Geochemistry of ultramafic–alkaline rocks of the Ziminsky complex (on the example of the Bol’shetagninsky and Beloziminsky massifs) (Eastern Sayan)

The paper compares the elemental composition of alkaline silicate rocks of the Bol’shetagninsky and Beloziminsky massifs, which are part of the Ziminsky complex of ultrabasic rocks and carbonatites. The rocks of the Bol’shetagninsky massif belong to the potassium series and are distinguished by increased concentrations of large ionic lithophilic elements; in the rocks of the Beloziminsky massif, the rocks of the sodium series predominate and the contents of highly charged elements are increased. Judging by the lack of correlation between the highly charged elements in alkaline and subalkaline rocks of the Bol’shetagninsky massif, their formation, in contrast to the rocks of the Beloziminsky massif, is not associated with the process of fractional crystallization.

Genome and Transcriptome Sequencing of Novel Pseudomonas sp. NLX-4 Strain Involved in Bio-Restoration of Over Exploited Mining Sites

Microbial weathering processes can significantly promote soil properties and enhance rock to soil ratio. Some soil-inhabiting bacteria exhibit efficient rock-dissolution abilities by releasing organic acids and other chemical elements from the silicate rocks. However, our understanding of the molecular mechanisms involved during bacterial rock-dissolution is still limited. In this study, we performed silicate rock-dissolution experiments on a novel Pseudomonas sp. NLX-4 strain isolated from an over-exploited mining site. The results revealed that Pseudomonas sp. NLX-4 strain efficiently accelerates the dissolution of silicate rocks by secreting amino acids, exopolysaccharides, and organic acids. Through employing genome and transcriptome sequencing (RNA-seq), we identified the major regulatory genes. Specifically, fifteen differentially expressed genes (DEGs) encoding for siderophore transport, EPS and amino acids synthesis, organic acids metabolism, and bacterial resistance to adverse environmental conditions were highly up-regulated in silicate rock cultures of NLX-4 strain. Our study proposes a novel bacterial based approach for improving the ecological restoration of over-exploited rock mining-sites.

Thermodynamic modelling of carbonate-silicate rocks from the Sakar unit, Sakar-Strandzha zone, SE Bulgaria

The P-T evolution of carbonate-bearing metasedimentary rocks from the Sakar unit (Sakar-Strandzha Zone, SE Bulgaria) has been obtained using Perple_X modelling and conventional geothermometry. The metamorphic conditions vary from greenschist facies (250–350 °C/2–4 kbar) in the Klokotnitsa village area to amphibolite facies (550–650 °C/4.5–6.5 kbar) in the Topolovgrad town area, confirming a general increase of the metamorphic grade at east-west direction.

Hydrochemical Characteristics and Cause Analysis of Natural Water in the Southeast of Qinghai-Tibet Plateau

This study investigated the hydrochemical characteristics and formation mechanism of natural water in the southeastern Qinghai-Tibet Plateau. To this end, 19 groundwater samples were collected, tested, and analyzed using various methods, such as mathematical statistics, a Piper diagram, correlation analysis, Gibbs plots, and an ion ratio analysis. The results show that the dominant anions are HCO3− and SO42−, and the dominant cations are Ca2+ and Mg2+, which accounted for 98.50% and 85.94% of the total amount of anions and cations, respectively. The samples were weakly alkaline water, where the TDS (total dissolved solids) ranged from 28.00 mg/L to 242.00 mg/L, with an average value of 129.10 mg/L. The hydrochemical types were mainly Ca·Mg-HCO3·SO4—accounting for 42.10%. The hydrochemical evolution process was found to be mainly controlled by the weathering and dissolution of carbonate and silicate rocks. The main sources of Na+ and K+ are rock salt and silicate rocks, and those of Ca2+, Mg2+, HCO3−, and SO42− are from the dissolution of dolomite, calcite, gypsum, and other calcium and magnesium bearing minerals. In addition, atmospheric precipitation serves as a replenishment source of natural water in the region, and the recharge is affected by evaporation.

The Maz Metasedimentary Series (Western Sierras Pampeanas, Argentina). A relict basin of the Columbia supercontinent?

The Maz Metasedimentary Series is part of the Maz Complex that crops out in the sierras of Maz and Espinal (Western Sierras Pampeanas) and in the Sierra de Umango (Andean Frontal Cordillera), northwestern Argentina. The Maz Complex is found within a thrust stack of Silurian age, which later underwent open folding. The Maz Metasedimentary Series mainly consists of medium-grade garnet–staurolite–kyanite–sillimanite schists and quartzites, with minor amounts of marble and calc-silicate rocks. Transposed metadacite dykes have been recognized along with amphibolites, metagabbros, metadiorites and orthogneisses. Schist, quartzite and metadacite samples were analysed for SHRIMP U–Pb zircon dating. The Maz Metasedimentary Series is polymetamorphic and records probably three metamorphic events during the Grenvillian orogeny, at c. 1235, 1155 and 1035 Ma, and a younger metamorphism at c. 440–420 Ma resulting from reactivation during the Famatinian orogeny. The sedimentary protoliths were deposited between 1.86 and 1.33–1.26 Ga (the age of the Andean-type Grenvillian magmatism recorded in the Maz Complex), and probably before 1.75 Ga. The main source areas correspond to Palaeoproterozoic and, to a lesser magnitude, Meso-Neoarchaean rocks. The probable depositional age and the detrital zircon age pattern suggest that the Maz Metasedimentary Series was laid down in a basin of the Columbia supercontinent, mainly accreted between 2.1 and 1.8 Ga. The sedimentary sources were diverse, and we hypothesize that deposition took place before Columbia broke up. The Rio Apa block, and the Río de la Plata, Amazonia and proto-Kalahari cratons, which have nearby locations in the palaeogeographic reconstructions, were probably the main blocks that supplied sediments to this basin.

Testing Landscape, Climate and Lithology Impact on Carbon, Major and Trace Elements of the Lena River and Its Tributaries during a Spring Flood Period

Transport of carbon, major and trace elements by rivers in permafrost-affected regions is one of the key factors in circumpolar aquatic ecosystem response to climate warming and permafrost thaw. A snap-shot study of major and trace element concentration in the Lena River basin during the peak of spring flood revealed a specific group of solutes according to their spatial pattern across the river main stem and tributaries and allowed the establishment of a link to certain landscape parameters. We demonstrate a systematic decrease of labile major and trace anion, alkali and alkaline-earth metal concentration downstream of the main stem of the Lena River, linked to change in dominant rocks from carbonate to silicate, and a northward decreasing influence of the groundwater. In contrast, dissolved organic carbon (DOC) and a number of low-soluble elements exhibited an increase in concentration from the SW to the NE part of the river. We tentatively link this to an increase in soil organic carbon stock and silicate rocks in the Lena River watershed in this direction. Among all the landscape parameters, the proportion of sporadic permafrost on the watershed strongly influenced concentrations of soluble highly mobile elements (Cl, B, DIC, Li, Na, K, Mg, Ca, Sr, Mo, As and U). Another important factor of element concentration control in the Lena River tributaries was the coverage of the watershed by light (for B, Cl, Na, K, U) and deciduous (for Fe, Ni, Zn, Ge, Rb, Zr, La, Th) needle-leaf forest (pine and larch). Our results also suggest a DOC-enhanced transport of low-soluble trace elements in the NW part of the basin. This part of the basin is dominated by silicate rocks and continuous permafrost, as compared to the carbonate rock-dominated and groundwater-affected SW part of the Lena River basin. Overall, the impact of rock lithology and permafrost on major and trace solutes of the Lena River basin during the peak of spring flood was mostly detected at the scale of the main stem. Such an impact for tributaries was much less pronounced, because of the dominance of surface flow and lower hydrological connectivity with deep groundwater in the latter. Future changes in the river water chemistry linked to climate warming and permafrost thaw at the scale of the whole river basin are likely to stem from changes in the spatial pattern of dominant vegetation as well as the permafrost regime. We argue that comparable studies of large, permafrost-affected rivers during contrasting seasons, including winter baseflow, should allow efficient prediction of future changes in riverine ‘inorganic’ hydrochemistry induced by permafrost thaw.

The Garies Wollastonite Deposit, Namaqualand, South Africa: High-Temperature Metamorphism of a Low-δ18O Skarn?

ABSTRACT The Garies wollastonite deposit is located in the Bushmanland terrane of the Namaqualand Metamorphic Province and is part of a discontinuous calc-silicate unit bounded by granulite facies gneiss that experienced peak metamorphic temperatures above 800 °C. In bulk, the deposit is dominated by wollastonite, but varied proportions of garnet, diopside, quartz, calcite, and vesuvianite are also present. Mineral chemistry variations across the deposit are minor, and the absence of inclusions indicates textural and chemical equilibrium. The wollastonite-bearing rocks have unusually low mineral δ18O values: –0.6 to +2.2‰ for garnet, –0.2 to +2. 6‰ for clinopyroxene, and –0.2 to +0.4‰ for wollastonite. Calcite δ18O values range from 6.8 to 11. 8‰ and δ13C values from –6.4 to –3.2‰. Calcite δ18O values are unusually low for calc-silicate rocks, but Δcalcite-garnet values from 3 to 12‰ indicate O-isotope disequilibrium between calcite and the silicate minerals. Garnet-biotite metapelitic and diopside gneisses have unexpectedly low δ18O values (<7‰). The approach to O-isotope equilibrium displayed by coexisting silicate minerals, and low mineral δ18O values in calc-silicate and metapelite and metapsammite gneisses, is consistent with low δ18O values being acquired before peak metamorphism. Low δ18O values in the minerals of the calc-silicate rocks require interaction with external fluid at high water/rock ratio. We suggest that the deposit represents a metamorphosed skarn that developed at the contact between the original carbonate rocks and intruding felsic magmas.