Variable Amounts Of Quartz Research Articles

Geochemical characteristics of Early Cambrian phosphate bearing sedimentary rocks from the Mussoorie Syncline, India: Implications for paleo-redox conditions

The phosphate bearing sedimentary rocks of Masrana and Kimoi blocks of Mussoorie Syncline are found to occur associated with a variety of chert-shale-carbonate with some pyrites of Tal Group of Early Cambrian age. Petro-mineralogical studies have revealed that apatite is a dominant phosphate mineral with gangue constituents as calcite, dolomite, variable amounts of quartz, pyrite, hematite as well as some organic structures. Quartz veins are also found cutting across the pellets of collophane. Major element analysis indicates that high P2O5 and CaO values designate high apatite, calcite or gypsum. The antipathetic correlation of P2O5 with most of the major oxides represents, replacement, leaching and weathering of major elements with P2O5 in the voids, cavities and veins during the formation of deposit. The results of trace elements reveal that the phosphorites are more enriched in V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Ba, Pb than Sc, Cs, Hf, Ta, Th, U. Higher concentration of V may be due to the presence of organic matter and its close affinity with P2O5. Vanadium (V) therefore occurs associated with Ni-Cr-Zn-Cu-Ag, which is distinctive of the organic matter obtained from the marine sediments. Rich Concentration of Ba, Cu, Ni and Zn in these phosphorites might be due to the presence of organic matter derived from marine plankton. Ni/Co ratios are low in the phosphate bearing sedimentary rocks (<5), which indicates oxic conditions. The plotted binary diagram of V/(V + Ni) versus Ni/Co also confirms oxic conditions for these samples. In the present study most of the samples have values of V/Cr below 2, whereas two samples show value above 2, indicating dominant oxic environmental conditions with mild reducing conditions. Oxic and anoxic diagenetic environment has been also supported by negative Ce and positive Eu on Post-Archean Australian Shale (PAAS) normalised REE patterns.

The control of shear‐zone development and electric conductivity by graphite in granulite: An example from the Proterozoic Lofoten‐Vesterålen Complex of northern Norway

AbstractGraphite impacts crustal rheology and electric conductivity in the lower crust. In a combined geophysical and geological study from the Proterozoic Lofoten‐Vesterålen Complex, Norway, we show the enrichment of graphite resulted in zones with strong schistosity and a sharp strain gradient towards host massive granulite gneiss. Increased graphite content resulted in high‐conductivity zones with true resistivity values &lt;10 Ωm compared with a resistivity of &gt;3,000 Ωm in the low‐conductive crust. The regionally distributed graphite zones contain up to 39% graphite with variable amounts of quartz, feldspars, biotite and pyroxenes and where graphite is present in stable assemblage to orthopyroxene. High‐ordered graphite and biotite with a strong‐preferred orientation define the well‐developed foliation. Our results demonstrate that graphite accounts for the high electric conductivity of this former Proterozoic lower‐crustal segment. The presence of graphite causes strain localisation in the granulite facies crust, reducing crustal strength and may thereby influence continental architecture and evolution of collision zones.

Characteristics of primary rare earth elements and yttrium in carbonate rocks from the Mesoproterozoic Gaoyuzhuang Formation, North China: Implications for the depositional system

Interpretations of depositional environments of Precambrian carbonates are commonly difficult because of their monotonous appearance and paucity of biological components. The REE + Y signatures of Precambrian carbonates can, however, provide insights into their original depositional environments, terrestrial contamination, and/or diagenetic modifications. This is exemplified by consideration of the REE + Y signatures from strata in the Mesoproterozoic Gaoyuzhuang Formation (~1543 m thick in Jixian region, China) that is formed of dolomite, calcite, silica cement, detrital quartz, and silicate grains. The basal members of the formation (1, 2, and 3-L) are formed of dolostone-dominated successions that contain variable amounts of quartz and chert cement and detrital quartz, K-feldspar, and mica grains. In contrast, the upper members (3-M, 3-T, and 4) are dominated by intercalated limestone-dolostone successions that are locally characterized by quartz and chert cements. The low Th concentration and little evidence of siliciclastic components from petrographic and XRD analyses indicate that the REE + Y values in samples from members 3-M to 4 were inherited from the coeval seawater. Their chondrite-normalized REE + Y patterns are characterized by a slight enrichment of LREE ([Nd/Yb]C = 1.5–3.9; [Sm/Yb]C = 0.9–2.1) and a superchondritic Y/Ho ratio (>38.3). These primary REE + Y features are different from those found in carbonates from other eras, suggesting that the Mesoproterozoic seawater may have had a different REE + Y composition. If siliciclastic components are present in the carbonates, as in some parts of members 1 to 3-L, the REE + Y profiles are characterized by higher LREE and MREE enrichments ([Nd/Yb]C = 3.4–8.9; [Sm/Yb]C = 1.9–4.6) and a less positive Y anomaly (Y/Ho = 27.2–35.6) than the primary Mesoproterozoic REE + Y values evident in the carbonate members 3-M to 4. From the basal members to the upper members, the increase in the Y/Ho ratio and decrease in [Nd/Yb]C and [Sm/Yb]C reflect a decrease in the amount of terrestrial detrital material that was transported into the depositional basin while the carbonate sediments accumulated on the seafloor.

Material characterization and restoration of mural paintings of El-Muzzawaka Tombs, Dakhla Oases, Egypt

The present study demonstrates scientific procedures applied to study mural paintings in two Graeco-Roman tombs of El-Muzzawaka, Dakhla Oases, Egypt. First, a series of analytical methods was applied to determine the chemical and mineralogical composition of pigment and plaster samples collected from the studied tombs. The analyses were performed by means of digitalized optical microscopy (OM), polarized light microscopy (PLM), scanning electron microscopy attached with X-ray microanalysis detector (SEM−EDS), X−ray diffraction analysis (XRD), and Fourier transform infrared spectroscopy (FT−IR). Analyses of the pigment samples revealed Egyptian blue, Egyptian green, green earth, black magnetite, and red/yellow ochres. The paintings were applied on a coarse plaster layer made of gypsum, anhydrite, calcite, and quartz. The preparation layer was made of two phases of calcium sulphate (gypsum and anhydrite). Further, the detection of an organic binder, of gum Arabic, confirms the application of tempera technique. The results showed that the bed rock samples contain variable amounts of quartz, anhydrite, montmorillonite, kaolinite, gypsum, and sodium chloride (halite). In situ observations showed several deterioration forms on the studied mural paintings. The destructive climatic condition of the region and the defects of the rock structure have contributed seriously in the deterioration process. Based on experimental tests, multi restoration procedures were applied in form of cleaning, reattaching paint flakes, applying injection grouts to detached layers, reconstruction of missing parts in the plaster, repair of wide-open cracks, and final protective consolidation of the painted surfaces. Further, recommendations to minimize any future damage were discussed.

The “intraorogenic” Svecofennian Herräng mafic dyke swarm in east-central Sweden: age, geochemistry and tectonic significance

ABSTRACTThe Herräng mafic dykes form an E-W-trending dyke swarm within the Bergslagen lithotectonic unit of the Svecofennian orogen in east-central Sweden. They intrude the Svecofennian supracrustal rocks and early-orogenic granitoids, but are themselves cut by late Svecofennian pegmatites, and have undergone Svecofennian amphibolite-facies metamorphism, leading to their classification as “intraorogenic” Svecofennian dykes. They can be assigned an age between 1870 and 1850 Ma, with metamorphism of the dykes dated at 1848 ± 13 Ma by U-Pb in titanite. Their current mineralogy is dominated by metamorphic plagioclase and amphibole, with variable amounts of quartz and biotite, and minor to accessory titanite, apatite, epidote, pyrite, magnetite, ilmenite and zircon. Textures range from massive to strongly foliated. Twenty samples of dyke rocks from three subareas in the Roslagen region, including the Herräng type area, range in composition from basaltic to andesitic with 47 to 60 wt% SiO2, broadly similar to the Dannemora dykes and the Avesta-Östhammar gabbros and diorites. Initial 87Sr/86Sr ratios (at 1870 Ma) varies between 0.7026 and 0.7038, corresponding to initial εSr between +5 and +21, and initial εNd between −0.4 and +1.3, suggesting a slightly enriched to mildly depleted mantle source, similar to other Svecofennian mafic rocks. The dykes dominantly show a calc-alkaline volcanic arc signature related to subduction. They formed during an extensional episode, possibly related to incipient back-arc spreading or subduction roll-back following the main early-orogenic subduction-related Svecofennian magmatism, but penecontemporaneous with amphibolite-facies metamorphism in the area.

Spatio-temporal variations in the Mesozoic sedimentary record, Golfo San Jorge Basin (Patagonia, Argentina): Andean vs. cratonic sources

The continental succession of the Cretaceous Chubut Group (Aptian-Maastrichtian) in the Golfo San Jorge Basin (GSJB), central extra-Andean Patagonia (Argentina) contains a high proportion of volcaniclastic input derived from explosive volcanism at the Andes Cordillera. Cutting records obtained from regionally distributed oil-wells distanced by hundreds of kilometers show a significant west-to-east decreasing in the proportion of tuffaceous components. These regional lithologic changes currently difficult the recognition of lithostratigraphic units both in the western Río Mayo sub-basin (high tuffaceous content) and in the eastern basin center-offshore (low tuffaceous content). We use seismic sections and cutting records for: a) to study a basement intra-basin paleo-high in the Northern Flank (Río Chico High) and b) to analyze the marginal basin substrate in offshore areas of the Northern Flank. The sedimentary record adjacent to the igneous-metamorphic Río Chico High contains variable amounts of quartz and detrital muscovite, identified in marine, pre-rift sequences of Lower Jurassic age and within the continental units of the Chubut Group. Basement influence in the infill composition decreases both upward and away from the Río Chico High, regarding the gradual burial of the paleo-high. Our data reveal that the igneous-metamorphic basement remained as a positive paleorelief compartmentalizing the basin and providing siliciclastic sediments at least during 100 millions of years, from early Jurassic to late Cretaceous, even before the beginning of the extensional phase that originated the basin in the uppermost Jurassic. Thus, the GSJB displays a spatially variable volcaniclastic record derived from the Andes, distorted by the presence of inherited morpho-structures that supply siliciclastic sediments provided from cratonic sources.

Trondhjemitic leucosomes in paragneisses from NE Sardinia: Geochemistry and P-T conditions of melting and crystallization

The sedimentary-derived migmatites from Porto Ottiolu consist of mesosomes and tonalitic to trondhjemitic leucosomes. These rocks contain quartz + plagioclase + muscovite + biotite in different proportions and locally fibrolite, K-feldspar and kyanite relicts. The contact between leucosomes and mesosomes is commonly marked by mm- to cm-thick melanosomes mainly formed by oriented biotite and fibrolite, muscovite, and variable amounts of quartz and plagioclase. Pressure-temperature (P-T) modeling using pseudosections and their contouring by isopleths for modal abundances of minerals and melt and Si/Al and Na/K ratios of the melt suggests that anatexis occurred at ~700 °C and 1.1 GPa with the contribution of ~2 wt% of free water. The complete crystallization of the leucosome melt was finalized at P-T conditions of 640–690 °C and 0.40–0.55 GPa. The leucosomes are folded or parallel to the S2 schistosity indicating their pre to syn-D2 formation. The leucosomes are enriched in SiO2, CaO, Na2O, Sr and depleted in Fe2O3, MgO, TiO2, K2O, Rb, Ba, Cr, V, Zr, Nb, and REE, except Eu, compared to the surrounding mesosomes. The high CaO contents up to 3.3 wt%, the low K2O contents (mean 0.57 wt%) and Rb/Sr ratios (<0.15), and the moderately fractionated REE pattern with positive Eu anomalies support the formation of water-fluxed melts from a sedimentary source. Mica segregation during crystallization of the melt and/or disequilibrium melting contributed to the geochemical signature of these leucosomes. Especially the former process is responsible for the very low K content in the leucosomes and the mismatch between measured and predicted Si/Al and Na/K ratios in the leucosomes without mica segregation.

Identification and Conservation State of Painted Wall Plasters at the Funerary House in Necropolis of Tuna El-Gebel, El-Minia-Upper Egypt

During this study, the principal aim carried out was to obtain more information about technique and conservation conditions of the Egyptian wall paintings during the Roman period in the funerary house in necropolis of Tuna el-Gabal, El-Minia-Upper Egypt. It’s going back to 2nd century AD and involves different sites of Ptolemaic and Roman chapels; some are in the immaculate established style while others are a blend of Pharaonic-Greek style and both are secured with mural painting. Deterioration problems observed on the wall paintings of the funerary house are, loss of plaster layers, disintegration of plaster layers, loss of paint layers (blistering and peeling), discoloration and severely damaged owing to a lot of deterioration factors as weakness of mud brick support, deterioration of surface treatments and to the widespread presence of different salts. The materials used in the painting, preparation layers and the state of conservation of the mural painting at funerary house were investigated by integrated physio-chemical measurements, particularly micro-Raman spectroscopy (µRaman), light optical microscopy (LOM), scanning electron microscopy (SEM) coupled with an energy dispersive X-ray analysis system (EDX), X-ray powder diffraction (XRD) and Fourier transform infrared (FT-IR). In addition, the morphology of multilayer plaster from wall painting was investigated using atomic force microscopy (AFM). A wide color palette utilized as a part of the necropolis has been identified with mineral pigments and pigment mixtures. It is found that, the paints were based on an organic binder and traditional pigments (azurite, hematite, ochre, vegetable black) were used as colorants on plaster. The examination demonstrated that the preparatory layer is verging on made of pure lime while the plaster layer based mainly of lime and gypsum with variable amounts of quartz. The obtained results provided information about the painting technique, chemical composition, crystal structure in addition to the stratigraphy of the paint layers and the state of preservation and on the causes of the painting deterioration. Furthermore, the obtained results can be used in the conservation and restoration interventions of these sites.

Provenance of sandstone on the western flank of Anambra Basin, Southwestern Nigeria

Petrographic and heavy mineral studies were carried out on clastic deposits that crop out in Ikpeshi, Auchi and Fugar localities in order to determine the provenance of the sediments and the tectonic setting of the source area. The localities are in the western flank of the Anambra basin, southwestern Nigeria. Petrographic study shows that the sandstone deposits are composed of variable amounts of quartz, feldspars and lithic fragments with minor occurrence of authigenic silica and chlorite cements. Quartz is the predominant detrital mineral in all the samples accounting for over 87 % of the total framework composition. The representative samples from all the localities contain 88-94 % quartz, 1-8 % lithic fragment, 1-4 % cement and 0-4 % matrix. Feldspar is present in small amount only in samples from Fugar locality. The sandstones each classify as quartz arenites and sublitharenites. Both opaque and transparent heavy minerals occur in the sandstones. The opaques are magnetite, ilmenite and leucoxene. Together, they account for 35 – 55 % of the total heavy mineral abundance. The transparent heavy minerals are zircon, tourmaline, rutile, staurolite, and apatite listed in order of decreasing abundance. The heavy mineral assemblages in the localities are similar except for the absence of rutile from the sediments of Ikpeshi locality. The heavy mineral grains are subangular to rounded. The zircon-tourmaline-rutile (ZTR) index for the sediments from the three localities are generally high and range from 90.5 to 100% indicating high degree of mineralogical maturity of the sandstones. The heavy mineral suites and the petrographic signatures of the sandstones suggest derivation mainly from acid igneous rocks, gneisses and older sandstones in both stable tectonic and recycled orogenic settings. However, the absence of rutile in sandstone from Ikpeshi may suggest derivation from lithologically more restricted provenance.

Preservation of glacial and interglacial phases in Tethys Himalaya: evidence from geochemistry and petrography of Permo-Carboniferous sandstones from the Spiti region, Himachal Pradesh, India

Through a multidisciplinary approach, including petrology and geochemistry, the sedimentary provenance and paleo-weathering of the Permo-Carboniferous Spiti sandstones of Tethys Himalaya are investigated. The Spiti region consists of texturally immature to mature sandstones composed of unsorted to sorted and subangular to subrounded clastic grains dominated by variable amounts of quartz and feldspar accompanied by lithic fragments (mostly metasedimentary, sedimentary, and plutonic grains). They are characterized by moderate to high SiO2 contents, moderate K2O/Na2O ratios, but relatively low mafic contents. Uniform rare earth element (REE) patterns similar to upper continental crustal (UCC) with light REE (LREE) enrichment (LaN/SmN = 3.91), flat heavy REE (HREE; GdN/YbN = 1.21–2.5), and negative Eu anomalies with variable amounts of ΣREE and Eu anomalies (0.4–0.8) suggest that hydraulic sorting played a significant role. The striking similarities of the multi-elemental spider diagrams of the Spiti sandstones and the Himalayan granitoids indicate that sediments are sourced from the Proterozoic and Cambro-Ordovician orogenic belts of the Himalayan region. The nature of the feldspar observed in thin sections from most altered to euhedral pristine minerals corresponding to Carboniferous to lower Permian sandstones strongly indicates a change in climate from most favorable conditions for rapid feldspar alteration (humid) to conditions where negligible alteration is possible (arid and glacial). It is found that the chemical index of alteration (CIA) values of these sandstones accorded with inferences based on modified chemical index of alteration (CIX) and αCa values, and sedimentologic and paleontological evidence, discriminating well between warm-humid (indicated by high CIA values) and arid-glacial (representing low CIA) conditions in the Spiti basin. Thus, these results document a complete record of glacial and interglacial phases in the Permocarboniferous Spiti sandstones, and the interpretations are consistent with other such studies on the Phanerozoic glaciation events on Gondwana supercontinent.

Synthesis and Structural Characterization of CSH-Phases in the Range of C/S = 0.41 - 1.66 at Temperatures of the Tobermorite Xonotlite Crossover

Calcium-Silicate-Hydrate-phases (CSH-phases) are important binding agents of building materials. The synthesis of CSH phases and their structural characterization was done to investigate the crystallization in dependence of an increasing CaO/SiO2 ratio (C/S ratios) from 0.41 up to 1.66 at temperatures in the crossover region of tobermorite to xonotlite (180℃ and 230℃). Parallel runs with the same C/S ratio but on the one hand with constant mass of quartz and variation of lime and on the other hand under reverse conditions (constant mass of lime but variable amounts of quartz) were performed at both temperatures. The aim was to clarify the connections of crystallization mechanism and kinetics of phase formation with structure, crystallinity and morphology of the CSH’s in the mentioned C/S ratio for both temperatures in the tobermorite-xonotlite crossover region. The parallel experiments with different mass ratios of the educts are important to study the influence of time evaluation of supersaturation within the solution under the peculiarities of the retrograde solubility of lime but accelerated solubility of quartz. The products were characterized by XRD, SEM/EDX, FTIR and 29Si MAS NMR spectroscopy (using the Q-site nomenclature [1]). The experiments could clarify some important connections of crystallization process and the reaction pathway.

Investigations by Raman microscopy, ESEM and FTIR-ATR of wall paintings from Qasr el-Ghuieta temple, Kharga Oasis, Egypt

In the present work, a multi-analytical approach was used to analyze samples collected from the wall paintings of Qasr el-Ghuieta temple, Kharga Oasis, Egypt. The temple is dating back to the 27th dynasty (525–404 BC) and was completed during the Ptolemaic period. The samples were analyzed by optical microscopy (OM), environmental scanning electron microscopy (ESEM) coupled with an energy dispersive X-ray analysis system (EDX), Raman microscopy and Fourier transform infrared–attenuated total reflectance spectroscopy (FTIR–ATR). The chromatic palette used in the temple was identified as Egyptian blue (cuprorivaite), red ochre (haematite), yellow ochre (goethite) and carbon black (from a vegetable origin). The green pigment was identified as green earth, however, a green tonality was also obtained through a mixture of Egyptian blue and yellow ochre, and in some samples, carbon black was also found. Several amounts of anatase and carbon black were found in the red and yellow ochre samples, respectively. The analysis showed that the preparation layer is almost made of pure gypsum, while the plaster layer based mainly on gypsum with variable amounts of quartz, calcite and clay minerals. The results showed that the painting materials and techniques used in the temple are almost the same of those used in the Egyptian temples with respect to the stratigraphy of paint layers, chromatic palette and the painting technique employed.

Genesis of Si-rich carbonatites in Huanglongpu Mo deposit, Lesser Qinling orogen, China and significance for Mo mineralization

The Huanglongpu carbonatite-related Mo ore field is located in the Lesser Qinling Orogenic belt in the southern margin of the North China block. The ore field is composed of six deposits, Yuantou, Wengongling, Dashigou, Shijiawan, Taoyuan and Erdaohe, all of which are genetically related to carbonatite dykes except for the Shijiawan deposit which is associated with a granitic porphyry. The Yuantou carbonatite dykes intruded into Archean gneiss and other carbonatites emplaced into Mesoproterozoic volcanic and sediment rocks. The carbonatites are mainly composed of calcite and variable amounts of quartz and K-feldspar and minor molybdenite. Re–Os dating of molybdenite from the Yuantou carbonatite yields a weighted average age of 225.0±7.6Ma, consistent with the molybdenite age (221Ma) from the Dashigou deposit. The rocks are characterized by high heavy REE (HREE) contents and consistent flat REE distribution patterns with La/Ybcn ~1. Quartz in the carbonatites from Yuantou and Dashigou deposits shows consistent O isotopes (8.1–10.2‰) similar to the associated calcite (7.2–9.5‰). The quartz and associated K-feldspar contain lower Zr, Hf and higher HREE abundances and negligible Eu anomaly relative to those from the granite porphyry in Shijiawan. Both minerals are primary products in the carbonatitic liquid, and not captured from the wall-rocks or crustal-derived silicate magmas, or a hydrothermal origin. Thus, the Huanglongpu carbonatitic liquids were enriched in Si and Mo, which may be produced by intensely fractional crystallization of non-silicate minerals.

First Report of Florencite from the Singhbhum Shear Zone of the East Indian Craton

Metamorphic florencite is being reported from kyanite-rich rocks from the eastern part of the Palaeo- to Mesoproterozoic Singhbhum shear zone. This is the first report of florencite from the Precambrian rocks of the Indian Shield. Host rock of florencite is a kyanite-rich rock (&gt;80 vol%) with small and variable amounts of quartz, lazulite, augelite, and rutile. Florencite forms small (&lt;20 microns) idioblastic-to-subhedral crystals that are included in large kyanite grains. Rarely, florencite replaces kyanite. The florencite has small proportion of crandallite (8.7–11.8 mol%) and goyazite (&lt;2 mol%) components. Florencite of this study is dominated by Ce (~49 mol%) with significant La (~30 mol%) and Nd (~21 mol%). Compared to other florencite occurrences of the world, florencite of the studied rock is impoverished in S, Sr, and Ba and rich in P. Stability of the assemblage florencite-kyanite-augelite-lazulite and the quantitative thermobarometry in the adjoining rocks suggest that florencite was formed during Palaeoproterozoic metamorphism that culminated at theP-Trange of490±40∘Cand6.3±1 kbar. Integrating all the geological features it is postulated that florencite was formed due to metasomatism of some aluminous protolith by infiltration of acidic fluids charged withPO4-3and LREE.

Investigations by Raman microscopy, ESEM and FTIR-ATR of wall paintings from Qasr el-Ghuieta temple, Kharga Oasis, Egypt

In the present work, a multi-analytical approach was used to analyze samples collected from the wall paintings of Qasr el-Ghuieta temple, Kharga Oasis, Egypt. The temple is dating back to the 27th dynasty (525–404 BC) and was completed during the Ptolemaic period. The samples were analyzed by optical microscopy (OM), environmental scanning electron microscopy (ESEM) coupled with an energy dispersive X-ray analysis system (EDX), Raman microscopy and Fourier transform infrared–attenuated total reflectance spectroscopy (FTIR–ATR). The chromatic palette used in the temple was identified as Egyptian blue (cuprorivaite), red ochre (haematite), yellow ochre (goethite) and carbon black (from a vegetable origin). The green pigment was identified as green earth, however, a green tonality was also obtained through a mixture of Egyptian blue and yellow ochre, and in some samples, carbon black was also found. Several amounts of anatase and carbon black were found in the red and yellow ochre samples, respectively. The analysis showed that the preparation layer is almost made of pure gypsum, while the plaster layer based mainly on gypsum with variable amounts of quartz, calcite and clay minerals. The results showed that the painting materials and techniques used in the temple are almost the same of those used in the Egyptian temples with respect to the stratigraphy of paint layers, chromatic palette and the painting technique employed.

Petrological and Geochemical Constraints On Provenance, Paleoweathering, and Tectonic Setting of the Neoproterozoic Sedimentary Basin In the Eastern Jiangnan Orogen, South China

Abstract The Neoproterozoic (830–815 Ma) Shuangqiaoshan (SQS) and (833–817 Ma) Xikou (XK) groups are two of a series of sedimentary sequences in the Jiangnan Orogen, which are located in the southeastern Yangtze Block, South China and witnessed the assemblage and breakup of the supercontinent Rodinia. Through a multidisciplinary approach, including petrology and geochemistry of the clastic sedimentary rocks, we reconstruct the sedimentary provenance and paleoweathering of the sedimentary basin and characterize the formation and evolution of the Jiangnan Orogen and its role in Rodinia. The SQS Group consists of texturally immature sandstones composed of unsorted and angular to subangular clastic grains dominated by lithic fragments (54–80%) (mostly chert, metasedimentary, and sedimentary grains) accompanied by variable amounts of quartz (14–40%) and feldspar (0–18%). Sandstones from the XK Group are characterized by lower quartz (5–16%) but higher feldspar (16–47%) and lithic fragments (47–78%) (mostly volcanic detritus). All samples lie along a provenance-dependent compositional trend, suggesting that hydraulic sorting and recycling of heavy minerals were insignificant. Moderate Eu/Eu* (0.6–1.0) and (La/Yb)n (4.8–8.4) values and predominant Neoproterozoic euhedral detrital zircons indicate that sedimentary detritus was largely sourced from locally distributed Neoproterozoic intermediate to felsic igneous rocks. Potential sources include the ca. 930–900 Ma Pingshui plagiogranite, the ca. 930–890 Ma Shuangxiwu andesite, and the ca. 850 Ma Zhenzhushan dacite and basalt. The modeled average composition of the SQS detritus consists of 80% dacite, 10% andesite, and 10% basalt, whereas the XK detritus consists of 70% dacite, 20% andesite, and 10% basalt. The SQS and XK rocks record mild to moderate chemical weathering in their source areas. Some samples plot away from the predicated weathering trend in the A-CN-K diagram, reflecting replacement of the detrital calcic plagioclase by authigenic albite during postdepositional metasomatism. Textural and chemical immaturity, non-steady-state weathering, and signatures of immobile elements are indicative of a tectonically active setting, likely a continental arc environment, for deposition of the SQS and XK groups. The Yangtze Block is thus considered to be located in the periphery of Rodinia during ca. 833–815 Ma.

Field relationships, petrology, age, and tectonic setting of the Late Cambrian–Ordovician West Barneys River Plutonic Suite, southern Antigonish Highlands, Nova Scotia, Canada

The West Barneys River Plutonic Suite consists of gabbro, syenite-monzonite, alkali-feldspar syenite to quartz alkali-feldspar syenite, and alkali-feldspar granite outcropping in an area of ∼100 km2 in the southern Antigonish Highlands. Magma mixing and mingling textures indicate a comagmatic relationship between some of the mafic and intermediate–felsic lithologies. However, nine U–Pb (zircon) ages, three by thermal ionization mass spectrometry (TIMS) and six by laser-ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS), from the West Barneys River suite and the lithologically similar Cape Porcupine Complex located 60 km to the east range from ca. 495 to 460 Ma, indicating that emplacement occurred over a significant span of time. Intermediate to felsic rocks consist mainly of perthitic K-feldspar and variable amounts of quartz; interstitial granophyre is present in some samples, consistent with shallow emplacement. Mafic phases are Fe-rich amphibole and clinopyroxene, and in some units, fayalite. Intermediate and felsic samples have chemical characteristics of within-plate ferroan A-type granitoid rocks. Gabbroic rocks consist of plagioclase (oligoclase–labradorite) and augite/diopside with less abundant orthopyroxene, olivine, biotite, and ilmenite/magnetite. Their chemical compositions are transitional from tholeiitic to alkalic and characteristic of continental within-plate mafic rocks. The εNd values are similar in gabbroic, syenitic, and granitic samples, ranging between 0.9 and 4.9, consistent with a co-genetic origin for the mafic and intermediate/felsic components of the suite, and derivation from Avalonian subcontinental lithospheric mantle in an extensional environment.

Mixing of crystal mushes and melts in the genesis of the Bogács Ignimbrite suite, northern Hungary: An integrated geochemical investigation of mineral phases and glasses

The 16.4Ma old Bogács Ignimbrite, located south of the Bükk Mountains, northern Hungary, was formed during a silicic ignimbrite flare-up in the Pannonian Basin that occurred from 20Ma to 13Ma. It comprises two main units, a lower, variably welded pumiceous and an upper, scoriaceous pyroclastic flow unit. Bulk chemistry of the juvenile clasts indicates a gradual change of geochemical character with an upward decreasing SiO2 content through the stratigraphic section. A detailed in-situ major and trace element investigation of the main mineral phases and glasses combined with petrogenetic model calculations reveals complex magma reservoir processes. Based on the major and trace element variability, six juvenile clast types were distinguished and each contain fresh glass fractions with distinct compositions. The mineral assemblage consists of plagioclase, orthopyroxene, biotite with minor and variable amounts of quartz, amphibole, ilmenite, zircon and allanite. The anorthite content of the plagioclases varies from 20 to 90mol%, whilst the Enstatite content of orthopyroxenes covers also a wide range from 40 to 90mol%. This large compositional variation can be detected even in single crystals. This extreme geochemical variability can be explained by mixing of crystal mush bodies evolved from both basaltic and more silicic magmas. The calcic plagioclases (An=80–90mol%) and magnesian orthopyroxenes (En=70–90mol%) clearly indicate the role of primitive mafic magmas in the growth of the silicic magma reservoir, even though no basaltic volcanic activity was associated with the Miocene silicic volcanism in the Pannonian basin. The prolonged crystallization in the mushy sills resulted in compositionally different residual melt fractions that moved upwards and accumulated in separated melt pods at the roof of the magma reservoir. Intermittent intrusions of mafic and intermediate magmas into this silicic magma system could have resulted in thorough stirring of the crystal mush bodies and the melt pods, leading to eruptive products having compositionally heterogeneous glass and mineral assemblage.

Quantitative Mineralogy from Infrared Spectroscopic Data. I. Validation of Mineral Abundance and Composition Scripts at the Rocklea Channel Iron Deposit in Western Australia

Visible-near to shortwave infrared reflectance spectra (VNIR-SWIR—400–2,500 nm wavelength region) provide quantitative measurements of mineral abundances and mineral physicochemistries from drill core samples of channel iron ore. The infrared spectral reflectance measurements of drill core samples from the Rocklea channel iron deposit, located in the Hamersley Basin of Western Australia, were validated against X-ray flouresence (XRF) and X-ray diffraction (XRD). The reflectance data were collected using a CSIRO Hy-Logging™ system from 180 reverse circulation and 14 diamond drill cores spanning a depth from surface to 55 m below surface, intersecting the Rocklea deposit. The mineralogy of this channel iron deposit comprises chiefly goethite (both vitreous and ochreous forms) with lesser amounts of hematite and variable amounts of quartz, kaolinite, smectite (both dioctahedral and trioctahedral varieties), and carbonate (both dolomite and calcite). Iron ore and waste rock mineralogy were extracted from the infrared spectroscopic reflectance data using the geometry (depth/wavelength) of continuum-removed reflectance spectra, with depths of absorption features proportional to mineral abundance and wavelength positions proportional to chemical composition. For any one mineral, a number of its diagnostic spectral features are used to determine its mineral abundance and composition, in order to avoid complications with minerals that spectrally overlap with part of the diagnostic spectral features of the mineral of interest. This method that combines multiple spectral features to identify and quantify minerals is transferable to all types of infrared reflectance spectroscopic data collected from drill core to satellites. Final products include: iron (oxyhydr-)oxide content (root mean square error (RMSE) 9.1 wt % Fe); Al clay content (RMSE 3.9 wt % Al 2 O 3 ); hematite/goethite ratio (RMSE 9.0 wt % goethite); vitreous versus ochreous goethite (not easily measured using other analytical techniques); clay mineral type (kaolinite, montmorillonite and nontronite); and carbonate composition (dolomite vs. calcite). The Rocklea infrared reflectance spectroscopy-based mineral abundance and composition results have been used in an associated study to characterize the architecture of the Rocklea channel iron deposit, with implications for exploration, mining, and ore genesis.

The potential use of Tithonian–Barremian detrital deposits from central Tunisia as raw materials for ceramic tiles and pigments

The aim of this study is to evaluate Tunisian Tithonian–Barremian deposits for the manufacture of ceramic tiles and pigments. Three major geological domains were sampled: the North–South axis, Central Atlas and Southern Atlas. The Tithonian clay sediments (Sidi Khalif Formation) and Barremian sands (Sidi Aich Formation) outcrop exclusively in central Tunisia. X-ray diffraction revealed a predominance of illite and kaolinite and variable amounts of quartz, dolomite and feldspars in the Tithonian clays. Their technological properties were assessed in pressed ceramic tiles after firing at different temperatures. Lab-scale tests involved determinations of porosity, bending strength and linear shrinkage, and results were compared with those of commercial tiles from Tunisia and Italy. The main constituents of the Barremian sands are quartz and K-feldspars. Lab-scale tests were carried out to produce blue Co-olivine and Co-willemite pigments. Formulations showed stability and high crystallinity after calcination at 1300 °C. CIELab measurements confirmed the development of interesting blue coloration by the pigments when applied in transparent and opaque glazes. Their coloring performance was similar to that of the commercial equivalents tested.