Search

In this study, laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA–MC–ICP–MS) of apatites and LA–ICP–MS of zircons are used to collect U–Pb geochronological data, Rb–Sr isotope chronology is used to analyze alkaline feldspar and plagioclase, and archival apatite geochemistry data for the exposed Naitoushan basalt and Heishigou dike in the Changbaishan Tianchi volcano (CTV) are accessed to examine the petrogenesis and determine the origin of basaltic magmatism in the CTV. The Naitoushan basalt and Heishigou dike formed at 22.2–18.7 and 0.230–0.218 Ma, respectively. In situ oxides, volatiles, trace element geochemistry and Sr–Nd isotopes of apatite are reported for two samples. Most apatites are in the early crystallization phase and form inclusions in plagioclase that are euhedral or subhedral. They have higher MgO and K2O/Na2O concentrations; lower F and Cl concentrations; Ba, Sr, Nb, Ta, Zr, Hf, K, and Ti depletion; and Th, U, Ce, Pb, P, and Nd enrichment. All apatite samples are enriched in light rare earth elements (REEs) relative to heavy REEs and have relatively homogeneous Th/U, Zr/Hf, La/Sm, and Nd/Tb ratios and Sr–Nd isotopic compositions; thus, their host magmas potentially have the same magmatic origin as oceanic island basalt. The apatite La, Yb, and U contents, Eu/Eu* and La/Yb values, and high REE contents show a weak crystallization sequence in the mafic magma. This study demonstrates that the pre-shield and post-shield mafic magmas in the CTV were likely derived from an enriched mantle source with an I-type signature related to the rollback of the Pacific plate. [ABSTRACT FROM AUTHOR]

Late Carboniferous–Early Permian granitoids are widespread in the Tianshan area and their tectonic setting is controversially discussed. Our research presents fresh whole-rock geochemical and Pb isotopic data, along with zircon U-Pb ages and Hf isotopic data for representative monzonitic and granitic intrusions in the Kumishi area. The aim is to decipher their magma sources and illuminate their geodynamic evolution. Zircon U-Pb dating results reveal that biotite monzonites in the Central Tianshan Belt were emplaced at 312.7 ± 2.9 Ma, while the quartz-monzonites and syenogranites in the South Tianshan Belt were formed at 284.5 ± 2.4 Ma and 283.4 ± 3.9 Ma, respectively. The biotite monzonites generally exhibit metaluminous and high-K calc-alkaline characteristics. They have a positive εHf(t) value (+4.9–+14.1), and are enriched in LREEs and LILEs but depleted in HREEs and HFSEs. These characteristics indicate that they were derived from a mixed magma source of the lower crust and the input of components derived from the mantle wedge above the subduction zone. The quartz-monzonites and syenogranites are high-K calc-alkaline to shoshonitic I-type granites, with εHf(t) values of +14.9–+15.5 and +6.6–+14.9, respectively. They are enriched in LREEs but depleted in HFSEs (e.g., Nb, Ta, and Ti), displaying relatively flat HREE patterns and negative Eu anomalies. The genesis of these rocks is attributed to a partial melting of the lower crust in which mantle-derived magmas participated, which was triggered by an upwelling asthenosphere in a post-collisional extensional geodynamic setting. These granitoids, together with regional analysis of other magmatism in the study area, suggest that the Kumishi area has experienced an evolution from subduction to post-collision from the Late Carboniferous to the Early Permian, which constrains the local closure of the Paleo-Asian Ocean. [ABSTRACT FROM AUTHOR]

The subduction-related Sunda-Banda arc hosts several giant and major Cu–Au–Mo porphyry and epithermal Au systems, making it one of the most important magmatic-related metallogenic belts in Indonesia. They are accompanied by a number of smaller systems, one of which is the recently discovered Randu-Kuning porphyry Cu-Au deposit on Java Island. The present study investigates the geochemical characteristics of this deposit through whole-rock and mineral geochemistry and mineral geothermobarometry, focusing on three sequential dioritic intrusions that make up the host igneous complex, two barren and the third mineralized. Moreover, a comparative analysis is performed between other porphyry deposits in the Sunda-Banda arc and with Grasberg in Papua. This study shows that the older porphyry deposits have mostly similar geochemical characteristics to the younger deposits, suggesting the same magma source, which is mantle-derived oxidized I-type magma. Amphibole geothermobarometry shows that the formation of syn-ore intrusion in the older porphyry was higher in temperature and pressure than those at the younger porphyry. The halogen and oxygen fugacities inferred from biotite and amphibole chemistry indicate an oxidized, water- and halogen-rich melt. Our study shows that combining amphibole and biotite chemistry and whole-rock geochemical data is useful to fingerprint the magmatic-hydrothermal processes, especially where multiple magmatic phases occur. This research also provides valuable insights into the magmatic-hydrothermal physiochemical conditions during the formation of the mineralized system. [ABSTRACT FROM AUTHOR]

Basalts from the Late Carboniferous to Early Permian are extensively developed in the central Lhasa subterrane, southern Tibet. Studying the petrogenesis of these rocks may have implications for the late Paleozoic arc magmatism along the central Lhasa subterrane uncovering more of the evolution of the Sumdo Paleo‐Tethys Ocean and its dynamic mechanism. Basalt samples from the Luobadui Formation in the Leqingla area, NW of Linzhou City in the central Lhasa subterrane, southern Tibet exhibit arc‐like geochemical signatures in a subduction‐zone tectonic setting characterized by high Al2O3 and low TiO2 contents, fractionated REE patterns with low Nb/La ratios and high LREE concentrations, and negative HFSE anomalies. Based on their higher Th/Ce, Nb/Zr, and lower Ba/Th, Pb/Nd ratios, slightly negative to positive εNd(t) values, and the relatively high Sr‐Pb isotopic compositions, these samples were probably derived from partial melting of a depleted mantle source of garnet + spinel lherzolite, metasomatized by subducted sediments around 297 Ma. Modeling of the trace elements indicates that these basalts experienced fractional crystallization of olivine, clinopyroxene and minor plagioclase during magma ascent and eruption. It is proposed that these Late Carboniferous–Early Permian basalts are associated with the northward subduction of the Sumdo Paleo‐Tethys Ocean seafloor along the southern margin of the central Lhasa subterrane. [ABSTRACT FROM AUTHOR]

We present bulk-rock and mineral Fe isotope data of ultramafic to mafic xenoliths and basaltic to andesitic lavas from Adagdak Volcano (Adak Island, Central Aleutians) to study the effects of early differentiation on the Fe isotopic evolution of island arc basalts and their crystallization products. The Fe isotope composition of ultramafic cumulate xenoliths increases from dunite (δ56Fe = –0.09 to –0.02 ‰) to clinopyroxenite (δ56Fe = +0.06 to +0.09 ‰), consistent with higher modal proportions of clinopyroxene (δ56Fe = –0.05 to +0.11 ‰) relative to olivine (δ56Fe = –0.10 to +0.06 ‰) in the latter. Mid-crustal cumulate amphibole gabbro and hornblendite cumulates also record heavier Fe isotope compositions (δ56Fe = +0.04 to +0.08 ‰) due to the abundance of isotopically heavy amphibole (δ56Fe = +0.07 to +0.09 ‰) and magnetite (δ56Fe = +0.11 to +0.13 ‰) in these rocks. High inter-mineral fractionations observed in spinel-olivine and spinel-clinopyroxene pairs (Δ56Fe spl-ol = +0.12 to +0.28 and Δ56Fe spl-cpx = +0.06 to +0.19) suggest that spinel is not recording equilibrium crystallization conditions for the ultramafic assemblages, likely due to subsolidus Fe-Mg exchange. Our data also include Fe isotope measurements of one mantle dunite (δ56Fe = +0.03 ± 0.05 ‰). Five Adagdak lavas, spanning from basalts to andesites, yield a narrow range of δ56Fe between +0.03 and +0.06 ‰. Our results highlight the potential of amphibole in driving the Fe isotope depletion trends observed in many erupted arc lavas, as amphibole hosts 28–99 % of the FeO T budget in the amphibole gabbro and hornblendite cumulates. This is also supported by single-crystal synchrotron Mössbauer spectroscopy of two amphibole grains, the first from an amphibole gabbro and the second from a hornblendite, which yield Fe3+/ΣFe ratios of 0.55 ± 0.06 and 0.58 ± 0.02, respectively. Water content and hydrogen isotope compositions determined by secondary-ion mass spectrometry from the same amphibole grains indicate partial dehydrogenation. Using Rayleigh fractionation modeling to account for oxidation during post-crystallization dehydrogenation, we calculate magmatic Fe3+/ΣFe ratios of 0.41 ± 0.04 for the amphibole gabbro and 0.30 ± 0.05 for the hornblendite. These data are then used to estimate an appropriate Fe force constant for Adagdak amphibole and quantitatively evaluate the effects of amphibole fractionation. Through a fractional crystallization model, we show how arc melts may experience periods of increasing δ56Fe during olivine-dominated fractionation, followed by decreasing δ56Fe once magnetite and amphibole saturate as cumulate phases. Notably, this dichotomy between fractionation of isotopically light versus heavy cumulate assemblages and its effects on the Fe isotope evolution of arc magmas is not captured by the Adagdak lava record, highlighting the utility of cumulates in chronicling the early isotopic evolution of magmatic systems. [ABSTRACT FROM AUTHOR]

The physical process of crystal-melt separation is responsible for the accumulation of small to very large volumes (>100 km3) of eruptible rhyolitic melt in the shallow crust. Granitic intrusions, although providing a terminal, time-integrated image of melt segregation processes, host an unmatched record of the physical properties controlling mechanisms and rates of interstitial melt extraction from a crystal-rich source. We applied mass balance calculations and thermodynamic modeling simulations to an extensive bulk rock geochemistry dataset (>150 samples) collected in a Permian upper-crustal granitoid intrusion of the Italian Southern Alps. Textural and geochemical evidence indicate that this intrusion constituted a single, zoned magma body, with a crystal-rich base and a thick (~2 km), high-silica cap (75–77 wt% SiO₂). The large compositional variability of the crystal-rich materials suggests variable degrees of melt extraction efficiency and corresponding terminal porosities. Specifically, the loosely bimodal distribution of porosity values (φ) indicates that at least two distinct melt segregation mechanisms were operating in this system, which produced both high (0.65–0.45) and low terminal porosities (0.45–0.25) in the crystal-rich, cumulate materials. Modeling of latent heat budget shows that coexistence of cumulate products with differing terminal porosity signature can be explained by melt segregation processes taking place at different depths across a thick, interconnected magmatic reservoir with an initial homogenous water content (~4 wt% H2O). Deep in the mush column, low water activities (a H₂O < 0.5) promoted thermal buffering of cooling magma at high crystallinities, enabling residual melt extraction by percolation through a crystalline framework accompanied by compaction. Instead, at shallower depths, high water activities (a H₂O > 0.5) ensured prolonged magma residence at porosities that promoted crystal melt separation via hindered settling. Distinct melt extraction processes, acting synchronously but at different depths in vertically extensive silicic mush columns, can account for the large volumes of residual, haplogranitic melt mobilized during the relatively short lifespan of upper crustal magma reservoirs (~105 years). [ABSTRACT FROM AUTHOR]

High‐silica granitoids record the formation and evolution of the continental crust. A new intrusive complex has been recognized among silicic volcanic rocks of the Weixi arc, Southwest China. The intrusions consist of granites, granitic porphyries, and granodiorites. Zircon U‐Pb age data indicate that the Weixi granitoids formed at 248–240 Ma and were coeval with silicic volcanic rocks of the Weixi arc. The Weixi granitoids are enriched in Rb, Th, and U, depleted in Ba, Sr, Nb, Ta, and Ti, and have high light/heavy rare earth element ratios and slightly negative Eu anomalies. The Weixi granitoids have negative εNd(t) values (–9.8 to –7.8) and negative zircon εHf(t) values (–12.02 to –5.11). The geochemical and isotopic features suggest the Weixi granitoids were derived by partial melting of ancient crustal material. The Weixi granitoids and silicic volcanic rocks were derived from the same magma by crystal accumulation and melt extraction, respectively, and they record the formation of a continental arc in the central Sanjiang orogenic belt. [ABSTRACT FROM AUTHOR]

The Hesar pluton in the northern Urumieh–Dokhtar magmatic arc hosts numerous mafic‐microgranular enclaves (MMEs). Whole rock geochemistry, mineral chemistry, zircon U‐Pb and Sr‐Nd isotopes were measured. It is suggested that the rocks are metaluminous (A/CNK = 1.32–1.45), subduction‐related I‐type calc‐alkaline gabbro to diorite with similar mineral assemblages and geochemical signatures. The host rocks yielded an U‐Pb crystallization age of 37.3 ± 0.4 Ma for gabbro‐diorite. MMEs have relatively low SiO2 contents (52.9–56.6 wt%) and high Mg# (49.8–58.7), probably reflecting a mantle‐derived origin. Chondrite‐ and mantle‐normalized trace element patterns are characterized by LREE and LILE enrichment, HREE and HFSE depletion with slight negative Eu anomalies (Eu/Eu* = 0.86–1.03). The host rocks yield (87Sr/86Sr)i ratios of 0.70492–0.70510, positive εNd(t) values of +1.55–+2.06 and TDM2 of 707–736 Ma, which is consistent with the associated mafic microgranular enclaves ((87Sr/86Sr)i = 0.705014, εNd(t) = +1.75, TDM2 = 729 Ma). All data suggest magma‐mixing for enclave and host rock formation, showing a complete equilibration between mixed‐mafic and felsic magmas, followed by rapid diffusion. The TDM1(Nd) and TDM2(Nd) model ages and U‐Pb dating indicate that the host pluton was produced by partial melting of the lower continental crust and subsequent mixing with injected lithospheric mantle‐derived magmas in a pre‐collisional setting of Arabian–Eurasian plates. Clinopyroxene composition indicates a crystallization temperature of ∼1000°C and a depth of ∼9 km. [ABSTRACT FROM AUTHOR]

Iron oxide-copper-gold (IOCG) deposits are a vital source of copper and critical elements for emerging clean technologies. Andean-type IOCG deposits form in continental arcs undergoing extension, and they have a temporal relationship with magmatism although they do not exhibit a close spatial relation with the causative intrusions. The processes required to form IOCG deposits and their potential connections to iron oxide–apatite (IOA)-type mineralization remain poorly constrained, as well as the characteristics of magmatism linked to both deposit types. Here we combine zircon U–Pb geochronology with zircon trace element geochemistry of intrusive rocks associated with the Candelaria deposit, one of the world's largest IOCG deposits, to unravel distinctive signatures diagnostic of magmatic fertility. Our results reveal a marked transition in the geochemistry of intrusions in the Candelaria district, characterized by changes in the redox state, water content and temperature of magmas over time. The oldest magmatic stage (~ 128–125 Ma), prior to the formation of the Candelaria deposit, was characterized by zircon Eu/Eu* ratios of 0.20–0.42, and redox conditions of ΔFMQ − 0.4 to + 1.0. The earliest magmatic stage related to the formation of Fe-rich mineralization at Candelaria (118–115 Ma) exhibits low zircon Eu/Eu* ratios (0.09–0.18), low oxygen fugacity values (ΔFMQ ~− 1.8 to + 0.2) and relatively high crystallization temperatures. In contrast, the youngest stage at ~ 111–108 Ma shows higher zircon Eu/Eu* (~ 0.37–0.69), higher oxygen fugacity values (ΔFMQ ~ + 0.4 to + 1.3) and a decrease in crystallization temperatures, conditions that are favorable for the transport and precipitation of sulfur and chalcophile elements. We conclude that Candelaria was formed through two distinct ore-forming stages: the first associated with a reduced, high temperature, water-poor magma developed under a low tectonic stress, followed by a more oxidized, water-rich, and low temperature magmatic event related to a compressional regime. The first event led to Fe-rich and S-poor IOA-type mineralization, while the second event with geochemical signatures similar to those of porphyry copper systems, generated the Cu- and S-rich mineralization. This late stage overprinted preexisting IOA mineralization resulting in the formation of the giant Candelaria IOCG deposit. [ABSTRACT FROM AUTHOR]

Studies have revealed the key role of deepseated, ore-forming fluids and metals in the generation of the Early Cretaceous largescale gold deposits in the Jiaodong gold province of eastern China. However, how the ore-forming materials were transported to shallow crustal levels remains unclear. Here, we investigate trace elements and sulfur isotopes of pyrite within mafic microgranular enclaves (MMEs) of Gushan granite to evaluate the role of the syn-mineralization of mafic enclaves in the transportation of ore-forming materials. Zircon U-Pb and molybdenite Re-Os dating indicate that the magmatichydrothermal event in the potassic-altered Gushan granite occurred at ca. 120 Ma, which is contemporaneous with the Jiaodong gold mineralization. The texture and geochemical compositions of pyrite indicate that pyrite grains hosted by Gushan MMEs are of deuteric hydrothermal origin and precipitated during or shortly after magma mixing. The distribution of elements (i.e., Co, Cu, Ni, Zn, As, Ag, Au, Pb, and Bi) and the sulfur isotope (4.14‰-8.8‰) data for pyrites from Gushan MMEs are quite identical to those of the Xiejia diorite intrusion (DI) and other ores from the Jiaodong gold province, which indicates a common source of these pyrites. The common origin of the pyrites, combined with evidence from previous work, suggest that the ore-forming fluids and materials originated from the metasomatized lithospheric mantle, which was the repository of water, sulfur, and volatiles from the subducted Paleo-Pacific plate, rather than by direct release from the subducted sediments of the Paleo-Pacific plate. Our results collectively show that the arc-like mafic magmas derived from the metasomatized lithospheric mantle at ca. 120 Ma were the intermediary that transported the gold and other oreforming components from the deep mantle to the shallow crustal levels where gold and ore-related material were injected into the Weideshan granitic suite during magma mixing. Thus, the Weideshan granitic suite may have played a critical role by continuously transferring gold to the shallow crustal faults where it precipitated. Therefore, future research or deep-drilling exploration programs in the area should emphasize the Weideshan granitic suite rather than the Xiejia DI. [ABSTRACT FROM AUTHOR]

Modeling the behavior of trace elements during lunar magma ocean solidification is important to further our understanding of the chemical evolution of the Moon. Lunar magma ocean evolution models rely on consistent datasets on how trace elements partition between a lunar silicate melt and coexisting minerals at different pressures, temperatures, and redox conditions. Here we report new experimental trace element partition coefficients (D) between clinopyroxene (cpx), pigeonite, orthopyroxene, plagioclase, olivine (ol), and silicate melt at conditions relevant for the lunar magma ocean. The data include Dcpx−melt at ambient and high pressures (1.5 GPa and 1310 °C), and partition coefficients at ambient pressure for pig, opx, ol, and pl. Overall, clinopyroxene is a phase that may control the fractionation of key geochemical trace element ratios, such as Lu/Hf and Sm/Nd, during the evolution of the lunar magma ocean. We explore the impact of the new silicate Dmineral−melt on the trace element evolution of the lunar magma ocean and we find that accessory phosphate minerals, such as apatite or whitlockite are of critical importance to explain the observed trace element and isotopic signature of the KREEP reservoir on the Moon. The new partition coefficients were applied to calculate the trace element evolution of the residual melts of the crystallizing lunar magma ocean and we propose a new trace element composition for the urKREEP reservoir. The new data will be useful for future thermo-chemical models in order to adequately predict the duration of the lunar magma ocean and the age of the Moon. [ABSTRACT FROM AUTHOR]

The study area lies in the south of Mamoniyeh, a part of the Zaviyeh 1:100000 geological map, which covers the middle part of the Urumieh-Dokhtar magmatic arc. The volcanic phases and the intrusive masses constitute the predominant rocks of the area which has been subjected to magmatic and tectonic activities. Thus, owing to the lack of detailed studies on the volcanic rocks of this area, we try to link the tectonic setting and the magmatic evolution of the rocks under study. In addition, magma evolution processes, such as fractional crystallization, crustal contamination, and magma mixing may play an important role in the genesis of these rocks. The present paper presents new petrological and geochemical data on these volcanic rocks, which were formed during the Eocene. The Urumieh Dokhtar Magmatic arc is characterized by a series of volcanic and plutonic rocks that formed during the Late Cretaceous to Early Miocene, approximately 95 to 20 million years ago, and extends for about 2,000 kilometers. [ABSTRACT FROM AUTHOR]

Subduction zone magmatism is a major control of volcanism, the generation of modern continental crust and the formation of economically important porphyry Cu–(Mo–Au) deposits. Reading the magmatic record of individual arc segments and constraining the rates of magmatic changes are critical in order to fully understand and quantify the processes that drive magma evolution in subduction settings during arc growth. This study focuses on the San Francisco Batholith and the Rio Blanco-Los Bronces porphyry deposit cluster in central Chile, which provides an igneous rock record over ~13.5 Myr of arc evolution. We use whole-rock geochemistry, zircon geochronology and Hf isotope geochemistry to track changes in the crustal magmatic system of this arc segment during crustal thickening and porphyry Cu deposit formation. By combining the analytical dataset with Monte Carlo fractional crystallisation and assimilation fractional crystallisation modelling, we test a model for significant crustal involvement during magma evolution. Systematic and continuous increases in Dy/Yb, La/Yb, V/Sc and Sr/Y in the magmas over time indicate a transition in the main fractionation assemblage from plagioclase-dominated to amphibole-dominated that reflects deeper crystallisation and/or a higher meltwater content. Concomitant decreases in εHf and Th/La as well as increasing Ba/Th are best explained by assimilation of progressively deeper crustal lithologies from low (Chilenia) to high Ba/Th (Cuyania) basement terranes. Our study highlights that an increasingly hydrous magma and a deepening locus of crustal magma differentiation and assimilation, driven by crustal thickening contemporaneous with increased tectonic convergence and ingression of the aseismic Juan Fernandez ridge, can account for all investigated aspects of the multi-Myr magmatic evolution leading up to the formation of the Rio Blanco-Los Bronces porphyry Cu deposits. Our findings corroborate the importance of high-pressure differentiation of hydrous magma for the formation of Andean-style porphyry deposits. Once magmas favourable for porphyry Cu mineralisation were generated in the lower crust, multiple episodes of efficient magma migration into the upper crust fed several, discrete, shallow magmatic-hydrothermal systems over ~3.5 Myr to form the world's largest known Cu resource at Rio Blanco-Los Bronces. [ABSTRACT FROM AUTHOR]

The Messejana–Plasencia great dyke (MPGD) is a Late Triassic tholeiitic gabbro intrusion related to the Central Atlantic Magmatic Province. Its large outcrop extent (~530 km), combined with its prolongation below the Duero basin (additional 100 km), makes it one of the world's largest dykes known. We have studied felsic granophyric bodies appearing in its northernmost segment at different scales, from mm-sized (interstitial micrographic pockets) to felsic dykes of up to 10 m thick and 1.5 km long, intruding within the gabbros. Significant differences exist in the mineral and whole-rock composition of gabbros and granophyres, including the Sr–Nd isotopic ratios. The chemical variation in the gabbros is coherent with fractionation of olivine, clinopyroxene and plagioclase at depth. However, the presence of a compositional gap between gabbros and granophyres (absence of intermediate compositions) and the formation of these late-stage intergranular felsic melts within the gabbro mesostasis suggest that they could be derived by liquid immiscibility. The Sr–Nd isotopic heterogeneity in the MPGD gabbros and the presence of zircons with Variscan ages (~286 Ma), inherited from granulitic rocks, indicate that the mafic magmas experienced some degree of lower crust assimilation during fractionation close to the Moho depth. On the contrary, the scarce xenocrystic Variscan zircon crystals found in a granophyric dyke within the MPGD gabbro display similar textures and ages (~299 Ma) to those of the country rock granites and point to contamination at a different crustal level. [ABSTRACT FROM AUTHOR]

The gabbro-dioritoid rocks from Veľké Železné (Nízke Tatry Mts., Western Carpathians, Slovakia) were recently studied in order to better understand the age, origin, and evolution of the basic/intermediate magmas associated with Variscan granitic rocks. Their genesis was investigated from the points of view of petrology, whole-rock geochemistry (including Sr, Nd, and Pb isotopic characteristics), as well as U-Th-Pb zircon and apatite dating. The Famennian magmatic crystallization age of ca. 360 Ma (determined from zircon: 362.4 ± 2.9 Ma and apatite: 358.4 ± 2.8 Ma) is older than the Tournaisian-Visean ages for granite intrusions in the Tatric Unit. Geochemically, the studied rocks have an affinity to arc-related basalts, consisting of a metaluminous, magnesian, and high-potassium calc-alkaline character. Isotope data (i.e., (87Sr/86Sr)360 = 0.7035-0.7044 and εNd360 = +1.4 to +1.6) demonstrate that these gabbro-dioritoids were formed from the mantle-influenced, lower crustal and/or sub-continental lithospheric mantle (SCLM) sources, whereas the unsystematic increase of Pb isotope ratios indicate either the melting of an ancient Enriched mantle-II (EM-II) reservoir or the upper crustal assimilation and/or local fluid alteration. The data presented in this paper favour the origin of the studied gabbro-dioritoids at a continental arc, although we cannot rule out their genesis as a result of the subsequent slab break-off. [ABSTRACT FROM AUTHOR]

This study focus on the Mt Etna December 2018 eruption with the aim of investigating the geochemical characteristics of the feeding magma. New data on major and trace element geochemistry of olivine-hosted melt inclusions (MI) in volcanic products are presented together with the noble gas geochemistry of fluid inclusions (FI) in olivines. The noble gas geochemistry of fluid inclusions (FIs) in olivines was also investigated. The major element composition of MIs is variable from tephrite/trachybasalt to phonotephrite/basaltic trachyandesite, with SiO2 = 45.51-52.72 wt%, MgO = 4.01-6.02 wt%, and CaO/Al2O3 = 0.34-0.72. Trace element patterns of MIs present a typical enrichment in LILE and LREE, depletion in HFSE, and relatively fractionated REE patterns: (La/Lu) N= 18.8-41.08, with Eu/Eu* = (0.5-1.8). Positive anomalies in Sr (Sr/Sr* = 0.8-2.3) and Ba can be ascribed to the assimilation of plagioclase-rich cumulates in the magmatic reservoir. The variable Ba/La (9.8-15.8), K/Nb (260-1037), Ce/Nb (1.9-3.4), Rb/La (0.4-1.6), and Ba/Nb (10.8-25.8) ratios reveal mixing between two types of end-member magmas comparable to those emitted from 1) the 2001 Upper Vents and 2002-03 Northern Fissures (Type-1) and 2) the 2001 Lower Vents and 2002-03 Southern Fissures (Type-2), respectively. Type-2 represents a magma that was under the influence of a crustal component, whereas Type-1 is compatible with a HIMU-MORB-type heterogeneous mantle source. It appears that the 2018 MIs have captured the two different types of magmas, and the lack of homogenization may imply a very fast ascent (a few months). Compatible with the contemporary presence of primordial HIMU-MORB and crust-contaminated end-members are the data on noble gases from FI that highlighted an ³He/[sup 4]He value of 6.5-6.6Ra. The hypothesis of two different types of magmas, identified by the trace element geochemistry in MIs, is, thus, reinforced by helium isotopic data on FI of the 2018 eruption together with data from other Etnean eruptions and allows the inference of a bicomponent magma mixing. [ABSTRACT FROM AUTHOR]

The study area is located in the Poli Group, Western Cameroon Domain of the Central African Fold Belt. It is constituted mainly of Pan‐African granitoids intruding Neoproterozoic volcano‐sedimentary rocks, schists and gneisses. The granitoids host dykes of gabbroic and dioritic rocks which are the focus of this study. Gabbroic and dioritic rocks are clinopyroxene‐hornblende gabbros, clinopyroxene‐hornblende melagabbro, clinopyroxene‐hornblende leucogabbro and quartz‐diorite. Geochemically, the rocks are characterized by: SiO2 (46.03–58.88 wt. %); Mg# (27.78–79.46); MgO (2.10–18.40 wt.%); total alkali (0.97–10.7 wt.%); Fe2O3 (8.42–13.19 wt.%); and CaO (4.90–16.57 wt. %), meanwhile all the rare earth elements are enriched with respect to chondrites. The rocks are mainly medium‐K calc‐alkaline with subordinate low‐K and alkaline samples. The ratios of La/Ta (4.0–76.0), La/Nb (0.8–9.88) and Zr/Ba (0.11–0.52) indicate that their source is both asthenospheric and lithospheric. This source has characteristics of NMORB to EMORB, overprinted by fluids‐enriched silicic and carbonatitic metasomes likely as a result of slab‐mantle interactions in a subduction environment. The weak to strong fractionation of La/Yb ratio (La/YbN = 0.9–13.51) and non‐fractionation of the Dy/Yb ratio (Dy/YbN = 0.6–1.5) together with the behaviour of the rocks in the La/Sm versus Sm/Yb modelization diagram are consistent with a polybaric melting which started in the asthenosphere at a small rate, yielding the limited volume of alkaline rocks. It then continued in the lithosphere where a more extensive degree of melting produced medium‐K calc‐alkaline rocks. The melting was likely induced by the adiabatic decompression of the metasomatized mantle during the post‐collisional relaxation closing the tectonic stage of the Pan‐African Orogeny in the Poli area. The magma generated was near‐primitive and evolved by assimilation‐fractional crystallization. [ABSTRACT FROM AUTHOR]

The current debate on volcanic-plutonic connection is centered on whether eficient liquid-crystal segregation dominates the evolution of a mushy reservoir to produce evolved, crystal-poor rhyolite and cumulate leftover. However, magma recharge may remarkably influence the evolution of a mushy reservoir and obscure the evidence of liquid-crystal segregation. This complexity poses a challenge to exploring the connection of volcanic-plutonic rocks. This study investigates the Qinzhou Bay granitic complex (~250–248 Ma) from South China, which contains crystal-poor (<19 vol%) peraluminous rhyolites and subsequent crystal-rich (28–54 vol%) porphyries. Although the rhyolite and porphyry units have a close spatio-temporal link, they do not share a fractionation trend and similar whole-rock Sr-Nd-O isotopic compositions; thus, a direct connection is not evidenced. We further present textural analyses, mineral and melt inclusion compositions, thermobarometry (the combination of Ti-in-zircon thermometer and Ti-in-quartz thermobarometer), and thermodynamic modeling to examine the alternative interpretations, i.e., the two units may have intrinsically independent origins or the connection of the two units has been obscured. For the rhyolite unit, thermobarometric results reveal a polybaric storage system consisting of middle (>600 ± 80 MPa) and upper (~150 ± 40 and ~60 ± 20 MPa) crustal reservoirs. Variations in quartz Fe content and chlorine-rich, metaluminous melt inclusions suggest that magma hybridization with less-evolved metaluminous magmas occurred at both crustal levels. In particular, the elevated Fe contents in the quartz population that crystallized at the shallowest level (~60 ± 20 MPa) suggest that recharge magmas were directly injected into the shallowest reservoir. Deviation of the whole-rock composition from the liquid evolution trend recorded in melt inclusions suggests a combined efect of magma mixing and crystal-melt segregation processes in upper crustal reservoirs. Thermodynamic modeling and mass balance calculations suggest that the whole-rock composition of the rhyolite could be reproduced by mixing between regionally exposed dacites and segregated melts at crystallinities of 50–60% (using parental magma represented by the least-evolved melt inclusion). For the porphyry unit, thermobarometric results reveal magma storage at middle (more than 450 ± 40 to 550 ± 40 MPa) and upper (110 ± 20 to 140 ± 20 MPa) crustal levels. The small-scale oscillatory zonation of plagioclase, the pervasive resorption of quartz and alkali feldspar, and the presence of peraluminous microgranular enclaves in the porphyries suggest a recharge event of metasediment-sourced magmas, triggering reactivation and convection of the reservoir. Autoclastic and overgrowth textures of quartz, plagioclase, and alkali feldspar phenocrysts and development of columnar jointing suggest that the reactivated porphyritic magmas ascended and emplaced at ultrashallow levels (~30 ± 10 MPa). Because of the similar storage pressures, the porphyries may represent remobilized cumulates of rhyolitic magmas, whereas the texture and geochemistry of the cumulate-liquid pair were modified, a key factor rendering a cryptic connection between the rhyolite and porphyry. Alternatively, the plumbing systems feeding the rhyolite and porphyry units are horizontally independent or vertically discrete, but this circumstance is inconsistent with the same evolution trend of quartz Fe and Al contents of the rhyolite and porphyry. Our study highlights that whole-rock composition may record blended information of complex processes, and caution should be taken when whole-rock composition is used to extract information of a single process. Multi-method constraints are required to evaluate the influence of recharge processes on the modification of liquid-cumulate records, and big data analysis on the basis of geochemistry should be conducted with caution to avoid biased understanding. [ABSTRACT FROM AUTHOR]

The southern margin of the North China Craton (SNCC) contains 8 giant (> 0.5 Mt Mo resources), 4 large (0.1–0.5 Mt Mo resources) and many small (< 0.1 Mt Mo resources) porphyry Mo deposits. Their magmatism ages are concentrated within 150–131 Ma, but it is unclear what determines the size of porphyry Mo systems. Herein, we synthesize new and existing data for the Mo-bearing intrusions in the SNCC to investigate the optimal conditions for giant deposit formation. These intrusions share similar whole-rock geochemistry characteristics and highly differentiated features, with SiO2 and K2O contents ranging from 68.55 to 79.13 wt.% and 2.63 to 11.18 wt.%, respectively. They share similar lower crustal sources with a variable input of mantle materials. Their εNd(t) and εHf(t) values range from -19.1 to -12.7 and -29.5 to -9.3, respectively, and indicate no relationship with metal fertility. The similar ΔFMQ values calculated from zircon geochemistry also suggest that the porphyry Mo deposit size is unrelated to magma redox conditions. High magmatic water contents and high differentiation features (SiO2 > 73 wt.%) exhibit significant positive correlations with the deposit size. Therefore, we propose that magma with a high water content triggered by intensive fractional crystallization is the fundamental requirement to produce large Mo endowment in the SNCC. This conclusion is consistent with the criteria that pulsed release of mineralizing fluids from a large magma chamber through fractional crystallization play an important role in the formation of giant porphyry Mo deposits in other molybdenum belts in the world. [ABSTRACT FROM AUTHOR]

The Dunde iron-zinc polymetallic deposit is one of large iron deposits occurred in the Awulale Metallogenetic Belt, Western Tianshan (NW-China). This study reports new geochronology and geochemistry for granite in the Dunde mining area in order to constrain the tectonic-magmatic activities and metallogenesis of this region. Granites in the southwest of Dunde mining area are mainly syenogranites intruded into volcanics of the Dahalajunshan Formation in the Early Carboniferous, and they are far from the area where ore bodies and mineralized altered rocks are widely developed. LA-ICP-MS U–Pb zircon dating indicates that Dunde syenogranite was at 306.8 ± 1.0 Ma, which could constrain the upper limit of metallogenic age for this deposit. The Dunde granites are high SiO2 (73.41–80.07 wt%), high differentiation index (D.I. = 89.7–95.0), weakly peraluminous to metaluminous (A/CNK = 0.94–1.08), and they are enriched in LILE and LREE and depleted in Eu, Ba, Sr and P2O5, indicating that they belong to highly fractionated I-type granite. Based on εHf values (+ 9.2 to + 10.5) for zircon and high εNd(t) values (+ 4.7 to + 5.8) for whole-rock, and the two-stage model ages for 601–735 Ma, suggest that the magma source could be the juvenile lower crust. Combined with regional geological setting, the 306.8 Ma Dunde granites are formed in post-collision extensional tectonic setting. [ABSTRACT FROM AUTHOR]

At least 28 rhyolitic lava flows, domes, and tuffs erupted within Yellowstone caldera following its formation 631 ka. Understanding the timing of intracaldera eruptions is essential for characterizing natural hazards posed by Yellowstone volcano. We present 40Ar/39Ar eruption ages for the Mallard Lake Member and Central Plateau Member of the Plateau Rhyolite, which comprise products from 22 eruptions spanning ~160 to ~70 ka. These eruptions occurred along two linear vent zones within Yellowstone caldera that appear to be extensions of major extracaldera normal faults. Eruptions took place in five brief clusters with group mean ages of 160.3±1.0 ka (2σ), 149.8±4.0 ka, 111.4±0.9 ka, 104.1±0.8 ka, and 70.8±0.7 ka. All mapped products within each informal group have indistinguishable 40Ar/39Ar eruption ages implying brief eruption durations. Eruption products of each group are spatially clustered, with only one of the two linear vent zones being active during an eruption group. Using the oldest group (160 ka), we apply paleomagnetic and geochemical analyses to investigate the duration of these eruption groups and their pre-eruptive magma reservoir configuration. Paleomagnetic analyses suggest that the nine rhyolite eruptions ~160 ka spanned 400 years or less. Glass and sanidine compositions of each rhyolite are nearly identical, which is consistent with pre-eruptive storage of a large (~130 km3), interconnected melt body within Yellowstone volcano's crystal-rich magma reservoir. These characteristics differ from intracaldera eruptions that vented near the caldera's inner ring fracture system, which tend to be compositionally disparate with less temporal clustering. These insights inform hazard mitigation scenarios. [ABSTRACT FROM AUTHOR]

Deep crustal cumulates in arcs offer a window into the chemistry and crystallization conditions (P–T–H2O– f O2) of primitive basalts in the upper mantle and lower crust and can be studied in ancient exhumed terranes or in xenoliths erupted in young arc lavas. Here, we expand on previous studies and thoroughly characterize the extensive xenolith suites erupted from the Mt. Moffett and Mt. Adagdak volcanic centers (Adak Island, Central Aleutians), which range from primitive ultramafic cumulates to more evolved amphibole gabbros and hornblendites. We present detailed petrography as well as in situ trace and major element mineral chemistry. We use these data to calculate pressure, temperature, and f O2 estimates for the xenoliths, and compare these findings to experimental results to understand the crystallization sequence and P–T–H2O– f O2 under which the cumulates formed. The Moffett crystallization sequence is defined by early amphibole fractionation and an abrupt shift in oxide compositions from chromite to magnetite, while the Adagdak suite is characterized by simultaneous saturation of amphibole+plagioclase and oxide compositions that become increasingly aluminous before magnetite saturation. Olivine–spinel oxybarometry of the Adagdak xenoliths indicates that they are oxidized relative to mid-ocean ridge basalt (MORB:FMQ +0.1 to +2.1). Highly fractionated REE and elevated Sr/Y ratios are observed in clinopyroxene from the most primitive cumulates, consistent with a contribution from a basaltic eclogite melt. This basaltic eclogite melt is hypothesized to come from partial melting of the slab or through melting of basalt introduced into the subarc mantle through forearc subduction erosion. These signatures are greatly diminished in the more evolved lithologies, which can be explained through fractionation of plagioclase and amphibole. Our findings support the presence of a complex magmatic plumbing system beneath Adak, with Mt. Moffett and Mt. Adagdak volcanic centers tapping compositionally distinct sources. More broadly, our results are consistent with studies suggesting that low-degree basaltic eclogite melts through slab melting or forearc subduction erosion contribute to arc magmas in the Aleutians, although the associated geochemical signatures are easily obscured by differentiation in the crust. [ABSTRACT FROM AUTHOR]

The Yalguba Ridge volcanic rocks form part of the Middle Paleoproterozoic (ca. 1.97 Ga) volcano-sedimentary sequence within the Karelian Craton in the Fennoscandian Shield. Yalguba variolitic textures are known worldwide and have been previously considered to originate from liquid immiscibility. The present study reveals two new variolite types recognized in the Yalguba sequence: (1) Variolites with unzoned varioles have distinct chemical and mineralogical compositions of varioles and matrix that support an origin by liquid immiscibility. They were recognized in quenched zones of pillows, so it might be assumed that melt separation caused by liquid immiscibility occurred before magma emplacement. The difference from the previously described variolites lies in the variole microtexture and might be caused by the various cooling conditions. (2) Spherulitic variolites have varioles composed of andesine–oligoclase spherulites embedded in the cryptocrystalline matrix with oligoclase–anorthoclase composition, thus the variole and matrix have similar chemical and mineralogical composition. The mineralogical and textural features of these variolites suggest that the spherulites have a primary magmatic origin due to the rapid cooling of superheated magma. The variety of variolitic textures in the Yalguba section might be caused by the different H2O saturation of parental magma and cooling conditions. [ABSTRACT FROM AUTHOR]

Shoshonitic rocks represent the transition between calcalkaline and alkaline rocks, often formed during the last stages of uplift in zones of continental collision. This study describes the characterization of Kyrdem granitoids of Shillong plateau, Meghalaya, North East India, as felsic shoshonites. The study also documents petrogenesis of the shoshonites and suggests significant magma mixing and crust–mantle melt interaction as prime mechanisms for parental magma evolution. Crustal melt has most probably been sourced from a metabasaltic middle crust, while the mantle source is represented by an enriched sub-continental lithospheric mantle, metasomatized by sediment melt, during an earlier subduction event. [ABSTRACT FROM AUTHOR]

Copyright of World Nuclear Geoscience is the property of World Nuclear Geoscience Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

There are several different models for the origin of syenites, but the role of magma mixing in the formation of syenites remains unclear. The Wulingshan alkaline complex in the northern North China Craton consists mainly of porphyritic syenite and syenite with abundant enclaves. These enclaves may provide new insights into the petrogenesis of syenites. We obtained zircon U–Pb age, mineral chemistry, whole‐rock major and trace elements, and Sr–Nd isotopic data for the enclaves and their host rocks to constrain the petrogenesis and identify the role of magma mixing during the formation of the different syenites in the Wulingshan alkaline complex. The results of zircon U–Pb dating indicate that the enclaves and host rocks crystallized contemporaneously at ca. 133 Ma. The enclaves contain abundant clinopyroxene, amphibole, and biotite, and their average Nb/Ta (18.46) and Th/Ce (0.04) ratios are similar to those of the mantle. The enclaves have relatively high Fe2O3T, MgO, and CaO contents, and their SiO2 contents are equivalent to those of intermediate rocks, indicating that they formed by mixing the mafic and felsic magmas to some extent. The different mineral assemblages, major and trace elements and isotopic compositions of the enclaves in the porphyritic syenite and syenite indicate that they are two batches of parental magma with different properties derived from the mantle. The porphyritic syenite and syenite have high SiO2 and low Fe2O3T, MgO, and CaO contents, as well as low V, Cr, Co, and Ni contents. These major and trace element characteristics of the host rocks require the involvement of crustal components. The Sr–Nd isotopic compositions of the enclaves and the host syenitoids plot on a mixing curve between enriched lithospheric mantle and lower crust, indicating that these rocks are the products of magma mixing and crust–mantle interaction. Considering the contact relationships, the geochemistry data, and the mixing model presented in the paper, we propose that the upwelling of the hot asthenosphere heated the overlying enriched lithospheric mantle and triggered low‐degree partial melting. The alkalic mafic magmas derived from enriched mantle sources were mixed with felsic magmas generated by partial melting of the lower (or upper) crust to form the different syenites. [ABSTRACT FROM AUTHOR]

Volatile element abundance is a crucial factor triggering mineralization and controlling the enrichment of molybdenum in porphyry deposits. The Chalukou deposit is the largest porphyry Mo deposit in NE China, with an average grade of 0.087% Mo. In this contribution, we present petrology, bulk geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes, and apatite geochemistry for the Chalukou deposit. The intrusive rocks include pre‐mineralization monzogranite, syn‐mineralization quartz porphyry, fine‐grained porphyry and granite porphyry, and post‐mineralization monzogranite and feldspar porphyry. These granitoids are metaluminous to peraluminous, and belong to alkali‐calcic to calc‐alkalic series. Zircon εHf(t) values of granitoids range from +0.2 to +5.7 with corresponding Hf crustal model ages of 805–1170 Ma, indicating a Mesoproterozoic juvenile crustal source modified by mantle‐derived magma. They are characterized by logf(O2) of −16.1 to −9.4, with an average of −12.5, ΔFMQ of +0.8 to +7.9, with an average of +4.5, showing a relatively high oxidation state for the syn‐mineralization magma. The apatites in quartz porphyry have the highest F contents, ranging from 3.61 to 4.62 wt%. At Chalukou, F‐rich magma is conducive to the convection of magma and promotes the efficient separation of differentiation magma, making the magmatic‐hydrothermal fluid circulate many times, eventually resulting in the accumulation of ore‐forming materials on the top of the magma chamber and gradually aggravating mineral enrichment processes. [ABSTRACT FROM AUTHOR]

To ascertain the Early-to-Middle Jurassic tectonic setting in the central Great Xing'an Range, this study investigated the Early and Middle Jurassic granitoids exposed in the Chaihe area in the central Great Xing'an Range based on isotopic chronology and petrogeochemistry. The results of this study show that the Early and Middle Jurassic granitoids have emplacement ages of 179–172 Ma. Moreover, the Early and Middle Jurassic granitoids are high-K calc-alkaline unfractionated I-type granitoids and high-K calc-alkaline fractionated I-type granitoids, respectively. The magma sources of the Early and Middle Jurassic granitoids both originated from the partial melting of newly accreted lower crustal basaltic rocks. Meanwhile, the Middle Jurassic magma sources were mixed with mantle-derived materials or ocean-floor sediments formed by the dehydration and metasomatism of subducted slabs. The Early and Middle Jurassic granitoids in the study area were formed in the subduction environment of the oceanic crust, in which the Mongol-Okhotsk oceanic plate was subducted southward beneath the Eerguna and Xing'an blocks. Moreover, the Siberian plate began to collide and converge with northeast China during the Middle Jurassic. [ABSTRACT FROM AUTHOR]

The Soarinho Alkaline Intrusion, southeastern Brazil, makes up part of the Serra do Mar Igneous Province, and it is composed of alkali feldspar syenite, alkali feldspar trachyte, quartz syenite, and monzonite. Geochemical and geochronological analyses of the Soarinho were compared with data from its neighbors, Rio Bonito and Tanguá. Zircon U-Pb Laser Ablation ages show that Soarinho is younger than Rio Bonito and Tanguá. Ages obtained from the monzonite (60 ± 2 Ma), alkali feldspar syenite (58 ± 2 Ma), and quartz syenite (58 ± 2 Ma) are indistinguishable within error. One nepheline syenite sample from Tanguá gives an age equal to those of Rio Bonito already published (65 ± 1 Ma). Petrographic and geochemical data show a clear contrast among Soarinho, Rio Bonito, and Tanguá. Lu-Hf isotopic data for the three alkaline intrusions (all negative) point to some similarities in their sources. The data suggest an enriched mantle source for Soarinho; however, an older continental crust contribution cannot be discarded. [ABSTRACT FROM AUTHOR]

The occurrence of Permian magmatic rocks in the Colombian Andes is restricted to a few localities. Previous works have focused mainly on explaining its tectonic setting, whereas petrogenesis has received less attention. This study closes this gap by reporting whole‐rock geochemistry, zircon U–Pb geochronology, trace elements and Hf isotopes from massive and mylonitic granitoids along central Colombia to constrain their age, source and petrogenesis. Our results show that the granitoids have a calc‐alkaline character, are rich in light‐rare elements (LREEs) and large‐ion lithophile elements (LILEs), present negative Nb and Ti anomalies, crystallized between ca. 276–265 Ma and show variable εHf(i) values ranging from −1.5 to +1.7. Combining our results with published geochemical, geochronological and isotopic data from this region, we suggest that the Middle Permian granitoids from the Tolima region were formed in a continental magmatic arc installed at the western margin of Gondwana, where partial melting of the mantle wedge and further crustal assimilation of the magmas with an old radiogenic and heterogeneous crust were essential processes for the modification of the source of the magmas that generated the granitoids. The Middle Permian may have reached the peak magmatic conditions (ca. 280–270 Ma), according to the recurrence of ages in this time interval. This period of magmatic activity may have been interrupted by the Triassic extensional period related to the beginning of the Pangea breakup. [ABSTRACT FROM AUTHOR]

Late Paleozoic pillow basalts are well preserved in the Youjiang Basin of SW China. In this study, we conducted geochemical and Sr−Nd isotopic study on the Late Devonian and Late Carboniferous basalts in Napo area, Youjiang Basin. The analyzed samples comprise moderate SiO2, TiO2, Mg#, and REE contents, with slightly positive or negative Eu anomalies, similar to the chemical nature of OIB (Oceanic island basalt). All basalts show low (143Nd/144Nd)i and (87Sr/86Sr)i values, close to EMI-type (I-type Enriched Mantle) magma source. Late Carboniferous basalts display higher (87Sr/86Sr)i, Nb/Th, and lower εNd(t), Zr/Nb values than those of the Late Devonian basalts, implying progressively decreased enrichment components in the magma source processes. Such evolution trend reflects a continuous lithospheric thinning event, supporting a progressive rifting setting of the Youjiang Basin along the southwestern margin of the Yangtze Block in Late Paleozoic. Combined with regional geological background, the Youjiang Basin is viewed as a continental rift basin related to the opening of the Paleo-Tethys Ocean in Late Devonian and became a passive continental margin basin in Carboniferous. The Paleo-Tethys branch ocean probably extended further to the southern Youjiang Basin, likely corresponding to the Song Ma suture zone. [ABSTRACT FROM AUTHOR]

The St. Ignace Island complex in Northern Ontario is a package of dominantly felsic rocks emplaced within the upper portions of the Osler Volcanic rocks of the ~1.1 Ga Midcontinent Rift System. The Osler volcanic rocks are predominantly tholeiitic basalts intercalated with rare interflow sediments and rhyolites. The St. Ignace Island complex is an ~26-km2 stock with a felsic core of quartz–feldspar–phyric rhyolites and dacites and an outer ring of anorthosite and gabbro. Textures at a variety of scales within the rocks of the complex show clear evidence of the mingling and mixing of partially crystallized mafic and felsic liquids. Two multigrain (zircon/baddeleyite) fractions from a sample of the gabbro define a Discordia line with an upper intercept date of 1107 ± 8.9 Ma. The core of the complex consists of dacites and rhyolites with similar REE abundances with negative Nb anomalies, whereas the surrounding mafic rocks are gabbros to monzogabbros that are less LREE-enriched than the felsic rocks but with similar HREE. Felsic units have a narrow range of 87Sr/86Sri (0.7032–0.7045) and 143Nd/144Ndi (0.51051–0.51057), whereas the mafic end members have similar 87Sr/86Sri (0.7040–0.7061) but more radiogenic 143Nd/144Ndi (0.51067–0.51085). Very well-preserved silicate melt inclusions (MI), many completely glassy, were observed in quartz, clinopyroxene, and some plagioclase phenocrysts from the complex. These represent some of the oldest unrecrystallized silicate melt inclusions described to date. Melt inclusions within quartz from the felsic volcanics are broadly rhyolitic in composition, whereas MI from plagioclase in the mafic volcanics range from basalt to basaltic andesite; these felsic and mafic melt compositions are interpreted to represent the end-member liquids in the system and bulk rock analyses affirm mixtures of the two. Concentrations of Cu and Ag (in both mafic and felsic MI), and Mo (in felsic MI), are up to an order of magnitude higher in the mafic and felsic MI than in continental crust. Bulk rock metal concentrations are also significantly lower than in the MI, suggesting that the melt inclusions may preserve pre-eruptive metal tenors that were subsequently modified by sulfide saturation, degassing, or post-solidus hydrothermal alteration. The whole rock and MI geochemistry of the St. Ignace complex are broadly similar to the Central Osler Group and, given the broad similar ages, suggests they may have been derived from a similar mantle source, but distinct from the source of rhyolites in the Black Bay Peninsula. The negative Nb anomalies and negative εNd values for the St. Ignace complex are consistent with mixing with older continental crust during ascent and emplacement. The rocks of the St. Ignace Island complex likely formed as the result of emplacement of a large mafic magma chamber at the base of the Osler volcanic pile that triggered partial melting to generate the rhyolite end members. The felsic melts ascended to shallower levels in the crust where they mixed with mafic magmas derived directly from the deeper chamber. Generally, melt inclusions in the complex have very high Cu and Ag contents, similar to those observed in arc-related and extremely oxidized early rift-related rocks and may account for the world-class volcano-sediment-hosted Cu–(Ag) deposits within the rift and the presence of small porphyry-style deposits. [ABSTRACT FROM AUTHOR]

The Dassa region is part of the Pan-African Trans-Saharan Belt, located between the West African craton and the Sahara metacraton. This region, with widespread granitoids and volcanites, is cut by the Kandi Shear Zone (KSZ) that could be connected to the 4°50' shear zone northwards in the Hoggar mountains and to the "Transbrasiliano lineamento" Northeast Brazil. The LA-ICP-MS U–Pb isotopes of zircon, whole-rock geochemistry and Sr–Nd isotope were analysed to constrain the emplacement ages and chronology of granitoids and volcanic rocks in the Dassa region in relation to the KSZ dynamics and the geochemical signatures and genesis of the magmas. Five intrusions (Dassa, Tré, Gobada, Tchetti and Fita) with the igneous rocks of the volcano-sedimentary basin of Idaho-Mahou have been investigated. Radiometric ages (U–Pb) obtained on zircons from the intrusions and the alkaline rhyolites from the Idaho-Mahou volcano-sedimentary basin indicate the Ediacaran timing emplacement in the Pan-African Dahomeyide orogen. The Dassa intrusion is dated at 633 ± 19 Ma while the Tchetti, Gobada and Tré intrusions yield 607 ± 11 Ma, 603 ± 10 Ma and 595 ± 12 Ma, respectively. The alkaline Fita granite and rhyolite of the Idaho-Mahou volcano-sedimentary basin provide U–Pb on zircon ages of 594 ± 32 Ma and 583 ± 9 Ma, respectively. Geochemical investigations reveal that the granitoids are ferroan and metaluminous; alkali-calcic (Dassa and Tré) and alkali-calcic to alkalic (Gobada, Tchetti and Fita). The mafic to intermediate volcanites and trachyte of Idaho-Mahou volcano-sedimentary basin are alkali-calcic whereas the rhyolite displays an alkalic signature. Sm–Nd isotopic analyses reveal that the ε Nd values at c. 600 Ma in the Fita granite and alkalic rhyolite of Idaho-Mahou basin are the highest (− 6.94 and − 6.07). In the other intrusions, the ε Nd values at c. 600 Ma are lower, ranging between − 9.66 and − 9.28 (Tchetti and Godada granites) and − 8.84 and − 8.56 (Dassa and Tré granites). The Tré monzonite shows an intermediate value around − 7.70. The calculated TDM model ages are very close and range between 1.80 and 2.05 Ga. All this suggests hybridization processes between an Archean to Paleoproterozoic continental crust source and a juvenile mantle (600 Ma) source for the parent magmas. But the significantly high ε Nd values of Fita granite and the alkaline rhyolite are in agreement with higher mantle contribution and a distinct more enriched mantle source for the parent magmas of alkaline rocks compared to the alkali-calcic felsic ones for which the mantle contribution is from the depleted mantle. According to these data, the Ediacaran magmatic events in the Dassa region can be divided into two main episodes with respect to the main transcurrent shearing event that started at about c. 610 Ma: a pre-transcurrent shear alkali-calcic plutonic magmatism c. 635–610 Ma and the transcurrent shear magmatism c. 610–580 Ma with contemporaneous alkali-calcic and alkaline plutonic and volcanic magmatism. The integration of existing U–Pb on zircon dating in the Benin basement indicates that in the Dahomeyide orogen, the reactivation of the Kandi shear zone toward the end of Ediacaran timing at around c. 550–540 Ma allowed emplacement of the third suite of magmatism as intrusions and volcanoes. [ABSTRACT FROM AUTHOR]

The genesis of intermediate intrusions is highly controversial, and one of the hot topics is whether they represent frozen melts or cumulates in the evolution of magmatic systems. Distinguishing accumulation from crystallization melt differentiated along the liquid line of descent is the key issue. The Paleoproterozoic intermediate intrusions in southern North China Craton provide an excellent case to decipher this issue. Multiple lines of evidence, including mineral textures, geochemistry as well as alphaMELTS modeling, indicate disequilibrium between whole‐rock and minerals, with melt extraction occurring at temperatures of 760°–820°C and with 10–40 wt.% of trapped melts. Effective water storage, revealed by amphibole and clinopyroxene hygrometers, plays a crucial role in promoting crystal‐melt segregation in pluton‐sized reservoirs in the upper crust. This study demonstrates that the accumulation in intermediate magmas can be identified even without evident complementary initial and extracted melts and provides deep insights into the genesis of intermediate continental crust. Plain Language Summary: The genesis of intermediate rocks has long been controversial since they are analogs of the average composition of continental upper crust. The key topic is whether intermediate rocks represent frozen melts of intermediate magmas or crystal residues after melt extraction in the evolution of felsic magmatic systems. Here we carried out a comprehensive study on the Paleoproterozoic intermediate intrusions in the southern North China Craton, which is considered to have recorded the process of crystal accumulation and melt segregation in the shallow crust. Upon mineral texture, geochronologic, whole‐rock and mineral geochemical, and thermodynamic investigation, we propose that crystal accumulation and crystal‐melt segregation processes can be identified in intermediate magmas with the melt extraction temperatures and proportions of trapped melts recorded by zircon trace elements. Amphibole and clinopyroxene hygrometers revealed high water content of the melts, which likely decreased the viscosity of melts and facilitated effective cumulate‐melt segregation. This study provides a powerful reference to see through the accumulation in intermediate magmas, record the processes of crystal‐melt segregation, and definitively resolve the debate concerning the genesis of intermediate intrusions. Key Points: Crystal accumulation in intermediate magmas can be identified by mineral texture and geochemistryThe effective water storage system in the reservoirs is key to promoting crystal‐melt segregationCrystal‐melt segregation and accumulation are fundamental processes to form evolved continental upper crust [ABSTRACT FROM AUTHOR]

Ca isotope geochemistry has great potential for improving our understanding of magmatic systems and for tracing the deep Earth carbon cycle. There are still many open questions, however, regarding the proper application of this relatively novel proxy to the study of mantle-derived magmas, including (i) the possible effects of pressure on mineral-melt Ca isotope fractionation factors, and (ii) the potential for Ca isotopes to be used as tracers of recycled marine carbonates in mantle-derived magmas. Kimberlites are mantle-derived melts that are highly enriched in CO 2 and are the deepest-sourced magmas (>200 km depth) known to erupt at Earth's surface, providing an excellent opportunity to explore these questions. We present Ca isotope data combined with detailed petrographic observations, bulk-carbonate C-O isotope data, and bulk-rock major element analyses, for a suite of 23 well-characterized kimberlite samples from their type-locality (Kimberley, South Africa). These kimberlites have abundant previous evidence for recycled surface materials in their mantle source, including low S isotope and moderately radiogenic Sr isotope compositions, yet display only limited variations in their Ca isotope compositions (δ44Ca BSE of −0.08‰ to −0.27‰), with an average of −0.17 ± 0.02‰ (2SE, n = 21). This composition is indistinguishable from average carbonatites [−0.19 ± 0.03‰ (2SE, n = 106)] and OIB from recent studies [−0.16 ± 0.01‰ (2SE, n = 41)], and slightly lower than average MORB [−0.11 ± 0.02‰ (2SE, n = 31)]. Although our samples display a wide range of emplacement styles, alteration conditions, extents of magmatic differentiation, and degrees of mantle-cargo entrainment (i.e., xenocryst accumulation), we find no correlations between Ca isotopes and any of these factors. Instead, we find that low-degree partial melting of the likely kimberlite source lithology (i.e., carbon-bearing garnet lherzolite) yields modelled melt δ44Ca BSE values ranging between −0.12‰ and −0.16‰ (at 1400–1500 °C), in agreement with the measured Ca isotope compositions of the Kimberley kimberlites. This observation, and the lack of heavy carbon isotope signatures in the examined samples, indicates that kimberlites do not require subducted carbonates in their mantle sources, despite their very high CO 2 contents. Although several recent studies have suggested that equilibrium mineral-melt Ca isotope fractionation factors (e.g., 1000lnα grt-melt) could be significantly different at higher pressures (i.e., due to pressure-induced changes in Ca O bond lengths and coordinations), our models successfully reproduce the kimberlite data using pressure-independent predictions for mineral-melt fractionations. It remains possible, however, that differences in isotopic fractionation due to the peculiar composition of kimberlite melts (e.g., high CO 2 , low SiO 2) are effectively cancelled out by competing pressure effects, and future work independently targeting these factors will be especially important for our understanding of Ca isotope fractionation in mantle-derived melts and the Ca isotope systematics of Earth's mantle. [ABSTRACT FROM AUTHOR]

Dikes of Paleoproterozoic ultramafic rocks from the Kun-Manie area were studied within the southeastern framing of the Siberian Platform. At the end of the Paleoproterozoic, this area was spanned by the processes of overthrust faultings, the latest of which were accompanied by the emplacement of mafic-ultramafic dikes and sills that control the distribution of Cu–Ni–PGE sulfide mineralization. The petrographic texture of ultramafic dikes suggests their emplacement in tectonically active settings. The elevated concentrations of LREE relative to HREE coupled with other data allowed us to ascribe them to high-Mg ultramafic rocks of the picrite–tholeiite series, which were derived from picrobasaltic rather than from ultramafic magma. The REE level and normalized patterns in ultramafic rocks indicate the involvement of sufficiently enriched sources in the generation of primary melts, which produced rocks that radically differed from peridotites of ophiolite associations and typical komatiite melts. In terms of trace-element patterns and contents of indicator elements (Nb, Yb and Th), they are close to an E-MORB type "enriched" mantle source, but differ in the lower REE concentrations. The Zr/Y–Nb/Y relations in the ultramafic rocks suggest a nonplume source of their primary melts in the upper depleted mantle. Rocks derived from such a melt are characteristically enriched in fluid components (S, Cl, F, As, Te, Se, and H2O), which is evident in the presence of hydroxyl-rich minerals: amphiboles and phlogopite of igneous origin. The ore-forming system evolved from Ni-bearing at the early magmatic stage during the formation of disseminated mineralization to Cu-rich at the postmagmatic stage. The geological data indicate that it was formed during the collision between the Paleoproterozoic island arc and the microcontinent. The combination of subduction and intraplate geochemical characteristics in magmatic rocks is characteristic of a transform margin as a result of the oceanic (Upper Maya) and continental (Uchur) microplates sliding horizontally relative to each other. [ABSTRACT FROM AUTHOR]

The origin of the anorthosite-rapakivi granite-bearing rock complexes was a topic of research for geologists for more than a century. Magmatic systems that produce these complexes were widely developed in the Precambrian and have no direct analogues in modern times. The main goal of this study was to characterize the conditions under which primitive granitoids formed and to shed light on the history of ore matter transport during these stages. The object of the research was granite porphyry dikes—a subeffusive analogue of rapakivi granite from the Salmi batholith in the Fennoscandian Shield. Characteristic solid-phase inclusions of a mineral paragenesis of mafic rocks, as well as inclusions of sulfide melts, were found in zircon from this type of rock. These sulfide inclusions were homogenized by heating, and subsequently, the trace element composition was determined by the LA-ICP-MS method. The geochemistry of zircons was studied by the SIMS method, and the temperature of their formation was determined using a Ti-geothermometer. The temperature of the studied zircon grain formation varied from 925 to 765 °C. The values of ƒO2 for the early stages of the rock formation were in the region below the boundary of the FMQ buffer. The presence of two sulfide melts at the time at which the sulfide inclusions were captured by the zircon, pyrrhotite-chalcopyrite, and sphalerite-chalcopyrite compositions was established. The capture of sulfide inclusions from the pyrrhotite-chalcopyrite composition occurred above 841 °C, while in sphalerite-chalcopyrite, they occurred at a lower temperature of 765 °C. The connection between the formation of granite porphyry with mafic melts that form rocks of the gabbro and anorthosite types was established. [ABSTRACT FROM AUTHOR]

The processes of crystallization differentiation, retrograde isotopic exchange, and autometamorphism are considered with reference to the Eocene granites of the Raumid massif, which consists of eight intrusive phases and serves as an example of a "natural laboratory". The work is based on oxygen isotope, petrographic, and geochemical study of representative samples from each intrusive phase of the massif. The isotopic and geochemical studies were carried out for all rock-forming minerals (Qz, Pl, Kfs, Bt) and their altered varieties. Based on geochemical features, the Raumid granites correspond both to A-type granites and to highly fractionated I-type granites. Our results show that the rocks of the Raumid massif are not the geochemical analog of the Eocene granitoids from the Qiangtang terrane of the Central Tibet or the Vanj complex, as it previously assumed (Chapman et al., 2018). We estimated that differentiation of felsic melts of the Raumid pluton occurred at T = 750–800°C, and P = 4.5–7.8 kbar and was mainly controlled by Pl crystallization. The melts were intruded into the hypabyssal zone in at least two stages: early (γ1–γ3) and late (γ4–γ8), although it is possible that the rocks of the γ7 and γ8 phases formed an additional separate stage. The closure temperature of the oxygen isotopic system of quartz (TQz) ranges from 420 to 610°C. The effect of the multiple intrusions of the melts on the TQz and apparent cooling rates is considered. The study of altered and unaltered minerals showed that autometamorphism partially overlapped with the retrograde oxygen isotope exchange in the cooling rock. The modelled δ18О values during Pl and Kfs alteration describes well the observed isotope data when the crystallization takes place at limited content of water fluid (W/M = 0.3–0.05) which could release during the Raumid's magmas crystallization. [ABSTRACT FROM AUTHOR]

The Craters of the Moon (COM) Volcanic Field in Idaho is the largest mostly Holocene lava field in the conterminous U.S. and the site of the most recent volcanism in the Yellowstone‐Snake River Plain province. This prominent example of a polygenetic fissure field has produced over 60 eruptions over the past 15,000 years from the Great Rift fissure system. The eight most recent lava flows, known as Period A, were erupted between about 2,500 and 2,000 years ago. In this study, major and trace element and Pb‐Sr‐Nd isotope data were obtained, with several samples collected from each flow from widely spaced locations to evaluate heterogeneity in their source magmas. The results reveal three previously unrecognized compositional groups that may represent separate magma batches, and that assimilation and fractional crystallization (AFC) controlled the evolution of the entire Period A suite. The three oldest flows were periodic withdrawals from a body of highly evolved and poorly homogenized magma, and four later flows represent successive samplings from a stratified body of more primitive magma. These two flow groups are related via variable AFC modeled with Magma Chamber Simulator software, with Neogene rhyolite as a plausible crustal assimilant. A third compositional type that requires a different parent magma and AFC history is represented by a single flow erupted from vents a few km away from the others. The compositional evolution and variability observed in this sequence of flows provide new insights into how magmas are generated, modified, and delivered in such polygenetic fissure systems. Plain Language Summary: The Craters of the Moon Volcanic Field is a prominent example of a long‐lived eruptive fissure system in a continental setting, where lava flows are produced at the Great Rift, a linear zone of fracturing and extending crust on the Snake River Plain in southern Idaho. Craters of the Moon has produced more than 60 eruptions over the past 15,000 years, including young lavas with high‐silica compositions that are relatively uncommon in the region. The eight most recent lava flows, known as Period A, were erupted between about 2,500 and 2,000 years ago. This sequence of flows provides snapshots of the evolving system over time and constrains processes that modify and feed magmas to this type of volcanic system. New chemical and isotope data with higher precision than in previous studies reveal that the flows fall into three compositional groups, likely reflecting separate magma batches with distinct histories of cooling, crystallization, and contamination by wall rock. These results illuminate the processes that deliver and alter magmas in such long‐lived fissure systems. Key Points: Compositions of the eight most recent Craters of the Moon lava flows elucidate magma evolution in this polygenetic fissure systemThis compositional study revealed the flows were fed by three previously unrecognized magma compositions with distinct petrologic historiesThe magmas were heterogenous, stratified, and culminated in the eruption of increasingly less evolved flows [ABSTRACT FROM AUTHOR]

The occurrence and compositional diversity of granitic pluton is determined by properties of source rocks and conditions of partial melting, and can be further modified by magmatic processes such as magma mixing, crystal fractionation and assimilation during the transfer. However, the role and relative importance of each process during pluton construction are still elusive. Several representative Early Mesozoic granitic plutons in the West Qinling orogen were chosen to illustrate how the magmatic processes control the compositional variation of granitic plutons. The S-type granites in the West Qinling orogen were derived from partial melting of metapelite and can be classified into two categories based on geochemical features, i.e., high Sr content, and low Rb/Sr ratio and REE content (Group A), and low Sr content, and high Rb/Sr ratio and REE content (Group B). Groups A and B might have been produced through fluid-present and fluid-absent incongruent melting of muscovite, respectively, which can well explain respective contrasting major and trace elemental characteristics, and zircon and monazite saturation temperatures. Three types of zircon were identified in the microgranular mafic enclaves(MMEs)from Mishuling pluton based on the morphology. They have consistent zircon U-Pb age but different trace elemental and Hf isotopic compositions. Type-3 zircon develops {100} prisms and has εHf(t)similar to these of zircon in the host granite. Hence type-3 zircon is interpreted as xenocryst captured from the host granitic magma. Type-1 and type-2 zircons are characterized by {100}+{110} and {110} prisms, respectively. They have relatively higher Th/U ratio and εHf(t)values than type-1 zircon, and may have crystallized from hybridized magmas with varying degrees of the mixing. The mafic endmember of the hybridized magma likely has mantle-derived affinity. Thus, the MMEs in Mishuling pluton record crust-mantle interaction. Zhongchuan pluton is comprised of five rock units from the periphery to the center, which mostly have indistinguishable zircon U-Pb ages. The peripheric porphyritic granodiorite is intruded by phenocryst-bearing (K-feldspar and quartz) medium-grained biotite monzogranite; medium-grained biotite monzogranite is crosscut by medium-grained two-mica tourmaline granite, which is inversely invaded by fine-grained biotite monzogranite in the center. Moreover, the correlations between contents of Rb and Ba, and contents of Rb and Sr for these rock units are not observed. Therefore, Zhongchuan pluton might have been formed by incremental assembly of at least five magma batches. [ABSTRACT FROM AUTHOR]

The NW–NNW trending Paleoproterozoic (2.5–1.6 Ga) mafic dykes from Pakhanjore, Muramgaon and Gariaband–Chhura areas of central Bastar craton are medium-grained, consisting of orthopyroxene, clinopyroxene and plagioclase with ophitic texture. They represent basalt to basaltic trachyandesite composition in TAS (total alkali silica) and tholeiitic magma series in AFM diagram. On element ratio plots, the dykes exhibit fractional crystallisation of plagioclase, clinopyroxene and olivine. High Th concentrations, deviation from MORB-OIB array observed in Nb/Yb vs. Th/Yb plot, and positive Zr–Hf anomalies in multi-element spidergram support crustal contamination of the dykes. Geochemical characteristics such as affinity towards subduction-modified lithospheric mantle (SZLM) field and diagonal trend towards plume array in TiO2/Yb vs. Th/Nb diagram, support the generation of the magma from different degrees of interactions between plume and SZLM. Non-modal REE modelling implies derivation of the magma from different degrees of partial melting of spinel-garnet containing lherzolitic source. Reynolds numbers in order of 103–104 obtained from quantitative calculations of the dyke widths support turbulent ascent of the magma. Our calculations suggest while magma ascending from lower crust to upper crust, parameters such as magma flow rate (Q), heat flow (H), wall-rock melting rate (U) values change depending upon the nature of magma flow and dyke thickness. [ABSTRACT FROM AUTHOR]

The Neogene post-collisional volcanism in eastern Iran is represented by the Sikh Kuh and Bobak high-Na rocks including trachybasalt, trachyandesite, trachydacite, and dacite. We report whole rock geochemistry and Nd–Sr isotopic data which constrain the characteristics of the mantle source. The rocks are highly enriched in incompatible trace elements, suggesting a metasomatized subcontinental lithospheric mantle (SCLM) as the magma source. Felsic rocks record abundant petrographic evidence, major and trace element data, and isotopic (87Sr/86Sr(i) = 0.70727–0.70902) signatures indicative of fractional crystallization, and potentially, crustal assimilation. Such processes however, have not significantly affected the isotopic signatures (87Sr/86Sr(i) = 0.70417–0.70428) of the mafic members, suggesting that they are derived from a mantle source. The geochemical and isotopic data for the Sikh Kuh and Bobak volcanic rocks suggest that these Neogene magmas were derived from a small degree of partial melting (~ 2–10 vol%) of a spinel-bearing subcontinental lithospheric mantle source in a post-collisional setting. The generated more unfractionated mafic magmas erupted during an episode of extensional tectonics, presumably caused by extension that followed Eocene collision between the Lut and Afghan continental blocks. These melts interacted with continental crust during ascent, experiencing crystal fractionation, and crustal assimilation, to produce more evolved felsic volcanic rocks. [ABSTRACT FROM AUTHOR]

We investigate the geology and petrology of Cumaçay, one of the Plio-Quaternary eruption centers of postcollisional volcanism in Eastern Turkey, using a combination of geochronology, bulk-rock geochemistry, thermobarometry, and thermodynamic simulations. Our new K-Ar ages reveal an age of 3.5-0.97 Ma for the eruptive products, which spread around an area of approximately 1000 km². Mineral-melt equilibria for olivine, orthopyroxene, clinopyroxene, and plagioclase allow estimation of crystallization pressures, and temperatures indicate two separate crustal storage of crystallization at 14-28 km and 5-15 km. The temperature estimation from diverse methods ranges from 954 °C to 1224 °C. Thermodynamic modelings using Magma Chamber Simulator (MCS) at a representative pressure (5 kbar) imply that the assimilation and crustal contamination (AFC) resulted in evolved melts with various SiO2 contents at mid to lower crustal depths. Calculated wide range of temperatures, compositional variety from evolved members, and MCS recharge simulation at a representative pressure (2.5 kbar) reveal that the magma mixing between contrasted melts characterizes the final chemical dispersal of the erupted lavas. [ABSTRACT FROM AUTHOR]

The Bushveld Complex of South Africa is underlain by a fine-grained sill complex which most workers interpret to represent the quenched parent magmas to the intrusion. The sills have unusually high Pt contents (up to ~ 25 ppb) and Pt/Pd ratios (average 1.50) exceeding those in most other mantle magmas globally. Unusually high Pt/Pd is also found in many Bushveld cumulates. Understanding the origin of the high Pt/Pd is important for exploration, in view of the contrasting monetary value of the metals, but also for unravelling the petrogenesis of the intrusion. Here, we review existing platinum-group element (PGE) data and present the first radiogenic W isotope data on a Bushveld rock, to evaluate a range of potential models, including PGE fractionation prior to final magma emplacement and within the Bushveld magma chamber, magma derivation from the sub-continental lithospheric mantle (SCLM), contamination of Bushveld magma with Pt-rich continental crust, and a meteoritic component in the mantle source to the magmas or in the crust with which the magmas interacted. We identify three key processes causing fractionation of metals prior to final magma emplacement and within the Bushveld chamber, namely crystallisation of Pt alloys, partial melting of cumulus sulfides triggered by flux of volatiles followed by sulfide melt percolation, and mobilisation of PGE by percolation of volatiles through the cumulate pile. The currently available W and Ru isotope data are inconsistent with derivation of the Bushveld magmas from mantle or crustal sources containing an enhanced meteoritic component relative to normal post-Hadean mantle. [ABSTRACT FROM AUTHOR]

The Abu Ghalaga pluton in the southern eastern desert of Egypt (SED) consists of undeformed norite and hornblende gabbro intruding island arc metavolcanics, ophiolitic rocks, and syn-tectonic older granitic rocks. The Fe-Ti ore (mainly ilmenite) occurs in the form of lenses at the base of the norite. Based on microtextures, mineralogy, and chemical composition, three types of ilmenites are recognized: massive high-Mg type, disseminated high-Mg type, and disseminated low-Mg ilmenite. The three ilmenite types are chemically distinguished by their MgO, MnO, TiO2, Fe2O3, FeO, and V2O3 contents. The variations in the concentration of these oxides are interpreted as a function of variations in T, fO2, and the composition of the parental magma. Reconstruction of the orthomagmatic conditions shows that T and fO2 of the magma from which the norite and its Fe-Ti deposit formed decrease during the course of magmatic differentiation, whereas the hornblende gabbro and its Fe-Ti mineralization have formed from a more evolved magma under relatively lower T and fO2. The REE patterns and variation diagrams support a model of crystal fractionation as the primary means of formation of the Fe-Ti deposits. Chemical features also suggest that the parent magma of both types of gabbroic rocks was generated in the mantle, but in two different pulses. Subduction zone, MORB, and WPB chemical signatures for these gabbroic rocks suggest a complex tectonic history consistent with compression followed by within plate extension possibly contributing to the development of a back-arc/intra-arc basin. [ABSTRACT FROM AUTHOR]

Early Carboniferous (359.3–323.4 Ma) volcanic complexes are widespread in the Southern Ural tectonic province, a fragment of the western (in present-day coordinates) segment of the Central Asian Orogenic Belt. Here, the Lower Carboniferous sequences crop out within the following N–S-trending tectonic zones (from west to east): Magnitogorsk, Ui River, East Ural, Transural, and Valeryanovka. We describe and discuss the geology and geochemistry of the Early Carboniferous volcanic complexes on the basis of published and newly obtained data, with implications for paleo-tectonic models. The western zones are dominated by bimodal rhyolite-basalt series, with the basalts relatively enriched in Ti and Zr but depleted in Nb. The volcanics of the Valeryanovka zone belong to the typically evolved calc-alkaline series, with the derivatives depleted in Ti and Nb. Almost all of the selected groups of volcanics bear geochemical signatures transitional between those of subduction-related and intraplate igneous rocks. The relative enrichment of the volcanics of the East Ural and Transural Zones may be interpreted as a result of a contribution from asthenospheric mantle and/or from subcontinental lithospheric mantle. The volcanics of the Valeryanovka zone reveal features common to subduction-related series of the Andean type. The data obtained allow us to compare the Early Carboniferous geodynamic settings in the western zones with the modern setting of the Northeastern Pacific, whereas the geodynamic setting of the Valeryanovka zone resembles that at the western margin of South America. [ABSTRACT FROM AUTHOR]

We have identified signs showing mixing of moderately potassic magnesian and high alumina magmas on Klyuchevskoi Volcano based on the analysis of mineral compositions and the geochemistry of trace elements during crystallization. The mineralogy and distribution of Mg, Fe, Cr, Ni, Co, and Al in olivines and clinopyroxenes which are contained in the magnesian basalts and high alumina basaltic andesites discharged by the flank and summit eruptions of Klyuchevskoi in 1938, 1966, 1945, and 1994, all provide evidence of an injection of magnesian basaltic melts into high alumina magma. [ABSTRACT FROM AUTHOR]

The Qushandao Granite, mainly composed of alkali‐feldspar granite, is situated in the eastern Zhejiang province of coastal southeast China. In this paper, we present whole‐rock geochemistry, zircon U–Pb geochronology, and Hf isotopes to constrain the age, magma sources, and geodynamic setting of the Qushandao Granite. LA‐ICP‐MS zircon U–Pb dating results revealed that the Qushandao Granite was emplaced in the Late Cretaceous (101–98 Ma). Geochemically, the Qushandao Granite exhibits relatively high silica and alkali contents, metaluminous to weakly peraluminous (A/CNK = 0.98–1.02), and low abundances of phosphorus, titanium, magnesium, and calcium. It is also characterized by enrichment in Rb, K, Th, and depletion in Nb, Ta, P, Ti, and Sr with moderately to weakly negative europium anomalies (Eu/Eu* = 0.71–0.87). Furthermore, the Qushandao Granite displays lower FeOT/MgO, 104 × Ga/Al, and Zr + Nb + Ce + Y values relative to typical A‐type granites. Therefore, we classify the Qushandao Granite as calc‐alkaline I‐type granite based on a synthesis of geological and geochemical characteristics. The Qushandao Granite shows variable zircon Hf isotopic compositions (εHf(t) = −7.6 to +2.3) and TDM2 model ages of 1.40–0.83 Ga with a mean value of 1.17 Ga. We argue that the Qushandao Granite was most likely generated by mixing of mantle‐derived mafic magma and crust‐derived felsic magma in the lower crust, and that it was formed during post‐collisional extension in the Late Cretaceous, related to the gradually increasing subduction angle of the Paleo‐Pacific plate. [ABSTRACT FROM AUTHOR]

The study of Re–Os isotopic systematics of the Mesozoic magmas in East Antarctica and its comparison with Sr–Nd–Pb–Os published data allowed us to reveal the main features of Antarctic magmatism associated with the activity of the Karoo–Maud (Dronning Maud Land (DML), Karoo and Ferrar provinces) and the Kerguelen (Lambert rift area) plumes. It is shown that a melt source of the 180-Ma Karoo–Maud plume could be enriched lithospheric mantle. Variations of the 187Os/188Os ratio in the range of 0.1242–0.1426 characterize almost all types of melts in the Karoo and DML provinces, including both high- and low-Ti magmas as well as high-Mg ferropicrites produced by melting of mantle pyroxenite. This observation is consistent with previous assumption that magmas derived from pyroxenite mantle at the initial stage of plume impact represented melts of deep lithospheric fragments of ancient Gondwana paleocontinent that were entrapped by plume. Thereby, mantle heterogeneity recorded in the Nd–Pb–Sr isotopic compositions of the basalts is not expressed in the systematic variations of Re–Os isotope system. The magmatic source of the basalts of the Ferrar province differs from the source of Mesozoic magmatism in the Karoo and DML provinces by great variations in the 187Os/188Os ratio: from 0.1 to 0.31, and by the lower osmium contents, with limited variations of other isotopic systems, indicating an admixture of enriched EM-II source. This is consistent with inferred subduction reworking of the mantle of the western Antarctic margin (Sushchevskaya et al., 2022). Ultramafic picritic magmas from the Lambert Glacier area are characterized by a radiogenic osmium isotopic composition: 187Os/188Os 0.1582–0.2388. Source of these magmas could be ancient depleted mantle, which later experienced mantle metasomatism due to the multiple interactions with fluid-saturated melts. Picritic melts of the paleorift zone of the Lambert Glacier are close to a magma source of the Karoo and DML provinces in terms of Sr-Nd isotopic composition, but differ in more radiogenic lead. [ABSTRACT FROM AUTHOR]

Aus is located in the southern part of Namibia within the Aus Domain of the Palaeo- to Mesoproterozoic Namaqua-Natal Metamorphic Province. The area is characterised by voluminous granitoids which intruded supracrustal rocks of the pre-tectonic Garup group. In this study, the geochemical characteristics of the intrusive rocks were investigated, showing them to be acidic, peraluminous and derived from shoshonitic and high-K calc-alkaline magmas of anorogenic origin. Chondrite-normalised spidergrams display characteristics of rocks originated in an arc environment, while plots of K2O vs SiO2 exhibit considerable scatter indicative of crustal contamination. Three geotectonic settings are indicated, i. e. Syn-Collisional, Volcanic Arc and Within Plate, supporting collision of continental fragments. [ABSTRACT FROM AUTHOR]