Composition Of Inclusions Research Articles

The origin of the Late Quaternary back-arc volcanic rocks from Kamchatka: evidence from the compositions of olivine and olivine-hosted melt inclusions

The origin of the Late Quaternary back-arc volcanic rocks from Kamchatka: evidence from the compositions of olivine and olivine-hosted melt inclusions

Periodically Released Magmatic Fluids Create a Texture of Unidirectional Solidification (UST) in Ore-Forming Granite: A Fluid and Melt Inclusion Study of W-Mo Forming Sannae-Eonyang Granite, Korea

The Upper Cretaceous Sannae-Eonyang granite crystallized approximately 73 Ma and hosted the Sannae W-Mo deposit in the west and the Eonyang amethyst deposit in the east. The granite contained textural zones of miarolitic cavities and unidirectional solidification texture (UST) quartz. The UST rock sampled in the Eonyang amethyst mine consisted of (1) early cavity-bearing aplitic granite, (2) co-crystallization of feldspars and quartz in a granophyric granite, and (3) the latest unidirectional growth of larger quartz crystals with clear zonation patterns. After the UST quartz was deposited, aplite or porphyritic granite was formed, repeating the prior sequence. Fluid and melt inclusions occurring in the UST quartz and quartz phenocrysts were sampled and studied to understand the magmatic-hydrothermal processes controlling UST formation and W-Mo mineralization in the granite. The composition of melt inclusions in the quartz phenocrysts suggested that the UST was formed by fractionated late-stage granite. Some of the melt inclusions occurring in the early-stage UST quartz were associated with aqueous inclusions, indicating fluid exsolution from a granitic melt. Hypersaline brine inclusions allowed the calculation of the minimum trapping pressure of 80–2300 bars. Such a highly fluctuating fluid pressure might be potentially due to a lithostatic-hydrostatic transition of pressure-attending fluid loss during UST formation. Highly fluctuating lithostatic-hydrostatic pressures created by fluid exsolution allowed shifting of the stability field from a quartz-feldspar cotectic to a single-phase quartz. The compositions of brine fluid assemblages hosted in the quartz phenocrysts deviated from the fluids trapped in the UST quartz, especially regarding the Rb/Sr and Fe/Mn ratios and W and Mo concentrations. The study of melt and fluid inclusions in the Eonyang UST sample showed that the exsolution of magmatic fluid was highly periodic. A single pulse of magmatic fluids of variable salinities/densities might have created a single UST sequence, and a new batch of magmatic fluid exsolution would be required to create the next UST sequence.

The Origin of Late Cenozoic Magmatism in the South China Sea and Southeast Asia

AbstractBasaltic lavas sample recycled crustal materials from their mantle source. Constraining the location and residence time of these recycled materials in the mantle is critical to understand global mantle dynamics. In this study, we present new whole‐rock major and trace element abundances, Sr‐Nd‐Mo‐Os isotopes, water contents and He isotopes of volcanic glasses, U‐Pb ages of zircons, and compositions of melt inclusions, spinels and olivines from the South China Sea (SCS) seamounts lavas. These new data are compared with literature data from intraplate volcanism of similar age from Southeast (SE) Asia. The isotope data of late Cenozoic lavas from the SCS seamounts and SE Asia can be explained by mixing between enriched mantle 2 (EM2) and depleted mid‐ocean ridge basalt mantle components. Our data are consistent with the EM2 signature of late Cenozoic lavas derived from recycled young oceanic crust and sediments. The compositions of olivine phenocrysts indicate an olivine‐dominated (peridotitic) mantle source. There is currently no evidence for a high‐3He/4He mantle plume component beneath the SCS. Our results combined with geophysical data and plate reconstructions suggest that the late Cenozoic magmatism is related to the upwelling of instabilities from the mantle transition zone (MTZ) triggered by a stagnant slab. The SCS seamount lavas sample an enriched MTZ containing young recycled materials, consistent with regional past subduction. Our study provides additional evidence that storage and recycling of crustal materials in or near the MTZ is an important mechanism to develop global mantle heterogeneities sampled by intraplate volcanoes.

Effect of Calcium Treatment on Inclusions in H08A Welding Rod Steel

The effect of calcium treatment on inclusions in H08A welding rod steel was studied by industrial experiment and using thermodynamics theory. The effects of inclusion composition, morphology, quantity, and size in H08A welding rod steel before and after calcium treatment were studied by metallographic microscope, scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). Thermodynamic studies show that the addition of calcium can form various forms of xCaO·yAl2O3, under the condition that the composition of molten steel remains unchanged, the control of calcium content is the key to generate low melting point calcium-aluminate complex non-metallic inclusions and improve the quality of molten steel. The production practice in steel plant shows that for welding rod steels, the calcium content in a suitable range can meet the requirements of calcium treatment. Effective calcium treatment can not only transform the high melting point Al2O3 inclusions into the low melting point complex non-metallic inclusions between 3CaO·Al2O3 and 12CaO·7Al2O3, but also make the original shape-diversified inclusions into the spherical calcium-aluminate complex non-metallic inclusions. Meanwhile, the total number of inclusions and large-scale inclusions in welding rod steel are reduced, and the inclusions tend to disperse in the steel, which is very conducive to the improvement of steel quality. The results show that the modification path of magnesium aluminate spinel in steel is as follows: Al2O3 → MgO-Al2O3 → MgO-CaO-Al2O3. In addition, calcium treatment can modify MgO-Al2O3 spinel in steel into liquid MgO-CaO-Al2O3 complex non-metallic inclusions with low melting point.

Melt-rock interaction in the lower crust based on silicate melt inclusions in mafic garnet granulite xenoliths, Bakony–Balaton Highland

Major and trace element composition of silicate melt inclusions (SMI) and their rock-forming minerals were studied in mafic garnet granulite xenoliths from the Bakony–Balaton Highland Volcanic Field (Western-Hungary). Primary SMIs occur in clinopyroxene and plagioclase in the plagioclase-rich domains of mafic garnet granulites and in ilmenite in the vicinity of these domains in the wall rock. Based on major and trace elements, we demonstrated that the SMIs have no connection with the xenolith-hosting alkaline basalt as they have rhyodacitic composition with a distinct REE pattern, negative Sr anomaly, and HFSE depletion. The trace element characteristics suggest that the clinopyroxene hosted SMIs are the closest representation of the original melt percolated in the lower crust. In contrast, the plagioclase and ilmenite hosted SMIs are products of interaction between the silicic melt and the wall rock garnet granulite. A further product of this interaction is the clinopyroxene–ilmenite±plagioclase symplectite. Textural observations and mass ­balance calculations reveal that the reaction between titanite and the silicate melt led to the formation of these assemblages. We propose that a tectonic mélange of metapelites and (MOR-related) metabasalts partially melted at 0.3–0.5 GPa to form a dacitic–rhyodacitic melt leaving behind a garnet-free, plagioclase+clinopyroxene+orthopyroxene+ilmenite residuum. The composition of the SMIs (both major and trace elements) is similar to those from the middle Miocene calc-alkaline magmas, widely known from the northern Pannonian Basin (Börzsöny and Visegrád Mts., Cserhát and Mátra volcanic areas and Central Slovakian VF), but the SMIs are probably the result of a later, local process. The study of these SMIs also highlights how crustal contamination changes magma compositions during asthenospheric Miocene ascent.

FRAnCIs calculation program with universal Raman calibration data for the determination of PVX properties of CO2–CH4–N2 and CH4–H2O–NaCl systems and their uncertainties

Many experimental calibration data linking the variation of Raman spectral parameters (i.e., peak position, peak area/intensity ratio …) with the PVX properties of pure gases or mixtures of CO2–CH4–N2 or CH4–H2O–NaCl systems have been published in literature by different laboratories. However, there is a significant discrepancy between these calibrations, leading possibly to inaccurate results when applied in another laboratory. In this paper, the inter-laboratory applicability of the existing calibration data is examined. Universal calibration data based on 78 regression equations and applicable for any Raman apparatus within any laboratory are provided in the form of a calculation program. The FRAnCIs (acronym for Fluids: Raman Analysis of the Composition of Inclusions) Python user-friendly interface facilitates the application of these calibrations as well as to estimate the uncertainty of the measurements.

Characterization of Nonmetallic Inclusions in Low‐Alloyed Steels Using Pulse Distribution Analysis Optical Emission Spectroscopy and Offline Investigation Methods

The characteristics of nonmetallic inclusions (NMIs) in low‐alloyed steel samples taken during ladle treatment before and after Ca treatment are evaluated using the pulse distribution analysis optical emission spectroscopy (PDA/OES) method, INCA‐Feature investigations of inclusions on a polished surface of steel samples, and 3D investigations of NMIs after electrolytic extraction (EE) of steel samples. The investigation results of NMIs using the different methods were compared. The PDA/OES results show a clear tendency of a change in the average composition and quantity of NMIs during ladle treatment, which correlates well with the results obtained from the other two methods. Overall, it is found that the application of the PDA/OES method is appropriate to enable a fast online evaluation of inclusion compositions and their behaviors during steelmaking. This, in turn, provides the means for establishing an online control and correction of technological operations of the ladle treatment to implement necessary modification of NMIs to improve the cleanliness of steels and avoid clogging problems during casting.

EVALUATION OF THE EFFICIENCY OF USING SK30 WIRE IN STEEL PROCESSING AT THE LADLE FURNACE PLANT

The paper presents studies showing the effectiveness of the use of wire with SiCa filler in the out-of-furnace processing of steels. The efficiency of use was evaluated by calculating the contamination with non-metallic inclusions, as well as by determining the phase composition of non-metallic inclusions at the stages of out-of-furnace processing and casting. (installation bucket furnace→vacuum cleaner→continuous casting). The study found that the adjustment of the content of aluminum before casting leads to the formation of refractory inclusions of corundum - (AlO), spinels - (AlO·MgO), which are deposited on the walls of the steel filling path and worsen the spillability of steel. The use of SK30prov with SiCa filler at the final stages of extra-furnace processing (after the introduction of aluminum), leads to the modification of refractory inclusions in low-melting calcium aluminates of the type (CaO·AlO). The presence of low-melting inclusions is more preferable, since this type of inclusions is not deposited on the walls of the filling cup and does not have a negative effect on the contamination of the continuously cast billet and products obtained from them with inclusions.

Aluminum-Free Steelmaking: Desulfurization and Nonmetallic Inclusion Evolution of Si-Killed Steel in Contact with CaO-SiO2-CaF2-MgO Slag

In some applications, deep desulfurization and deoxidation of steels without the use of aluminum are required, using Si as a deoxidant instead, with double-saturated slags in the CaO-SiO2-CaF2-MgO system. This work studied the desulfurization and nonmetallic inclusion evolution for the system using an induction furnace and compared the results with FactSage kinetic simulations. Steel samples were taken from the steel melt and analyzed with ICP-MS and combustion analysis for chemistry, and SEM/EDS for nonmetallic inclusion quantity, size, and composition. The results indicate that the steel was deeply desulfurized, with a final sulfur partition coefficient of 580; MgO was reduced from the slag, yielding dissolved [Mg] that transformed liquid Mn–silicate inclusions into forsterite and MgO. Intentional reoxidation of the melt with oxidized electrolytic iron demonstrated a significant concentration of dissolved [Mg] in the steel, by the formation of additional forsterite and MgO upon reoxidation.

The Origin of Rhyolitic Magmas at Krafla Central Volcano (Iceland)

AbstractWe present a detailed petrologic study of rhyolites from seven eruptions spanning the full (∼190 ky) history of rhyolitic volcanism at Krafla volcano, northeast Iceland. The eruptions vary widely in size and style, but all rhyolites are crystal-poor (<6 modal%: plagioclase + augite ± pigeonite ± orthopyroxene ± titanomagnetite ± fayalite) and have similar evolved compositions (73.7–75.8 wt% normalized whole-rock SiO2) and trace element patterns. Macrocryst rim compositions from each eruption cluster within a narrow range and are appropriate for equilibrium with their carrier melt. Crystal cores and interiors display complex growth patterns and commonly host resorption surfaces, but compositional variations are slight (e.g. typically <10 mol% An for plagioclase, Mg# <10 for pyroxene), and consistent with an overall trend of cooling and differentiation by crystal fractionation. Although most crystal core and interior compositions are broadly appropriate for equilibrium with melts similar to their host whole-rock, variable growth histories, juxtaposition of grains with distinct trace element compositions, and scatter in melt inclusion compositions indicate mixing of antecrysts from compositionally similar evolved melts and/or assimilated felsic mush or intrusions before final rim growth. Evidence for mafic recharge (e.g. coupled increases in An and Fe in plagioclase) is absent in most crystals; rhyolite storage and fractionation thus occurred largely in isolation from the underlying mafic system. Comparison of observed matrix glass compositions with published experimental work on melting of altered (meta)basalts casts doubt on previous models favouring rhyolite generation by partial melting of hydrothermally altered basalts, instead supporting recent isotopic and modelling arguments for a crystallization-driven process [Hampton, R. L. et al. (2021). Journal of Volcanology and Geothermal Research 414, 107229]. MELTS fractional crystallization and assimilation-fractional crystallization (AFC) models at 1 kbar predict liquid major and trace element compositions similar to Krafla rhyolites after ∼60–70 vol% crystallization of a quartz tholeiite melt representative of the evolved crystal-poor basalts commonly erupted within Krafla caldera. We thus suggest that stalling and crystallization of these evolved basalts at shallow depth forms crystal mushes from which evolved (broadly dacitic to rhyolitic) melts are extracted. These melts ascend and mix with other compositionally similar melt bodies and/or assimilate felsic intrusive material in the uppermost crust. The Daly gap between ∼57 and 71 wt% SiO2 at Krafla is consistent with preferential extraction of evolved melts from quartz tholeiite mushes in the ∼50–70% crystallinity window. Residual solid (cumulate) compositions predicted by MELTS are exclusively mafic, hence efficient silicic melt extraction from quartz tholeiite mushes may also explain the apparent compositional bimodality in some Icelandic plutonic suites.

Evaluation of Thermodynamic Driving Force and Effective Viscosity of Secondary Steelmaking Slags on the Dissolution of Al<sub>2</sub>O<sub>3</sub>-Based Inclusions from Liquid Steel

Dissolution of Al2O3-based inclusions are paramount during production of special steel and slag engineering is key to enhance this phenomenon. This work evaluates the influence of thermodynamic driving force (ΔC) and effective viscosity (ηe) on steel cleanliness of three distinct steel grades and slag composition (Steel/Slag A, Steel/Slag B and Steel/Slag C). Initial and final steel and slag samples were withdrawal on an electric steelmaking facility. The first samples after addition of aluminum as deoxidizer and the second after vacuum degassing stage. X-ray fluorescence and optical spectrometry obtained initial and final samples chemical composition. An ASPEX Explorer acquired inclusions data and FactSage v.7.2 performed thermodynamic calculations. Analysis of steel Al and O content highlighted an inefficient dissolution of Al2O3-based inclusions for Steel/Slag A, deteriorating steel cleanliness. Furthermore, this phenomenon is supported by average inclusions composition on initial and final samples plotted in pseudo-ternary diagram. Steel/Slag B and C provided improved results regarding the dissolution of Al2O3-based inclusions with a final inclusion density below 0.50 mm-2. These two slags composition achieved values of ΔC above 25 and ηe close to 0.10 Pa·s. In addition, their combined effect (ΔC/ηe) presented values above 250 and had the highest linear fit among these analyses. These properties are influenced by slags chemical composition and can be improved controlling parameters as binary basicity and CaO/Al2O3 ratio. Slags B and C were selected to define an optimal range for these parameters, with binary basicity between 3.00–3.50 and CaO/Al2O3 ratio in a range from 2.50–3.50.

The significance of inclusion morphology and composition in governing hydrogen transportation and trapping in steels

In this paper, two steels with different morphology of inclusions are studied. Scanning electron microscopy, finite element calculations, and electrochemical hydrogen permeation tests were conducted. Furthermore, in-situ observations of hydrogen de-trapping from the surface of steels were achieved using a hydrogen charging device and optical microscope. Results show that stripe-shaped complex inclusions exhibit a higher level of residual stress, especially at the boundary of oxide components. The hydrogen molecule is also prone to emerge at the oxide composition and intensifies the risks of cracking. In contrast, the residual stress levels around spherical inclusions are comparatively lower due to discrete sites of stress concentration. Thus, the effect of dispersed tiny dioxide sphere inclusions can help relieve the local hydrogen pressure and promote the resistance against hydrogen-induced cracking.

Warm and Slightly Reduced Mantle Under the Off-Rift Snæfellsnes Volcanic Zone, Iceland

AbstractOlivine (Fo75-91) with spinel inclusions (Cr# 10–61) in basaltic lavas/tephras from the off-rift Snæfellsnes Volcanic Zone in Iceland record the chemistry, temperature and oxygen fugacity of fractionating magmas. After a detailed assessment of equilibrium conditions, crystallization temperatures and oxygen fugacity can be calculated from the composition of homogeneous Cr-spinel and Al-chromite inclusions in olivine phenocrysts. Geologically meaningful results can occasionally be obtained when homogenous spinel is enclosed in mildly zoned olivine and KDMg-Fe [(Mg/Fe)olivine/(Mg/Fe2+)spinel] is within the range for homogenous spinel in homogeneous olivine (3.5–4.3 for our samples). Spinel in normal zoned Fo84.7–90.9 olivine records the primitive stages of magma fractionation and has crystallized from clinopyroxene-free primitive melts, probably at Moho depth and/or below. Discrepancies between Tol-liq (Mg-Fe2+ diffusion sensitive) and TAL (diffusion insensitive) suggest that some primitive olivines experienced magma mixing, completely overprinting their Fo content. Consequentially, Tol-liq in primitive olivines occasionally records residence rather than crystallization conditions. Temperature (1187–1317°C) gradually decreases across normal zoned Fo84.7–90.9 olivine and controls fO2 (Δlog fO2 (QFM) −0.6 ± 0.2). Recharge-related primitive Fo83.8–86.8 mantles of reverse zoned olivine contain the most primitive Cr-spinel linked to crustal magma storage zones. These spinels are mostly antecrysts with high Cr# (41.1–47.9) similar to spinel in normal zoned olivines that were captured by olivine and equilibrated in terms of Mg-Fe2+. A rare olivine macrocryst crystallized alongside clinopyroxene (wehrlite) and includes abundant homogeneous Al-rich Cr-spinels. These are unique because they appear to record closed-system fractional crystallization rather than magma mixing and because they show that Cr-poor, Al-rich spinel crystallized alongside clinopyroxene. The macrocryst olivine–spinel pairs record lower crustal crystal mush conditions with fO2 around the QFM buffer and Tol-liq of ∼1200°C, similar to recharge-related mantles of reverse zoned olivine. More evolved compositions occur in the cores of reverse zoned olivine (Fo75-85) that contain Cr-spinel, Fe-spinel and Al-magnetite. Contrary to spinel in more primitive olivine, these compositions are diverse and follow increasing 100Fe3+/(Cr+Al+Fe3+) of 12.3 to 54.8 and TiO2 (3.3 to 14.7 wt %) at decreasing Mg# (57.4 to 24.1) and Cr# (30.4 to 9.9) and rapidly increasing oxygen fugacities (Δlog fO2 (QFM) +0.2 to +2.0) over only a limited temperature decrease (Tol-liq: 1190 to 1145°C). These compositions span the ‘spinel gap’ and are extremely rare globally. Their preservation is probably related to high-temperature crystallization followed by rapid cooling. These compositions occur at two of the four investigated volcanic centres (Búðahraun and Berserkjahraun) and indicate a strong influence of crustal magmatic processes on crystal composition and fO2, which is absent in the other two locations (Ólafsvíkurenni and Nykurhraun). Spinel and olivine compositions support the tectonically controlled decompression melting of a fertile peridotitic source at elevated mantle temperatures relative to MORB and more reducing conditions than other off-rift magmatism in Iceland.

Chromite Paleoplacer in the Permian Sediments at the East Edge of the East European Platform: Composition and Potential Sources

A chromite occurrence called the Sabantuy paleoplacer was discovered in the Southern Pre-Ural region, at the east edge of the East-European Platform in the transitional zone to the Ural Foredeep. A ca. 1 m-thick chromite-bearing horizon is traced at a depth of 0.7–1.5 m from the earth’s surface for the area of ca. 15,000 m2. The chromspinel content in sandstones reaches 30–35%, maximum values of Cr2O3 are 16–17 wt.%. The grain size of detrital chromspinel ranges from 0.15 to 0.25 mm. Subangular octahedral crystals dominate; rounded grains and debris are rare. The composition of detrital chromspinel varies widely and is constrained by the substitution of Al3+ and Cr3+, Fe2+ and Mg2+ cations. Chemically, low-Al (Al2O3 = 12 wt.%) and high-Cr (Cr2O3 = 52–56 wt.%) chromspinel prevail. The compositional analysis using discrimination diagrams showed that most chromites correspond to mantle peridotites of subduction settings. Volcanic rocks could be an additional source for detrital chromites. It is confirmed by compositions of monomineralic, polymineralic and melt inclusions in chromspinels. The presented data indicates that ophiolite peridotites and related chromite ore associated with oceanic and island-arc volcanic rocks, widespread in the Ural orogen, could be the main sources of the detrital chromspinel of the Sabantuy paleoplacer.

Two billion years of episodic and simultaneous websteritic and eclogitic diamond formation beneath the Orapa kimberlite cluster, Botswana

The Sm–Nd isotope systematics and geochemistry of eclogitic, websteritic and peridotitic garnet and clinopyroxene inclusions together with characteristics of their corresponding diamond hosts are presented for the Letlhakane mine, Botswana. These data are supplemented with new inclusion data from the nearby (20–30 km) Orapa and Damtshaa mines to evaluate the nature and scale of diamond-forming processes beneath the NW part of the Kalahari Craton and to provide insight into the evolution of the deep carbon cycle. The Sm–Nd isotope compositions of the diamond inclusions indicate five well-defined, discrete eclogitic and websteritic diamond-forming events in the Orapa kimberlite cluster at 220 ± 80 Ma, 746 ± 100 Ma, 1110 ± 64 Ma, 1698 ± 280 Ma and 2341 ± 21 Ma. In addition, two poorly constrained events suggest ancient eclogitic (> 2700 Ma) and recent eclogitic and websteritic diamond formation (< 140 Ma). Together with sub-calcic garnets from two harzburgitic diamonds that have Archaean Nd mantle model ages (TCHUR) between 2.86 and 3.38 Ga, the diamonds studied here span almost the entire temporal evolution of the SCLM of the Kalahari Craton. The new data demonstrate, for the first time, that diamond formation occurs simultaneously and episodically in different parageneses, reflecting metasomatism of the compositionally heterogeneous SCLM beneath the area (~ 200 km2). Diamond formation can be directly related to major tectono-magmatic events that impacted the Kalahari Craton such as crustal accretion, continental breakup and large igneous provinces. Compositions of dated inclusions, in combination with marked variations in the carbon and nitrogen isotope compositions of the host diamonds, record mixing arrays between a minimum of three components (A: peridotitic mantle; B: eclogites dominated by mafic material; C: eclogites that include recycled sedimentary material). Diamond formation appears dominated by local fluid–rock interactions involving different protoliths in the SCLM. Redistribution of carbon during fluid–rock interactions generally masks any potential temporal changes of the deep carbon cycle.

THE INVESTIGATION OF STIFFNESS OF HYBRID BISTEEL I-SECTION BEAMS

The stiffness analysis of the simple supported hybrid bisteel I-section beam subjected by uniformly distributed load is considered in this paper. The hybrid bisteel I-section beam presents a composition of high-strength steel inclusions for the flanges in the region of maximum stresses and of low-strength steel for remaining volume of the beam. The explicit analytical model for evaluation of stiffness of the beams mentioned is presented. The geometrical linear approach and elastic plastic material model have been assumed. The application of high-strength steel inclusion in case perfectly elastic state of the hybrid bisteel I-section beam, increase the deflection insignificantly (up to 10%). While strain hardening effect reduces the deflection by about 4 times compared to the perfect plasticity. The verification of the theoretical analysis has been performed by the FEM. After simple transformations, the proposed model can be easily applied to the evaluation of stiffness of otherwise loaded and supported hybrid bisteel I-section beams.

Halogenases of Qarhan Salt Lake in the Qaidam Basin: Evidence From Halite Fluid Inclusions

The fluid inclusion composition of halite can help track chemical composition of ancient fluids and, thus, serves as a reliable index to analyze ancient brine in salt lakes. Qarhan Salt Lake (QSL) is the largest potash brine deposit in China. Although the mixing of modern river water and Ca-Cl deep water is widely accepted as potassium formation, the mixing characteristics in the time domain and driving factors of deep water are still unclear. Here, the chemical composition of fluid inclusions in primary halite samples collected from the ISL1A borehole in QSL was measured by LA-ICP-MS technology. The analysis results show that, during the formation stage of the S4 salt layer in QSL, the main potassium salt layer, the contents of Ca2+ and Sr2+ in brine increased significantly. There is evidence confirming that Ca-Cl deep water is beneficial to the enrichment of potassium and the surrounding rivers generally develop terraces. It suggests that, during the formation stage of the QSL potassium salt layer, more Ca-Cl inflow water of the northern margin supplies the salt lake, inferring that it was driven by tectonic activities. In addition, the chemical composition of halite fluid inclusions shows that there is an anomaly in geochemistry at the early stage of salt formation in QSL. By combining the time of tectonic activities, it is inferred that the anomaly is not caused by tectonic activities but maybe caused by a salt-forming event. This work indicates that deep water and tectonic movement have a huge impact on the evolution of salt lakes. Therefore, it is necessary to consider the influence of deep water and tectonic activities on the salt-forming evolution stage of salt lakes when studying the salt-forming evolution stage of salt lakes and paleoclimate by using salt lake deposition.

Unraveling sedimentary precursors and metal enrichment of high-grade metamorphosed manganese-rich rocks from the Borborema Province, northeastern Brazil

The Paleoproterozoic Lagoa do Riacho manganese deposit in the Borborema Province is central to unravelling the genesis of Paleoproterozoic manganese deposits, Paleoproterozoic redox evolution and genetic relationship to the West African Craton. With manganese contents averaging 35 wt%, the Lagoa do Riacho manganese unit is lithologically subdivided into oxidized and silicate manganese ores and a garnetite (garnet-rich rocks) subgroup. The oxidized manganese ore consists mainly of pyrolusite, manganese-oxyhydroxide and spessartine. The silicate manganese ore has rhodonite, tephroite and spessartine. Garnetite contains spessartine and minor quartz and rhodonite. The main host rocks include garnet quartzite and graphite-bearing pelitic gneiss. The composition of carbonate inclusions in spessartine-rhodonite and Ca-Mn fractionation between garnet core and rim suggests all these manganese-rich rocks probably formed from protoliths of marl composition. Biogenic, syn-sedimentary graphite in the manganese-rich rocks and their host rocks indicates organic matter was deposited along with the marl protolith. Within this general context and through chemical-petrological relations, we outline an initial environment involving anoxic sediments' deposition (eg., organic matter-rich manganese marl and black shales, and wackes) on the seafloor. The presence of spessartine, rhodonite, and tephroite suggests peak metamorphic conditions reached amphibolite facies conditions (6–7 kbars and 550–700 °C). Amphiboles indicate later retrograde stages and carbonate veins suggest a possible hydrothermal stage after manganese deposition. The metamorphosed manganese-rich rocks were upgraded to medium-grade manganese ores during exposure to surface water. Our results indicated that the manganese-rich rocks and their host rocks were generated in a sedimentary context, possibly in a marine setting with carbonate and organic matter contribution.

Potassium-rich granite melt inclusions in zircon from gabbro-hosted felsic stringers, Mid-Atlantic Ridge at 13°34′N: E-MORB connection

We present new data on crystallized micro-inclusions in zircon from clinopyroxene-bearing felsic stringers within gabbronorite of gabbro-peridotite oceanic core complex at Mid-Atlantic Ridge, 13°34′ N. A relatively large (about 49 × 22 μm) crystallized inclusion exposed in situ in thin section consists of the muscovite + biotite + plagioclase + K-feldspar + quartz assemblage. Smaller inclusions (≤20 μm) found in zircon separates consist of silicate minerals, interstitial water solution, and gas bubbles. At temperature close to 800 °C and estimated pressure about 1.5 kbar the inclusions completely homogenize into a K2O-rich (3.9 ± 0.1 wt%), H2O-bearing (about 4 wt%) granite (SiO2 70 ± 2 wt%) melt. Calculations employed DOMINO software show that complete closed-system crystallization of the analyzed melt exactly reproduces mineral assemblage of the large crystallized inclusion (+H2O) at about 1.5 kbar below 600 °C. Granitoid mineralogy of felsic stringers hosting zircon does not correspond to that of the crystallized melt inclusions, with a significantly lower K2O in the former. The K2O loss might result from interaction of the melt with pyroxenes of the host gabbro. This implies that considering felsic granitoid veins, often present in the oceanic lower crustal sections, as simply “frozen melt” is not always justified. Compositional variations of basalt lava glasses from the 13°25′–14° portion of the Mid-Atlantic Ridge show continuous geochemical trends from D-MORB to E-MORB with K2O enrichment up to 0.9 wt%, suggesting mixing from two sources. The most K2O-enriched E-MORB composition (K2O = 0.9 wt%, H2O = 0.7 wt%, K2O/TiO2 = 0.42, (La/Sm)N = 2.45) was assumed as a source of the granitoid inclusions. Computer simulation of equilibrium crystallization of this E-MORB composition returned a granite residual melt closely matching the average composition of the zircon-hosted melt inclusions at 820 °C, 1.5 kbar and melt fraction 5.2 vol%. The result suggests a direct link between the E-MORB magma occurring in the studied area, and the origin of the K-rich granite melt in zircon-hosted inclusions.

Geochemical and lead isotope compositions of olivine-hosted melt inclusions from the Yaeyama Graben in the southern Okinawa Trough: Implications for slab subduction and magmatic processes

Chemical compositions were measured in olivine-hosted melt inclusions in basaltic volcanic rocks from the Yaeyama Graben in the southern Okinawa Trough to investigate the magmatic processes of erupted lavas in an incipient epicontinental back-arc basin in the western Pacific. Melt inclusions have widely variable element and Pb isotope compositions, while erupted host whole-rock compositions are homogeneous, suggesting that melt inclusions preserve more information about magmatic processes than their host whole rocks. Two groups of melt inclusions can be distinguished by their trace elements and Pb isotopes. Group 1 melt inclusions have geochemical compositions similar to those of their host whole rocks, which have low 207Pb/206Pb ratios (<0.850), and may be attributed to the contributions of recycled continental crust and subducted sediments to magma sources during Philippine Sea Plate subduction. Group 2 melt inclusions have higher 207Pb/206Pb ratios (>0.850) and Li, Rb, and U contents and lower Cu, Zn, and Pb contents than their host whole rocks. High Li, Rb, and U contents may be induced by specific melts generated by possible breakdown reactions of some accessory minerals, such as phengite and cordierite, while low Cu, Zn, and Pb contents are attributed to sulfide precipitation, metal flushing and/or metallic element fractionation during magma evolution. The Pb isotopes of the group 2 melt inclusions are similar to those of the Kuanhsi-Chutung basalts, which are correlated with some intraplate volcanism in the Fujian-Taiwan region. We infer that the group 2 melts were preexisting small volumes of magma that were emplaced in the middle-lower continental crust (~11 km), experienced extensive magma evolution and were entrained by upwelling magma. Our melt inclusion data suggest that magma sources are compositionally heterogeneous and that the mixing of magmas from different sources may be widespread beneath the southern Okinawa Trough because of Philippine Sea Plate subduction and preexisting intraplate magmatism.