The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Simon M Peacock - One of the best experts on this subject based on the ideXlab platform.
-
Subduction factory 1. Theoretical mineralogy, densities, seismic wave speeds, and H 2 O contents
Journal of Geophysical Research: Solid Earth, 2003Co-Authors: Bradley R. Hacker, Geoffrey A. Abers, Simon M PeacockAbstract:[1] We present a new compilation of physical properties of minerals relevant to subduction zones and new phase diagrams for Mid-Ocean Ridge Basalt, lherzolite, depleted lherzolite, harzburgite, and serpentinite. We use these data to calculate H2O content, density and seismic wave speeds of subduction zone rocks. These calculations provide a new basis for evaluating the subduction factory, including (1) the presence of hydrous phases and the distribution of H2O within a subduction zone; (2) the densification of the subducting slab and resultant effects on measured gravity and slab shape; and (3) the variations in seismic wave speeds resulting from thermal and metamorphic processes at depth. In considering specific examples, we find that for ocean basins worldwide the lower oceanic crust is partially hydrated (< 1.3 wt % H2O), and the uppermost mantle ranges from unhydrated to &SIM;20% serpentinized (&SIM;2.4 wt % H2O). Anhydrous eclogite cannot be distinguished from harzburgite on the basis of wave speeds, but its &SIM;6% greater density may render it detectable through gravity measurements. Subducted hydrous crust in cold slabs can persist to several gigapascals at seismic velocities that are several percent slower than the surrounding mantle. Seismic velocities and V-P/V-S ratios indicate that mantle wedges locally reach 60-80% hydration.
-
subduction factory 1 theoretical mineralogy densities seismic wave speeds and h2o contents
Journal of Geophysical Research, 2003Co-Authors: Bradley R. Hacker, Geoffrey A. Abers, Simon M PeacockAbstract:[1] We present a new compilation of physical properties of minerals relevant to subduction zones and new phase diagrams for Mid-Ocean Ridge Basalt, lherzolite, depleted lherzolite, harzburgite, and serpentinite. We use these data to calculate H2O content, density and seismic wave speeds of subduction zone rocks. These calculations provide a new basis for evaluating the subduction factory, including (1) the presence of hydrous phases and the distribution of H2O within a subduction zone; (2) the densification of the subducting slab and resultant effects on measured gravity and slab shape; and (3) the variations in seismic wave speeds resulting from thermal and metamorphic processes at depth. In considering specific examples, we find that for ocean basins worldwide the lower oceanic crust is partially hydrated (<1.3 wt % H2O), and the uppermost mantle ranges from unhydrated to � 20% serpentinized (� 2.4 wt % H2O). Anhydrous eclogite cannot be distinguished from harzburgite on the basis of wave speeds, but its � 6% greater density may render it detectable through gravity measurements. Subducted hydrous crust in cold slabs can persist to several gigapascals at seismic velocities that are several percent slower than the surrounding mantle. Seismic velocities and VP/VS ratios indicate that mantle wedges locally reach 60–80% hydration. INDEX TERMS: 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); 3660 Mineralogy and Petrology: Metamorphic petrology; 3919 Mineral Physics: Equations of state; 5199 Physical Properties of Rocks: General or miscellaneous; 8123 Tectonophysics: Dynamics, seismotectonics; KEYWORDS: subduction, seismic velocities, mineral physics, H2O
-
subduction factory 1 theoretical mineralogy densities seismic wave speeds and h 2 o contents
Journal of Geophysical Research, 2003Co-Authors: Bradley R. Hacker, Geoffrey A. Abers, Simon M PeacockAbstract:[1] We present a new compilation of physical properties of minerals relevant to subduction zones and new phase diagrams for Mid-Ocean Ridge Basalt, lherzolite, depleted lherzolite, harzburgite, and serpentinite. We use these data to calculate H2O content, density and seismic wave speeds of subduction zone rocks. These calculations provide a new basis for evaluating the subduction factory, including (1) the presence of hydrous phases and the distribution of H2O within a subduction zone; (2) the densification of the subducting slab and resultant effects on measured gravity and slab shape; and (3) the variations in seismic wave speeds resulting from thermal and metamorphic processes at depth. In considering specific examples, we find that for ocean basins worldwide the lower oceanic crust is partially hydrated (<1.3 wt % H2O), and the uppermost mantle ranges from unhydrated to � 20% serpentinized (� 2.4 wt % H2O). Anhydrous eclogite cannot be distinguished from harzburgite on the basis of wave speeds, but its � 6% greater density may render it detectable through gravity measurements. Subducted hydrous crust in cold slabs can persist to several gigapascals at seismic velocities that are several percent slower than the surrounding mantle. Seismic velocities and VP/VS ratios indicate that mantle wedges locally reach 60–80% hydration. INDEX TERMS: 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); 3660 Mineralogy and Petrology: Metamorphic petrology; 3919 Mineral Physics: Equations of state; 5199 Physical Properties of Rocks: General or miscellaneous; 8123 Tectonophysics: Dynamics, seismotectonics; KEYWORDS: subduction, seismic velocities, mineral physics, H2O
Dominique Weis - One of the best experts on this subject based on the ideXlab platform.
-
submarine Basalts of the northern kerguelen plateau interaction between the kerguelen plume and the southeast indian Ridge revealed at odp site 1140
Journal of Petrology, 2002Co-Authors: Dominique Weis, F A FreyAbstract:During Ocean Drilling Program Leg 183, Basaltic cores were retrieved from the Northern Kerguelen Plateau (NKP) at Site 1140 on the extreme north of the plateau, ~ 270 km north of the Kerguelen Archipelago. Amongst the six basement units recovered, five were pillow Basalts with fresh glassy rims together with flow lobes. This is the first evidence for submarine eruption anywhere on the Kerguelen Plateau. Each flow unit has distinct geochemical and isotopic characteristics that span the range from Southeast Indian Ridge (SEIR) mid ocean Ridge Basalt to tholeiitic transitional Basalts derived from the Kerguelen mantle plume. Relationships between element abundance ratios involving incompatible elements and isotopic ratios reflect mixing of near-primary melts from an SEIR source and the Kerguelen plume with an increasing role for an incompatible element-rich end-member in the order: Unit 1
-
Temporal evolution of the kerguelen plume: Geochemical evidence from 38 to 82 ma lavas forming the Ninetyeast Ridge
Contributions to Mineralogy and Petrology, 1995Co-Authors: Frederick A. Frey, Dominique WeisAbstract:Basaltic basement has been recovered by deep-sea drilling at seven sites on the linear Ninetyeast Ridge in the eastern Indian Ocean. Studies of the recovered lavas show that this Ridge formed from ~ 82 to 38 Ma as a series of subaerial volcanoes that were created by the northward migration of the Indian Plate over a fixed magma source in the mantle. The Sr, Nd and Pb isotopic ratios of lavas from the Ninetyeast Ridge range widely, but they largely overlap with those of lavas from the Kerguelen Archipelago, thereby confirming previous inferences that the Kerguelen plume was an important magma source for the Ninetyeast Ridge. Particularly important are the ~ 81 Ma Ninetyeast Ridge lavas from DSDP Site 216 which has an anomalous subsidence history (Coffin 1992). These lavas are FeTi-rich tholeiitic Basalts with isotopic ratios that overlap with those of highly alkalic, Upper Miocene lavas in the Kerguelen Archipelago. The isotopic characteristics of the latter which erupted in an intraplate setting have been proposed to be the purest expression of the Kerguelen plume (Weis et al. 1993a,b). Despite the overlap in isotopic ratios, there are important compositional differences between lavas erupted on the Ninetyeast Ridge and in the Kerguelen Archipelago. The Ninetyeast Ridge lavas are dominantly tholeiitic Basalts with incompatible element abundance ratios, such as La/Yb and Zr/Nb, which are intermediate between those of Indian Ocean MORB (Mid-Ocean Ridge Basalt) and the transitional to alkalic Basalts erupted in the Kerguelen Archipelago. These compositional differences reflect a much larger extent of melting for the Ninetyeast Ridge lavas, and the proximity of the plume to a spreading Ridge axis. This tectonic setting contrasts with that of the recent alkalic lavas in the Kerguelen Archipelago which formed beneath the thick lithosphere of the Kerguelen Plateau. From ~ 82 to 38 Ma there was no simple, systematic temporal variation of Sr, Nd and Pb isotopic ratios in Ninetyeast Ridge lavas. Therefore all of the isotopic variability cannot be explained by aging of a compositionally uniform plume. Although Class et al. (1993) propose that some of the isotopic variations reflect such aging, we infer that most of the isotopic heterogeneity in lavas from the Ninetyeast Ridge and Kerguelen Archipelago can be explained by mixing of the Kerguelen plume with a depleted MORB-like mantle component. However, with this interpretation some of the youngest, 42–44 Ma, lavas from the southern Ninetyeast Ridge which have^206pb/^204Pb ratios exceeding those in Indian Ocean MORB and Kerguelen Archipelago lavas require a component with higher^206Pb/^204Pb, such as that expressed in lavas from St. Paul Island.
Takumi Matsumoto - One of the best experts on this subject based on the ideXlab platform.
-
Three-dimensional numerical modeling of thermal regime and slab dehydration beneath Kanto and Tohoku, Japan
Journal of Geophysical Research: Solid Earth, 2017Co-Authors: Yingfeng Ji, Vlad Constantin Manea, Marina Manea, Shoichi Yoshioka, Takumi MatsumotoAbstract:©2016. American Geophysical Union. All Rights Reserved. Although the thermal regime of the interface between two overlapping subducting plates, such as those beneath Kanto, Japan, is thought to play an important role in affecting the distribution of interplate and intraslab earthquakes, the estimation of the thermal regime remains challenging to date. We constructed a three-dimensional (3-D) thermal convection model to simulate the subduction of the Pacific plate along the Japan Trench and Izu-Bonin Trench, including the subduction of the Philippine Sea beneath Kanto and investigated the slab thermal regime and slab water contents in this complex tectonic setting. Based on the subduction parameters tested in generic models with two flat oceanic plates, a faster or thicker plate subducting in a more trench-normal direction produces a colder slab thermal regime. The interplate temperature of the cold anomaly beneath offshore Kanto was approximately 300°C colder than that beneath offshore Tohoku at a same depth of 40 km and approximately 600°C colder at a depth of 70 km. The convergence between the two subducting plates produces an asymmetric thermal structure in the slab contact zone beneath Kanto, which is characterized by clustered seismicity in the colder southwestern half. The thermo-dehydration state of the Mid-Ocean Ridge Basalt near the upper surface of the subducted Pacific plate controls the interplate seismicity beneath the Kanto-Tohoku region according to the spatial concurrence of the thermo-dehydration and seismicity along the megathrust fault zone of the subducted Pacific plate.
-
Three‐dimensional numerical modeling of thermal regime and slab dehydration beneath Kanto and Tohoku, Japan
Journal of Geophysical Research, 2017Co-Authors: Yingfeng Ji, Vlad Constantin Manea, Marina Manea, Shoichi Yoshioka, Takumi MatsumotoAbstract:Although the thermal regime of the interface between two overlapping subducting plates, such as those beneath Kanto, Japan, is thought to play an important role in affecting the distribution of interplate and intraslab earthquakes, the estimation of the thermal regime remains challenging to date. We constructed a three-dimensional (3-D) thermal convection model to simulate the subduction of the Pacific plate along the Japan Trench and Izu-Bonin Trench, including the subduction of the Philippine Sea beneath Kanto and investigated the slab thermal regime and slab water contents in this complex tectonic setting. Based on the subduction parameters tested in generic models with two flat oceanic plates, a faster or thicker plate subducting in a more trench-normal direction produces a colder slab thermal regime. The interplate temperature of the cold anomaly beneath offshore Kanto was approximately 300°C colder than that beneath offshore Tohoku at a same depth of 40 km and approximately 600°C colder at a depth of 70 km. The convergence between the two subducting plates produces an asymmetric thermal structure in the slab contact zone beneath Kanto, which is characterized by clustered seismicity in the colder southwestern half. The thermo-dehydration state of the Mid-Ocean Ridge Basalt near the upper surface of the subducted Pacific plate controls the interplate seismicity beneath the Kanto-Tohoku region according to the spatial concurrence of the thermo-dehydration and seismicity along the megathrust fault zone of the subducted Pacific plate.
Erik H Hauri - One of the best experts on this subject based on the ideXlab platform.
-
two component mantle melting mixing model for the generation of mid ocean Ridge Basalts implications for the volatile content of the pacific upper mantle
Geochimica et Cosmochimica Acta, 2016Co-Authors: Kei Shimizu, Erik H Hauri, A E Saal, Corinne Myers, A N Nagle, Donald W Forsyth, Vadim S. KamenetskyAbstract:We report major, trace, and volatile element (CO2, H2O, F, Cl, S) contents and Sr, Nd, and Pb isotopes of Mid-Ocean Ridge Basalt (MORB) glasses from the Northern East Pacific Rise (NEPR) off-axis seamounts, the Quebrada-Discovery-GoFar (QDG) transform fault system, and the Macquarie Island. The incompatible trace element (ITE) contents of the samples range from highly depleted (DMORB, Th/La ⩽ 0.035) to enriched (EMORB, Th/La ⩾ 0.07), and the isotopic composition spans the entire range observed in EPR MORB. Our data suggest that at the time of melt generation, the source that generated the EMORB was essentially peridotitic, and that the composition of NMORB might not represent melting of a single upper mantle source (DMM), but rather mixing of melts from a two-component mantle (depleted and enriched DMM or D-DMM and E-DMM, respectively). After filtering the volatile element data for secondary processes (degassing, sulfide saturation, assimilation of seawater-derived component, and fractional crystallization), we use the volatiles to ITE ratios of our samples and a two-component mantle melting-mixing model to estimate the volatile content of the D-DMM (CO2 = 22 ppm, H2O = 59 ppm, F = 8 ppm, Cl = 0.4 ppm, and S = 100 ppm) and the E-DMM (CO2 = 990 ppm, H2O = 660 ppm, F = 31 ppm, Cl = 22 ppm, and S = 165 ppm). Our two-component mantle melting-mixing model reproduces the kernel density estimates (KDE) of Th/La and 143Nd/144Nd ratios for our samples and for EPR axial MORB compiled from the literature. This model suggests that: (1) 78% of the Pacific upper mantle is highly depleted (D-DMM) while 22% is enriched (E-DMM) in volatile and refractory ITE, (2) the melts produced during variable degrees of melting of the E-DMM controls most of the MORB geochemical variation, and (3) a fraction (∼65% to 80%) of the low degree EMORB melts (produced by ∼1.3% melting) may escape melt aggregation by freezing at the base of the oceanic lithosphere, significantly enriching it in volatile and trace element contents. Our results are consistent with previously proposed geodynamical processes acting at Mid-Ocean Ridges and with the generation of the E-DMM. Our observations indicate that the D-DMM and E-DMM have (1) a relatively constant CO2/Cl ratio of ∼57 ± 8, and (2) volatile and ITE element abundance patterns that can be related by a simple melting event, supporting the hypothesis that the E-DMM is a recycled oceanic lithosphere mantle metasomatized by low degree melts. Our calculation and model give rise to a Pacific upper mantle with volatile content of CO2 = 235 ppm, H2O = 191 ppm, F = 13 ppm, Cl = 5 ppm, and S = 114 ppm.
-
osmium isotopes and mantle convection
Philosophical transactions - Royal Society. Mathematical physical and engineering sciences, 2002Co-Authors: Erik H HauriAbstract:The decay of 187 Re to 187 Os (with a half–life of 42 billion years) provides a unique isotopic fingerprint for tracing the evolution of crustal materials and mantle residues in the convecting mantle. Ancient subcontinental mantle lithosphere has uniquely low Re/Os and 187 Os/ 188 Os ratios due to large–degree melt extraction, recording ancient melt–depletion events as old as 3.2 billion years. Partial melts have Re/Os ratios that are orders of magnitude higher than their sources, and the subduction of oceanic or continental crust introduces into the mantle materials that rapidly accumulate radiogenic 187 Os. Eclogites from the subcontinental lithosphere have extremely high 187 Os/ 188 Os ratios, and record ages as old as the oldest peridotites. The data show a near–perfect partitioning of Re/Os and 187 Os/ 188 Os ratios between peridotites (low) and eclogites (high). The convecting mantle retains a degree of Os–isotopic heterogeneity similar to the lithospheric mantle, although its amplitude is modulated by convective mixing. Abyssal peridotites from the ocean Ridges have low Os isotope ratios, indicating that the upper mantle had undergone episodes of melt depletion prior to the most recent melting events to produce mid–ocean–Ridge Basalt. The amount of rhenium estimated to be depleted from the upper mantle is 10 times greater than the rhenium budget of the continental crust, requiring a separate reservoir to close the mass balance. A reservoir consisting of 5–10% of the mantle with a rhenium concentration similar to mid–ocean–Ridge Basalt would balance the rhenium depletion of the upper mantle. This reservoir most likely consists of mafic oceanic crust recycled into the mantle over Earth9s history and provides the material that melts at oceanic hotspots to produce ocean–island Basalts (OIBs). The ubiquity of high Os isotope ratios in OIB, coupled with other geochemical tracers, indicates that the mantle sources of hotspots contain significant quantities (greater than 10%) of lithologically distinct mafic material which represents ancient oceanic lithosphere cycled through the convecting mantle on a time–scale of 800 million years or more.
-
vapour undersaturation in primitive mid ocean Ridge Basalt and the volatile content of earth s upper mantle
Nature, 2002Co-Authors: A E Saal, Erik H Hauri, Charles H. Langmuir, 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.
Michael R Perfit - One of the best experts on this subject based on the ideXlab platform.
-
vapour undersaturation in primitive mid ocean Ridge Basalt and the volatile content of earth s upper mantle
Nature, 2002Co-Authors: A E Saal, Erik H Hauri, Charles H. Langmuir, 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.
-
Insights into Mid-Ocean Ridge Basalt petrogenesis: U-series disequilibria from the Siqueiros Transform, Lamont Seamounts, and East Pacific Rise
Journal of Geophysical Research, 1999Co-Authors: Craig Campbell Lundstrom, Michael R Perfit, D. E. Sampson, James B. Gill, Quentin WilliamsAbstract:Parent-daughter disequilibria between (230Th)/(238U), (231Pa)/(235U) and (226Ra)/(230Th) (parentheses refer to activities) have been measured by thermal ionization mass spectrometry and inductively coupled plasma-mass spectrometry in Basalts from three tectonomagmatic settings of the East Pacific Rise (EPR) at 8°20′-10°N. Mid-Ocean Ridge Basalts (MORB) from the Siqueiros Transform, the Lamont Seamounts, and the EPR Ridge crest span a large compositional range from primitive, high-MgO Basalts with strong incompatible element depletions (DMORB) to typical normal MORB (NMORB) to rare incompatible element enriched Basalts (EMORB) derived from a more enriched source isotopically. Concentrations of U vary from 400 ppb in EMORB while Th/U ranges from 2 in DMORB up to 3 in EMORB. The young-looking high-MgO Basalts have (226Ra)/(230Th) that ranges from 3.2 to 4.2, while EMORB appear old being near secular equilibrium. Initial (231Pa)(235U) are very high (>2.5) in all of the Siqueiros Basalts. Three Basalts from the Lamont Seamounts have low incompatible element concentrations and low Th/U and are in secular equilibrium for (226Ra)/(230Th) while the sample located closest to the Ridge axis has significant 226Ra and 231Pa excesses and minor 230Th excess. DMORB lack 230Th excess, have high excesses of226Ra and 231Pa, and resemble experimentally determined melts of peridotite at 1 GPa, implying derivation from relatively shallow level melting of spinel lherzolite at low residual porosity. Disequilibria for all three parent-daughter pairs are consistent with typical axial NMORB resulting from mixing of melts derived from heterogeneous sources, specifically 90–95% DMORB with 5–10% EMORB. The observation that all samples, regardless of tectonomagmatic setting, lie on the same mixing trend suggests that melting beneath seamounts and transforms is similar to melting beneath the Ridge axis. Variations in 230Th excess over short spatial scales imply that garnet-bearing mafic veins create all of the 230Th excess observed in typical NMORB.
-
Petrology and geochemistry of Basalts from the southern Juan de Fuca Ridge: Controls on the spatial and temporal evolution of Mid-Ocean Ridge Basalt
Journal of Geophysical Research, 1994Co-Authors: Matthew C. Smith, Michael R Perfit, Ian R. JonassonAbstract:Three morphologically distinct regions within the neovolcanic zone of the Cleft segment of the southern Juan de Fuca Ridge were investigated and sampled in detail using the DSRV Alvin. Additional along-strike and off-axis samples were recovered by dredge. The southernmost region, the Southern Cleft site, is characterized by a 3-km-wide axial valley floored by ponded sheet flows and bisected by a 30- to 50-m-wide cleft. Farther north at the “Young Sheet Flow” site, the Ridge axis is characterized by a distinct 500-m-wide inner graben that is largely covered by distinctly younger looking sheet flows. The northernmost of the three regions is defined by a linear series of discontinuous constructional pillow mounds that extend the trend of the Cleft segment well into the zone of overlap with the neighboring Vance segment. The pillowed lavas at the “Young Pillow Mound” site represent the most recent episode of volcanism along the Cleft segment. Strong correlations exist between degrees of fractionation, relative ages of lavas, and latitude; lavas are progressively younger looking and more mafic to the north. The compositional range of Mid-Ocean Ridge Basalts from the neovolcanic zone can generally be accounted for by 35–40% low-pressure fractional crystallization of relatively primitive, but not primary, depleted (N-type) melts. Scatter of the geochemical data about calculated liquid lines of descent is probably the result of mixing of magmas with slightly different parental compositions, generated from small-scale mantle heterogeneities. Furthermore, the chemical variability may be the result of mixing of very depleted and more enriched sources or melts that are present beneath the southern Juan de Fuca Ridge. The more primitive nature of the young pillow mound Basalts and their slightly different chemical characteristics indicates they cannot be simply related to the older southernmost lavas by along-axis flow in a continuous axial magma chamber or conduit. Rather, the data suggest lavas were derived from discrete magma chambers or lenses, each in a different stage of evolution. The youngest events may be associated with a new influx of magma into the northern part of the segment and subsequent northward diking and propagation to form the new pillow mounds. The oldest stage (∼40% additional crystallization of the most mafic composition) is associated with focused hydrothermal activity and tectonic extension, whereas the youngest events are characterized by Ridge inflation, diking, and dispersed hydrothermal activity. Geochemical and tectonomagmatic features observed along the Cleft segment are similar to those recently documented along the East Pacific Rise from 9°30′N–10°N suggesting the scales, processes, and stages of magmagenesis are similar along medium to fast spreading Ridge segments.
-
Evidence from rare gases for magma-chamber degassing of highly evolved Mid-Ocean-Ridge Basalt
Nature, 1990Co-Authors: David E. Fisher, Michael R PerfitAbstract:HIGHLY evolved lavas have been recovered from moderate- to fast-spreading centres along the Mid-Ocean Ridge system, most commonly near propagating rifts and overlapping spreading centres1–7. Their origin and occurrence are generally explained by extensive modification of a primary Basalt magma by fractional crystallization at shallow levels in the oceanic crust (model I)1–4,6–9. Other crustal processes have also been invoked, including periodic magma mixing of a highly fractionated liquid with multiple primary liquids (model 2)10,11, and seawater interaction with the mantle-derived magma (model 3)12–14. Here we report the first 4He and argon isotope data for several highly evolved Mid-Ocean-Ridge Basalts (MORBs) and andesites. The samples were recovered with the submersible Alvin from a very limited section (