High Ba Contents Research Articles

Coeval high Ba-Sr arc-related and OIB Neoproterozoic rocks linking pre-collisional magmatism of the Ribeira and Araçuaí orogenic belts, SE-Brazil

Two arc systems have been described within the Neoproterozoic Ribeira Belt: the inner continental magmatic arc and the outer intra-ocean magmatic arc. New geochemical and U-Pb and Lu-Hf (LA-ICPMS) data from zircons of the Marceleza-Leopoldina stocks, belonging to the inner magmatic arc system, in the boundary region between the Ribeira and Araçuaí orogenic belts are presented. The intermediate to felsic magmatic rocks have high Ba, Sr, K/Rb, LILE and LREE contents. Low Rb, Th, U, Nb, and very low Y and HREE contents point to their generation in a supra-subduction tectonic scenario, from melting of the asthenospheric wedge above a subducting oceanic plate. Zircon U-Pb (LA-ICPMS) data indicates crystallization ages between ca. 650 and 600 Ma, with high-grade metamorphic overprint at ca. 582 Ma. Tonian inherited zircons were found in the older rocks, suggesting that the development of the continental magmatic arc might have begun earlier. Associated basic (gabbros and monzogabbros) to intermediate (diorites and monzodiorites) rocks are geochemically heterogeneous. Some represent less evolved calc-alkaline basaltic magmas, while relatively more enriched varieties are intraplate basalts with OIB components. Together with lithogeochemical data, Lu-Hf signatures showing TDM model ages between ca. 1.7 to 1.3 Ga, with initial ɛHf values ranging from slightly negative values (−0.9 to −3.75) to strongly negative (up to −10.4) indicate a magmatic arc developed on continental margin environment (i.e., continental-type arc). The studied rocks represent the Rio Doce arc in the studied region and are correlated with other arc segments located from the north, in the Araçuaí Orogen, to the southernmost Ribeira Orogen, defining a c. 1000 km long continental-type magmatic arc. This inner arc system first collided against the São Francisco craton during the Neoproterozoic Brasiliano orogeny around 580 Ma. The geochemical diversity of coeval intermediate to felsic rocks and the variability of associated basic rocks are suggestive of a complex evolution of the subduction zone system. Possible mechanisms for the enrichment in incompatible elements of magmatic products may have involved slab roll-back and subduction of fore-arc rocks, and the influx of ascending asthenosphere associated with slab windows (slab break off, ridge subduction) prior to collision.

Shoot proliferation and in vitro organogenesis from shoot apex and cotyledonary explants of royal poinciana (Delonix regia), an ornamental leguminous tree

Cytokinin supplementation was essential for the induction of shoot proliferation and in vitro organogenesis from shoot apices and cotyledons of D. regia, respectively. Micropropagation techniques have been established for woody species to facilitate their mass clonal propagation and to better understand their processes of regeneration. The goal of this work was to evaluate the potential of shoot apex and cotyledonary explants of Delonix regia, commonly known as royal poinciana, to be induced to undergo shoot proliferation and in vitro organogenesis, respectively. Shoot apices and cotyledons obtained from in vitro-germinated seedlings were inoculated onto Murashige and Skoog (MS) medium supplemented with different concentrations (0.125, 0.250, 0.5, 1.0 and 2.0 mg L−1) of 6-benzyladenine (BA) and a control without BA. After 30 days of cultivation, multiple shoot formation and adventitious shoots were observed in shoot apices and cotyledonary segments of D. regia, respectively. Both explant sources exhibited a dose-dependent behavior with increased fresh mass and shoot number with increasing BA concentrations. The greatest number of shoots was observed in explants cultured on BA-supplemented (2.0 mg L−1) medium; however, the leaflets of shoots grown in MS medium with higher BA concentrations were smaller. Histological analysis revealed that the formation of adventitious shoots occurred through the reprogramming of mesophyll cells in the edge regions of the cotyledonary explants. The results obtained here provide new information for optimizing and establishing efficient regeneration systems and micropropagation of royal poinciana, an important ornamental tree species.

Geochemical characterization of surface sediments from Tongo Gandima (Eastern Cameroon): implications for gold exploration

This paper deals with the mineralogy and geochemistry of alluvial sediments from the Tongo Gandima (Eastern Cameroon) using XRD, XRF, and ICP-MS instruments. The main aim of this work is to discuss the provenance of sediments and carry out a geochemical exploration in the areas where gold mining is taking place. Granites and monzonites outcrop as large masses of several decameters with granular texture. Petrographic description and SiO2, Al2O3, and TiO2 contents reveal the intermediate igneous rock nature of monzonites and the felsic igneous rock nature of granites. Both rocks fall into the field of peraluminous and S-type granites. The high proportion of feldspars and biotite led to high Al2O3, Fe2O3, CaO, Ba, Sr, Th, Zn, Zr, and REE (rare earth element) contents particularly in monzonites. The presence of accessory minerals results in high trace element contents including REEs. The alluvial sediments are composed of quartz, kaolinite, rutile, smectite, zircon, magnetite, and gibbsite. They are mainly classified as shale, wacke, Fe-shale, and Fe-sand. The chemical index of alteration (CIA) reveals moderate to intense weathering of the source rock highlighted by the depletion of alkaline (Na+, K+, and Ca2+) and the enrichment of Al2O3. The high Th/Sc ratio which is an indicator of chemical differentiation suggests a high degree of sediment recycling. The variable chemical differentiation corroborates with the variable contents in Zr, Hf, TiO2, P2O5, and REEs. The chondrite-normalized REEs show high REE contents and negative Eu-anomalies. The negative Eu-anomalies in sediments indicate reduction conditions or the depletion of europium bearing minerals. The few amounts of Cr, V, Ni, and Sc as well as the abundance of Th and REEs justify the felsic nature of rocks. There is a similarity between REE behavior of host rocks (granites and monzonites) and sediments. These rocks may contribute a lot as the sediment sources. The felsic source is confirmed by light REE-abundance and negative Eu-anomalies. In addition, both lithotypes show high REE contents while alluvial sediments possess attractive contents in Ba, Sr, Au, and REEs. These data suggest that the potential of the surface sediments of Tongo Gandima as gold deposits is low.

Effect of Crystallinity of Apatite in Cremated bone on Carbon exchanges during burial and reliability of Radiocarbon Dating

ABSTRACTThis study characterized cremated bone to better understand isotope exchanges during burial, using archeological samples. The cremated bones of Jokei, a Buddhist monk (AD 1155–1213), found in an urn from the Jisho-in Temple, Nara Prefecture, Japan, were used for the analysis. 14C dates were determined for eight of Jokei bone fragments of different colors (black, gray, and white). The white fragments had the highest x-ray diffractometry (XRD) crystallinity index (CI) values (0.89–1.05), Fourier-transform infrared spectroscopy (FTIR) splitting factor values (IRSF) of 5.3–7.1, and the lowest Ba concentrations. The calibrated date of the white bone fragments is 1152–1216 cal AD, consistent with Jokei’s lifespan, showing these fragments yield reliable 14C ages. Meanwhile, the black and gray fragments, which probably experienced lower temperatures during cremation, had lower CI and IRSF values of 0.25–0.46 and 4.2–4.9, respectively, and higher Ba concentrations. The black and gray fragments tended to show unreliable younger 14C dates and higher 87Sr/86Sr values close to the soil value due to soil contamination. The results in this study indicate that it is important to check crystallinity of apatite and soil contamination using chemical indexing methods such as Ba capture, to clarify the reliability of 14C dates for cremated bone samples.

Petrogenesis of late Mesozoic high-Ba–Sr granites in the Qiushuwan Cu[sbnd]Mo orefield: Implications for the distribution of porphyry Mo mineralization in the East Qinling area of Central China

The Qinling–Dabie orogenic belt of China is well known for its large Mo resources. There have been many studies of the genesis of the Mo deposits, but the reasons for the intensive mineralization during the late Mesozoic and the spatially uneven distribution of the resulting ore deposits are not fully understood. Deposits with reserves of >6 Mt. of Mo occur predominantly in the southern margin of the North China Craton (NCC) and are mostly late Mesozoic porphyry deposits. In comparison, a few relatively insignificant and Cu-dominated porphyry ore deposits have been identified in the North and South Qinling terranes. This study presents new whole-rock geochemical, isotopic, and zircon UPb age data for ore-bearing granites associated with the Qiushuwan CuMo deposit, the largest porphyry deposit in the North Qinling (NQ) terrane, which provide insights into the asymmetric distribution of Mo mineralization in this region. The rocks display high-K calc-alkaline to shoshonitic affinities, and are metaluminous to weakly peraluminous with high Ba and Sr contents, low Rb, Nb, and Ta contents, and depletion in heavy rare earth elements and Y, which are features typical of high-Ba–Sr granites. Zircon UPb dating indicates that the granites crystallized at ca 145 Ma. Their narrow ranges of whole-rock initial 87Sr/86Sr ratios (0.7056–0.7069) and εNd(t) (−7.4 to −9.7), zircon εHf(t) (−2.49 to −5.13), and δ18O (+5.58‰ to +6.49‰) values, together with the presence of significant NdHf isotopic decoupling (ΔHf = +7.61 to +11.3), indicate that the parent magma was derived from partial melting of enriched subcontinental lithospheric mantle with minor assimilation of the lower crust. In contrast, late Mesozoic granitic rocks in the southern margin of the NCC (including both mineralized and barren intrusions) are geochemically associated with the crust of the northern margin of the Yangtze Block (YB). The YB contains Mo-rich shales that are thought to have been subducted beneath the southern margin of the NCC during the Triassic. Melting of these Mo-rich black shales would have mobilized Mo, a process that enabled the formation of the extensive Mo mineralization associated with the late Mesozoic granites of the southern margin of the NCC. This indicates that the extensive Mo mineralization within the southern margin of the NCC is genetically related to a Mo-rich source that was generated by the stagnation of subducted YB continental crust beneath the southern margin of the NCC. In comparison, the less significant Mo mineralization within the East Qinling orogenic belt might reflect the variable removal of the subducted YB continental slab during post-collisional intracontinental orogenesis.

Petrogenesis and geodynamic implications of Early Palaeozoic granitic rocks at the Hongshi Cu deposit in East Tianshan Orogenic Belt, NW China: Constraints from zircon U–Pb geochronology, geochemistry, and Sr–Nd–Hf isotopes

The Early Palaeozoic granitoid rocks represent a volumetrical component of the eastern part of the Dananhu–Tousuquan island arc belt of the East Tianshan and preserve useful information about the tectonomagmatic history of this region. The Hongshi intrusion primarily consists of granodiorite, which intrudes the Ordovician–Silurian Daliugou Formation in the Kalatag area. Zircon U–Pb dating of magmatic zircons from the granodiorite was formed at 426.6 ± 2.3 Ma, suggesting that the intrusion was emplaced in the Middle Silurian. Geochemically, granodiorite belongs to the metaluminous calc‐alkaline I‐type granitoids associated with a narrow range of SiO2 concentration (63.53–67.71 wt.%), A/CNK values ranging from 1.01 to 1.12. They have high Ba, LREE, and LILE contents and low abundance of HREE and HFSE. These samples displayed MgO contents of 1.38–1.52 wt.%, resulting in low K2O/Na2O ratios of 0.11–0.33 and intermediate Mg# values of 29.03–37.31, with high Sr/Y, La/Yb, and Ba/Th ratios, positive εNd(t) (6.60 to 7.95) and εHf(t) (13.1–16.0), low (87Sr/86Sr)i (0.704113–0.704312), and low Nb/U and Ta/U ratios. These features indicated that the parental magma of the granodiorite was probably derived from a juvenile crust with no significant mantle component involvement. Based on the regional geology and geochemical evidence, the Hongshi granodiorite is considered to have formed in an arc setting, associated with the northward subduction of the young Kangguer Ocean slab beneath the Dananhu island arc.

Early Carboniferous High Ba‐Sr Granitoid in Southern Langshan of Northeastern Alxa: Implications for Accretionary Tectonics along the Southern Central Asian Orogenic Belt

Voluminous granitoids are widely distributed in the Langshan region, northeast of the Alxa block, and record the evolutionary processes of the southern Central Asian Orogenic Belt. The Dabashan pluton was emplaced into the Paleoproterozoic Diebusige complex. Early Carboniferous zircon LA‐ICP MS U‐Pb ages were from 327 Ma to 346 Ma. The Dabashan pluton can be classified as monzogranite and syenogranite, and exhibits high K2O contents and K2O/Na2O ratios, which reveal a high‐K calc‐alkaline nature. The samples display strongly fractionated REE patterns, and are enriched in large ion lithophile elements (LILE) relative to high field strength elements (HFSE). The Dabashan plutons display unusually high Ba (823–2817 ppm) and Sr (166–520 ppm) contents and K/Rb ratios (315–627), but low Rb/Ba ratios (0.02–0.14), and exhibit fertile zircon Hf isotopic compositions [εHf(t)=–14 to –20], which are comparable to those of typical high Ba–Sr granitoids. Based on the geochemical compositions of the samples, we suggest that subducted sediments and ancient crustal materials both played important roles in their generation. Basaltic melts were derived from partial melting of subcontinental lithophile mantle metasomatized by subducted sediment‐related melts with residual garnet in the source, which caused partial melting of ancient lower crust. Magmas derived from underplating ascended and emplaced in the middle–upper crust at different depths. The resultant magmas experienced some degree of fractional crystallization during their ascent. Given these geochemical characteristics, together with regional tectonic, magmatic, and structure analysis data, an active continental margin environment is proposed for the generation of these rocks.

Late Paleocene adakitic granitoid from NW Iran and comparison with adakites in the NE Turkey: Adakitic melt generation in normal continental crust

Late Paleocene adakitic granitoids are rare in Iran except in the northwest. We focused on the adakitic Saqqez-Takab pluton, which occupies an area of ~600 km2. New U-Pb zircon dating yield crystallization ages of 58–56 Ma (Thanetian). These granitoids comprises granite, quartz monzonite and monzogranite with granular to mylonitic textures. They have high SiO2 abundances (59.1–78.6 wt%), high ratios of Sr/Y (50–490) and La/Yb ratios (19–237), along with high Ba (779–2466 ppm) and light rare earth element contents (e.g., La = 11–70 ppm). Saqqez-Takab granitoids have compositions that are similar to high-silica adakites, including low Mg- number (Mg# < 0.5), TiO2 (<0.93 wt%), Cr (<38 ppm) and Ni (<55 ppm). K2O/Na2O ratios of these granitoids are high (>0.7), resembling K-rich adakitic granitoids. Initial ratios of 87Sr/86Sr and εNd(t) vary from 0.7044 to 0.7053 and −2.8 to +2.0 respectively. These isotopic signatures differ from those of typical subducting slab-derived adakites (O-type adakite) with high positive εNd(t) and from collision-related adakites (C-type adakite) with negative εNd(t). The geochemical and isotopic characteristics of Saqqez-Takab granitoids are most consistent with magma being produced by amphibole-dominated fractionation of hydrous melts of subcontinental lithospheric mantle accompanied by minor assimilation of lower mafic calc alkaline continental crust. Distribution of similar-ages adakites in the NW Iran and E Pontides of Turkey suggests that these melts formed similarly. Upwelling of hot asthenosphere due to Neotethys slab rollback led to partial melting of lower continental crust calc alkaline mafic rocks and/or amphibole fractionation from mafic magma produced K-rich adakitic rocks in eastern Turkey and NW Iran during the late Paleocene.

A novel model for silicon recycling in the lithosphere: Evidence from the Central Asian Orogenic Belt

Global-scale cycling of silicon through the biosphere, atmosphere, and hydrosphere has received much attention although, silicon cycling in the Earth’s lithosphere remains poorly understood. As the products of internal heat and material exchange, igneous rocks preserve significant information of silicon migration through the lithosphere. Here we report silicon isotopic compositions of nine peraluminous granites from the Chinese Altai, which forms part of the Central Asian Orogenic Belt. These rocks are characterized by the heaviest δ30Si values (−0.13 ± 0.03‰ to +0.78 ± 0.05‰) compared to global granites, with a linear variation in the silicon isotopic values against silica content, with high silica-rich granites displaying more depleted isotopic compositions. In conjunction with the whole rock weakly negative ɛNd(t) and uniform δ26Mg values, as well as high δ18O values, we suggest that the δ30Si values of these granites were mainly inherited from the magma source, rather than produced by magmatic fractionation. In addition, the wide range of initial 87Sr/86Sr ratios and high Ba content of the samples suggest the role of aqueous fluids. The Chinese Altai is considered to have formed through accretion of volcanic arcs associated with subduction of the Paleo-Asian oceanic lithosphere. The magma derived through partial melting of metasomatic mantle scavenges the heavy 30Si isotopes derived through fluids released from oceanic sediments and transfers to the upper crust where partial melting of crustal sedimentary rocks occur. Mixing of these two melts generated the peraluminous granites. Our study offers a novel insight into a potentially important mechanism of silicon cycling in the lithosphere.

Different LED Light Intensities and 6-Benzyladenine Concentrations in Relation to Shoot Development, Leaf Architecture, and Photosynthetic Pigments of Gerbera jamesonii Bolus In Vitro

A mixture of red and blue light-emitting diodes (LEDs; at a ratio of 7:3, respectively) were used to analyze the effects of different photosynthetic photon flux densities (PPFDs) (40, 80, and 120 µmol m−2 s−1 hereafter known as LED 40, 80, and 120, respectively) on the micropropagation of Gerbera jamesonii Bolus shoots. The experiment also examined the effect of 6-benzyladenine (BA) in 1, 2.5, and 5 µM concentrations in the media. Biometrical observations and analyses of leaf morphometry and photosynthetic pigment content were conducted. Shoot multiplication increased with an increasing BA concentration. A PPFD of 80 µmol m−2 s−1 and 5 µM BA is suggested as efficient for shoot propagation and economically viable. LED 120 increased the leaf blade area and its width, and circularity and elongation ratios. The intensity of light did not affect the fresh weight, which increased at higher BA concentrations (2.5 and 5 μM). The dry weight content decreased with increasing cytokinin concentration; the greatest content was observed on media with 1 µM BA under PPFD 120 µmol m−2 s−1. LED 80 increased the photosynthetic pigments content in the leaves in comparison to the standard intensity of LED 40. Increased BA concentration raises the content of chlorophyll a.

Determination of rare earth elements in environmental samples with high concentrations of barium by quadrupole inductively coupled plasma mass spectrometry

This paper proposes a new method of sample preparation for the determination of rare earth elements (REE) by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) in challenging environmental samples with high Ba concentrations. The method consists in adding 10% (v/v) sulfuric acid to the wet sample digest, obtained after acid decomposition in an open system, in order to precipitate and separate BaSO4. The removal of BaO interference in Eu isotopes was efficient for Ba concentrations in solution higher than 0.1 mg L−1. The methodology was applied to asphalt pavement and the crushed stone used to produce it. Accuracy was assessed using two certified materials, NIST 688 Standard Reference Material of basalt rock and Geological Survey G2 granite, resulting in acceptable recoveries. Additionally, all samples were decomposed by fusion, and the concentrations of major elements and Eu were determined by inductively coupled plasma optical emission spectrometry (ICP OES). Eu results were in agreement with the proposed methodology, and limits of detection for REE varied from 0.003 mg L−1 (Lu) to 0.010 mg L−1 (Gd). The NASC normalized profiles of REE in the crushed stone showed a positive Eu anomaly, that was not observed in the asphalt sample. As well, the latter was enriched in heavy REE (Tb-Lu), suggesting a loss of carbonatite minerals, consequently to the weathering of the pavement.

Magmatic response to slab tearing and resultant crustal evolution during scissor-like oblique continental collision: Insights from Triassic mafic and felsic intrusions in the Qinling orogen, China

Characterization of the magmatic response to scissor-like oblique continental collision and of the associated geodynamic mechanisms and crustal evolution is crucial to understanding the formation of collisional orogens. This paper presents geochronological, elemental, and isotopic data of three Triassic mafic–felsic intrusions formed during scissor-like continental collision in the Qinling orogenic belt (QOB), China. The biotite pyroxenite, gabbro, quartz monzonite, and syenite of the Jiuzigou (JZG) mafic–felsic intrusive complex were emplaced at 233–231 Ma and have extremely high Ba and Sr contents, fractionated rare-earth elements, insignificant Eu anomalies, and enriched Sr-Nd isotopes. A negative relationship between εNd(t) values and SiO2 content suggests that the JZG complex was formed by assimilation and fractional crystallization (AFC) processes of enriched-mantle-derived melts. The Pangjiahe (PJH) and Laowangou (LWG) granite porphyries were emplaced at 224 Ma and 215 Ma, respectively, and are characterized by enriched large-ion lithophile elements, depleted high-field-strength elements, and enriched Sr and Nd isotopic compositions (0.70565–0.70648 and − 3.22 to −5.33 respectively), which indicate that these granite porphyries were sourced from mafic lower crust of the South Qinling terrane. The relatively high Mg numbers (45.8–49.4) might indicate mixing of crustal melt and minor mafic magma for the PJH granite porphyries. In contrast, the low Mg numbers (24.8–41.4) and obvious negative Eu anomalies of the LWG granite porphyries suggest an origin by fractional crystallization of crustal melts. The spatial–temporal distribution of the Triassic intrusions emplaced during the continental collision is proposed to have been produced by southeastward slab tearing in the QOB. Slab tearing may be a common geodynamic process during oblique collision generally. The origin and evolution of Triassic mafic and felsic intrusions in the QOB reveal that this oblique-collisional orogenic belt likely underwent a transition from net crustal growth to crustal reworking as collision progressed.

Barium concentration, phytoavailability, and risk assessment in soil-rice systems from an active barium mining region

Barium (Ba) is a non-essential and toxic element. In China, intensive Ba mining and Ba salt manufacturing have led to sharp increases in Ba in the environment, but little information is available regarding Ba concentrations in paddy soil and rice. The total concentrations and phytoavailability of Ba in paddy soils and paired rice samples collected from the world's largest Ba mine in Dahebian, Tianzhu, Guizhou Province, southwestern China, were investigated. Risk assessments of Ba exposure via rice consumption were also evaluated. The results indicated that extremely high Ba concentrations existed in paddy soils, ranging between 518 mg/kg and 65,760 mg/kg, which demonstrated severe Ba contamination, as expected. The concentrations of rice Ba varied from 0.10 to 3.5 mg/kg, and a significantly positive correlation (r = 0.51, p < 0.05) between rice Ba and water-extractable Ba was observed, suggesting that water, rather than weak acid (0.43 M CH3COOH), chelating agents (DTPA) or neutral salts (0.1 M NaNO3, 0.01 M CaCl2 or 1 M NH4OAc), is a suitable extractant for predicting the phytoavailable Ba in the studied soils. Risk assessments showed that residents experienced low Ba exposure via rice consumption when considered in isolation of other sources in this study area.

Water quality and solute sources in the Marsyangdi River system of Higher Himalayan range (West-Central Nepal)

Surface waters, cold and hot springs were collected in different catchments along the Marsyangdi basin, in the Himalayan Range of West-Central Nepal, during the post-monsoon season in 2017 and analyzed for major ions and trace elements, with the aim of assessing the sources of dissolved species and to contribute in watershed planning. The major element data indicate that surface waters coming from the Tethyan Himalayan Sequence (THS) range from the Ca-Mg-HCO3 to the Ca-Mg-HCO3-SO4 water-types and reflect a two-component mixing of waters from carbonate- and sulfate-bearing sources. The latter component is attributable to sulfide oxidation with minor silicate weathering. In the Greater Himalaya Sequence (GHS), alteration of pedogenetic carbonates formed in response to silicate weathering under a variable CO2 gas pressure dominates, yielding a Ca-HCO3 signature. The stability diagram in the K2O-Al2O3-SiO2-H2O system and the paired increases in Ca2+, Na+, K+ and silica indicate that degradation of silicate minerals through kaolinization and possibly plagioclase albitization reactions is the main process for hot groundwater. Cold and hot springs define a trend of increasing Li, SiO2 and Cl−, suggesting that lithium was leached from silica-rich sources, such as pegmatite dykes and sills occurring in host rocks, and concentrated into halite-bearing salt aquifers. In hot waters Sb, As and Tl exceed the EU and USEPA thresholds. Tl is usually incorporated into pyrite and correlates with Li indicating the occurrence of an ore-bearing zone possibly related to hydrothermal activity at the transition zone between THS and GHS, as suggested by the relatively high Ba, Ni, Cu, Sb, As and Mn contents. The obtained data on water quality have significant implications for people living along the Upper Marsyangdi River in the management of water resources, especially in terms of the enhancement of cold water aquaculture and hot water uses for recreation purposes and tourism.

Phlogopite in mantle xenoliths and kimberlite from the Grib pipe, Arkhangelsk province, Russia: Evidence for multi-stage mantle metasomatism and origin of phlogopite in kimberlite

We present petrography and mineral chemistry for both phlogopite, from mantle-derived xenoliths (garnet peridotite, eclogite and clinopyroxene–phlogopite rocks) and for megacryst, macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle (SCLM) and the origin of phlogopite in kimberlite. Based on the analysed xenoliths, phlogopite is characterized by several generations. The first generation (Phl1) occurs as coarse, discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene–phlogopite xenoliths. The second phlogopite generation (Phl2) occurs as rims and outer zones that surround the Phl1 grains and as fine flakes within kimberlite-related veinlets filled with carbonate, serpentine, chlorite and spinel. In garnet peridotite xenoliths, phlogopite occurs as overgrowths surrounding garnet porphyroblasts, within which phlogopite is associated with Cr-spinel and minor carbonate. In eclogite xenoliths, phlogopite occasionally associates with carbonate bearing veinlet networks. Phlogopite, from the kimberlite, occurs as megacrysts, macrocrysts, microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts. Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains, which indicates that they are the disintegrated fragments of previously larger grains.Phl1, within the garnet peridotite and clinopyroxene–phlogopite xenoliths, is characterised by low Ti and Cr contents (TiO2 < 1 wt.%, Cr2O3 < 1 wt.% and Mg# = 100 × Mg/(Mg + Fe) > 92) typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences. They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene–phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas. One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H2O. Rb–Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma. Compared with peridotite xenoliths, eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr2O3 despite a wider range of TiO2 concentrations. The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite. Phl2 has high Ti and Cr concentrations (TiO2 > 2 wt.%, Cr2O3 > 1 wt.% and Mg# = 100 × Mg/(Mg + Fe) < 92) and compositionally overlaps with phlogopite from polymict breccia xenoliths that occur in global kimberlite formations. These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phl1 grains or crystallized directly from stalled batches of kimberlitic magmas. Megacrysts, most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths. Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts. Based on the results of this study, we propose a schematic model of SCLM metasomatism involving phlogopite crystallization, megacryst formation, and genesis of kimberlite magmas as recorded by the Grib pipe.

Elevated Barium concentrations in rain water from east-coast of India: role of regional lithology

Alkaline earth metals act as dominating acid-neutralizing species in atmosphere and hence, regulate the rain water chemistry significantly. In this contribution, concentrations of these metals (Mg, Ca, Sr and Ba) and other major ions in rain water samples, collected during south-west monsoon of year 2017, from a coastal location (Berhampur) in eastern part of India have been analyzed to trace their provenances and controlling factors. The chemical compositions of rain water reveal oceanic and continental supply of Mg and Sr to the site, whereas Ca and Ba are pre-dominantly supplied through continental sources. The dominancy of continental fluxes at this coastal site is mainly due to particulate fluxes from regional lithologies and favorable wind pattern for long-range transport from south-western/western directions. An inverse model involving chemical mass balance between rain water composition and its possible sources have been adopted in this study to quantify the source(s) contributions. These model results show that the continental Mg is mainly derived from long-range transport of mafic minerals from Deccan Traps (40 ± 21%) with sub-ordinate contribution (15 ± 6%) from regional lithologies. On average, about 70% of rain water Ca at Berhampur is derived from carbonates, whereas most of the Ba (~95%) is supplied from regional silicates (charnockites and khondalites). Owing to faster dissolution kinetics of these silicates with higher Ba content, the silicates contribute most of the rain water Ba concentration over this region. The median Ba content (29 nM) at this location is systematically higher than available literature Ba data for rain water worldwide (1-22 nM). The observed higher concentrations of Ba, a micronutrient, in rain water emphasize important role of regional lithology in the biogeochemical cycling of nutrients over the region via wet deposition.

Sediment contribution in post-collisional high Ba-Sr magmatism: Evidence from the Xijing pluton in the Alxa block, NW China

High Ba-Sr granitoids occur in a number of tectonic settings, and variable petrogenetic models have been proposed. Those from post-collisional settings are rarely studied and are the focus of this study. Zircon U-Pb geochronology and whole-rock elemental and Sr-Nd-Hf isotopic data are presented for a suite of high Ba-Sr granitoids from the southern margin of the Alxa block, NW China. U-Pb zircon dating shows that the Xijing high Ba-Sr granitoids were emplaced in two periods at ~440 Ma and ~410 Ma, and they are characterized by elevated Ba and Sr contents. The older ~440 Ma high Ba-Sr granitoids range from monzodiorite to quartz monzonite, and the younger ~410 Ma high Ba-Sr granites tend to be more evolved. Both suites have similar enriched Sr-Nd-Hf isotopic ratios, low Ba/Th and Sr/Th ratios, and high Th contents and Th/Ce ratios indicative of a sediment contribution. This is potentially linked to previous subduction of the North Qilian ocean slab. Major and trace element calculations suggest that the older ~440 Ma granitoids experienced up to ~60% fractionation at 4–6 kbar with a crystallizing assemblage dominated by amphibole and plagioclase. The younger ~410 Ma granites could in turn have been formed by a further 80% fractional crystallization at lower pressures (1–2 kbar). Trace element and Sr-Nd isotopic modeling suggest incorporation of ~5% slab-derived sediment into mantle magma source of these high Ba-Sr granitoids. We note that post-collisional granitoids with high Ba and Sr characteristics may also reflect a sediment contribution in their source region, and this may be a key aspect of why such granites plot in the field of post-collisional granites in the Rb vs Y + Nb diagram. Some sanukitoids with high Ba and Sr contents in the late Archean also appear to reflect sediment subduction and they hence may represent early stages of crustal recycling.

Barium as doping element tuning both toxicity and optoelectric properties of lead-based halide perovskites

Organic-inorganic halide perovskites &lt;i&gt;ABX&lt;/i&gt;&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;A&lt;/i&gt; = CH&lt;sub&gt;3&lt;/sub&gt;NH&lt;sub&gt;3&lt;/sub&gt;, HC(NH&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;; &lt;i&gt;B&lt;/i&gt; = Pb; &lt;i&gt;X&lt;/i&gt; = Cl, Br, I) have recently attracted increasing attention due to their advanced optoelectronic properties. However, the poor stability and toxicity of organic lead halogen perovskites are still a major challenge for deploying the outdoor solar cells. Element substitution is a simple and effective strategy to solve these problems. For example, the substitution of the I ions with Cl and Br has been regarded as a reliable method to improve the device stability. &lt;i&gt;A&lt;/i&gt;-site engineering, i.e., replacing organic ions with inorganic cations (such as Cs&lt;sup&gt;+&lt;/sup&gt;, Rb&lt;sup&gt;+&lt;/sup&gt;), has also been reported. The &lt;i&gt;B&lt;/i&gt;-site alloying approach has been demonstrated with Zn, Sr, Sn, etc. Inorganic halide perovskites can be synthesized by the low-cost solution spin-coating method and have similar optoelectronic properties and improved stability to their organic counterparts. Here in this paper, we report a comprehensive study of the alloyed perovskite CsPb&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ba&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;&lt;i&gt;X&lt;/i&gt;&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;X&lt;/i&gt; = Cl, Br, I) by combining the disorder alloy structure search method with first-principles energy calculations. We find that it is not easy to dope barium into the perovskite lattice when Ba concentration is low and the stable disordered solid solution can exist in the high Ba concentration case. Carrier effective mass and bandgap increase with the increase of Ba concentration and the bandgap change range is wide, owing to the difference in both electronegativity and ionic radius between Pb and Ba. After inducing Ba into CsPb&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ba&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;&lt;i&gt;X&lt;/i&gt;&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;X&lt;/i&gt; = Cl, Br, I), the higher electron concentration on the I sites also enhances the Coulomb interaction of the Pb—I bonds. Moreover, the electrons and holes tend to be located on Pb sites, and this may give rise to the formation of local potential wells, which would further induce the large lattice deformation to accommodate the self-trapped excitons. Especially, CsPbI&lt;sub&gt;3&lt;/sub&gt;-&lt;i&gt;Pnma&lt;/i&gt; perovskite is metastable in the ambient environment with a suitable photon absorption threshold. The CsPb&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ba&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;I&lt;sub&gt;3&lt;/sub&gt; can be used as a capping layer on CsPbI&lt;sub&gt;3&lt;/sub&gt; in solar cells, thereby significantly improving the power conversion efficiency and long-term stability. Overall, the alloyed perovskite CsPb&lt;sub&gt;1–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ba&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;&lt;i&gt;X&lt;/i&gt;&lt;sub&gt;3&lt;/sub&gt; (&lt;i&gt;X&lt;/i&gt; = Cl, Br, I) with high Ba concentration can be stable and less-toxic, and they can be used in short wave light-emitting diodes, radiation detectors or other fields because of their large bandgaps (&gt; 2.8 eV).

Compositional and Thermodynamic Variability in a Stratified Magma Chamber: Evidence from the Green Tuff Ignimbrite (Pantelleria, Italy)

The Green Tuff Ignimbrite, Pantelleria, is compositionally zoned from pantellerite at the base to comenditic trachyte at the top, the variation apparently representing an inverted vertical zonation in the pre-eruptive reservoir. The main phenocryst assemblages are alkali feldspar + olivine + clinopyroxene + ilmenite + apatite in the trachytes and alkali feldspar + aenigmatite + clinopyroxene ± quartz in the rhyolites. Thermodynamic modelling indicates that the temperature range was ∼900–700°C, fO2 FMQ –1·5 to FMQ –0·5 (where FMQ is fayalite–magnetite–quartz buffer) and aSiO2 (relative to quartz saturation) 0·74–1·00. Melt water contents ranged from ∼1 wt % in the trachytes to ∼4 wt % in the pantellerites. Matrix glass analyses in the more evolved rocks are highly variable, showing that compositional layers in the upper parts of the reservoir, formed by fractional crystallization, were mixed during eruption, the proportion of rhyolitic to trachytic melts increasing towards the top of the reservoir. Some areas of glass have low Al2O3 contents (5·16–5·46 wt %) and high FeO* contents (9·66–10·02 wt %), making them the most evolved melts yet reported from Pantelleria. The new glass data reveal how whole-rock analyses do not truly reflect the complete range of melt compositions in the pre-eruptive reservoir. The trachytes contain >40% modal phenocrysts, which with relatively high Ba contents and positive Eu anomalies are considered to have originated in a feldspar-accumulitic layer. Phenocrysts in the trachytes are commonly heavily resorbed, inferred to be a result of heating by influxes of intermediate composition magma, which, however, were not erupted. It is argued that magmas of intermediate composition were present in the Green Tuff reservoir but were efficiently trapped in a crystal-rich layer below the Green Tuff magmas, which was eventually erupted during a resurgent phase as the Montagna Grande Trachyte.

The Neoproterozoic volcanic complex of the Boumalne inlier (Saghro massif, Eastern Anti-Atlas; Morocco): petrological and geochemical characteristics

Neoproterozoic volcanic series are exposed in the northern edge of the Saghro massif (Eastern Anti-Atlas, Morocco). Four volcanic rock types (basalt, andesite, dacite, and rhyolite) were distinguished in the Boumalne inlier within the so-called Saghro volcanic sequences based on petrographic and geochemical observations. Boumalne volcanic rocks contain high Al2O3, Fe2O3, Ba, Sr, Zr, Rb, and Nb contents, including calc-alkaline affinity in composition. Boumalne volcanic rocks are similar to other lower-Neoproterozoic volcanic rocks such Agouiniy formation in Sirwa inlier and in other parts of Bou-Azzer inlier. Indeed, they indicate an active subduction signature. The geochemical data show a LREE enrichment compared to HREE. The fractional crystallization has played a major role during the evolution of the magma. The less-siliceous dacitic rocks could have been formed after a low degree of partial melting of mafic parental magma source, whereas the rich-siliceous rhyolite may have been derived from dacitic magma source by a higher degree of fractional crystallization.