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Showing papers on "Incompatible element published in 2017"


Journal ArticleDOI
TL;DR: In this paper, the authors examined the interplay of crustal thickness and magmatic differentiation using a global geochemical dataset compiled from active volcanic arcs and elevation as a proxy for thickness.

137 citations


Journal ArticleDOI
01 May 2017-Geology
TL;DR: In this paper, an integrated study of in situ Hf-O isotopes in zircons from two Triassic alkaline complexes in the northeastern Sino-Korean craton is presented.
Abstract: Post-orogenic and intraplate extensional alkaline rocks are believed to have formed by partial melting of metasomatized ultramafic rocks in the subcontinental lithospheric mantle. Their variable incompatible element abundances and radiogenic isotopic ratios reflect recycling of subducted oceanic or continental crustal material into their source reservoirs. However, whole-rock geochemical and Sr-Nd isotopic data do not well constrain the nature of this recycled crustal material because of complex petrogenetic processes, i.e., crustal assimilation, fractional crystallization, magma mixing, and post-magmatic alteration. Here we present an integrated study of in situ Hf-O isotopes in zircons from two Triassic alkaline complexes in the northeastern Sino-Korean craton, i.e., the Hekanzi and Saima alkaline complexes. The Hekanzi alkaline rocks have zircon eHf(t) values of —2.5 to +0.6 and sub-normal mantle δ18O (+3.8‰ to +5.4‰), indicating a component of high-temperature altered oceanic crust involved in their mantle source prior to magma generation. In contrast, the Saima alkaline rocks have extremely negative zircon eHf(t) (—11 to —14) and elevated δ18O (+7.1‰ to +8.4‰) values, suggesting continental crust recycled into their mantle source prior to magma generation. Our results show that the combined zircon Hf and O isotopes are powerful tracers to distinguish recycled continental crust from recycled oceanic crust and, importantly, provide compelling evidence for recycled continental crust in the sources of alkaline rocks.

69 citations


Journal ArticleDOI
TL;DR: In this paper, the authors focus on the Lower Cretaceous volcanic rocks in the Nagqu area, northern Lhasa subterrane, and present their zircon LA-ICP-MS U-Pb ages, in situ Hf isotopic data, whole-rock major and trace element compositions, and Sr-Nd isotope data.

59 citations


Journal ArticleDOI
TL;DR: The Central Tianshan Block (CTB) is one of the major continental constituents of the western Central Asian Orogenic Belt (CAOB) and its nature and origin is essential for understanding the accretionary processes and the reconstruction of the architectural framework of the CAOB.

59 citations


Journal ArticleDOI
TL;DR: The trace element content of magnetite from precisely known geographic locations and geologic environments from the Precambrian magnetite-apatite ore and host rocks in Kiruna, Sweden, and the Pliocene-Holocene El Laco volcano in the Atacama desert of Chile was analyzed in this paper.
Abstract: Interpretation of the mineralizing environment of magnetite-apatite deposits remains controversial with theories that include a hydrothermal or magmatic origin or a combination of those two processes. To address this controversy, we have analyzed the trace element content of magnetite from precisely known geographic locations and geologic environments from the Precambrian magnetite-apatite ore and host rocks in Kiruna, Sweden, and the Pliocene-Holocene El Laco volcano in the Atacama desert of Chile. Magnetite samples from Kiruna have low trace element concentrations with little chemical variation between the ore, host, and related intrusive rocks. Magnetite from andesite at El Laco, and dacite from the nearby Lascar volcano, has high trace element concentrations typical of magmatic magnetite. El Laco ore magnetite have low trace element concentrations and displays growth zoning in incompatible elements (Si, Ca, and Ce), compatible elements (Mg, Al, and Mn), large-ion lithophile element (Sr), and high field strength element (Y, Nb, and Th). The El Laco ore magnetite are similar in composition to magnetite that has been previously interpreted to have crystallized from hydrothermal fluids; however, there is a significant difference in the internal zoning patterns. At El Laco, each zoned element is either enriched or depleted in the same layers, suggesting the magnetite crystallized from a volatile-rich, iron-oxide melt. In general, the compositions of magnetite from these two deposits plot in very wide fields that are not restricted to the proposed fields in published discriminant diagrams. This suggests that the use of these diagrams and genetic models based on them should be used with caution.

58 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that Magnesiocarbonatites are characterized by extreme enrichment in incompatible elements with high total rare earth element (REE) contents of 372-36965ppm.

57 citations


Journal ArticleDOI
TL;DR: Zhang et al. as discussed by the authors studied the early Paleozoic dioritic and granitic plutons in the Eastern Tianshan Orogenic Belt (ETOB) in order to constraint the initiation of a magmatic arc formed in this region.

54 citations


Journal ArticleDOI
TL;DR: The Qiangtang flood basalt province (QFBP) as mentioned in this paper was recently recognized in northern Tibet, China, and it erupted during the Sakmarian-Kungurian and covered an area of > 6.84×10 5 ǫkm 2, reaching a maximum thickness of 1.5-2.0 ǔ.

53 citations


Journal ArticleDOI
TL;DR: The Takidani pluton as mentioned in this paper is one of the few locations where melt extraction from a crystal mush is preserved in the natural rock record, making it an extremely good case study for investigating the generation of evolved melt reservoirs in the upper crust.
Abstract: The Takidani pluton represents one of a few locations where melt extraction from a crystal mush is preserved in the natural rock record, making it an extremely good case study for investigating the generation of evolved melt reservoirs in the upper crust. Located in the Japan Alps, the Takidani pluton shows a clear vertical zonation consisting of granite and granodiorite in the lower and mid- dle section, a fine-grained porphyritic granitic unit in the upper section and a marginal granodiorite at the roof contact with the host-rock. We present a detailed petrographic and geochemical study using samples collected along a section that traverses the entire vertical section of the pluton. No sharp contacts are found between units. Instead, gradual changes in rock fabric and mineralogy are observed between the lower granodiorite and overlying porphyritic unit. Major and trace elem- ent bulk-rock compositions show sigmoidal variations from the bottom to top of the pluton. Incompatible elements and silica contents increase roofwards within the porphyritic unit. Plagioclase chemistry reveals three main crystal populations (P1, P2 and P3) with Fe contents increasing towards the base of the pluton. Comparison with existing crystallization experiments, thermobarometry and hygrometry indicate that the magmas were emplaced at around 200 MPa, 850–900 C and bulk water contents of 3–4wt %. Whole-rock major and trace element analyses to- gether with mineral chemistry and textural observations suggest that the fine-grained porphyritic unit was extracted from the underlying granodiorite at temperatures between 800 and 740 C and crystallinities of 45–65 wt %. Radiogenic isotopes indicate only minor assimilation (2–6 wt %) and support melt evolution through crystal fractionation. The fine-grained matrix of the porphyritic unit may have been the result of pressure quenching associated with a volcanic eruption.

46 citations


Journal ArticleDOI
TL;DR: In this paper, high-precision isotopic and trace element data for 49 of the most primitive arc magmas from seven major High Cascades volcanic centers are used to assess whether the basalt groups are derived from geochemically distinct mantle sources.

40 citations


Journal ArticleDOI
TL;DR: In this paper, the Rodinia supercontinent of the Neoproterozoic mafic magmatism in the western segment of the Jiangnan Orogen in South China was evaluated.

Journal ArticleDOI
TL;DR: In this article, the authors compare the Manihiki volcanic rocks and Troodos boninites using a new dataset on the major and trace element composition of whole rocks and glasses from these locations, and new high-precision, electron microprobe analyses of olivine and Cr-spinel in these rocks.
Abstract: High-Mg, low-Ti volcanic rocks from the Manihiki Plateau in the Western Pacific share many geochemical characteristics with subduction-related boninites such as high-Ca boninites from the Troodos ophiolite on Cyprus, which are believed to originate by hydrous re-melting of previously depleted mantle. In this paper we compare the Manihiki rocks and Troodos boninites using a new dataset on the major and trace element composition of whole rocks and glasses from these locations, and new high-precision, electron microprobe analyses of olivine and Cr-spinel in these rocks. Our results show that both low-Ti Manihiki rocks and Troodos boninites could originate by re-melting of a previously depleted lherzolite mantle source (20–25% of total melting with 8–10% melting during the first stage), as indicated by strong depletion of magmas in more to less incompatible elements (Sm/Yb 0.5). In comparison with Troodos boninites, the low-Ti Manihiki magmas had distinctively lower H2O contents ( 2 wt% in boninites), ~ 100 °C higher liquidus temperatures at a given olivine Fo-number, lower fO2 (ΔQFM + 0.2) and originated from deeper and hotter mantle (1.4–1.7 GPa, ~ 1440 °C vs. 0.8–1.0 GPa, ~ 1300 °C for Troodos boninites). The data provide new evidence that re-melting of residual upper mantle is not only restricted to subduction zones, where it occurs under hydrous conditions, but can also take place due to interaction of previously depleted upper mantle with mantle plumes from the deep and hotter Earth interior.

Journal ArticleDOI
01 Feb 2017-Lithos
TL;DR: In this paper, the authors analyzed whole-rock major and trace elements and Pb isotope ratios of Cenozoic basalts in Southeast China to investigate their mantle source characteristics and melting process.

Journal ArticleDOI
TL;DR: In this article, the authors investigated Carboniferous-Permian, Triassic and Jurassic igneous basement rocks around the Erlian Basin in northeast China through detailed mineralogical, whole-rock geochemistry, geochronological data and Sm-Nd isotope studies.
Abstract: Carboniferous–Permian, Triassic and Jurassic igneous basement rocks around the Erlian Basin in northeast China have been investigated through detailed mineralogical, whole-rock geochemistry, geochronological data and Sm–Nd isotope studies. Carboniferous–Permian biotite granites and volcanic rocks belong to a calc-alkaline association and were emplaced during the Late Carboniferous–Early Permian (313 ± 1–286 ± 2 Ma). These rocks are characterised by positive eNd(t) (3.3–5.3) and fairly young T DM model ages (485–726 Ma), suggesting a dominant derivation from partial melting of earlier emplaced juvenile source rocks. Triassic biotite granites belong to a high-K calc-alkaline association and were emplaced during the Middle Triassic (243 ± 3–233 ± 2 Ma). Their negative eNd(t) (−2 to −0.1) and higher T DM model ages (703–893 Ma) suggest a contribution from Precambrian crust during the magma generation processes, leading to a strong enrichment in K and incompatible elements such as Th and U. Highly fractionated magmas crystallised in U-rich biotite (up to 21 ppm U) and two-mica granites. In biotite granite, the major U-bearing minerals are uranothorite and allanite. They are strongly metamict and the major part of their uranium (90 %) has been released from the mineral structure and was available for leaching. Mass balance calculations show that the Triassic biotite granites may have, at least, liberated ∼14,000 t U/km3 and thus correspond to a major primary uranium source for the U deposits hosted in the Erlian Basin.

Journal ArticleDOI
TL;DR: In this paper, the authors presented a detailed petrological study of a typical eclogitic mantle xenolith from the Roberts Victor kimberlite mine in South Africa and found that its textural and mineralogical features present strong evidence for incipient melting.

Journal ArticleDOI
TL;DR: In this paper, the melting-rock interaction between ascending melt and peridotite results in mantle metasomatism and also leads to compositional modification of the primary melt.
Abstract: Melt-rock interaction between ascending melt and peridotite results in mantle metasomatism and also leads to compositional modification of the primary melt. While this process is known to occur, it is less well understood how the reactions and the composition of the resulting magma temporally evolve. Here whole-rock major and trace element, Sr-Nd-Pb-Hf isotopes, and olivine major element composition of Quaternary Nuominhe basalts in the Greater Khingan Range of northeast China are presented to unravel how melt-rock interaction modified the composition of the high-MgO potassic basalts as time progressed. The Nuominhe basalts are predominantly basanite with high MgO (8.1–16.8 wt %) and high total alkali content (K2O + Na2O = 6.0–9.2 wt %). They have high K2O/Na2O ratios (K2O/Na2O = 0.77–1.24) and low SiO2 and Al2O3 content (SiO2 = 44.4–48.7 wt %, Al2O3 = 10.5–13.2 wt %). They are characterized by enrichment in strongly incompatible elements, positive Ba, K, and Sr and negative Th, U, Zr, Hf, and Ti anomalies, similar to the composition of enriched mantle (EM1)-type oceanic island basalts (OIBs). Their isotopic composition also compares to that of EM1-type OIBs (i.e., with 87Sr/86Sr = 0.70467–0.70483, eNd = −4.1 to −1.5, eHf = −0.3 to 2.3, 206Pb/204Pb = 17.03–17.36). These elemental and isotopic characteristics are consistent with the interpretation that the potassium-rich melts were derived from recycled crustal materials with EM1 signature. Phlogopite-bearing mantle xenoliths and zoned olivine xenocrysts with high Fo89–92 and low CaO ( 0.1 wt %) rim composition record interaction between the ascending melt and mantle peridotite. Basalts erupted during late stages (Late Pleistocene and Holocene) of activity at the Nuominhe volcanic field show notably higher SiO2 content, Rb/Nb, Ba/Nb, K/La, and Ba/La, and lower MgO content than early-stage basalts (Early and Middle Pleistocene), which we infer to reflect a temporally decreasing extent of melt-rock interaction. During early stages of melt ascent, a reaction zone between melt channels and unreacted peridotite formed; at later stages this reaction zone effectively sealed the ascending melt from further reaction, resulting in increasing Rb/Nb, Ba/Nb, K/La, and Ba/La signatures of the erupted lavas.

Journal ArticleDOI
TL;DR: Zircon U-Pb geochronology, Hf isotope and whole-rock geochemistry were performed on the tuffs of the Yeba Formation in the Gangdese magmatic belt, South Tibet.
Abstract: Zircon U-Pb geochronology, Hf isotope and whole-rock geochemistry were performed on the tuffs of the Yeba Formation in the Gangdese magmatic belt, South Tibet. The results are used to detail the age, source nature and tectonic processes that led to the formation of the Gangdese belt. Dating results indicate that the rhyolitic-andesitic tuffs were formed at 174-170 Ma. Positive and variable zircon e Hf(t) values of the rhyolitic tuffs reveal that the source was dominated by juvenile material, however, experienced crustal contamination. The basaltic tuffs have low HREEs, high contents of compatible elements (V and Cr) and no Eu anomaly. In contrast, the rhyolitic-andesitic tuffs show low compatible trace elements, depletion in Eu but enrichment in incompatible elements (Rb, Zr and Hf). According to the discrimination diagrams of P2O5-SiO2 and Th-Rb, the rhyolitic-andesitic tuffs show a close affinity to I-type granitoids. Moreover, these tuffs are marked by significant depletion in Nb, Ta and Ti, plotted in calc-alkaline field, and with the andesitic-rhyolitic tuffs falling into an active continental margin setting. We suggest that these tuffs of the Yeba Formation were probably generated in an active continental margin above the northward subduction of the Neo-Tethyan oceanic lithosphere.

Journal ArticleDOI
TL;DR: In this paper, partial melting experiments at 1 and 1.5 GPa were performed to investigate the melting under mantle conditions of an olivine-websterite (GV10), which represents a natural proxy of secondary pyroxenite.
Abstract: We performed partial melting experiments at 1 and 1.5 GPa, and 1180–1400 °C, to investigate the melting under mantle conditions of an olivine-websterite (GV10), which represents a natural proxy of secondary (or stage 2) pyroxenite. Its subsolidus mineralogy consists of clinopyroxene, orthopyroxene, olivine and spinel (+garnet at 1.5 GPa). Solidus temperature is located between 1180 and 1200 °C at 1 GPa, and between 1230 and 1250 °C at 1.5 GPa. Orthopyroxene (±garnet), spinel and clinopyroxene are progressively consumed by melting reactions to produce olivine and melt. High coefficient of orthopyroxene in the melting reaction results in relatively high SiO2 content of low melt fractions. After orthopyroxene exhaustion, melt composition is controlled by the composition of coexisting clinopyroxene. At increasing melt fraction, CaO content of melt increases, whereas Na2O, Al2O3 and TiO2 behave as incompatible elements. Low Na2O contents reflect high partition coefficient of Na between clinopyroxene and melt ( $$D_{{{\text{Na}}_{ 2} {\text{O}}}}^{{{\text{cpx}}/{\text{liquid}}}}$$ ). Melting of GV10 produces Quartz- to Hyperstene-normative basaltic melts that differ from peridotitic melts only in terms of lower Na2O and higher CaO contents. We model the partial melting of mantle sources made of different mixing of secondary pyroxenite and fertile lherzolite in the context of adiabatic oceanic mantle upwelling. At low potential temperatures (T P < 1310 °C), low-degree melt fractions from secondary pyroxenite react with surrounding peridotite producing orthopyroxene-rich reaction zones (or refertilized peridotite) and refractory clinopyroxene-rich residues. At higher T P (1310–1430 °C), simultaneous melting of pyroxenite and peridotite produces mixed melts with major element compositions matching those of primitive MORBs. This reinforces the notion that secondary pyroxenite may be potential hidden components in MORB mantle source.

Journal ArticleDOI
01 Jul 2017-Lithos
TL;DR: In this article, two Neoproterozoic carbonatite suites of spatially related carbonatites and associated silicate alkaline rocks from Sevattur and Samalpatti, south India, have been investigated in terms of petrography, chemistry and radiogenic-stable isotopic compositions in order to provide further constraints on their genesis.

Journal ArticleDOI
TL;DR: In this paper, a sheet or laccolith shape is inferred for the Penouta peraluminous low-phosphorous granite from the Iberian Massif, and the absence of compositional gaps in variation diagrams, coupled with continuous evolutionary trends of compatible and incompatible elements with height, discard a multi-pulse intrusion and point to a single magma pulse.

Journal ArticleDOI
TL;DR: In this article, the Yichun Ta-Nb deposit is divided into four lithological zones (from bottom upward): two-mica granite, muscovite granite, albite granite, and lepidolite-albite granite zones.

Journal ArticleDOI
TL;DR: ABS5 as discussed by the authors is a forward geochemical and petrological model that can be used to examine the element mass balance in primary arc magmas including the source and nature of slab materials and flux melting of the mantle-wedge peridotite.
Abstract: Arc Basalt Simulator version 5 (ABS5) is a forward geochemical and petrological model that can be used to examine the element mass balance in primary arc magmas including the source and nature of slab materials and flux melting of the mantle-wedge peridotite. The inverse problem approach using ABS5 allows the estimation of intensive and extensive geophysical variables in arc magma genesis. The intensive variables are slab dehydration depth ( P SS ) and temperature ( T SS ) and mantle melting pressure ( P perid ) and temperature ( T perid ). The extensive variables are the amount of slab liquid added to the mantle ( F slab liq ) and the degree of melting of the mantle ( F perid ) along with the amounts of water in the slab liquid ( XH 2 O slab liq ), mantle ( XH 2 O perid ), and magma ( XH 2 O melt ). Subordinate geochemical variables that also can be estimated using ABS5 include the degree of chemical reaction between slab liquids and the solid slab ( %R ); slab liquid fractions derived from igneous oceanic crust [ F liq ( AOC )], sediment [ F liq ( SED )], and metasomatized mantle peridotite layers [ F liq ( DMM )]; and the degree of depletion of the mantle wedge ( %MORB ext ). The mass balances for 26 incompatible elements, six major elements including H 2 O and Sr, Nd, Hf, and Pb isotopes are calculated based on the same scheme. Monte Carlo calculations are used to estimate the aforementioned variables by fitting the calculated magma composition to observed values. This paper describes the ABS5 calculation scheme and presents examples of its successful use. The geophysical variables determined for these example cases are compared with those estimated by other methods. The spatial variations of the magma productivity and implications for the location of the volcanic front are also discussed.

Journal ArticleDOI
21 Sep 2017
TL;DR: The Veria-Naousa ophiolite represents a dismembered unit in north Greece, which includes variably serpentinised lherzolite and harzburgite, locally intruded by a sparse network of dykes or thin layers of websterite and olivine-orthopyroxenite composition as discussed by the authors.
Abstract: The Veria-Naousa ophiolite represents a dismembered unit in north Greece, which includes variably serpentinised lherzolite and harzburgite, locally intruded by a sparse network of dykes or thin layers of websterite and olivine-orthopyroxenite composition. The websterite and the olivine-orthopyroxenite show abundant petrographic and geochemical evidence (relic olivines with mantle affinities, Cr-rich spinels, low Al2O3, depletions in incompatible elements, and concave upwards rare earth element patterns) that they comprise replacive bodies from refractory subarc mantle precursors. The occurrence of these pyroxenites in dykes implies that channelled percolation of melts account for their replacive character. High CaO/Al2O3, low Zr and crystallisation of diopside suggest that a melt of ankaramitic/carbonatitic composition percolated in lherzolite replacing porphyroclastic olivine and forming the pyroxenes in the websterite. At a shallower level, harburgites were impregnated by boninitic melts (inferred by U-shape rare earth element patterns and very rich in Cr spinels) triggering the replacement of porphyroclastic olivine by orthopyroxene for the formation of olivine-orthopyroxenite. These peritectic replacements of olivine commonly occur in a mantle wedge regime. The peculiar characteristics of the Veria-Naousa pyroxenites with LREE and compatible elements enrichments resemble the subarc pyroxenites of Cabo Ortegal implying a similar environment of formation. Whole-rock and mineralogical (spinel and clinopyroxene) compositions are also in favour of a backarc to arc environment. It is recommended that the evolution of the Veria-Naousa pyroxenites record the evolution of the subarc region and the opening of a backarc basin in a broad SSZ setting in the Axios Zone of eastern Greece.

Journal ArticleDOI
TL;DR: In this paper, the authors presented a new comprehensive isotope and trace element dataset for north and central Tongan lavas including high-precision High Field Strength Element measurements, which indicated that significant amounts of Nb and Ta can be mobilized from distinct subducting oceanic lithologies-a process that may probably also operate beneath other island arcs.
Abstract: We present a new comprehensive isotope and trace element dataset for north and central Tongan lavas including high-precision High Field Strength Element measurements. The emphasis of our study is on lavas from the northernmost volcanic islands of Tafahi and Niuatoputapu that exhibit unique compositions compared with other Tongan volcanoes, in particular elevated high-precision Nb/Ta ratios as high as similar to 28. These lavas are extremely depleted in incompatible, fluid-immobile elements such as Ti, Zr, Sc and Yb, suggesting about 6% depletion of their mantle wedge source relative to average upper mantle prior to 20-30% partial melting. The extremely depleted mantle wedge was re-enriched in highly incompatible elements including Nb and Ta from the subducting slab. Three slab components-fluids from altered oceanic crust, pelagic sediments, and Louisville Seamount Chain lavas-have contributed to the source region of the magmas. A fluid from the subducted Louisville lavas has been added after the other two slab components and has radiogenic Pb-206/Pb-204. Components from the altered oceanic crust and Louisville sea-mounts exhibit little Nb/Ta fractionation, as demonstrated by the nearly uniform and mid-ocean ridge basalt-like Nb/Ta ratios. We suggest that the apparently large slab fluid flux beneath Tafahi and Niuatoputapu results from focused flow through subducting Louisville Seamount crust that had no or little sediment cover, allowing the fluids to pass through the subducting lithosphere more efficiently. Thus, the high Nb/Ta ratios indicate that the Louisville-derived fluids had probably equilibrated with residual rutile. Our results imply that significant amounts of Nb and Ta can be mobilized from distinct subducting oceanic lithologies-a process that may probably also operate beneath other island arcs. We propose a model in which the appearance of the subducted seamount signatures some 3-4Myr after their actual subduction is explained by storage in shallow metasomatized lithospheric mantle. This relic Louisville seamount signature is subsequently reactivated and added to transiting magmas 4 Myr later. This reactivation may result from slab rollback of the subducting Pacific plate towards the east. Our new temporal and spatial model also provides a viable explanation for the conundrum of the occurrence of Louisville signatures even though the Louisville seamount chain is, at present, being subducted several hundred kilometres further south.

Journal ArticleDOI
TL;DR: In this paper, combined oxygen isotope and mineral-scale trace element analyses of amoeboid olivine aggregates (AOA) and chondrules in ungrouped carbonaceous chondrite, Northwest Africa 5958.
Abstract: We report combined oxygen isotope and mineral-scale trace element analyses of amoeboid olivine aggregates (AOA) and chondrules in ungrouped carbonaceous chondrite, Northwest Africa 5958. The trace element geochemistry of olivine in AOA, for the first time measured by LA-ICP-MS, is consistent with a condensation origin, although the shallow slope of its rare earth element (REE) pattern is yet to be physically explained. Ferromagnesian silicates in type I chondrules resemble those in other carbonaceous chondrites both geochemically and isotopically, and we find a correlation between 16O enrichment and many incompatible elements in olivine. The variation in incompatible element concentrations may relate to varying amounts of olivine crystallization during a subisothermal stage of chondrule-forming events, the duration of which may be anticorrelated with the local solid/gas ratio if this was the determinant of oxygen isotopic ratios as proposed recently. While aqueous alteration has depleted many chondrule mesostases in REE, some chondrules show recognizable subdued group II-like patterns supporting the idea that the immediate precursors of chondrules were nebular condensates.

Journal ArticleDOI
01 Jul 2017-Lithos
TL;DR: In this article, the major and trace element concentrations of olivine-hosted melt inclusions in basalts from the active Baekdusan volcano were determined to understand better the nature of the mantle source and the geodynamic processes that gave rise to volcanism at this site.

Journal ArticleDOI
01 Jul 2017-Lithos
TL;DR: In this article, the authors used multidimensional discrimination diagrams and conventional normalized multi-element diagrams for the komatiites and high-Mg basalts from the Rio das Velhas and Pitangui greenstone belts.

Journal ArticleDOI
TL;DR: In this paper, elemental and Nd-isotope geochemistry of basement gneisses of the Mangalwar Complex and constrain its origin and evolution are reported.
Abstract: The Banded Gneissic Complex (BGC) of the Aravalli Craton is divided into BGC-I and BGC-II; the BGC-II (central Rajasthan) is comprised of the Sandmata Complex and the Mangalwar Complex. We report elemental and Nd-isotope geochemistry of basement gneisses of the Mangalwar Complex and constrain its origin and evolution. Geochemically, the basement gneisses have been classified as low-SiO 2 gneisses (LSG) and high-SiO 2 gneisses (HSG). Both the LSG and HSG are potassic, calc-alkaline and peraluminous in nature. The LSG are enriched in incompatible (K, Sr, Ba, large ion lithophile elements) and compatible elements (MgO, Cr, and Ni). They display fractionated rare earth element patterns (avg. La N /Yb N = 12.1) with small Eu-anomaly ( δ Eu = 0.9), and exhibit negative anomalies of Nb and Ti in primitive mantle-normalized multi-element diagram. In terms of Nd-isotope geochemistry, the LSG are characterized by e Nd ( t ) = −4.2 and depleted mantle model age of 3.3 Ga. To account for these geochemical characteristics we propose a three-stage petrogenetic model for the LSG: (1) fluids released from dehydration of subducting slab metasomatised the mantle-wedge; (2) the subducting slab underwent slab-breakoff causing upwelling and decompression melting of the asthenosphere during waning stage of subduction; and (3) upwelling asthenosphere provided the requisite heat for partial melting of the metasomatised mantle-wedge leading to generation of the LSG parental magma. Asthenospheric upwelling also contributed in the LSG petrogenesis which is evident from its high Mg# (avg. 0.53). The LSG formed in this way are contemporary and chemically akin to sanukitoids of the BGC-I and Archean sanukitoids reported elsewhere. This provides a basis to consider the LSG as a part of the BGC-I. Contrary to the LSG, the HSG are depleted in compatible elements (MgO = avg. 1.1 wt.%; Cr = avg. 8 ppm; Ni = avg. 6 ppm) but enriched in incompatible elements (Sr = avg. 239 ppm, Ba = avg. 469 ppm). Its e Nd ( t ) values vary from −9.5 to −5.4. These chemical features of the HSG are akin to potassic granitoids found elsewhere. In this backdrop, we propose that the HSG suite of the Mangalwar Complex was derived from re-melting (partial) of an older crust (TTG?) occurring within the BGC-II.

Journal ArticleDOI
TL;DR: Soltan Maidan Basaltic Complex with thickness up to about 1300m is located in the eastern Alborz zone, north of Iran as mentioned in this paper, and is dominantly composed of transitional to mildly alkaline basaltic lava flows, agglomerates and tuffs, together with a few thin sedimentary interlayers.
Abstract: Soltan Maidan Basaltic Complex with thickness up to about 1300 m is located in the eastern Alborz zone, north of Iran. This complex is dominantly composed of transitional to mildly alkaline basaltic lava flows, agglomerates and tuffs, together with a few thin sedimentary interlayers. Field geological evidence and study of palynomorph assemblages in the shale interlayer show Late Ordovician to Early Late Silurian ages. Chondrite- and primitive-mantle normalized multi-element patterns of Soltan Maidan basalts demonstrate enrichment in highly incompatible elements relative to less incompatible ones and their patterns are most similar to OIB. Trace elemental and Sr-Nd isotopic compositions indicate interaction and mixing of asthenospheric mantle source (OIB-type) with enriched subcontinental lithospheric mantle components (EM1-type). This asthenosphere-lithosphere interaction occurred in an extensional continental setting, which resulted in opening of the Paleotethys Ocean in the north of Gondwana during the Late Silurian to Middle Devonian.

Journal ArticleDOI
TL;DR: In this article, the authors report radiogenic isotope (Pb, Sr, Nd, Hf) and geochemical data for twenty-four basalt whole-rock and glass samples collected from the length of the Southern Explorer Ridge (SER) and from Explorer Deep, a rift to the north of the SER.