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The exact geological processes involved in the formation of subduction zone-related carbonatites remain ambiguous, along with their implications for crustal/carbon recycling in carbonatite melt generation. This study provides new geochemical and stable (C, O) and radiogenic (Sr, Nd, Pb) isotope data for Huangshuian carbonatite, located within the Lesser Qinling Orogen, with the aim to decipher its complex petrogenetic history. The carbonatites display elevated CaO, low MgO and alkali contents, and significant enrichments of Pb, Mo, and HREEs compared to typical carbonatites. The δ13CPDB (−4.6 to −4.9‰) and δ18OSMOW (+6.6 to +7.8‰) values plot within the field of primary igneous carbonatites. The carbonatites are characterized by consistent radiogenic isotopic compositions [(87Sr/86Sr)i = 0.70599–0.70603; εNd = −10.4 to −12.8; 206Pb/204Pb =16.24–17.74]. These combined results suggest that the carbonatites represent late-stage differentiation products of a parental, mantle-derived carbonatite melt. Their corresponding Sr-Nd-Pb isotopic compositions support the hypothesis that the Lesser Qinling carbonatites originate from a heterogeneous upper mantle source involving an EMI-like mantle component coupled with minor assimilation of the basement rocks. The parental carbonatite melt was derived by the melting of carbonate-bearing subcontinental lithospheric mantle metasomatized as the result of Early Triassic subduction of the Mianlue Ocean. [ABSTRACT FROM AUTHOR]

Continental intraplate volcano is an ideal probe to unravel the composition and structure of the deep Earth. The intraplate Changbaishan‐Tianchi volcano was one of the most hazardous eruptions on the Earth's planet. The long‐term activity of this volcano from the Pleistocene to 946 CE has erupted materials with a broad compositional range from basalt to rhyolite, which are expected to be associated with the continuous northeastward subduction of the Pacific plate, but the magma source remains controversial. In this paper, we present a comprehensive data set of in situ zircon Hf and O isotope data, combined with whole‐rock element and Sr‐Nd‐Pb isotope compositions, for selected eruptions of the Changbaishan‐Tianchi volcano, aiming to provide new insights into their magma source and the associated geodynamics. Radiogenic isotopic ratios and incompatible trace element compositions indicate that the erupted volcanic rocks at different stages, although with a varied differentiation degree, were derived from a common magma source characterized by a mixture of DM and EM1 end‐members. Zircon Hf and O isotopes are both relatively homogeneous for different lithologies and eruption stages, with the εHf(t) values varying between −5 and +5, and δ18O values between 3.58‰ and 5.97‰. Modeling of source mixing indicates that high‐temperature altered oceanic crust materials are an important component in the source of Changbaishan‐Tianchi volcano, likely derived from an ancient stagnant slab that has been reactivated by the subduction of the Pacific plate. This study demonstrates that the recycling of deeply subducted oceanic crust is potentially an important source and trigger for continental intraplate volcanism. Plain Language Summary: The Millennium Eruption (ME) of the Changbaishan‐Tianchi intraplate volcano at 946 common era (CE) was one of two largest explosive eruptions in the past 2,000 years, but its source is poorly constrained. This paper represents a comprehensive data set of in situ zircon Hf and O isotope data, combined with whole‐rock element and Sr‐Nd‐Pb isotope compositions, for providing a full picture of magma evolution and new insights into the magma source and the associated geodynamics. Our data indicate that high‐temperature altered oceanic crust, likely a former part of the subduction of the Pacific plate, has been an important component in the source of the Changbaishan‐Tianchi volcano. Therefore, the Changbaishan‐Tianchi volcano demonstrates that continental intraplate volcanism can also be impacted by long‐distance subduction of oceanic crusts. Key Points: The long‐term eruptions of the intraplate Changbaishan‐Tianchi volcano from the Pleistocene to 946 CE were derived from a common magma sourceZircon Hf and O isotopes indicate important contributions from subducted oceanic crust [ABSTRACT FROM AUTHOR]

Model calculations were used to estimate the compositions of melts during fractional crystallization corresponding to the formation of the Malyi Zadoi massif, which is located in the Irkut block of the Sharyzhalgai uplift in the southwest of the Siberian craton. It is shown that the gabbronorites of the massif are comagmatic to the plagioperidotites and olivine gabbronorites. The estimates obtained for the composition of the model melts are used to characterize the composition of the mantle source of the parental melt. The geochemical characteristics led us to suggest that the parental melt of the Malyi Zadoi massif was formed by melting an enriched source, a conclusion consistent with isotope data that indicate that the mantle Sm/Nd ratio decreased in the Archean. The probable source of the parental melt could consist of depleted lithospheric mantle material metasomatized by felsic melts coming from rocks of a subducting oceanic plate. [ABSTRACT FROM AUTHOR]

Metamorphosed dacitic porphyry dikes were first found in the western part of the Vorontsovka terrane, which is located in the Paleoproterozoic Volga–Don orogen at the margin of Archean Sarmatia and Volga–Ural cratons. The magmatic protolith age for the metadacites is ca. 2.07 Ga. These are ferrous, metaluminous calc-alkali I-type granitoids. The sodium specialization of the rocks and their low concentrations of Mg, Cr, Ni, and incompatible elements, with significant REE fractionation, the absence of Eu* anomalies, high Sr/Y ratio, remarkably high (Gd/Yb)n values (>10), and the radiogenic Nd isotopic composition indicate that the dacitic melts were derived from a juvenile mafic source. According to petrogenetic estimations, such conditions could be caused by the partial melting of depleted N-MORB basites in equilibrium with an eclogitic residue. The dacitic magmas were likely generated by the partial melting of mafic rocks at lower levels of the significantly thickened crust (>60 km) in relation to collision processes. [ABSTRACT FROM AUTHOR]

The Nagaland–Manipur Hill Ophiolite (NMHO) is an NNE-SSW trending linear ophiolite zone exposed in the northeastern states of Nagaland and Manipur in India. Basaltic rocks of NMHO are geochemically divisible into two broad groups in the Zr/Ti versus Nb/Y classification diagram. Samples with TiO2 < 2 wt% and Zr = 38–118 ppm plot within the basalt field, whereas samples with TiO2 > 2 wt% plot within the alkali basalt field. The latter can be subdivided into the alkali basalt group-1 (AB-1) with Zr = ~ 200 ppm and the alkali basalt group-2 (AB-2) with Zr = ~ 400 ppm. In a normal mid-ocean ridge basalt (N-MORB) normalized trace element pattern, basalt displays a near-horizontal trend from Lu to Pr at rock/N-MORB = ~ 1 and then increases slightly from Pr to Rb, whereas alkali basalt is relatively more enriched than basalt. In the chondrite-normalized rare earth element (REE) pattern, basalt displays near-horizontal trends with (La/Yb)CN ranging between 0.78 and 1.89. On the other hand, alkali basalt displays parallel and steadily increasing enrichment trends from Lu to La [(La/Yb)CN = 11.07–17.61], with a slight drop at Eu and Sm. Mantle melting models suggest: (1) partial melting of N-MORB-like sources at degrees of melting (F) = 4–8% for basalts; and (2) partial melting of ocean island basalt (OIB)-like sources at F = 7.5–17.8% for alkali basalt. Occurrences of basalts with N-MORB-like and and alkali basalt with OIB-like signatures within the NMHO complex suggest their origin from distinct magma batches with direct or indirect involvement of the Kerguelen plume. Chondrite normalised pattern for elements Nb, Zr and REE showing estimated compositions of source S1 and residue R1 for alkali basalt (estimated using DMI modeling) and source S2 for basalt (estimated using NBM modeling) in this study. DMM and OIB (Workman and Hart 2005) values are also shown for comparison. Average abyssal peridotite value is from Niu (2004) database. [ABSTRACT FROM AUTHOR]

Understanding the compositional heterogeneity of the deep mantle requires identifying the nature of recycled crustal materials in the sources of mantle-plume-related magmas. However, it is still unclear whether or not the deep mantle contains recycled carbonates from the Earth's surface. In this study, we present comprehensive data on whole-rock high-precision zinc isotopes, as well as major- and trace-element geochemistry, and Sr–Nd–Pb isotopes of basalts on Hainan Island to examine the influence of recycled materials (particularly carbonates) on the mantle source heterogeneity of the Hainan mantle plume. The basalts have highly variable δ66Zn values ranging from 0.21‰ to 0.42‰. These variable Zn isotopic compositions cannot be accounted for by processes such as post-magmatic alteration and crustal contamination, or by fractional crystallization and partial melting; instead, they reflect mantle heterogeneity. Comparisons of the major- and trace-element compositions (e.g., CaO and TiO2 contents and Zn/Fe and Fe/Mn ratios), FC3MS and FCKANTMS peridotite and pyroxenite melting parameters, as well as pseudo-ternary projections of the primary Hainan basaltic magmas with experimental data suggest that the primary magmas were partial melts of silica-deficient pyroxenitic lithologies with peridotite residue. The heterogeneous geochemical and lithological compositions of the Hainan basalts indicate that recycled sedimentary carbonates and siliceous rocks were important constituents in their mantle source. Quantitative modeling reveals that the addition of 1–10% subducted sediments into the source of the Hainan basalts closely reproduces their Zn–Sr–Nd–Pb isotopic values. The source component with the heaviest Zn isotopic composition measured for the Hainan basalt samples could have contained more than 9% recycled carbonate. Our findings provide insights into the role of subducted materials to mantle heterogeneity and highlight the contribution of subducted sedimentary carbonates in the deep recycling of oceanic slabs, including—in the case of the Hainan mantle plume—recycled deep mantle (i.e., the mantle transition zone and lower mantle). [ABSTRACT FROM AUTHOR]

Abstract Continental intraplate volcano is an ideal probe to unravel the composition and structure of the deep Earth. The intraplate Changbaishan‐Tianchi volcano was one of the most hazardous eruptions on the Earth's planet. The long‐term activity of this volcano from the Pleistocene to 946 CE has erupted materials with a broad compositional range from basalt to rhyolite, which are expected to be associated with the continuous northeastward subduction of the Pacific plate, but the magma source remains controversial. In this paper, we present a comprehensive data set of in situ zircon Hf and O isotope data, combined with whole‐rock element and Sr‐Nd‐Pb isotope compositions, for selected eruptions of the Changbaishan‐Tianchi volcano, aiming to provide new insights into their magma source and the associated geodynamics. Radiogenic isotopic ratios and incompatible trace element compositions indicate that the erupted volcanic rocks at different stages, although with a varied differentiation degree, were derived from a common magma source characterized by a mixture of DM and EM1 end‐members. Zircon Hf and O isotopes are both relatively homogeneous for different lithologies and eruption stages, with the εHf(t) values varying between −5 and +5, and δ18O values between 3.58‰ and 5.97‰. Modeling of source mixing indicates that high‐temperature altered oceanic crust materials are an important component in the source of Changbaishan‐Tianchi volcano, likely derived from an ancient stagnant slab that has been reactivated by the subduction of the Pacific plate. This study demonstrates that the recycling of deeply subducted oceanic crust is potentially an important source and trigger for continental intraplate volcanism.

The study area is located in the south of Damghan, 160 km south of Shahrood, and 17 to 30 km south of Torud village. The area geologically, lies in the Cenozoic magmatic belt, a part of the Alpine-Himalayan belt, in the north of the structural zone of Central Iran (Aghanabati, 2004). The Cenozoic magmatic belt has been studied by many researchers (e.g., Ghorbani, 2005; Khajehzadeh, 2009; Mardani-Beldaji, 2011; Tayefi, 2014; Yousefi, 2017). The volcanic rocks in the southern part of the Torud area have not been comprehensively studied. Therefore, it requires a detailed study. So, for the purpose of this study attempt has been made to investigate and to study the nature of magma, tectonic setting, and the petrogenesis of the volcanic rocks using the geochemical data of the whole rock. Also, the results of this study have been compared with some areas belonging to the Cenozoic Era located in the north of the structural zone of Central Iran.Regional GeologyThe area under study in the Torud-Moalleman magmatic belt belongs to the Chah-Shirin-Sabzevar-Khaf magmatic complex, located in the western part of this magmatic complex. In this magmatic belt, the Eocene volcanic rocks, including the main volume of igneous rocks are basic to acidic in composition. The predominant rocks are basaltic to intermediate rocks. The Torud-Moalleman magmatic belt is mainly composed of volcanic rocks with a lithological composition consisting of olivine-basalt, basalt, andesite, and dacite rocks and their pyroclastic equivalents, as well as plastic and limestone interlayers.Analytical methodsDuring field surveying, 50 samples of the volcanic rocks with the least alteration were collected. From these samples, 30 thin sections were prepared for microscopic studies and 11 samples were selected for ICP-MS geochemical analyses for minor elements and XRF for major elements and were sent to ACME Laboratory in Vancouver (Canada). GCDkit, Excel, and Corel Draw software were used to check the results obtained from the whole rock chemistry analyses and drawing diagrams.PetrographyThe study rocks include volcanic rocks ranging from andesite to basalt. The basalts are dark gray to black in color with glomeroporphyritic, microlithic, sieve, and trachytic textures containing plagioclase and clinopyroxene as the main minerals. These minerals along with olivine and magnetite can also be seen in the form of microcrystals in the background of the rock, and their accumulation have created the glomeroporphyritic texture in these rocks. Secondary minerals are chlorite, iron oxide, zeolite (natrolite and analcime), calcite, and gypsum, filling the holes.The andesites are light gray to slightly dark with porphyritic and glomeroporphyritic textures and are dominated by amphibole (green and brown hornblende), plagioclase, and clinopyroxene as the main, biotite, iron oxide, sphene, and zircon. as the minor, as well as sericite, chlorite, calcite, and epidote as the secondary minerals.Whole Rocks Chemistry The data obtained from the whole rock geochemical analyses display that the volcanic samples of the Torud area are classified as the andesite and basalt, placed mostly in the range of calc-alkaline series (medium potassium). LREE and LILE enrichment, HREE and HFSE depletion and Nb, Ta, and Ti negative anomalies of these rocks point to their formation in subduction zones. Also, as the tectonic diagrams display the rocks belong to the active continental margin. The rocks under study have mostly mantle origin and are derived from an enriched lithospheric mantle. The flat HREE patterns also show that melting occurred in the mantle, above the stability field of garnet. Therefore, the parent magmas were formed by the melting of spinel lherzolite at a depth of 80 to 100 km and evolved due to fractional crystallization as well as contamination caused by subducted sediments and the continental crust.DiscussionThe rare elements pattern of the study rocks in spider diagrams show the cogenesis of these rocks and the role of differential crystallization as the main mechanism of their formation. Based on geochemical data, the study samples and compared volcanic rocks share similar characteristics. Therefore, the normalized REE patterns with chondrite (Nakamura, 1974) NMORB (Sun and McDonough, 1989) and MORB (Pearce, 1983), indicate the enrichment of LREEs (such as La, Ce) and LILEs (e.g., Ba, K, U, Pb, Cs) compared to HREEs and HFSEs (i.e. Nb, Ta, Ti, P) indicating that the rocks under study were formed in the active continental arc margin. The samples have no negative anomaly of Eu. Volcanic rocks with the age of late Eocene and Oligo-Miocene and basaltic to trachy-basaltic composition range from alkaline to sub-alkaline rocks and volcanic rocks with the age of middle Eocene with andesite to trachy-andesite composition have the nature of calc-alkaline.ConclusionsThe volcanic rocks in the south of Torud, with calc-alkaline and medium potassium nature, are mainly composed of basalt and andesite characterized by LREE enrichment, negative Nb-Ta-Ti anomaly, and the high ratio of LILE/HFSE. These characteristics point to the formation of these rocks in the subduction zones.The rocks under investigation have low SiO2 content, high amounts of Sr, no significant Eu anomaly, and Mg# content greater than 40. These geochemical features indicate a mantle source for the studied volcanic rocks. The changes of Rb/Y versus Nb/Y show the enrichment by subduction components or crustal contamination in the magmatic evolution of these rocks. Based on the geochemical investigations, the productive magma originated from a spinel lherzolitic source at a depth of about 80 to 100 km; during the ascent of magma, as a result of fractional crystallization and contamination, the magma derived from the mantle has been enriched and gave rise to lithological diversity.

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Petrogeochemical data on basalts (lithophile elements and Sr–Nd–Pb isotopes, liquidus olivine and spinel compositions) from the transition zone of the Southwest Indian Ridge (SWIR) in the Du Toit–Andrew Bain fault zone indicate significant differences in their composition. Tholeiites enriched in Na and depleted in Fe (Na-TOR genetic type) are developed within the rift valley adjacent to the faults. Deep-type basalts (TOR-1) are present in the western wall of the Andrew Bain Fault. The outpouring of these magma types reflects a possible change in geodynamic setting during formation of this zone: from deep and high temperature to shallower magma generation conditions (Sushchevskaya et al., 2022). Differences in the primary melts of tholeiites from the rift valley and the Andrew Bain Transform Fault are also traced in the composition of liquidus olivine. The olivines from rift valley are similar to the typical Na-TOR olivines with Mg number of Fo88-87, low Ni and elevated Mn contents. On the contrary, olivines in tholeiite from the Andrew Bain Fault Zone are enriched in Ni and depleted in Mn, which may indicate the involvement of pyroxenite in melt generation. This component is either oceanic lithosphere recycled through the deep mantle or fragments of previously formed oceanic crust, which were subsequently involved in melting during the spreading axes jumping. A similar process is typical of the Bouvet Triple Junction, where the trace-element composition of olivine shows significant heterogeneity. The radiogenic composition of Pb and Sr of the Andrew Bain Fault tholeiites are similar to those of enriched magmas from such Indian Ocean rises as Crozet, Marion and Bouvet, but differ from those of the Conrad and Af. Nikitin rises. The source of such tholeiite melts is close in composition to the model HIMU type (with high U/Pb), which likely contains an admixture of EM-II component (with elevated Rb/Sr). [ABSTRACT FROM AUTHOR]

Abstract—This paper presents numerous new data on the geochemical composition of olivine, clinopyroxene, and leucite phenocrysts, as well as spinel inclusions in olivine and quench glass from lamproites of Gaussberg volcano (East Antarctica). Most of the olivine phenocrysts in the Gaussberg lamproites are high Mg varieties (Fo89–91) with elevated Ni contents (up to 4900 ppm) and high Ni/Co ratios. According to data of about 320 clinopyroxene analyses, two groups of diopsidic phenocrysts have been established. Group I consists mainly of high-Mg varieties (Mg#>80), while group II clinopyroxenes are less magnesian (Mg# 52–80). The main difference between the clinopyroxenes of the two groups is the elevated contents of Al2O3, FeO and reduced TiO2, Cr2O3, and NiO in the compositions of group II compared to group I, as well as different contents of trace elements, which may reflect their crystallization from different types of primary melts. According to the study of ~550 grains of leucite phenocrysts in the Gaussberg lamproites, it was shown that they correspond to the ideal stoichiometry of leucite K[AlSi2O6] and are enriched in Na2O (0.05–0.35 wt %), but depleted in K2O (19.9–20.9 wt %) compared to leucites from lamproites of other provinces. The BaO content reaches 0.3 wt %, SrO –0.04 wt %. The iron content in most leucite phenocrysts varies within 0.7–1.2 wt % Fe2O3, but some grains have the low Fe2O3 contents (<0.5 wt %). In leucite microlites of the groundmass and rims of phenocrysts, the Fe2O3 content can reach 2.4 wt %, which may indicate more oxidized conditions at lava eruption. Based on the study of natural samples, existing experimental data and numerical models, the order and conditions of crystallization of the Gaussberg lamproites were obtained. Crystallization proceeded in the following order: chromian spinel → chromian spinel + olivine → olivine + leucite (± chromian spinel) → olivine + leucite + clinopyroxene (± chromian spinel). The near-liquidus assemblage represented by high-Mg olivine phenocrysts with inclusions of Cr-spinel was formed in the temperature range from 1180 to 1250°C. Further crystallization of the melt with the formation of an association of olivine+leucite+clinopyroxene phenocrysts could occur at pressures below 2 GPa and temperatures of 1070–1180°C, corresponding to the presence of water in the magmatic system. Estimates of the redox conditions of crystallization of lamproites obtained using different oxybarometers vary in a wide range from QFM-0.5 to QFM+2.3. The elevated Ni contents in liquidus olivines of Gaussberg indicate the high nickel contents in the source. It is shown that the formation of ultra-alkaline magmas in the Gaussberg volcano area is likely related to melting of the continental lithosphere, which was heterogeneous and included both the peridotite mantle and hydrous pyroxenite fragments. [ABSTRACT FROM AUTHOR]

A key effect of subduction is the upward infiltration of slab-derived melts and fluids to create a chemically and lithologically heterogeneous region in the mantle wedge. Magmatism within the post-subduction setting of peninsular Italy is derived from a sediment-metasomatised lithospheric mantle source, with primitive products recording substantial temporal and spatial variations in the nature and extent of metasomatism. The Roman magmatic province, in central Italy, is host to ultrapotassic (HKS), leucite-bearing magmas that require source modification that is not yet well-constrained in terms of mineralogy and sediment provenance. Here, we present the chemistry and Sr-Nd-Pb isotope compositions of melt inclusions in forsterite-rich olivine (Fo 88−92) from three key Roman volcanic centres (Vulsini, Sabatini, Alban Hills) to characterise the metasomatic imprint of their mantle sources. The melt inclusion suites (Vulsini HKS, Vulsini melilite-bearing HKS, Sabatini HKS, Alban Hills HKS) have clear differences in major-element (K, Ca, Al, P, Ti), volatile (F, Cl, B, Be), trace-element (e.g., Rb, Sr/Y, Th/Nb), and radiogenic-isotope (87Sr/86Sr) compositions that reflect the diversity of the primary melts beneath the region. For each suite, the extraction of melt batches from different domains in a heterogeneous (veined) source rock with different compositions and mineralogies can explain the chemical characteristics of the melts. At least three metasomatic vein types are required to form the respective parental melts and we infer phase assemblages consisting of phlogopite + Ca-amphibole + clinopyroxene ± apatite. The Sr-isotope differences between Vulsini melilite-bearing HKS and Vulsini and Sabatini HKS require at least two distinct metasomatic events to have occurred beneath the Roman province. These events need not be associated with two distinct subduction systems. Instead, we infer that different metasomatic agents could have originated under different P-T-t conditions from different domains in the same subducting slab. [ABSTRACT FROM AUTHOR]

Principal component analysis (PCA) was employed to determine the implications of geochemical and isotopic data from Cenozoic volcanic activities in the Southeast Asian region, including China (South China Sea (SCS), Hainan Island, Fujian-Zhejiang coast, Taiwan Island), and parts of Vietnam and Thailand. We analyzed 15 trace element indicators and 5 isotopic indicators for 623 volcanic rock samples collected from the study region. Two principal components (PCs) were extracted by PCA based on the trace elements and Sr-Nd-Pb isotopic ratios, which probably indicate an enriched oceanic island basalt-type mantle plume and a depleted mid-ocean ridge basalt-type spreading ridge. The results show that the influence of the Hainan mantle plume on younger volcanic activities (<13 Ma) is stronger than that on older ones (>13 Ma) at the same location in the Southeast Asian region. PCA was employed to verify the mantle-plume-ridge interaction model of volcanic activities beneath the expansion center of SCS and refute the hypothesis that the tension of SCS is triggered by the Hainan plume. This study reveals the efficiency and applicability of PCA in discussing mantle sources of volcanic activities; thus, PCA is a suitable research method for analyzing geochemical data. [ABSTRACT FROM AUTHOR]

The Bafoussam area in western Cameroon is part of the central Cameroon Volcanic Ligne (CVL). This study presents the mineralogy, major and trace element compositions, Sr-Pb-Hf isotopes, and new K–Ar geochronological data about mafic and felsic volcanic rocks. These rocks belong to two different series: A transitional series made of basalts, basaltic andesite, and trachytes and an alkaline mafic series with basalts, hawaiites, and basanites. New age data show that the transitional series belongs to the oldest part of the CVL and was emplaced between 47 and 35 Ma. The alkaline volcanism is younger, with ages ranging from 10 to 4.5 Ma. Magmatic evolution in both series is accomplished through a fractional crystallization process, with the removal of olivine and clinopyroxene, while plagioclase does not seem to be a major crystallizing phase. All the samples are enriched in incompatible trace elements, but the rocks from the alkaline series have more fractionated REE patterns and high Nb content compared to the transitional mafic lavas. Alkaline lavas have lower initial 87Sr/86Sr and higher 176Hf/177Hf and Pb isotopic ratios than the transitional lavas. Low La/Nb and high 87Sr/86Sri ratio are among chemical characteristics that show that some samples from the transitional series have interacted with a crustal component during their evolution in the crust. They cannot be used for discussing the mantle source of the volcanic rocks from this series. Trace elements show that primary magmas for both series formed in a garnet-bearing mantle source, with higher partial melting degrees (3–5%) for the transitional magmas than for the alkaline magmas (< 2.5%). Combining trace elements and isotopic ratios, we show that the Bafoussam lavas formed from two different mantle sources. Transitional magmas formed from a pyroxenite-bearing enriched mantle with low Pb isotopic composition. This mantle source is present in all the oldest lavas from the CVL. Alkaline magmas formed from an HIMU-like mantle source, different from the Mt Cameroon HIMU mantle source. The depleted asthenospheric mantle is not involved in the Bafoussam magmatism and the two mantle sources are probably located in the lithospheric mantle, in agreement with recent geophysical models presenting the CVL as a consequence of the partial melting of the lithospheric mantle in response to edge convection along the margin of the Congo craton. [ABSTRACT FROM AUTHOR]

Late Miocene to Late Pleistocene alkaline lavas in the northernmost part of the Antarctic Peninsula and its off-lying islands are the latest stage of magmatic activity that took place in response to lithospheric extension in the back-arc region of the South Shetland subduction system. The alkaline magmatism occurred much later than the main pulse of Cretaceous arc magmatism and generated basaltic extrusive rocks during several sub-aqueous/sub-glacial and sub-aerial eruption periods. The suite consists primarily of alkali olivine basalts with oceanic island basalt (OIB)-like trace element signatures, characterized by elevated highly to less incompatible element ratios compared to MORB. The samples have higher 87Sr/86Sr (0.70301–0.70365), and lower 143Nd/144Nd (0.51283–0.51294) and 176Hf/177Hf (0.28291–0.28298) than depleted MORB mantle. Their lead isotope ratios vary within a limited range with 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb ratios of 18.797–18.953, 15.577–15.634, and 38.414–38.701, respectively. Sr, Nd, Hf and Pb isotope systematics suggest involvement of diverse source materials in the genesis of the alkaline magmas. Evaluation of radiogenic isotope and trace element data indicates that the source of the alkaline melts had a complex petrogenetic history, reflecting the effects of mantle hybridization along the slab mantle interface through interaction of mantle wedge peridotites with volatile-bearing, siliceous melts produced by melting of subducted sediments and basaltic oceanic crust. Hf-Nd isotope and trace element projections further demonstrate that the metasomatizing melt was likely generated by eclogite partial melting at sub-arc to post-arc depths, in equilibrium with a garnet-bearing residue and involved breakdown of high field strength elements (HFSE) retaining phases. Consumption of metasomatic amphibole during partial melting of hybridized peridotite at the wet solidus appears to have had a significant effect on the final melt compositions with high HFSE, Na and H2O contents. [ABSTRACT FROM AUTHOR]

The relevance of the study is in the need to expand the mineral resource base of Russia. Eastern Transbaikalia is one of the oldest mining regions of the country. Barun- Shiveinskoe field is mercury-antimony-tungsten ore formations. For the region, there is an urgent need to search for and discover new ore deposits. For successful completion of such a task, the data are needed from a detailed study of already known ore deposits, which can be used to develop scientifically reasonable criteria for searching for ore deposits and forecasting mineralisation. Such data includes determination of sources of ore-bearing melts and conditions of formation of mercury-antimony-tungsten ore formation deposits. The aim of the study is to prove participation in ore formation of several ore-bearing sources with different characteristics based on the data of isotopic composition of oxygen of ore-bearing quartz and sulphur sulfides, as well as comparative analysis of elemental composition of quartz-wolframite ores of Barun-Shiveinskoe deposit with quartz-wolframite ores of tungsten deposits in Eastern Transbaikalia. Object of the study is Barun-Shiveinskoe tungsten deposit located in Eastern Transbaikalia. Methods. To determine the elemental composition of rocks, the X-ray fluorescence method and standard chemical analysis were used at the Geological Institute of the Siberian Branch of the Russian Academy of Sciences (GIN SB RAS, Ulan-Ude). Oxygen isotopic composition was determined at the analytical centre (GIN SO RAS, Ulan-Ude) using a MIR 10-30 laser heating system with a 100 Watt CO2 laser and a 10,6 μm wavelength in the infrared region, in the presence of the BrF5 reagent using the Z.D. Sharp method (1990). Mineral composition study was carried out in GIN SO RAS on the LEO-1430VP scanning electron microscope with the INCA Energy 350 energy dispersion spectrometer (Oxford Instruments) at an accelerating voltage of 20 kV, probe current is less than 0,5 nA, probe size is 0,1 µm. In the analysis mode, the spectral set time was 50 s. Isotope composition of sulphur sulfides study was carried out at the collective use centre for multi-element and isotope studies of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). Results. The isotopic composition of oxygen in the fluid was determined in equilibrium with quartz of the productive stage at 210–150 °C, varying from 4,25 to 14,22 ‰, which corresponds to aqueous fluid of magmatic nature. The isotopic composition of sulfur cinnabar, the final ore stage of the deposit formation, corresponding to mantle values, has been established. A narrow interval of δ34S, ‰ CDT values for cinnabar sulphur from –3,5 to to –4,5 indicates a single source. For the first time, a rare cinnabaric minerals (metacinobarite, corderoite) formed in the oxidation zones of mercury deposits under low-temperature conditions were identified at the deposit. Their elemental composition was determined. In quartz-wolframite ores from tungsten deposits in Eastern Transbaikalia, including Barun-Shiveinskoe, a close correlation relation (r – 0,53–0,96) with a number of elements (As, Ta, Nb, Hf) was identified, indicating common sources of their formation. Ore formation at Barun-Shiveinskoe deposit was carried out from different levels of ore-bearing sources. Wolframites were formed from a crust source and mercury from a mantle one.

• Fogo (Cape Verde) mantle source has a crustal-like signature for carbon. • A carbon enriched crustal component could be recurrent in global OIB magmatism. • Fogo mantle source has a MORB-like 3He/4He (8 ± 1 Ra). • He isotopes in OIB inversely correlate with the degree of mantle partial melting. • Global OIB He isotopic signature relate with plume buoyancy flux and plate velocity. Fluid inclusions (FI) entrapped in phenocrysts carried by Ocean Island Basalts (OIB) contain key information on volatiles' abundance and origin in their mantle sources. Here, we add new piece of knowledge to our understanding of volatile geochemistry in global OIB magmas, by presenting new noble gas (He-Ne-Ar) and carbon (C) isotope results for olivine- and clinopyroxene-hosted FI from enclaves, lavas, tephra and volcanic gas samples from Fogo, the only frequently active volcano at the Cape Verde archipelago (eastern Atlantic Ocean). FI, together with crater fumaroles, constrain the Fogo 3He/4He signature at 7.14–8.44 R c /R a (where R C is the air-corrected 3He/4He isotope ratio, and R a is the same ratio in air), which is within the typical MORB (Mid-Ocean Ridge Basalt) mantle. The carbon isotopic ratio (δ13C vs. Pee Dee Belemnite) of CO 2 in FI and fumaroles range from -6.04 to -4.41 ‰. We identify systematic variations of δ13C and He/Ar* with FI entrapment pressure (estimated from a combination of host mineral barometry and FI microthermometry), from which we develop a model for volatile degassing in the mantle-to-crustal magma storage system. The model predicts a crustal-like signature for carbon (δ13C of -0.4 ± 1.0 ‰) in primary melts formed by mantle melting at ∼2200 MPa (∼77 km) and a source He/Ar* ratio of 0.90–0.24, which are indicative of variably depleted mantle metasomatized by carbon enriched melts/fluids from a crustal component. We also use our results to characterise regional (in the Cape Verde and Canary archipelagos) and global trends in C and He isotope composition from OIB. From a comparison with the few other OIB localities for which δ13C are available, we propose that a carbon enriched crustal component could be recurrent at a global scale in OIB magmatism, although often masked by isotope fractionation during magmatic degassing. We additionally find that, at regional scale, He isotopes in OIB scale inversely correlate with the degree of partial melting of the mantle beneath individual islands' (inferred from the La/Yb ratio of erupted basalts). More widely, our results corroborate previously established global relationships between OIB He isotopic signature, plume buoyancy flux and overlying plate velocity. In this interpretation, the MORB-like 3He/4He (8 ± 1 Ra) at Fogo reflects a combination of (i) low to medium magma productivity, (ii) relatively low plume buoyancy flux (∼1.1 Mg/s), and (iii) slow average velocity (∼3 cm/yr) of the overlying plate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Late Carboniferous gabbros and Early Permian diabases were identified at Awulale. • Gabbros were derived from a metasomatic peridotite-rich mantle source. • Diabases originated from a juvenile lithospheric mantle that incorporated subduction components. • Western Tianshan experienced a subduction to post-collisional tectonic transition. The evolution of the western Tianshan Orogen in the southern Central Asian Orogenic Belt involved prolonged accretion and collision processes in response to the closure of the Paleo-Asian Ocean during the Late Paleozoic. However, the timing for the tectonic transition from subduction to post-collision is still poorly constrained. Herein, we address this issue based on geochronological, geochemical and Sr-Nd-Hf isotopic investigations on representative mafic dikes from the Awulale Mountains in the heart of the western Tianshan. Zircon U-Pb dating suggest two episodes of mafic magmatism during the Late Carboniferous (ca. 324–310 Ma) and Early Permian (ca. 299–290 Ma). The Late Carboniferous gabbro dikes exhibit large variations in MgO (2.79–10.97 wt%) and Ni (7.58–244 ppm), and arc-like trace element patterns with high Th/Yb (0.55–2.26) ratios, relatively low εNd (t) (+0.2 to +2.5) and variable εHf (t) (+1.3 to +10.4) values, indicating that they were derived from fractional crystallization of a peridotite-bearing mantle source metasomatized by sediment-derived hydrous melts. In contrast, the Early Permian diabase dikes have slightly variable MgO (5.88–7.78 wt%) and Ni (59.90–104 ppm) with apparently low Th/Yb ratios (0.20–0.34, except for one sample: 0.86) and depleted εNd (t) (+5.0 to +7.8) and εHf (t) (+8.0 to +14.6) values, which indicates derivation from partial melting of a juvenile lithospheric mantle source with contributions from early subduction metasomatic components. In context with relevant published data, our study indicates that the Late Carboniferous magmatism of the Awulale Mountains was likely induced by breakoff of the North Tianshan oceanic slab during ongoing subduction; conversely, the Early Permian magmatism may have originated from delamination of the lower crust and lithospheric mantle in the subsequent post-collisional setting. Furthermore, the tectonic transition from Carboniferous subduction to Permian post-collisional extension of the western Tianshan suggests that terminal closure of the North Tianshan Ocean took place at Carboniferous-Permian boundary at ∼ 300 Ma. [ABSTRACT FROM AUTHOR]

The unusually prolonged volcanism at the Chang'e‐5 (CE‐5) landing site remains a mystery. To constrain the geochemical features of the CE‐5 mantle source, we performed in situ sulfur isotope analysis on sulfides of the CE‐5 basalts. The modal abundance of sulfides is ∼0.1 wt%, dominated by troilite with trace cubanite, chalcopyrite and pentlandite, yielding a S‐abundance of ∼360 ± 180 ppm for the bulk CE‐5 basalts. Our analysis shows a decreasing trend of δ34S in the magma with crystallization and degassing, suggesting ∼40% degassing loss of S, and accordingly the maximum S‐abundance in CE‐5 primitive magma was calibrated to approximately 600 ± 300 ppm. Considering an extensive fractional crystallization following a low‐degree partial melting of the CE‐5 basalts, the estimated sulfur abundance in the mantle source is ∼1–10 ppm. This result suggests a strong depletion of volatiles in the CE‐5 mantle source, which may be caused by prolonged magmatic activity. Plain Language Summary: The Chang'e‐5 (CE‐5) basalts are the youngest lunar samples identified so far, extending our knowledge of the duration of lunar volcanism, but the main factors of prolonging the volcanic activity are still unclear. Sulfur, with four stable isotopes (32S, 33S, 34S, and 36S) and an active component in magmatic activity, can constrain the magmatic processes and geochemical features of the mantle source. Here, we report the S isotope compositions of troilite in the CE‐5 samples. The sulfides are mainly troilite, with trace Cu‐ and Ni‐sulfides. We counted the modal abundance of sulfides and then obtained the S abundance of the bulk CE‐5 basalts. Analysis indicates that S isotope fractionation exists in the CE‐5 troilite and is mainly due to magma degassing. According to the variation in S isotope compositions, we corrected for the degassing loss of S and obtain the S abundance of the CE‐5 magma before eruption. Furthermore, we estimated the S abundance of the CE‐5 basalt source based on the formation of the CE‐5 magma. This estimated value is significantly lower than the estimations for Apollo basalt sources, implying multiple extractions of sulfur‐bearing melts from the CE‐5 mantle source due to its prolonged magmatic activity. Key Points: The δ34S values of troilite in the Chang'e‐5 basalts range from −1.6‰ to +2.0‰The δ34S of troilite in the fine‐grained mesostasis are lighter than the inclusions in pyroxene, explained mainly by magma degassingIt is expected that the mantle source of the Chang'e‐5 basalts is depleted in sulfur, which is ∼1–10 ppm with a δ34S of ∼0.5‰ [ABSTRACT FROM AUTHOR]

Metavolcanic rocks are well-exposed in the Kribi area within the Nyong Group, Congo craton, but their origin, age, and tectonic significance are poorly known. Here we report integrated field mapping and petrography, geochemistry, and LA-ICP-MS zircon U-Pb ages of these metavolcanic rocks to constrain their petrogenesis and geodynamic implications. The studied rocks consist of mafic granulite, garnet-amphibole gneiss, and garnet-biotite gneiss, and occur interbanded with sharp contact and intruded by syenite dyke. These metavolcanic rocks are classified as MORB-like tholeiitic to calc-alkaline basalts, basaltic andesite, and rhyodacite rocks with within-plate setting geochemical signatures. The metabasite rocks (basalt to basaltic andesite protolith) are likely the equivalent of a spinel peridotite product representing ~ 2–5 % partial melting of metasomatized mantle source, while the metarhyodacite rocks are derived from the fractional crystallization of the same parental magma. Zircon U-Pb data revealed that the rhyodacite rocks initially formed at 2671 ± 51 Ma and underwent later metamorphism at 2065 ± 55 Ma. The Neoarchean protolith age is comparable to the ca. 2628 Ma tholeiitic magmatism and ca. 2666 Ma high-K granites, suggesting bimodal Neoarchean magmatic event within the Ntem Complex, while the metamorphic ages fall within the ca. 2100–2000 Ma high-grade tectono-metamorphic event attributed to Eburnean/Trans-Amazonian orogeny. At the regional scale, metavolcanic rocks with similar origins and ages are documented in the São Francisco Craton in Brazil, suggesting comparable geodynamic evolution on both sides of the south Atlantic during the Paleoproterozoic. [ABSTRACT FROM AUTHOR]

Petrological, mineral chemical and geochemical results are reported for the Cenozoic en-echelon tholeiitic dykes of the Multai area of Deccan flood basalt province, Madhya Pradesh (India) to estimate the pressure and temperature of fractionated and primary melt for these dykes. The rocks are composed of plagioclase, augite and olivine phenocrysts set in a holocrystalline groundmass of plagioclase microlites, augite, Ti–magnetite, ilmenite and interstitial glass. Plagioclases are labradorite in composition (An48–70), and pyroxenes are augite with a composition of Wo24–40, En24–52 and Fs13–56. Forsterite (Fo) contents of olivine phenocrysts range from Fo51 to Fo73. These tholeiitic dykes are rich in Al2O3, Rb, Ba and Sr and show enrichment in light rare-earth element relative to heavy rare-earth element with respect to enriched mid-ocean ridge basalt and normal mid-ocean ridge basalt. Studied samples have lower Ni, Cr, Co and MgO contents than primary compositions suggesting evolved nature of these rocks. The Sr–Nd isotopic ratios of the studied dyke samples indicate affinity to the Mahabaleshwar and Poladpur formations of the southwestern Deccan stratigraphy and the positive εNd(t) values suggest depleted mantle source. The fractionated melt for these dykes last equilibrated at P = 0.2–4.4 kbar and T = 1128–1169°C before the eruption, based on olivine, clinopyroxene and plagioclase mineral-melt equilibria thermo-barometers. The estimated mantle source and primary melt compositions suggest melting in the spinel stability field (P < 28 kbar). It was followed by melt equilibration with mantle olivine Fo89.6 at P = 18–22 kbar and T = 1419–1463°C. The evaluation of whole-rock geochemistry and mineral chemistry supports the hypothesis of fractional crystallisation of plagioclase + clinopyroxene ± olivine ± Fe–Ti oxides for the evolution of these basaltic dykes. Research highlights: This study is on the en-echelon tholeiitic dykes trending east–west in Multai and Dunawa area of Madhya Pradesh (India), located in the northeastern part of the main Deccan province of Deccan flood basalt. Temperature and pressure estimated for crystallisation of clinopyroxene in these samples, using the clinopyroxene-liquid thermometer of Putirka (2008, equation 33) and barometer of Neave and Putirka (2017), range from 1128 to 1175°C and 0.2–4.4 kbar. The H2O content estimated for these samples using the plagioclase hygrometer of Waters and Lange (2015) range from −0.29 to 0.08 wt%. Temperature and pressure calculated for the primary melt in equilibrium with mantle olivine Fo89.6 range between 1419–1463°C and 1.8–2.2 GPa. The estimated pressures correspond to depths of 59–71 km in the Earth's lithosphere, assuming lithosphere–asthenosphere boundary at 90–100 km. [ABSTRACT FROM AUTHOR]

Whole rock O-isotopes of the Panjal Traps are presented in order to assess the influence of crustal contamination and hydrothermal alteration in their genesis. The basalts from the eastern Kashmir Valley and Lidder Valley have enriched δ18OVSMOW values (9.0‰ to 12.0‰). The basalt with the lowest δ18OVSMOW values (9.0‰ and 9.2‰) were likely affected by deuteric alteration but their values could be close to the original melt composition as the rocks do not show trace element (Th/NbPM ≈0.8; Nb/U ≈ 50; Th/La ≈0.1) or isotopic evidence of crustal contamination (87Sr/86Sri = 0.7043 to 0.7045; εNd(t) = +1.1 to +1.3). The δ18OVSMOW (> 12‰) values and Nd isotopes (εNd(t) < −8.6) of the silicic Panjal Traps are consistent with derivation from continental crust. The remaining mafic rocks have enriched Sr-Nd-O isotopic values that indicate crustal (10–30%) contamination (εNd(t) = −1.9 to −6.1; 87Sr/86Sri = 0.7051 to 0.7087; δ18O = 10.1‰ to 12.0‰) with the upper flows exhibiting further enrichment by hydrothermal alteration. The basalts from the Pir Panjal Range, western Kashmir Valley, have variable Nd isotopic values (εNd(t) = −6.8 to +4.3) and the lowest δ18OVSMOW values (6.8‰ to 7.9‰) of the study. The results demonstrate that the rocks from the Pir Panjal Range preserved not only differences in radiogenic isotopes but also the O-isotopes as well. The change in the Nd and O isotopes of the basalt from Guryal Ravine and Lidder Valley to the more depleted values of the Pir Panjal Range is likely due to a transition from a chondritic mantle source to a depleted mantle source as the continental rift evolved to a sea-floor spreading environment. [ABSTRACT FROM AUTHOR]

There are many volcanic districts in the Adamawa Volcanic Massif in the eastern branch of the Cameroon Volcanic Line. The origin of the volcanism and its mantle sources are still highly debated. Basaltic lavas from the Wakwa plain, one of these districts, provide information on processes that took place beneath this area of anomalous lithospheric and crustal thinning. Major and trace element compositions as well as mineral chemistry are presented in this study. The lavas are basanites, basalts, hawaiites, and foïdites, with porphyritic to glomero-porphyritic and sub-aphyric textures. The minerals are mainly olivine (chrysolite), clinopyroxenes (diopside and augite), plagioclases (andesine, labradorite, and oligoclase), Fe-Ti oxides (titano-magnetite and titano-hematite), and accessory amphibole (kaersutite) and apatite. Whole-rock geochemistry data show little compositional variations in all the samples. The lavas present high Mg# (> 60), Cr, and Ni contents and low Nb and Zr contents. The trace element patterns suggest a common magma source with HIMU and EM1 affinities and OIB-like mantle signatures. The above-mentioned geochemical features indicate that the rocks originated from a low degree of partial melting at high pressures of different garnet peridotite source triggered, probably, by changes in mantle temperatures. The variation in composition of the lavas is controlled by variable degrees of partial melting, but possible subsequent enrichment processes can be envisaged. Some distinct magmatic processes "metasomatic events" occurred and affected the composition of the mantle source. In the nutshell, the genesis of melt beneath the Wakwa plain is dominated by a small-scale heterogeneous lithospheric mantle. [ABSTRACT FROM AUTHOR]

The gabbroic plutonic bodies of the Southern Caspian Sea are located in the North of Iran and are made up of olivine, clinopyroxene, plagioclase, and Fe-Ti oxides. They show a narrow range of SiO2 and MgO and are relative to two distinct groups: one enriched in TiO2 with alkali signature and another one low TiO2 with tholeiitic signature. The rocks are enriched in incompatible trace elements such as Zr, Nb, and Y. Normalized trace element patterns and diagnostic elemental ratio are very similar to those of modern ocean-island basalts (OIB) and may be derived from a high U/Pb (HIMU) source with slightly elevated K and Ba contents. There is no evidence of significant crustal contamination; this may be related to the rapid ascent of the parental magma. Rare earth element modelling shows that a low degree of partial melting (1–5% for alkali and 5–20% for tholeiite) of an asthenospheric mantle source in the Garnet + Spinel lherzolite stability field should be responsible for the magmatic origin of that. All data show the studied rocks were generated in a within-plate extension setting above of S.A.Q subduction zone. Activity of a deep plume source with together of rollback of Sevan-Akera-Qaradagh subducted slab, provides the material needed for the investigated OIB gabbros magma source. Therefore, a series of OIA-OIT-OIA-ARC (BAB) rocks are created from S.A.Q. suture zone to south. [ABSTRACT FROM AUTHOR]

Many studies focus on mineralization of huge magnetite ore deposits and petrogenesis of their large-volume host rocks. However, magma generation of those small-scale intrusions with enrichment of magnetite is poorly reported and paid attention to. We here carry out an integrated study of magnetite chemistry, U−Pb zircon dating, geochemistry, and Sr−Nd−Hf isotopes for the magnetite-rich intermediate-mafic rocks from the Helishan pluton in the southwestern Alxa Block, Northwest China. This, together with several previously reported magnetite/iron-rich intrusions nearby, is capable of providing some constraints on magma generation of magnetite/iron-rich intrusive rocks. The Helishan pluton, dated at ca. 290 Ma, consists of hornblende gabbro, diorite, and quartz monzodiorite with ∼3%–5% magnetite in all the lithologies. Study on magnetite chemistry manifests a magmatic origin for them. All the lithologies display high TFeO/MgO ratio (1.71–1.89), weakly fractionated REE patterns ((La/Yb)N = 1.82–10.17), enrichment of Rb, Sr, and Pb, and depletion of high field strength elements. They have (87Sr/86Sr)i values of 0.705 2 to 0.705 8, εNd(t) values of +0.03 to +0.64, and zircon εHf(t) values of +6.5 to +12.0. We propose that they were derived from partial melting of iron-rich metasomatized lithospheric mantle. The systematic variations of Sr/Y ratios and Nd-Hf isotopic compositions with time for the Paleozoic igneous rocks at the southwestern Alxa Block indicate ever existence of thinning and rebirth of lithospheric mantle. This geodynamic process could be the potential mechanism to give rise to the iron-rich signature of the reborn mantle sources of the Helishan pluton. For intermediate-mafic intrusions at subduction zones, they are unlikely to form considerable magnetite ore deposits since their modest magmatic flux and early fractional crystallization of magnetite at a high oxygen fugacity and H2O condition. [ABSTRACT FROM AUTHOR]

Major and trace element data are presented for basaltic lavas from western rift margin of central Main Ethiopian Rift located at Kella area to investigate the processes involved in the petrogenesis of the erupted magmas and the nature of mantle source compositions. Kella area is composed of Quaternary (

The compositional variability of ocean island basalts (OIBs) is thought to reflect partial melting of a lithologically-heterogeneous mantle source dominated by either pyroxenite or peridotite. The Pohnpei Island in Micronesia, which is associated with the Caroline hotspot, is suggested to have been generated from partial melting of a pyroxenite-rich mantle. To examine this hypothesis, we present new major- and trace-element compositions of olivine phenocrysts in basalts from the island. The olivines exhibit large systematic inter- and intra-crystalline compositional variability. In Sample DS1, olivines record compositional zonation, in which cores have relatively high Fo (77–85), Ni (550×10−6–2 392×10−6), and Fe/Mn ratios (66–82), whereas rims have lower Fo (71–78), Ni (526×10−6–1 537×10−6), and Fe/Mn ratios (51–62). By contrast, olivines within other samples preserve no clear compositional zonation, exhibiting similar or slightly lower Fo values (66–78), Ni contents (401×10−6–1 268×10−6), and Fe/Mn ratios (53–69) as the rims of zoned crystals. The distinct chemical contrast between the two different types of olivine suggests they formed in magma chambers at different depths. Analysis using forward petrological modeling and multi-element indicators (Fe/Mn, Zn/Fe, FC3MS (FeOT/CaO-(3×MgO/SiO2)), Mn/Zn, and Ni/(Mg/Fe)) of whole-rock samples and high-Fo olivines is inconsistent with a pyroxenite-rich mantle source. We suggest these inconsistencies reflect an influence on the partition coefficients of Ni and Mn between olivine and liquid during melting at variable pressures and temperatures. In addition, magma recharge and mixing within the magmatic plumbing system can change the composition of olivine. We suggest that identification of the mantle source of OIBs in volcanic islands such as the Pohnpei Island using olivine geochemistry should be treated with caution. [ABSTRACT FROM AUTHOR]

The paper presents the results of isotope-geochronological and petrological-geochemical study of young volcanic rocks in the Geghama highland (Central Armenia), which were formed at the Pliocene–Early Quaternary stage of the Late Cenozoic post-collisional magmatism of the Lesser Caucasus. The boundaries of the area of volcanic activity manifested during this stage were established. The total duration (3.5–1.9 Ma) of the Pliocene–Early Quaternary stage, the time range of its main phases, and the scale and nature of eruptions were determined. Petrological and geochemical data indicate that the studied young volcanic rocks from Central Armenia belong to the mildly alkaline series and are represented by a continuous association of (trachy-)basalt–mugearite–latite–trachyte–rhyolite. The geochemical evolution of parental basaltic melts was mainly controlled by the fractional crystallization with Cpx as the main cumulus phase. Crustal assimilation and mixing of magmas were of limited importance: their possible contribution was recorded only in the most silicic rocks. The deep source responsible for magma generation under the studied part of the Lesser Caucasus at the Pliocene–Pleistocene boundary was represented by the asthenospheric mantle that was enriched during previous long-term (tens of millions of years) subduction of the Neotethys slab. Melting occurred in the Grt-peridotite stability zone; the composition of derived melts was geochemically similar to E-MORB basalts. An important feature of the regional mantle source was the notable admixture of subduction component. The generalization of the obtained petrological–geochemical and isotope–geochemical data on the young igneous rocks formed at different stages of Late Cenozoic magmatism at the Geghama highland allowed us to trace the evolution of the main parameters (mineral, chemical, and isotopic composition, depth of location, degree of melting) of mantle reservoirs responsible for magma generation beneath Central Armenia at the post-collisional stage (from the Late Miocene to the Holocene). [ABSTRACT FROM AUTHOR]

New petrogeochemical data (lithophile element contents and Sr, Nd and Pb isotope composition) on basalts recovered in the DSDP hole 332B in the 37° N region showed that the generation area of deep tholeiites 3 Ma experienced impact of the Azores plume. This led to the formation of tholeiites weakly enriched in a component compositionally similar to the enriched basalts of the Azores. In turn, sources of basaltic melts of the Azores Archipelago resemble those of enriched alkaline magmas of the Iberian margin, which were formed through melting of continental lithospheric fragments of Eurasia. Two types of olivines with different trace element fractionation trends (Ni, Co, Ca) were identified for the first time in the tholeiites from the DSDP hole 332B at the Azores Triple Junction (ATJ). The compositions of olivines with an elevated Ni content are close to those of the basalts of the Azores Archipelago and indicate the presence of lithospheric mantle fragments in the area of tholeiitic magma generation. The observed global and local compositional mantle heterogeneities could have arisen from the complex geodynamic evolution of the ATJ, the formation of which was accompanied by the impact of the Azores plume near fracture zone, spreading axis jumping, and the involvement of continental lithospheric fragments in melting. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) experienced three episodes of seafloor spreading and left three fossil spreading centers presently located at 18°N, 17°N and 15.5°N. Spreading ceased at these three locations during magnetic anomaly 10, 8, and 5c, respectively. Daimao Seamount (16.6. Ma) was formed 10. my after the cessation of the 17°N spreading center. Volcaniclastic rocks and shallow-water carbonate facies near the summit of Daimao Seamount provide key information on the seamount's geologic history. New major and trace element and Sr-Nd-Pb isotopic compositions of basaltic breccia clasts in the volcaniclastics suggest that Daimao and other SCS seamounts have typical ocean island basalt-like composition and possess a 'Dupal' isotopic signature. Our new analyses, combined with available data, indicate that the basaltic foundation of Daimao Seamount was formed through subaqueous explosive volcanic eruptions at 16.6. Ma. The seamount subsided rapidly (>. 0.12. mm/y) at first, allowing the deposition of shallow-water, coral-bearing carbonates around its summit and, then, at a slower rate (

The South China Sea (SCS) experienced three episodes of seafloor spreading and left three fossil spreading centers presently located at 18°N, 17°N and 15.5°N. Spreading ceased at these three locations during magnetic anomaly 10, 8, and 5c, respectively. Daimao Seamount (16.6. Ma) was formed 10. my after the cessation of the 17°N spreading center. Volcaniclastic rocks and shallow-water carbonate facies near the summit of Daimao Seamount provide key information on the seamount's geologic history. New major and trace element and Sr-Nd-Pb isotopic compositions of basaltic breccia clasts in the volcaniclastics suggest that Daimao and other SCS seamounts have typical ocean island basalt-like composition and possess a 'Dupal' isotopic signature. Our new analyses, combined with available data, indicate that the basaltic foundation of Daimao Seamount was formed through subaqueous explosive volcanic eruptions at 16.6. Ma. The seamount subsided rapidly (>. 0.12. mm/y) at first, allowing the deposition of shallow-water, coral-bearing carbonates around its summit and, then, at a slower rate (

Alkaline-silicate complexes host some of the world's largest resources of rare-earth elements and high-field-strength elements (REE & HFSE) and represent the most fractionated magmatic systems on our planet. Geochemical evidence indicates that they are mantle melts, but while various studies highlight a role for lithospheric mantle, we do not know the precise origin of their contained REE and HFSE, and whether enrichment of the mantle source for these magmas can be attributed to specific geodynamic processes or events. We present new Nd-Hf isotope measurements (▪/▪ &▪/▪) made by LA-MC-ICP-MS, as well as a compilation of existing isotopic data for a suite of alkaline igneous rocks from the Gardar Province, a Mesoproterozoic continental rift in southern Greenland. Neodymium and hafnium isotopes are unaffected by crystal fractionation and can directly fingerprint the source of REE and HFSE. The dataset covers both phases of Gardar magmatism (1325–1261 and 1184–1140 Ma) and incorporates mafic dyke swarms and km-scale intrusive complexes, including Ilimmaasaq (Ilímaussaq) and Motzfeldt, which host some of the world's largest REE and HFSE deposits. The majority of Gardar complexes have a narrow range of positive median initial ε Nd (0 to +3.3) and ε Hf values (+0.2 to +6.0). Only two granite intrusions and the Eriksfjord basaltic lavas have crustally contaminated Nd-Hf isotope compositions, with the vast majority of Gardar igneous rocks preserving the isotope signature of their mantle source. Considering the diversity of rock types in the Gardar Province, initial ε Nd - ε Hf compositions are remarkably homogeneous, indicating a derivation of the Gardar's REE and HFSE from a laterally-extensive mantle melt source. Several Gardar systems have low initial ε Hf for a given ε Nd (▪ ε Hf to -9.7), a distinctive signature as few geological processes decouple the Nd and Hf isotope systems. The decoupled Nd-Hf isotope signatures are consistent with contributions from isotopically-matured phlogopite-bearing metasomatic veins (commonly known as PIC: phlogopite-ilmenite-clinopyroxene) in the lithospheric mantle. The metasomatising fluids that formed these source rocks were introduced via Palaeoproterozoic subduction, but the Gardar isotopic signatures indicate that REE and HFSE enrichment of these metasomes was not derived from subducted sediment; instead it is likely that metals were scavenged from the mantle wedge overlying the ancient subduction zone. The Gardar Nd-Hf isotope evolution trends overlap with a global compilation of kimberlites through time and allow us to tie the origin of the PIC metasomes to the regional geodynamic history of South Greenland. We identify PIC metasomes as a key metal source for the Gardar and by extension perhaps other REE-mineralised igneous provinces globally. • Nd Hf isotopes reported for alkaline rocks from REE rich Gardar continental rift. • Negative ▪ ε Hf discounts enrichment of mantle source by subducted sediment. • REE & HFSE derive from isotopically matured metasomatic veins in lithospheric mantle. • Origin of enriched source tied to regional geodynamic history. • Provides conceptual basis for distribution of REE HFSE provinces globally. [ABSTRACT FROM AUTHOR]

Abstract Magmatic products of the Karoo Large Igneous Province can be divided into a volumetrically dominant, compositionally uniform low‐Ti tholeiitic suite, and a subordinate, geographically restricted, compositionally diverse, incompatible‐rich high‐Ti suite. High‐Ti picrites contain up to 2,400 ppm Sr, 1,900 ppm Ba, and 550 ppm Zr, which seems unusual for olivine‐enriched rocks. We studied six Karoo picrites to determine the phase(s) in which Sr resides. Samples consist of 10–30% olivine phenocrysts in a groundmass of brown glass, augite, feldspar, ilmenite, and apatite. Glass compositions vary, but are generally evolved, ranging from basaltic trachyandesite to dacite. X‐ray intensity maps demonstrate that most of the Sr resides in the glasses, and to a lesser extent, in feldspars, if present. Some samples contain two texturally and compositionally distinct glasses, best modeled in terms of magma hybridization: variably accumulated olivine phenocrysts surrounded by evolved Sr‐rich (to 9,470 ppm) Type 2 melts formed by extensive olivine fractionation were infiltrated by chemically distinct Type 1 melts. Upon eruption, Type 2 melt quenched to minor glass around olivine phenocrysts, and the dominant Type 1 glass acquired its evolved composition by quench crystallization of groundmass mineral phases. Both glasses are rich in H2O (up to 3.8 wt. %) but are nearly devoid of CO2. Calculated parental melts have much higher K2O and incompatible trace elements (e.g., Sr or Ba >1,200 ppm) relative to low‐Ti tholeiites. The unusual parental melt compositions imply derivation by small degrees of partial melting from SCLM mantle sources enriched in Sr and other incompatibles.

Magmatic products of the Karoo Large Igneous Province can be divided into a volumetrically dominant, compositionally uniform low‐Ti tholeiitic suite, and a subordinate, geographically restricted, compositionally diverse, incompatible‐rich high‐Ti suite. High‐Ti picrites contain up to 2,400 ppm Sr, 1,900 ppm Ba, and 550 ppm Zr, which seems unusual for olivine‐enriched rocks. We studied six Karoo picrites to determine the phase(s) in which Sr resides. Samples consist of 10–30% olivine phenocrysts in a groundmass of brown glass, augite, feldspar, ilmenite, and apatite. Glass compositions vary, but are generally evolved, ranging from basaltic trachyandesite to dacite. X‐ray intensity maps demonstrate that most of the Sr resides in the glasses, and to a lesser extent, in feldspars, if present. Some samples contain two texturally and compositionally distinct glasses, best modeled in terms of magma hybridization: variably accumulated olivine phenocrysts surrounded by evolved Sr‐rich (to 9,470 ppm) Type 2 melts formed by extensive olivine fractionation were infiltrated by chemically distinct Type 1 melts. Upon eruption, Type 2 melt quenched to minor glass around olivine phenocrysts, and the dominant Type 1 glass acquired its evolved composition by quench crystallization of groundmass mineral phases. Both glasses are rich in H2O (up to 3.8 wt. %) but are nearly devoid of CO2. Calculated parental melts have much higher K2O and incompatible trace elements (e.g., Sr or Ba >1,200 ppm) relative to low‐Ti tholeiites. The unusual parental melt compositions imply derivation by small degrees of partial melting from SCLM mantle sources enriched in Sr and other incompatibles. Plain Language Summary: Rocks rich in the mineral olivine should contain only small amounts of elements unable to be accommodated in its crystal structure. But picrites from the Jurassic Karoo Large Igneous Province in southern Africa are extraordinarily enriched in K, Sr, Ba, Zr, and P. We used microbeam instruments to locate the repositories of these elements in six picrite samples, and found that they are highly concentrated in the glasses that formed as the magmas were quenched near the Earth's surface after having ascended from deeper levels. The glasses represent residual melts after extensive earlier precipitation of mineral phases during fractional crystallization. Elements excluded from the minerals became concentrated in residual melts and eventually quenched to form glass. Calculated original parental melt compositions for the picrites have much higher K, Sr, Ba, Zr, and other "incompatible elements" relative to the vast majority of Karoo basaltic melts. This implies that magmas parental to the picrites were derived by partial melting of small regions in the Earth's mantle that are unusually enriched in such elements, at depths of a few hundred kilometers. This implies a possible link between the Karoo picrites and kimberlites, which have similar chemical features and mantle sources. Key Points: Microbeam measurements in six incompatible element‐rich Karoo picrites show the glasses to be the repositories for K, Sr, Ba, Zr, and H2OGlasses formed by fractional crystallization of olivine, pyroxene, ilmenite, and apatite from enriched melts derived from mantle lithosphereThe alkali picrites are mixtures of accumulated olivine phenocrysts and evolved residual melts, and do not represent primitive magmatic rocks [ABSTRACT FROM AUTHOR]

We present the first K-Ar geochronological and geochemical data (major and trace elements, as well as Sr, Nd, Pb, and Hf isotopes) on volcanic rocks from the Fotouni lavas in the central part of the Cameroon volcanic line (CVL). Two distinct compositional groups can be discriminated: alkaline and transitional lavas. The alkaline series ranges in composition from basanite and basalt to hawaiite and formed 14 to 3 Ma ago while the transitional series ranges from basalt and trachybasalt to basaltic trachyandesite and formed 47 to 38 Ma ago. All samples display trace element patterns dominated by light rare-earth element enrichments compared to heavy rare-earth elements. The alkaline samples have (87Sr/86Sr)i ranging from 0.70292 to 0.70340, εNd = 3.45 to 5.98, ɛHf = 1.95 to 5.63, and relatively radiogenic Pb isotopic compositions: 206Pb/204Pb = 19.891–20.592; 207Pb/204Pb = 15.639–15.693; 208Pb/204Pb = 39.566–40.044. Transitional basalts are characterized by relatively radiogenic Sr and unradiogenic Nd, Hf, and Pb: (ɛNd)i = − 10.82 to + 3.43; ɛHf = − 14.00 to + 3.13; 206Pb/204Pb = 18.0716 to 18.9274; 207Pb/204Pb = 15.532 to15.704; 208Pb/204Pb = 37.8141 to 39.4735. Several geochemical characteristics indicate that the transitional lavas have interacted with the continental crust while alkaline lavas did not suffer significant amounts crustal contamination. Both transitional and alkaline lava series can be explained by mixing between two mantle components: an enriched component and a HIMU-like component. These two mantle sources are probably located within the lithospheric mantle and are different from both the Saint Helena and the Mont Cameroon mantle. [ABSTRACT FROM AUTHOR]

The Late Mesozoic tectonic evolution of the eastern North China Craton (NCC) remains controversial. In this study, a suite of Early Cretaceous mafic-intermediate dyke swarms found in the same section in the Jiaodong Peninsula, eastern NCC, were used to trace the nature of lithospheric mantle and crust–mantle interaction. Zircon U-Pb dating demonstrates that these dykes emplaced into the Jiaodong Peninsula during the same period (112–121 Ma). Diorite dykes have SiO2 contents of 52.7–54.1 wt.%, Na2O+K2O contents of 5.77–6.10 wt.%, a limited range of MgO (4.43–5.13 wt.%), Cr (64.8–85.5 ppm) and Ni (23.6–27.7 ppm), and a narrow range of (87Sr/86Sr)i isotopic ratios (0.709240–0.709246), ƐNd(t) values (−20.0 to −19.1) and ƐHf(t) values (ca. −23.9). Lamprophyre and dolerite dykes have low contents of SiO2 (50.5–55.4 wt.%) and Na2O+K2O (4.88–7.28 wt.%), high contents of Al2O3 (14.6–15.8 wt.%), MgO (5.83–8.60 wt.%), Cr (210–292 ppm) and Ni (114–149 ppm), and a narrow range (87Sr/86Sr)i isotopic ratios (0.709134–0.709788), ƐNd(t) values (−19.9 to −17.4) and ƐHf(t) values (−22.1 to −15.1). Both intermediate and mafic dykes exhibit strong large ion lithophile elements (LILE) enrichment and high field strength element (HFSE) depletion. These geochemical characteristics demonstrate that the magma was primarily derived from relatively low degrees of the partial melting of garnet-lherzolite mantle, which was modified by fluids from a subducting oceanic slab with marine sediments. Both the mafic dykes and intermediate dykes originated from the same magma source and formed in different stages of magma fractionation crystallization. The magma experienced the fractional crystallization of clinopyroxene and more ferromagnesian minerals in a hydrous condition, thus forming mafic dykes. Then, the residual calc-alkaline liquids upwelled into a low-H2O and low-pressure environment, in which more plagioclase crystallized from liquid, thus increasing the degree of differentiation and producing the Ca- and Al-rich diorite dyke. Combined with Late Mesozoic mantle-derived mafic-intermediate dykes and crust-derived volcanic rocks in the region, the eastern NCC has experienced considerable lithospheric thinning along with regional extensional tectonics, which was caused by the prolonged thermo-mechanical-chemical erosion on the lithosphere induced by the rollback of the subducted paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

Petrological, whole-rock major and trace element, and Sr–Nd–Pb isotopic data are reported for the late Mesozoic Dzheltula alkaline igneous complex in the Aldan–Stanovoy Shield, Russia. The alkaline rocks are emplaced into the Tyrkanda mélange zone. The Dzheltula complex consists of monzonites, foid monzonites, and alkaline syenites; granite dykes intrude the complex. All alkaline rocks have high LILE contents (e.g., Ba and Sr), high light REE/HFSE ratios, strongly fractionated REE patterns, and typically lack Eu anomalies. Granite shows different major and trace-element characteristics in comparison to monzonites and syenites. The major and trace-element characteristics of the Dzheltula complex rocks and minerals are consistent with formation by combined assimilation and fractionation processes of an alkaline parental magma of lamproitic composition. The alkaline rocks have moderately radiogenic Sr (87Sr/86Sr(t) = 0.7057–0.7065) and unradiogenic Nd (ɛNd(t) = − 11.3 to − 15.2) and Pb (206Pb/204Pb = 17.17–17.26); granite has more enriched 87Sr/86Sr(t) value (0.707408) but similar ɛNd(t) = − 12.93 The trace element and Sr–Nd–Pb isotopic data for the Dzheltula complex indicate its mantle source experienced ancient metasomatic enrichment, probably associated with subduction. [ABSTRACT FROM AUTHOR]

The alkaline oceanic island basalts (OIBs) with under-saturated SiO2 and high contents of CaO and alkaline are usually attributed to mantle sources different from typical tholeiitic OIBs. Based on the results of high pressure and temperature experiment study, the genesis of silica under-saturated alkaline basaltic melts could be explained by the role of CO2, thus, the genetic relationship of alkaline basalts with CO2 has become a topic of relevance because it is closely related to the deep carbon cycle. The Magellan Seamount chain in the West Pacific Seamount Province has wide distribution of alkali basalts. For the first time, we collected alkaline basalt samples from the Kocebu Seamount of the Magellan Seamount chain and found that magmatic apatites widely occur in the less evolved volcanic rock samples, and the high contents of phosphorus should be a feature of the alkaline OIBs of the Magellan Seamounts. Compared with typical OIBs, these alkaline volcanic rocks have higher CaO and P2O5, lower SiO2 content, negative anomaly of high field strength elements (HFSEs), more distinctly negative anomaly of potassium (K) and the ubiquity of titanaugite, indicating a CO2-rich mantle source. Based on the relatively high K2O and TiO2 contents and La/Yb ratio and low MgO content of these alkaline rocks, we suggest that the volcanic rocks of the Magellan Seamounts are originated from carbonated eclogites derived possibly from ancient subducted altered oceanic crust. [ABSTRACT FROM AUTHOR]

Sulfide Cu isotope systematic has been used as a metallogenic tracer in various deposits; however, only rarely in magmatic Ni-Cu sulfide deposits. Here we present chalcopyrite δ34S and δ65Cu data for the Kalatongke and Baishiquan Ni-Cu sulfide deposits in the Central Asian Orogenic Belt. The Kalatongke deposit yields δ34S of −3.99‰ to 3.30‰ and δ65Cu of −1.32‰ to 0.07‰, whereas chalcopyrite from the Baishiquan deposit has δ34S values ranging from 1.70‰ to 4.98‰ and δ65Cu from −0.40‰ to 0.59‰. These isotopic ratios show no correlation with intrusion/orebody shape, location of sample in the orebody, lithofacies or type of mineralization. Based on Kalatongke and Baishiquan δ34S data, our multicomponent modeling suggests that, with an increase in the relative crustal component contribution, the measured δ34S values in sulfide ores approach the value of the contaminant. Mass ratios (R′) of silicate magma/(xenomelt + sulfide xenomelt + resitite + crystalline olivine) of 250–800 in the Kalatongke and 10–1000 in the Baishiquan deposit, yield δ34S values of −1.78‰ to 1.74‰ and 1.70‰ to 4.98‰ in these deposits. Contamination by host tuff and shale material with δ34S values of −7.2‰ to 3.3‰ reasonably explains the negative δ34S in the Kalatongke ores. A lack of correlation between the Kalatongke and Baishiquan chalcopyrite δ65Cu values and Cu or S contents (or Cu/Ni ratios) indicates that Cu isotopic fractionation was not controlled by sulfide fractional crystallization, but instead by contamination and the mantle source. Multicomponent modeling shows that an R′ factor between 10 and 1000 can reproduce most δ65Cu signatures in sulfide ores from the Kalatongke and Baishiquan deposits, with the exception of a few negative δ65Cu values. Undetected contamination and heterogeneous mantle resulting from different degrees of partial melting and metasomatism in the mantle source may explain these negative values and the wide range of δ65Cu noted in magmatic sulfide deposits worldwide. The Cu and S isotopes in sulfide from the magmatic Ni-Cu sulfide deposits can be utilized as indicators of crustal contamination and the nature of the mantle source. [ABSTRACT FROM AUTHOR]

The Tertiary volcanic rocks in the Khan area have vast outcrops and alternatively include of lava and pyroclastic rocks. The composition of most lavas are dacite, andesite and basaltic trachyandsite with medium potassium calc-alkaline nature. The most phenocrysts in these rocks include oscillatory chemical zonal plagioclases with andesine to oligoclase composition, hornblende, pyroxene, and quartz with apatite as a common accessory mineral. The most important textures of these rocks are porphyritic with microgranular and microlitic matrix, glomeroporphyritic, flow and vesicular. The essential mineral textures are sieve, gulf corrosion and zoning, which point to inequilibrium and magma mixing processes during magma ascension. Depletion of Ti and Nb of these rocks can be indication of magmatism of subduction zone.Nb negative anomaly in the rocks under study is indicator of continental rocks and may be related to crustal involvement in magmatic processes. Based on normalized spider diagrams for rare and rare earth elements, depletion of incompatible elements with high ionic potential such as Ti, Nb, P and Zr in the studied samples can be attributed to magmatism of subduction zone and may be ascribed to the presence of an enriched and metasomatized mantle source by subduction processes and also the occurrence of amphibole and high oxygen fugacity in the magma. Based on the interpretation of tectono-magmatic diagrams, the study volcanic rocks are related to active continental margin subduction zone.