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Despite the scientific and economic significance of kimberlites and related magmas, their origin is unclear. Here, we address this issue using whole‐rock and perovskite‐derived Sr‐Nd‐Hf isotopes for the three occurrences of kimberlite, lamproites and ultramafic lamprophyres (UMLs) in Finland. Mesoproterozoic olivine lamproites at Lentiira‐Kuhmo and UMLs at Kuusamo have different isotopic signatures yet were emplaced contemporaneously at 1,200 Ma in response to an extensional regime linked to the Baltica‐Laurentia breakup. The low εNd(i) and εHf(i) values of the olivine lamproites are consistent with an enriched subcontinental lithospheric mantle (SCLM) source while UML compositions are intermediate between those of typical kimberlites and lamproites and are interpreted to reflect mixing of asthenospheric melts and ∼10%–15% of melts sourced from metasomatized SCLM. The ∼750 Ma Kuusamo kimberlites, are probably linked to the mantle plume activity that initiated Rodinia's break‐up, exhibiting homogenous isotopic compositions which mirror the prominent Geodynamic and Source Constraints for ∼1,200 Ma Olivine Lamproite and Ultramafic Lamprophyre Magmatism in Eastern Finland (PREMA)‐like signature of kimberlites globally. By contrast, ∼620–585 Ma Kaavi‐Kuopio kimberlites show limited range in εNd(i) and 87Sr/86Sr(i) but have remarkably heterogeneous εHf(i) (+6.5 to −6.3) with a temporal trend toward lower εHf(i) values. While the Kuusamo kimberlites erupted during the early stage of continental break‐up, the Kaavi‐Kuopio kimberlites were emplaced when Rodinia break‐up was completed, coeval with formation of the Central Iapetus large igneous province. Magmas forming the Kaavi‐Kupio kimberlites may have formed from an upwelling mantle source similar to PREMA modified by increasing incorporation (up to 10%) of recycled crustal material through time accounting for the trend toward lower εHf(i) in these kimberlites. Plain Language Summary: Kimberlites and related rocks are of great economic and scientific importance as they are some of the deepest derived mantle melts (> 150–200 km) and carry a diverse cargo of mantle material, including diamonds. In this study, we utilize new radiogenic isotope data combined with geochemical modeling and existing geodynamic reconstructions to propose genetic models for the emplacement of kimberlites, ultramafic lamprophyres (UMLs) and olivine lamproites in Finland. The UMLs and olivine lamproites may be genetically related given their close temporal overlap and their compositions testify to progressively increasing contributions by geochemically enriched lithospheric mantle sources. We propose that kimberlite activity in Finland is fueled by melting of deep mantle sources that bookends both the onset and completion the break‐up of an ancient supercontinent, Rodinia. This supercontinent disintegration and, potentially, kimberlite activity, was likely driven by the deep mantle upwellings, or plumes, beneath the region. In addition, our modeling suggests the unique, isotopic evolution of the mantle source for the youngest Finnish kimberlites occurrence reflects progressive incorporation of ancient, recycled material into their mantle plume source. Key Points: New radiogenic isotope data reveals distinct sources and petrogenesis for three occurrences of kimberlite and related magmatism in FinlandKimberlite magmatism in Finland is synchronous with initiation and completion of Rodinia's break‐up with potential links to mantle plumesThe primitive source region of the Kaavi‐Kuopio kimberlites was significantly modified by increasing incorporation of recycled material [ABSTRACT FROM AUTHOR]

The Late Devonian postorogenic Cobaw batholith, in southeastern Australia, is an oval, east-west-orientated, terranestitching lopolith that intruded low-grade metaturbidites. The initial intrusion (at 370 Ma) was the small, hypabyssal, S-type Rainy Creek Rhyolite (RCR). At 369 Ma, the foliated S-type Pyalong pluton was emplaced, apparently along an east-west-orientated fracture zone. Around 367 Ma, the main I-type Baynton pluton intruded as numerous shallowdipping sheets. The last plutonic event was the intrusion of the broad, thin, flat-lying, and crosscutting sheet of the Itype Beauvallet pluton. The Cobaw plutons had independent origins, with magmas derived from contrasting, internally heterogeneous source rocks. For both the RCR and the Pyalong pluton, the sources were old metasedimentary rocks, while the magmas for the Baynton and Beauvallet plutons formed through partial melting of metadacitic to meta-andesitic rocks, probably with an admixture of immature volcaniclastic graywackes. The source rocks for the Baynton magmas were more crustally evolved than those for the Beauvallet magmas. Heterogeneity in the Baynton pluton did not result from crystal fractionation or magma mixing, despite the relatively high abundance of igneoustextured microgranular enclaves (MEs). The MEs show neither chemical nor isotope mixing trends with each other or with the host magmas. Variations in the Baynton magmas were derived from the heterogeneity of the source terrane, with individual magma batches formed from mixtures of metaigneous and metasedimentary rocks. Baynton MEs are isotopically less evolved than their host rocks. Their chemistry, textures, and field relations suggest that they represent small volumes of hybrid magmas formed through near-source mixing between crustal melts and mantlederived mafic magmas. Further modification occurred through melt loss and ingestion of host crystals as the MEs were deformed, in the plastic state, during magmatic flow of their hosts. [ABSTRACT FROM AUTHOR]

Ulleung Island is the top of a 3000 m (from sea floor) intraplate alkalic volcanic edifice in the East Sea/Sea of Japan. The emergent 950 m consist of a basaltic lava and agglomerate succession (Stage 1, 1·37–0·97 Ma), intruded and overlain by a sequence of trachytic lavas and domes, which erupted in two episodes (Stage 2, 0·83–0·77 Ma; Stage 3, 0·73–0·24 Ma). The youngest eruptions, post 20 ka bp, were explosive, generating thick tephra sequences of phonolitic composition (Stage 4), which also entrained phaneritic, porphyritic and cumulate accidental lithics. Major element chemistry of the evolved products shows a continuous spectrum of trachyte to phonolite compositions, but these have discordant trace element trends and distinct isotopic characteristics, excluding a direct genetic relationship between the two end-members. Despite this, the Stage 3 trachytes and some porphyritic accidental lithics have chemical characteristics transitional between Stage 2 trachytes and Stage 4 phonolites. Within the phonolitic Stage 4 tephras three subgroups can be distinguished. The oldest, Tephra 5, is considerably enriched in incompatible elements and chondrite-normalized rare earth element (REE) patterns display negative Eu anomalies. The later tephras, Tephras 4–2, have compositions intermediate between the early units and the trachyte samples, and their REE patterns do not have significant Eu anomalies. The last erupted, Tephra 1, from a small intra-caldera structure, has a distinct tephriphonolite composition. Trace element and isotopic chemistry as well as textural characteristics suggest a genetic relationship between the phaneritic lithics and their host phonolitic pumices. The Stage 4 tephras are not related to earlier phases of basaltic to trachytic magmatism (Stages 1–3). They have distinct isotopic compositions and cannot be reliably modelled by fractional crystallization processes. The differences between the explosive phonolitic (Stage 4) and effusive trachytic (Stage 2–3) eruptions are mainly due to different pre-eruptive pressures and temperatures, causing closed- versus open-system degassing. Based on thermodynamic and thermobarometric modelling, the phonolites were derived from deeper (subcrustal) magma storage and rose quickly, with volatiles trapped until eruption. By contrast, the trachytes were stored at shallower crustal levels for longer periods, allowing open-system volatile exsolution and degassing before eruption. [ABSTRACT FROM PUBLISHER]

Jeju is a volcanic field that has erupted from around 1·8 Myr to c. 1 kyr ago. Activity began with dispersed, basaltic, monogenetic, phreatomagmatic eruptions. Continuing monogenetic volcanism was later joined by more voluminous lava effusion events building a central composite shield. Samples from older (>0·7 Ma) and younger (<0·2 Ma) monogenetic centres were analysed for their whole-rock major element, trace element and Sr–Nd–Pb isotopic compositions. Pyroclastic products from the monogenetic centres are dominantly alkali basalt to trachybasalt, whereas the more voluminous lava flows and domes of the central edifice consist of subalkali basalt and alkali basalt to trachyte. Lavas from the Early Pleistocene monogenetic centres are depleted in MgO, Cr and Ni, reflecting considerable olivine fractionation. By contrast, Late Pleistocene–Holocene monogenetic centre magmas fractionated clinopyroxene + olivine at deeper levels. Isotopic compositions show little variation across the suite; however, the Late Pleistocene–Holocene monogenetic centres have generally lower 87Sr/86Sr and 208Pb/204Pb and higher 143Nd/144Nd than the older centres and subalkali lavas. Major and trace element and isotope data suggest a common, shallower source for the high-Al alkali and subalkali lavas, in contrast to a deeper source for the low-Al alkali magmas. We propose that mantle melting was initiated under partially hydrous conditions at a pressure of near 2·5 GPa, followed by drier conditions and extension of the melting zone to 3–3·5 GPa, with a concomitant increase in the volume of melt derived from the shallower part of the system to produce subalkaline magmas. Increasing melt production at shallow depths may be related to accelerated heat transfer resulting from deepening of the melting zone, or increased mantle upwelling. Mantle lenses were uplifted, probably lubricated by shear zones created during the opening of the Sea of Japan c. 15 Myr ago, and reactivated during rotation of the Philippine Sea plate direction of subduction at around 2 Ma. This is the first hypothesized link between subduction processes and intraplate volcanism at Jeju. [ABSTRACT FROM PUBLISHER]

The kimberlite rocks of the Udachnaya-East pipe (Siberia) are uniquely fresh and contain very high abundances of primary volatiles (Cl, CO2, S). Alkali elements and chlorine are extremely abundant in the reconstructed kimberlite melt compositions, and this enrichment is very important for our understanding of deep-mantle melting and melt transport. Here we present new isotopic data that confirm a mantle origin for these kimberlitic chlorides and carbonates, and constrain the kimberlite emplacement age as ca. 347 Ma. The initial Nd and Pb isotope ratios in a large salt aggregate, in a Cl-S-enriched water leachate of the groundmass, and in the silicate fraction of the groundmass are very similar (ϵNd = +3 to +4, 206Pb/204Pb = 18.6, 207Pb/204Pb = 15.53), implying a comagmatic origin of the chlorides and carbonates and the silicates. Combined Sr, Nd, and Pb isotope data are used to rule out any significant contributions to the kimberlite chlorine budget from crustal sources, such as the Cambrian evaporite sequences of the Siberian platform. Our data support the interpretation that exsolved Na-K chloride and Na-K-Ca carbonate formed directly from original uncontaminated kimberlite magma. High Cl abundances in kimberlites suggest the presence of a Cl-rich reservoir in the deep sublithospheric mantle. [ABSTRACT FROM AUTHOR]

The South Auckland Volcanic Field is a Pleistocene (1·59–0·51 Ma) basaltic intraplate, monogenetic field situated south of Auckland City, North Island, New Zealand. Two groups of basalts are distinguished based on mineralogy and geochemical compositions, but no temporal or spatial patterns exist in the distribution of various lava types forming each group within the field: Group A basalts are silica-undersaturated transitional to quartz-tholeiitic basalts with relatively low total alkalis (3·0–4·6 wt %), Nb (7–29 ppm), and (La/Yb)N (3·4–7·6); Group B basalts are strongly silica-undersaturated basanites to nepheline-hawaiites with high total alkalis (3·3–7·9 wt %), Nb (32–102 ppm), and (La/Yb)N (12–47). Group A has slightly higher 87Sr/86Sr, similar ɛNd, and lower 206Pb/204Pb values compared with Group B. Contrasting geochemical trends and incompatible element ratios (e.g. K/Nb, Zr/Nb, Ce/Pb) are consistent with separate evolution of Groups A and B from dissimilar parental magmas derived from distinct sub-continental lithospheric mantle sources. Differentiation within each group was controlled by olivine and clinopyroxene fractionation. Group B magmas were generated by <8% melting of an ocean island basalt (OIB)-like garnet peridotite source with high 238U/204Pb mantle (HIMU) and enriched mantle (EMII) characteristics possibly inherited from recycled oceanic crust. Group A magmas were generated by <12% melting of a spinel peridotite source also with HIMU and EMII signatures. This source type may have resulted from subduction-related metasomatism of the sub-continental lithosphere modified by a HIMU plume. These events were associated with Mesozoic or earlier subduction- and plume-related magmatism when New Zealand was at the eastern margin of the Gondwana supercontinent. [ABSTRACT FROM PUBLISHER]

Presents a study which revealed significant isotopic heterogeneity on a single crystal and also inter-mineral scale in a pluton which shows well constrained evidence for magma mingling in Australia. Details on magma mingling and mixing; Importance of megacrysts in enclaves; Methodology; Ability of feldpars to record isotopic change in magmatic systems.

The Deddick Granodiorite, a mafic S-type pluton in the Lachlan Fold Belt, contains abundant enclaves. Most are derived from high-grade metasediments of pelitic–psammitic composition, and migmatites are common. Among these, discrete fragments of melanosomes rich in cordierite and garnet are restites from partial melting. However, compositional and Nd–Sr isotopic data indicate they are not restite in equilibrium with the melt component of the host magma, but may have formed part of a spectrum of diverse magma source lithologies. Alternatively, they may be accidental xenoliths. Regardless of their origin, data for these enclaves suggest their precursors could represent deeply buried age equivalents of the ubiquitous Ordovician turbidites of the Lachlan Fold Belt. Three types of microgranular enclaves with igneous textures are distinguished. The most common type are small and rounded mafic enclaves of tonalitic composition. They carry xenocrysts derived from the host magma, and some contain high-Mg pyroxene derived from a mafic magma. Isotopic data form an array with εNd from −6 to −12, and 87Sr/86Sr from 0.7130 to 0.7167 (host rock −10 and 0.715, respectively). These enclaves formed as globules of hybrid mafic magma commingled with, and contaminated by, the more felsic host magma. Other enclave types were derived from disrupted syn-plutonic dykes having a distinct isotopic composition, and from a cogenetic marginal facies of the host. [ABSTRACT FROM AUTHOR]

We present new high-precision geochemical and isotopic data showing that magmas related to the Central Atlantic Magmatic Province (CAMP) were emplaced at the base of the continental crust in the Ivrea Zone of northwest Italy. These results significantly extend the known footprint of one of the largest examples of a large igneous province (LIP) on the planet. The La Balma--Monte Capio (LBMC) intrusion ranges from dunitic at the base to plagioclasebearing pyroxenitic at the top. Zircons were extracted from two samples at different levels, and dated using the chemical abrasion--isotope dilution--thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb method. The two weighted-mean 206Pb/238U ages at 200.5 ± 0.3 Ma and 200.1 ± 0.5 Ma indicate a short-lived magmatic system that fractionated in place. The timing of emplacement is different from that of all other mafic-ultramafic intrusions in the Ivrea Zone and is consistent with magmatism associated with the CAMP. We suggest that exposure in the Ivrea Zone provides a unique glimpse into the presently unknown character of LIP magmas at the base of the continental crust, where the emplacement of this intrusion was facilitated by its location at a lithospheric suture. [ABSTRACT FROM AUTHOR]

• Western side of study area consists of ∼300 × 50 km corridor of variably sediment-fluxed mantle wedge-sourced volcanic rocks. • Eastern side of study area consists of ∼400 km corridor of back arc-like volcanic rocks. • Multiple 2820–2838 Ma magmatic units show evidence for hydrous melt compositions. • AncientAncient isotopic input into sub-Youanmi mantle interpreted as subduction of Narryer Terrane crust under the Youanmi Terrane. This study defines a comprehensive chemostratigraphic framework for the 2820–2738 Ma magmatic rocks of the northwestern Youanmi Terrane of the Yilgarn Craton. Sixteen chemostratigraphically distinct units can be correlated between greenstone belts that are separated by later voluminous granitic plutons. On a regional scale, the chemostratigraphic units define discontinuous, broadly NNE striking zones up to 350 km long and 50 km wide (including later granitic plutons). Neodymium isotope and trace element systematics of magmatic rocks require an increasing component of metasomatised mantle from c. 2820 to 2738 Ma and variable recycling of a 3050–2920 Ma crustal component. We interpret the first magmatic episode at 2820–2782 Ma to reflect lithospheric thinning and asthenosphere upwelling in a back-arc-like setting and attribute the metasomatism of sources for multiple mafic units to subduction of 3050–2920 Ma, predominantly isotopically juvenile, mafic crust. Following an approximate 16 Ma hiatus, a second magmatic episode at 2766–2738 Ma is dominated by crustal-derived transitional TTGs with lower volumes of mantle-derived shoshonitic and sanukitoid-like rocks, and LILE-LREE enriched tholeiitic mafic to felsic rocks. The compositions of the transitional TTG and shoshonitic rocks in this study area are similar to potassic granites and shoshonitic rocks (including shoshonitic lamprophyres) from post-orogenic continental collision settings, such as the Mesozoic Tibetan Plateau. We interpret this later episode as reflecting post-orogenic melting of crustal and upper (modified) mantle sources caused by upwelling mantle related to delamination of arc-crust or slab breakoff. The northwestern Youanmi Terrane preserves an extensive package of Archean magmatic rocks that can be confidently attributed to subduction-magmatism and provides a reference point to show that some form of subduction occurred in the Meso-Neoarchean. [ABSTRACT FROM AUTHOR]

Highlights • The youngest known (2 Ma) volcanically-active subduction system. • Exceptionally diverse range of magma compositions coeval and spatially juxtaposed. • Mixing of an upwelling asthenospheric mantle melt and a slab melt. • Modern example of an immature subduction system building its proto forearc. • Modern analog of the environment where SSZ ophiolites lithosphere forms. Abstract The development of ideas leading to a greater understanding of subduction initiation is limited by the scarcity of present-day examples. Furthermore, the few examples identified so far unfortunately provide few insights into the nature of magmatism at the inception of subduction. Here we report new observations from the Matthew and Hunter (M&H) subduction zone, a very young subduction zone located in the South-West Pacific. Tectonics of the area show it is younger than 2 Ma, making the M&H the youngest known volcanically-active subduction system and hence providing unique insights into the earliest stages of subduction initiation. Volcanism in this area comprises an exceptionally diverse range of contemporaneously erupting magma compositions which are spatially juxtaposed. Pb isotopic compositions and abundance of LILE and REE strongly suggest melting of upwelling asthenospheric mantle (Indian MORB) and subducted oceanic crust (Pacific MORB of the South Fiji Basin) and the mixing of these two components. Volcanism occurs much closer to the trench compared to volcanism in more mature subduction zones. We demonstrate that the M&H subduction zone is a modern example of an immature subduction system at the stage of pre-arc, near-trench magmatism. It is not yet building an arc but what we propose to call a Subduction Initiation Terrane (SITER). Today, the proto-forearc of the M&H subduction zone is a collage of these SITERs, coeval back-arc domains and remnants of pre-existing terranes including old Vitiaz Arc crust. The M&H area represents a modern analog of a Supra Subduction Zone setting where potentially a majority of ophiolites have formed their crustal and lithospheric components. Present-day magmatism in the M&H area therefore provides clues to understanding unforeseen distribution of contrasted magmatic rock types in fossil forearcs, whether they are at the front of mature subduction zones or in ophiolites. [ABSTRACT FROM AUTHOR]

The lack of consensus on the possible range of initial kimberlite melt compositions and their evolution as they ascend through and interact with mantle and crustal wall rocks, hampers a complete understanding of kimberlite petrogenesis. Attempts to resolve these issues are complicated by the fact that kimberlite rocks are mixtures of magmatic, xenocrystic and antecrystic components and, hence, are not directly representative of their parental melt composition. Furthermore, there is a lack of direct evidence of the assimilation processes that may characterise kimberlitic melts during ascent, which makes understanding their melt evolution difficult. In this contribution we provide novel constraints on the interaction between precursor kimberlite melts and lithospheric mantle wall rocks. We present detailed textural and geochemical data for a carbonate-rich vein assemblage that traverses a garnet wehrlite xenolith [equilibrated at ~ 1060 °C and 43 kbar (~ 140–145 km)] from the Bultfontein kimberlite (Kimberley, South Africa). This vein assemblage is dominated by Ca–Mg carbonates, with subordinate oxide minerals, olivine, sulphides, and apatite. Vein phases have highly variable compositions indicating formation under disequilibrium conditions. Primary inclusions in the vein minerals and secondary inclusion trails in host wehrlite minerals contain abundant alkali-bearing phases (e.g., Na–K bearing carbonates, Mg-freudenbergite, Na-bearing apatite and phlogopite). The Sr-isotope composition of vein carbonates overlaps those of groundmass calcite from the Bultfontein kimberlite, as well as perovskite from the other kimberlites in the Kimberley area. Clinopyroxene and garnet in the host wehrlite are resorbed and have Si-rich reaction mantles where in contact with the carbonate-rich veins. Within some veins, the carbonates occur as droplet-like, globular segregations, separated from a similarly shaped Si-rich phase by a thin meniscus of Mg-magnetite. These textures are interpreted to represent immiscibility between carbonate and silicate melts. The preservation of reaction mantles, immiscibility textures and disequilibrium in the vein assemblage, suggests quenching, probably triggered by entrainment and rapid transport toward the Earth's surface in the host kimberlite magma. Based on the Sr-isotope systematics of vein carbonate minerals, and the close temporal relationship between carbonate-rich metasomatism and kimberlite magmatism, we suggest that the carbonate-rich vein assemblage was produced by the interaction between a melt genetically related to the Bultfontein kimberlite and wehrlitic mantle wall rock. If correct, this unique xenolith sample provides a rare snapshot of the assimilation processes that might characterise parental kimberlite melts during their ascent through the lithospheric mantle. [ABSTRACT FROM AUTHOR]

Abstract: An ultrabasic/ultramafic composition of kimberlite magmas is difficult to reconcile with existing models of the kimberlite mantle source and melting conditions, inferred magma temperatures and rheological properties, and the style of magma ascent and emplacement. The inconsistencies in current thinking indicate serious flaws in understanding kimberlite magma compositions. Much of the uncertainty over true kimberlite compositions may stem from almost ubiquitous hydration and leaching of kimberlite rocks. This study presents petrographic and geochemical data for kimberlite samples largely unaffected by postmagmatic modification, from the Devonian Udachnaya–East pipe in Siberia. These samples are unusually enriched in chlorine and sodium, yet they are essentially anhydrous. These features are consistent with the phase composition of the groundmass which is dominated by minerals such as Na-Ca carbonates, Na–K chlorides and sulphates which appear to be – in our samples – co-magmatic with common silicates and oxides, but are unknown in other kimberlites, or rarely found within magmatic assemblages. We suggest that a kimberlite parent melt of essentially non-silicate composition, with high concentrations of alkalis, CO2 and Cl may be a viable alternative to the currently favoured water-rich, high-Mg model primary melt. Entrainment of mantle silicates into such a melt en route to the surface, followed by gravitational accumulation of mantle olivine and liquidus oxides (perovskite, Cr-spinel) at the bottom of vertically extensive magma bodies after emplacement, would explain the observed properties of kimberlite magma/rock, notably enrichment in olivine and trace elements in the hypabyssal kimberlite facies. A carbonate melt composition would retain attributes of the standard model such as trace element enrichment via low degrees of partial melting, it would explain low temperatures of crystallisation and the exceptional rheological properties that enable kimberlite primary melts to segregate from the lithospheric source and buoyantly ascend at high speed, while mixing and reacting with country rocks. [Copyright &y& Elsevier]

Abstract: Jeju Island is the emergent portion of a basaltic volcanic field developed over the last c. 1.8Ma on continental crust. Initial volcanism comprised dispersed, small-volume (<0.01km3) alkali basaltic eruptions that incrementally constructed a tuff pile. Lavas and scoria from continuing small-scaled monogenetic volcanism capped this foundation. From c. 0.4Ma large-volume (>1km3) eruptions began, with lavas building a composite shield. Three magma suites can be recognized: Early Pleistocene high-Al alkali (HAA), and Late Pleistocene to Holocene low-Al alkali (LAA) and subalkali (SA). The chemical similarity between small-volume and primitive large-volume eruptions suggests analogous parent magmas and fractionation histories that are independent of erupted volumes. The large-volume magmas evolved to trachyte, which erupted in two distinct episodes: the HAA Sanbangsan suite at c. 750ka and the LAA Hallasan suite at c. 25ka. Sr and Nd isotopes indicate that the early trachytes were contaminated by upper crustal material, whereas the later magmas were not. Both suites bear a Nd isotope signature indicative of lower crustal interaction. Sub-suites transitional between HAA and LAA, and between LAA and SA, indicate that melting occurred in discrete, but adjacent, mantle domains. Throughout the evolution of this volcano, each magma batch erupted separately, and a centralized plumbing system was never created. The Island''s central peak (Mt. Halla 1950ma.s.l.) is therefore not a sensu stricto stratovolcano, but marks the point of peak magma output in a distributed magmatic system. Jeju''s shape and topography thus represent the spatial variation of fertility of the mantle below it. An increase in melt production in the Late Pleistocene was related to a deepening of the melting zone due to regional tectonic rearrangements. Temporal coincidences between magmatic pulses on Jeju and large-scale caldera eruptive events along the nearest subduction system in Kyushu, Japan, suggest that tectonic extension and changing strain rates may drive volcanism on a regional basis, influencing the intraplate volcanism of Jeju Island. [Copyright &y& Elsevier]

Kimberlite magmas, as the deepest probe into Earth's mantle (>150 km), can supply unique information about volatile components (hydrogen, carbon, chlorine, sulfur) in mantle-derived melts and fluids. All known kimberlite rocks are not suitable for studies of mantle volatiles because of their pervasive postmagmatic alteration; however, this study discusses an exceptionally fresh group I kimberlites (<0.5 wt% H2O) from the Udachnaya-East diamondiferous pipe in Siberia. Kimberlite groundmass, in addition to euhedral olivine and calcite, is extremely enriched (at least 8 wt%) in water-soluble alkali chlorides, alkali carbonates, and sulfates (ratio 5:3:1), and often shows immiscibility textures. A primary magmatic origin of alkali chlorides and alkali carbonates is confirmed by the study of strontium isotopes in the water- and dilute acid-leachates of the groundmass (87Sr/86Sr = 0.7069 and 0.7050) that contrast with much more radiogenic isotope composition of the Cambrian platform sedimentary rocks and the Udachnaya-East mine-site brines. Melt inclusions in groundmass olivine, composed of halite, sylvite, alkali-Ca carbonates, phlogopite, olivine, and CO2 fluid, were used to determine the composition and evolution of the kimberlite melt prior to emplacement. Melt inclusions show immiscibility between chloride and carbonate liquids at <600 °C in heating stage experiments. The chloride and carbonate enrichment in the kimberlite parental magma suggests the presence of a powerful agent for chemical modifications (metasomatism) in the mantle and crust. [ABSTRACT FROM AUTHOR]

Tectonic reconstructions of the Cretaceous paleo-Pacific system show several significant tectonic and magmatic events, including the formation of several spreading centers, microplates and intra-oceanic arcs, and the initiation (>76–81 Ma) of magmatic activity which formed the Emperor-Hawaiian seamount chain. The Olyutorsky (syn. Achayvayam-Valaginsky, ~80 Ma) and Kronotsky (~90 Ma) intra-oceanic arcs were formed in the NW part of the paleo-Pacific and migrated northwest until their accretion onto the NW Asia margin in the Late Paleocene – Early Eocene and Late Eocene – Early Miocene, respectively. Tectonic remnants of these arcs are preserved as volcanic-sedimentary terranes in the accretionary basement of the Kamchatka Peninsula (Russia). Fragments of the Olyutorsky terrane (OT) are exposed in Eastern Kamchatka, including (from south to north) in the Valaginsky Range (VR), Tumrok Range (TR), and Koryak Highlands (KH). The OT volcanic rocks are characterized by unusually primitive mafic-ultramafic compositions, with low- and high-K characteristics in the north (KH) and high-K in the south (VR and TR), respectively. The primitive compositions of these olivine-phyric (picrites) and basalts provides an opportunity to characterize the magmatic sources of intra-oceanic arcs during the Cretaceous. High-Mg compositions in TR and VR (up to 40 wt% MgO) contain olivine phenocrysts with Fo content up to 94 mol% and high-Cr# spinel (up to 87 mol%), suggesting formation from an unevolved initial melt. Melt inclusions in spinel and olivine are Mg-rich (up to 15 wt% MgO) and have high K 2 O contents (1.8–3.7 wt% for TR, and 2.3–3.9 wt% for VR). Picrite whole-rock compositions show strong HFSE depletion and LILE enrichment typical of modern arc rocks. However, LREE-Th enrichment is observed only in VR picrites, suggesting subduction-related modification is particularly strong in the source of magmas erupted in the southern OT. Isotopic compositions in OT picrites (87Sr/86Sr 80 0.7026 to 0.7039, ε Nd80 ± 10.6 to +8.4, ε Hf80 + 20.6 to +16.7) resemble those in modern MORB (particularly Indian MORB) and arc picrites, suggesting that primitive OT arc magmatism originates in mantle wedge peridotite modified by melts and fluids derived from subducted oceanic crust without obvious contributions from continental and oceanic sediments. Compositional similarities between OT arc rocks and coeval early magmatism in the Emperor-Hawaiian melting anomaly suggests that the depleted component of the latter was an Indian-type MORB mantle in the paleo-Pacific region at the start of the Late Cretaceous. Longitudinal variations in OT magmas compositions (e.g. high-K signature, subtly higher 87Sr/86Sr-206Pb/204Pb, and lower ε Nd -ε Hf in VR and TR) may be related to subduction of thicker and possibly older lithosphere in the southern segment of the Olyutorsky arc. Steeper dip angle and stronger deformation/flexure of the subducting plate below this part of the arc could drive the percolation of low-degree alkaline melts from the asthenosphere through the slab, resulting in generation of the "petit-spot" volcanoes, similar to those in the modern Japan Trench. Further subduction of such alkali-volcanoes may produce the high-K geochemical signature recorded in the southern OT arc terranes. [ABSTRACT FROM AUTHOR]