Mineral Modes Research Articles

Characterization of Heavy Minerals and Their Possible Sources in Quaternary Alluvial and Beach Sediments by an Integration of Microanalytical Data and Spectroscopy (FTIR, Raman and UV-Vis)

Quaternary stream sediments and beach black sand in north-western Saudi Arabia (namely Wadi Thalbah, Wadi Haramil and Wadi Al Miyah) are characterized by the enrichment of heavy minerals. Concentrates of the heavy minerals in two size fractions (63–125 μm and 125–250 μm) are considered as potential sources of “strategic” accessory minerals. A combination of mineralogical, geochemical and spectroscopic data of opaque and non-opaque minerals is utilized as clues for provenance. ThO2 (up to 17.46 wt%) is correlated with UO2 (up to 7.18 wt%), indicating a possible uranothorite solid solution in zircon. Hafnoan zircon (3.6–5.75 wt% HfO2) is a provenance indicator that indicates a granitic source, mostly highly fractionated granite. In addition, monazite characterizes the same felsic provenance with rare-earth element oxides (La, Ce, Nd and Sm amounting) up to 67.88 wt%. These contents of radionuclides and rare-earth elements assigned the investigated zircon and monazite as “strategic” minerals. In the bulk black sand, V2O5 (up to 0.36 wt%) and ZrO2 (0.57 wt%) are correlated with percentages of magnetite and zircon. Skeletal or star-shaped Ti-magnetite is derived from the basaltic flows. Mn-bearing ilmenite, with up to 5.5 wt% MnO, is derived from the metasediments. The Fourier-transform infrared transmittance (FTIR) spectra indicate lattice vibrational modes of non-opaque silicate heavy minerals, e.g., amphiboles. In addition, the FTIR spectra show O-H vibrational stretching that is related to magnetite and Fe-oxyhydroxides, particularly in the magnetic fraction. Raman data indicate a Verwey transition in the spectrum of magnetite, which is partially replaced by possible ferrite/wüstite during the measurements. The Raman shifts at 223 cm−1 and 460 cm−1 indicate O-Ti-O symmetric stretching vibration and asymmetric stretching vibration of Fe-O bonding in the FeO6 octahedra, respectively. The ultraviolet-visible-near infrared (UV-Vis-NIR) spectra confirm the dominance of ferric iron (Fe3+) as well as some Si4+ transitions of magnetite (226 and 280 nm) in the opaque-rich fractions. Non-opaque heavy silicates such as hornblende and ferrohornblende are responsible for the 192 nm intensity band.

A REE Inverse Model From Bulk Distribution Coefficients and Boundary Conditions: Results for Shield and Rejuvenated Stage Hawaiian Volcanoes

AbstractA major challenge in mantle geochemistry is determining the source composition and melt fraction involved in melting. We provide a new Rare‐Earth Element (REE) inverse model that provides source concentration, source and melt mineral modes, and melt fraction based on the difference between separate determinations of bulk distribution coefficients and constrained by boundary conditions. An analytical inverse of the batch melting equation provides expressions for source, , and bulk distribution coefficient of the mantle, , with two unknowns, the initial concentration of La in the mantle, , and Pi, the bulk distribution coefficient of the melt. We traverse through a range of steps and examine thousands of melt modes, Pi, at each step. Thousands of trial melt modes fail by generating that are inconsistent with partition coefficients. Many surviving trials cannot be inverted to estimate a mantle mode. Other boundary conditions eliminate even more trials. Surviving trials are ordered by the difference between calculated from the REE data of a lava suite and calculated from partition coefficients and mantle mode. We select the solution with the closest fit that passes all the boundary conditions. We tested our new model with lava suites from Hawaii where different lines of evidence suggest that they melted from different mantle sources, Mauna Kea representing shield‐stage lava and submarine Kiekie representing rejuvenated stage lava. Our inverse determination of mantle composition and melting parameters was consistent with earlier models based on assumptions of HREE composition.

An evolutionary system of mineralogy, Part VIII: The evolution of metamorphic minerals

Abstract Part VIII of the evolutionary system of mineralogy focuses on 1220 metamorphic mineral species, which correspond to 755 root mineral kinds associated with varied metamorphic rock types, most of which likely formed prior to the Phanerozoic Eon. A catalog of the mineral modes of 2785 metamorphic rocks from around the world reveals that 94 mineral kinds often occur as major phases. Of these common metamorphic minerals, 66 are silicates, 14 are oxides or hydroxides, 8 are carbonates or phosphates, 4 are sulfides, and 2 are polymorphs of carbon. Collectively, these 94 minerals incorporate 23 different essential chemical elements. Patterns of coexistence among these 94 minerals, as revealed by network analysis and Louvain community detection, point to six major communities of metamorphic phases, three of which correspond to different pressure-temperature (P-T) regimes of metamorphosed siliceous igneous and sedimentary rocks, while three represent thermally altered carbonate and calc-silicate lithologies. Metamorphic rocks display characteristics of an evolving chemical system, with significant increases in mineral diversity and chemical complexity through billions of years of Earth history. Earth's first metamorphic minerals 27 formed in thermally altered xenoliths and contact zones (hornfels and sanidinite facies) associated with early Hadean igneous activity (> 4.5 Ga). The appearance of new Hadean lithologies, including clay-rich sediments, arkosic sandstones, and carbonates, provided additional protoliths for thermal metamorphism prior to 4.0 Ga. Orogenesis and erosion exposed extensive regional metamorphic terrains, with lithologies corresponding to the Barrovian sequence of index mineral metamorphic zones appearing by the Mesoarchean Era (> 2.8 Ga). More recently, rapid subduction and rebound of crustal wedges, coupled with a shallowing geothermal gradient, has produced distinctive suites of blueschist, eclogite, and ultrahigh pressure metamorphic suites (< 1.0 Ga). The evolution of metamorphic minerals thus exemplifies changes in physical and chemical processes in Earth's crust and upper mantle.

A Yokenella regensburgei strain effectively removes Cu(II), Pb(II), and Cd(II) through a combination of absorption and mineralization modes

Microbial-based heavy metal removal from wastewater is a widely embraced and environmentally friendly method. Nevertheless, its sustainability and efficacy necessitate further improvement. In this study, the strain Yokenella regensburgei GXAS49-I was isolated and characterized for its bioremediation potential. The strain exhibited remarkable resistance to heavy metals, demonstrating a high removal efficiency of 85 % and 90 % for Cu(II) and Pb(II), respectively. The extracellular polymeric substance of GXAS49-I, rich in CO and CO groups, facilitated heavy metal adsorption and played a role in the removal of heavy metal ions. Additionally, GXAS49-I produced hydrogen sulfide, transforming heavy metals into sulfide sediments. Immobilizing GXAS49-I on aerobic granular sludge ensured consistently high removal efficiency for Cu(II) and Pb(II) over four consecutive cycles. The unique dual modes of absorption and mineralization of heavy metals by GXAS49-I, in conjunction with aerobic granular sludge immobilization, position it as an excellent candidate for the sustainable and effective removal of hazardous metals.

The critical role of deformation-assisted melt migration in the formation of oceanic core complexes

Oceanic core complexes provide an accessible window into deep processes occurring at slow and ultra-slow-spreading mid-ocean ridges. We analyse samples from IODP ocean drilling of core complexes at the Atlantis Bank, Atlantis Massif, and near the Kane Transform at the South West Indian and Mid-Atlantic ridges. We correlate secondary minerals, including oxides, with sites of melt migration. We interpret changes to mineral assemblage and microchemistry, reaction textures and melt-pseudomorph microstructures as fingerprints of open-system melt-mediated processes. This micro-scale information is combined with a macro-scale review of legacy mineral chemistry data to show that melt-fluxed rocks share remarkably similar characteristics across the three core complexes investigated. These are rich in oxides and have olivine, orthopyroxene and clinopyroxene grains that are chemically distinct from oxide-poor gabbros. We propose that oceanic crust fluxed with external melt can be recognised by the following key features: (1) high modes of secondary minerals, such as oxides and olivine, (2) microstructural evidence for the former presence of melt, and (3) mineral chemistry differences between primary and secondary olivine, orthopyroxene, clinopyroxene and plagioclase. Importantly, olivine has previously only been reported as primary, that is, having crystallised from magma. However, our results show that gabbros with secondary olivine are reliable indictors of melt–rock interaction during deformation-assisted diffuse melt migration through the gabbroic oceanic crust. Finally, we propose a new model for the formation of oceanic core complexes where deformation-assisted melt migration plays a critical role in strain localisation, exhumation and evolution of the core complex.

The anisotropy of geomaterial granite

Abstract. Granites appear to be isotropic, which qualifies them as suitable crystalline host rocks for nuclear waste repository sites. However, despite their optical appearance, granites show a primary structural anisotropy (Bouchez, 1997) that evolved during emplacement and crystallization of the melt. The major processes involved are magmatic flow and oriented crystal growth (Müller et al., 2011). Hypothetically, it is expected that different tectonic environments, i.e. different orientations of the stress tensor, cause significant differences in the primary anisotropy, which is expressed by the crystallographic preferred orientation (CPO) of the rock-forming minerals. It is likely that primary anisotropic petrophysical properties control the orientation of post-magmatic structural features like extensional fractures and thus shape potential fluid pathways. We present the first results of a systematic study of felsic plutonites, i.e. the GAME project (Gefüge, Textur- und Anisotropie-Messungen von potenziell für die Endlagerung geeigneten Graniten zur Charakterisierung möglicher Fluidwegsamkeiten). The samples of syn-Variscan felsic plutons from two sites (Erzgebirge and Fichtelgebirge) represent different tectonic settings during intrusion: extension and compression. Furthermore, they depict different stages of fractionation of the peraluminous granite suites. The CPOs were analysed using the neutron time-of-flight (ToF) texture diffractometer SKAT (Keppler et al., 2014; Ullemeyer et al., 1998) and EBSD (electron backscatter diffraction). Using scanning electron microscope (SEM) automated mineral liberation analysis (Schulz et al., 2020), modal mineral compositions are quantified. This enables us to model primary or “intrinsic” petrophysical properties for these granites based on the elastic stiffness tensor of the individual rock-forming minerals (Mainprice et al., 2011). Main- and trace-element geochemical data (ICP-AES and ICP-MS) allow for a characterization of the different magmatic settings of the samples. All granites show distinct preferred orientations of rock-forming minerals. The quartz textures, for example, exhibit similar CPOs, with point maxima of the positive rhombs in combination with small circles to crossed-girdle c-axis distributions. However, the orientation with respect to the geographic reference system strongly varies. We will discuss the CPOs in relation to the stress tensor orientation during emplacement of the felsic plutons and compare the primary anisotropy with the post-magmatic fracture patterns of the particular granites.

Petrogenesis of Adang and Talaya volcanic rocks, in the Mamuju area and its surrounding, West Sulawesi

The Adang Volcanic and Talaya Volcanic complex located in the Mamuju area are ancient volcanic complexes of the Neogene period. These two complexes consist of pyroclastic, volcaniclastic, and basic-intermediate lava containing the main modal minerals of leucite and clinopyroxene, making these rocks unique and rarely found in Indonesia. This study aims to determine the petrological and geochemical characteristics as well as the tectonic setting of rock formation. The rocks are generally porphyritic and vitrophyric in texture with various rock types as a result of magma differentiation. The Adang Volcanic Lava is composed of trachyandesite, tephriphonolite, trachyte, phonolite, and leucitite. Talaya Volcanic Lava is composed of basalt and trachybasalt rocks. Based on geochemical content, rocks have high alkalinity with wide range concentrations of K2O (0.27 – 10.12%), Na2O (0.54 – 11.06%), and total alkali (4.6 – 12.6%), as well as evidenced by the presence of feldspathoids. Rocks are divided into three groups, sodic, potassic, and ultrapotassic. The ultrapotassic rocks have similarities with Group III (Active Orogenic Zone) and Group I (Lamproite). The intensive enrichment of incompatible elements such as Rb and Th as well as the negative Nb and Ti anomalies reflect that magma derived from mantle metasomatism and is associated with subduction events. The genesis of the rock occurred in the tectonic setting of alkaline arc magmatism or continental extensional zone which was formed after the collision of the Banggai-Sula microcontinent with West Sulawesi. This process is also indirectly influenced by pre-collision subduction of the oceanic lithosphere.

On the Diversity and Formation Modes of Martian Minerals

AbstractA systematic survey of 161 known and postulated minerals originating on Mars points to 20 different mineral‐forming processes (paragenetic modes), which are a subset of formation modes observed on Earth. The earliest martian minerals, as on Earth, were primary phases from mafic igneous rocks and their ultramafic cumulates. Subsequent primary igneous minerals were associated with products of limited fractional crystallization, including alkaline and quartz‐normative lithologies. Significant mineral diversification occurred via precipitation of primary phases from aqueous and atmospheric fluids, including authigenesis, hydrothermal and cryogenic precipitation, and evaporites, including freeze drying during eras of low atmospheric pressures. In particular, hydrothermal mineral formation associated with both volcanic fluids and sustained hydrothermal activity in impact fracture zones may have triggered significant mineral diversification, though as yet undocumented. At least 65 such primary minerals have been identified by flown missions to Mars and from martian meteorites. A host of secondary martian minerals were produced by near‐surface processes related to water/rock interactions, including hydration/dehydration, oxidation/reduction, serpentinization, metasomatism, and a variety of diagenetic alterations. Additional mineral diversity resulted from metamorphic events, including thermal and shock metamorphism, lightning, and bolide impacts. However, several dominant sources of mineral diversity on Earth, including (a) extensive fluid/rock interactions and element concentration associated with plate tectonics; (b) high‐pressure regional metamorphism associated with plate tectonics; and (c) biologically mediated mineralization—are not known to be in play on Mars. Consequently, we estimate the total mineral diversity of Mars to be an order of magnitude smaller than on Earth.

Mineral Carbonation Potential (MCP) of Mine Waste Material: Derivation of an MCP Parameter

The heterogenous mineralogy of ultramafic deposits hosting mining operations makes it challenging to accurately determine the waste rock’s mineral carbonation potential (MCP). Additionally, the significantly higher carbonation capabilities of olivine than serpentine add to the difficulty. To address this issue, in this work, a new and unique tool called the MCP calculator was developed as a Microsoft ExcelTM spreadsheet to accurately determine the amount of anthropogenic CO2 that a given rock mass can sequester through mineral carbonation. The program estimates the modal mineral abundance of ultramafic rocks to aid in MCP estimation. This tool is designed to be cost-effective and tailored for use by the mining industry, utilising abundant lithogeochemical data to evaluate their deposit as a potential substrate for industrial mineral carbonation operations. The paper introduces the MCP calculator, outlines a framework for developing the MCP parameter, and presents an example of its application. The calculator is specific to the mineral assemblage investigated at the Turnagain ultramafic complex in northern British Columbia but can be adjusted to study comparable deposits. The paper acknowledges that using waste rock in a mineral carbonation operation requires economic and practical decisions beyond the scope of the research.

Variations in lunar regolith properties with depth as revealed by Chang'e-5 samples

The lunar regolith layer preserves abundant information on the internal properties of the Moon as well as the space-surface interactions. By gardening and overturning through time, the regolith layer is heterogenous and soils from different depths could record the complex evolution history of the Moon. Chang'e-5 (CE-5) successfully returned scooped samples and drilled samples from the northeastern Oceanus Procellarum of the Moon. In this study, one scooped sample (0–3 cm depth, S0) and two drilled samples (~10 cm depth, S10; and ~ 65 cm depth, S65) were employed to analyze their granulometry and mineralogy by micro Raman spectroscopy. The grain size increases with depth, and the median grain size of S0, S10, and S65 are Φ5.45 (30.2 μm), Φ4.47 (45.0 μm), and Φ3.37 (96.4 μm), respectively. Their mineral types and contents are pyroxene (33.4–40.5 vol%), plagioclase (30.4–33.8 vol%), olivine (9.0–13.1 vol%), glass (6.9–10.7 vol%), FeTi oxide (6.7–7.5 vol%), cristobalite (0.2–3.8 vol%), quartz (0.4–0.9 vol%), and phosphate (0.2–0.6 vol%). The size-dependent mineral modes reveal the relationship between grain size and mineralogy. The mineral modal abundances of 3 soil samples at different depths are roughly similar to that of CE-5 basalts. Raman peak position of quartz may record a peak shock pressure of 31.4 GPa. 5–9 vol% plagioclase amorphization reflects that at least 2–9% exogenous materials in CE-5 soil samples are ejected from craters with diameters larger than 3 km located beyond 50 km from the landing site.

FTIR study of H2O in silicate minerals and mineral inclusions in chromite from the peridotite zone of the Stillwater complex (Montana, USA): Evidence for chromitite formation in an H2O-rich environment

Although the involvement of hydrous fluids has been frequently invoked in the formation of stratiform chromitites in layered intrusions, there is a lack of natural evidence to signify their presence and mechanism. Here, Fourier-transform infrared spectroscopy (FTIR) of H2O in silicate minerals in the lowermost layer and G chromitite layer of the Stillwater complex, Montana, USA, shows that olivine grains have 20−55 ppm H2O, orthopyroxene has 30−45 ppm H2O, and clinopyroxene has 144−489 ppm H2O. The jointly increasing H2O contents of olivine and orthopyroxene in silicate cumulates along with magma differentiation record a negative correlation in chromitites. On the basis of poikilitic clinopyroxene, we calculated that the interstitial melts had averages of 1.3 wt% and 2.3 wt% H2O in dunite and chromitite, respectively, showing significant differences between chromitites and silicate cumulates. More than 10% of the chromite grains contained polymineralic inclusions up to 100 μm in size that were composed mainly of orthopyroxene, hornblende, plagioclase, and phlogopite. Most of these minerals were characterized by higher MgO and fluid-mobile element contents, such as Na and K, than minerals in associated silicates. Based on the mineral modes of the hydrous phases and their compositions, the trapped fluids contained ∼2.6 wt% H2O, consistent with the FTIR estimates, indicating the inclusion compositions represent interstitial melts instead of parental magmas. These observations indicate that the chromite microlites collected fluids during early crystallization, leading to a heterogeneous fluid redistribution in the melt. The fluids were collected on the surface of chromite grains during crystallization and then dissolved into poikilitic pyroxene. Chromite grains could also be efficiently floated by these fluids, causing them to migrate away from the silicate minerals in the magma channel and leading to the formation of nearly monomineralic chromitite seams. This process serves as a kinetic model indicating that chromite could be completely separated from silicates during mechanical sorting in layered intrusions.

Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 2. Trace element compositions of melts and minerals

The trace element compositions of melts and minerals from high-pressure experiments on hydrous pyroxenites containing K-richterite are presented. The experiments used mixtures of a third each of the natural minerals clinopyroxene, phlogopite and K-richterite, some with the addition of 5% of an accessory phase ilmenite, rutile or apatite. Although the major element compositions of melts resemble natural lamproites, the trace element contents of most trace elements from the three-mineral mixture are much lower than in lamproites. Apatite is required in the source to provide high abundances of the rare earth elements, and either rutile and/or ilmenite is required to provide the high field strength elements Ti, Nb, Ta, Zr and Hf. Phlogopite controls the high levels of Rb, Cs and Ba.Since abundances of trace elements in the various starting mixtures vary strongly because of the use of natural minerals, we calculated mineral/melt partition coefficients (DMin/melt) using mineral modes and melting reactions and present trace element patterns for different degrees of partial melting of hydrous pyroxenites. Rb, Cs and Ba are compatible in phlogopite and the partition coefficient ratio phlogopite/K-richterite is high for Ba (136) and Rb (12). All melts have low contents of most of the first row transition elements, particularly Ni and Cu ((0.1–0.01) × primitive mantle). Nickel has high DMin/melt for all the major minerals (12 for K-richterite, 9.2 for phlogopite and 5.6 for Cpx) and so behaves at least as compatibly as in melting of peridotites. Fluorine/chlorine ratios in melts are high and DMin/melt for fluorine decreases in the order apatite (2.2) > phlogopite (1.5) > K-richterite (0.87). The requirement for apatite and at least one Ti-oxide in the source of natural lamproites holds for mica pyroxenites that lack K-richterite. The results are used to model isotopic ageing in hydrous pyroxenite source rocks: phlogopite controls Sr isotopes, so that lamproites with relatively low 87Sr/86Sr must come from phlogopite-poor source rocks, probably dominated by Cpx and K-richterite. At high pressures (>4 GPa), peritectic Cpx holds back Na, explaining the high K2O/Na2O of lamproites.

Elemental Gains and Losses during Hydrothermal Alteration in Awak Mas Gold Deposit, Sulawesi Island, Indonesia: Constraints from Balanced Mineral Reactions

Hydrothermal gold mineralization is commonly associated with metasomatic processes resulting from interaction of hostrock with infiltrating hot aqueous fluids. Understanding of the alteration mechanism requires quantification of element changes in altered rock, relative to the unaltered or least-altered rock, representing the protolith. Balanced mineral reactions are used to gain quantitative insight into the alteration process associated with gold mineralization at the Awak Mas deposit. Three representative samples were carefully selected from the least-altered pyllite and the two alteration zones bordering the mineralization. Mineral mode, textural features, and mineral compositions were studied by microscopy and electron microprobe analyzer (EMPA). Quantitative modal analysis was performed with a Quanta 650 F QEMSCAN® system. The hydrothermal alteration sequence around the mineralization starts with the proximal albite–ankerite–pyrite alteration zone via the distal albite–chlorite alteration zone to the least-altered phyllite wall-rock. Balanced mineral reaction calculations were performed to evaluate elemental gains and losses. Most noticeable is the addition of Si, Na and Ca to each alteration zone. This alteration is represented by the almost complete replacement of muscovite by albite. The addition of Fe and S was highest in the albite–ankerite–pyrite alteration zone. Alteration of the least altered phyllite to the albite–chlorite zone involved a mass increase of 14.5% and a neglectable volume increase of 0.6%. The mass and a volume increase from the least altered phyllite to the albite–ankerite–pyrite zone was 40.5% and 0.47%, respectively. The very low volume change during alteration is also corroborated by the textural preservation indicating isovolumetric metasomatic reactions. The replacement of muscovite by albite may have had an important effect on the change of the rock failure mode from ductile to brittle, with consequences for the focusing of fluid flow.

ICDP Oman Drilling Project: varitextured gabbros from the dike–gabbro transition within drill core GT3A

Abstract. The Oman ophiolite (Samail massif, Sultanate of Oman) is the largest sub-aerial exposure of oceanic lithosphere on Earth and provides the opportunity to study the accretion and alteration of oceanic lithosphere formed under fast-spreading conditions. Drill hole GT3A (23∘06′50.7′′ N, 58∘12′42.2′′ E) of the ICDP (International Continental Scientific Drilling Program) Oman Drilling Project with a length of 400 m aimed at penetrating the dike–gabbro transition of the Samail ophiolite paleocrust in order to shed light on the role of the axial melt lens (AML) during accretion of the lower plutonic crust. AMLs beneath fast-spreading mid-ocean ridges are sandwiched between the sheeted dike complex and the uppermost gabbros and are believed to feed the upper crust and, at least partially, the underlying crystal mush. Typical gabbroic rocks from dike–gabbro transitions of fast-spreading systems are the so-called “varitextured gabbros”, often showing considerable variations in mineral mode, texture and grain size, which are regarded as the frozen fillings of axial melt lenses. Here, we present a detailed petrographic, microanalytical and bulk-chemical investigation of 36 mafic rocks from the drill hole GT3A, which represent mostly varitextured gabbros, revealing a complex formation with several evolution stages. Poikilitic domains formed first, corresponding to an early crystallization stage, where only plagioclase and clinopyroxene of more primitive composition crystallized. Later, domains of granular textures containing also interstitial amphibole and Fe–Ti oxide were formed. This stage is characterized by a magma evolution that underwent crystal fractionation established by lower temperatures due to more efficient hydrothermal cooling at the margin of the AML. A last stage is characterized by pervasive hydrothermal alteration, where all primary minerals have been altered under temperature conditions, varying from the magmatic regime down to greenschist facies. A highlight of this stage is amphiboles showing noticeable compositional zoning. The observation of peculiar microgranular domains, representing relics of stoped exogenic material from the sheeted dike complex, documents the upward migration of an AML in a replenishment event, forcing the AML to burn through previously altered sheeted dikes. This process is responsible for significant assimilation of hydrothermally altered components, indicated by a marked Cl enrichment in the outer zones of magmatic amphiboles. Petrological modeling involving gabbros and basalts revealed that the GT3A rock suite followed a fractional crystallization evolution trend, with a primitive MORB as parental melt with an estimated water content of 0.2 wt % to 0.8 wt %. The modeled liquid lines of descent suggest a magmatic evolution via fractional crystallization, where the basalts correspond to frozen liquids, while the gabbros, especially the more primitive ones, show a significant cumulate component.

Multistage growth of garnet fingerprints the behavior and property of metamorphic fluids in a Paleotethyan oceanic subduction zone

Metamorphic fluids released from the subducting crust are of great importance to understand the recycling of volatile materials at convergent plate margins. Garnet in metamorphic rocks can retain chemical zonation and crystal inclusions produced during crustal subduction, providing the record of geochemical recycling in subduction zones. This paper presents a combined study of mineralogy and geochemistry for metamorphic garnets in oceanic-type eclogite from the Paleotethyan subduction zone in the Hong'an orogen, east-central China. The results show distinct zonation of major and trace elements, crystal inclusions, water contents, and oxygen fugacity in garnet. Five stages of garnet growth were recognized based on the garnet composition and phase equilibrium modelling. Growth of Stage I to IV garnets occurs during prograde metamorphism of the Paleotethyan oceanic crust from blueschist to eclogite facies along low geothermal gradients of 7.8–9.7 °C/km. Stage V garnet was formed through dissolution and reprecipitation during mineral-fluid reaction in the early exhumation stage. Garnet grains exhibit a decrease of water content from core to rim, indicating a gradual decrease of bulk water content in host eclogite during the garnet growth. Combined with the theoretical calculation based on the mineral modes and mineral water contents, it is suggested that the subducting oceanic crust would release reduced amounts of fluids during prograde metamorphism from greenschist to eclogite facies. The different garnet zones have f O 2 values varying from ΔFMQ+1.77 to ΔFMQ+3.26, suggesting that the fluids released from the subducting oceanic crust were oxidizing during subduction to peak eclogite facies and its early exhumation stage. These garnet f O2 values are correlated with the water contents of water-saturated garnet, implying that the water content of metamorphic garnet is a potential means to recover the redox state of its host eclogite. The increase of f O2 values during prograde metamorphism of the eclogite indicates the breakdown of chlorite and possible fluid influx from serpentinite, whereas the significant drop of f O2 values during the early exhumation stage indicates the breakdown of lawsonite to release the oxidized fluid. This study demonstrates that a combined study of water content, major and trace elements, and mineral inclusions in metamorphic garnet can potentially provide a new perspective into the behavior and property of fluids released from the subducting oceanic crust. • Garnet exhibits zoning in inclusions, major-trace elements, water content and oxygen fugacity. • Multiple stages of garnet growth were recognized along the P-T path of Hong'an eclogite. • Garnet water contents reflect decrease of fluid release from subducting oceanic crust. • Garnet water contents are correlated with redox conditions of its host eclogite. • Oxidized fluid is released during the dehydration of the subducting oceanic crust.

An evolutionary system of mineralogy, Part VII: The evolution of the igneous minerals (>2500 Ma)

AbstractPart VII of the evolutionary system of mineralogy catalogs, analyzes, and visualizes relationships among 919 natural kinds of primary igneous minerals, corresponding to 1665 mineral species approved by the International Mineralogical Association—minerals that are associated with the wide range of igneous rock types through 4.566 billion years of Earth history. A systematic survey of the mineral modes of 1850 varied igneous rocks from around the world reveals that 115 of these mineral kinds are frequent major and/or accessory phases. Of these most common primary igneous minerals, 69 are silicates, 19 are oxides, 13 are carbonates, and 6 are sulfides. Collectively, these 115 minerals incorporate at least 33 different essential chemical elements.Patterns of coexistence among these minerals, revealed by network, Louvain community detection, and agglomerative hierarchical clustering analyses, point to four major communities of igneous primary phases, corresponding in large part to different compositional regimes: (1) silica-saturated, quartz- and/or alkali feldspar-dominant rocks, including rare-element granite pegmatites; (2) mafic/ultramafic rock series with major calcic plagioclase and/or mafic minerals; (3) silica-undersaturated rocks with major feldspathoids and/or analcime, including agpaitic rocks and their distinctive rare-element pegmatites; and (4) carbonatites and related carbonate-bearing rocks.Igneous rocks display characteristics of an evolving chemical system, with significant increases in their minerals’ diversity and chemical complexity over the first two billion years of Earth history. Earth’s earliest igneous rocks (>4.56 Ga) were ultramafic in composition with 122 different minerals, followed closely by mafic rocks that were generated in large measure by decompression melting of those ultramafic lithologies (4.56 Ga). Quartz-normative granitic rocks and their extrusive equivalents (>4.4 Ga), formed primarily by partial melting of wet basalt, were added to the mineral inventory, which reached 246 different mineral kinds. Subsequently, four groups of igneous rocks with diagnostic concentrations of rare element minerals—layered igneous intrusions, complex granite pegmatites, alkaline igneous complexes, and carbonatites—all first appeared ~3 billion years ago. These more recent varied kinds of igneous rocks hold more than 700 different minerals, 500 of which are unique to these lithologies.Network representations and heatmaps of primary igneous minerals illustrate Bowen’s reaction series of igneous mineral evolution, as well as his concepts of mineral associations and antipathies. Furthermore, phase relationships and reaction series associated with the minerals of a dozen major elements (H, Na, K, Mg, Ca, Fe, Al, Si, Ti, C, O, and S), as well as minor elements (notably Li, Be, Sr, Ba, Mn, B, Cr, Y, REE, Ti, Zr, Nb, Ta, P, and F), are embedded in these multi-dimensional visualizations.

Formation, cooling history and age of impact events on the IIE iron parent body: Evidence from the Miles meteorite

Most iron meteorites formed in planetary cores during differentiation, but the IIE iron meteorites have chemical and physical features that are inconsistent with this origin. By combining mineral chemistry, mineral modes and three-dimensional petrography, we reconstruct the bulk chemistry of the felsic silicate-bearing Miles IIE iron meteorite and demonstrate that the silicate inclusion compositions are similar to partial melts produced experimentally from an H chondrite composition. We use the reconstructed bulk composition, mineralogy and thermodynamic modelling to show that melting above ∼1200°C under reducing conditions formed metal (Fe-Ni alloy) and felsic silicate partial melts. Upon cooling, the melts crystallized Mg-rich pyroxenes, Na- and K-rich feldspars, and tridymite. Importantly, this mechanism enriches cosmochemically volatile elements (i.e., those with a 50% condensation temperature of ∼430–830°C, like Na and K) to the level found in the felsic silicate inclusions.The presence of crystallographically disordered srilankite (only stable above 1160°C) and an absence of Widmanstätten texture require both high peak temperatures and rapid cooling, which cannot be explained by core formation. Instead they point to small melt volumes, a transient heat pulse, and small thermal mass, and imply efficient physical segregation of silicate and metallic melts through buoyancy separation followed by rapid cooling that arrested the separation of metal and silicate liquid phases. In situ 207Pb/206Pb age of 4542.3 ± 4.0 Ma in Zr-oxide and phosphate minerals dates the melting event that formed the silicate inclusions. This age aligns with the earliest ages found in other IIE iron meteorite silicates and requires a heating event ∼25 million years after the solar system formed. We found 39Ar/40Ar ages of 3495 ± 52 Ma (low-T) and 4303 ± 7 Ma (high-T) in a K-feldspar grain, with the 3495 Ma age aligning with later thermal events recorded in other IIE iron meteorites. Dating reveals the complex petrogenetic and thermal history of Miles and the IIE iron meteorites. This is the first IIE iron meteorite found to record evidence of heating at 4.5 and 3.5 Ga likely from impact events.We propose that high-velocity impact(s) into an iron-rich, porous chondritic parent body at ∼4.54 Ga produced immiscible metal and silicate melts that cooled rapidly and trapped low density silicate inclusions within high density metal. Other IIE irons that formed at lower peak temperatures (900–1000°C) contain chondritic silicate inclusions and relict chondrules, supporting this conceptual model. This petrogenesis is consistent with thermodynamic modelling, experimental data and the wide range of peak temperatures and cooling rates observed in the IIE iron meteorites.

Petrological and geochemical characteristics of the mafic–ultramafic Americano do Brasil Complex, central Brazil, and the implications for its genesis

The Americano do Brasil Complex occurs in the Neoproterozoic Goias Magmatic Arc, central Brazil. It is composed of two mafic–ultramafic cumulate sequences, intruded into granodioritic gneisses. Although deformed and partially recrystallized by a regional metamorphic overprint, the complex still preserves relict igneous features, such as adcumulate to heteradcumulate textures. The Northern sequence is mostly composed of olivine and olivine-clinopyroxene cumulates, whereas the Southern consists mainly of two-pyroxene cumulate rocks, with plagioclase and olivine cumulates occurring in lesser amounts. The complex has three main orebodies, with textures that range from disseminated to massive sulfide breccias with durchbewegung texture. Thermodynamic modeling using a single picrite parental magma composition can predict cumulate rock compositions and mineral modes similar to all of the observed cumulate rock compositions of the Americano do Brasil Complex. Equilibrium crystallization of the liquid and assimilation-batch-crystallization involving up to 45 % of the host gneisses in the upper crust produces solids similar to the cumulates described in the Northern and Southern sequences, respectively. Modeled pressure–temperature emplacement conditions of the magma were c.a. 2.5 kbar and 1310 °C. Both sequences have similar incompatible trace element patterns which, together with the results of the modeling, imply a broadly comagmatic origin.

WISTFUL: Whole‐Rock Interpretative Seismic Toolbox for Ultramafic Lithologies

AbstractTo quantitatively convert upper mantle seismic wave speeds measured into temperature, density, composition, and corresponding and uncertainty, we introduce the Whole‐rock Interpretative Seismic Toolbox For Ultramafic Lithologies (WISTFUL). WISTFUL is underpinned by a database of 4,485 ultramafic whole‐rock compositions, their calculated mineral modes, elastic moduli, and seismic wave speeds over a range of pressure (P) and temperature (T) (P = 0.5–6 GPa, T = 200–1,600°C) using the Gibbs free energy minimization routine Perple_X. These data are interpreted with a toolbox of MATLAB® functions, scripts, and three general user interfaces: WISTFUL_relations, which plots relationships between calculated parameters and/or composition; WISTFUL_geotherms, which calculates seismic wave speeds along geotherms; and WISTFUL_inversion, which inverts seismic wave speeds for best‐fit temperature, composition, and density. To evaluate our methodology and quantify the forward calculation error, we estimate two dominant sources of uncertainty: (a) the predicted mineral modes and compositions, and (b) the elastic properties and mixing equations. To constrain the first source of uncertainty, we compiled 122 well‐studied ultramafic xenoliths with known whole‐rock compositions, mineral modes, and estimated P‐T conditions. We compared the observed mineral modes with modes predicted using five different thermodynamic solid solution models. The Holland et al. (2018, https://doi.org/10.1093/petrology/egy048) solution models best reproduce phase assemblages (∼12 vol. % phase root‐mean‐square error [RMSE]) and estimated wave speeds. To assess the second source of uncertainty, we compared wave speed measurements of 40 ultramafic rocks with calculated wave speeds, finding excellent agreement (Vp RMSE = 0.11 km/s). WISTFUL easily analyzes seismic datasets, integrates into modeling, and acts as an educational tool.

Mineralogy and Origin of the Manganese Deposit in the Sulaimani Province, Kurdistan Region of Iraq: Insight to Serpentinization-Induced Manganese Production Scenario

The Manganese deposits in Sulaimani metallogenic province mainly occur within the top Qulqula Radiolarite chert unit of the Penjween ophiolite complex as strata bound type deposits near Kani Saif village, 15 km south of the Penjween district within the Imbricated zone, Kurdistan Region of Iraq. A restricted occurrence of massive manganese boulders was identified, 1 km north to the Mawat District, associated with the Oligocene Merga Red beds Group. The Qulqula Radiolarite represents the Middle Jurassic-Early Cretaceous sedimentary cover of Neo-Tethys oceanic crust deposits throughout the early to mature stages of the Neo-Tethys ocean opening along the northern and eastern margins of the Afro-Arabian plate. The field and petrographical data indicated that the nature of manganese mineralization in the area is of various forms including veins, brecciated, micronodules, banded and massive types. Reflected light microscopy, high resolution scanning electron microscope and X-ray diffraction reveal that the mineral assemblages are dominated by barunite, rhodinite, hematite, quartz and carbonate for the massive metamorphosed type deposit in the Mawat area. Meanwhile, the mineralogy of the vein, micronodule and banded types are simple and dominated by pyrolusite, hollandite minerals close to Kain Saif village. Combinations of the modal manganese minerals, filed and textural observations, a paragenetic-time model suggests that the manganese deposit in the area formed via a sequence of multiple processes (1) serpentinization of the upper mantle at mid oceanic ridge during the Cretaceous period, (2) deposition from diluted hydrothermal fluids in the Neo-Tethys mature oceanic basin, (3) the diagenetic modification of the manganese bearing sediment and (4) metamorphism of sediment a combing Zagros orogeny in Paleogene. Overall data suggest that the manganese deposits in the Kurdistan region of Iraq are cogenetic and spatially related to those which occur along the entire margin of the Arabian plates from Oman to Turkey associated with the radiolarite facies.