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Shoji Arai - One of the best experts on this subject based on the ideXlab platform.
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Alkali Basalt from the seifu seamount in the sea of japan post spreading magmatism in a back arc setting
Solid Earth, 2020Co-Authors: Shoji Arai, Tomoaki Morishita, Naoto Hirano, Hirochika Sumino, Hiroshi Sato, Tomoyuki Shibata, Masako Yoshikawa, Rie Nauchi, Akihiro TamuraAbstract:Abstract. We present geochemical and 40Ar∕39Ar age data for a peridotite xenolith-bearing Basalt dredged from the Seifu Seamount (SSM Basalt) in the northeast Tsushima Basin, southwest Sea of Japan. An 40Ar∕39Ar plateau age of 8.33±0.15 Ma (2 σ ) was obtained for the SSM Basalt, indicating that it erupted shortly after the termination of back-arc spreading in the Sea of Japan. The SSM Basalt is a high-K to shoshonitic Alkali Basalt that is characterized by light rare earth element enrichment. The trace element features of the Basalt are similar to those of ocean island Basalt, although the Yb content is much higher, indicating formation by the low-degree partial melting of spinel peridotite. The Nd, Sr, and Pb isotopic compositions of the SSM Basalt differ from those of back-arc basin Basalts in the Sea of Japan. The Sr–Nd isotopic composition of the SSM Basalt suggests its source was depleted mid-ocean ridge mantle containing an enriched mantle (EM1) component. The SSM Basalt was formed in a post-back-arc extension setting by the low-degree partial melting of an upwelling asthenosphere that had previously been associated with the main phase of back-arc magmatism.
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silica and lree enriched spinel peridotite xenoliths from the quaternary intraplate Alkali Basalt jeju island south korea old subarc fragments
Lithos, 2014Co-Authors: Yonghoon Woo, Kyounghee Yang, Youngwoo Kil, Sunghyo Yun, Shoji AraiAbstract:Abstract Spinel harzburgite to lherzolite xenoliths are entrapped in Quaternary intraplate Alkali Basalts on Jeju Island, South Korea. These xenoliths are unusual in containing late-stage secondary orthopyroxene, free of deformation and exsolution that is replacing olivine as the main pervasive metasomatic mineral. These xenoliths are characterized by high Mg# in olivine, orthopyroxene, and clinopyroxene (89–93) and variable Cr# of spinel (9–53), representing residues left after variable degrees of melt extraction (~ 25%). In contrast to their depleted major-element compositions, clinopyroxenes in the xenoliths are enriched in most incompatible trace elements. Clinopyroxenes display enrichment in light rare earth elements (LREE) or spoon-shaped REE with a general enrichment in La over Ce, and depletion in high field strength elements (HFSE; e.g., Nb-Ta, Zr-Hf, Ti). Orthopyroxenes (either primary or secondary) are characterized by low TiO2, high Al2O3, and moderate CaO contents, and resemble those of sub-continental arc peridotites from the eastern Pacific. The geochemical evidence, in addition to the formation of secondary orthopyroxene, indicates that Jeju peridotite xenoliths have been subjected to different degrees of metasomatism by subduction-related silica- and LREE-enriched fluids (or melts). However, chemical equilibrium is evident between the primary and secondary orthopyroxene, implying that the duration of post-metasomatic high temperatures enabled complete resetting/reequilibration of the mineral compositions. The metasomatic enrichment pre-dates the host Jeju Quaternary magmatism, and a genetic relationship with the host magmas is considered unlikely. We therefore propose that the Jeju peridotite xenoliths went through a two-stage evolution, with their composition primarily controlled by early fractional melt extraction, which was subsequently modified by residual slab-derived fluids (or melts). Following enrichment in the peridotite protolith in the mantle wedge, the upper mantle beneath proto-Jeju Island was transformed from a subarc environment to an intraplate environment. The Jeju peridotites, representing old subarc fragments, were subsequently transported to the surface, incorporated into ascending Quaternary intraplate Alkali Basalt. The result of this study implies that long term material transfer in the transformation of geotectonic setting from a subarc to intraplate may have played a significant role in the evolution of the subcontinental lithospheric mantle, resulting in the enriched mantle domains, such as EMI or EMII.
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silica enrichment of group ii xenoliths by evolved Alkali Basalt from jeju island south korea implication for modification of intraplate deep seated rocks
Mineralogy and Petrology, 2012Co-Authors: Kyounghee Yang, Shoji Arai, Csaba Szabo, Hoonyeong JungAbstract:Group II xenoliths, corresponding to the lithology of dunite, wehrlite to olivine clinopyroxenite and olivine websterite to websterite, occur in Pleisto-Holocene Alkali Basalts from Jeju Island, South Korea. The large grain size (up to 5 mm), moderate mg# [=100 × Mg/(Mg + Fetotal) atomic ratio] of olivine (79–82) and pyroxenes (77–83), and absence of metamorphic textural features indicate that they are cumulates of igneous origin. Based on textural features, mineral equilibria and major and trace element variations, it can be inferred that the studied xenoliths were crystallized from Basaltic melts enriched in incompatible trace elements and belong to the Jeju Pleisto-Holocene magma system. They appear to have been emplaced near the present Moho, an estimated 5–8 kbars beneath Jeju Island. Consolidation of cumulates was followed by infiltration of silica-enriched metasomatic melt, producing secondary orthopyroxenes at the expense of olivine. The metasomatic agent appears to have been a silica-enriched residual melt evolved from an initially slightly silica-undersaturated Alkali Basalt to silica-saturated compositions by fractional crystallization under relatively high pressure conditions. The result of this study indicates that relatively young olivine-bearing cumulates could have been metasomatized by a silica-enriched melt within underplates, suggesting that silica enrichment can occur in intraplate Moho-related rocks as well as in the upper mantle of the subarc area.
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A new type of orthopyroxenite xenolith from Takashima, Southwest Japan: silica enrichment of the mantle by evolved Alkali Basalt
Contributions to Mineralogy and Petrology, 2006Co-Authors: Shoji Arai, Yohei Shimizu, Tomoaki Morishita, Yoshito IshidaAbstract:We found fine-grained Fe-rich orthopyrox- ene-rich xenoliths (mainly orthopyroxenite) containing partially digested dunite fragments of Group I from Takashima, Southwest Japan. Orthopyroxenite vein- lets, some of which contain plagioclase at the center, also replace olivine in dunite and wehrlite xenoliths of Group I. This shows high reactivity with respect to olivine of the melt involved in orthopyroxenite for- mation, indicating its high SiO2 activity. The secondary orthopyroxene of this type is characterized by low Mg# (= Mg/(Mg + total Fe) atomic ratio) (down to 0.73) and high Al2O3 contents (5-6 wt%). It is differ- ent in chemistry from other secondary orthopyroxenes found in peridotite xenoliths derived from the mantle wedge. Clinopyroxenes in the Fe-rich orthopyroxenite show a convex-upward REE pattern with a crest around Sm. This pattern is strikingly similar to that of clinopyroxenes of Group II pyroxenite xenoliths and of phenocrystal and xenocrystal clinopyroxenes, indicat- ing involvement of similar Alkali Basaltic melts. The Fe- rich orthopyroxenite xenoliths from Takashima formed by reaction between evolved Alkali Basalt melt and mantle olivine; Alkali Basalt initially slightly undersat- urated in silica might have evolved to silica-oversatu- rated compositions by fractional crystallization at high- pressure conditions. The Fe-rich orthopyroxenites oc- cur as dikes within the uppermost mantle composed of dunite and wehrlite overlying pockets of Group II pyroxenites. The orthopyroxene-rich pyroxenites of this type are possibly common in the uppermost mantle beneath continental rift zones where Alkali Basalt magmas have been prevalent.
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comments on garnet bearing spinel harzburgite xenolith from arato yama Alkali Basalt southwest japan by yamamoto et al
Japanese Magazine of Mineralogical and Petrological Sciences, 2001Co-Authors: Natsue Abe, Shoji AraiAbstract:Yamamoto et al. (1999) obtained a low-temperature geotherm typical of continental shield from a “garnet peridotite” xenolith in the Arato-yama Alkali Basalt. Their geotherm is, however, possibly erroneous. Their data of the “garnet peridotite” suggest discrepancies from the chemical equilibration of minerals, and the pressure obtained is too large for the depth of xenolith entrainment by Alkali Basalt magma. The lack of thin section descriptions is also a cause of uncertainty.
G. Rivalenti - One of the best experts on this subject based on the ideXlab platform.
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co2 fluid and silicate glass as monitors of Alkali Basalt peridotite interaction in the mantle wedge beneath gobernador gregores southern patagonia
Lithos, 2009Co-Authors: Marco Scambelluri, Riccardo Vannucci, A. De Stefano, M Preitemartinez, G. RivalentiAbstract:Abstract A suite of mantle-wedge amphibole + phlogopite-bearing spinel peridotite xenoliths in Plio-Pleistocene Alkali Basalts from Southern Patagonia (Gobernador Gregores, Santa Cruz Province, Argentina) contains carbonic fluid inclusions, glass and carbonate in several textural domains. Here we present a microstructural and fluid inclusion study showing that fluid (corresponding to pure CO 2 ) and glass post-date the hydrous mantle assemblage and formed soon before and/or during xenolith entrainement in the host Alkali Basalt. The high densities preserved by a number of CO 2 inclusions indicate that fluid infiltration took place at mantle depths. The low densities pertaining to the majority of analyzed fluid inclusions derive from inclusion re-equilibration during xenolith ascent. Glass occurs in reaction haloes around clinopyroxene, amphibole and phlogopite, where it hosts microlites of new pyroxene, olivine and locally carbonate. Glass veins cut the mantle minerals and locally contain primary carbonate. Glasses vary widely in composition depending on the textural domains and attain Si- and Alkali-rich compositions (SiO 2 = 47.0–68.3 wt.%; Na 2 O + K 2 O = 5.8–12.2 wt.%). Incompatible trace element patterns of glasses in anhydrous xenoliths are closely similar to those of the host Alkali Basalts, whereas the compositions of interstitial and vein glasses in the hydrous xenoliths indicate that a compositional control has been exerted by the local mineral assemblage (mainly amphibole). The δ 18 O values of carbonate from the glass pockets and veins in the xenoliths, as well as of carbonate globules and amygdales in the host Basalts are in the range 19.62 to 21.04‰. Corresponding δ 13 C values are − 9.25 to − 10.12‰ and − 7.59 to − 9.32‰, respectively. These values are very different from those of primary carbonatites and the δ 18 O values clearly exceed those expected for minerals and glasses from mantle assemblages. The similarity of isotopic ratios of carbonates from both xenoliths and host lavas and their shift towards low δ 13 C and high δ 18 O values may be the result of Basalt-peridotite interaction during ascent of the mantle xenoliths. Our study points to a close relationship between the infiltration of carbonic fluid together with fractions of the host Alkali Basalt, and melting of hydrous peridotite-forming minerals. Assuming an initial average content of 1.5–2 wt.% CO 2 in the primary Alkaline melt and considering that the dissolved amounts of CO 2 and H 2 O in such a melt at 400 MPa can be in the order of 0.3 wt.% and 3.5% respectively, approximately 75 to 50% of the total carbon dioxide load was released by the uprising host magma. This process led to infiltration and entrapment of high-density CO 2 inclusions in the GG mantle rocks, to hydrous phase breakdown and to carbonate precipitation in veins and at some reaction sites after the primary mantle minerals. We propose that formation of CO 2 inclusions, glass and carbonate in hydrated mantle xenoliths is not unique of carbonatite metasomatism: comparable effects can be produced by degassing Alkaline magmas.
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CO2 fluid and silicate glass as monitors of Alkali Basalt/peridotite interaction in the mantle wedge beneath Gobernador Gregores, Southern Patagonia
Lithos, 2008Co-Authors: Marco Scambelluri, Riccardo Vannucci, A. De Stefano, M. Preite-martinez, G. RivalentiAbstract:Abstract A suite of mantle-wedge amphibole + phlogopite-bearing spinel peridotite xenoliths in Plio-Pleistocene Alkali Basalts from Southern Patagonia (Gobernador Gregores, Santa Cruz Province, Argentina) contains carbonic fluid inclusions, glass and carbonate in several textural domains. Here we present a microstructural and fluid inclusion study showing that fluid (corresponding to pure CO 2 ) and glass post-date the hydrous mantle assemblage and formed soon before and/or during xenolith entrainement in the host Alkali Basalt. The high densities preserved by a number of CO 2 inclusions indicate that fluid infiltration took place at mantle depths. The low densities pertaining to the majority of analyzed fluid inclusions derive from inclusion re-equilibration during xenolith ascent. Glass occurs in reaction haloes around clinopyroxene, amphibole and phlogopite, where it hosts microlites of new pyroxene, olivine and locally carbonate. Glass veins cut the mantle minerals and locally contain primary carbonate. Glasses vary widely in composition depending on the textural domains and attain Si- and Alkali-rich compositions (SiO 2 = 47.0–68.3 wt.%; Na 2 O + K 2 O = 5.8–12.2 wt.%). Incompatible trace element patterns of glasses in anhydrous xenoliths are closely similar to those of the host Alkali Basalts, whereas the compositions of interstitial and vein glasses in the hydrous xenoliths indicate that a compositional control has been exerted by the local mineral assemblage (mainly amphibole). The δ 18 O values of carbonate from the glass pockets and veins in the xenoliths, as well as of carbonate globules and amygdales in the host Basalts are in the range 19.62 to 21.04‰. Corresponding δ 13 C values are − 9.25 to − 10.12‰ and − 7.59 to − 9.32‰, respectively. These values are very different from those of primary carbonatites and the δ 18 O values clearly exceed those expected for minerals and glasses from mantle assemblages. The similarity of isotopic ratios of carbonates from both xenoliths and host lavas and their shift towards low δ 13 C and high δ 18 O values may be the result of Basalt-peridotite interaction during ascent of the mantle xenoliths. Our study points to a close relationship between the infiltration of carbonic fluid together with fractions of the host Alkali Basalt, and melting of hydrous peridotite-forming minerals. Assuming an initial average content of 1.5–2 wt.% CO 2 in the primary Alkaline melt and considering that the dissolved amounts of CO 2 and H 2 O in such a melt at 400 MPa can be in the order of 0.3 wt.% and 3.5% respectively, approximately 75 to 50% of the total carbon dioxide load was released by the uprising host magma. This process led to infiltration and entrapment of high-density CO 2 inclusions in the GG mantle rocks, to hydrous phase breakdown and to carbonate precipitation in veins and at some reaction sites after the primary mantle minerals. We propose that formation of CO 2 inclusions, glass and carbonate in hydrated mantle xenoliths is not unique of carbonatite metasomatism: comparable effects can be produced by degassing Alkaline magmas.
Brian J Fryer - One of the best experts on this subject based on the ideXlab platform.
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trace element evidence for volatile influenced differentiation in a flow of Alkali Basalt peng hu island taiwan
Canadian Mineralogist, 2008Co-Authors: John D Greenough, Brian J FryerAbstract:A 20-m-thick Alkali Basalt flow on the Peng Hu Island, Taiwan, shows three well-developed segregation veins in its upper 8.5 meters. Each pegmatitic and “vesicular” (ocelli-bearing?) segregation displays distinct whole-sample chemical traits that are shared with the enclosing Basalt. Augite, plagioclase and olivine exhibit major-element (electron-microprobe data) and trace element compositions (laser ablation microprobe – inductively coupled plasma – mass spectrometry) that reflect this whole-rock chemical stratification. Thus the chemical stratification is a product of igneous processes and is not the result of secondary alteration. Elements defining the stratification (K, Rb, Li, Na, Zn in minerals and whole-rock data, but Cl, S, As, Pb and Sr are also important based on whole-rock data) tend to be complexed and moved by volatiles in various geological environments. Conventional crystal-fractionation models do not reproduce the observed variations in these elements up through the flow. The patterns of data suggest that rising plumes of vesicles carried volatile-complexed (scavenged) elements to high levels in the flow at the time the segregation veins were forming and the interior of the flow was largely molten.
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trace element evidence for volatile influenced differentiation in a flow of Alkali Basalt peng hu island taiwan
Canadian Mineralogist, 2008Co-Authors: John D Greenough, Brian J FryerAbstract:A 20-m-thick Alkali Basalt flow on the Peng Hu Island, Taiwan, shows three well-developed segregation veins in its upper 8.5 meters. Each pegmatitic and “vesicular” (ocelli-bearing?) segregation displays distinct whole-sample chemical traits that are shared with the enclosing Basalt. Augite, plagioclase and olivine exhibit major-element (electron-microprobe data) and trace element compositions (laser ablation microprobe – inductively coupled plasma – mass spectrometry) that reflect this whole-rock chemical stratification. Thus the chemical stratification is a product of igneous processes and is not the result of secondary alteration. Elements defining the stratification (K, Rb, Li, Na, Zn in minerals and whole-rock data, but Cl, S, As, Pb and Sr are also important based on whole-rock data) tend to be complexed and moved by volatiles in various geological environments. Conventional crystal-fractionation models do not reproduce the observed variations in these elements up through the flow. The patterns of data suggest that rising plumes of vesicles carried volatile-complexed (scavenged) elements to high levels in the flow at the time the segregation veins were forming and the interior of the flow was largely molten.
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evidence for volatile influenced differentiation in a layered Alkali Basalt flow penghu islands taiwan
Bulletin of Volcanology, 1999Co-Authors: John D Greenough, Brian J FryerAbstract:An approximately 20-m-thick Alkali Basalt flow on the Penghu Islands contains ∼20 cm thick, horizontally continuous (>50 m), vesicular layers separated by ∼1.5 m of massive Basalt in its upper 8.5 m. The three layers contain ocelli-like "vesicles" filled with nepheline and igneous carbonate. They are coarse grained and enriched in incompatible elements relative to the massive Basalt with which they form sharp contacts. These vesicular layers (segregation veins) formed when residual liquid in the underlying crystal mush was forced (gas filter pressing) or siphoned into three thermally induced horizontal cracks that opened successively in the advancing crystal mush of the flow's upper crust. Most vesicular layer trace elements can be modelled by residual melt extraction after 25–40% fractional crystallization of massive Basalt underlying each layer. Sulphur, Cl, As, Zn, Pb, K, Na, Rb, and Sr show large concentration changes between the top, middle, and bottom layers, with each vesicular and underlying massive Basalt forming a chemically distinct "pair." The large changes between layers are difficult to account for by crystal fractionation alone, because other incompatible elements (e.g., La, Sm, Yb, Zr, Nb) and the major elements change little. The association of these elements (S, Cl, etc.) with "fluids" in various geologic environments suggests that volatiles influenced differentiation, perhaps by moving Alkali, Alkaline earth, and chalcophile elements as magma-dissolved volatile complexes. Volatiles may have also led to large grain sizes in the segregation veins by lowering melt viscosities and raising diffusion rates. The chemical variability between layers indicates that a convection and concentration mechanism acted within the flow. The specific process cannot be determined, but different rates of vesicle plume rise (through the flow) and/or accumulation in the upper crust's crystal mush might account for the chemical pairing and extreme variations in Cl, S, As, and C. This study emphasizes the importance of sampling vesicular rocks in flows. It also suggests that volatiles play important physical and chemical roles in rapidly differentiating mafic magmas in processes decoupled from crystal fractionation.
John M Bartley - One of the best experts on this subject based on the ideXlab platform.
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eruption of Alkali Basalts during crustal shortening in southern california
Tectonics, 1994Co-Authors: Allen F Glazner, John M BartleyAbstract:The common occurrence of Alkali Basalts in continental rifts has led to the widespread assumption that late Cenozoic Alkali Basalts of the western United States indicate an extensional tectonic regime. However, field relations of late Cenozoic Alkali Basalt flows and cinder cones in the Mojave Desert area, including flows that bear mantle xenoliths, indicate that many were erupted in contractional or transpressional tectonic settings. These observations call into question models of extensional magmatism in which lithospheric extension facilitates transport of magmas to the surface and suggest that an association of Alkali Basalts and coarse clastic sedimentary rocks need not indicate rifting.
Allen F Glazner - One of the best experts on this subject based on the ideXlab platform.
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Experimental study on the effects of temperature cycling on coarsening of plagioclase and olivine in an Alkali Basalt
Contributions to Mineralogy and Petrology, 2013Co-Authors: Ryan D. Mills, Allen F GlaznerAbstract:We conducted experiments on an Alkali Basalt at 1-atmosphere in order to investigate the effects of temperature cycling on crystal coarsening. Experiments at 1,150 °C near the Ni–NiO buffer indicate that coarsening of plagioclase and olivine crystals is greatly accentuated by temperature cycling. For a given experiment duration, crystal number density decreases with temperature cycle amplitude and average crystal size increases with increasing amplitude. We observed little correlation between cycle period and crystal number density or average crystal size. We suggest that dissolution and size-proportional crystal growth during repeated heating and cooling decrease crystal number density and increase average crystal size. These experiments indicate that the texture of silicate minerals can be modified by temperature cycling and that phenocrysts may develop quicker in silicate magmas when the magma temperature is cycled.
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eruption of Alkali Basalts during crustal shortening in southern california
Tectonics, 1994Co-Authors: Allen F Glazner, John M BartleyAbstract:The common occurrence of Alkali Basalts in continental rifts has led to the widespread assumption that late Cenozoic Alkali Basalts of the western United States indicate an extensional tectonic regime. However, field relations of late Cenozoic Alkali Basalt flows and cinder cones in the Mojave Desert area, including flows that bear mantle xenoliths, indicate that many were erupted in contractional or transpressional tectonic settings. These observations call into question models of extensional magmatism in which lithospheric extension facilitates transport of magmas to the surface and suggest that an association of Alkali Basalts and coarse clastic sedimentary rocks need not indicate rifting.