Mafic Minerals Research Articles

A Review of the Mineral Chemistry and Crystallization Conditions of Ediacaran–Cambrian A-Type Granites in the Central Subprovince of the Borborema Province, Northeastern Brazil

Ediacaran–Cambrian magmatism in the Central Subprovince (Borborema Province, NE Brazil) generated abundant A-type granites. This study reviews published whole-rock and mineral chemistry data from thirteen Ediacaran–Cambrian A-type intrusions and a related dike swarm. It also presents new mineral chemistry and whole-rock data for one of these intrusions, along with zircon trace element data for five of the intrusions. Geochronological data from the literature indicate the formation of these A-type intrusions during a 55 Myr interval (580–525 Ma), succeeding the post-collisional high-K magmatism in the region at c. 590–580 Ma. The studied plutons intruded Paleoproterozoic basement gneisses or Neoproterozoic supracrustal rocks. They are ferroan, metaluminous to peraluminous and mostly alkalic–calcic. The crystallization parameters show pressure estimates mainly from 4 to 7 kbar, corresponding to crustal depths of 12 to 21 km, and temperatures ranging from 1160 to 650 °C in granitoids containing mafic enclaves, and from 990 to 680 °C in those lacking or containing only rare mafic enclaves. The presence of Fe-rich mineral assemblages including ilmenite indicates that the A-type granites crystallized under low ƒO2 conditions. Zircon trace element analyses suggest post-magmatic hydrothermal processes, interpreted to be associated with shear zone reactivation. Whole-rock geochemical characteristics, the chemistry of the Fe-rich mafic mineral assemblages, and zircon trace elements in the studied granitoids share important similarities with A2-type granites worldwide.

Influence of intensive parameters on the mafic paragenesis of nepheline syenites: the Monte de Trigo alkaline suite, southeastern Brazil

The Monte de Trigo Alkaline Suite is a Late Cretaceous syenite–gabbroid occurrence from the Serra do Mar Alkaline Province, southeastern Brazil. It has a zoned nepheline syenitic stock with nepheline syenite I (NSI), the most SiO 2 -undersaturated, in the centre, surrounded by nepheline syenite II (NSII) and alkali feldspar syenite with nepheline (SN). Synplutonic miaskitic and agpaitic nepheline microsyenite (MNM and ANM, respectively) dykes cut across the stock. Extensive fractionation of alkali feldspar and mafic minerals is attributed to the formation of the syenitic facies and dykes. Mineral chemical data indicate that SN crystallized at relatively high silica activity ( a SiO 2 ; 0.5–0.7), a H 2 O (0.24–0.11) and f O 2 (difference from the fayalite–magnetite–quartz buffer in log units, ΔFMQ + 0.2 to ΔFMQ − 0.2), in contrast to NSII and NSI ( a SiO 2 , ∼0.41; a H 2 O, 0.05–0.02; and f O 2 , ΔFMQ − 1.4 to ΔFMQ − 1.1). These parameters vary with magma evolution towards the phonolite eutectic and appear to control variations in paragenesis, from hastingsite + biotite ± diopside/hedenbergite in SN to hastingsite in NSII and hastingsite + hedenbergite in NSI. The MNM have high a H 2 O (0.31) and hastingsite + biotite + aegirine–augite assemblages. In contrast, the ANM are characterized by an F-rich anhydrous agpaitic assemblage.

Accounting of weathering enhancement by mafic mineral spreading for CO 2 storage

The reduction of atmospheric CO 2 is an urgent global issue in the mitigation of global warming. Carbonate acts as a carbon sink in Earth's surface layer, and the weathering of terrestrial silicates and the deposition of oceanic calcium carbonate and organic matter mainly determine atmospheric and oceanic carbon dynamics on geological time scales. Various CO 2 reduction approaches have been evaluated, and the weathering acceleration method is expected to be a low-cost approach. This study attempts to estimate carbonate precipitation potential and dissolution rate from alkali leaching rates using weathering tests on mafic rocks. Based on Japan's annual average rainfall, the in situ carbonate precipitation potential obtained by spreading an olivine mineral or basalt rock powder at 40 ton-powder/ha was on the order of 10 -3 ton/year/ton-rock. This weathering rate could not be greatly accelerated under natural temperature conditions and fine granulation of the minerals.

Geochemical and geochronological evidences from Cambrian to Ordovician protracted magmatism in the Istranca Massif, NW Türkiye

Plutonic rocks in different ages are cropted out and form the basement rocks in the Istranca Massif. One of the plutons located at the basement is the Cambrian-Ordovician Vize pluton (Vize-Kırklareli) and is distinguished from other plutons by some of its characteristic features. This pluton intruded into the high-grade metamorphic sedimentary rocks, and is unconformably overlay by Triassic low-grade metamorphic rocks and Eocene aged coral reef limestones (Soğucak Formation). Based on new whole rock geochemical and zircon UPb data concentrated in two different ages, it can be said that the Vize pluton was affected by protracted magmatic activity. The igneous minerals and texture of Vize pluton are partly preserved, It has a mylonitic texture, a distinct foliation consisting of light and dark zones. In addition, metagranites contain mafic magmatic enclaves (MMEs) in some places.The Vize pluton is an I-type pluton with predominantly peraluminous and slightly metaluminous character. It is also High-K, calc-alkaline, and reflecting volcanic arc and post-collisional tectonic settings. Mineral chemical analyses show that the mafic minerals in the Vize pluton consist of Fe-biotite and calcic amphibole (hornblende). Ti-in biotite thermometry shows that the temperature of the pluton in the final crystallization temperatures are between 834 and 850 °C (mean = 845 ± 4 °C), while the crystallization temperatures of amphiboles are between 876 and 910 °C (mean = 893 ± 22 °C). Crystallization depths are estimated to be a range of 6.5 to 7.9 km. It can be assumed that the oxygen fugacity of calcic amphiboles (logƒO2) is stabilized between −10.7 and − 11.3 bar (mean = −11.05 ± 0.4 bar). ∆NNO values are between 0.72 and 1.11 (mean = 0.96 ± 0.12) and H2O melt content is between 4.63 % and 5.43 % (mean = 5.04 ± 0.4 %). Oxygen fugacity values are among the typical values of calc-alkaline magma crystallization.The Vize pluton was crystallized in Cambrian to Ordovician times according to zircon UPb dating is concentrated in two different populations as 526.16 ± 3.26 Ma and 452.93 ± 2.76 Ma. All data obtained are consistent with the ages of the magmatism that produced the Vize Pluton in the Balkanides and Istranca Massif of 420–470 Ma (mean 447.17 ± 3.24 Ma) and indicate that it probably formed in the northern Gondwana. It was affected by the magma-mixing processes of coeval felsic and mafic magmas, and anatexis processes. Geochronological and geochemical data indicate the existence of a protracted magmatic activity related to convergent setting (long-lived magmatic arc) that forced the Vize-Pluton to undergo multi-stage melting-crystallization processes.

Peridotites and other ultramafic rocks

Peridotites are a group within the category of ultramafic rocks. These are usually dark‐coloured rocks rich in magnesium, poor in silica and lacking feldspars. Earth's mantle, which makes up 83 percent by volume and 67 percent by weight of the planet, consists largely of peridotite, which, although relatively sparse at the surface, therefore, is Earth's most abundant rock type. Unfortunately, the mantle, which lies on average at >7 km under the oceans and >35 km under the continents, is not directly accessible for observation and our information comes largely from seismic studies, inclusions in volcanic rocks and sections of the ocean floor which have been tectonically emplaced into the crust: the ophiolite complexes and abyssal peridotites of the oceans. Such rocks also occur when mafic minerals, such as olivine, pyroxene and spinel, accumulate in magma chambers. An unusual occurrence of ultramafic rocks is the lava called komatiite, representing ultramafic liquids, which are largely restricted to Precambrian environments.

Anatomy of a Lunar Silicic Construct—The Wolf Crater Complex, Mare Nubium and Implications for Early Silicic Magmatism on the Moon

AbstractSilicic lithologies on planetary surfaces indicate magmatic evolutionary processes in their interiors. The Wolf crater complex within Mare Nubium on the Moon is one such silicic construct associated with a high thorium anomaly. This study integrates morphological, compositional, chronological and gravity anomaly analyses of high‐resolution data from various lunar missions to establish this construct as a silicic volcanic caldera. Lobate flows with steeply sloping fronts indicate that the crater rims comprise high‐viscosity silicic lavas, while the structurally controlled inner crater walls suggest caldera collapse triggered by magma depletion. In the crater rims, low Christiansen Feature position values reaffirm the presence of silicic lithologies, consistent with the low gravity anomaly signature beneath the complex, while spectroscopic data reveal low mafic mineral abundances and negligible hydration features. Chronological analyses yield silicic volcanism ages coeval with surrounding mare basalts (3.8–3.6 Ga), while intra‐caldera basalts have 2.36–2.02 Ga ages, indicating prolonged magmatism in this region. Melting of suitable crustal protoliths like alkali gabbronorite/monzogabbro/troctolite by basaltic underplating is inferred to have generated silicic magmas that formed the Wolf volcanic complex, instead of basaltic magma fractionation or silicate‐liquid immiscibility processes. Large impacts during the Late Heavy Bombardment may have enhanced partial melting of the mantle and created crustal fractures that facilitated the ascent of viscous silicic melts through the lunar crust. Contemporaneous existence of suitable protoliths and adequate crustal pathways for magma ascent may have controlled silicic volcanism on the Moon, and can explain the sporadic occurrence and overlapping ages of the lunar silicic constructs.

Cognate Mafic Enclaves Formed by Cumulated Mush Convection in a Granitic Magma Chamber: Evidence from Mineral Chemistry of the Triassic Zhashui Pluton, Qinling Orogen

AbstractMafic enclaves in granites are generally considered to represent coeval mafic melts that derived from metasomatized mantle, which can provide valuable information about crust–mantle interaction. Exploring the genetic links between the mafic enclaves and their host monzogranite from the Triassic Zhashui Pluton, Qinling orogenic belt. The enclaves (220 ± 4.6 Ma) and the monzogranite (220 ± 2.8 Ma) display identical zircon U‐Pb ages, and they also share similar trace element and zircon Lu‐Hf isotopes, indicating a cognate source. The monzogranite displays zircon εHf(t) values of –0.99 to +1.98, while the mafic enclaves show similar values of –0.45 to +3.26; however, differences in mineral chemistry reveal different crystallization conditions. The amphibole from the mafic enclaves has higher temperature and pressure (757°C; 2.65 kbar) compared to those of the host monzogranite (733°C; 1.96 kbar), suggesting that mafic minerals in the enclaves crystallized at an early stage. Moreover, apatite in the mafic enclaves displays slightly higher volatile contents (0.72 wt%) than those of the monzogranite (0.66 wt%), indicating a volatile‐rich condition. These results suggest that the mafic enclaves represent early hydrous mafic cumulates in the granitic chamber, and subsequent magma convection would have led to the formation of the mafic enclaves.

Magmatic degassing and fluid metasomatism promote compositional variation from I-type to peralkaline A-type granite in the late Cretaceous Fuzhou felsic complex, SE China

Abstract A-type granites generally have much lower water, higher temperature, and incompatible element concentrations than I-type granitoids. Yet it remains unclear why I-A-type granitic complexes occur in convergent plate margins. Here we conduct geochemical analyses on apatite and mafic minerals from the late Cretaceous I-A-type granitic complex in Fuzhou area, SE China, aiming to decipher differentiation, fluid metasomatism, and degassing that primarily control the compositional diversity of felsic magmas. Apatites in both rock types are F-rich and show large H2O and δD variations, i.e., 341–3892 ppm H2O and –325 to +336‰ δD in I-type granitoids; 67–1366 ppm H2O and –251 to +1439‰ δD in A-type granites. H2O in apatite is negatively correlated with La/Sm and Sr/Y in the I-type granitoids, whereas it is positively correlated with Ce and total rare earth element (REE) concentrations in the A-type granites. Once H2O increases up to hundreds of ppm, both rock types show a rapid decrease of H2O/Ce, an increase of F/Cl, and extensive H isotope fractionation. Arfvedsonite occurs as a late crystallizing mineral in the A-type granite and has much higher contents of Na2O, K2O, F, and high field strength elements (HFSE) than hornblende in the I-type granitoids, indicating the addition of F-HFSE-rich alkaline fluids during its magmatic evolution. The consumption of arfvedsonite and formation of aegirine further indicate the role of fluid metasomatism and H2 degassing via a reaction of 3Na3Fe5Si8O22(OH)2 + 2H2O = 9NaFeSi2O6 + 2Fe3O4 + 6SiO2+5H2. The combined geochemical data demonstrate that the systematic differences in mineral assemblage, whole-rock composition, magma temperature, H2O content, and δD of apatite between the I- and A-type granites are likely attributed to varying degrees of differentiation, fluid metasomatism and magmatic degassing. The I-type granitoids experienced hornblende, biotite, plagioclase, K-feldspar, and apatite fractionation and close-system degassing. The A-type granite was likely formed from the I-type monzogranitic magma that was metasomatized by the mantle-derived F-HFSE-rich alkaline fluids to produce the peralkaline magma, which further experienced K-feldspar + plagioclase + biotite + apatite fractionation and open-system degassing. Further numerical estimation indicates that the primary magma of Fuzhou granitic complex contained ~3.0 wt% H2O, and the lower water content of A-type granite was likely attributed to strong degassing during its emplacement. Our results indicate that some peralkaline A-type granites can be generated from relatively water-poor I-type granitic magmas by fluid metasomatism and degassing.

Hydrothermal alteration and its geochemistry of the Xiadian gold deposit, Jiaodong Peninsula, China: Implications for fluid-rock interaction processes and mineral exploration

The interaction between hydrothermal fluids and host rocks, along with associated alteration geochemistry within the Mesozoic Jiaodong gold system, presents significant gaps in our understanding. This study systematically examines the petrographic, mineralogical, and geochemical characteristics of alteration at the Xiadian gold deposit, including comprehensive whole-rock geochemistry analyses, mass balance calculations, and phase equilibria modeling. The alteration history of Xiadian could be divided into four stages. Amid Stage 1, the predominant process involves the replacement of plagioclase by K-feldspar-albite, accompanied by the simultaneous bleaching of amphibolite and associated significant depletion of MgO (ΔCi/CiO = −21.2 %) and Fe2O3 (−27.2 %) owing to the decomposition of mafic minerals. Stage 2a involves sericitization of albite and continued mafic mineral decomposition, resulting in the lowest recorded MgO (avg. 0.23 wt%) and Fe2O3 (avg. 0.92 wt%) contents in all alteration lithologies. Stage 2b is characterized by abundant chlorite vein formation, corresponding to the proximal enrichment of MgO (158.1 %) and Fe2O3 (108.2 %), accompanied by aMg2+/(aH+)2 decreased in the fluid. Stage 3, the main stage of gold mineralization, involves chlorite substitution with sericite during quartz-sericite-pyrite (QSP) alteration, suggesting mild acidification of the ore-forming fluid. Insights from phase equilibrium modeling suggest that sulfidation has contributed to gold precipitation, leading to increased fO2 and reduced fH2S (extending into quartz-carbonate alteration of stage 4). Mass balance calculations indicate gold is enriched compared to protolith at all stages, with the most intense enrichment in stage 3. This suggests that hydrothermal fluids at Xiadian were auriferous throughout their evolution. The process may induce fluid modifications, particularly through the dissolution of mafic minerals, more so in mafic mineral-rich rocks (e.g., amphibolite) than in granite, promoting the incorporation of hydrothermal chlorite into the Au system to contribute to sulfidation. Our results provide insights into lithology controls on gold mineralization at Xiadian, indicating that felsic rocks (Linglong granite and quartz porphyry) with lower initial CaO contents often develop K-metasomatism and Au-bearing QSP alteration, while mafic rocks (amphibolite and lamprophyre) with higher CaO contents develop carbonization. This is likely due to the influence of lower CaO contents on alteration minerals, which promote rock porosity, affecting rock deformation, pore-fluid flow, and reacting with wall rocks. Principal component analysis (PCA) results indicate that elements including Au, Ag, As, Bi, W, and Cu are proxies for Au mineralization, suggesting their mobilization and deposition together during the gold mineralization process. This highlights their significance as a proxy for gold exploration.

Why are oceanic arc basalts Ca-rich and Ni-poor? Insights from olivine-hosted melt inclusions from Kibblewhite Volcano in the Kermadec arc

Ankaramites, which are clinopyroxene-rich basalts with primitive whole-rock compositions (Mg# >65), are common in oceanic arcs and are characterized by high whole-rock CaO/Al2O3 (>1.0) ratios and olivine crystals with anomalously low nickel contents (<0.2 wt% NiO). These geochemical characteristics cannot be explained by the melting of ordinary mantle peridotite. However, their origin is critical for understanding the formation of primary magmas in oceanic arcs. Here, we investigated olivine-hosted melt inclusions (MIs) from ankaramites and magnesian andesites of the Kibblewhite Volcano in the Kermadec arc. The MIs from the ankaramites have similar major and trace element characteristics to the host rocks, indicating that the ankaramites did not result from an accumulation of mafic minerals but rather represent the primary magma in the Kibblewhite Volcano. The MIs from the magnesian andesites were hosted in forsteritic olivine xenocrysts with a wide range of NiO contents (Fo90–92; 0.13–0.39 wt% NiO) and have similar major element compositions to the ankaramites but exhibit a wide range of CaO/Al2O3 (0.85–1.54). The trace element characteristics of the MIs from the magnesian andesites do not match those of the host rocks, indicating that they are not primary melts of the magnesian andesites but primitive basaltic melts generated before the magnesian andesites formed.Interestingly, the CaO/Al2O3 ratio of MIs from the magnesian andesites was negatively correlated with the NiO content of their host olivines. This correlation suggests that the composition of the primary basaltic magmas of the Kibblewhite Volcano changed continuously from peridotite-derived to ankaramitic. This correlation could not be explained by grain-scale process, crustal anatexis, or contribution of slab-derived carbonate-rich fluids. Instead, we propose that this correlation can be explained by the interaction of the ascending primary basaltic melts with the lithospheric mantle. During melt-mantle interaction, the assimilation of clinopyroxene and fractionation of olivine and orthopyroxene caused the CaO/Al2O3 ratio to increase in the melt and the Ni content to decrease. Furthermore, because the magnesian andesites have low CaO/Al2O3 ratios and could be derived from a clinopyroxene-poor mantle lithology, the interaction between the melt and mantle may also be closely related to the origin of the magnesian andesites at Kibblewhite Volcano. This interpretation provides a new perspective on the origin of the oceanic arc ankaramites and why primary andesitic and basaltic magmas coexist in the Kibblewhite Volcano.

1.88 Ga granitoids at Sorsakoski, Central Finland: A-type magmatism within the Raahe-Ladoga suture zone

Four quartz monzonite – granite intrusions forming the Sorsakoski granite lithodeme, are found within the Raahe-Ladoga suture zone in Central Finland. The prevailing potassium feldspar megacrystic quartz monzonites and granites form a bimodal association with diorites and gabbros. The granitoids are mainly calc-alkaline, ferroan, per- to metaluminous, and have high Zr and REE contents. Dominant mafic minerals are biotite and hornblende, clinopyroxene and orthopyroxene are locally present. The mafic units display effects of fractionation of clinopyroxene. In our interpretation, these intrusions were emplaced during regional late stages of deformation and post-crystallisation deformation partitioned into major shear zones leaving bulk of the intrusions relatively undeformed. Based on one new (1876 ± 6 Ma) and one pre-existing (1882 ± 5 Ma) U-Pb zircon age determination, the crystallisation age of the granitoids can be assumed at ca. 1880 Ma. Based on mineralogy, petrography, geochemistry, bimodal nature of magmatism and age, we correlate these intrusions to the A-type rocks of the previously described Saarijärvi suite. This shows that the syn-orogenic A-type magmatism extended eastwards beyond the Central Finland Granitoid Complex.

Metal bioaccumulation and effects of olivine sand exposure on benthic marine invertebrates

Due to the anthropogenic increase of atmospheric CO2 emissions, humanity is facing the negative effects of rapid global climate change. Both active emission reduction and carbon dioxide removal (CDR) technologies are needed to meet the Paris Agreement and limit global warming to 1.5 °C by 2050. One promising CDR approach is coastal enhanced weathering (CEW), which involves the placement of sand composed of (ultra)mafic minerals like olivine in coastal zones. Although the large-scale placement of olivine sand could beneficially impact the planet through the consumption of atmospheric CO2 and reduction in ocean acidification, it may also have physical and geochemical impacts on benthic communities. The dissolution of olivine can release dissolved constituents such as trace metals that may affect marine organisms. Here we tested acute and chronic responses of marine invertebrates to olivine sand exposure, as well as examined metal accumulation in invertebrate tissue resulting from olivine dissolution. Two different ecotoxicological experiments were performed on a range of benthic marine invertebrates (amphipod, polychaete, bivalve). The first experiment included acute and chronic survival and growth tests (10 and 20 days, respectively) of olivine exposure while the second had longer (28 day) exposures to measure chronic survival and bioaccumulation of trace metals (e.g. Ni, Cr, Co) released during olivine sand dissolution. Across all fauna we observed no negative effects on acute survival or chronic growth resulting solely from olivine exposure. However, over 28 days of exposure, the bent-nosed clam Macoma nasuta experienced reduced burrowing and accumulated 4.2 ± 0.7 μg g ww−1 of Ni while the polychaete Alitta virens accumulated 3.5 ± 0.9 μg g ww−1 of Ni. No significant accumulation of any other metals was observed. Future work should include longer-term laboratory studies as well as CEW field studies to validate these findings under real-world scenarios.

Changes in soil bacterial community structure in a short-term trial with different silicate rock powders

BackgroundThe use of rock powders in soil has emerged as a nature-based technology to improve soil properties relevant to crop development and for atmospheric carbon dioxide removal (CDR) via enhanced rock weathering (ERW). Although modeling this process is crucial, the soil microbiome has been identified as the main reason why several experimental and field results do not fit the geochemical and kinetic theoretical models. Here, the hypothesis that the bacterial community structure is modulated by the application of different silicate rock powders was tested. One phonolite, three basalt variations and one granite, as well as KCl treatments, were applied to a Ferralsol cultivated with Brachiaria in short-term pedogeochemical experiments and assessed after 1 (1M), 4 (4M) and 8 (8M) months.ResultsThe main changes in soil bacterial structure were observed at 8M and found to be modulated according to rock type, with petrochemistry and mineralogy acting as the main drivers. The content of microbial biomass carbon tended to decrease over time in the Control and KCl treatments, especially at 4M, while the rock treatments showed constant behavior. The sampling time and treatment affected the richness and diversity indices. The Si, Ca and Fe from mafic minerals were the main chemical elements related to the soil bacterial changes at 8M.ConclusionsThe type (acidity) of silicate rock powder modulated the soil bacterial community (SBC) in a pot experiment with tropical soil. The specificity of the SBC for each rock type increased with time until the end of the experiment at 8 months (8M). The carbon content in the microbial biomass was lower in the rock powder treatments in the first month (1 M) than in the control and KCl treatments and was equal to or higher than that in the 8 M treatment. This result illustrates the challenge of modeling rock powder dissolution in soil since the soil medium is not inert but changes concurrently with the dissolution of the rock.Graphical

Mineralogical Characterization of the Lunar South Polar Region: 1. The Artemis Exploration Zone

AbstractThe lunar south pole is a region of focused scientific and exploration interest, with several crewed and robotic missions to this region planned within the next decade. Understanding the mineralogy of the region is essential to inform landing site characterization and selection and provides the key context for interpreting samples and in situ observations. At high latitudes, extreme illumination conditions (high phase angles) can negatively impact the data quality of orbital instruments. This is especially true for passive near‐infrared spectrometers such as the Moon Mineralogy Mapper (M3) and the Kaguya Spectral Profiler, which measure the spectral properties of the surface using reflected sunlight. Using Moon Mineralogy Mapper data, we observed that the south polar region is associated with a detectable mafic signature consistent with the presence of pyroxenes. The strongest mafic signatures are associated with the South Pole—Aitken Basin, suggesting that impact melt and basin ejecta from the lower crust and upper mantle are present within this region. This observation is validated in several ways: (a) comparisons between M3 data acquired during different mission phases, (b) comparisons between multiple spectral parameters sensitive to the presence of mafic minerals, (c) comparisons between the north and south lunar polar regions, and (d) comparisons with publicly available Kaguya polar mineralogy maps and Lunar Prospector elemental abundances. We also investigate the nature of an anomalous high‐albedo region within 2–3° of the south pole observed in Lunar Orbiter Laser Altimeter reflectance data exhibiting a spatially conflicting apparent FeO abundance pattern between several data sets.

Are the Fe-rich-clay veins in the igneous rock of the Kansas (USA) Precambrian crust of magmatic origin?

The North American Mid-Continent rift (MCR) is a 1.1 Ga aborted rift, which has recently become an area of intense focus for energy resource exploration following the report of H2 emissions. To document the nature of the producing rocks, we conducted a multi-scale study on preserved drill-core samples from the DR1-A well located in the same area as the H2-producing wells in Kansas. We showed that this well reaches an unmapped part of the MRS composed of fayalite-bearing monzo-diorites in which we identified atypical veins of iddingsite, a complex mixing of Fe-rich phyllosilicates. Combining scanning and transmission electron microscopy (SEM and TEM) with scanning transmission X-ray microscopy (STXM) allowed us to differentiate at least two types of sub-micro-meter Fe-rich veins. A central reduced vein cutting the fayalite, other mafic minerals, the plagioclase, and to a lesser extent the alkali feldspar, contains a complex mix of serpentine, chlorite, and mica. Furthermore, a border vein, with a higher degree of Fe-oxidation, is found to be contained only within the fayalite. This external vein mainly contains iron and silicon, together with a few percent of potassium and calcium, and can be divided into two sub-veins composed of Fe3+-rich interstratified chlorite-smectite and Fe3+-rich serpentine in direct contact with the fayalite. Textures and microstructures of these phyllosilicates suggest that they have crystallized from a late magmatic and differentiated fluid, which precipitation produced the central vein together with the exsolution of an H2O-enriched fluid phase. This exsolved fluid, chemically far from equilibrium with the fayalite, appears to have induced a deuteric alteration of the fayalite, leading to the crystallization of the external veins enriched in ferric iron. These observations bring new perspectives on the history of formation of iron-rich clay minerals, which may, somehow, be related to H2 production.

Partitioning of tin between mafic minerals, Fe-Ti oxides and silicate melts: Implications for tin enrichment in magmatic processes

The partition coefficients of Sn (tin) between minerals and silicate melts (DSnmin/melt) are vital for understanding the Sn enrichment during magmatic processes related to tin-granites. However, experimentally determined DSnmin/melt values remain scarce due to the difficulty in avoiding severe Sn loss to noble metal capsules. In this study, we performed mineral/melt Sn partitioning experiments at 0.5–1.0 GPa, 850–1000 °C, and fO2 of FMQ + 8 to ∼ FMQ − 1. The fO2s were imposed by solid buffers of Ru–RuO2, Re–ReO2, Ni–NiO, Co–CoO and graphite using three improved capsule designs: 1) a single sample capsule (Pt) for the Ru–RuO2 buffered runs, 2) double capsules with Pt95Rh05 as outer capsule and Re as inner sample capsule for the graphite and Re–ReO2 buffered runs, and 3) triple capsules for the Co–CoO and Ni–NiO buffered runs, with Pt95Rh05 (or Au) as outer capsule, Re lined Pt as inner sample capsule. These new capsule designs avoided significant Sn loss and enabled us to obtain accurate DSnmin/melt at a controlled fO2. The experimental results show that DSnmin/melt values are 0.08–12.66 for amphibole, 0.01–5.55 for biotite, 0.09–10.39 for clinopyroxene, 0.004–0.97 for orthopyroxene, < 0.01 for olivine, 1.34–108.43 for Ti-magnetite, 0.04–4.17 for spinel and 0.10–0.64 for ilmenite. The large variation of DSn for each mineral was mainly ascribed to the effect of fO2, which results in an arresting decrease of DSn with decreasing fO2. Under the reducing conditions (fO2 < FMQ), Sn is highly incompatible (DSn < 0.1) in almost all the minerals. Modeling results indicate that partial melting at low fO2 conditions results in Sn enrichment in the derived magma, while subsequent high degree of fractional crystallization is also important for the Sn enrichment in the residual melt. The experimental and modeling results thus explain why major primary tin deposits are always related to reducing and highly fractionated granites.

A Tall Tale of a Tiny Pluton: The L’Enfer Norite, Grenville Province, Québec

Abstract We present new field observations and mineral and whole-rock geochemical data for the L’Enfer norite, a small pluton in the central Grenville Province of Québec. Although tiny, its plagioclase-rich and noritic character suggested that it might hold clues (possible parental magma?) to the origin of closely associated andesine anorthosites in this part of Québec. The pluton is characterized by spectacular coarse-grained diabasic textures and varies from relatively massive to locally layered varieties. Both coarse- and medium-grained types occur and may be present together in some outcrops. Rare occurrences of snowflake-textured plagioclase are also present. The mafic mineralogy is dominated by orthopyroxene and Fe-Ti oxides (ilmenite and magnetite) with minor clinopyroxene, amphibole (Ti-pargasite), and Ti-rich biotite. Olivine occurs in one of the norites and in a single occurrence of an ultramafic rock that is also enriched in Fe-Ti oxides. Plagioclase compositions range from An32 to An48, but can be divided into two groups on the basis of texture: in one subset of samples, the plagioclase contains exsolution lamellae of orthoclase (i.e., antiperthitic), whereas plagioclase in the remaining samples lacks such lamellae and has not exsolved. Despite these textural contrasts, whole-rock compositions of the two groups are similar. Surprisingly, the compositions of pyroxene, biotite, and ilmenite reveal two non-overlapping compositional groups that correlate with those defined by plagioclase texture. Specifically, mafic minerals in the group with unexsolved plagioclase are consistently enriched in minor elements compared to those in the group with antiperthitic plagioclase. We interpret these contrasts to reflect differences in cooling rate for at least two injections of noritic magma. Moreover, the snowflake plagioclase grains are consistent with some degree of undercooling and supersaturation brought about by magma mixing. Although the norite shares some mineralogical and geochemical features with nearby anorthosites, it does not appear to represent a viable parent magma, primarily due to a pronounced difference in Fe-Ti oxide assemblage (hemo-ilmenite in the anorthosites versus ilmenite + magnetite in L’Enfer).

Geochemistry of Granites in Panggong Lalat, Gua Musang, Kelantan

Granites are among the most significant rock formations in the Earth’s crust and play a crucial role in various geological processes. This study focuses on examining the geology and granitic rock formations in Panggong Lalat, Gua Musang, Kelantan through field surveys, geological mapping, and geochemical analysis for better understand the geological framework and characteristics of granite in this area. The findings indicate that the lithology of the study area includes granitoids, well-bedded limestone, volcanic rocks, fine-grained sediments, and meta-sedimentary rocks. Petrographic analysis of five samples identified three granitoid types: quartz-rich granitoid, quartz alkali feldspar syenite, and alkali feldspar granite, classified using the IUGS scheme. The X-ray Fluorescence (XRF) data reveals that both samples exhibit typical felsic granite compositions, with high SiO₂ contents in AF 01 (61.61%) and 60.72% in AF02. However, AF 02 displays higher concentrations of TiO₂, FeO, and MnO, suggesting a greater contribution of mafic minerals compared to AF 01. Additionally, CaO content is slightly higher in AF02, indicating a more significant presence of plagioclase feldspar, while AF01 is enriched in K₂O. The Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) data further reinforce the distinction between AF 01 and AF 02. Both samples are enriched in Rare Earth Elements (REE), particularly Ce, Er, and La. A F02 shows significantly higher concentrations of Ce (213.85 ppm) and Er (7554.11 ppm) compared to AF 01 (166.12 ppm for Ce and 3047.54 ppm for Er), indicating a stronger REE enrichment in AF 02.The distribution of Heavy Rare Earth Elements (HREE) is more abundant than that of Light Rare Earth Elements (LREE), with Er exhibiting the highest concentration and Nd the lowest.

Petrology of the Skaergaard Layered Series

The Skaergaard intrusion is a layered, ferrobasaltic intrusion emplaced during the Early Eocene into the rifting volcanic margin of East Greenland. The magma chamber crystallised in response to cooling from the roof and margins upwards and inward, forming upper, marginal and bottom series, the latter referred to as the Layered Series. The phase layering in the bottom series suggests an evolved, olivine-normative tholeiitic melt saturated in plagioclase and olivine, followed by augite, and then simultaneously by ilmenite and magnetite forming primocrysts. Pigeonite appears in the lower parts and continues until the centre of the series. Apatite appears in the upper part concurrently with liquid immiscibility. Cryptic variations of the individual primocrysts record a systematic upward increase in iron and decrease in magnesium for the mafic minerals and a systematic increase in sodium and decrease in calcium for plagioclase. The appearance of pigeonite is caused by reactions and crystallisation in the trapped melt and by subsolidus adjustments without this phase reaching liquidus saturation. The high mode of olivine at the base of the upper part with the appearance of apatite is interpreted to mark the onset of liquid immiscibility. This may have led to the separation of conjugate melts with granophyre migrating upward and the basic component largely staying stationary or sinking. Petrologic and geochemical observations indicate differentiation in the lower part of the intrusion, principally controlled by crystal fractionation with the efficiency of fractionation controlled by the evolution and escape of liquid from the solidifying mush. During the final stages of solidification, the onset of liquid immiscibility and termination of melt convection impeded differentiation. Modelling by perfect Rayleigh fractionation shows that major and included trace elements conform reasonably to observations, while excluded elements deviate from model predictions. This decoupling is caused by the mobility of a granophyre component formed in the trapped melt and in the main residual magma chamber. Consequently, the sampled gabbros may not be representative of the final solid-melt mush. By restoring the gabbros to their original mush compositions, it is possible to constrain granophyre migration pathways. We suggest that the granophyre formed in the trapped melt in the lower part of the intrusion mostly migrated laterally through pressure release pathways to form lenses and pockets with only limited upward migration into the main magma reservoir. Near the end stage of differentiation, the residual magma exsolved and formed complex mixtures of ferrobasaltic and granophyric melts. Estimates predict that a substantial amount of the granophyric melt penetrated as sills into the downward crystallising, upper part of the body as well as into the host rocks. The redistribution of granophyric melts within the solidifying crystal mush complicates predictions of trapped-melt content and mass-balance calculations but helps to explain apparent decoupling of included and excluded trace elements, especially towards the end stages of evolution. Final crystallisation was controlled mostly by in situ crystallisation leaving complex mixtures of ferrodiorite and granophyre components.

Lunar spinels in the Aristarchus crater and cobra head

On the lunar surface we identify and map Mg-spinel-bearing deposits on the southern section of the Aristarchus Plateau, including the Aristarchus and Herodotus craters and the Cobra Head using the color rations C (950-750 nm) and C (2650/1550 nm). The main concentrations of spinel-bearing material are located on the peak and floor of the Aristarchus crater, with some minor deposits also detected on the walls. Most of these deposits are associated with surface areas covered by massive boulders. The crater peak reveals a bimodality of spectral characteristics and surface types: The smooth, darker surface of the northernmost face has a strong absorption band near 1 μm that is evidence of mafic mineral presence. The brighter and rougher surface of the peak midportion reveals absorption starting from 1.55 μm. This suggests a dominant plagioclase/Mg-spinel mineralogic composition of Fe-poor minerals. The Mg-spinel deposits outside the crater are represented by a single unit located on the southern slope of the Cobra Head. The intrusive volcanism and further uplifting by the impact is discussed as a possible origin of the Mg-spinel deposits of the region.