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Vamdev Pathak - One of the best experts on this subject based on the ideXlab platform.
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mineral carbonation reactions under water saturated hydrothermal like conditions and numerical simulations of co2 sequestration in Tholeiitic Basalt of the eastern deccan volcanic province india
Applied Geochemistry, 2017Co-Authors: Amit Kumar, J P Shrivastava, Vamdev PathakAbstract:Abstract Previous water-CO 2 interaction studies have studied few Basalt types (rich in Ca, Mg, and Fe cations) to determine pyroxene, olivine and plagioclase reaction rates; however, limited research has examined the Deccan Basalt. Therefore, in this study, Basalt-CO 2 -water-saturated interaction experiments and numerical simulations were performed under hydrothermal-like conditions. X-ray Diffraction (XRD) data revealed the appearance of calcite, aragonite, ankerite, huntite and siderite; additionally, smectite, chlorite, smectite/chlorite mixed layers and chabazite were also formed. SEM images showed that tiny calcite crystals developed over larger calcite crystals, incipient-disordered calcite formed with imperfections on its crystal faces and cubic chabazite crystals were bounded by smectite grains. Furthermore, these observations were confirmed by EDS analyses and mineral formulae calculations. Major shifts in the carbonate peaks observed at 155 and 282, 178, and 849 cm −1 on Raman spectra confirmed the formation of calcite, dolomite and aragonite, respectively. Mixing trends between Basalt and Ca-Mg-Fe carbonates and chlorite/smectite were observed in the case of phyllosilicates. However, ankerite, calcite and siderite recorded the enrichment of (i) Ca, (ii) Fe-Mg and (iii) Fe. High degrees of carbonation and progressive mineral growth were observed with the increasing pH of the solution. The formation of secondary carbonates predominated over that of silicates in short-term experiments; however, with increasing reaction time, the carbonates no longer persisted in the system, as they were dissolved and replaced by silicates. However, the degree of carbonation increased with the increasing pCO 2 and pH of the solution. Transition-state-theory (TST)-based numerical simulation models do not agree well with the results of experiments, as carbonate growth was greater in the former case. These models work well to predict the dissolution rates of most minerals but overpredict the growth of non-hydrous Mg carbonates at low temperatures.
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mineral carbonation reactions under water saturated hydrothermal like conditions and numerical simulations of co 2 sequestration in Tholeiitic Basalt of the eastern deccan volcanic province india
Applied Geochemistry, 2017Co-Authors: Amit Kumar, J P Shrivastava, Vamdev PathakAbstract:Abstract Previous water-CO 2 interaction studies have studied few Basalt types (rich in Ca, Mg, and Fe cations) to determine pyroxene, olivine and plagioclase reaction rates; however, limited research has examined the Deccan Basalt. Therefore, in this study, Basalt-CO 2 -water-saturated interaction experiments and numerical simulations were performed under hydrothermal-like conditions. X-ray Diffraction (XRD) data revealed the appearance of calcite, aragonite, ankerite, huntite and siderite; additionally, smectite, chlorite, smectite/chlorite mixed layers and chabazite were also formed. SEM images showed that tiny calcite crystals developed over larger calcite crystals, incipient-disordered calcite formed with imperfections on its crystal faces and cubic chabazite crystals were bounded by smectite grains. Furthermore, these observations were confirmed by EDS analyses and mineral formulae calculations. Major shifts in the carbonate peaks observed at 155 and 282, 178, and 849 cm −1 on Raman spectra confirmed the formation of calcite, dolomite and aragonite, respectively. Mixing trends between Basalt and Ca-Mg-Fe carbonates and chlorite/smectite were observed in the case of phyllosilicates. However, ankerite, calcite and siderite recorded the enrichment of (i) Ca, (ii) Fe-Mg and (iii) Fe. High degrees of carbonation and progressive mineral growth were observed with the increasing pH of the solution. The formation of secondary carbonates predominated over that of silicates in short-term experiments; however, with increasing reaction time, the carbonates no longer persisted in the system, as they were dissolved and replaced by silicates. However, the degree of carbonation increased with the increasing pCO 2 and pH of the solution. Transition-state-theory (TST)-based numerical simulation models do not agree well with the results of experiments, as carbonate growth was greater in the former case. These models work well to predict the dissolution rates of most minerals but overpredict the growth of non-hydrous Mg carbonates at low temperatures.
J E Snow - One of the best experts on this subject based on the ideXlab platform.
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effect of oxygen fugacity and water on phase equilibria of a hydrous Tholeiitic Basalt
Contributions to Mineralogy and Petrology, 2010Co-Authors: Jürgen Koepke, Sandrin T. Feig, J E SnowAbstract:The influence of oxygen fugacity and water on phase equilibria and the link between redox conditions and water activity were investigated experimentally using a primitive Tholeiitic Basalt composition relevant to the ocean crust. The crystallization experiments were performed in internally heated pressure vessels at 200 MPa in the temperature range 940–1,220°C. The oxygen fugacity was measured using the H2-membrane technique. To study the effect of oxygen fugacity, three sets of experiments with different hydrogen fugacities were performed, showing systematic effects on the phase relations and compositions. In each experimental series, the water content of the system was varied from nominally dry to water-saturated conditions, causing a range of oxygen fugacities varying by ~3 log units per series. The range in oxygen fugacity investigated spans ~7 log units. Systematic effects of oxygen fugacity on the stability and composition of the mafic silicate phases, Cr–spinel and Fe–Ti oxides, under varying water contents were recorded. The Mg# of the melt, and therefore also the Mg# of olivine and clinopyroxene, changed systematically as a function of oxygen fugacity. An example of the link between oxygen fugacity and water activity under hydrogen-buffered conditions is the change in the crystallization sequence (olivine and Cr–spinel) due to a change in the oxygen fugacity caused by an increase in the water activity. The stability of magnetite is restricted to highly oxidizing conditions. The absence of magnetite in most of the experiments allows the determination of differentiation trends as a function of oxygen fugacity and water content, demonstrating that in an oxide-free crystallization sequence, water systematically affects the differentiation trend, while oxygen fugacity seems to have a negligible effect.
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effect of water on Tholeiitic Basalt phase equilibria an experimental study under oxidizing conditions
Contributions to Mineralogy and Petrology, 2006Co-Authors: Sandrin T. Feig, Jürgen Koepke, J E SnowAbstract:To investigate the effect of water on phase relations and compositions in a Basaltic system, we performed crystallization experiments at pressures of 100, 200 and 500 MPa in a temperature range of 940 to 1,220°C using four different water contents. Depending on the water activity, the oxygen fugacity varied between 1 and 4 log units above the quartz-magnetite-fayalite buffer. Addition of water to the dry system shifts the solidus > 250°C to lower temperatures and increases the amount of melt drastically. For instance, at 1,100°C and 200 MPa, the melt fraction increases from 12.5 wt% at a water content of 1.6 wt% to 96.3% at a water content of 5 wt% in the melt. The compositions of the experimental phases also show a strong effect of water. Plagioclase is shifted to higher anorthite contents by the addition of water. Olivine and clinopyroxene show generally higher MgO/FeO ratios with added water, which could also be related to the increasing oxygen fugacity with water. Moreover, water affects the partitioning of certain elements between minerals and melts, e.g., the Ca partitioning between olivine and melt. Plagioclase shows a characteristic change in the order of crystallization with water that may help to explain the formation of wehrlites intruding the lower oceanic crust (e.g., in Oman, Macquarie Island). At 100 MPa, plagioclase crystallizes before clinopyroxene at all water contents. At pressures > 100 MPa, plagioclase crystallizes before clinopyroxene at low water contents (e.g. 3 wt%. This change in crystallization order indicates that a paragenesis typical for wehrlites (olivine–clinopyroxene–without plagioclase) is stabilized at low pressures typical of the oceanic crust only at high water contents. This opens the possibility that typical wehrlites in the oceanic crust can be formed by the fractionation and accumulation of olivine and clinopyroxene at 1,060°C and > 100 MPa in a primitive Tholeiitic Basaltic system containing more than 3 wt% water. The comparison of the experimental results with evolution trends calculated by the thermodynamic models “MELTS” and “Comagmat” shows that neither model predicts the experimental phase relations with sufficient accuracy.
Sandrin T. Feig - One of the best experts on this subject based on the ideXlab platform.
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effect of oxygen fugacity and water on phase equilibria of a hydrous Tholeiitic Basalt
Contributions to Mineralogy and Petrology, 2010Co-Authors: Jürgen Koepke, Sandrin T. Feig, J E SnowAbstract:The influence of oxygen fugacity and water on phase equilibria and the link between redox conditions and water activity were investigated experimentally using a primitive Tholeiitic Basalt composition relevant to the ocean crust. The crystallization experiments were performed in internally heated pressure vessels at 200 MPa in the temperature range 940–1,220°C. The oxygen fugacity was measured using the H2-membrane technique. To study the effect of oxygen fugacity, three sets of experiments with different hydrogen fugacities were performed, showing systematic effects on the phase relations and compositions. In each experimental series, the water content of the system was varied from nominally dry to water-saturated conditions, causing a range of oxygen fugacities varying by ~3 log units per series. The range in oxygen fugacity investigated spans ~7 log units. Systematic effects of oxygen fugacity on the stability and composition of the mafic silicate phases, Cr–spinel and Fe–Ti oxides, under varying water contents were recorded. The Mg# of the melt, and therefore also the Mg# of olivine and clinopyroxene, changed systematically as a function of oxygen fugacity. An example of the link between oxygen fugacity and water activity under hydrogen-buffered conditions is the change in the crystallization sequence (olivine and Cr–spinel) due to a change in the oxygen fugacity caused by an increase in the water activity. The stability of magnetite is restricted to highly oxidizing conditions. The absence of magnetite in most of the experiments allows the determination of differentiation trends as a function of oxygen fugacity and water content, demonstrating that in an oxide-free crystallization sequence, water systematically affects the differentiation trend, while oxygen fugacity seems to have a negligible effect.
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effect of water on Tholeiitic Basalt phase equilibria an experimental study under oxidizing conditions
Contributions to Mineralogy and Petrology, 2006Co-Authors: Sandrin T. Feig, Jürgen Koepke, J E SnowAbstract:To investigate the effect of water on phase relations and compositions in a Basaltic system, we performed crystallization experiments at pressures of 100, 200 and 500 MPa in a temperature range of 940 to 1,220°C using four different water contents. Depending on the water activity, the oxygen fugacity varied between 1 and 4 log units above the quartz-magnetite-fayalite buffer. Addition of water to the dry system shifts the solidus > 250°C to lower temperatures and increases the amount of melt drastically. For instance, at 1,100°C and 200 MPa, the melt fraction increases from 12.5 wt% at a water content of 1.6 wt% to 96.3% at a water content of 5 wt% in the melt. The compositions of the experimental phases also show a strong effect of water. Plagioclase is shifted to higher anorthite contents by the addition of water. Olivine and clinopyroxene show generally higher MgO/FeO ratios with added water, which could also be related to the increasing oxygen fugacity with water. Moreover, water affects the partitioning of certain elements between minerals and melts, e.g., the Ca partitioning between olivine and melt. Plagioclase shows a characteristic change in the order of crystallization with water that may help to explain the formation of wehrlites intruding the lower oceanic crust (e.g., in Oman, Macquarie Island). At 100 MPa, plagioclase crystallizes before clinopyroxene at all water contents. At pressures > 100 MPa, plagioclase crystallizes before clinopyroxene at low water contents (e.g. 3 wt%. This change in crystallization order indicates that a paragenesis typical for wehrlites (olivine–clinopyroxene–without plagioclase) is stabilized at low pressures typical of the oceanic crust only at high water contents. This opens the possibility that typical wehrlites in the oceanic crust can be formed by the fractionation and accumulation of olivine and clinopyroxene at 1,060°C and > 100 MPa in a primitive Tholeiitic Basaltic system containing more than 3 wt% water. The comparison of the experimental results with evolution trends calculated by the thermodynamic models “MELTS” and “Comagmat” shows that neither model predicts the experimental phase relations with sufficient accuracy.
Toshiro Takahashi - One of the best experts on this subject based on the ideXlab platform.
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water content of primitive low k Tholeiitic Basalt magma from iwate volcano ne japan arc implications for differentiation mechanism of frontal arc Basalt magmas
Mineralogy and Petrology, 2014Co-Authors: Takeshi Kuritani, Junichi Kimura, Takeyoshi Yoshida, Yuka Hirahara, Toshiro TakahashiAbstract:The water content of low-K Tholeiitic Basalt mag- ma from Iwate volcano, which is located on the volcanic front of the NE Japan arc, was estimated using multi- component thermodynamic models. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78-85) correlates positively with the An content of coexisting plagioclase phenocrysts (An85-92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase phenocrysts. It is inferred from these observations that the phenocrysts with vari- able compositions were primarily derived from mushy boundary layers along the walls of a magma chamber. By using thermodynamic calculations with the observed petrological features of the lavas, the water content of the Iwate magma was estimated to be 4-5 wt.%. The high water content of the magma supports the recent consensus that frontal-arc magmas are remarkably hydrous. Using the estimated water content of the Iwate magma, the water content and temperature of the source mantle were estimated. Given that the Iwate magma was derived froma primarymagmasolelybyolivinefractionation, the water content and temperature were estimated to be ~0.7 wt.% and ~1,310 °C, respectively. Differentiation mech- anisms of low-K frontal-arc Basalt magmas were also exam- ined by application of a thermodynamics-based mass balance model to the Iwate magma. It is suggested that magmatic differentiation proceeds primarily through fractionation of crystals from the main molten part of a magma chamber when it is located at <~200 MPa, whereas magma evolves through a convective melt exchange between the main magma and mushy boundary layers when the magma body is located at
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origin of late oligocene to middle miocene adakitic andesites high magnesian andesites and Basalts from the back arc margin of the sw and ne japan arcs
Journal of Petrology, 2013Co-Authors: Makoto Sato, Miho Ayabe, Kenji Shuto, Hiroyuki Ishimoto, Katsuya Takanashi, Toshiro Takahashi, M Uematsu, Hiroshi KawabataAbstract:Late Oligocene to Middle Miocene adakitic andesites are found in the southern part of Okushiri Island, the northern Noto Peninsula and in theToyama region in the present-day back-arc margin of the SWand NE Japan arcs. On Okushiri Island, adakitic andesite is accompanied by moderately alkaline Basalt, whereas on the Noto Peninsula, adakitic andesite has been erupted along with high magnesian andesite (HMA), bronzite andesite and Tholeiitic Basalt. Adakitic andesites from all three locations are characterized by high Sr/Yand lowY, and have higher MgO contents than adakitic melts generated by experimental melting of metaBasalt and amphibolite. They also have higher Ni and Cr contents than either Archaean tonalite^trondhjemite^granodiorite (TTG) suites or Early Cretaceous adakitic granites, which have been attributed to partial melting of subducted oceanic crust. The Noto Peninsula adakitic andesite has Sr and Nd isotopic compositions identical to normal mid-ocean ridge Basalt (N-MORB), whereas the Okushiri Island and Toyama adakitic andesites are more isotopically primitive than N-MORB.The Noto Peninsula primary adakitic melt was derived from subducted oceanic N-MORB crust, whereas the Okushiri Island andToyama primary adakites are interpreted as melts of subducted N-MORB and sediment that have subsequently interacted with the overlying mantle wedge peridotite.To explain the comagmatism of adakite, HMA and Basalt, the following model is proposed. A hydrated adakitic diapir ascends from the subducting slab and is heated because it enters the overlying hot mantle wedge.The subsequent establishment of thermal and H2O gradients in the adakitic diapir and surrounding mantle wedge peridotite results in concurrent generation of adakitic andesite magma in the inner adakitic diapir region (low temperature and high H2O content), HMAand bronzite andesite magmas in the intermediate peridotite region (intermediate temperature and H2O content), and Tholeiitic Basalt magma in the outer peridotite region (high temperature and lower H2O content).
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new insights into andesite genesis the role of mantle derived calc alkalic and crust derived Tholeiitic melts in magma differentiation beneath zao volcano ne japan
Journal of Petrology, 2008Co-Authors: Yoshiyuki Tatsumi, Toshiro Takahashi, Junichi Kimura, Yuka Hirahara, Qing Chang, Takashi Miyazaki, Masao Ban, A SakayoriAbstract:Two distinctive differentiation trends, Tholeiitic and calc-alkalic, are recognized in Zao volcano, which is located immediately behind the volcanic front of the NE Japan arc. The genetic relationship between these two magma series is critical for a better understanding of andesite genesis, because they often coexist in close spatial and temporal proximity in arc volcanoes. Petrographic features indicative of ‘disequilibrium’ , such as reversely zoned pyroxene phenocrysts, the wide and bimodal compositional distribution in Ca/(CaþNa) of plagioclase phenocrysts, honeycomb textures and dusty zones that these plagioclase phenocrysts often exhibit, and the presence of olivine^pyroxene pairs with different Mg/Fe, are observed exclusively in calc-alkalic rocks. In Tholeiitic rocks the Sr isotopic ratios of plagioclase phenocrysts, determined by both micromilling combined with thermal ionization mass spectrometry, and laser-ablation inductively coupled plasma mass spectrometry techniques, are constant at 0 7042^0 7044. On the other hand, those in calc-alkalic rocks (0 7033^0 7042) show more complex characteristics, which can be best understood if at least three end-member components, a calc-alkalic Basaltic melt, a Tholeiitic Basaltic melt and a Tholeiitic felsic melt, contribute to the production of mixed calc-alkalic magmas.The Sr/Sr and trace element compositions of the leastdifferentiated Basalt magmas, which are inferred from the composition of the calcic plagioclase [Ca/(CaþNa)40 9], suggest that two types of Basaltic magma, calc-alkalic and Tholeiitic, exist beneath the volcano. The Tholeiitic Basalt magma has a higher Sr/Sr than the calc-alkalic magma (0 7042 vs 0 7038) and a characteristic trace element signature consistent with the presence of plagioclase and amphibole as melting residues.This suggests that the Tholeiitic magmas are produced via anatexis of amphibolitic crust caused by underplating and/or intrusion of mantle-derived calcalkalic Basalt magmas into the sub-Zao crust. The mantle-derived calc-alkalic Basalt magma mixes with crust-derived Tholeiitic melts to form calc-alkalic andesite magmas.The hypothesis proposed here requires revision (or even abandonment) of the general consensus that calc-alkalic magmas have greater contributions of a crustal component than Tholeiitic magmas.
Junichi Kimura - One of the best experts on this subject based on the ideXlab platform.
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water content of primitive low k Tholeiitic Basalt magma from iwate volcano ne japan arc implications for differentiation mechanism of frontal arc Basalt magmas
Mineralogy and Petrology, 2014Co-Authors: Takeshi Kuritani, Junichi Kimura, Takeyoshi Yoshida, Yuka Hirahara, Toshiro TakahashiAbstract:The water content of low-K Tholeiitic Basalt mag- ma from Iwate volcano, which is located on the volcanic front of the NE Japan arc, was estimated using multi- component thermodynamic models. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78-85) correlates positively with the An content of coexisting plagioclase phenocrysts (An85-92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase phenocrysts. It is inferred from these observations that the phenocrysts with vari- able compositions were primarily derived from mushy boundary layers along the walls of a magma chamber. By using thermodynamic calculations with the observed petrological features of the lavas, the water content of the Iwate magma was estimated to be 4-5 wt.%. The high water content of the magma supports the recent consensus that frontal-arc magmas are remarkably hydrous. Using the estimated water content of the Iwate magma, the water content and temperature of the source mantle were estimated. Given that the Iwate magma was derived froma primarymagmasolelybyolivinefractionation, the water content and temperature were estimated to be ~0.7 wt.% and ~1,310 °C, respectively. Differentiation mech- anisms of low-K frontal-arc Basalt magmas were also exam- ined by application of a thermodynamics-based mass balance model to the Iwate magma. It is suggested that magmatic differentiation proceeds primarily through fractionation of crystals from the main molten part of a magma chamber when it is located at <~200 MPa, whereas magma evolves through a convective melt exchange between the main magma and mushy boundary layers when the magma body is located at
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new insights into andesite genesis the role of mantle derived calc alkalic and crust derived Tholeiitic melts in magma differentiation beneath zao volcano ne japan
Journal of Petrology, 2008Co-Authors: Yoshiyuki Tatsumi, Toshiro Takahashi, Junichi Kimura, Yuka Hirahara, Qing Chang, Takashi Miyazaki, Masao Ban, A SakayoriAbstract:Two distinctive differentiation trends, Tholeiitic and calc-alkalic, are recognized in Zao volcano, which is located immediately behind the volcanic front of the NE Japan arc. The genetic relationship between these two magma series is critical for a better understanding of andesite genesis, because they often coexist in close spatial and temporal proximity in arc volcanoes. Petrographic features indicative of ‘disequilibrium’ , such as reversely zoned pyroxene phenocrysts, the wide and bimodal compositional distribution in Ca/(CaþNa) of plagioclase phenocrysts, honeycomb textures and dusty zones that these plagioclase phenocrysts often exhibit, and the presence of olivine^pyroxene pairs with different Mg/Fe, are observed exclusively in calc-alkalic rocks. In Tholeiitic rocks the Sr isotopic ratios of plagioclase phenocrysts, determined by both micromilling combined with thermal ionization mass spectrometry, and laser-ablation inductively coupled plasma mass spectrometry techniques, are constant at 0 7042^0 7044. On the other hand, those in calc-alkalic rocks (0 7033^0 7042) show more complex characteristics, which can be best understood if at least three end-member components, a calc-alkalic Basaltic melt, a Tholeiitic Basaltic melt and a Tholeiitic felsic melt, contribute to the production of mixed calc-alkalic magmas.The Sr/Sr and trace element compositions of the leastdifferentiated Basalt magmas, which are inferred from the composition of the calcic plagioclase [Ca/(CaþNa)40 9], suggest that two types of Basaltic magma, calc-alkalic and Tholeiitic, exist beneath the volcano. The Tholeiitic Basalt magma has a higher Sr/Sr than the calc-alkalic magma (0 7042 vs 0 7038) and a characteristic trace element signature consistent with the presence of plagioclase and amphibole as melting residues.This suggests that the Tholeiitic magmas are produced via anatexis of amphibolitic crust caused by underplating and/or intrusion of mantle-derived calcalkalic Basalt magmas into the sub-Zao crust. The mantle-derived calc-alkalic Basalt magma mixes with crust-derived Tholeiitic melts to form calc-alkalic andesite magmas.The hypothesis proposed here requires revision (or even abandonment) of the general consensus that calc-alkalic magmas have greater contributions of a crustal component than Tholeiitic magmas.
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submarine sliver in north kona a window into the early magmatic and growth history of hualalai volcano hawaii
Journal of Volcanology and Geothermal Research, 2006Co-Authors: Julia E Hammer, Michelle L Coombs, Patrick J Shamberger, Junichi KimuraAbstract:Two manned submersible dives examined the Hualalai Northwest rift zone and an elongate ridge cresting at 3900 mbsl during a 2002 JAMSTEC cruise. The rift zone flank at dive site S690 (water depth 3412–2104 m) is draped by elongated and truncated pillow lavas. These olivine-rich Tholeiitic lavas are compositionally indistinguishable from those examined further south along the bench, except that they span a wider range in dissolved sulfur content (200–1400 ppm). The elongate ridge investigated in dive S692, located at the base of the bench, is a package of distinct lithologic units containing volcaniclastic materials, glassy pillow breccias, and lava blocks; these units contain a range of compositions including Tholeiitic Basalt, transitional Basalt, and hawaiite. The textures, compositions, and stratigraphic relationships of materials within the elongate ridge require that a variety of transport mechanisms juxtaposed materials from multiple eruptions into individual beds, compacted them into a coherent package of units, and brought the package to its present depth 10 km from the edge of the North Kona slump bench. Sulfur-rich hawaiite glasses at the base of the elongate ridge may represent the first extant representatives of juvenile alkalic volcanism at Hualalai. They are geochemically distinct from shield tholeiite and post-shield alkalic magmas, but may be related to transitional Basalt by high-pressure crystal fractionation of clinopyroxene. Tholeiitic glasses that compose the majority of the exposed outcrop are similar to Mauna Kea tholeiites and other Hualalai tholeiites, but they differ from younger Basalts in having greater incompatible element enrichments and higher CaO for a given MgO. These differences could arise from small extents of partial melting during the transition from alkalic to shield stage magmatism. Low sulfur contents of most of the volcaniclastic tholeiites point to early emergence of Hualalai above sea level relative to the development of the midslope slump bench. D 2005 Elsevier B.V. All rights reserved.