Magma Genesis Research Articles

Crustal Contamination Versus Subducted Components: An Example from The West Java Arc, Indonesia and Its implications in Magma Genesis

New Sr isotope and K2O data are presented for Papandayan and Cikuray Volcanoes in West Java. The data are combined with published Sr isotope and K2O data, and compared with arc that has a similar geological setting, namely Northeast Japan Arc (NJA, N 38° ~ 41°) to constrain the relative importance of crustal assimilation and subducted input of crustal material in magma genesis beneath West Java Arc (WJA). New strontium isotope and K2O data from fifty-four Quaternary volcanic rocks from WJA were collected and compared to forty-six Quaternary volcanic rocks from NJA. The increasing K2O and decreasing of 87Sr/86Sr ratios with distance from trench have been found in NJA, but there are rough and no across arc variation of K2O and Sr isotopic ratios in WJA. This study shows that the across arc variation of magma chemistry on the WJA is attributed to the crustal assimilation and the involvement of subducted sediments and slab fluids from altered oceanic crust.

Time-space variations in the East African Rift magmatism: the role of different mantle domains

The East African Rift System (EARS) is the classic example of an active continental rift where extensional tectonics and lithospheric thinning have been closely associated to the generation of large volumes of magmas and represents the environment with the largest range of erupted magma types all over the world. The geochemical signature of erupted magmas testifies the involvement of different mantle domains and depths (i.e., subcontinental lithosphere, asthenosphere and deeper mantle sources). Our aim is to investigate the variable contribution of different mantle domains in the genesis of the EARS magmas through space and time, considering not only the geochemical signature of erupted magmas but also the geochemical message of mantle xenoliths. The main goal is to provide a large-scale view of the common process driving the origin of magmas in the EARS beyond the local peculiarities linked to specific settings. To this aim, we screened an exhaustive geochemical database of basalts and mantle xenoliths from the EARS, and we report original trace element and Sr-Nd isotope data of new samples collected from the Main Ethiopian Rift and Turkana depression. The data were subdivided according to spatial and temporal criteria. From a spatial point of view, the samples were ascribed to five groups, namely: Afar, Ethiopia, Turkana, Eastern Branch, and Western Branch; from a temporal point of view, the magmatic activity of the EARS was subdivided into three main temporal intervals: 45-25 Ma, 25-10 Ma and 10-0 Ma. The geochemical and radiogenic isotope (Sr, Nd, Pb) signature of the selected basalts denotes the variable contributions of a mantle plume, a more depleted asthenospheric mantle (DMM), and different SubContinental Lithospheric Mantle (SCLM) domains, depending on their temporal and spatial distribution. The geochemistry of the selected basalts shows a marked correspondence with the compositional heterogeneity of mantle xenoliths, whose isotopic systematics (Sm-Nd, Re-Os) indicates the formation of the local SCLM in the Archean and during the Pan-African orogeny. Both SCLM domains contributed significantly to magma genesis in the Western Branch (whose signature points towards a contribution of the Pan-African lithosphere) and Eastern Branch (which is also affected by Archean SCLM domains) magmas. The contribution of the SCLM generally increases with time, possibly related to an increase of the geothermal gradient in response to the arrival and flattening of the plume head at the base of the lithosphere and later extension, thinning and shallower melting. Our interpretation supports a pivotal role of the different SCLM domains in magma genesis that is able to fully explain the large compositional heterogeneity of the EARS basalts and represents a reasonable alternative to the putative presence of multiple mantle plumes or a heterogeneous mantle upwelling.

Elemental abundances and isotopic composition of Italian limestones: Glimpses into the evolution of the Tethys

Biogenic limestones from three sections (north, central, and south) across peninsular Italy have been analysed for major and trace elements and Nd, Pb, and Sr isotopic ratios. These data are used to monitor the evolution of the Tethys Ocean from the Triassic through to the Miocene. Limestones’ major, trace, and REE elements contents are consistent with their formation in seawater with little sign of crustal, volcanic, or hydrothermal input. V/Cr and Ce/Ce* ratios indicate their deposition in oxygenated waters. Rb-Sr-Ba discrimination diagram, consistent with the immobile trace element distribution, indicates that limestone deposition took place in either marginal or open ocean environments. Ages based on stratigraphy are in good agreement with the chronostratigraphic Sr curves implying that the Tethys ocean, throughout its history, was in contact with the open, global, ocean system. Although the isotopic values of Sr and Nd are relatively restricted, Pb is extremely variable and highly radiogenic. High Pb isotope ratios characterise limestones deposited during the rifting of the southern Tethyan ocean in the Lower Jurassic and in the Lower Cretaceous, suggesting stronger crustal inputs in small basins. The weighted average, present-day, isotope values (AIL = average Italian limestone) for the Italian limestones, excluding anomalous samples, are 87Sr/86Sr = 0.70785, 143Nd/144Nd = 0.51227, and 206Pb/204Pb = 18.94, 207Pb/204Pb = 15.69, 208Pb/204Pb = 38.66. These values are useful in monitoring the fate of limestones during orogenesis and the role that they may have played in magma genesis.

Geochemistry, zircon U Pb ages and Lu Hf isotopes of Triassic plutons in the eastern Gyeonggi Massif, Korean Peninsula: Magma genesis and geodynamic implications for East Asia

Geochemistry, zircon U Pb ages and Lu Hf isotopes of Triassic plutons in the eastern Gyeonggi Massif, Korean Peninsula: Magma genesis and geodynamic implications for East Asia

Neogene calc-alkaline volcanism in Bobak and Sikh Kuh, Eastern Iran: Implications for magma genesis and tectonic setting

Neogene calc-alkaline volcanism in Bobak and Sikh Kuh, Eastern Iran: Implications for magma genesis and tectonic setting

Multistage Neoarchean magma genesis in the Bundelkhand Craton, India: Evidence from whole-rock elemental and Nd isotopic study of mafic magmatic enclaves and granitoids

Using field, petrography and geochemistry (elemental and Nd isotopic compositions), an integrated study has been carried out on the Neoarchean lithologies comprising mafic magmatic enclaves (MMEs) and undeformed granitoids of the Bundelkhand Craton (Central India) to understand their genesis and crustal evolution. Based on the degree of mingling/mixing with the host granitoids, the MMEs are classified into three types as E-1, E-2 and E-3 types. The E-1 type MMEs represent the early fragments formed by fractional crystallization of mafic/ultramafic magma. The E-2 type MMEs formed due to restricted mingling and rapid crystallization of a hot mafic magma that interacted with felsic granitoid magma. The E-3 type MMEs show compositional similarity with its felsic host and are proposed to have formed by magma mixing process. The MMEs underwent varying degrees of isotopic equilibration with the host granitoids. The E-1 and E-2 type MMEs were resulted from depleted mantle-wedge and the E-3 type MMEs formed from a metasomatized mantle-wedge during subduction. Underplating of basaltic magma probably played a key role in the crustal formation and also provided heat for large scale melting of the crustal rocks giving rise to granitic magma. Such tectono-magmatic events also produced mafic magmas that variably interacted with the granitic magma and played a significant role in the generation of huge Bundelkhand granitoid massif during the Neoarchean.

Effects of Mantle Hybridization by Interaction with Slab Derived Melts in the Genesis of Alkaline Lavas across the Back-Arc Region of South Shetland Subduction System

AbstractLate 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.

Genesis of hydrous-oxidized parental magmas for porphyry Cu (Mo, Au) deposits in a postcollisional setting: examples from the Sanjiang region, SW China

Genesis of hydrous-oxidized parental magmas for porphyry Cu (Mo, Au) deposits in a postcollisional setting: examples from the Sanjiang region, SW China

Effects of mantle flow on the chemistry of Coriolis Troughs backarc magmas

Ridge subduction along convergent plate margins can cause a tear to develop in the underlying slab, which allows the influx of hot sub-slab mantle materials into the mantle wedge. Such a process has a profound influence on the chemistry of Vanuatu arc magmas, but its effect on the genesis of Vanuatu backarc magmas remains to be assessed. Here we present new geochemical data for samples from the Coriolis Troughs (part of the Vanuatu backarc) and combine our new data with published analyses of samples from the entire Vanuatu arc. Many samples from the Coriolis Troughs have major element systematics, chalcophile element systematics and trace element ratios (i.e., Ba/Nb, Th/Nb) that are more similar to the global MORB array than Vanuatu arc samples. These systematics can be attributed to slab rollback prior to ridge subduction, which caused a progressive decline in the proportion of slab fluxes to the mantle source of the Coriolis Trough magmas. As rollback progressed, deep upwelling of enriched mantle components beneath the North Fiji Basin influenced the compositions of the erupted backarc basin magmas. Melting of this enriched mantle source generated the most recent Nifonea Caldera Floor magmas. In contrast to the other recent Coriolis Trough magmas, the Young Lava Plain samples have geochemical characteristics that are comparable to Vanuatu arc magmas. The Young Lava Plain magmas are situated to the southeast of a slab tear. We therefore suggest that influx of hot sub-slab mantle materials through a slab tear caused southeast flow (i.e., mantle flow away from the trench) of sub-arc mantle (i.e., mantle that was enriched by hydrous and oxidising components released from the slab at sub-arc depths) and that this sub-arc mantle source generated the Young Lava Plain magmas. In particular, we suggest that this oxidised source can account for the anomalous chalcophile element signatures of the Young Lava Plain samples compared to the other Coriolis Trough samples. Because all of the Coriolis Trough samples have similar depth-to-slab, we propose that changes in mantle flow patterns caused by ridge subduction and the development of a slab tear can account for the genesis of proximal magmas with comparable ages but distinct compositions.

Trace elements in olivine fingerprint the source of 2018 magmas and shed light on explosive-effusive eruption cycles at Kīlauea Volcano

Understanding magma genesis and the evolution of intensive parameters (temperature, pressure, composition, degree of melting) in the mantle source of highly active volcanic systems is crucial for interpreting magma supply changes over time and recognizing cyclic behavior to anticipate future volcanic behavior. Major and trace elements in olivine are commonly used to study variations in mantle lithologies and melting conditions (e.g., temperature, pressure, oxygen fugacity) affecting the mantle over time. Here, we track the temporal evolution of primary melts through the most recent cycle of explosive and effusive eruptions at Kīlauea (Hawai‘i), which spans the last ∼500 years. We report major and trace elements in olivine from the last explosive period (∼1500 – early 1820’s Keanakāko‘i Tephra) and the most recent decade of the current effusive period (2018 LERZ, 2015–2018 Pu‘u‘ō‘ō, 2008–2018 lava lake and 2020 eruption in Halema‘uma‘u). Scandium concentrations in olivine allow characterizing changes in mantle source between 1500 and 2018, and suggest that the recent (2015–2018) magma feeding the Pu‘u‘ō‘ō cone did not significantly interact with the magma that erupted in the LERZ in 2018. The evolution of olivine and melt compositions over the past 500 years is not easily reconcilable with variations in mantle potential temperature, pressure of mantle melt pooling and storage, or oxygen fugacity. Instead, Sc, Mn, and Co concentrations and Ni/Mg ratio in high forsterite (Fo >87) olivine advocate for an increase in the proportion of clinopyroxene in the mantle source associated with a slightly higher degree of partial melting from 1500 to 2018. Changes in primitive melt compositions and degrees of mantle melting may well modulate magma supply to the crust and formation-replenishment of steady or ephemeral summit reservoirs, and thereby control transitions between explosive and effusive periods at Kīlauea. Analyzing trace elements in olivine at Kīlauea and elsewhere could therefore provide important clues on subtle changes occurring at the mantle level that might herald changes in volcanic behavior.

Petrological and Geochemical Study of Sundoro Volcano, Central Java, Indonesia: Temporal Variations in Differentiation and Source Processes During the Growth of an Individual Volcano

Abstract Volcanic rocks of the Java sector of Sunda arc have a wide range of isotopic compositions that indicate significant addition of subjected sediment. What processes control these geochemical characteristics is a topic of long-standing debate. Here we report Sr–Nd–Pb radiogenic isotope ratios and geochemical data from stratigraphically well-constrained rocks of Sundoro volcano in central Java that represent the volcano’s activity since 34 ka. The rocks range from basalt (51 wt % SiO2) to andesite (63 wt % SiO2) and are dominated by basaltic andesite. We divide them into magma types A, B and C, having low, medium and high 87Sr/86Sr and Pb isotopic ratios, respectively. According to various differentiation indices, the three magma types have separate, parallel 87Sr/86Sr, Ba/Zr and La/Yb trends and disparate Pb isotopic trends. The dominant process of intracrustal differentiation appears to be magma mixing, in which each of the three magma types represents the mixing of a distinct mafic end-member and a distinct felsic end-member. The distinct geochemical profiles of these magma types indicate that the three mafic end-members are genetically unrelated and that their differences may represent characteristics of their magma sources. On the basis of trace element ratios (Ba/Yb and La/Yb) and Sr–Nd–Pb isotopic compositions, we estimate that magma types A, B and C represent mantle wedge materials fluxed by ~1%, ~1.5% and ~2% slab-derived materials containing 50%, 55% and 65% sediment component, respectively, reflecting increasing proportions of sediments and increasing slab flux. Geochemical data from Merapi volcano, interpreted using the same approach, reveal a similar increase in the slab-derived flux to the magma source, raising the possibility that such short-lived variations in magma genesis, perhaps related to the subduction of bathymetric relief features, characterize the unusual magmatism beneath the volcanic front of the central Java sector of the Sunda arc.

Fluid-rock interactions at shallow depths in subduction zone: Insights from trace elements and B isotopic composition of metabasites from the Mariana forearc

To reveal the spatial variations of slab-derived fluids and to trace the in-situ dehydration in the shallow subduction zone, we investigated the petrography, mineral chemistry, and whole-rock B isotopes of metabasites that were recovered from the Fantangisña and Asùt Tesoru serpentinite mud volcanoes and originated from the shallow subduction channel at the forearc of the Mariana subduction zone. The alteration mineral assemblages in the investigated metabasites suggest zeolite- to prehnite-pumpellyite-facies metamorphism and lawsonite-blueschist facies metamorphism beneath Fantangisña and Asùt Tesoru seamounts, respectively. The fluid mobile elements (e.g., B, As, Sb, Pb) are preserved in the low grade metamorphic phyllosilicate minerals (e.g., glauconite, pumpellyite, celadonite), thus fixing the B concentrations of the subducted oceanic crust during shallow subduction (<18 km). Both B concentrations (16.7 to 43.9 μg/g) and δ 11 B values (−5.0 to +3.2‰) of the investigated metabasites are significantly higher than fresh normal mid-ocean ridge basalts (N-MORB) and ocean island basalts (OIB), and are generally comparable to the uppermost altered oceanic slab. Notably, the recovered metabasites from the Mariana forearc exhibit a decreasing trend in δ 11 B values with increasing distance to the trench from Fantangisña (62 km) through Asùt Tesoru (72 km) to South Chamorro (78 km) Seamounts. This trend together with Rayleigh dehydration modeling indicate that the 11 B-enriched aqueous fluids were released from the subducting slab during prograde metamorphic dehydration. The estimated B isotopic compositions of the slab-derived fluids released at arc magma genesis depths are generally comparable to that of the Mariana arc lavas. However, the fluids released by dehydration of subducted sediments at shallow depths should be characterized by lower δ 11 B values than fluids released from the slab at depths of magma genesis beneath the island arc. Then, the recycling of the hydrated forearc mantle is necessary to explain the high δ 11 B values of the Mariana arc lavas. While, the variable B isotope compositions of Mariana arc lavas should be controlled by the different ratios of sediment/AOC ratios. • The investigated metabasites experienced low-grade metamorphism. • Both B concentrations and δ 11 B values are significantly higher than their protolith. • δ 11 B values exhibit a decreasing trend with increasing distance to the trench axis. • Subducted serpentine is necessary to explain the high δ 11 B values of the arc lavas.

The Bazman and Taftan volcanoes of southern Iran: Implications for along-arc geochemical variation and magma storage conditions above the Makran low-angle subduction zone

Bazman and Taftan are two Late Miocene-Quaternary volcanoes of the Makran continental arc formed by the subduction of Arabian oceanic lithosphere beneath southern Eurasia. This study compares their bulk rock compositions as well as major and trace element contents of major mineral phases. Bazman is composed of a geochemically heterogeneous suite of low to medium-K basic to acidic compositions, while Taftan exposes more homogenous mainly andesitic rocks of medium to high-K affinity. Both volcanoes are characterized by the enrichment of LILE compared to HFSE and depletion of Nb, Ta, and Ti, reminiscent of subduction zone magmatism. At a given SiO2 content, the Taftan volcanics have higher concentrations of incompatible elements and, La/Yb, Th/Yb, and Sr/Y ratios (adakitic signature), here interpreted as being related to the more enriched mantle source, higher contribution of subducted sediments in magma genesis and thicker continental crust beneath Taftan. Thermobarometric calculations based on mineral chemistry (amphibole, orthopyroxene, clinopyroxene, and plagioclase) indicate pre-eruptive T = ∼1050–800 °C, P = 250–100 MPa and H2Omelt > 3.5 wt%. Bazman lavas record slightly lower P and T, and higher H2Omelt, suggesting a shallower magma reservoir and thus a more developed magma plumbing system. Trace element abundances in minerals show consistent distinctions between the two volcanoes, e.g., amphibole is REE-enriched in Taftan over Bazman samples. The features of trace element compositions and zoning patterns of minerals (amphibole, plagioclase and, pyroxene) along with available major element data are suggestive of both recharged magmatic systems and convective self-mixing magma chambers.

Radiogenic isotope record of magma genesis and lithospheric geodynamics of the Rukwa Rift Basin, Tanzania, from mid Mesozoic to present

The Western Branch of the East African Rift System has experienced multiple episodes of basin development and intraplate alkaline volcanism since the Jurassic, however the geodynamic processes and lithospheric evolution involved in this protracted geological history remains poorly defined. Here, we present Sm-Nd, Lu-Hf, and Rb-Sr isotopic data of igneous minerals for three magmatic episodes that coincide with basin reactivation in the Rukwa Rift of southwestern Tanzania, respectively represented by: (1) the Jurassic to Cretaceous Panda Hill carbonatite; (2) the late Oligocene phonolitic‑carbonatitic Nsungwe Formation tuffs; and (3) the Miocene–recent bi-modal volcanism of the Rungwe Volcanic Province. Of these, the Nsungwe Formation tuffs offer a discrete record of the early phases of lithospheric disturbance associated with modern rifting of the Western Branch.Alkaline magmas erupted prior to the Miocene are isotopically distinct (ɛNd +0.5 to +1.5 and 87Sr/86Sr 0.7041) from modern Rungwe lavas and likely originate from a lithospheric mantle that experienced enrichment during the Pan-African Orogeny (~550–700 Ma). Consistent with previous studies, our results indicate that Rungwe Volcanic Province magmas were generated from a mixed, isotopically-enriched component of the lithospheric mantle that may have developed during the ca. 1.0 Ga Irumide Orogeny. The observed change in the source region of rift lavas though time is consistent with progressing melting of a compositionally layered lithosphere. Combined with existing geophysical and sedimentological data, we hypothesise that the lithosphere beneath the Rukwa-Malawi-Usangu junction of the Western Branch experienced an episode of destabilisation and foundering (lithospheric drip), during the early stages of East African Rift development.

The Roraima Alkaline Province: A cretaceous alkaline province in the Amazonian Craton

The rift-related magmatism that generated the Roraima Alkaline Province (RAP) took place along main faults and shear zones that stretch out for circa 200 km in the central Guyana Shield, northern Amazonian Craton. As such, RAP is the first alkaline province proposed to the Guyana Shield. It encompasses felsic and mafic rock types – the former constituting foid-syenites and phonolites, while the latter including lamprophyre, tephrite and tephriphonolite dikes. In this paper, we examine whether these rocks are cogenetic and construct a genetic model for RAP with coupled petrography, geochemistry, and U-Pb zircon geochronology. Our data show that the RAP rocks are nepheline-normative, metaluminous to peralkaline, and miaskitic to agpaitic. The geochemical signatures indicate that fractional crystallization was the primary mechanism that produced the compositional variability between mafic and felsic magmas. Increasing peralkalinity is attributed to extensive alkali feldspar fractionation. Elemental, isotopic, geochronological and petrographic features show that crustal assimilation also played a role in magma genesis. Both ages obtained in this study and compiled from previous works range from 100 to 116 Ma, indicating that the Cretaceous alkaline magmatism in the Guyana Shield was short-lived. The Sr-Nd isotopic signatures of the least-contaminated samples require mixing of depleted and enriched mantles. Depleted-mantle model ages obtained from the least-contaminated samples fall in relatively short intervals, between 548 and 657 Ma, which coincide with the model ages of the Central Atlantic Magmatic Province (CAMP) tholeiites, suggesting that the same metasomatic event affected both Mesozoic alkaline and tholeiite magmatic occurrences of the Guyana Shield. It is concluded that the lithospheric mantle metasomatism took place shortly before magmatism, triggered by an extensional tectonic event involving the Tacutu rifting and the opening of the Atlantic.

Reassessing the intrusive tempo and magma genesis of the late Variscan Aar batholith: U–Pb geochronology, trace element and initial Hf isotope composition of zircon

The Variscan orogeny was responsible for the formation of a significant volume of igneous basement throughout present-day Europe. Detailed understanding of these rocks has, however, been obfuscated by significant overprinting during younger geologic events. In order to better understand the formation of this basement, we present U–Pb dates, trace element concentrations and Hf isotope compositions of zircon from 17 intrusions of the Variscan Aar batholith, located in the Aar Massif, Central Alps, Switzerland. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was used to generate a large set of U–Pb dates, trace element and Hf isotope compositions on untreated zircon, as well as zircon pretreated by chemical abrasion. Furthermore, a subset of samples was also analyzed for high-precision U–Pb geochronology using chemical abrasion, isotope dilution, thermal ionization mass spectrometry (CA-ID-TIMS). The U–Pb dates of both dating techniques are significantly dispersed, indicating that they are influenced by multiple forms of complexity, including inheritance, domains of secondary alteration likely related to Alpine overprint or growth, decay damage related Pb-loss, and potentially protracted magmatic growth. Decay-damage related Pb-loss is likely a subordinate source of age scatter within the data, therefore chemical abrasion pretreatment is not capable of completely mitigating the observed analytical scatter. After rejection of outliers, the remaining data still exhibit excess scatter of several percent among 206Pb/238U dates in individual samples, however it is possible to interpret reasonable geologic ages from these data. These new U–Pb zircon age interpretations indicate the Aar batholith grew incrementally through four major magmatic pulses, which occurred at approximately 348, 333, 309 and 298 Ma. Based on the trace element and Hf isotope geochemistry, the melt source(s) of the Aar batholith evolved throughout the duration of batholith formation and growth. The transitioning from (i) melting of depleted mantle at 348 Ma during a stage of active continental arc magmatism (εHf = + 12 to + 10), (ii) melting of metasomatically enriched lithospheric mantle, possibly contaminated by crust during the 333 Ma pulse (εHf = − 10 to − 3), followed by (iii) an increasing incorporation of a juvenile mantle components during the 309 and 298 Ma pulses (εHf = − 3 to + 6). Finally, these new U–Pb ages yield a more detailed understanding of the Variscan Aar batholith by integrating the new detailed mapping of Aar Massif for the Geological Atlas of Switzerland, allowing for more accurate characterization and categorization of variably deformed heterogeneous intrusive bodies.

Diverse mantle components with invariant oxygen isotopes in the 2021 Fagradalsfjall eruption, Iceland

The basalts of the 2021 Fagradalsfjall eruption were the first erupted on the Reykjanes Peninsula in 781 years and offer a unique opportunity to determine the composition of the mantle underlying Iceland, in particular its oxygen isotope composition (δ18O values). The basalts show compositional variations in Zr/Y, Nb/Zr and Nb/Y values that span roughly half of the previously described range for Icelandic basaltic magmas and signal involvement of Icelandic plume (OIB) and Enriched Mid-Ocean Ridge Basalt (EMORB) in magma genesis. Here we show that Fagradalsfjall δ18O values are invariable (mean δ18O = 5.4 ± 0.3‰ 2 SD, N = 47) and indistinguishable from “normal” upper mantle, in contrast to significantly lower δ18O values reported for erupted materials elsewhere in Iceland (e.g., the 2014–2015 eruption at Holuhraun, Central Iceland). Thus, despite differing trace element characteristics, the melts that supplied the Fagradalsfjall eruption show no evidence for 18O-depleted mantle or interaction with low-δ18O crust and may therefore represent a useful mantle reference value in this part of the Icelandic plume system.

Vanadium and Cobalt Occurrence in the Fe-Ti-V Oxide Deposits Related to Mesoproterozoic AMCG Complex in NE Poland

On the basis of geochemical whole-rock and mineralogical point analyses, the concentrations of V and Co were determined in magnetite-ilmenite oxide ores, associated with sulphides, at the Krzemianka and Udryn deposits in the Mesoproterozoic Suwałki Anorthosite Massif (SAM) in NE Poland. EPMA analyses showed that the main carrier of vanadium was magnetite (mean = 0.42 wt%) and, to a lesser extent, ilmenite (mean = 0.14 wt%) and minor Al-spinels (mean = 0.04 wt%). In turn, cobalt was found mainly in the form of isomorphic substitutions in magmatic sulphides such as pentlandite (mean = 4.41 wt% Co), pyrrhotite (mean = 0.16 wt%), and chalcopyrite (mean = 0.11 wt%). Moreover, Co-enrichments were also recognized in the secondary sulphides, such as pyrite and bravoite, replacing pyrrhotite (means = 1.6 and 2.7 wt% Co, respectively), and in the form of different thiospinels ((Fe, Ni) (Co, Ni)2S4), mainly siegenite (mean = 22.0 wt% Co), replacing pyrrhotite and pentlandite. Vanadium cations were substituted in Fe, Ti oxide minerals in place of Fe+3 cations, and in the case of cobalt, Fe+2 cations were substituted in sulphides and thiospinels. Vanadium and cobalt showed high Person’s correlation coefficients (r = 0.70), indicating their close spatial coexistence and a common source, which was parental anorthosite-norite magma of the SAM suites. The common magma genesis of magnetite-ilmenite and sulphide mineralization was also confirmed by the very similar shapes of the curves of REE content in the oxide-sulphide ores in relation to chondrite, in which negative Eu anomalies and positive Sm anomalies are clearly visible. Although the average contents of vanadium and cobalt were low (arithmetic means = 960 ppm, and 122 ppm, respectively), the resources of these metals were estimated to be large due to the enormous reserves of magnetite-ilmenite ores hosted by the SAM. However, the Fe-Ti-V ores associated with Fe, Ni, Co, and Cu sulphides were considered to be sub-economic because of their depth of occurrence (mainly 1.0 km below the surface level); their metal contents, which were usually too low; and additionally the fact that the location is in a highly environmentally protected landscape and lake area.

Major and trace element geochemistry of Permo-Triassic granitoids from NW Sonora, Mexico: Constraints on the origin of the Late Paleozoic-early Mesozoic Cordilleran magmatic arc along SW Laurentia

Permo-Triassic granitoids (PTGs) (284–224 Ma) crop out in Sierra Los Tanques (SLT) and surrounding areas in NW Sonora, Mexico. Based on mineralogical and geochemical characteristics, the PTGs are subdivided into three main suites: melanocratic (MS), leucocratic (LS) and pegmatitic-aplitic (PAS) suites. MS has I-type signatures (mostly metaluminous: biotite and hornblende), while LS is weakly peraluminous with biotite, muscovite, and garnet. PAS is composed of garnet-bearing pegmatite-aplite dikes of Permo-Triassic age. MS is slightly older than LS based upon field relations and age dating. PAS cut both granitoid suites and local Paleoproterozoic banded gneisses. PTGs are petrologically and geochemically classified as granodiorites, granites, and quartz monzonites, with medium-to high-K calc-alkaline affinity, and volcanic-arc granite (VAG) signatures. The enrichment in LILE (such as K, Rb, Ba, Sr, and Pb) and LREE over HFSE and HREE, respectively, together with negative Nb, Ta, P, and Ti anomalies, suggest derivation from a crustal source in a continental arc setting. Trace-element ratios of Ba/Ta≫1000, Th/Yb > 1, and Th/Ta>6–20 also support a setting in an active continental margin. All these geochemical features imply that crustal assimilation did play a major role in magma genesis. Crustal contamination is supported by field evidence, including xenoliths, stoped blocks, and roof pendants of Proterozoic basement rocks (Yavapai-type? crust). We propose that the PTGs from NW Sonora formed in a continental arc setting likely derived from the heat-fluxed melting of crustal material induced by mafic (basaltic?) underplating, thus the PTGs record the initiation of subduction and the generation of the early magmas in the nascent Late Paleozoic Cordilleran arc in SW Laurentia.

Three types of Triassic granitoids in Changning‐Menglian suture zone: Petrological, geochemical, and geochronological constraints for source characteristics and petrogenesis

The Triassic granitoids are widely exposed along the Changning‐Menglian suture zone (CMSZ) in SW China, which are the products of Palaeo‐Tethyan closure and are characterized by highly variable geochemical compositions. However, details of the implied source heterogeneity and magma genesis have not been well constrained. In this study, we present zircon U–Pb isotopes and trace elements, whole‐rock major and trace element compositions and Sr–Nd isotopes of Triassic granitoids from the giant Yunling and Lincang plutons developed in the CMSZ. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating indicates that they were emplaced at ca. 227–216 Ma. Geochemically, these Triassic granitoids can be classified into three types. The Yunling low‐silica granodiorites (Type 1) are characterized by the presence of amphibole‐bearing mineral assemblages, high TiO2 and FeOT + MgO, belonging to I‐type granite and calc‐alkaline series. The Lincang low‐silica granodiorites (Type 2) are metaluminous to peraluminous with the occurrence of amphibole, consistent with transitional I‐S‐type granites. Compared to Type 1 and 2, the Lincang high‐silica (SiO2 &gt; 70%) alkali feldspar granites and syenogranites (Type 3) display lower CaO, TiO2, P2O5, MgO + FeOT, Eu, Sr, and Zr contents, belonging to fractionated‐type granites. Three types of granitoids collectively show enriched Rb, Th, K, and Pb, depleted Ba, Sr, Ti, and Eu, negative whole‐rock εNd(t) (−11.0 to −10.7) and old TDM2 ages of 1,886–1,855 Ma, indicating the affinity of middle‐upper crustal derivation. New zircon U–Pb dating yields an age range of 2,391–322 Ma for inherited zircons with two clusters at ca. 460 and 956 Ma, suggesting that their crustal source might be the basement of the Simao Block rather than the basement of the Proterozoic Lancang Group. Diverse geochemical compositions indicate that the parental magma of the Triassic granitoids in the CMSZ originated from the partial melting of a heterogeneous source, and experienced magma mixing, assimilation with Lancang Group meta‐sandstone and fractional crystallization. Considering the exhumation of the high‐pressure metamorphic rocks in the CMSZ at Triassic, the upwelling of the asthenosphere after the Palaeo‐Tethyan closure increased the geothermal gradient of the lithosphere and triggered extensive crust melting in a post‐collisional setting.