, Southwest Japan ». Journal of the Geological Society of Japan 117, n^o 8 (2011) : 439–50. http://dx.doi.org/10.5575/geosoc.117.439.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

8

Al-Juboury, A. I., T. McCann et M. M. Ghazal. « Provenance of Miocene sandstones in northern Iraq : constraints from framework petrography, bulk-rock geochemistry and mineral chemistry ». Russian Geology and Geophysics 50, n^o 6 (juin 2009) : 517–34. http://dx.doi.org/10.1016/j.rgg.2008.09.005.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

9

V, Thirukumaran, Biswal T.K, Sundaralingam K, Sowmya V, Boopathi S et Mythili R. « Strain Pattern Analysis of Mylonites From Sitampundi-Kanjamalai Shear Zone, Thiruchengode, South India ». International Journal of Civil, Environmental and Agricultural Engineering 1, n^o 1 (30 mai 2019) : 25–34. http://dx.doi.org/10.34256/ijceae1914.

Texte intégral

Résumé :

This study aims to investigate the petrography and strain pattern of mylonites from parts of N-S trending Sitampundi-Kanjamalai Shear Zone (SKSZ) around Thiruchengode. The petrographic study indicates the presence of recrystallized quartz, K-feldspar, plagioclase, biotite and some hornblende. The kinematic analysis of Mylonites was done with the help of shear sense indicators such as recrystallized type quartz (quartz ribbon) around the cluster of feldspar, S-C fabric shows dextral shear sense and some sinisterly shear sense in some parts of SASZ which can be considered as a product of partitioning of both strain and vorticity between domains. These all indicates the simple shear extension along E-W direction and the mylonitic foliation shows the pure shear compression along N-S direction. Further the study of bulk strain analysis by Flinn plot method using L and T section of mylonite shows k<1 which lies in the field of flattening zone of finite strain. The kinematic vorticity number is calculated by Rxz/β method which gives the value of 0.36 indicating the general shear. The rigid grain graph shows that the pure shear component is more dominant than the simple shear component. The analysis leads to the conclusion that the mylonite has experienced a high temperature shearing of above 700°cat deep crustal level.

Styles APA, Harvard, Vancouver, ISO, etc.

10

Kilias, Stephanos P., Magnus Ivarsson, Ernest Chi Chi Fru, Jayne E. Rattray, Håkan Gustafsson, Jonathan Naden et Kleopatra Detsi. « Precipitation of Mn Oxides in Quaternary Microbially Induced Sedimentary Structures (MISS), Cape Vani Paleo-Hydrothermal Vent Field, Milos, Greece ». Minerals 10, n^o 6 (13 juin 2020) : 536. http://dx.doi.org/10.3390/min10060536.

Texte intégral

Résumé :

Understanding microbial mediation in sediment-hosted Mn deposition has gained importance in low-temperature ore genesis research. Here we report Mn oxide ores dominated by todorokite, vernadite, hollandite, and manjiroite, which cement Quaternary microbially induced sedimentary structures (MISS) developed along bedding planes of shallow-marine to tidal-flat volcaniclastic sandstones/sandy tuffs, Cape Vani paleo-hydrothermal vent field, Milos, Greece. This work aims to decipher the link between biological Mn oxide formation, low-T hydrothermalism, and, growth and preservation of Mn-bearing MISS (MnMISS). Geobiological processes, identified by microtexture petrography, scanning and transmission electron microscopy, lipid biomarkers, bulk- and lipid-specific δ13Corganic composition, and field data, and, low-temperature hydrothermal venting of aqueous Mn2+ in sunlit shallow waters, cooperatively enabled microbially-mediated Mn (II) oxidation and biomineralization. The MnMISS biomarker content and δ13Corg signatures strongly resemble those of modern Mn-rich hydrothermal sediments, Milos coast. Biogenic and syngenetic Mn oxide precipitation established by electron paramagnetic resonance (EPR) spectroscopy and petrography, combined with hydrothermal fluid flow-induced pre-burial curing/diagenesis, may account for today’s crystalline Mn oxide resource. Our data suggests that MISS are not unique to cyanobacteria mats. Furthermore, microbial mats inhabited by aerobic methanotrophs may have contributed significantly to the formation of the MnMISS, thus widening the spectrum of environments responsible for marine Mn biometallogenesis.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Hussein, Mohammad Ali, Mohammad Alqudah, Sander van den Boorn, Sadat Kolonic, Olaf G. Podlaha et Jörg Mutterlose. « Eocene oil shales from Jordan - their petrography, carbon and oxygen stable isotopes ». GeoArabia 19, n^o 3 (1 juillet 2014) : 139–62. http://dx.doi.org/10.2113/geoarabia1903139.

Texte intégral

Résumé :

ABSTRACT Sediment petrographic studies combined with carbon and oxygen stable-isotope analyses are considered to be powerful tools in deciphering the depositional and diagenetic history of carbonate rocks. These studies have been found valuable for understanding the environmental controls and global changes of climate and oceanography. Two cores of Eocene bituminous marls (OS-22 and OS-23) from central Jordan with thicknesses of 222.4 m and 256.3 m, respectively, were logged. A total of 103 thin sections were analyzed for sediment petrographic investigations. Another 295 bulk rock samples from Core OS-23 were selected for stable-isotope analysis (δ13C, δ18O). The two cores show similar lithologic variations that correspond to third-order sea-level changes. The sediment petrographic study reveals the presence of six major microfacies that range from mudstones to grainstones. The distribution of these six types of microfacies in the two cores indicates an overall shallow-marine environment in an interior carbonate-platform setting. Within this environment, conditions fluctuated between open and restricted marine. The stratigraphic variability of the carbon-isotope data of Core OS-23 reflects a highly dynamic depositional system that exhibits a variable rate of organic matter accumulation in the sediments, which can be directly linked to the interaction between primary organic-matter burial and oxidative weathering of reworked organic matter. Within the overall diagenetically controlled δ18Ocarb profile an excursion is observed for a specifically enriched organic matter interval. This excursion is believed to coincide with the Middle Eocene Climatic Optimum (MECO), suggesting that next to seawater, porewaters were influenced by this event and making it the first record of this event in the region.

Styles APA, Harvard, Vancouver, ISO, etc.

12

Lupin, Janifar H., et Gary J. Hampson. « Sediment-routing controls on sandstone bulk petrographic composition and texture across an ancient shelf : Example from Cretaceous Western Interior Basin, Utah and Colorado, U.S.A. » Journal of Sedimentary Research 90, n^o 10 (1 octobre 2020) : 1389–409. http://dx.doi.org/10.2110/jsr.2020.044.

Texte intégral

Résumé :

ABSTRACT Sediment-routing controls on sandstone texture and bulk petrography have been evaluated in linked alluvial–coastal–shelfal deposits of the Upper Cretaceous Castlegate Sandstone, Blackhawk Formation, Star Point Sandstone, and Mancos Shale (Western Interior Basin, Utah and Colorado, USA) using thin-section analysis of representative outcrop samples in the context of a high-resolution sequence stratigraphic and paleogeographic framework. The studied strata record deposition from two styles of sediment-routing system within an overfilled foredeep and contiguous intra-continental seaway. First, multiple transverse drainages supplied sand to fluvial, shoreline, and shelf segments of sediment-routing systems characterized by down-dip transport distances of 150–450 km and significant strike-oriented sediment transport along the shoreline. Second, the distal shoreline–shelf segment of an axially supplied sediment-routing system was characterized by sand transport for a distance of c. 300 km. Bulk petrographic composition indicates that transverse sediment-routing systems were sourced from catchments that supplied quartz-rich sand with a subordinate lithic component, while the large axial sediment-routing system was sourced from a catchment(s) supplying slightly more feldspathic sand. Thin-section measurements of mean grain size, sorting, skewness, and ratio of minimum-to-maximum diameter (a proxy for sphericity) are similar for sandstones deposited in fluvial, shoreline, and shelf segments of the transverse sediment-routing systems and in the shoreline–shelf segment of the axial sediment-routing systems, although hydrodynamic sorting is important in locally segregating grain-size populations within each segment. Further, textural analysis of detrital quartz, feldspar, and lithic sand-grain populations shows little evidence of relative change in mean grain size or apparent grain sphericity with downsystem distance, implying that sand-grain populations of different petrographic composition did not undergo significant differential mechanical breakdown during transport. Instead, the textural characteristics of these sand-grain populations are inferred to have been controlled mainly by bedrock lithology and recycling in source catchments. The textural signal of sediment-source areas then propagated downsystem in the sand fraction of detrital sediment supply. This inference is supported by the fine- to medium-grained, well- to very well-sorted character of all sandstone samples, consistent with recycling of sandstones and quartzites from the Sevier fold-and-thrust belt.

Styles APA, Harvard, Vancouver, ISO, etc.

13

Nistor, Mărgărit M., Nicolae Har, Simona Marchetti Dori, Simona Bigi et Alessandro F. Gualtieri. « Progress in mineralogical quantitative analysis of rock samples : application to quartzites from Denali National Park, Alaska Range (USA) ». Powder Diffraction 31, n^o 1 (17 février 2016) : 31–39. http://dx.doi.org/10.1017/s0885715615000871.

Texte intégral

Résumé :

This work deals with the determination of the mineralogical composition of three quartzite samples, selected as case study to verify the viability and accuracy of various experimental techniques commonly used in geometallurgy and petrography for the determination of the mineralogical composition of rock samples. The investigated samples are from the North-Eastern side of the Denali National Park (Alaska Range, USA). The mineralogical phase abundance of the samples was determined by digitally assisted optical modal point counting, scanning electron microscopy (SEM) + energy dispersive spectroscopy (EDS) modal and digital image analysis, normative calculation from bulk chemistry calculation, and modal Rietveld X-ray powder diffraction. The results of our study indicate that the results provided by modal optical and SEM digitalized counting seem less accurate than the others. The determination with EDS mapping was found to be inaccurate only for one sample. Agreement was found between the X-ray diffraction estimates and bulk chemistry calculation. For both modal optical and SEM digitalized counting, the statistics was probably insufficient to provide accurate results. The estimates obtained from the various methods are compared with each other in the attempt to attain general indications on the precision, accuracy, advantages/disadvantages of each method.

Styles APA, Harvard, Vancouver, ISO, etc.

14

Chi, Guoxiang, Larryn W. Diamond, Huanzhang Lu, Jianqing Lai et Haixia Chu. « Common Problems and Pitfalls in Fluid Inclusion Study : A Review and Discussion ». Minerals 11, n^o 1 (24 décembre 2020) : 7. http://dx.doi.org/10.3390/min11010007.

Texte intégral

Résumé :

The study of fluid inclusions is important for understanding various geologic processes involving geofluids. However, there are a number of problems that are frequently encountered in the study of fluid inclusions, especially by beginners, and many of these problems are critical for the validity of the fluid inclusion data and their interpretations. This paper discusses some of the most common problems and/or pitfalls, including those related to fluid inclusion petrography, metastability, fluid phase relationships, fluid temperature and pressure calculation and interpretation, bulk fluid inclusion analysis, and data presentation. A total of 16 problems, many of which have been discussed in the literature, are described and analyzed systematically. The causes of the problems, their potential impact on data quality and interpretation, as well as possible remediation or alleviation, are discussed.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Odey, J. U., A. C. Ugwu et B. N. Ekwueme. « Petrography, geochemistry and industrial quality of the Etono limestone in Ugep Southwest, Southeastern Nigeria ». Global Journal of Geological Sciences 19, n^o 1 (29 septembre 2021) : 145–53. http://dx.doi.org/10.4314/gjgs.v19i1.12.

Texte intégral

Résumé :

Petrographic and geochemical analyses were carried out on limestones occurring in Etono, Southwest Ugep, Southeastern Nigeria to determine their chemical composition, industrial uses and classification. Samples of limestone in the area were subjected to petrographic study and analyzed geochemically using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and X-Ray Fluorescence (XRF) techniques. The petrographic analysis reveals that the Etono limestone contains high percentage of carbonate materials with scanty organic remains and patches of iron. The bulk- rock composition of the limestone shows that the average SiO2 = 9.02%, Al2O3 = 1.95%, Fe2O3 = 2.08%, MgO = 0.39%, K2O = 0.47%, Na2O = 0.00%, CaO = 47.92%, SO2 = 0.24% and LOl = 37.37%. The limestone is classified based on their moderately high CaO, SiO2 and LOl and very low MgO. The mean CaO (47.92%) of Etono Limestone is high relative to the mean CaO of Agoi Ibami Limestone (43.83%) but low relative to the Mfamosing Limestone (55.30%) and the mean SiO2 values of 9.02% is high relative to Mfamosing Limestone (0.38%) but low relative to Agoi Ibami Limestone (13.93%). Results of the geochemical investigation reveal a shallow marine environment of deposition (EOD) for Etono Limestone. The higher values of CaO and LOl and lower values of SiO2 of the limestone suggest that it can be used for cement production, building stone, filler and agricultural purposes.

Styles APA, Harvard, Vancouver, ISO, etc.

16

SWINDLE, T. D., D. A. KRING, M. K. BURKLAND, D. H. HILL et W. V. BOYNTON. « Noble gases, bulk chemistry, and petrography of olivine-rich achondrites Eagles Nest and Lewis Cliff 88763 : Comparison to brachinites ». Meteoritics & ; Planetary Science 33, n^o 1 (janvier 1998) : 31–48. http://dx.doi.org/10.1111/j.1945-5100.1998.tb01605.x.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

17

KROT, A. N., A. J. BREARLEY, A. A. ULYANOV, V. V. BIRYUKOV, T. D. SWINDLE, K. KEIL, D. W. MITTLEFEHLDT, E. R. D. SCOTT, R. N. CLAYTON et T. K. MAYEDA. « Mineralogy, petrography, bulk chemical, iodine-xenon, and oxygen-isotopic compositions of dark inclusions in the reduced CV3 chondrite Efremovka ». Meteoritics & ; Planetary Science 34, n^o 1 (janvier 1999) : 67–89. http://dx.doi.org/10.1111/j.1945-5100.1999.tb01733.x.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

18

Xia, Mei, Chao Sun, Xiaoyong Yang et Jian Chen. « Assessment of Gold-Bearing Quartz Vein as a Potential High-Purity Quartz Resource : Evidence from Mineralogy, Geochemistry, and Technological Purification ». Minerals 13, n^o 2 (13 février 2023) : 261. http://dx.doi.org/10.3390/min13020261.

Texte intégral

Résumé :

High-purity quartz (HPQ) is an important material widely used in many high-tech industries. It is a product processed from pure natural quartz raw materials, so selecting suitable quartz raw material is the key to successfully processing HPQ. Hydrothermal quartz vein is one of the most likely raw materials to be purified into HPQ because of its high SiO2 content. This study focuses on the evaluation of HPQ raw material potential of the two gold-bearing quartz vein tailing resources in Chibougamau (CBG) and Tianjingshan (TJS). Petrography and the contents of impurity elements in the two vein quartz samples before and after processing were studied by optical microscope, SEM, Raman spectrometry, XRD, LA-ICP-MS, and bulk solution ICP-OES. Petrographic results reveal that major impurities in quartz are feldspar, mica, iron compounds, ankerite, rutile, silicate melt, and fluid inclusions. LA-ICP-MS analysis result shows that the SiO2 contents are between 99.953–99.971 wt.% in CBG raw quartz and 99.969–99.976 wt.% in TJS raw quartz, respectively, with very low contents of impurity elements, except for Ca. Bulk solution ICP-OES analysis demonstrates that the CBG processed quartz sand has total impurity contents of 56.8 µg·g−1, with 13.1 µg·g−1 Al and 6.6 µg·g−1 Ti, and the TJS processed quartz sand has the total impurity contents of 85.2 µg·g−1 with 29.4 µg·g−1 Al and 6.1 µg·g−1 Ti. Both the contents of Al and Ti fit with the lattice-bound criteria for HPQ. These results, for most of the impurities, are likely hosted by silicate melt, fluid, and mineral inclusions, indicating that these two hydrothermal raw vein quartz samples can be upgraded to HPQ after processing by more advanced methods. Therefore, the CBG and TJS quartz vein deposits would be considered as potential future resources for HPQ to realize efficient recovery and utilization of tailings resources and to improve mine economic benefits.

Styles APA, Harvard, Vancouver, ISO, etc.

19

Potere, Davide, Vittorio Scisciani, Monica Piochi, Pietro Paolo Pierantoni, Angela Mormone, Manuela Nazzari, Piergiorgio Scarlato et Gianluca Iezzi. « The Volcanic-Rich Layer of the “Camporotondo (Marche, Italy)” Section : Petrography and Sedimentation of an Unknown Distal Messinian Eruption ». Minerals 12, n^o 7 (16 juillet 2022) : 893. http://dx.doi.org/10.3390/min12070893.

Texte intégral

Résumé :

A Messinian and lithified horizon enriched in volcanic particles with thicknesses of 170–180 cm crops in the Camporotondo (CR) section (Marche, Italy). This volcanic-rich layer (VRL) was investigated by field plus mesoscopic observations, X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), bulk composition methods and electron-microprobe analysis (EMPA). The quantitative textural features of volcanic and sedimentary components were determined by 2D image analysis. The lowermost massive 70–80 cm portion is free of sedimentary structure or characterised only by plane-parallel ones, whereas the uppermost one is undulated and cross-laminated. The XRPD and SEM outcomes unveil that the VRL of CR is mainly composed of glassy shards (≥80 area%), a variable amount of sedimentary minerals (<20 area%) and a very low content of magmatic minerals (few area%). The bulk and micro-chemical attributes of volcanic and glassy materials are rhyolitic and almost identical to previous VRLs dated at 5.5 Ma (VRL-5.5). The signatures of immobile elements and the high amount of H2O present in the glass fraction suggest a provenance from a convergent geodynamic setting. The 2D image analysis on SEM observations show that the VRL-5.5 of CR is composed of very fine and sorted (averages of MZ of 5,72 and σi of 0,70), scarcely vesicular, glass shards, with similar long and short size dimensions, shape and roundness. The VRL-5.5 of CR is free of large minerals and fossils. The coupling of mesoscopic and microscopic determinations indicates that the lowermost interval was deposited such as a primary tephra, i.e., fallout pyroclasts sinking in seawater. Instead, the uppermost interval derives from local, low-energy and sin-depositional remobilisation of the same VRL-5.5. The textural attributes of the volcanic fractions, the sedimentological features and the thickness of the VRL at CR correspond to the westward deposit of a still unknown eruption likely occurred at 5.5 Ma.

Styles APA, Harvard, Vancouver, ISO, etc.

20

Issachar, Ran, Ram Weinberger, Tsafrir Levi, Jessica Barabasch et Janos L. Urai. « Magnetic Fabrics and Petrography of Rocksalts Reveal Preferred Orientation of Anhydrites within a Halite Matrix ». Minerals 12, n^o 2 (31 janvier 2022) : 192. http://dx.doi.org/10.3390/min12020192.

Texte intégral

Résumé :

We investigate the magnetic fabrics and microstructures of diamagnetic rocksalt samples from the Sedom salt wall (diapir), Dead Sea Basin, as possible strain markers. A comprehensive study of anisotropy of magnetic susceptibility (AMS), combined with magnetic, microtextural, geochemical and mineralogical analyses allows us to depict the deformation mechanisms and to reveal the mineral sources of the AMS. The rocksalts are composed of halite as the major mineral phase (>80%) and anhydrite as a minor phase (5–20%), and have an average magnetic susceptibility value of −13.4 ± 0.7 × 10−6 SI. Ferromagnetic and paramagnetic minerals make a negligible contribution to the bulk magnetic properties of the samples. The AMS indicates and reveals significant anisotropy with the maximum susceptibility axis (K1) subparallel to the bedding strike, although the cubic halite crystals are isotropic. Polarizing microscope and SEM images show preferred alignment of needle-like anhydrite crystals parallel to the direction of the K1 axis. Petrographic investigation of gamma irradiated thin sections reveals the deformation recorded in the microstructures of the rocksalts and points to a dominant contribution by dislocation creep, although both dislocation creep and pressure solution were active deformation mechanisms. We infer that during dislocation creep, the thin bands of anhydrite crystals deform along with the surrounding halite grains. We suggest that although the shape preferred orientation of halite grains is not indicative of finite strain because of resetting by grain boundary migration, the preferred orientation of the anhydrite crystals may be. These results suggest that the AMS of the rocksalts provides a textural proxy that reflects deformation processes of the rocksalts, despite their very low magnetic susceptibility.

Styles APA, Harvard, Vancouver, ISO, etc.

21

Gray, Connor, et Adrian Van Rythoven. « A Comparative Study of Porphyry-Type Copper Deposit Mineralogies by Portable X-ray Fluorescence and Optical Petrography ». Minerals 10, n^o 5 (11 mai 2020) : 431. http://dx.doi.org/10.3390/min10050431.

Texte intégral

Résumé :

Porphyry-type deposits are crucial reserves of Cu and Mo. They are associated with large haloes of hydrothermal alteration that host particular mineral assemblages. Portable X-ray fluorescence analysis (pXRF) is an increasingly common tool used by mineral prospectors to make judgments in the field during mapping or core logging. A total of 31 samples from 13 porphyry copper deposits of the Western Cordillera were examined. Whole-rock composition was estimated over three points of analysis by pXRF. This approach attempts to capture the rapid and sometimes haphazard application of pXRF in mineral exploration. Modes determined by optical petrography were converted into bulk rock compositions and compared with those determined by pXRF. The elements S, Si, Ca, and K all were underestimated by optical mineralogy, and the elements Cu, Mo, Al, Fe, Mg, and Ti were overestimated by optical mineralogy when compared with pXRF results. Most of these porphyry samples occur in veined porphyritic quartz monzonite that is characteristic of these deposits. Sulfide and silicate vein stockworks are pervasive in most of the samples as well as dissemination of sulfides outwards from veinlets. Ore minerals present include chalcopyrite and molybdenite with lesser bornite. Chalcocite, digenite, and covellite are secondary. Potential sources of analytical bias are discussed.

Styles APA, Harvard, Vancouver, ISO, etc.

22

Ashu, Richard. « A Petrographic Study of the Three Forks Formation (Upper Devonian), Williston Basin, North Dakota : Based on Thin Section Analysis, XRD and SEM ». Journal of Geological Research 2014 (17 avril 2014) : 1–9. http://dx.doi.org/10.1155/2014/264170.

Texte intégral

Résumé :

Deeply buried below 8,000 ft, the Three Forks Formation in North Dakota displays a variety of interesting diagenetic characteristics including dolomitization and hematite precipitation. Samples from three lithofacies are analyzed by thin section and SEM petrography and combined bulk and clay XRD analyses. Key aspects controlling the porosity and permeability of this formation are revealed by focusing on the detail mineralogy, rock type and diagenetic mineral distribution, and overall reservoir quality. Results prove that the Three Forks mineralogy is dominated by dolomite, along with substantial hematite, monocrystalline quartz, and mica flakes with trace feldspar, calcite, and pyrite. Clays mainly consist of illite together with minor chlorite and kaolinite and are associated with the scattered clasts. The reservoir quality is controlled by intercrystalline, rare microvuggy, and microporosity types that result from diagenetic and depositional events. Three stages of the dolomitization process are identified and discussed. Our hypothesis is that dolomitization commenced soon after deposition and was pervasive as no original carbonate texture is detectable.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Mukhametdinova, Aliya, Andrey Kazak, Tagir Karamov, Natalia Bogdanovich, Maksim Serkin, Sergey Melekhin et Alexey Cheremisin. « Reservoir Properties of Low-Permeable Carbonate Rocks : Experimental Features ». Energies 13, n^o 9 (3 mai 2020) : 2233. http://dx.doi.org/10.3390/en13092233.

Texte intégral

Résumé :

This paper presents an integrated petrophysical characterization of a representative set of complex carbonate reservoir rock samples with a porosity of less than 3% and permeability of less than 1 mD. Laboratory methods used in this study included both bulk measurements and multiscale void space characterization. Bulk techniques included gas volumetric nuclear magnetic resonance (NMR), liquid saturation (LS), porosity, pressure-pulse decay (PDP), and pseudo-steady-state permeability (PSS). Imaging consisted of thin-section petrography, computed X-ray macro- and microtomography, and scanning electron microscopy (SEM). Mercury injection capillary pressure (MICP) porosimetry was a proxy technique between bulk measurements and imaging. The target set of rock samples included whole cores, core plugs, mini cores, rock chips, and crushed rock. The research yielded several findings for the target rock samples. NMR was the most appropriate technique for total porosity determination. MICP porosity matched both NMR and imaging results and highlighted the different effects of solvent extraction on throat size distribution. PDP core-plug gas permeability measurements were consistent but overestimated in comparison to PSS results, with the difference reaching two orders of magnitude. SEM proved to be the only feasible method for void-scale imaging with a spatial resolution up to 5 nm. The results confirmed the presence of natural voids of two major types. The first type was organic matter (OM)-hosted pores, with dimensions of less than 500 nm. The second type was sporadic voids in the mineral matrix (biogenic clasts), rarely larger than 250 nm. Comparisons between whole-core and core-plug reservoir properties showed substantial differences in both porosity (by a factor of 2) and permeability (up to 4 orders of magnitude) caused by spatial heterogeneity and scaling.

Styles APA, Harvard, Vancouver, ISO, etc.

24

Guice, George L., Michael R. Ackerson, Robert M. Holder, Freya R. George, Joseph F. Browning-Hanson, Jerry L. Burgess, Dionysis I. Foustoukos, Naomi A. Becker, Wendy R. Nelson et Daniel R. Viete. « Suprasubduction zone ophiolite fragments in the central Appalachian orogen : Evidence for mantle and Moho in the Baltimore Mafic Complex (Maryland, USA) ». Geosphere 17, n^o 2 (5 février 2021) : 561–81. http://dx.doi.org/10.1130/ges02289.1.

Texte intégral

Résumé :

Abstract Suprasubduction zone (SSZ) ophiolites of the northern Appalachians (eastern North America) have provided key constraints on the fundamental tectonic processes responsible for the evolution of the Appalachian orogen. The central and southern Appalachians, which extend from southern New York to Alabama (USA), also contain numerous ultramafic-mafic bodies that have been interpreted as ophiolite fragments; however, this interpretation is a matter of debate, with the origin(s) of such occurrences also attributed to layered intrusions. These disparate proposed origins, alongside the range of possible magmatic affinities, have varied potential implications for the magmatic and tectonic evolution of the central and southern Appalachian orogen and its relationship with the northern Appalachian orogen. We present the results of field observations, petrography, bulk-rock geochemistry, and spinel mineral chemistry for ultramafic portions of the Baltimore Mafic Complex, which refers to a series of ultramafic-mafic bodies that are discontinuously exposed in Maryland and southern Pennsylvania (USA). Our data indicate that the Baltimore Mafic Complex comprises SSZ ophiolite fragments. The Soldiers Delight Ultramafite displays geochemical characteristics—including highly depleted bulk-rock trace element patterns and high Cr# of spinel—characteristic of subduction-related mantle peridotites and serpentinites. The Hollofield Ultramafite likely represents the “layered ultramafics” that form the Moho. Interpretation of the Baltimore Mafic Complex as an Iapetus Ocean–derived SSZ ophiolite in the central Appalachian orogen raises the possibility that a broadly coeval suite of ophiolites is preserved along thousands of kilometers of orogenic strike.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Sugimoto, Takeshi, Hidemi Ishibashi, Sadatsugu Wakamatsu et Takeru Yanagi. « Petrologic evolution of Pre-Unzen and Unzen magma chambers beneath the Shimabara Peninsula, Kyushu, Japan : Evidence from petrography and bulk rock chemistry ». GEOCHEMICAL JOURNAL 39, n^o 3 (2005) : 241–56. http://dx.doi.org/10.2343/geochemj.39.241.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

26

Patrick, Mackenzie, et Aphrodite Indares. « Petrography and phase equilibria modeling of mid-pressure aluminous gneisses derived from hydrothermally altered protoliths, Grenville Province, Canada ». Canadian Journal of Earth Sciences 54, n^o 11 (novembre 2017) : 1103–18. http://dx.doi.org/10.1139/cjes-2016-0162.

Texte intégral

Résumé :

A large portion of the hinterland of the central Grenville Province is characterized by mid-pressure granulite-facies metamorphic rocks. In the Manicouagan – Lac du Milieu region of Quebec, aluminous gneisses derived from hydrothermally altered felsic protoliths provide a record of anatectic processes and of the pressure–temperature (P–T) evolution during orogenesis. Samples collected in areas separated by several tens of kilometres consist of garnet + biotite + quartz + K-feldspar ± plagioclase ± sillimanite, with retrograde cordierite in some, and most display microstructural evidence of partial melting. However, they have a wide range of bulk compositions and textures, and may be grouped into two types: sillimanite-rich rocks, with a high alumina index and sillimanite-poor rocks with low alumina index and in which sillimanite is not part of the peak assemblage. Phase equilibria modeling with THERMOCALC software constrained the P–T field of the peak mineral assemblage(s) at 800–900 °C and 6–11 kbar (1 kbar = 100 MPa), with melt solidification in the range of 800–865 °C and 6–8 kbar. The presence of sillimanite inclusions in garnet, and the scarcity of retrograde cordierite are consistent with moderate dP/dT gradient “hairpin” P–T paths. The data suggest that this part of the mid-P hinterland in the central Grenville experienced a rather uniform high-temperature metamorphic evolution, with large temperature variations relative to pressure. This is consistent with the thermal evolution of middle crust beneath an orogenic plateau.

Styles APA, Harvard, Vancouver, ISO, etc.

27

Weller, Derek J., María Eugenia De Porras, Antonio Maldonado, César Méndez et Charles R. Stern. « Holocene tephrochronology of the lower Río Cisnes valley, southern Chile ». Andean Geology 44, n^o 3 (29 septembre 2017) : 229. http://dx.doi.org/10.5027/andgeov44n3-a01.

Texte intégral

Résumé :

Sediment cores from lakes and bogs in the Río Cisnes valley contain tephra from explosive eruptions of volcanoes in the southern part of the Andean Southern Volcanic Zone (SSVZ). These tephra, which thicken and coarsen to the west, are attributed to eruptions from Melimoyu, Mentolat, Hudson, and potentially either Macá, Cay or one of the many minor eruptive centers (MEC) located both along the Liquiñe-Ofqui Fault Zone (LOFZ) and surrounding the major volcanoes. Correlation of the tephra between two new cores in the lower Río Cisnes valley, and amongst other cores previously described from the region, and source volcano identification for the tephra, has been done using lithostratigraphic data (tephra layer thickness and grain size), petrography (tephra glass color, vesicle morphology, and type and abundance of phenocryst phases), and by comparison of bulk tephra trace-element characteristics with previously published whole-rock and bulk tephra chemical analysis. Four tephras in these cores are attributed to eruptions of Mentolat, four to eruptions from Melimoyu, one possibly to Hudson, and six cannot be assigned to a specific source volcano. Some of these tephra correspond to pyroclastic tephra fall deposits previously observed in outcrop, including the MEL2 eruption of Melimoyu and the MEN1 eruption of Mentolat. However, others have not been previously observed and represent the products of newly identified small to medium sized eruptions from volcanoes of the SSVZ. These results provide new information concerning the frequency and magnitude of explosive eruption of SSVZ volcanoes and contribute to the evaluation of volcanic hazards in the region.

Styles APA, Harvard, Vancouver, ISO, etc.

28

Jeong, Gi Young, Stephen Hillier et Rob A. Kemp. « Changes in mineralogy of loess–paleosol sections across the Chinese Loess Plateau ». Quaternary Research 75, n^o 1 (janvier 2011) : 245–55. http://dx.doi.org/10.1016/j.yqres.2010.09.001.

Texte intégral

Résumé :

AbstractQuantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the Chinese Loess Plateau (CLP). Mineralogy, geochemistry, and single-particle petrography of loess and paleosols are relatively uniform over the CLP. However, in detail, there are mineralogical changes related to eolian process and chemical weathering. Particle-size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals. After deposition, detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite, dolomite, biotite, illite, chlorite, amphibole, and plagioclase. The weathering of biotite, chlorite, and illite resulted in a significant increase of expandable phyllosilicate contents. The sequential weathering of the minerals is reflected chemically in the decrease of Na and Mg and the increase of iron oxidation. Mineralogy of the Chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient, and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the CLP.

Styles APA, Harvard, Vancouver, ISO, etc.

29

Ahmad, Sajjad, Bilal Wadood, Suleman Khan, Sohail Ahmed, Fahad Ali et Abdus Saboor. « Integrating the palynostratigraphy, petrography, X-ray diffraction and scanning electron microscopy data for evaluating hydrocarbon reservoir potential of Jurassic rocks in the Kala Chitta Range, Northwest Pakistan ». Journal of Petroleum Exploration and Production Technology 10, n^o 8 (18 juillet 2020) : 3111–23. http://dx.doi.org/10.1007/s13202-020-00957-7.

Texte intégral

Résumé :

Abstract In this paper, we present the palynostratigraphy, petrography, scanning electron microscopy (SEM) and X-ray diffraction (XRD) investigations to evaluate hydrocarbon reservoir potential of the Jurassic clastic-carbonate mixed sequence of the Kala Chitta Range, northwest Pakistan. The chronostratigraphic sub-divisions of the diverse lithologies within the sequence were made by using palynostratigraphy. The clastic dominated sequence of Datta Formation was assigned Toarcian-Bajocian age, while the Shinawari Formation was deposited during the Bajocian-middle Bathonian. The carbonate shoal facies of the Samana Suk Formation showed late Bathonian-Tithonian time of deposition. The primary and secondary porosities augmented by the plug porosity and permeability data suggest that the sandstone of Datta Formation is an excellent reservoir. The dominance of diverse matrix within the Shinawari Formation occluded the primary porosity. However, based on dissolution and dolomitization, the Shinawari Formation is categorized as a moderate reservoir. The dominance of various types of matrix and cement with superimposed burial diagenesis has occluded the primary porosity within the Samana Suk Formation. However, the diagenetic dissolution and dolomitization during the telogenetic stage were supported by the SEM and bulk geochemical data. Such diagenetic overprinting has significantly enhanced the reservoir potential of the unit.

Styles APA, Harvard, Vancouver, ISO, etc.

30

Konstantopoulos, Panagiotis A., et Avraam Zelilidis. « Provenance analysis of Eocene–Oligocene turbidite deposits in Pindos Foreland Basin, fold and thrust belt of SW Greece : constraints from framework petrography and bulk-rock geochemistry ». Arabian Journal of Geosciences 6, n^o 12 (17 novembre 2012) : 4671–700. http://dx.doi.org/10.1007/s12517-012-0766-4.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

31

Santi, Patrizia, Franco Foresta Martin, Francesca Spatafora, Sandro de Vita et Alberto Renzulli. « Volcanic Grinding Tools in Ustica Island (Tyrrhenian Sea, Italy) : Local Production vs. Import of Morgantina-Type Millstones in the Hellenistic-Roman Period ». Minerals 10, n^o 5 (26 avril 2020) : 389. http://dx.doi.org/10.3390/min10050389.

Texte intégral

Résumé :

This archaeometric study was focused on 28 grey to dark-grey lava artifacts found in Ustica Island (Southern Tyrrhenian Sea, Italy) and referable to different grinding tools: saddle querns, rotary Morgantina-type millstones, rotary hand-mills and one small mortar. Mineralogy, petrography and bulk rock geochemical analyses emphasized that most of the grinding artifacts belonged to the Na-Alkaline series of Ustica, mainly basalts, hawaiites and mugearites. Nevertheless, some millstone samples did not match major and trace elements of Ustica lavas, in particular, one high-TiO2 Na-Alkaline basalt from Pantelleria Island, some tholeiitic/transitional basalts from the Iblei Mountains and one Calcalkaline basaltic andesite, most likely from the Aeolian Archipelago. The Hellenistic–Roman re-colonisation of Ustica Island, after ca. one millennium of nearly complete abandonment, was testified by the import of the non-local Morgantina-type rotary millstones, very widespread in the Mediterranean area from 4th–3rd century BC. This import of millstones represented, for the Ustica inhabitants, a real breakthrough for developing a local production of grinding artifacts on the basis of the new rotary technique which was much more efficient than that of the archaic saddle querns, largely used in the Middle Bronze Age. The results are also discussed in the framework of the overall volcanic millstone trade in the Mediterranean area and the different milling technology in antiquity.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Gilstrap, William D., Jennifer L. Meanwell, Elizabeth H. Paris, Roberto López Bravo et Peter M. Day. « Post-Depositional Alteration of Calcium Carbonate Phases in Archaeological Ceramics : Depletion and Redistribution Effects ». Minerals 11, n^o 7 (9 juillet 2021) : 749. http://dx.doi.org/10.3390/min11070749.

Texte intégral

Résumé :

The final stage in the life history of prehistoric pottery prior to archaeological recovery is usually the longest, and frequently the most dynamic. The remains of archaeological ceramics spend hundreds to thousands of years deposited within the upper layers of the earth’s crust where they encounter the same diagenetic environmental processes as the surrounding natural materials. Harsh conditions of subterranean environments induce physical stresses and chemical reactions, causing alterations of ceramic structure and composition. This is especially true of carbonate-rich ceramics, as carbonate phases are soluble when deposited within acidic environments. This paper examines common carbonate depletion and accretion effects of post-depositional environments on ancient ceramics from two rather different geological and archaeological contexts: Mesoamerica and the Mediterranean. Potters in both regions produce vessels with carbonate-rich materials—clays, calcite, limestone—that alter due to long exposure to low-pH sediments and continual water table fluctuations. Ceramic petrography is employed to identify traces of carbonate alterations within ceramic microstructure and to characterize fabrics. Elemental compositions of the same sherds are characterized through either scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS), inductively coupled plasma mass spectrometry and optical emission spectrometry (ICP-MS/OES) or neutron activation analysis (NAA). This method enabled comparison of the differing effects of post-depositional alteration of carbonate phases on bulk composition signatures commonly used to determine provenance.

Styles APA, Harvard, Vancouver, ISO, etc.

33

Newton, David E., Maya G. Kopylova, Jennifer Burgess et Pamela Strand. « Peridotite and pyroxenite xenoliths from the Muskox kimberlite, northern Slave craton, Canada ». Canadian Journal of Earth Sciences 53, n^o 1 (janvier 2016) : 41–58. http://dx.doi.org/10.1139/cjes-2015-0083.

Texte intégral

Résumé :

We present petrography, mineralogy, and thermobarometry for 53 mantle-derived xenoliths from the Muskox kimberlite pipe in the northern Slave craton. The xenolith suite includes 23% coarse peridotite, 9% porphyroclastic peridotite, 60% websterite, and 8% orthopyroxenite. Samples primarily comprise forsteritic olivine (Fo 89–94), enstatite (En 89–94), Cr-diopside, Cr-pyrope garnet, and chromite spinel. Coarse peridotites, porphyroclastic peridotites, and pyroxenites equilibrated at 650–1220 °C and 23–63 kbar (1 kbar = 100 MPa), 1200–1350 °C and 57–70 kbar, and 1030–1230 °C and 50–63 kbar, respectively. The Muskox xenoliths differ from xenoliths in the neighboring and contemporaneous Jericho kimberlite by their higher levels of depletion, the presence of a shallow zone of metasomatism in the spinel peridotite field, a higher proportion of pyroxenites at the base of the mantle column, higher Cr2O3 in all pyroxenite minerals, and weaker deformation in the Muskox mantle. We interpret these contrasts as representing small-scale heterogeneities in the bulk composition of the mantle, as well as the local effects of interaction between metasomatizing fluid and mantle wall rocks. We suggest that asthenosphere-derived pre-kimberlitic melts and fluids percolated less effectively through the less permeable Muskox mantle, resulting in lower degrees of hydrous weakening, strain, and fertilization of the peridotitic mantle. Fluids tended to concentrate and pool in the deep mantle, causing partial melting and formation of abundant pyroxenites.

Styles APA, Harvard, Vancouver, ISO, etc.

34

Glaas, Carole, Patricia Patrier, Jeanne Vidal, Daniel Beaufort et Albert Genter. « Clay Mineralogy : A Signature of Granitic Geothermal Reservoirs of the Central Upper Rhine Graben ». Minerals 11, n^o 5 (30 avril 2021) : 479. http://dx.doi.org/10.3390/min11050479.

Texte intégral

Résumé :

Clay minerals are the signature of hydrothermal alterations related to fluid circulation in volcanic and crystalline rocks. In the French part of the Upper Rhine Graben, in the deep-seated granites, illitic minerals (illite and I/S mixed layers (ml)) are typical products of the structurally-controlled argillic alteration in the Paleozoic granitic basement. In the new Illkirch geothermal well, GIL-1, drill-cuttings were studied with various petrographic methods to determine the characteristics of illite in paleo- and present-permeable zones, and to compare the alteration mineralogy with that of geothermal Soultz-sous-Forêts and Rittershoffen sites. Alteration petrography, crystal structure as well as the chemical composition of the illitic minerals and the altered bulk rocks were performed all along the well. This complete characterization, combined with geophysical logs and structural results, highlighted that the illitic minerals at Illkirch, Soultz-sous-Forêts, and Rittershoffen are composed of illite and illite-rich illite-smectite mixed layers (I/S ml) (<10% smectite). Two mineralogical assemblages were distinguished: chlorite + illite resulting from the propylitic alteration after the emplacement of the granitic basement under temperatures higher than 350 °C, and illite + I/S ml + carbonates + quartz resulting from the argillic alteration due to fluid circulation in the fractures at temperatures between 130 and 160 °C. Fracture zones are characterized by the occurrence of illitic minerals (illite and I/S ml), and specifically, by higher quantities of I/S ml in present-day permeable zones than in paleo-permeable zones. A conceptual model of the fracture zones at the interface between the overlying sedimentary rocks and the granitic basement is proposed. The present-day permeability distribution is controlled by the fault and fracture network, which consists of sealed zones and unsealed zones. Fluid convection in the URG implies paleo and present fluids circulating in both fractured sedimentary and crystalline reservoirs. Such circulations develop illitic minerals that could be considered as exploration guides for future geothermal sites in the URG. At Illkirch, the repartition of the present-permeable fracture zones (KFZs) in the GIL-1 well indicates that the moderately argillically altered granite distally situated from the Eschau fault is more permeable than the intensely argillically altered granite close to the Eschau fault.

Styles APA, Harvard, Vancouver, ISO, etc.

35

Jodry, Florent, Marion Delloul, Christophe Croutsch, Philippe Duringer et Gilles Fronteau. « Rock procurement and use during the Middle Neolithic : The macrolithic tools of Dambach-la-Ville (Alsace, France) ». Journal of Lithic Studies 7, n^o 3 (15 décembre 2020) : 1–13. http://dx.doi.org/10.2218/jls.3090.

Texte intégral

Résumé :

A preventive archaeological excavation carried out in 2012 at Dambach-la-Ville (Bas-Rhin, France) uncovered a large Middle Neolithic settlement (Upper Rhine West Bischheim group) dating from the second half of the 5th millennium BCE. The site comprised a very large assemblage of well-dated macrolithic tools (more than 600). Grinding stones, including about roughouts, make up the bulk of the assemblage. Morphological analyses indicate that certain types of use-wear are linked directly to specific types of rock. The variety of rock types is unusual for this period. In fact, contrary to other assemblages from the same period mainly made up of Lower Triassic sandstone (Vosges sandstone; 43%), the tools fashioned on this settlement are mostly made from sedimentary rocks of the Permian and Lower Triassic (possible sources at 15 km), and more rarely from plutonic and metamorphic rocks (possible sources between 5 and 15 km). The use of rough textured rocks such as arkosic sandstone or microconglomerate largely dominating the assemblage. This one also includes a large group of hammerstones from different rock types (sedimentary, plutonic, volcanic and metamorphic). More than half are silicified micritic limestones, a rock that is extremely rare and can be unambiguously traced to a single outcrop about 15 kilometres from the site. This systematic interdisciplinary study of the tools and their petrography offers the opportunity to explore questions regarding provenance and procurement networks in Alsace around 4150 BCE.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Lasheen, El Saeed R., Gehad M. Saleh, Farrage M. Khaleal et Mamdooh Alwetaishi. « Petrogenesis of Neoproterozoic Ultramafic Rocks, Wadi Ibib–Wadi Shani, South Eastern Desert, Egypt : Constraints from Whole Rock and Mineral Chemistry ». Applied Sciences 11, n^o 22 (9 novembre 2021) : 10524. http://dx.doi.org/10.3390/app112210524.

Texte intégral

Résumé :

This contribution deals with new geology, petrography, and bulk-rock/mineral chemistry of the poorly studied ultramafics of Wadi Ibib–Wadi Shani (WI–WS) district, South Eastern Desert, Egypt. These ultramafics are dismembered ophiolitic rocks that can be subdivided into serpentinites and serpentinized peridotites. Primary minerals such as olivine and pyroxene are absent in serpentinites, but relics of them occur in serpentinized peridotites. Pseudomorph after olivine is indicated by common hourglass textures with less mesh, whilst schistose bastites reflect a pyroxene pseudomorph. Chromite can be subdivided into Cr-spinel and Al-spinel. Cr-spinel ranges from chromite to magnesochromite in composition, whereas Al-spinel belongs to the spinel field. Cr-spinel includes YCr (Cr/(Cr+Al+Fe+3), YAl (Al/(Al+Cr+Fe+3), and YFe+3 (Fe+3/(Fe+3+Al+Cr), similar to forearc peridotite, whilst Al-spinel is more similar to abyssal peridotite, and may be formed during inanition of subduction processes in proto forearc environments. The main secondary minerals are tremolite, talc, and chlorite—which is subdivided into pycnochlorite and diabantite—and their temperature ranges from 174 to 224 °C. The examined rocks had undergone high partial melting degrees (>25%), as indicated by the Cr# of their unaltered cores (Cr-spinel, >0.6), whole rocks (Al2O3, SiO2, CaO, and MgO), trace and REEs, depleted Na2O, Al2O3, and Cr2O3 of clinopyroxene, and high forsterite content ((Fo = 100 Mg/Mg + Fe), av. 95.23 mol%), consistent with forearc settings.

Styles APA, Harvard, Vancouver, ISO, etc.

37

Bateman, Richard M., et Andrew C. Scott. « A reappraisal of the Dinantian floras at Oxroad Bay, East Lothian, Scotland. 2. Volcanicity, palaeoenvironments and palaeoecology ». Transactions of the Royal Society of Edinburgh : Earth Sciences 81, n^o 3 (1990) : 161–94. http://dx.doi.org/10.1017/s0263593300005228.

Texte intégral

Résumé :

ABSTRACTThe classic late Tournaisian plant-bearing locality at Oxroad Bay was investigated by detailed field mapping, lithological logging, studies of clast orientation, thin-section petrography and analyses of bulk geochemistry. The lithologically and structurally complex,c. 45 m-thick succession includes eight plant-bearing exposures (each consisting of up to 16 phytofossiliferous horizons) that have yielded 43 anatomically-preserved organ-species and 19 adpressed organ-species. All floral assemblages are allochthonouss.l.and demonstrate a wide range of preservation states. They occur in five successive facies (braided flood-plain, shallow volcanigenic lacustrine, terrestrial mass-flow/base-surge, shallow biogenic lacustrine, dominantly terrestrial reworked ashes) that reflect increasing influence of several basaltic tuff-ring volcanoes on an ocean-marginal lowland bordering the Southern Uplands Massif. The variable local climate reflected proximity to the proto-North Sea and eruptive seeding of the atmosphere with ash particles. Base-surges, seismically-initiated mass-flows and volcanically-induced wildfires restricted the development of mature soils and of edaphic climax communities. These disturbances created a sequence of mosaic palaeocatenas that supported a wide range of sub-communities at any one moment in time. At least some of the relativelyk-selected species that occupied the preceding, fluvially-dominated terrain were extirpated by the persistent volcanism, yielding to immigrants that were better pre-adapted to the unstable environment. Low levels of competition allowed non-adaptiven-selection, enhancing the establishment potential of evolutionary innovations.

Styles APA, Harvard, Vancouver, ISO, etc.

38

Slovenec, Damir, et Branimir Šegvić. « Middle Triassic high-K calc-alkaline effusive and pyroclastic rocks from the Zagorje-Mid-Transdanubian Zone (Mt. Kuna Gora ; NW Croatia) : mineralogy, petrology, geochemistry and tectonomagmatic affinity ». Geologica Acta 19 (4 mars 2021) : 1–23. http://dx.doi.org/10.1344/geologicaacta2021.19.2.

Texte intégral

Résumé :

This study uses mineralogical, petrological, geochemical, and Sr and Nd isotope data along with K-Ar ages to infer the petrogenesis and geodynamic evolution of Middle Triassic high-K calc-alkaline lavas and their associated pyroclastics of Mt. Kuna Gora in NW Croatia. Their analogue mineralogy and bulk-rock geochemistry testify to the coeval origin of both rock types. Sanidine and plagioclase accompanied by inor augite and Ti-bearing magnetite are the major phases found in a matrix of devitrified volcanic glass and plagioclase microlites. Hydrothermal anddiagenetic processes in the pyroclastics originated the formation of chlorite and white mica, and mixed-layer clay minerals, respectively. Petrography reveals the following crystallization order: spinel→clinopyroxene→plagioclase→alkali-feldspar±Fe-Ti oxides. Geochemical and isotopic data suggests that the studied rocks had a complex origin that included the contamination of subduction-generated magmas by lithospheric mantle melts. This presumes an interplay between fertile arc mantle, subducted continental crust, and depleted or ocean island basalts-like mantle. A low degree of crustal contamination stands as a last step in the formation of such “hybrid” magmas. The subducted Paleotethyan oceanic lithosphere went through processes of partial melting at depths of ~45-49km and pressures of ≤1.6GPa and fractionation that produced melts which gave rise to the studied rocks. In the model we are proposing herein such formed partial melts are related to the demise of the northward subduction of the Paleotethys oceanic lithosphere during the Early to Middle Triassic epoch, which is consistent with an active, ensialic mature volcanic arc developing along Laurussian southern active margins.

Styles APA, Harvard, Vancouver, ISO, etc.

39

COLOMBIÉ, CLAUDE, CHRISTOPHE LÉCUYER et ANDRÉ STRASSER. « Carbon- and oxygen-isotope records of palaeoenvironmental and carbonate production changes in shallow-marine carbonates (Kimmeridgian, Swiss Jura) ». Geological Magazine 148, n^o 1 (2 juillet 2010) : 133–53. http://dx.doi.org/10.1017/s0016756810000518.

Texte intégral

Résumé :

AbstractCarbon- and oxygen-isotope ratios are commonly used to correlate shallow- and deep-marine successions. Carbon- and oxygen-isotope analyses were performed on bulk-carbonate samples from two Kimmeridgian sections of the Swiss Jura platform in order to correlate them with biostratigraphically well-dated coeval sections in the adjacent basin. On the platform, a general decrease in δ13C and δ18O values from the base to the top of the studied interval is measured, whereas time-equivalent pelagic–hemipelagic carbonates record an increase in carbon- and oxygen-isotope ratios. Moreover, the measured δ13C and δ18O values are generally lower than those indicated for the Kimmeridgian open ocean and show high-frequency variations superimposed on the general trend. Samples were screened for diagenetic alteration using optical and cathodoluminescence petrography and coupled carbon- and oxygen-isotope and trace-element analyses. Some observations favour a role for diagenetic alteration, but isotopic and elemental trends as well as sedimentological evidence suggest that the more negative values of δ13C and δ18O relative to Kimmeridgian seawater are also due to local environmental conditions. High-frequency changes in δ18O and δ13C values most likely result from variations in salinity and carbonate production and accumulation rates. These variations were produced by different water masses that were isolated from the open ocean and developed their own geochemical signatures. Repeated isolation was induced by high-frequency sea-level fluctuations and helped by irregular platform morphology. Consequently, carbon- and oxygen-isotope records in shallow-marine carbonates can be used for stratigraphic correlation only if their origin is well known.

Styles APA, Harvard, Vancouver, ISO, etc.

40

Antonini, P., P. Comin-chiaramonti, C. B. Gomes, P. Censi, B. F. Riffel et E. Yamamoto. « The Early Proterozoic carbonatite complex of Angico dos Dias, Bahia State, Brazil : geochemical and Sr-Nd isotopic evidence for an enriched mantle origin ». Mineralogical Magazine 67, n^o 5 (octobre 2003) : 1039–57. http://dx.doi.org/10.1180/0026461036750142.

Texte intégral

Résumé :

AbstractBorehole samples of carbonatites and phlogopite-pyroxenites from the Angico dos Dias (AdD) intrusive alkaline complex, State of Bahia, Brazil, have been investigated in terms of mineralogy, geochemistry and C-O-Sr-Nd isotopes. The AdD complex, of Early Proterozoic age (2 Ga), intrudes the northern side of the São Francisco Craton. Mineralogy and petrography indicate that the studied rocks only partially preserved their magmatic textural features owing to their metamorphic re-equilibration (greenschist facies). The REE contents and LREE/HREE ratios of the AdD carbonatites are very high (mean 3979±718 ppm and La/Yb = 215±23, respectively), as for most Precambrian magmatic carbonatites. The AdD carbonatites are also enriched in 18O (δ18O = 11.9 to 15.8‰), possibly due to secondary processes (e.g. metamorphism, alteration) whereas carbon isotopes are in the range of ‘primary carbonatites’ (δ13C = –5.7 to –7.1‰). Most of the initial 87Sr/86Sr and 143Nd/144Nd values of the studied carbonatites were not appreciably modified by secondary processes. Their εtSr and εtNd values (20.0 to 25 and 0.7 to –4.5, respectively) indicate enriched mantle sources very different from the ‘depleted’ ones related to many Precambrian carbonatites from North America (0.6 –2.6 Ga) and Africa (0.5 –2.0 Ga). The Early Proterozoic Sr-Nd isotopic signatures of the AdD carbonatites are similar to those of the Early Cretaceous carbonatites from the Paraná basin. The latter carbonatites show a great isotopic variability ranging from Bulk Earth to the related potassic magmatism from Asunción-Sapucai graben in the Eastern Paraguay (K-ASU magmatism: εtSr = 35 to 50 and εtNd = –12 to –20). The very similar isotopic compositions of Precambrian and post-Palaeozoic carbonatites worldwide indicate that the subcontinental mantle variability lasted for long periods of time and indicate a large-scale mantle heterogeneity.

Styles APA, Harvard, Vancouver, ISO, etc.

41

Proctor, Jacob M., André W. Droxler, Naum Derzhi, Heath H. Hopson, Paul (Mitch) Harris, Pankaj Khanna et Daniel J. Lehrmann. « Upscaling lithology and porosity-type fractions from the micro- to the core-scale with thin-section petrography, dual-energy computed tomography, and rock typing : Creation of diagenesis and porosity-type logs ». Interpretation 7, n^o 1 (1 février 2019) : B9—B32. http://dx.doi.org/10.1190/int-2017-0187.1.

Texte intégral

Résumé :

We have developed and validated a new approach to upscale lithology and porosity-type fractions from thin sections to cores using dual energy and multiscale computed tomography (CT). A new rock-typing approach (genetic rock typing [GRT]) is proposed to upscale ⇋diagenetic mineral and diagenetic pore-type fractions, from thin sections to the core domain, eventually to create a diagenesis and porosity types logs. An extensive set of short cores from Mason County (Texas) provides a representative sample set of Late Cambrian microbial buildups and their interbuildup sediments to test the GRT approach. GRTs were defined by using a dolomite log as a proxy for diagenesis and the average percentage of dolomite from each observed depositional facies (buildup interior, buildup rind, and interbuildup sediment) as a cutoff. Dolomite, diagenetic calcite, and diagenetic porosity fractions are summed to form a diagenesis log, which captures depositional facies and the diagenetic overprint at a 0.5 mm resolution. The diagenesis log was subdivided based on the number of pore-throat size classes within each GRT and provided a framework to distribute porosity-type fractions from thin sections to log form. A high correlation coefficient is observed when the predicted extent of diagenetic alteration from the log is compared with that quantified for each thin section using image processing ([Formula: see text]). Multiscale CT imaging and dual-energy-derived logs could be directly linked to well-log photoelectric factor and bulk-density logs. This approach thus has the ability to span six orders of magnitude in resolution (500–0.0005 mm). The diagenesis log can be used to extrapolate porosity-type fractions from thin sections to logs, from which qualitative geologic interpretations can be generally translated into quantitative values.

Styles APA, Harvard, Vancouver, ISO, etc.

42

Iqbal, Shahid, Michael Wagreich, Mehwish Bibi, Irfan U. Jan et Susanne Gier. « Multi-Proxy Provenance Analyses of the Kingriali and Datta Formations (Triassic–Jurassic Transition) : Evidence for Westward Extension of the Neo-Tethys Passive Margin from the Salt Range (Pakistan) ». Minerals 11, n^o 6 (27 mai 2021) : 573. http://dx.doi.org/10.3390/min11060573.

Texte intégral

Résumé :

The Salt Range, in Pakistan, preserves an insightful sedimentary record of passive margin dynamics along the NW margin of the Indian Plate during the Mesozoic. This study develops provenance analyses of the Upper Triassic (Kingriali Formation) to Lower Jurassic (Datta Formation) siliciclastics from the Salt and Trans Indus ranges based on outcrop analysis, petrography, bulk sediment elemental geochemistry, and heavy-mineral data. The sandstones are texturally and compositionally mature quartz arenites and the conglomerates are quartz rich oligomictic conglomerates. Geochemical proxies support sediment derivation from acidic sources and deposition under a passive margin setting. The transparent heavy mineral suite consists of zircon, tourmaline, and rutile (ZTR) with minor staurolite in the Triassic strata that diminishes in the Jurassic strata. Together, these data indicate that the sediments were supplied by erosion of the older siliciclastics of the eastern Salt Range and adjoining areas of the Indian Plate. The proportion of recycled component exceeds the previous literature estimates for direct sediment derivation from the Indian Shield. A possible increase in detritus supply from the Salt Range itself indicates notably different conditions of sediment generation, during the Triassic–Jurassic transition. The present results suggest that, during the Triassic–Jurassic transition in the Salt Range, direct sediment supply from the Indian Shield was probably reduced and the Triassic and older siliciclastics were exhumed on an elevated passive margin and reworked by a locally established fluvio-deltaic system. The sediment transport had a north-northwestward trend parallel to the northwestern Tethyan margin of the Indian Plate and normal to its opening axis. During the Late Triassic, hot and arid hot-house palaeoclimate prevailed in the area that gave way to a hot and humid greenhouse palaeoclimate across the Triassic–Jurassic Boundary. Sedimentological similarity between the Salt Range succession and the Neo-Tethyan succession exposed to the east on the northern Indian passive Neo-Tethyan margin suggests a possible westward extension of this margin.

Styles APA, Harvard, Vancouver, ISO, etc.

43

Al Habsi, Naima, Mohammed Al Shukaili, Sabah Al Tooqi, Stephen N. Ehrenberg et Michaela Bernecker. « Lithofacies, diagenesis and reservoir quality of Upper Shu’aiba reservoirs in northwestern Oman ». GeoArabia 19, n^o 4 (1 octobre 2014) : 145–82. http://dx.doi.org/10.2113/geoarabia1904145.

Texte intégral

Résumé :

ABSTRACT Core and log data from Lower Cretaceous limestones of the Upper Shu’aiba Member were used to characterize the distribution of lithofacies, clay and porosity within two low-angle clinoforms that form the reservoirs for an oilfield of northwestern Oman. Data from 15 vertical wells, including four with core, and four horizontal well cores were projected into a dip-oriented cross-section derived from a static reservoir model as a basis for visualizing the above variations. Each clinoform consists of a basal “argillaceous zone” and a thicker “reservoir zone” of clean limestone, together reflecting fourth-order cycles of progradation along the margin of the Bab intra-shelf basin. Lithofacies vary in a proximal direction from mudstone and wackestone (mid-ramp) to mud-dominated packstone (slope) to mud-rich floatstone, rudstone and boundstone (ramp crest) and are arranged in a pattern of decreasing water depth and increasing energy both upwards and landward within each clinoform. In contrast, the reservoir zone of a younger clinoform from a nearby oilfield consists of well-sorted grainstone and grain-dominated packstone, illustrating the wide range of depositional conditions that occurred in the ramp-crest facies belt of different units. Except within the proximal extent of the younger clinoform, where values are transitional toward reservoir zone values, the argillaceous zones have total porosity mostly < 10% and baseline-normalized gamma-ray (GR) activity > 23 API units, reflecting clay contents of around 10–18%. In contrast, most parts of the reservoir zones have GR of 15–23 API units and porosity of 10–35%. Higher clay content is suggested to be linked with lower porosity through facilitation of both mechanical and chemical compaction, the latter providing a local supply of calcite cement. XRD analyses show that the clays are kaolin, illite/smectite and illite, similar to the clays in the overlying Nahr Umr shale. Most former macropores have been filled by blocky calcite cement in the main oilfield studied, but all lithofacies have similar wide ranges of total porosity of 8% to > 30%. The cores were also studied for evidence of diagenesis related to the contact with the overlying Nahr Umr Formation, but profiles of stable-isotope ratios, bulk-rock strontium, petrography and porosity-permeability data show no trends indicative of upward-increasing meteoric diagenesis below this sequence boundary. Meteoric leaching could nevertheless be pervasive throughout the Upper Shu’aiba reservoirs, at least partially accounting for extensive aragonite dissolution and low Sr and δ18O values. Two of the cores show trends of upwards-increasing bulk-rock uranium, manganese and iron, possibly indicative of sea-floor authigenesis. In addition, saddle dolomite near the tops of these cores may reflect late influx of magnesium derived from clay in the Nahr Umr Formation.

Styles APA, Harvard, Vancouver, ISO, etc.

44

Alzahrani, Abdullah M., El Saeed R. Lasheen et Mohammed A. Rashwan. « Relationship of Mineralogical Composition to Thermal Expansion, Spectral Reflectance, and Physico-Mechanical Aspects of Commercial Ornamental Granitic Rocks ». Materials 15, n^o 6 (10 mars 2022) : 2041. http://dx.doi.org/10.3390/ma15062041.

Texte intégral

Résumé :

The aim of the present study is to link the thermal expansion, spectral reflectance, and physico-mechanical aspects of different types of commercial granitic rocks with their mineralogical and chemical composition. The granitic rock types were characterized using several analyses, including petrography, chemical, mineralogical, and thermo-gravimetrical analysis using XRF, XRD, and TG/DTG/DSC techniques. The rock types were subjected to several performance tests, such as tests of their thermal expansion, spectral reflectance, and physico-mechanical properties. The results revealed that quartz, albite, and potash feldspar with minor amounts of mica (biotite/muscovite/annite) are the main mineralogical constitutes, in addition to some alteration minerals, such as kaolinite, saussorite, and prehnite. The studied granitic rocks were classified as monzogranite/syenogranite of high K-calc-alkaline and peraluminous characters and are related to late- to post-collisional settings. The thermogravimetrical analysis revealed that the overall mass loss over the whole temperature range up to 978 °C did not exceed 3% of the initial weight for all studied rocks. The results of thermal expansion revealed that the maximum change in linear thermal expansion for all rock types did not exceed 0.015% of their initial lengths at an unusual air temperature of 50 °C. The spectral analysis revealed that iron and hydroxyl ions are the main spectral absorption features that appeared in the VIS-NIR and SWIR regions, in addition to the appearance of the common and distinctive absorption peaks of the main mineral composition. Furthermore, the spectral reflectance demonstrated that the granitic rock types of low iron oxide content achieved a high reflectivity percent in the VIS-NIR and SWIR spectral regions compared with those of high iron content. As a general trend, the granitic rock types of high iron content and/or lower quartz content exhibited a high performance regarding their physical and mechanical properties, such as water absorption, apparent porosity, bulk density, compressive strength, and abrasion resistance. The results of water absorption, density, strength, and abrasion resistance of the studied granitic rocks are in the range of 0.14–0.31%, 2582–2644 kg/m3, 77.85–222.75 MPa, and 26.27–55.91 Ha, respectively, conforming to the requirements of ornamental stones according to the ASTM standard.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Simonneau, A., E. Chapron, B. Vannière, S. B. Wirth, A. Gilli, C. Di Giovanni, F. S. Anselmetti, M. Desmet et M. Magny. « Mass-movement and flood-induced deposits in Lake Ledro, southern Alps, Italy : implications for Holocene palaeohydrology and natural hazards ». Climate of the Past 9, n^o 2 (21 mars 2013) : 825–40. http://dx.doi.org/10.5194/cp-9-825-2013.

Texte intégral

Résumé :

Abstract. High-resolution seismic profiles and sediment cores from Lake Ledro combined with soil and riverbed samples from the lake's catchment area are used to assess the recurrence of natural hazards (earthquakes and flood events) in the southern Italian Alps during the Holocene. Two well-developed deltas and a flat central basin are identified on seismic profiles in Lake Ledro. Lake sediments have been finely laminated in the basin since 9000 cal. yr BP and frequently interrupted by two types of sedimentary events (SEs): light-coloured massive layers and dark-coloured graded beds. Optical analysis (quantitative organic petrography) of the organic matter present in soil, riverbed and lacustrine samples together with lake sediment bulk density and grain-size analysis illustrate that light-coloured layers consist of a mixture of lacustrine sediments and mainly contain algal particles similar to the ones observed in background sediments. Light-coloured layers thicker than 1.5 cm in the main basin of Lake Ledro are synchronous to numerous coeval mass-wasting deposits remoulding the slopes of the basin. They are interpreted as subaquatic mass-movements triggered by historical and pre-historical regional earthquakes dated to AD 2005, AD 1891, AD 1045 and 1260, 2545, 2595, 3350, 3815, 4740, 7190, 9185 and 11 495 cal. yr BP. Dark-coloured SEs develop high-amplitude reflections in front of the deltas and in the deep central basin. These beds are mainly made of terrestrial organic matter (soils and lignocellulosic debris) and are interpreted as resulting from intense hyperpycnal flood event. Mapping and quantifying the amount of soil material accumulated in the Holocene hyperpycnal flood deposits of the sequence allow estimating that the equivalent soil thickness eroded over the catchment area reached up to 5 mm during the largest Holocene flood events. Such significant soil erosion is interpreted as resulting from the combination of heavy rainfall and snowmelt. The recurrence of flash flood events during the Holocene was, however, not high enough to affect pedogenesis processes and highlight several wet regional periods during the Holocene. The Holocene period is divided into four phases of environmental evolution. Over the first half of the Holocene, a progressive stabilization of the soils present through the catchment of Lake Ledro was associated with a progressive reforestation of the area and only interrupted during the wet 8.2 event when the soil destabilization was particularly important. Lower soil erosion was recorded during the mid-Holocene climatic optimum (8000–4200 cal. yr BP) and associated with higher algal production. Between 4200 and 3100 cal. yr BP, both wetter climate and human activities within the drainage basin drastically increased soil erosion rates. Finally, from 3100 cal. yr BP to the present-day, data suggest increasing and changing human land use.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Klemd, Reiner, Andreas Beinlich, Matti Kern, Malte Junge, Laure Martin, Marcel Regelous et Robert Schouwstra. « Magmatic PGE Sulphide Mineralization in Clinopyroxenite from the Platreef, Bushveld Complex, South Africa ». Minerals 10, n^o 6 (25 juin 2020) : 570. http://dx.doi.org/10.3390/min10060570.

Texte intégral

Résumé :

The Platreef, at the base of the northern limb of the Bushveld Complex in South Africa, hosts platinum-group element (PGE) mineralization in association with base-metal sulphides (BMS) and platinum-group minerals (PGM). However, whilst a magmatic origin of the stratiform mineralization of the upper Platreef has been widely confirmed, the processes responsible for the PGE and BMS mineralization and metasomatism of the host rocks in the Platreef are still under discussion. In order to contribute to the present discussion, we present an integrated petrographical, mineral-chemical, whole-rock trace- and major-element, sulphur- and neodymium-isotope, study of Platreef footwall clinopyroxenite drill core samples from Overysel, which is located in the northern sector of the northern Bushveld limb. A metasomatic transformation of magmatic pyroxenite units to non-magmatic clinopyroxenite is in accordance with the petrography and whole-rock chemical analysis. The whole-rock data display lower SiO2, FeO, Na2O and Cr (<1700 ppm), and higher CaO, concentrations in the here-studied footwall Platreef clinopyroxenite samples than primary magmatic Platreef pyroxenite and norite. The presence of capped globular sulphides in some samples, which display differentiation into pyrrhotite and pentlandite in the lower, and chalcopyrite in the upper part, is attributed to the fractional crystallization of a sulphide liquid, and a downward transport of the blebs. In situ sulphur (V-CDT) isotope BMS data show isotopic signatures (δ34S = 0.9 to 3.1 ‰; Δ33S = 0.09 to 0.32‰) close to or within the pristine magmatic range. Elevated (non-zero) Δ33S values are common for Bushveld magmas, indicating contamination by older, presumably crustal sulphur in an early stage chamber, whereas magmatic δ34S values suggest the absence of local crustal contamination during emplacement. This is in accordance with the εNd (2.06 Ga) (chondritic uniform reservoir (CHUR)) values, of −6.16 to −6.94, which are similar to those of the magmatic pyroxenite and norite of the Main Zone and the Platreef in the northern sector of the northern Bushveld limb. Base-metal sulphide textures and S–Se-ratios give evidence for a secondary S-loss during late- to post-magmatic hydrothermal alteration. The textural evidence, as well as the bulk S/Se ratios and sulphide S isotopes studies, suggest that the mineralization in both the less and the pervasively hydrothermally altered clinopyroxenite samples of Overysel are of magmatic origin. This is further supported by the PPGE (Rh, Pt, Pd) concentrations in the BMS and mass-balance calculations, in both of which large proportions of the whole-rock Pd and Rh are hosted by pentlandite, whereas Pt and the IPGE (Os, Ir, Ru) were interpreted to mainly occur in discrete PGM. However, the presence of pentlandite with variable PGE concentrations on the thin section scale may be related to variations in the S content, already at S-saturation during magmatic formation, and/or post-solidification mobilization and redistribution.

Styles APA, Harvard, Vancouver, ISO, etc.

47

Simonneau, A., E. Chapron, B. Vannière, S. B. Wirth, A. Gilli, C. Di Giovanni, F. S. Anselmetti, M. Desmet et M. Magny. « Multidisciplinary distinction of mass-movement and flood-induced deposits in lacustrine environments : implications for Holocene palaeohydrology and natural hazards (Lake Ledro, Southern Alps, Italy) ». Climate of the Past Discussions 8, n^o 4 (3 août 2012) : 3205–49. http://dx.doi.org/10.5194/cpd-8-3205-2012.

Texte intégral

Résumé :

Abstract. High-resolution seismic profiles and sediment cores from Lake Ledro combined with soil and river-bed samples from the lake's catchment area are used to assess the recurrence of natural hazards (earthquakes and flood events) in the southern Italian Alps during the Holocene. Two well-developed deltas and a flat central basin are identified on seismic profiles in Lake Ledro. Lake sediments are finely laminated in the basin since 9000 cal. yr BP and frequently interrupted by two types of sedimentary events: light-coloured massive layers and dark-coloured graded beds. Optical analysis (quantitative organic petrography) of the organic matter occurring in soils, river beds and lacustrine samples together with lake-sediment bulk density and grain-size analysis illustrate that light-coloured layers consist of a mixture of lacustrine sediments and mainly contain algal particles similar to the ones observed in background sediments. Light-coloured layers thicker than 1.5 cm in the main basin of Lake Ledro are dense and synchronous to numerous coeval mass-wasting deposits remoulding the slopes of the basin. They are interpreted as subaquatic mass movements triggered by historical and pre-historical regional earthquakes dated to 2005 AD, 1891 AD, 1045 AD and 1260, 2545, 2595, 3350, 3815, 4740, 7190, 9185 and 11495 cal. yr BP. Dark-coloured sedimentary event are dense and develop high-amplitude reflections in front of the deltas and in the deep central basin. These beds are mainly made of terrestrial organic matter (soils and ligno-cellulosic debris) and are interpreted as resulting from intense hyperpycnal flood events. Mapping and quantifying the amount of soil material accumulated in the Holocene hyperpycnal flood deposits of the sequence and applying the De Ploey erosion model allow estimating that the equivalent soil thickness eroded over the catchment area reached up to 4 mm during the largest Holocene flood events. Such significant soil erosion is interpreted as resulting from the combination of heavy rainfall and snowmelt. The recurrence of flash-flood events during the Holocene was however not high enough to affect pedogenesis processes and highlight several wet regional periods during the Holocene. The Holocene period is divided into four phases of environmental evolution. Over the first half of the Holocene, a progressive stabilization of the soils present through the catchment of Lake Ledro was associated with a progressive reforestation of the area and only interrupted during the wetter 8.2 event when the soil destabilization was particularly important. Lower soil erosion was recorded during the Mid-Holocene climatic optimum (8000–4200 cal. yr BP) and associated with higher algal production. Between 4200 and 3100 cal. yr BP, both wetter climate and human activities within the drainage basin drastically increased soil erosion rates. Finally, from 3100 cal. yr BP to the present-day, results suggest increasing and changing human land-use.

Styles APA, Harvard, Vancouver, ISO, etc.

48

Kopylova, M. G., E. Tso, F. Ma, J. Liu et D. G. Pearson. « The Metasomatized Mantle beneath the North Atlantic Craton : Insights from Peridotite Xenoliths of the Chidliak Kimberlite Province (NE Canada) ». Journal of Petrology 60, n^o 10 (1 octobre 2019) : 1991–2024. http://dx.doi.org/10.1093/petrology/egz061.

Texte intégral

Résumé :

Abstract We studied the petrography, mineralogy, thermobarometry and whole-rock chemistry of 120 peridotite and pyroxenite xenoliths collected from the 156–138 Ma Chidliak kimberlite province (Southern Baffin Island). Xenoliths from pipes CH-1, -6, -7 and -44 are divided into two garnet-bearing series, dunites–harzburgites–lherzolites and wehrlites–olivine pyroxenites. Both series show widely varying textures, from coarse to sheared, and textures of late formation of garnet and clinopyroxene. Some samples from the lherzolite series may contain spinel, whereas wehrlites may contain ilmenite. In CH-6, rare coarse samples of the lherzolite and wehrlite series were derived from P = 2·8 to 5·6 GPa, whereas predominant sheared and coarse samples of the lherzolite series coexist at P = 5·6–7·5 GPa. Kimberlites CH-1, -7, -44 sample mainly the deeper mantle, at P = 5·0–7·5 GPa, represented by coarse and sheared lherzolite and wehrlite series. The bulk of the pressure–temperature arrays defines a thermal state compatible with 35–39 mW m–2 surface heat flow, but a significant thermal disequilibrium was evident in the large isobaric thermal scatter, especially at depth, and in the low thermal gradients uncharacteristic of conduction. The whole-rock Si and Mg contents of the Chidliak xenoliths and their mineral chemistry reflect initial high levels of melt depletion typical of cratonic mantle and subsequent refertilization in Ca and Al. Unlike the more orthopyroxene-rich mantle of many other cratons, the Chidliak mantle is rich (∼83 vol%) in forsteritic olivine. We assign this to silicate–carbonate metasomatism, which triggered wehrlitization of the mantle. The Chidliak mantle resembles the Greenlandic part of the North Atlantic Craton, suggesting the former contiguous nature of their lithosphere before subsequent rifting into separate continental fragments. Another, more recent type of mantle metasomatism, which affected the Chidliak mantle, is characterized by elevated Ti in pyroxenes and garnet typical of all rock types from CH-1, -7 and -44. These metasomatic samples are largely absent from the CH-6 xenolith suite. The Ti imprint is most intense in xenoliths derived from depths equivalent to 5·5–6·5 GPa where it is associated with higher strain, the presence of sheared samples of the lherzolite series and higher temperatures varying isobarically by up to 200 °C. The horizontal scale of the thermal-metasomatic imprint is more ambiguous and could be as regional as tens of kilometers or as local as <1 km. The time-scale of this metasomatism relates to a conductive length-scale and could be as short as <1 Myr, shortly predating kimberlite formation. A complex protracted metasomatic history of the North Atlantic Craton reconstructed from Chidliak xenoliths matches emplacement patterns of deep CO2-rich and Ti-rich magmatism around the Labrador Sea prior to the craton rifting. The metasomatism may have played a pivotal role in thinning the North Atlantic Craton lithosphere adjacent to the Labrador Sea from ∼240 km in the Jurassic to ∼65 km in the Paleogene.

Styles APA, Harvard, Vancouver, ISO, etc.

49

Kallemeyn, Gregory W., Alan E. Rubin, Daode Wang et John T. Wasson. « Ordinary chondrites : Bulk compositions, classification, lithophile-element fractionations and composition-petrographic type relationships ». Geochimica et Cosmochimica Acta 53, n^o 10 (octobre 1989) : 2747–67. http://dx.doi.org/10.1016/0016-7037(89)90146-4.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

50

Xie, Zhuojun, Yong Xia, Jean S. Cline, Michael J. Pribil, Alan Koenig, Qinping Tan, Dongtian Wei, Zepeng Wang et Jun Yan. « Magmatic Origin for Sediment-Hosted Au Deposits, Guizhou Province, China : In Situ Chemistry and Sulfur Isotope Composition of Pyrites, Shuiyindong and Jinfeng Deposits ». Economic Geology 113, n^o 7 (1 novembre 2018) : 1627–52. http://dx.doi.org/10.5382/econgeo.2018.4607.

Texte intégral

Résumé :

Abstract The southwest Guizhou Province, China, contains numerous sediment-hosted Au deposits with Au reserves greater than 700 tonnes. To date, the source of ore fluids that formed the Guizhou sediment-hosted Au deposits is controversial, hampering the formulation of genetic models. In this study, we selected the Shuiyindong and Jinfeng Au deposits, the largest strata-bound and fault-controlled deposits in Guizhou, respectively, for detailed research on pyrite chemistry and S isotope composition using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS), respectively. Petrography and pyrite chemistry studies distinguished five generations of pyrite. Among these, pre-ore pyrite 2 and ore pyrite are the most abundant types in the deposits. Pre-ore pyrite 2 is anhedral to euhedral and with ~2,639 ppm As and wider ranges of Cu, Sb, and Pb (<~22–4,837 ppm, <~6 to 532 ppm, and <~4 to 1,344 ppm, respectively). Gold in pre-ore pyrite 2 is below the detection limit of LA-ICP-MS (~2 ppm). Pre-ore pyrite 2 is interpreted to have a sedimentary (syngenetic or diagenetic) origin. Ore pyrite commonly rims the four identified pre-ore pyrites or occurs as individual, anhedral to euhedral crystals. Ore pyrite is enriched in Au (~641 ppm), As (~9,147 ppm), Cu (~1,043 ppm), Sb (~188 ppm), Hg (~43 ppm), and Tl (~22 ppm) in both deposits. Ore pyrite formed mainly by sulfidation of Fe in Fe-bearing host rocks, mainly Fe dolomite, and As, Cu, Sb, Hg, and Tl, also in ore fluids, were incorporated into ore pyrite. In situ δ34S isotope ratios for pre-ore pyrite 2 and ore pyrite were measured by LA-MC-ICP-MS. Pre-ore pyrite 2 from Shuiyindong and Jinfeng deposits resulted in δ34S values ranging from −0.8 to +3.4‰ and from 5.1 to 10.5‰, respectively. Analyses of ore pyrite from the Shuiyindong have δ34S values that vary from −3.3 to +2.5‰, with a median of 0.7‰; analyses of ore pyrite from the Jinfeng range from 8.9 to 11.2‰, with a median at 10.3‰. Available bulk and in situ δ34S data in the literature for pre-ore pyrites 1 and 2 and ore-related sulfide minerals including ore pyrite, arsenopyrite, and late ore-stage stibnite, realgar, orpiment, and cinnabar from several Guizhou sediment-hosted Au deposits were compiled for comparison. Pre-ore-stage pyrites from Guizhou sediment-hosted Au deposits have a broad range of δ34S values, from −33.8 to + 17.9‰ (including in situ and available bulk δ34S data). Ore-related sulfide minerals in all Guizhou sediment-hosted Au deposits, except Jinfeng, have very similar δ34S values, and most data plot between ~−5 and +5‰. In the Jinfeng deposit, the ore-related sulfide minerals exhibit δ34S values ranging from 1.9 to 18.1‰, with most data plotting between 6 and 12‰. The broad range of S isotope compositions for the sedimentary pyrites (pre-ore pyrites 1 and 2) indicate that S in these pre-ore pyrites was most likely generated by bacterial reduction from marine sulfate. The narrow range of δ34S values (~−5–+5‰) for ore-related sulfide minerals in all Guizhou sediment-hosted Au deposits, excepting the Jinfeng deposit, suggests that the deposits may have formed in response to a single widespread metallogenic event. As the S isotope fractionation between hydrothermal fluids and sulfide minerals in a sulfide-dominated system is small (<2‰) at ~250°C, the initial ore fluids that formed the Guizhou sediment-hosted Au deposits would have had δ34S values similar to the ore-related sulfide minerals, between ~−5 and +5‰. At Jinfeng, initial ore fluids may have mixed with local fluids with heavier δ34S, possibly basin brine (δ34Sbasin brine >18‰), resulting in elevated δ34S values of ore-related sulfide minerals and especially late ore-stage sulfide minerals. Although few igneous rocks are exposed in the mining area around these deposits, there is evidence of magmatic activity ~20 km away. Furthermore, gravity and magnetic geophysical investigations indicate the presence of a pluton ~5 km below the surface of the Shuiyindong district. Based on in situ S isotope results and recent data indicating proximal intrusions, we interpret a deep magmatic S source for the ore fluids that formed the Guizhou sediment-hosted Au deposits. However, as the age for Au mineralization of Guizhou sediment-hosted Au deposits is still debated, the mineralization-magma connection remains hypothetical. Identifying an ore fluid source and time frame for Guizhou Au mineralization continues to be a critically important research goal for this district.

Styles APA, Harvard, Vancouver, ISO, etc.

Articles de revues sur le sujet « Bulk petrography »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres