Total Alkali Silica Research Articles

Fingerprint of magma mixture in the leucogranites: Spectroscopic and petrochemical approach, Kalebalta-Central Anatolia, Türkiye

Abstract Leucogranites of Kalebalta in Central Anatolia are composed of plagioclase, quartz, orthoclase, and biotite and contains mafic microgranular enclaves (MME) in sizes ranging from few cm to 70 cm. In the total alkali-silica diagram, they fall typically in the granite field and show a calc-alkaline nature in the alkalis-iron-magnesium diagram whereas enclaves are Medium K series calc-alkaline, which represents the transition from tholeiitic to calc-alkaline. Leucogranites which have A/CNK(mol%) > 1 are strong peraluminous and seen as the products of magma derived from a metasedimentary source. Signs of magma mixing expressing the mantle inputs are also observed in many bivariation diagrams. Zircon and apatite saturation temperatures calculated on the basis of whole rock chemistry are 744–829°C for leucogranites and 761–832°C for their enclaves. According to the Raman spectra, biotite and plagioclase minerals in leucogranites and their enclaves show similar Raman spectrums. The biotite minerals have Mg–O and/or Fe–O translational (transformation) bonds between 182 and 552 cm−1, Si–O–Si bending between 552 and 1,100 cm−1 and Si–O–Si vibrational bonds between 1,100 and 1,200 cm−1. The results of this study suggest that the leucogranites and enclaves are most probably derived from different magmas. In addition, according to geochemical and spectroscopic data, they may also have fractional crystallization, which is effective after the mixing process.

WNMS: A New Basaltic Simulant of Mars Regolith

The use of planetary regolith can be explored via the utilization of simulants. The existing Martian simulants have differences due to varying source materials and design parameters. Additional simulants are needed because the few available simulants do not replicate the compositional diversity of Martian regolith. This study discusses the development of a low-cost construction simulant of Mars. The area of Winder Nai in Pakistan was selected for field sampling of basalt because of local availability and easy access. The dust was produced from rock samples through mechanical crushing and grinding. The physical properties, composition, mineralogy, and surface morphology were evaluated via geotechnical tests, Energy Dispersive X-ray (EDX) spectroscopy, X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The designed simulant has a well-graded particle size distribution with a particle density and bulk density of 2.58 g/cm3 and 1.16 g/cm3, respectively. The elemental composition of Winder Nai Mars Simulant (WNMS) is within ±5 wt% of the Rocknest and the average Martian regolith composition except for SO3. For SiO2, Al2O3, and Fe2O3, WNMS has a good match with the Martian regolith. The content of CaO and TiO2 in WNMS is higher than, and content of MgO is lower than, the average Martian values. The rock can be classified as basalt based on the Total Alkali Silica (TAS) diagram. XRD spectrum indicates the occurrence of plagioclase and pyroxene as the main signature minerals of basalt. The particle morphology of WNMS is angular to subangular, and the simulant indicates the presence of 3.8 wt% highly paramagnetic particles. The volatile loss is 0.25 wt% at 100 °C, 1.73 wt% at 500 °C, and 3.05 wt% at 950 °C. The composition of WNMS, basaltic mineralogy, morphology, magnetic properties, and volatile content are comparable with MMS-2 and a few other simulants.

Reactivity of Basaltic Minerals for CO2 Sequestration via In Situ Mineralization: A Review

The underground storage of CO2 (carbon dioxide) in basalt presents an exceptionally promising solution for the effective and permanent sequestration of CO2. This is primarily attributed to its geochemistry and the remarkable presence of reactive basaltic minerals, which play a pivotal role in facilitating the process. However, a significant knowledge gap persists in the current literature regarding comprehensive investigations on the reactivity of basaltic minerals in the context of CO2 sequestration, particularly with respect to different basalt types. To address this gap, a comprehensive investigation was conducted that considered seven distinct types of basalts identified through the use of a TAS (total alkali–silica) diagram. Through a thorough review of the existing literature, seven key factors affecting the reactivity of basaltic minerals were selected, and their impact on mineral reactivity for each basalt type was examined in detail. Based on this analysis, an M.H. reactivity scale was introduced, which establishes a relationship between the reactivity of dominant and reactive minerals in basalt and their potential for carbonation, ranging from low (1) to high (5). The study will help in choosing the most suitable type of basalt for the most promising CO2 sequestration based on the percentage of reactive minerals. Additionally, this study identified gaps in the literature pertaining to enhancing the reactivity of basalt for maximizing its CO2 sequestration potential. As a result, this study serves as an important benchmark for policymakers and researchers seeking to further explore and improve CO2 sequestration in basaltic formations.

Geology and Rare Earth Element Geochemistry of Magnesian Granitoids Within Proterozoic Schist Belt of Southwest Nigeria

Abstract The increased global demand for and price of rare earth elements (REEs) has led to intensive search for them in rocks of the upper continental crust all over the world. This study is aimed at characterising the granitoids at Okeho within Southwestern Nigeria using geochemical data and assessing their potential for REE enrichment. Ten representative rock samples of the Proterozoic intrusives, syenite and granodiorite, were studied for their mineralogical and elemental compositions. Elemental concentrations were analysed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Average major oxide concentrations revealed SiO2 (57.53 wt. %), Al2O3 (13.25 wt. %), CaO (5.05 wt. %), and MgO (5.59 wt. %) for the syenite and SiO2 (62.39 wt. %), Al2O3 (14.98 wt. %), CaO (3.67 wt. %), and MgO (3.25 wt. %) for the granodiorite. Total Alkali–Silica (TAS), Aluminum Saturation Index (ASI), and La/10-Y/15-Nb/8 plots discriminated the granitoids as metaluminous monzonite-syenite and peraluminous diorite-granodiorite. Average total REE concentrations in the syenite (625.06 ppm) and porphyritic-granodiorite (364.51 ppm) were above values reported for the granites in some mines in Jiangxi Province, Southern China.

Classification and nomenclature of volcanic rocks using immobile elements: A novel approach based on big data analysis

The proper classification and nomenclature of igneous rocks are cornerstones of geology. In contrast to intrusive rocks, volcanic rocks cannot be named after their mineral assemblages, due to their glassy and dominantly glassy nature. Thus, they are commonly classified based on their major elemental compositions, such as the Total Alkali-Silica (TAS) classification. Unfortunately, these major elements (especially K and Na) are commonly mobile during metamorphism and alteration, making the use of the TAS diagram problematic for altered or metamorphosed volcanic rocks. Though it can be replaced by diagrams employing immobile or less mobile elements, the accuracy is relatively low. By compiling data on volcanic rocks from GEOROC dataset, we confirmed that the classification based on Zr/TiO2-Nb/Y relationship has low accuracy (45.3%), so the results can be misleading. Although we improve this classification to 68.84% accuracy through refinement based on big data, the accuracy is still not satisfying. Such a deficiency can be compensated by the application of Machine Learning methods on a large dataset. Employing the Random Forest algorithm for model training based on 13 immobile elements, we propose a new classification method where the training accuracy increases to 74% for the verification dataset. Our results show that the prediction accuracy of several major rock types, such as basalt and rhyolite, increase to 89.2% and 97.5%, respectively.

Global volcanic rock classification of Holocene volcanoes

This data descriptor assigns the major and minor rock names from worldwide Holocene volcanoes of the Global Volcanism Program (GVP) using the Total Alkali-Silica diagram (TAS) for the chemical classification of volcanic rocks using the Geochemistry of Rocks of the Oceans and Continents (GEOROC) database. The precompiled files of the GEOROC database provide the chemical composition of volcanic rock samples, from which we computed major and minor rocks for global Holocene volcanoes reported in GVP. The combined dataset associates each volcano with the relative abundance of each volcanic sample type (whole rock, glass, melt inclusion) and provides the five major (more than 10% abundance) and minor rock names. In total, over 138,000 GEOROC volcanic rock samples were considered, for ~1000 Holocene volcanoes. The resulting major rock compositions are in general consistent with those given in GVP. The dataset provides a global panorama of rock composition for Holocene volcanoes.

Precise Pb-Pb baddeleyite geochronology, geochemistry, and Sr-Nd isotopic constraints on the 2.36 & 1.88 Ga mafic dykes from the Bastar craton, India: Implications for their petrogenesis in conjunction with the Dharwar mafic dykes

This research focuses on the geochronology and geochemistry of WNW-NW-NNW trending Paleoproterozoic mafic dykes from the Bastar craton in India. The weighted mean 207Pb/206Pb ages of baddeleyite grains obtained from the Tuskal, Pakhanjore, and Gariaband regions were 2365.25 ± 0.54 Ma, 2365.70 ± 0.48 Ma, and 2363.85 ± 0.79 Ma, respectively. Baddeleyite grains from a mafic dyke near Narayanpur-Kondagaon yielded a weighted mean 207Pb/206Pb age of 1886.5 ± 1.8 Ma. In the TAS (Total Alkali Silica) diagram, the 2.36 Ga and 1.88 Ga mafic dykes have basalt to basaltic andesite composition. Dykes from both age groups are represented by the tholeiitic magma series in the AFM diagram. In the spidergrams, the dykes show LREE and LILE enrichment, with the 2.36 Ga dykes showing flat HREE and the 1.88 Ga dykes showing slightly inclined HREE patterns. The REE non-modal batch melting model indicates derivation of the 2.36 Ga mafic dykes from a shallower spinel lherzolitic source, whereas the 1.88 Ga mafic dykes were derived from a deeper spinel-garnet lherzolitic mantle source. The 2.36 Ga dykes have near chondritic to slight super chondritic initial Nd isotopic values (εNd(2.36 Ga) = −0.95 to 2.36), whereas the 1.88 Ga dykes have sub chondritic initial Nd isotopic values (εNd(1.88 Ga) = −2.37 to −9.67). Present-day orientations and similar precise ages of the mafic dykes reported from the Bastar and Dharwar cratons indicate the counter-clockwise rotation of the Bastar craton during the Paleoproterozoic.

A Preliminary Volcanological Study of North Eastern Kaba Volcano, Bengkulu Province, Indonesia

Mount Kaba is one of the active volcanoes located in the eastern part of Bengkulu Province. This research was conducted in Gunung Kaba Complex because the distribution location of the last eruption product is close to some monogenetic volcano and residential area. This is interesting to study considering because can be a potential threat of disaster. The results of this study are expected to support providing an overview of the potential threat of volcanic disasters in the Mount Kaba Complex. The research methods used include geomorphological, stratigraphic, petrographic, and geochemical analyses. The geomorphological unit of Mount Kaba consists of 6 units. The types of volcanic rocks in the research area are dominated by lava and pyroclastic rocks. Based on the petrographic analysis of 10 samples, the names of the rocks in the research area are basalt scoria, basalt, and andesite. Based on the geochemical analysis of 8 samples, it is known that silica content in the rocks ranging from 44.40925 - 63.2993 %. Based on the AFM diagram, all samples are included in the tholeiitic series. Based on the TAS (Total Alkali Silica) diagram, it is known that the igneous rocks of the study area consist of andesite, basalt, tephrite, and trachyandesite.

Spectral evidence for alkaline rocks and compositional diversity among feldspathic light-toned terrains on Mars

Previously reported plagioclase detections in the near-IR (NIR) are associated with crater-exposed subsurface materials as well as light-toned bedrock plains with poor crater retention. Because Fe-bearing plagioclase has a weak ~1.25 μm feature that can be easily obscured by stronger absorptions in most pyroxenes and olivines, candidate lithologies must be dominated by plagioclase (e.g., anorthosite) and/or by spectrally neutral materials (e.g., quartz, K-spar, some volcanic glasses, some Fe2+−poor pyroxenes). To further understand the lithologies associated with NIR plagioclase detections, we investigated the spectral nature of these materials with THEMIS and CRISM data, focused on six light-toned plains exposures in Nili Patera caldera and Terra Sabaea (~20–25°S, ~40–47°E). Thermal infrared data from THEMIS can discriminate between some of the candidate lithologies; however, it has a lower spatial resolution (100 m/pix) than CRISM (18 m/pix) thus increasing the likelihood of subpixel mixing of rock and sand. We forward modeled a range of spectral mixtures of mafic sands with alkaline and subalkaline volcanic lithologies spanning the total alkali-silica diagram to identify the suite of rock compositions that could plausibly fit the THEMIS observations. In Nili Patera, feldspathic materials likely consist of a plagioclase-dominated composition with silica content below ~60 wt%. However, in at least one location in Terra Sabaea, lithologies with significant alkali feldspar (trachyandesitic to trachytic) and with silica contents up to ~60–65% are inferred from THEMIS observations. Terra Sabaea feldspathic materials could contain silica contents that straddle the boundary between intermediate-to-felsic lithologies; however, highly silicic or quartz-bearing compositions (e.g., rhyolites, granite, dacites) are not associated with the locations studied. Last, these results indicate that NIR-based plagioclase detections are associated with differing lithologies.

Determination of major elements in igneous rocks using microwave plasma atomic emission spectrometry (MP-AES)

An analytical method for sample preparation of igneous rocks and subsequent determination of Si, Na, K, Ca, Mg, Al, Fe, Mn, Ba, Sr, and Ti by means of microwave induced emission spectrometry (MP-AES) was developed and validated. The proposed sample preparation procedure avoids the use of perchloric acid and provided accurate results even for silicon determination using an acid digestion with hydrofluoric acid. The determination of major elements in rocks is required for the design of classification diagrams that provides relevant information for geochemical analysis.•MP-AES showed to be an adequate technique to measure major and some trace elements that are relevant for classification of igneous rocks.•This method is in better agreement with the principles of the Green Analytical Chemistry and constitutes a reliable alternative to classical analytical and tedious procedures used for geochemical analysis.•The methodology was successfully applied to chemical classification of rocks from Valle Chico (Uruguay) using a Total Alkali-Silica Diagram (TAS).

From machine learning to transfer learning in laser-induced breakdown spectroscopy analysis of rocks for Mars exploration

With the ChemCam instrument, laser-induced breakdown spectroscopy (LIBS) has successively contributed to Mars exploration by determining the elemental compositions of soils, crusts, and rocks. The American Perseverance rover and the Chinese Zhurong rover respectively landed on Mars on February 18 and May 15, 2021, further increase the number of LIBS instruments on Mars. Such an unprecedented situation requires a reinforced research effort on the methods of LIBS spectral data analysis. Although the matrix effects correspond to a general issue in LIBS, they become accentuated in the case of rock analysis for Mars exploration, because of the large variation of rock compositions leading to the chemical matrix effect, and the difference in surface physical properties between laboratory standards (in pressed powder pellet, glass or ceramic) used to establish calibration models and natural rocks encountered on Mars, leading to the physical matrix effect. The chemical matrix effect has been tackled in the ChemCam project with large sets of laboratory standards offering a good representation of various compositions of Mars rocks. The present work more specifically deals with the physical matrix effect which is still lacking a satisfactory solution. The approach consists in introducing transfer learning in LIBS data treatment. For the specific application of total alkali-silica (TAS) classification of rocks (either with a polished surface or in the raw state), the results show a significant improvement in the ability to predict of pellet-based models when trained together with suitable information from rocks in a procedure of transfer learning. The correct TAS classification rate increases from 25% for polished rocks and 33.3% for raw rocks with a machine learning model, to 83.3% with a transfer learning model for both types of rock samples.

Phase Equilibrium and Trace-Element Modeling of the Partial Melting of Basaltic Rocks under Low Pressure: Implications for Plagiogranite Generation

AbstractPhase equilibria and trace-element modeling using two previously reported basaltic bulk-rock compositions (samples D11 and 104-16), were carried out in this study, in order to better understand mechanism of low-pressure (LP) partial melting of mafic rocks and associated melt compositions. The T–MH2O pseudosections for both samples at three pressures (i.e. 0.5, 1.0 and 2.0 kbar) display that the H2O-stability field gradually increased with decreasing pressure within the T–MH2O range of 600–1100°C and 0–12 mol.%. The H2O contents of 10, 5.0, and 0.5 mol.% were selected on the basis of the T–MH2O pseudosections to calculate Pressure–Temperature (P–T) pseudosections over a P–T window of 0.1–3 kbar and 600–1100°C, so that the reactions of both the H2O-fluxed and -absent meltings at LP conditions can be investigated. The solidus displays a negative or near-vertical P–T slope, and occurs between 710 and 900°C at pressure between 0.1 and 3.0 kbar. LP melting of metabasites is attributed to the reactions of the hydrous mineral (hornblende and/or biotite) melting and anhydrous mineral (plagioclase, orthopyroxene, and augite) melting. The hydrous mineral melting is gradually replaced by anhydrous mineral melting as pressure decreasing, as the stability of hornblende decreases with falling pressure. With increasing temperature at a given pressure, the modeled melt compositions are expressed as progressions of the granite-granodiorite-gabbroic diorite fields for sample D11and granite-quartz monzonite-monzonite-gabbroic diorite fields for sample 104-16 on the total alkali–silica diagram. The modeled melts produced through the H2O-fluxed melting display higher Al2O3, CaO, MgO, and lower SiO2 and K2O than those formed by H2O-absent melting at the same P–T conditions. Furthermore, the modeled melts formed by H2O-absent melting, become richer in Al2O3, CaO, MgO, FeO, Na2O, but poorer in SiO2 and K2O as increasing water content. The results of trace-element modeling suggest that the nearly flat rare earth elements (REE) patterns of modeled bulk-rock composition are inherited by all the modeled melts, and the negative Eu anomalies and Sr depletion of the modeled melts gradually decrease as melting degree increases. Combined with the geochemical characteristics of natural oceanic plagiogranites, which have low K2O contents and flat or slightly light rare earth (LREE)-depleted REE patterns, our results imply that a bulk-rock composition with low K2O (<0.17 wt.%) and slightly LREEs depletion is the most likely protolith composition (e.g. basalt D11) for plagiogranites, and the compositions of modeled melts formed by LP H2O-absent partial melting of the basalt D11 at relatively high temperatures (1000–1025°C) are coincident with those of 1256D tonalites.

Characterization of altered mafic and ultramafic rocks using portable XRF geochemistry and portable Vis-NIR spectrometry

The accurate characterization of mafic and ultramafic rocks is a challenging but necessary task given the spatial and genetic relationship of mineralization with specific lithologies (e.g. komatiite hosted nickel-sulfides preferentially associated with cumulate-rich ultramafic rocks). Rock classification is further complicated as most mafic and ultramafic rocks have undergone varying degrees of alteration. The accuracy and reproducibility of characterization can be significantly improved by using portable energy dispersive X-ray fluorescence (pXRF) chemical data with portable visible and near-infrared (pVis-NIR) mineralogical data. A new workflow using pXRF and pVis-NIR is presented and used to reliably characterize mafic and ultramafic rocks from the Yilgarn Craton, Western Australia. The workflow involves six steps: (1) Mitigate and identify compound processing and closure issues. For example, we used a pXRF with helium flush to reliably and rapidly measure light elements and mitigate closure, i.e. problems related to data failing to sum to 100%. (2) Identify and exclude geochemically heterogeneous samples. Heterogeneity may be unrelated to alteration and caused by veining or small-scale structure interleaving of different rock types. Geochemical heterogeneity was evaluated using skewness and kurtosis of SiO 2 data. (3) Relate rocks from similar magmatic, weathering and alteration events. This was achieved by interpreting data grouping of Vis-NIR ferric and ferrous iron data via a 852 nm/982 nm reflectance v. 651 nm/982 nm reflectance plot and the ferrous abundance index. Unrepresentative data were omitted. (4) Correct XRF iron data, and characterize lithology and alteration. Values ascribed to regions in the TAS (total alkali silica) diagram were used to approximate FeO and Fe 2 O 3 . Subsequently, geochemical indices (e.g. Mg#) were used to characterize the alteration box plot. (5) Characterize fractionation in detail. Fractionation variation diagrams were used to interpret fractionation, e.g. MgO v. Al 2 O 3 , Ca/Al v. Al 2 O 3 , Ni/Cr v. Ni/Ti, and MgO v. Cr. (6) Identify and quantify talc alteration and serpentinization. This included the use of a new alteration plot (Mg# v. 1410 nm RAD /Albedo) to estimate serpentinization and identify relationships between serpentine, carbonate, chlorite and talc abundances. The results and observations contained in this contribution have important implications for progressive technologies such as core logging platforms that are equipped with pXRF and pVis-NIR instruments.

Chemical classification of common volcanic rocks based on degree of silica saturation and CaO/K2O ratio.

Modal classifications of common volcanic rocks are expensive, difficult, or impossible to attain. As a consequence, these rocks are classified using the chemical composition. However, existing classificatory diagrams are unable to identify all 16 families of common volcanic rocks; the most used is the total alkali-silica (TAS) diagram that identifies six families. Rocks not in the TAS diagram are misclassified with other rock names; their names are evolving to extinction, e.g. latite and rhyodacite. Some diagrams use Na2O, which is a complicating element rather than discriminant. Na2O is present both in alkali feldspar and plagioclase making difficult the separation of the amount associated to either feldspar. Silicon, potassium, and calcium are the three major elements with highest variations among volcanic rocks. They are selected for use in two new diagrams confronting CaO/K2O ratio with K2O content (KCK diagrams). One diagram is designed for saturated (intermediate) rocks (quartz <5 vol.%) and the other for oversaturated (acid) volcanic rocks (quartz >5%). These diagrams are tested using compositions of volcanic rocks from Uatumã magmatism in the Amazon Craton and also by plotting compositions of rocks from type-localities and the world averages. The proposed limits between rock families agree with plotted rock compositions. The KCK diagrams are an alternative to existing diagrams to classify volcanic rocks.

Temporal-spatial analysis of alkaline rocks based on GEOROC

Alkaline rocks account for a small proportion of magmatic rocks with characteristics of the linear distribution, and can reveal the tectonic setting and in source mantle compositions. Based on the GEOROC global geochemical database, we studied the temporal-spatial evolution of alkaline rocks in the world through GIS spatial analysis and data statistical analysis techniques. The results show an abrupt increase of alkaline volcanic magmatism in the Cenozoic from the Mesozoic and Paleozoic, with the volcanic intensity in the Cenozoic being close to 100 times higher than the Paleozoic. The basalts fall mainly in the basanite and phonolite fields in the Total Alkali–Silica (TAS) discrimination diagram. Spatial analysis suggested that the Cenozoic basalts were usually produced along plate boundary or correlated with mantle-plume-related hot spots.

Inclusions in impact-formed zircon as a tracer of target rock lithology: Implications for Hadean continental crust composition and abundance

Impacts play an essential role in the formation and possible habitability on early Earth and are the dominant mechanism controlling surface geomorphology on many solar system bodies. Without a significant >4 Ga rock record, geochemical variations and micron-scale inclusions within detrital Hadean zircon (Earth's oldest material - primarily from the Jack Hills, Western Australia) have provided valuable insights into the near-surface conditions of this crucial period in Earth's evolution. We report primary inclusion mineralogy of impact-formed zircon and the host impact melt from the Sudbury and Morokweng impact structures with estimates of target rock lithology to probe the composition of Earth's earliest crust given the possibility that Hadean grains were created in ancient impacts. Applying the theory of uniformitarianism between preserved and ancient impactites and utilizing geochemical proxies, we highlight the compositional evolution of an impact melt from a given target rock and the associated primary inclusion assemblages. Whole-rock X-ray Fluorescence and thick-section analyses coupled with primary inclusion populations from known terrestrial impact-formed zircon yield proportional mineralogy of the impact melt sheet from which they crystallized. Additionally, target rock lithology consistently plots within an area on a Total Alkali Silica (TAS) diagram centered amongst the granophyre and noritic units of an impact melt. Deducing similar trends of the impact melt mineralogy combined with TAS and Quartz-Alkali-Plagioclase ternary diagram melt pathways, we infer that if Hadean zircons from Jack Hills were impact-formed, the target rock lithology (i.e. Earth's earliest crust) would be between the composition of quartz-rich granitoid and tonalite-trondhjemite-granodiorite.

Hawaiian and Azorean volcanic aggregates: a preliminary study of the potential alkali-silica reaction

The alkali-silica reaction (ASR) is a chemical deterioration of concrete that involves reactive forms of silica. Volcanic glass is one of the potentially reactive forms of silica that can be present in volcanic rocks such as basalts. The aggregates used for concrete purposes from the Azores and Hawaiian Archipelagos are mainly of basic composition (basalts s.l.). In general, there is no report of ASR damaged structures in both archipelagos. However, in order to evaluate the behavior of these rocks regarding ASR and to compare the rocks from the two archipelagos, a set of methodologies were performed on a total of twenty-one volcanic aggregates. Geochemical analysis, total alkali-silica diagram, CIPW norm calculation, and petrographic analysis are some of the methods used for the assessment and analysis of rocks. The study was also complemented by electron probe microanalysis (EPMA) in order to identify the composition of volcanic glass and by X-ray diffractometry (XRD) for the Hawaiian aggregates. The results obtained from the studied aggregates showed that there are some differences between the two archipelagos. The rocks from the Azores are alkaline while the majority of the rocks from Hawaiian Archipelago are tholeiitic. The petrographic study revealed that the analyzed rocks from the Hawaiian Islands contain a higher quantity of interstitial volcanic glass than those from the Azores Archipelago. The EPMA carried out in some samples from the Hawaii showed that the volcanic glass has a composition of silica higher than 65%, value that is considered in the literature as potentially reactive.

Total alkali silica classification of rocks with LIBS: influences of the chemical and physical matrix effects

The matrix effects in LIBS analyses have been considered with univariate and machine learning based multivariate regression models for TAS classification of rocks.

The Mount Cameroon southwest flank eruptions: Geochemical constraints on the subsurface magma plumbing system

With seven major eruptions in the 20th century, Mount Cameroon is one of the most active volcanoes in Africa. However, information on the volcano's plumbing system is still relatively scarce. In order to contribute to filling this knowledge gap, a geochemical, clinopyroxene geobarometry, and SrNd isotope study was carried out on samples collected from the 1922 and lower 1999 lava flows found on the SW flank of the volcano. Petrographic evidence shows a common crystallising mineral assemblage of olivine and clinopyroxene and/or plagioclase scattered in a microlite-rich groundmass. The total alkali-silica classification diagram shows that the lavas of 1922 exhibit basanitic compositions those of 1999 are predominantly basanites with some few hawaiites. The Sr isotope ratios for the 1999 samples in this study show values somewhat lower and higher than the limits obtained for historic Mount Cameroon samples so far. While major and trace element trends indicate fractional crystallisation processes, chemical and mineral disequilibrium textures are indicative of open-system processes such as magma mixing and magma chamber recharge. Variations in incompatible trace element ratios, which hardly change during fractional crystallisation, are also suggestive of open-system processes. Plots of K2O and Nb show a mixing trend between samples from these eruptions, implying a common magma chamber where remnant material from preceding eruptions was incorporated into succeeding eruptions. Clinopyroxene geobarometric calculations show this common dominant crystallisation depth at 23–29 km.

The role of magma injection and crystal sorting in the formation of early gabbros at the Coldwell Complex, Ontario, Canada

The Layered Series of the Midcontinent Rift related Coldwell Complex comprises thick sections of gabbro, without any known associated ultramafic rocks. It represents a major early intrusive unit of the Coldwell Complex and consists of thick accumulations of olivine gabbro and oxide augite melatroctolite. This study combines petrography, mineral chemistry, and lithogeochemistry to constrain the magma composition and petrogenesis of the Layered Series. The presence of cumulus orthoclase together with the observation that the Layered Series rocks plot in the alkaline field on a total alkali–silica diagram indicate that the Layered Series magma has an alkaline parentage. The stratigraphy of the Layered Series cannot be fully correlated between different areas using lithogeochemistry and mineral chemistry. This together with observed normal and reverse trends for mineral chemical compositions in different areas suggest that the processes related to magma emplacement and crystallization were different in different locations. The whole-rock concentrations of incompatible elements and the compositions of major minerals of the olivine gabbro and oxide augite melatroctolite units are chemically similar. However, major element lithogeochemistry is variable, dominantly due to differences in the abundances of olivine, clinopyroxene, plagioclase, and magnetite. An additional observation is that olivine and clinopyroxene are not in chemical equilibrium. Together, these observations are interpreted to reflect a combination of multiple injections of magma and crystal sorting in an open system.