Basaltic Rocks Research Articles

The role of geochemical and coal petrographic analyses to determine the depositional sets of Visean coal and shale sequence in Um Thora-Abu Hish area, Central Sinai, Egypt

The Visean time at the Sinai Peninsula is characterized by the deposition of two conformable formations of a siliciclastic (Abu-Thora) resting upon a calcareous (Um-Bogma). The Abu-Thora Formation (Fm) is informally divided into three rock units that comprise a lower and upper sandstone sandwiched with a middle coal and shale sequence. A combination of paleoenvironmental indices and ratios from petrographic and geochemical analyses of the middle sequence succeed to build up the depositional paleoenvironment and may apply to any other coal and shale sequence, especially in coal mine regions. Geochemical analysis reveals that the studied shale strata are not homogenous and can be subdivided into four units from the base to the top. The lower shale unit at the base is 4m in thickness and composed of kaolinite-rich shale (10–77%; nacrite mineral). The second is the middle shale unit of 5.10m in thickness composed of Fe-shale (Fe2O3; 2.04–16.45 wt%). The third is the coal unit of 0.55m in thickness comprising coal seam, and the fourth is the upper shale unit of 6m in thickness composed of wacke (SiO2; 71.63–72.83 wt%). X-ray diffraction (XRD), x-ray fluorescence (XRF) plus mineralogical analyses are applied on the first, second, and fourth units of almost pure shale, whilst the third unit of almost pure coal is subjected to a petrographic analysis instead to illustrate the depositional site and type of vegetation where coal was formed. The palaeoclimatology based on parameters of CIW, C-value, Rb/Sr, and Sr/Cu refers to the deposition of shale initiated at a warm-humid and then to a hot semi-arid climate. The precursor rock of the studied shale is a basaltic and intermediate igneous rock. The shale is of mature components subjected to intense weathering processes based on CIA and ICV of 91.71 and 0.34, respectively. Furthermore, discriminant functions F-1 and F-2 reveal the shale components came also from quartzose sediments that promoted a multi-source origin that was gathered from both preexisting mafic and sedimentary provenances. The accumulation and deposition took place at a marine anoxic shale-carbonate of the active continental margin and oceanic island arc tectonic setting. Maceral composition of the coal unit reveals a depositional setting of a coal-forming mire system that occurred at a paralic aquatic margin setting involving a dominated reed herbaceous vegetation in a hydrological water-logged of the limnic marsh.

Petrology and geochemistry of Plio-Quaternary high-Nb basalts from Shahr-e-Babak area:Insights into post-collision magmatic processes in the Kerman Cenozoic Magmatic Arc

Post-collision Pliocene-Quaternary basaltic rocks outcrop in the Kerman Cenozoic Magmatic Arc (KCMA) to the northwest and east of Shahr-e-Babak city. These porphyritic and vesicular basaltic rocks are composed essentially of clinopyroxene, olivine, and plagioclase. These basalts display alkaline affinity and negative Ta, Zr, Rb anomaly, but slightly negative Nb anomaly, relative to elements with similar compatibility, and positive Ba, K, Sr anomaly, suggesting their magma source related to subduction-accretion with implication of subducted slab derived components to the source. In the primitive mantle and chondrite normalized diagrams, these rocks show trace elements (except depletion in Nb, Ta) and Rare Earth Element (REE) patterns similar to the Ocean Island Basalts (OIB) and share trace and major element characteristics similar to High-Nb Basalts (HNBs). Geochemical analyses for major and trace elements suggest that the Shahr-e-Babak HNBs have undergone insignificant crustal contamination and minor olivine + Fe-Ti oxide ±clinopyroxene fractional crystallization. These HNBs derived from a partial melting (~5%) of garnet-peridotite mantle wedge, which have already metasomatized by overlying sediments, fluids, and adakitic (slab-derived) melts as major metasomatic agents in post-collision setting in the KCMA. We conclude that asthenospheric upwelling arising from slab break-off followed by the roll-back of subducting Neotethys slab also triggered metasomatized peridotite mantle wedge and caused its partial melting in the subduction zone.

40Ar/39Ar Geochronology, Geochemistry and Petrogenesis of the Volcanic Rocks in the Jiangling Basin, China

In this study, 40Ar/39Ar geochronology and major and trace element data were presented for Paleogene basaltic rocks from the Jiangling Basin, China. The volcanic rocks erupted at ca. 53.19–60.78 Ma and belonged to the sub alkaline series. These basaltic rocks are generally characterized by enrichment in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs) ((La/Yb)cn = 6.14–11.72) and lack of Eu anomalies (Eu/Eu* = 0.98–1.09), similar to ocean island basalts. The geochemical signatures of these rocks are similar to hotspot-related Paleogene volcanic rocks in the North China Block and late Cenozoic volcanic rocks in Southeast China. The Cenozoic lithospheric mantle, as well as the Mesozoic basalts that are beneath the northern Yangtze Blocks, might be inherited from the Mesozoic lithospheric mantle. The basaltic rocks from the Jiangling Basin in the northern Yangtze Block were generated from the partial melting of EMII (enrichedmantleII)-like lithospheric mantle due to the intracontinental extension.

Provenance Response to Rifting and Separation at the Jan Mayen Microcontinent Margin

The Eocene-Miocene successions recovered at DSDP sites on the Jan Mayen Ridge (NE Atlantic) and on the adjacent East Greenland margin provide a sedimentary record of the rifting and separation of the Jan Mayen Microcontinent from East Greenland. A combination of palynology, conventional heavy mineral analysis, single-grain major and trace element geochemistry and radiometric dating of amphibole and zircon has revealed a major change in sediment provenance took place at the Early/Late Oligocene boundary corresponding to a prominent seismic reflector termed JA. During the Eocene and Early Oligocene, lateral variations in provenance character indicate multiple, small-scale transport systems. Site 349 and Kap Brewster were predominantly supplied from magmatic sources (Kap Brewster having a stronger subalkaline signature compared with Site 349), whereas Site 346 received almost exclusively metasedimentary detritus. By contrast, Late Oligocene provenance characteristics are closely comparable at the two Jan Mayen sites, the most distinctive feature being the abundance of reworked Carboniferous, Jurassic, Cretaceous and Eocene palynomorphs. The Site 349 succession documents an evolution in the nature of the magmatic provenance component. Supply from evolved alkaline magmatic rocks, such as syenites, was important in the Middle Eocene and lower part of the Early Oligocene, but was superseded in the later Early Oligocene by mafic magmatic sources. In the latest Early Oligocene, the presence of evolved clinopyroxenes provides evidence for prolonged magmatic fractionation. Initial low degrees of partial melting led to generation of alkaline (syenitic) magmas. The extent of partial melting increased during the Early Oligocene, generating basaltic rocks with both subalkaline and alkaline compositions. Towards the end of the Early Oligocene, the amount of partial melting and magma supply rates decreased. In the Late Oligocene, there is no evidence for contemporaneous igneous activity, with scarce magmatic indicator minerals. The provenance change suggests that the hiatus at the Early/Late Oligocene boundary represents the initiation of the proto-Kolbeinsey Ridge and separation of the Jan Mayen Microcontinent from East Greenland.

Evolution of rare earth element and εNd compositions of Gulf of Mexico seawater during interaction with Mississippi River sediment

A closed-system batch reaction experiment was conducted for 270 days to evaluate the effects of interaction between Gulf of Mexico (GOM) seawater and Mississippi River sediments on the system’s dissolved rare earth elements (REE) concentrations and neodymium isotopic compositions (εNd). This study specifically focuses on geochemical reactions involving silicic sediments derived from weathering of the North American continent as they affect the REEs and εNd of seawater along continental margins, in contrast to previous studies that investigated the influence of basaltic rocks and sediments on REEs and εNd in the ocean. Our results show that the dissolution of labile phases of lithogenic Mississippi River sediments leads to an approximately 100-fold increase in dissolved REE concentrations within the first 33 days of the experiment. Secondary mineral precipitation appears to lower the REE concentrations between days 33 and 270 of the experiment, although seawater REE concentrations remain elevated compared to initial values. The two-way elemental transfer involving dissolution and precipitation results in a net increase by a factor of 24 ± 12 (mean ± 1σ) in the dissolved REE concentrations by the end of the experiment (i.e., day 270). The dissolved REE concentration maxima observed after 33 days of the experiment represent the mobilization of approximately 0.37 % of the REE content of the operationally defined “exchangeable” fraction of the riverine sediments. The εNd values of the reactive lithogenic components were −9.77 and −9.95, which are similar to the GOM value of −9.81 ± 0.36. Because of the similarity between εNd values, changes in the seawater Nd isotope value throughout the experiment were subtle (mean ± std, reacted seawater εNd of −9.87 ± 0.17). The highest REE concentrations coincided with the most radiogenic εNd (-9.65 ± 0.23; day 33), which suggests that REE concentrations and εNd compositions of the GOM may be buffered by fluxes from sediments in the system. Our results are comparable to previous studies involving basaltic rocks and/or sediments of basaltic composition in that they demonstrate that silicic, river sediments are highly reactive in marine environments with regard to REE mobilization. The experimental results further suggest that “boundary exchange” plays an important role in influencing the εNd of seawater along continental margins dominated by large river systems, although the impacts of boundary exchange will be most profound where ambient seawater and river sediments have distinct Nd isotopic compositions (e.g., basaltic, or Precambrian shield material). Finally, our results indicate that the εNd value of GOM seawater is largely controlled by the lithogenic sediment delivered to the basin by the Mississippi River.

New insights into the source of gold in the Youjiang basin, SW China

AbstractMantle plume rich in gold is considered to be important for the formation of giant epigenetic gold deposits. The Youjiang basin, SW China, is the world’s second largest Carlin-type gold province, but the ultimate source of its gold remains enigmatic. In this study, we report that the Middle–Late Permian basaltic rocks in the basin are rich in native gold grains. These gold grains are scattered in the interstices of pyrite and marcasite and in the amorphous silica cavities. Mineralogy and S-Pb isotope geochemistry of the auriferous sulfides suggest that the gold was largely derived from the gold-rich Late Permian (ca. 260 Ma) Emeishan plume and was released to a near-surface volcanogenic massive sulfide (VMS) metallogenic system, where it accumulated. The native gold grains from the basalts may have been inherited by the younger (ca. 140 Ma) Carlin-type ores in the Youjiang basin, which are indicative of gold pre-enrichment in the basin. Our study highlights that golden plume upwelling could carry abundant gold into the upper crust, even into shallow-level metallogenic systems, and thus provides an alternative view on the source of gold in the Youjiang basin.

Pressure-temperature evolution of the Qingshuiquan mafic granulite: Implications for Proto-Tethys subduction in the East Kunlun orogenic belt, northern Tibetan Plateau

AbstractGranulite is in general a key metamorphic rock that can be used to understand the tectonic architecture and evolutionary history of an orogenic belt. The Qingshuiquan mafic granulite in the East Kunlun orogenic belt, northern Tibetan Plateau, occurs as tectonic boudins together with lower-grade ophiolitic mélange assemblages within an amphibolite-facies crystalline basement. In this study, we investigated the geochemistry, geochronology, mineralogy, and phase modeling of the Qingshuiquan mafic granulite. Based on mineralogical observations and microstructures, three mineral assemblage generations were distinguished: an assemblage found as inclusions within garnet and amphibole comprising clinopyroxene + plagioclase + amphibole + quartz + ilmenite + rutile (M1); an inferred peak assemblage of garnet + clinopyroxene + plagioclase + amphibole + quartz + ilmenite ± orthopyroxene (M2) in the matrix; and a retrograde assemblage of amphibole and biotite coronae (M3) around clinopyroxene or orthopyroxene. Thermobarometric calculations and phase equilibrium modeling constrained a clockwise pressure-temperature (P-T) path for the Qingshuiquan mafic granulite with peak T conditions of 830–860 °C at 8.0–9.5 kbar. Prior to the peak T conditions, a pressure maximum of ~11 kbar at ~800 °C was recorded by rutile, ilmenite, and clinopyroxene inclusions in garnet and amphibole. The retrograde path was defined by a decompression segment followed by final cooling. The whole-rock geochemical results indicated that the protolith of the Qingshuiquan mafic granulite was similar to present-day enriched mid-ocean-ridge basalt (E-MORB) displaying low total rare earth element (REE) concentrations and a slight enrichment of light REEs, as well as flat high field strength element patterns in the primitive mantle–normalized trace-element diagram. Geochronologic results revealed that the protolith crystallization age of the mafic granulite is 507 ± 3 Ma, and the timing of granulite-facies metamorphic overprint is 457–455 Ma. This evidence, taken together with results from previous studies, indicates that the protolith of the Qingshuiquan mafic granulite can be interpreted as basaltic rocks of Proto-Tethys oceanic crust that experienced a first high-pressure granulite-facies imprint followed by subsequent decompression and granulite-facies overprint at slightly lower P and slightly higher T. This granulitefacies metamorphism can be attributed to the subduction of Proto-Tethys oceanic crust, which also generated numerous contemporaneous subduction-related magmatic rocks in the East Kunlun orogenic belt.

Mechanism of olivine and glass alteration under experimental H2O-CO2 based supercritical gas: Application to modern and ancient Venus

Extreme conditions encountered in some geological contexts (deep serpentinization, interaction of Venus atmosphere with its basaltic surface, volcanic degassing) activate mechanisms and rates of silicate alteration that are poorly understood. In the present study, we investigate the mechanisms of mineral reactions in a natural geological system at high temperature, under conditions where the low solvation of cations by fluids likely promotes surface reactions such as surface diffusion and/or local recrystallization. We focus on vitreous glasses and olivine, reputed to be the most alterable phases in volcanic rocks, by reacting samples for one week in a Ni-based alloy experimental vessel. For the framework of our experimental study, we chose to apply the deep atmosphere conditions on Venus: 470 °C and 90 bar of reconstituted Venus-like gas. We also tested the effect of water (Early Venus or wet volcanic degassing) by adding water vapor at up to 320 bar total pressure. The mineral reactions affecting the samples were identified by a set of spectroscopic surface analyses of the altered samples: Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction in grazing incidence mode, X-ray Photo electron Spectroscopy and Raman spectroscopy.Samples of obsidian and tholeiitic glasses are found to be sensitive to a threshold water pressure, depending on glass composition, below which the reaction is limited to some elemental mobility in the glass (alkali enrichment, calcium loss) leading to a possibly more stable surface layer of tens to hundreds of microns. Above this threshold water pressure (ca. 50 bar H2O for the obsidian but >250 bar H2O for the tholeiitic glass), water promotes the depolymerization of the glass and the crystallization of stable minerals. This crystalline rim is less protective that the chemically modified layer.Olivine samples react differently depending on whether the olivine is isolated or included in a basaltic rock. In the latter case only, iron coatings are formed, which are identified as hematite, suggesting that this phase is not fed by olivine itself but rather by surface diffusion from neighboring Fe-rich phases. This supports the conclusions from experimental studies and orbital observations on the short-term visibility of unaltered olivine in Venus lava flows: such a coating is enhanced when Fe-bearing minerals are in the proximity of olivine. Under high water vapor pressure, Fe-bearing talc (and not serpentine) forms by a likely topotactic reaction that also incorporates silica from the gas. This talc layer may form a protective layer, implying that serpentinization of ultramafic rocks at high temperature may not be as prevalent as one might think in a gas-dominated system like the Early Venus surface.

Assessment of rock-hydrogen and rock-water interfacial tension in shale, evaporite and basaltic rocks

Underground hydrogen storage (UHS) is a distinguished method for reducing anthropogenic greenhouse gases (GHGs) and meeting global energy demand. One of the important parameters for subsurface storage of gas is rock-fluid interfacial tension (γrock-fluid) as gas injection and production rate, spread and flow in porous media, storage capacity, and containment security can be derived by this parameter. However, it is impossible to experimentally measure γrock-fluid. Moreover, γrock-fluid data for rock/H2/water systems in various shales, evaporite, and basaltic formations at geo-storage conditions are scarce in the literature. Thus, advancing and receding contact angles data were used to theoretically compute it at various pressures, temperatures, and shale-TOC by the combination of Young's equation and Neumann's equation of state. For all the rocks evaluated in this study, it was found that γrock-gas decreased with pressure, temperature, and shale-TOC. Also, γrock-water decreased with temperature but increased with shale-TOC, assuming that it remained constant with pressure. Thus, this work provides a deep understanding of wetting characteristics at various rock/H2/water systems, leading to a better investigation of hydrogen storage beneath shales, evaporite, and basaltic formations.

Mineral surface area accessibility and sensitivity constraints on carbon mineralization in basaltic aquifers

Estimating mineral reactive surface areas in geologic media remains one of the key challenges limiting the accuracy of reactive transport modeling (RTM) predictions of subsurface processes, particularly those controlling the fate of carbon dioxide (CO2) during geologic storage. Although there have been numerous attempts to combine imaging and experimental techniques to estimate mineral reactive surface area for use in RTM predictions of geologic CO2 storage, these techniques have yet to be adapted to basaltic reservoirs, which have pore structure, mineralogy, and chemical composition that is unique compared to their more often-studied sedimentary counterparts. Here, we address this issue by quantifying fluid-accessible mineral surface areas through image analysis of scanning electron microscope (SEM) backscatter electron images (high-resolution 500 nm/pixel) and Raman spectroscopic mapping of a basaltic rock sample from the Eastern Snake River Plain, Idaho. To evaluate whether the determined pore fluid-accessible mineral surface area accurately reflects reactive surface area, a micro-continuum scale RTM was developed and compared with a high-temperature, high-pressure flow-through CO2 mineralization experiment conducted on the characterized basalt. Importantly, simulations employing the image-derived pore fluid-accessible mineral surface areas match the experimental effluent chemistry well within uncertainties. These mineral surface areas were then used to parametrize a field-scale model representative of the Cascadia basin, Northeastern Pacific, to evaluate impacts of surface area variations on mineral carbonation. Simulations were carried out using variations in image-derived surface areas that cover one to two orders of magnitude increase and decrease in surface area, analogous to previously reported magnitudes of difference between total and reactive surface areas. Carbonation efficiency in terms of CO2 volume mineralized over the simulated period was tracked and compared. Simulations with surface area increased and decreased by two orders of magnitude show basalt carbonation efficiency that is three times faster and six times slower, respectively, than predictions with image-derived mineral surface area. These sensitivity analyses demonstrate that accurate quantification of mineral surface area is crucial for efforts to predict CO2 mineralization, and that efforts such as those employed here can dramatically reduce the uncertainty of field-scale predictions of basalt carbonation.

Petrogenetic implications of Fe–Mg substitution in clinopyroxene lattices of basaltic suites of Khandwa area, eastern Deccan volcanic province, Central India

Field investigations and lava flow mapping around Khandwa (21°49′ N:76°21′ E), Central India (within the eastern Deccan volcanic province) record three distinct lava flows which are in general, characterized by several structural zones, for example, Lower Vesicular Zone, Lower Colonnade Zone, Entablature Zone (EZ), Upper Colonnade Zone (UCZ), and Upper Vesicular Zone (UVZ). Different lava flows (often with chilled zones) in the field have been marked by discontinuous thin intertrappean beds. The occasional presence of chilled dyke and feeder dyke (both associated with Flow II) has also been noticed. The entire lava succession rests over coarse‐grained (cumulate) gabbroic (apparent) basement. Deduced clinopyroxene ordering clearly indicates that 100% initial ordering had been achieved for Flow II chilled zone, Flow II UCZ, Flow III UCZ, Flow III EZ, and cumulate gabbro. On the contrary, Flow II UCZ (97.35% initial ordering), feeder dyke (98.76% initial ordering), chilled dyke (99.82% initial ordering), and Flow I chilled zone (99.07% initial ordering) show initial clinopyroxene disordering (<100% ordering), which were later subjected to a gradual process to achieve ordering. Second‐order regression analyses clearly indicate that the progressive clinopyroxene ordering‐process is controlled by several differentiation parameters namely An% of coexisting plagioclase, lower thermometric values, and FeOt/MgO. In addition, roles of AlVI, Ti4+, and Fe3 were also suggested to influence the clinopyroxene ordering‐style. Based on Ti/6ox versus Al/6ox relation of clinopyroxene, it was deduced that cooling rate appreciably controls the clinopyroxene ordering‐behaviour. We contemplate that variation in clinopyroxene ordering‐pattern in basaltic rocks of Khandwa represents interplay of differentiation parameters and cooling rate of the ambient magma.

Characterization of basaltic rock aquifer parameters using hydraulic parameters, Theis’s method and aquifer test software in the hard rock area of Buchakewadi watershed Maharashtra, India

The twelve wells were selected to carry out the various test, duration of pumping (min), maximum draw drown (m), duration of recovery (min), residual drawdown, and aquifer type in the basaltic rock aquifer parameters of Buchakewadi watershed. The source and flow of groundwater are essential concerns in hydrological systems that concern both spatially and temporally components of groundwater discharge and water supply problems. The content and temperature of groundwater flowing through an aquifer might change depending on the aquifer environment. As a result, hydrodynamic analyses can provide valuable information about a region's subsurface geology. The present research attempts of aquifer variables such as transmissivity (T) and storativity (S) estimation are significant for groundwater resource development and evaluation. There are numerous approaches for calculating precise aquifer characteristics (i.e., hydrograph analysis, pumping test, etc.). A most frequent in situ analysis is a well-pumping test, which accurately measures the decline and rise of groundwater levels. During an aquifer pumping test, to characterize aquifer properties in an undiscovered location to forecast the rate of depletion of the groundwater table/potentiometric surface. The shallow, weathering subsurface water accessible above the Deccan traps in an unconfined state is insufficient to satisfy the ever-increasing pressure on water supplies. Maharashtra is similarly dominated by hard rocks, whose rainfall susceptibility is limited by weathering and primary porosity, as is their volume to store and convey water. Based on the hydraulic parameters and Theis method, results are optimized. Aquifer mapping and pumping test results can be more important for solving problems such as water scarcity, nonpolluting water, health issues, and source of fresh water on the earth surface. However, the characterization of aquifer parameters should be significant role in the scientific planning and engineering practices.

Petrogenetic evolution of Lichi volcanics from Arunachal Himalaya, Northeast India: Insights from geochemical modelling

The Lichi volcanic rocks crop out along the Main Boundary Thrust (MBT) of the Arunachal Himalaya, northeast India are comprised primarily of sub‐alkaline basalt (SiO2 ranges from 48.66 to 50.62 wt%), with minor trachy‐andesite (SiO2 ranges from 57% to 61.42 wt%). The distribution of incompatible trace elements, low concentrations of large‐ion lithophile elements, and REE behaviour suggests an enriched nature of the studied rocks and limited influence of the crustal contamination during their evolution. Linear distribution trends of major oxide, consistent patterns of trace elements, and REEs on primitive mantle‐ and chondrite‐normalized diagrams suggest the cogenetic nature of mafic basaltic rocks and intermediate trachy‐andesite. The variation in Ti/Y (256.00–469.95) and Zr/Y (7.65–36.96) ratios indicates that garnet was present in the source. The well‐defined geochemical trends on variation diagram and the sub‐parallel trends on the chondrite‐normalized REE patterns suggest that fractional crystallization processes have played a major role in the evolution of parental magma. Petrogenetic modelling implies that the sub‐alkaline basalts and intermediate rocks were derived from low‐degree partial melting (1%–5%) of a garnet bearing peridotite source. The melt further evolved by fractional crystallization. We conclude that the geochemical attributes of the Lichi volcanics of the Arunachal Himalaya imply their emplacement in a continental extensional regime and possibly resulted from the Cretaceous Kerguelen plume activities.

Sulfide Dissolution on the Nickel Isotopic Composition of Basaltic Rocks

AbstractGlobal basaltic rocks show large variations in nickel (Ni) isotopic compositions relative to peridotites. The origin of this difference remains unknown. We analyzed Ni isotopic compositions of mineral separates from seven Beiyan peridotite xenoliths and 16 nephelinites from eastern China. Spinel is isotopically heavier, and clinopyroxene is systemically lighter than coexisting olivine and orthopyroxene. An ionic model predicts that olivine, orthopyroxene, and spinel are in Ni isotopic equilibrium, whereas clinopyroxene of metasomatic origin is out of equilibrium. The nephelinites have higher Fe3+/ΣFe but lower δ60/58Ni values than the peridotites. Mantle silicate melting likely leads to enrichment of heavy Ni isotopes in melts, and, importantly, it cannot explain the negative correlation between δ60/58Ni and Fe3+/ΣFe of the nephelinites. Therefore, the light Ni isotopic signature requires the involvement of a low‐δ60/58Ni component. Sulfide is a minor Ni‐rich component in the mantle and is isotopically lighter than the silicates. The relative proportion of Ni from sulfides vs. that from silicates varies in mantle‐derived magmas, depending on the sulfur content at sulfide saturation and melting degree. Thus, low‐degree melts with high abundance of dissolved sulfides can be variably enriched in light Ni isotopes. We propose that enhanced sulfide dissolution at high oxygen fugacity is a key reason for light Ni isotopic compositions in the nephelinites. This sulfide dissolution model may also be responsible for producing the Ni isotopic variation in global mafic lithologies. When the highly oxidized, low‐degree melts react with the peridotitic region, they can impart light Ni isotopic signatures to mantle rocks.

CO2 storage potential of basaltic rocks, Mpumalanga: Implications for the Just Transition

South Africa is the largest CO2 emitter on the African continent. These emissions stem from a heavy reliance on coal as the primary energy fuel and contributor toward socio-economic development. The South African government has targeted reducing CO2 emissions by more than half in the next 10 years. To meet climate change mitigation scenarios, while alleviating continued emissions, South Africa will look to technologies such as carbon capture, utilisation and storage. Initial assessments of South Africa’s potential for CO2 storage have focused on deep saline aquifers within volcano-sedimentary sequences along the near and offshore regions. Sustaining the Just Transition will, however, require additional storage capacity. In this study, we make an initial assessment of possible CO2 storage in basaltic sequences of the Ventersdorp Supergroup. Geological and mineralogical information was ascertained from borehole data. The geological information suggests that the subsurface extent of the Ventersdorp Supergroup is at least 80 000 km2 larger than previously mapped, extending beneath major point-source CO2 emitters and active coalfields. Furthermore, petrographic analyses suggest pore space of up to ca 15% with minimal alteration, and preservation of mafic silicate minerals that would enable reactive carbonation of injected CO2. Notable metasomatic and hydrothermal alteration is confined to significant contact horizons, such as the lowermost Ventersdorp Contact Reef. These results suggest that basaltic sequences may exponentially increase South Africa’s CO2 sequestration storage capacity and may have a significant impact on the country’s Just Transition. Significance: This study shows that basaltic sequences may support the permanent storage of anthropogenic CO2 in South Africa, in particular, proximal to significant point-source CO2 emitters. South Africa has voluminous and widespread basaltic sequences, which, in combination, increase South Africa’s geological CO2 storage potential by several orders of magnitude. These storage reservoirs can have a direct impact in South Africa by enabling a sustainable Just Transition toward a low-carbon economy while meeting intended climate change mitigation scenarios.

Incipient Sympatric Speciation and Evolution of Soil Bacteria Revealed by Metagenomic and Structured Non-Coding RNAs Analysis.

Simple SummaryThe microevolutionary dynamics of soil bacteria under microclimatic differences are largely unexplored in contrast to our improving knowledge of their vast diversity. In this study, we performed a comparative metagenomic analysis of two sharply divergent rocks and soil types at the Evolution Plateau (EP) in eastern Upper Galilee, Israel. We have identified the significant differences in bacterial taxonomic diversity, functions, and patterns of RNA-based gene regulation between the bacteria from two different soil types. Furthermore, we have identified several species with a significant genetic divergence of the same species between the two soil types, highlighting the soil bacteria’s incipient sympatric speciation.Soil bacteria respond rapidly to changes in new environmental conditions. For adaptation to the new environment, they could mutate their genome, which impacts the alternation of the functional and regulatory landscape. Sometimes, these genetic and ecological changes may drive the bacterial evolution and sympatric speciation. Although sympatric speciation has been controversial since Darwin suggested it in 1859, there are several strong theoretical or empirical evidences to support it. Sympatric speciation associated with soil bacteria remains largely unexplored. Here, we provide potential evidence of sympatric speciation of soil bacteria by comparison of metagenomics from two sharply contrasting abutting divergence rock and soil types (Senonian chalk and its rendzina soil, and abutting Pleistocene basalt rock and basalt soil). We identified several bacterial species with significant genetic differences in the same species between the two soil types and ecologies. We show that the bacterial community composition has significantly diverged between the two soils; correspondingly, their functions were differentiated in order to adapt to the local ecological stresses. The ecologies, such as water availability and pH value, shaped the adaptation and speciation of soil bacteria revealed by the clear-cut genetic divergence. Furthermore, by a novel analysis scheme of riboswitches, we highlight significant differences in structured non-coding RNAs between the soil bacteria from two divergence soil types, which could be an important driver for functional adaptation. Our study provides new insight into the evolutionary divergence and incipient sympatric speciation of soil bacteria under microclimatic ecological differences.

Fluid processes in the early Earth and the growth of continents

Water is an essential ingredient in transforming primitive mantle-derived (mafic) rocks into buoyant (felsic) continental crust, thereby driving the irreversible differentiation of Earth's lithosphere. The occurrence in Archaean cratons of sodic granites of the tonalite–trondhjemite–granodiorite (TTG) series, high-MgO variolitic basalts, high-Mg diorites (sanukitoids) and diamonds with harzburgitic inclusion assemblages, all require the presence of hydrous fluids in Earth's deep crust and upper (lithospheric) mantle since at least the Paleoarchaean (3.6–3.2 billion years ago). However, despite its importance, where and how water was stored in Archaean crust, and how some water was transported into the upper mantle, are poorly understood. Here, we investigate Archaean crustal fluid budgets through calculated phase equilibria for three protolith compositions — a low-MgO mafic (basaltic) composition, a high-MgO (picritic) composition and an ultrahigh-MgO ultramafic (komatiitic) composition — that are representative of mafic to ultramafic magmatic rocks in Archaean greenstone belts. We show that the mode and stability of hydrous minerals, in particular chlorite, is positively correlated with protolith MgO content, such that high-MgO basalts can store up to twice the amount of crystal-bound H2O than low-MgO basalts. Importantly, ultrahigh-MgO rocks such as komatiite can store four times as much H2O, most of which is retained until temperatures exceeding 700°C. Warmer geotherms in the early Archaean favoured dehydration of hydrated high-MgO and ultramafic rocks in the deep crust, leading to hydration and/or fluid-fluxed melting of overlying basaltic rocks to produce ‘high-pressure’ TTG magmas. Burial of Archaean mafic–ultramafic crust along cooler geotherms resulted in dehydration of ultramafic material within the lithospheric mantle, providing the source of enriched Archaean basalt that was parental to large volumes of ancient TTG-dominated continental crust.

Late Permian rift-related volcanic rocks from the Zhongba Terrane, Southern Tibet: implications for the opening of the Neotethys

ABSTRACT The questions of how and when the Neotethys Ocean opened are crucial for understanding the evolution of the Tethys Realm and the break-up of Gondwana. However, the evolution of the Neotethys remains controversial. Herein, we report the zircon U–Pb ages, whole-rock major as well as trace elements, and Sr–Nd isotopic data for the basaltic volcanic rocks from the Zhongba Terrane in the western Yalung–Zangbo Suture Zone. The results demonstrate that the Saga basalts were extruded during the Late Permian (257–258 Ma). All samples are characterized based on the low SiO2 content (44.03–50.33 wt%) and belong to the high-K calc-alkaline series. Furthermore, they exhibit light rare earth element enrichment ((La/Yb)N = 12.7–26.7); slightly positive Eu anomaly(Eu/Eu* = 1.01–1.14); prominent Nb and Ta positive anomalies; slightly negative Zr, Hf, and Ti anomalies and exhibit high ratios of Ta/Hf (0.93–1.21), Zr/Y (8.68–10.63), and Nb/Zr (0.39–0.45). The (87Sr/86Sr)i ratio varied from 0.7050 to 0.7063, with relatively constant and depleted εNd(t) values ranging from 0.52 to 1.08. The rocks were probably sourced from a low-degree partial melting of the asthenospheric mantle in a rift environment and had undergone the process of fractional crystallization. These characteristics indicate that the Saga basalts differ from the rift-related magmatic rocks produced by the Panjal Traps. Consequently, combined with the recently reported detailed fieldwork, the Zhongba Terrane disintegrated from the northern margin of Gondwana during the Late Permian, promoting the opening of the Neotethys Ocean, which is most likely caused by the northward subduction of the Paleotethys Ocean.

A shift of mantle sources for the post-collisional lavas and tectonic links with synchronous deformation in the SE Tibetan Plateau

Strong post-collisional deformation and contemporaneous magmatic flare-ups during the Cenozoic indicate large-scale continental lithospheric modification in the southeastern (SE) Tibetan Plateau. However, the relationship between regional deformation and magmatism is poorly understood. In this paper, we report for the first time the presence of 32–17 Ma mafic rocks within the Ailaoshan-Red River shear zone (ARSZ) and provide new insights into the correlation between deformation and magmatism. Using 369 Cenozoic mafic and felsic rocks (this study and literature data) in and around the ARSZ, we document a continuous magmatic record that delineates a consecutive depletion of their mantle sources through time, which is correlated with the development of regional deformation. The spatial distributions, rock associations, and geochemical features of these rocks indicate a three-stage magmatic evolution in the SE Tibetan Plateau. During the earliest episode (40–32 Ma), the strong emplacement of both mafic and felsic rocks shows a planar-shaped geographic distribution. The second episode (32–17 Ma) is characteristic of voluminous mylonitized granites and minor basaltic rocks generally along the ARSZ. The latest episode (<17 Ma) magmatic rocks are sporadically exposed with dominant OIB-type basaltic rocks and minor A-type granites. From the earliest to the latest episodes, the mafic rocks exhibit progressive depletion in SrNd isotopic compositions, with initial Sr isotopic ratios and εNd(t) values from 0.70509 to 0.71151 and − 12.5 ~ −0.3 to 0.70313–0.70734 and − 3.9 ~ +8.1, respectively. These data, together with the covariations in the (Nb/La)PM and Zr/Nb ratios, signify a dramatic mantle-source shift from enriched to depleted through time for these Cenozoic mafic rocks. Mafic rocks from the earliest episode were generated from an enriched lithospheric mantle through convective thinning. In contrast, the OIB-type basalts from the latest episode were pure asthenospheric magma from decompression melting. Therefore, we propose an interdependent evolution between the shift of mantle sources and the development of synchronous deformation in and around the ARSZ. Our discovery of 32–17 Ma mafic rocks stands as the first direct evidence for the key role of the synchronous development of the lithospheric-scale ARSZ in the shift of mantle sources, asthenospheric melt transportation, and heating-induced crustal magma generation.

Investigation of hydrogeological conditions of a fractured shale aquifer in Yala Area (SE Nigeria) characterized by saline groundwater

Geological, hydrogeological and geophysical investigations were carried out in Yala Area (SE Nigeria) to delineate potential zones for future groundwater development. The area is underlain by Turonian fractured shale rock intruded by basaltic rocks and saline water. High lineament density (> 30 km−1) recorded in the north suggest high permeable zone, compared with low lineament density (< 10 km−1) in the south and east. Geophysical results reveal four types of aquifers: an upper weathered, fractured shale aquifer with mean resistivity and thickness in the range 27–40 Ω m and 20–28 m and a lower fractured shale aquifer with mean resistivity in the range 28.5 to 36.0 Ω m and unresolved thickness; fractured saline shale aquifer with mean resistivity and thickness of 21 Ω m and 50 m; fractured silty shale aquifer with mean resistivity and thickness of 54.4 Ω m and 10 m and basaltic intrusive fractured shale aquifer with mean resistivity and thickness of 135.6 Ω m and 6 m. A broad range of aquifer parameters were obtained from resistivity data and pumping test. Groundwater quality on the mean indicated alkaline and good fresh water for drinking and irrigation use with minor level of salinization. Concentration of dissolved ions in the area are enhanced through weathering and ion exchange. On the basis of these data, the potential zones for groundwater harnessing have been delineated in Yala Area.