High Sr Research Articles

Rodingitization of Neoproterozoic Al-Barramiya ophiolite metagabbro in the Eastern Desert of Egypt, Arabian-Nubian Shield

ABSTRACT The present work studies the rodingite that is recorded for the first time as being associated to Al-Barramiya Neoproterozoic ophiolite at Eastern Desert of Egypt, Arabian-Nubian Shield (ANS). Al-Barramiya ophiolite is one of the most important ophiolitic sequences exposed in the ANS. It is affected by different styles of alterations included carbonatization, listvenitization, chloritization and rodingitization. The Neoproterozoic ophiolitic rocks of Al-Barramiya district consists of serpentinized peridotite and metagabbros. Serpentinized peridotites are highly altered to assemblages of talc-carbonate rocks, listvenite and magnesite, while metagabbro is partly converted into rodingite. The field studies indicate that serpentinite and rodingite in Al-Barramiya area display high-strain cataclastic deformation. Rodingite consists of garnet, diopside, vesuvianite and chlorite with minor epidote, prehnite, actinolite and opaque minerals. The garnets and vesuvianite are mostly concentrated near the peripheries of the studied rodingite masses, while clinopyroxene, chlorite, epidote and prehnite gradually increase inwards due to progressive decreasing water/rock ratio as fluids originally buffered by serpentinite move towards equilibrium with gabbroic bulk chemistry. Some rodingite samples preserve a few relics of igneous textures of ophiolitic metagabbros. Garnets are distinguished into andradite, hydroandradite and grossular. Pyroxene is represented mainly by secondary clinopyroxene beside primary fresh relics of diopside; the latter has high Mg# (0.92–0.97) similar to ophiolitic clinopyroxene in the ANS. Rodingite is enriched in CaO, Fe2O3 and MgO but depleted in SiO2, Al2O3 and Na2O compared to associated metagabbro. The association of rodingite with serpentinites and metagabbros suggests that Al-Barramiya rodingite is genetically related to serpentinization of ultramafic rocks. The rodingitization occurred during ocean floor alteration contemporaneous with the serpentinization process. The superposition of cataclastic deformation on the altered rocks indicates that alteration preceded obduction and occurred on the seafloor of the suprasubduction zone where Al-Barramiya ophiolite was originally emplaced. During serpentinization the olivine in the peridotite broke down and released Mg2+ in the metasomatic fluids and clinopyroxene broke down producing Ca-rich fluids. These fluids react with the mafic protoliths and enrich them in MgO and CaO. Also, serpentinization fluids react with the plagioclase of the metagabbro, releasing Ca from the mafic source and concentrated it in the rodingitized samples. The positive Eu anomalies beside high Sr contents of the rodingite can be inherited from a plagioclase-rich protolith such as ophiolitic metagabbro. The enrichment of rodingite in Th and U indicates two distinct solutions affected the gabbroic protolith because the alteration of depleted peridotite to serpentinite cannot be an efficient source to enrich these elements. The present study indicates that the rodingitization process underwent lower greenschist facies conditions associating metamorphism that caused serpentinization and released Ca-rich metasomatic fluids.

Tracing magmatic footprints: Influence of a CO2-rich melt on the mineral assemblage of the San José del Guaviare Syenite, SE Colombia

A combined optical and electron microscopy (SEM, EDS, and EPMA) study was conducted on ten rock samples from the Proterozoic San José del Guaviare Syenite (SJGS), southeastern Colombia, to utilize minor and trace minerals in interpreting the magmatic evolution of these silica undersaturated rocks. The major minerals of the sampled syenites are nepheline, Fe-rich clinopyroxene, amphibole, alkali feldspar, and biotite. The minor minerals are titanite, calcite, cancrinite, and sodalite. Trace minerals are the niobium- or rare earth element-rich minerals pyrochlore, columbite, euxenite, britholite, ancylite-Ce and wöhlerite. Apatite, rhodochrosite, strontianite, fluorite, zircon, magnetite, ilmenite, and pyrite occur as traces as well. Crystallization started with primary (magmatic) calcite and Nb-rich minerals pyrochlore, columbite, euxenite, and a first generation of apatite, which occur as inclusions in foids, feldspars, and Fe-rich clinopyroxenes. Calcite is enriched in light rare earth elements and Sr, with low Mg concentrations, while primary apatite has high Sr concentrations. Both minerals have a composition typical for minerals crystallized in carbonatites. The presence of calcite and high Fe and low Ti clinopyroxene point to CO2-saturated conditions. During cooling, fluorbritholite-Ce formed as individual grains or by a fluid-enhanced apatite-britholite transformation. The formation of Fe-rich amphibole, often at the expense of Fe-rich clinopyroxene, reveals a decreasing influence of CO2 and temperature. Presumably, the transformation of orthoclase into microcline occurred simultaneously. Perthitic microcline as a second K-feldspar generation indicates slow cooling from high temperatures. A late stage of CO2-rich hydrothermal-metasomatic processes is suggested by the growth of secondary cancrinite, Sr-Mn carbonates and ancylite-Ce. The composition of primary and early crystallized calcite and apatite makes their origin as residues of an early segregated or independently formed mantle-derived carbonatitic melt more likely than crystallization from a CO2-rich syenitic melt. An origin from melted crustal carbonates is unlikely as well. Therefore, the presence of a carbonatitic melt at an early magmatic evolutive stage, as opposed to a non-carbonatitic melt at a late stage, seems possible for the SJGS rocks.

Perancangan Perancangan Dan Penjadwalan Penambangan Tahun 2023 Di Pit 3 PT. Mutiara Fortuna Raya 180 Kabupaten Muaro Jambi

PT Mutiara Fortuna Raya's mining operations are currently guided by an annual mining design without detailed mining scheduling. However, variations in mining direction and sequence can lead to discrepancies in coal expose achievement, ultimately impacting coal production outcomes. High SR locations demand a more overburden volume and time. This research aims to evaluate various mining direction options to determine the most optimal approach. The research methodology uses a quantitative approach, comparing three mining scheduling scenarios: panel scenario, strip scenario, and block scenario. These scenarios are based on the 2023 reserve design results of 180,518 tons coal and 385,390 BCM of overburden. The outcomes of these three scenarios reveal varying stripping ratios across each period. Stripping ratio for the panel scenario: Quarter I SR 10.84, Quarter II SR 4.77, Quarter III SR 1.64, and Quarter IV SR 0.20. Stripping ratio for the strip scenario: Quarter I SR 5.11, Quarter II SR 2.40, Quarter III SR 1.67, and Quarter IV SR 0.53. Stripping ratio for the block scenario: Quarter I SR 8.93, Quarter II SR 3.10, Quarter III SR 1.74, and Quarter IV SR 0.21. Analysis of three scenarios indicates that block scenario presents the most favorable schedulling for implementation.

Miocene adakitic monzogranites in the Northeast Pamir: Evidence for post India-Eurasia collisional evolution

The Pamir Plateau contains critical information on the tectonic evolution of the Tethys domain. In this study, we report geochronology, geochemistry, and Sr-Nd-Hf isotopic compositions of the Cenozoic adakitic monzogranite in the Reskam and Taxkorgan areas, NE Pamir, to provide new insights into the post-collisional tectonic evolution following the India-Eurasian collision. Zircon UPb ages reveal these granitoids were emplaced at ca 12–8 Ma. Geochemically, they exhibit relatively uniform whole-rock major and trace element compositions, and share typical adakitic signatures with high SiO2 (68.55–73.30 wt%), moderate Al2O3 (14.11–15.84 wt%), elevated Sr (399–1710 ppm) and La (34–182 ppm), but low Y (5.53–15.10 ppm) and Yb (0.39–1.26 ppm), and thus in high Sr/Y (32−200) and (La/Yb)N ratios (20–236). Isotopically, these adakitic rocks show significantly enriched whole-rock SrNd (εNd(t) = −7.97 to −5.76; 87Sr/86Sr(t) = 0.7072–0.7110) and zircon Hf (mostly εHf(t) -5 to −2) isotopic compositions. Elemental and isotope signatures indicate their origin from partial melting of mafic-intermediate sources under high pressure, with a residuum of negligible feldspar but dominant garnet. Integrating the new findings with reported data of granitoids in the Pamir, we estimate the crustal thickness variations from the Cretaceous to Miocene. The crustal thickness in the Pamir region largely remained no more than 45 km before India-Asia collision, after which a significant increase in crustal thickness occurred, reaching a peak of 80–100 km around 10 Ma. We propose that the break-off of the subducted Neo-Tethys oceanic slab (ca. 40 Ma) and lithospheric delamination (ca. 25 Ma) led to two-stage rapid continental uplift events in Pamir Syntax.

Radionuclide Solid:liquid partitioning in an aged, reducing-grout wasteform recovered from a disposal facility

The Saltstone Disposal Facility on the Savannah River Site in South Carolina disposes of Low-Level Waste in a reducing-grout waste form. Reducing grout is presently being evaluated as a subsurface disposal waste form at several other locations in the United States, as well as in Europe and Asia. The objective of this study was to collect core samples directly from the Saltstone Disposal Facility and measure desorption distribution coefficients (Kd; radionuclide concentration ratio of saltstone:liquid; (Bq/kg)/Bq/L)) and desorption apparent solubility values (ksp; radionuclide aqueous concentration (moles/L)). An important attribute of this study was that these tests were conducted with actual aged, grout waste form materials, not small-volume simulants prepared in a laboratory. The reducing grout is comprised of blast furnace slag, Class F fly ash, ordinary portland cement, and a radioactive salt waste solution generated during nuclear processing. The grout sample used in this study underwent hydrolyzation in the disposal facility for 30 months prior to measuring radionuclide leaching. Leaching experiments were conducted either in an inert (no oxygen) atmosphere to simulate conditions within the saltstone monolith prior to aging (becoming oxidized) or they were exposed to atmosphere conditions to simulate conditions of an aged saltstone. Importantly, these experiments were designed not to be diffusion limited, that is, the saltstone was ground finely and the suspensions were under constant agitation during the equilibration period. Under oxidized conditions, measured Tc Kd values were 10 mL/g, which was appreciably greater than the historical best-estimate value of 0.8 mL/g. This difference is likely the result of a fraction of the Tc remaining in the less soluble Tc(IV) form, even after extensive oxidation during the experiment. Under oxidized and reducing conditions, the measured Ba and Sr (both divalent alkaline earth metals) Kd value were more than an order of magnitude greater than historical best-estimate values of 100 mL/g. The unexpectedly high Ba and Sr Kd values were attributed to these radionuclides having sufficient time to age (form strong bonds) in the sulfur-rich saltstone sample. Apparent ksp values under reducing conditions were 10−9 mol/L Tc and 10−13 mol/L Pu, consistent with values measured with surrogate materials. Measured apparent Ba, Sr, and Th ksp values were significantly greater than historical best-estimates. The implications of the generally greater Kd values and lower ksp values in these measurements is that these cementitious waste forms have greater radionuclide retention than was previously estimated based on laboratory studies using surrogate materials. This work represents the first leaching study performed with an actual aged, reducing-grout sample and as such provides an important comparison to studies conducted with surrogate materials, and provides high pedigree data for other programs around the world evaluating reducing grouts as a wasteform for subsurface nuclear waste disposal.

B-site nickel tuned high active Sr and Co-free Ba0.8Ca0.2Fe0.8Ni0.2O3-δ air electrode for reversible solid oxide cells

Reversible solid oxide cells (RSOCs) have aroused wide concern as a promising technology in conversion between chemical energy and electrical power. However, the double conducting (O2−/e−) air electrode with high electrocatalytic activity and thermomechanical stability keeps a significant challenge for practical application. Herein, a perovskite Ba0.8Ca0.2Fe0.8Ni0.2O3-δ (BCFNi) oxide is synthesized and used as the air electrode material, which is experimentally and theoretically demonstrated to have excellent oxygen reduction/evolution reactions (ORR/OER) activity. The density functional theory (DFT) calculations indicate that BCFNi oxide accelerates the oxygen desorption/desorption, thus promoting the OER/ORR kinetics. The cell with BCFNi air electrode achieves a peak power density of 1.29 W cm−2 in the fuel cell (FC) mode and an electrolysis current density of 1.47 A cm−2 with 50 % H2O-H2 at 1.3 V applied voltage in the electrolysis cell (EC) mode at 800 °C. Moreover, it maintains favorable durability of 225 h in the FC, reversible, and EC modes at 750 °C, respectively. The results suggest that the Ni doping in B-site of perovskite oxide is beneficial to improve the ORR/OER activity and BCFNi material has great potential as an air electrode for RSOCs.

Trace element geochemistry of mantle xenoliths from Zarnitsa kimberlite pipe, Daldyn field, Yakutia: Complex history of melts interactions with lithospheric mantle

Mantle xenoliths from Zarnitsa pipe studied in gray eruptive breccias (early) brown autholitic breccia (BAB) and black macrocrystic kimberlites (last dike; BMK), include garnet and spinel dunites-harzburgites, pyroxenites, eclogites, glimmerites and megacrysts. PT reconstructions using xenoliths reveal sharply layered structure (8 levels), estimated with the single grain mineral estimates mark hot (Cpx, Ilm) and cold (OPx, Gar) inflected geotherm. The interaction with plume melts is found at the lithosphere asthenosphere boundary (LAB), pyroxenite layer (3-4 GPa), Gar-Sp transition and Moho. Eclogites reveal Fe# growth from LAB to middle pyroxenites layer. Clinopyroxenes and ilmenite estimates marks melt refertilisations in interlayers between coupled subduction slabs. Source of capture from first to third stage deepening to LAB and Cr- rich garnets (to 19.5 Cr2O3) are below the LAB.The grey erupted breccia (GEB) includes mainly depleted and deformed peridotites. The later BAB includes pyroxenites, eclogites, and refertilised, deformed, and veined peridotites in BMK. Geochemistry of minerals changes from primary mid ocean ridge basalts (MORB) and back arc peridotites with low REE and large ion lithophile elements (LILE) and deeps in high field strength elements (HFSE) to metasomatized by alkaline (high Na and LILE) and adakitic melts (high Al, Na, Sr, and elevated HFSE) varieties and refertilised lherzolites due to plume at last stage. Mantle column metasomatized with scattered phlogopites in early grey eruptive breccia to amphibole-phlogopite ilmenite veins at last stages. Amphiboles trace mantle from lithosphere – asthenosphere boundary to Moho.Growth of the diamond grade from early eruptive breccia to later kimberlite phases refer to decreasing of the crust material and deepening of the xenoliths capture level. Metasomatism dissolve the diamonds but growth of megacrystic diamond crystals increase diamond grade.

Post-collisional reworking of juvenile mafic lower crust for the petrogenesis of late Triassic adakitic rocks in the East Kunlun Orogen

The East Kunlun Orogen (EKO), a major component of the Greater Tibetan Plateau, provides an excellent natural laboratory to investigate the tectonic evolution of the Paleo-Tethys Ocean (also known as the A'nyemaqen Ocean in the EKO). We present a combined study of in situ zircon UPb ages and LuHf isotopic compositions, and whole-rock major and trace element and Sr–Nd–Hf isotopic compositions of the post-collisional Xiangjia granodiorite at the eastern end of the EKO. Zircon UPb dating indicates that the Xiangjia granodiorites were emplaced at 225.0–217.1 Ma. Relict zircon cores yield ages of 267.5–239.5 Ma. These granodiorites are calc-alkaline to high-K calc-alkaline and metaluminous to weakly peraluminous, enriched in large-ion lithophile elements and light rare earth elements, and depleted in high field strength elements (e.g., Nb and Ta) and heavy rare earth elements. They yield trace element characteristics that are typical of adakitic rocks, including high Sr (493–590 ppm) and low Yb (0.74–1.12 ppm) and Y (8.83–12.24 ppm) contents, high Sr/Y (40.47–63.64) and (La/Yb)N (11.81–30.91) ratios, and positive Eu anomalies. The UPb ages and Hf isotopic compositions of the relict zircon cores and whole-rock SrNd isotopic compositions of the Xiangjia adakitic rocks are similar to those of the mafic arc magmatic rocks formed during the subduction of the Paleo-Tethys Ocean, suggesting they originated from the reworking of juvenile mafic lower crust. Phase equilibrium modelling suggests that the contemporaneous adakitic rocks from Xiangjia and other areas in the EKO are likely the products of partial melting of the juvenile mafic arc rocks under granulite-facies conditions at 10–11 kbar and 934–951 °C, possibly related to slab break-off in a post-collisional setting.

A-site alkali metal-doped SrTi0.3Fe0.7O3-δ: A highly stable symmetrical electrode material for solid oxide electrochemical cells

To addresses the limitations in electrode performance observed at temperatures ≤700 °C, attributed to the low oxygen surface exchange coefficient primarily caused by high Sr surface segregation, we developed an electrode performance enhancement strategy involving A-site alkali metal doping to SrTi1-xFexO3-δ (STF)-based perovskite. Here, we present the symmetrical electrode material for solid oxide electrochemical cells (SOCs), Sr0.95Mg0.05Ti0.3Fe0.7O3-δ (SMTF), demonstrating a unique combination of excellent symmetrical electrode performance and long-term stability. A-site Mg doping reduces the Sr surface segregation and improves the conductivity but also significantly enhances its electrochemical performance. At 700 °C, the performance of SMTF symmetric cell in both fuel cell and electrolysis modes is 1.5 times higher than that of STF. Moreover, under air atmosphere, SMTF demonstrates stable performance (>1000 h) at 1 A cm−2, with no degradation observed after 400 h testing under humidified hydrogen conditions. Additionally, SMTF exhibits excellent CO2 tolerance in CO2-rich atmospheres.

Ore–forming potential of the Wubaduolai monzogranite porphyry, western Gangdese copper belt, Tibet: Insights from geochronology and petrogeochemistry

The Wubaduolai deposit is a newly discovered porphyry copper deposit in the Zhunuo-Beimulang ore-concentrated area of the Gangdese belt. The monzogranite porphyry is the causative intrusion in the deposit with a zircon U-Pb age of ∼16 Ma. Monzogranites have high Sr (332–673 ppm) and Sr/Y ratios (35–69), typical of adakite affinity. They have initial 87Sr/86Sr ratios of 0.7083–0.7093 and εNd(t) values between −9.2 and −7.1. The zircon εHf(t) values range from −6.45 to −2.09 and zircon δ18O values have a narrow range of 7.4 to 8.1 ‰ for the porphyry. These geochemical characteristics indicate that the parental magma was derived from juvenile Tibetan lower crust, with contributions from Indian plate-released fluids and metasomatized mantle-derived mafic magmas. The porphyry shows high values of log w(Fe2O3/FeO) (>0) and V/Sc (mostly > 12) in whole rock and high values of △FMQ (4.13–5.79), 10000 × (δEu)/Y(>4), and low Dy/Yb (<0.3) in zircons, suggesting that the magma was oxidized and hydrous. The oxidized and hydrous parental magma is consistent with those evaluated for the Zhunuo and Beimulang deposits. The three-component mixing model result shows that compared with the ore-related porphyries in the Zhunuo and Beimulang deposits, the Wubaduolai intrusion has higher proportion of Indian plate-released fluids and mafic magmas and lower proportion of juvenile Tibetan lower crust. Therefore, we suggest that although the causative intrusions have similar oxygen fugacity and water content, the source has more Indian continental crust and mantle-derived materials and fewer juvenile Tibetan lower crust materials at Wubaduolai, implying that the Wubaduolai monzogranite porphyry has lower potential for mineralization.

Energy transfer and a novel SBR thermometry of SrY2O4:Sm3+/Eu3+ phosphor based on redshift of charge transfer band edge

In this study, a solid-state reaction was employed to synthesize SrY2O4: Sm3+, SrY2O4: Eu3+ and SrY2O4: Sm3+/Eu3+ phosphors. An intriguing redshift phenomenon from charge transfer band (CTB) edge was investigated for single-band ratiometric (SBR) thermometry applications. The phosphors synthesized exhibited an orthogonal CaFe2O4 structure with Pnam (62) space group. The Y3+ sites from host lattice were most likely to be replaced by Sm3+/Eu3+ ions. The sample of SrY2O4: 0.03 Sm3+/0.3Eu3+ showed a large degree of agglomeration with elongated particles, having an average size of approximately 4 μm. The energy bandgap decreased due to increased surface imperfections, resulting in enhanced defect level concentration. The dipole-dipole interaction could be used to explain energy transfer (ET) of Sm3+-Sm3+ and Sm3+-Eu3+. Furthermore, the energy transfer (ET) efficiency of Sm3+→Eu3+ in Sr2YO4 reached 77.7 %. The sample exhibited a good thermal stability (90.956 %@423 K) with Ea of 0.31 eV, which was an important parameter for broadening thermometry range. A thermometry strategy utilized this redshift phenomenon from CTB edge with anti-thermal quenching behavior and other peaks or bands with thermal quenching was therefore proposed. The high Sr value of 1.533 % K−1@298 K provides a great potential for optical thermometry application, contributing significantly to the advancement of single band ratiometric thermometry technologies.

Anatomy and genesis of the world’s largest carbonate-hosted Zn-Pb deposit: New insights from ore characteristics, Zn-Pb-C-O isotopes, and trace element constraints of the Huoshaoyun deposit, Karakorum Range, Xinjiang

The Huoshaoyun deposit in the Karakorum area of NW China is the world’s largest zinc-lead carbonate ore deposit. Here we investigate the genesis of the mineralization based on multiproxy investigations. The deposit contains zinc-lead carbonate and sulfide minerals, with smithsonite (Smt), cerussite (Cer), and sulfides accounting for 85%, 10%, and 5% of the total lead and zinc resources, respectively. Three ore-forming stages, involving Smt, Cer, and sulfides ores were summarized. The Smt mineralization is characterized by veined, massive, and stratified Smt forming horizontal sedimentary layered ore and vertical feeder veins similar to the SEDEX-type deposits. The sulfide and Cer veins display typical hydrothermal characteristics and are superimposed on the massive Smt ores. The Smt ores show high Li, Be, Cr, Y, Ba, Nd, Yb, and Zr contents, whereas the Cer veins have extremely high Sr contents (up to 3814–9174 ppm) and low Zr contents (less than 0.01 ppm). Galena and sphalerite show higher Cd concentrations compared to Smt and Cer ores.The Smt ores differ with different spatial locations, with Smt ores formed at the vent have δ66Zn values of +0.15‰ to +0.21‰, the massive Smt formed close to the vent show a value of +0.13‰, and those formed away from the vent show a value of 0.05‰, all values being close to 0. The sulfides have δ66Zn values of −0.09‰ to +0.04‰. The C-O isotopes of Smt ores are similar to both altered and unaltered host limestone, suggesting that the limestone was a potential source for carbon and oxygen. Quartz with veined Smt shows magmatic signatures with δ18OVSMOW of +1.14‰ to +2.23‰, high Pb (115–401 ppm) and Zn concentrations (390–997 ppm), whereas quartz associated with sulfide has meteoric fluid signature with the lowest δ18OVSMOW (−14‰ to −10.7‰), low Pb (11.6–49.0 ppm) and Zn (18.1–72.8 ppm) concentrations. The temperature of equilibration computed based on oxygen isotope fractionation between Smt and coeval quartz indicate a dual source with that of quartz derived from an aqueous fluid, whereas the source for Smt might involve CO2 or HCO3−.We trace multiple metallogenic stages for this deposit including exhalation, hydrothermal deposition, and fault-controlled sulfide vein formation. The largest orebody (III-1) preserves a 16 Mt reserve of Zn and was formed by crust-mantle interaction at ca. 195 Ma in the early development of the Linjitang post-arc rift system. Fluid convection, zinc enrichment driven by granitic magma, volcanic activity, and karst alteration induced by acid rain in a lagoonal environment promoted ore enrichment.

Dolomite occurrence within drift deposits, Maldives archipelago

Considerable attention has been dedicated to the sedimentological processes associated with carbonate drift and contourite deposits, but a noticeable gap exists in the understanding of the diagenetic aspects of those deposits, especially dolomitization. This study presents an examination of dolomites from Middle to Late Miocene drift deposits collected during IODP Expedition 359 to the Maldives archipelago. Multiple geochemical parameters and petrographic analysis are used to explore the potential role of closed versus open system dolomitization in the two oldest drift sequences, which are overlain by a multimillion year-long hiatus. Overall, dolomite abundance is variable, but 50 % to nearly 100 % in a 30 m thick interval below the unconformity surface at one of the examined sites. The dolomite in the study interval consists of very fine-to-fine-sized crystalline dolomite cements and mimetically replaced dolomite grains. All dolomite is non-stoichiometric (mean 42.7 ± 2.0 mol% MgCO3) and mostly poorly ordered. Geochemical attributes include relatively invariant δ13C (+1.3 ‰ to +1.7 ‰ VPDB) and relatively high Sr concentrations in dolomite cements (mean 505 ppm) and dolomitized grains (mean 784 ppm). δ18O values and the constraints of burial histories indicate dolomitization in normal marine seawater at burial depths of 0 to 300 m and temperatures of ∼10 °C–14 °C below an ocean water column 100 to 400 m deep. Sr-isotope ages suggest dolomitization of the most extensively dolomitized interval below the unconformity occurred between 12.3 Ma and 6.7 Ma. Overall, the geochemical data and previously published δ34SCAS data suggest a closed, diffusion-dominated system created most of the dolomite. However, the youngest dolomite's age and bulk rock Sr isotope ages of calcitic rocks at the base of the drift deposits can only be explained by the advective flux of seawater through all the drift deposits. Furthermore, the geological context, including permeable facies, ocean current patterns, and other indicators, such as the absence of hardground or permeability barriers, suggests that some open system dolomitization may have also occurred.

Rb-Sr constraints on the age of Moon formation

Determining the age of the Moon, which is commonly considered as the termination of Earth accretion has been a complex challenge for geochronology. A number of methods have been used to delineate the age of the Moon based either on absolute chronology of lunar rocks or have relied on more indirect methods using short-lived nuclides such as 182Hf that was present in the early history of the Solar System. Model ages usually require some assumptions that are sometimes controversial or harder to verify.In this study, new high precision Sr isotope data (2.4 ppm, 2SD) were obtained for a well-dated lunar anorthosite (60025) in order to better constrain the initial 87Sr/86Sr of the bulk silicate Moon. This new data is then used to model the Sr isotope evolution of the Earth-Moon starting from the beginning of the Solar System. To comply with the HfW and stable isotope constraints, we then assume that the Earth and Moon were equilibrated at the time of Moon formation. By investigating systematically all the sources of uncertainties in our model, we show that compared with previous work on anorthosites, one can tighten the constraints on the youngest age of Moon formation to no >79 Ma after the beginning of the Solar System, i.e. the Moon cannot be younger than 4488 Ma.

Petrogenesis of K-rich and high-mg adakitic rocks in the North Dabie terrane, China: products of early cretaceous orogenic collapse

ABSTRACT Understanding orogenic collapse is key to comprehending the evolution of continental collision orogens. The Dabie orogen is a collapsed continental collision orogen that provides an ideal window for revealing orogenic collapse. Here, we conduct fieldwork, whole-rock geochemistry, and zircon U-Pb dating of the Daoshichong pluton in the North Dabie terrane to elucidate the collapse mechanism of the Dabie orogen. The Daoshichong pluton is composed of quartz monzodiorite and mafic microgranular enclaves (MMEs) with an Early Cretaceous (~130 Ma) crystallization age. The Daoshichong pluton is strongly deformed and ductile, displaying a gneissic structure. The quartz monzodiorites are K-rich and high-Mg adakitic rocks. They contain 60.2–63.3 wt.% SiO2 and have high K2O (2.88–3.42 wt.%) and MgO (2.08–3.04 wt.%) contents with relatively high Mg# values (44.4–49.3). They exhibit high Sr (673–819 ppm) and low Y (11.4–20.9 ppm) and heavy rare earth elements (e.g. Yb: 0.94–1.87 ppm) contents, resulting in high Sr/Y (35.1–72.0) and (La/Yb)N (15.7–36.1) ratios. The MMEs exhibit geochemical characteristics similar to those of the Early Cretaceous mafic – ultramafic rocks of the Dabie orogen. They have low SiO2 contents (48.1–51.9 wt.%) and high MgO contents (3.27–5.62 wt.%) with high Mg# values (47.3–51.2). They also exhibit relatively high Ni (16.6–63.6 ppm), Cr (30.5–164.6 ppm), Y (18.2–25.8 ppm) and Yb (1.50–1.94 ppm) contents and high Sr/Y ratios (53.7–109.5). Evidence from fieldwork and geochemistry distinctly indicates magma mixing during magma evolution between the MMEs and the quartz monzodioritic host. Thus, the Daoshichong quartz monzodioritic host and the MMEs can be interpreted as a mixture of mantle-derived magma and over-thickened lower continental crust-derived adakitic melt. Previous studies suggest that the Early Cretaceous (~130 Ma) high-Mg adakite-like rocks are distributed only along the eastern margin of the Dabie orogen (i.e. along the Tan – Lu Fault). This study is the first to report a homochronous (~130 Ma) K-rich and high-Mg adakite-like pluton in the core of the Dabie orogen. Our results suggest that a whole delamination of the over-thickened orogenic root caused the orogenic collapse, subsequently triggering crust – mantle interactions, dome structure, and magmatism in the Dabie orogen.

Petrogenesis and Metallogenesis of Late Cretaceous Adakites in the Nuri Large Cu-W-Mo Deposit, Tibet, China: Constraints from Geochronology, Geochemistry, and Hf Isotopes

The Gangdese metallogenic belt in Tibet is an important polymetallic metallogenic belt formed during the subduction of the Neo-Tethys Ocean and subsequent India–Asia collision. Adakitic rocks are widely distributed in this belt and are considered to be closely related to porphyry–skarn Cu-Mo polymetallic mineralization. However, the petrogenesis and geodynamic setting of the Late Cretaceous adakites in the Gangdese belt remain controversial. In this study, we focus on the quartz diorite in the Nuri Cu-W-Mo deposit along the southern margin of the eastern Gangdese belt. LA-ICP-MS zircon U-Pb dating yields a Late Cretaceous age of 93.6 ± 0.4 Ma for the quartz diorite. Whole-rock geochemistry shows that the quartz diorite possesses typical adakitic signatures, with high SiO2, Al2O3, and Sr contents, but low Y and Yb contents. The relatively low K2O content and high MgO, Cr, and Ni contents, as well as the positive zircon εHf(t) values (+6.58 to +14.52), suggest that the adakites were derived from the partial melting of the subducted Neo-Tethys oceanic slab, with subsequent interaction with the overlying mantle wedge. The Late Cretaceous magmatic flare-up and coeval high-temperature granulite-facies metamorphism in the Gangdese belt were likely triggered by Neo-Tethys mid-ocean ridge subduction. The widespread occurrence of Late Cretaceous adakitic intrusions and associated Cu mineralization in the Nuri ore district indicate a strong tectono-magmatic-metallogenic event related to the Neo-Tethys subduction during this period. This study provides new insights into the petrogenesis and geodynamic setting of the Late Cretaceous adakites in the Gangdese belt, and has important implications for Cu polymetallic deposit exploration in this region.

Genesis of W mineralization in the Yangla Cu-polymetallic deposit (NW Yunnan, China): Constraints from scheelite microstructure, trace element, U-Pb dating and Sr isotope geochemistry

The Yangla Cu-polymetallic deposit is the largest skarn Cu deposit in the Jinshajiang suture zone. Recently, an new W orebody was identified in the depths of the Cu orebodies. However, the genetic relationship between W and Cu orebodies, along with the tungsten ore-forming processes, remains unclear. This study delves into the careful investigation of three types of scheelites focusing on microstructure, trace element compositions and Sr isotope geochemistry. The aim is to elucidate the source and evolution of ore-forming fluids and ore genesis in the multi-episodic metallogenic systems. Primary scheelite (Sch-I) generally displays oscillatory zoning in CL images with the lowest REE (3.8–142 ppm) and highest Sr (604–1480 ppm) contents. Secondary scheelite (Sch-III), commonly precipitated as overprinting rims on primary crystal, has the highest REE (145–1071 ppm) and lowest Sr (376–793 ppm) contents. In contrast, Sch-II represents a transitional stage from primary to secondary, with REE and Sr contents at intermediate levels. Sch-I is characterized by LREE enrichment and a positive Eu anomaly in the chondrite-normalized REE patterns, whereas Sch-III shows MREE-rich patterns with a weak positive Eu anomaly. Scheelite U-Pb dating (30.3 ± 1.5 Ma) indicates that the W mineralization is not genetically related to Triassic granitoids in the Yangla district. Instead, it is likely associated with magmatic activities and tectono-thermal events in the Jinshajiang fault zone during the Cenozoic. The high initial 87Sr/86Sr ratios (0.71771–0.72229) in the scheelite, significantly higher than those of Triassic granites and ore-hosting marble, suggest that the geochemical features of Sch-I are inherited from the parental ore-forming fluids. These fluids are likely derived from the mixed hydrothermal fluids involved by the Neoproterozoic strata and/or concealed magmatism.

Evidence from adakitic rocks for a switch in magmatic source at ca. 460 Ma in the Karamaili Ocean of East Junggar, NW China

Early Paleozoic magmatism can preserve critical geological records related to subduction-accretion in the Central Asian Orogenic Belt (CAOB). Here, we report new geochemical, geochronological and isotopic results for diorites-granitoids in the Karamaili region of East Junggar, Northwest China. These rocks record high Sr, but low Y and Yb contents, with high Sr/Y ratios but low La/Yb ratios, and can be divided into low-silica adakite and high-silica adakite. All samples are with typical features of subduction-related magmas and show relatively juvenile Sr, Nd and Hf isotopic ratios. Zircon LA-ICP-MS UPb ages are between 468 ± 4 Ma and 441 ± 5 Ma. The low-silica adakite has relatively high Mg# and Cr, Co and Ni contents, implying a possible mantle origin. The Hongliuxia diorite (low-silica adakite) has relatively high Th contents and Th/Yb ratios, but records lower ɛNd(t) (+4.1) and ɛHf(t) (+8.9 − +12.2) values than those of the granitoids (high-silica adakite), implying the low-silica adakite was influenced by the subduction of sediments. The low-silica adakite likely originated from partial melting of a mantle wedge, metasomatized by subduction-related fluids and sediments, whereas the high-silica adakite was likely derived from partial melting of juvenile mafic lower crust. There is little involvement of garnet in the magma source, consistent with fluid-flux melting at pressures between 10 and 12.5 kbar (corresponding to 30–40 km depth). We suggest that the increase in Nd and Hf isotopic ratios at ∼460 Ma may imply that subduction began to retreat at this time in the Karamaili Ocean during evolution of the CAOB.

Revisiting the fluid regime during anatexis of metasedimentary rocks: New constraints from an integrated approach on the Cenozoic Himalayan granites

Water plays a critical role in the formation of granitic magmas and continental crust, but distinguishing water-present and water-absent anatectic scenarios using the geochemistry of granites is controversial. In this study we use an integrated approach that combines whole-rock major and trace element geochemistry, Ti-in-zircon thermometry, phase equilibrium modeling and trace element modeling to study the water regime that produced the Miocene granites from the Malashan-Gyirong area in central Himalaya to solve this controversy. The Gyirong granites have relatively low CaO, Sr and Ba and high Rb and (87Sr/86Sr)i and the Malashan granites have relatively high CaO, Sr and Ba and low Rb and (87Sr/86Sr)i, and were classified as group A and group B granites, respectively. Following previous interpretation, group A and group B granites are consistent with the products of water-absent and water-present melting of metasedimentary rocks, respectively. Ti-in-zircon thermometry yielded maximum values of 761–796 °C for the Gyirong granites and 730–764 °C for the Malashan granites. Distinct variation trends in zircon trace element compositions indicate that these two groups of granites were not linked by crystallization differentiation. Using average compositions of Proterozoic pelite as starting materials, phase equilibrium modeling was carried out at a variety of P–T–H2O conditions typical of the Himalayan orogen, P = 5, 10 and 15 kbar, T = 600–800 °C, H2O = 0–10 wt%. Pelite can produce melts with coupled CaO–Na2O contents for both groups at 10 kbar. Specifically, constraints from compositions and temperatures require that the bulk H2O content is ca. 1–2 wt% for group A granites and > ca. 4 wt% for group B granites. Compared with the maximum structural water content of the pelite at 10 kbar (1.77 wt%), this study testifies that group A granites formed under water-absent conditions and group B granites under water-present melting conditions. Modeling shows that water-present melting can produce melts with high Sr–Ba and low Rb contents resembling group B granites, while water-absent melting can produce melts with low Sr–Ba and high Rb contents resembling group A granites. This study highlights that water can indeed cause differences in granite geochemistry but a comprehensive investigation is required to better determine the role of water during crustal anatexis.

Diverse apatite geochemical compositions in early Paleozoic granitoids of the North Qinling orogen, China: Insights into their petrogenesis and magma sources

Apatite geochemistry in granitoids is controlled primarily by the original melt compositions and partition coefficients. However, additional factors (e.g., post-crystallization effects, mineral crystallization sequences, and crustal assimilation) can also contribute to variations in apatite compositions. In this study, we collected three groups of early Paleozoic granitoids from the North Qinling Orogen and obtained in situ geochemical data for apatite. The granitoids were formed by partial melting of oceanic arc crust (group A), recycling of ancient crust (group B), and melting of the lithospheric mantle and extensive fractionation (group C). Trace element and Nd isotope data show the apatite from the Taiping and Manziying plutons (group A) were affected by post-crystallization processes and crustal assimilation, respectively. In addition, crystallization of plagioclase/allanite and apatite resulted in the variable Eu anomalies and rare earth element contents of apatite in the group A granitoids. In contrast, apatite compositions in group C were controlled primarily by the fractionation of hornblende. However, the decoupling of Eu anomalies of apatite and their host rocks, particularly for group B, cannot be easily explained by the aforementioned factors. As such, the redox state may also have been an important factor. We used a ternary diagram (10 × [Eu/Eu*]N–V–Ga) to constrain the redox state from the apatite data, and provide insights into the types and petrogenesis of the host granitoids. Combined with the whole-rock and zircon geochemical data, we found that the apatite from the rocks derived from continental crust (group B and cratonic adakites) is generally reduced, whereas apatite from the mafic rocks and high BaSr granitoids is highly oxidized. The highest degree of oxidation was found for the altered apatite from the group A granitoids and unaltered apatite in the orogenic adakites, possibly due to interactions with fluid derived from oceanic crust. Moreover, unaltered group A granitoids exhibit a transitional trend from an oxidized to a reduced state. Apatite geochemistry can be used to constrain the redox state of adakitic rocks and whether they have a continental or oceanic crustal origin. The high Sr contents of high BaSr granitoids are inherited from their mantle source.