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Michael R Perfit - One of the best experts on this subject based on the ideXlab platform.
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Petrography and Petrogenesis of a Mid-Ocean Ridge Lava Suite
2007Co-Authors: Matthew C. Smith, Michael R PerfitAbstract:Over 60% of the Earth’s magma flux, > 21 km 3 /yr, takes place at Mid-Ocean Ridges (MOR). These divergent plate boundaries are the loci of volcanism and plutonism that form the oceanic crust, which covers over 70% of Earth’s surface. Mid-Ocean Ridge magmas typically undergo less modification and differentiation from their original primary melt composition than magmas erupted in continental settings or at oceanic islands. With a less complicated history, these MOR lavas provide a clearer window into mantle melting and magma chamber processes. Much insight into many different magmatic rock suites can be gained by understanding the magmatic processes involved in the formation of Mid-Ocean Ridge lavas and determining their petrogenetic histories. The major rock type recovered at MOR is basalt. In fact, because it is so common, basalt found at spreading Ridges are called MORB, or Mid-Ocean Ridge basalts. Other terms that have commonly been used to describe MORB include ocean Ridge basalts (ORB), abyssal tholeiites, ocean Ridge tholeiites and low-K olivine tholeiites, implying certain compositional characteristics. In this investigation you will examine the petrography and geochemistry of 6 samples of Mid-Ocean Ridge basalt and related differentiated lavas recovered from the Cleft segment of southern Juan de Fuca Ridge (JdFR), a medium spreading-rate MOR in the northeast Pacific Ocean (Figure 1). The goals of this investigation are to: 1. Investigate magmatism in a Mid-Ocean Ridge environment
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vapour undersaturation in primitive mid ocean Ridge basalt and the volatile content of earth s upper mantle
Nature, 2002Co-Authors: A E Saal, Charles H Langmuir, Erik H Hauri, Michael R PerfitAbstract:The analysis of volatiles in magmatic systems can be used to constrain the volatile content of the Earth’s mantle and the influence that magmatic degassing has on the chemistry of the oceans and the atmosphere. But most volatile elements have very low solubilities in magmas at atmospheric pressure, and therefore virtually all erupted lavas are degassed and do not retain their primary volatile signatures. Here we report the undersaturated pre-eruptive volatile content for a suite of Mid-Ocean-Ridge basalts from the Siqueiros intra-transform spreading centre. The undersaturation leads to correlations between volatiles and refractory trace elements that provide new constraints on volatile abundances and their behaviour in the upper mantle. Our data generate improved limits on the abundances of carbon dioxide, water, fluorine, sulphur and chlorine in the source of normal Mid-OceanRidge basalt. The incompatible behaviour of carbon dioxide, together with the CO2/Nb and CO2/Cl ratios, permit estimates of primitive carbon dioxide and chlorine to be made for degassed and chlorine-contaminated Mid-Ocean-Ridge basalt magmas, and hence constrain degassing and contamination histories of Mid-Ocean Ridges.
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vapour undersaturation in primitive mid ocean Ridge basalt and the volatile content of earth s upper mantle
Nature, 2002Co-Authors: A E Saal, Charles H Langmuir, Erik H Hauri, Michael R PerfitAbstract:The analysis of volatiles in magmatic systems can be used to constrain the volatile content of the Earth’s mantle and the influence that magmatic degassing has on the chemistry of the oceans and the atmosphere. But most volatile elements have very low solubilities in magmas at atmospheric pressure, and therefore virtually all erupted lavas are degassed and do not retain their primary volatile signatures. Here we report the undersaturated pre-eruptive volatile content for a suite of Mid-Ocean-Ridge basalts from the Siqueiros intra-transform spreading centre. The undersaturation leads to correlations between volatiles and refractory trace elements that provide new constraints on volatile abundances and their behaviour in the upper mantle. Our data generate improved limits on the abundances of carbon dioxide, water, fluorine, sulphur and chlorine in the source of normal Mid-OceanRidge basalt. The incompatible behaviour of carbon dioxide, together with the CO2/Nb and CO2/Cl ratios, permit estimates of primitive carbon dioxide and chlorine to be made for degassed and chlorine-contaminated Mid-Ocean-Ridge basalt magmas, and hence constrain degassing and contamination histories of Mid-Ocean Ridges.
Fabrice J Fontaine - One of the best experts on this subject based on the ideXlab platform.
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a si cl geothermobarometer for the reaction zone of high temperature basaltic hosted mid ocean Ridge hydrothermal systems
Geochemistry Geophysics Geosystems, 2009Co-Authors: Fabrice J Fontaine, William S D Wilcock, Dionysis E Foustoukos, David A ButterfieldAbstract:[1] The chemical composition of Mid-Ocean Ridge hydrothermal vent fluids is thought to reflect conditions within a deep-seated reaction zone. Although temperature and pressure conditions within this region are key parameters that characterize the subseafloor hydrothermal regime and the cooling of Mid-Ocean Ridges, they are poorly constrained. In this paper, we developed a model in which high-temperature, vapor-type (low-salinity) vent fluid silica (Si) and chlorine (Cl) concentrations can be used to define lines in pressure-temperature space whose intersection is used to estimate conditions at the top of the reaction zone, under the simplifying assumption that Si and Cl reflect a common point of equilibration. We apply this model to various basaltic-hosted Mid-Ocean Ridge sites. Results suggest a minimal variation in inferred temperatures, ranging from 415 to 445°C. This lends support to the fluxibility model in which upwelling hydrothermal plumes rise at temperatures that maximize the energy flux. Quartz precipitation due to reequilibration during upflow tends to lower temperature and pressure estimates and can artificially indicate shallower transition from reaction to upflow zone. However, maximum equilibration pressures are site-dependent and compare well with depth to magma chamber imaged by seismic studies. This suggests that vapors circulate close to magma chambers and is difficult to reconcile with models in which Mid-Ocean Ridge hydrothermal circulation occurs in two layers with a substantial layer of convecting brine. Accordingly, equilibration pressure predicted by our model can also be used to infer the depth of the magma chamber at sites where seismic data are not available but where vapor-like fluids have been collected and analyzed.
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dynamics and storage of brine in mid ocean Ridge hydrothermal systems
Journal of Geophysical Research, 2006Co-Authors: Fabrice J Fontaine, William S D WilcockAbstract:[1] Mid-Ocean Ridge hydrothermal systems are known to vent fluids with salinities substantially different from seawater as a result of phase separation and segregation of the resulting vapor and brine phases. Time series of vent temperature and salinity (chlorinity) show that some black-smoker vent fields such as the Main Endeavour Field on the Juan de Fuca Ridge have vented fluids with salinities well below seawater for over a decade, which raises important questions concerning the fate of brines in these systems. One widely accepted model is that high-density brines formed by supercritical phase separation sink to the base of hydrothermal systems, leading to the development of a two-layer system in which a recirculating brine layer underlies a single-pass seawater cell. We first present theoretical arguments to constrain the dynamics of such a deep brine layer in a system still undergoing phase separation, and we conclude that if brines are stored in a basal layer, they are unlikely to convect because they will be stably stratified. One consequence of this result is that the brine layer beneath black smoker systems has to be thin (<10 m) to match the high heat fluxes. However, estimates of the rate at which brines are accumulating in the crust below the main field on the Endeavour segment of the Juan de Fuca Ridge suggest that the brine layer is likely at least 100 m thick. To resolve this apparent paradox, we propose an alternative model. We argue that interfacial tensions between fluid and solid phases will likely favor the segregation of vapor into the main fractures and brine into the smaller fissures and backwaters. This allows the vapor to flow efficiently through the system and transport large heat fluxes while most of the porosity in the lower part of the system fills with brines. It is generally believed that the pressure gradients in Mid-Ocean Ridge hydrothermal systems are close to cold hydrostatic. At the high temperatures and pressures characteristic of the deeper parts of these systems, brines with salinities as high as 20 wt % NaCl have densities around 800–900 kg m−3 and will be buoyant in a cold-hydrostatic system. Rather than sinking to the base of the system, it is possible that brines produced by supercritical phase separation rise slowly until they reach a level of neutral buoyancy as they cool or enter high-permeability regions in which the pressure gradients decrease.
Rita Fonseca - One of the best experts on this subject based on the ideXlab platform.
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discovery of a black smoker vent field and vent fauna at the arctic mid ocean Ridge
Nature Communications, 2010Co-Authors: Rolf B Pedersen, Ingunn H. Thorseth, Hans Tore Rapp, Fernando J A S Barriga, Tamara Baumberger, K Flesland, Rita Fonseca, Gretchen L Fruhgreen, Steffen L JorgensenAbstract:The Arctic Mid-Ocean Ridge spreads extremely slowly and hydrothermal vent fields have not been reported in its vicinity. Pedersen et al. describe a black smoker vent field with large hydrothermal deposits and novel fauna distinct from those found in similar environments in the Atlantic.
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discovery of a black smoker vent field and vent fauna at the arctic mid ocean Ridge
Nature Communications, 2010Co-Authors: Rolf B Pedersen, Ingunn H. Thorseth, Hans Tore Rapp, Fernando J A S Barriga, Tamara Baumberger, K Flesland, Rita Fonseca, Marvin D Lilley, Gretchen L FruhgreenAbstract:The Arctic Mid-Ocean Ridge (AMOR) represents one of the most slow-spreading Ridge systems on Earth. Previous attempts to locate hydrothermal vent fields and unravel the nature of venting, as well as the provenance of vent fauna at this northern and insular termination of the global Ridge system, have been unsuccessful. Here, we report the first discovery of a black smoker vent field at the AMOR. The field is located on the crest of an axial volcanic Ridge (AVR) and is associated with an unusually large hydrothermal deposit, which documents that extensive venting and long-lived hydrothermal systems exist at ultraslow-spreading Ridges, despite their strongly reduced volcanic activity. The vent field hosts a distinct vent fauna that differs from the fauna to the south along the Mid-Atlantic Ridge. The novel vent fauna seems to have developed by local specialization and by migration of fauna from cold seeps and the Pacific. The Arctic Mid-Ocean Ridge spreads extremely slowly and hydrothermal vent fields have not been reported in its vicinity. Pedersenet al. describe a black smoker vent field with large hydrothermal deposits and novel fauna distinct from those found in similar environments in the Atlantic.
Marvin D Lilley - One of the best experts on this subject based on the ideXlab platform.
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discovery of a black smoker vent field and vent fauna at the arctic mid ocean Ridge
Nature Communications, 2010Co-Authors: Rolf B Pedersen, Ingunn H. Thorseth, Hans Tore Rapp, Fernando J A S Barriga, Tamara Baumberger, K Flesland, Rita Fonseca, Marvin D Lilley, Gretchen L FruhgreenAbstract:The Arctic Mid-Ocean Ridge (AMOR) represents one of the most slow-spreading Ridge systems on Earth. Previous attempts to locate hydrothermal vent fields and unravel the nature of venting, as well as the provenance of vent fauna at this northern and insular termination of the global Ridge system, have been unsuccessful. Here, we report the first discovery of a black smoker vent field at the AMOR. The field is located on the crest of an axial volcanic Ridge (AVR) and is associated with an unusually large hydrothermal deposit, which documents that extensive venting and long-lived hydrothermal systems exist at ultraslow-spreading Ridges, despite their strongly reduced volcanic activity. The vent field hosts a distinct vent fauna that differs from the fauna to the south along the Mid-Atlantic Ridge. The novel vent fauna seems to have developed by local specialization and by migration of fauna from cold seeps and the Pacific. The Arctic Mid-Ocean Ridge spreads extremely slowly and hydrothermal vent fields have not been reported in its vicinity. Pedersenet al. describe a black smoker vent field with large hydrothermal deposits and novel fauna distinct from those found in similar environments in the Atlantic.
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CO2 and 3He in hydrothermal plumes: implications for Mid-Ocean Ridge CO2 flux
Earth and Planetary Science Letters, 2004Co-Authors: Joseph A. Resing, John E. Lupton, Richard A. Feely, Marvin D LilleyAbstract:Abstract Measurements of pH and total carbon dioxide (ΣCO2) from Axial Volcano in the 2 years following its eruption and from the Southern East Pacific Rise from 27°S to 32°S are used to demonstrate that decreases in pH in hydrothermal plumes at Mid-Ocean Ridges are primarily caused by the emission of CO2-rich hydrothermal fluids. As a result, changes in pH can be directly related to the amount of CO2 added to the hydrothermal plumes. Because hydrothermal plumes integrate the hydrothermal output and chemical signatures from multiple sources in a vent field area, the chemistry in plumes reflects that in fluids being emitted from vent field areas as a whole. We use directly measured CO2, CO2 inferred from changes in pH, and 3He data to constrain the ratio of CO2/3He in hydrothermal plumes along extensive segments of the Mid-Ocean Ridge and over time following a volcanic eruption. There are a limited number of CO2/3He values reported for Mid-Ocean Ridge basalts and hydrothermal fluids, and thus the CO2/3He ratios determined here greatly increase their geographic and temporal distribution and demonstrate that this ratio is fairly constant along the Mid-Ocean Ridges (MORs), having a value of ∼2×109. These data suggest that a large degree of fractionation between 3He and CO2 does not occur during magmatic degassing, eruption, and hydrothermal circulation. If a CO2/3He ratio of 2×109 is representative of the ratio found in the mantle beneath the MOR, then hydrothermal fluxes of CO2 can be estimated for the global oceans based on the flux of 3He from the mantle and MORs. These results suggest a MOR CO2 flux of 0.5–2×1012 mol year−1, which is consistent with other estimates.
Gretchen L Fruhgreen - One of the best experts on this subject based on the ideXlab platform.
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discovery of a black smoker vent field and vent fauna at the arctic mid ocean Ridge
Nature Communications, 2010Co-Authors: Rolf B Pedersen, Ingunn H. Thorseth, Hans Tore Rapp, Fernando J A S Barriga, Tamara Baumberger, K Flesland, Rita Fonseca, Gretchen L Fruhgreen, Steffen L JorgensenAbstract:The Arctic Mid-Ocean Ridge spreads extremely slowly and hydrothermal vent fields have not been reported in its vicinity. Pedersen et al. describe a black smoker vent field with large hydrothermal deposits and novel fauna distinct from those found in similar environments in the Atlantic.
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discovery of a black smoker vent field and vent fauna at the arctic mid ocean Ridge
Nature Communications, 2010Co-Authors: Rolf B Pedersen, Ingunn H. Thorseth, Hans Tore Rapp, Fernando J A S Barriga, Tamara Baumberger, K Flesland, Rita Fonseca, Marvin D Lilley, Gretchen L FruhgreenAbstract:The Arctic Mid-Ocean Ridge (AMOR) represents one of the most slow-spreading Ridge systems on Earth. Previous attempts to locate hydrothermal vent fields and unravel the nature of venting, as well as the provenance of vent fauna at this northern and insular termination of the global Ridge system, have been unsuccessful. Here, we report the first discovery of a black smoker vent field at the AMOR. The field is located on the crest of an axial volcanic Ridge (AVR) and is associated with an unusually large hydrothermal deposit, which documents that extensive venting and long-lived hydrothermal systems exist at ultraslow-spreading Ridges, despite their strongly reduced volcanic activity. The vent field hosts a distinct vent fauna that differs from the fauna to the south along the Mid-Atlantic Ridge. The novel vent fauna seems to have developed by local specialization and by migration of fauna from cold seeps and the Pacific. The Arctic Mid-Ocean Ridge spreads extremely slowly and hydrothermal vent fields have not been reported in its vicinity. Pedersenet al. describe a black smoker vent field with large hydrothermal deposits and novel fauna distinct from those found in similar environments in the Atlantic.