Calculation of the thermodynamic consequences of dehydration in subducting oceanic crust to 100 kb and &gt; 800 degrees C

Delany, J.M.; Helgeson, Harold C.

doi:10.2475/ajs.278.5.638

Cited by 202 publications

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“…This dichotomy is logically ascribed to the influence of the hydrated ocean crust subducted beneath volcanic arcs (Delany and Helgeson, 1978). Dehydration of this crust should release H 2 O and other volatiles into the mantle overlying the crust, and these presumably could cause melting of the mantle to produce arc magmatism.…”

Section: Discussionmentioning

confidence: 99%

Petrology of Volcanic Rocks from the Fore-Arc Sites

Meijer¹,

Anthony²,

Reagan³

1982

Initial Reports of the Deep Sea Drilling Project

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Late Eocene and Oligocene submarine lavas recovered along the Mariana arc-trench slope appear to represent an early stage of arc volcanism along the Palau-Kyushu-Mariana trend. At Site 458, 90 km west of the Mariana Trench, the oldest lavas recovered were two pyroxene andesites with chemical and mineralogic characteristics generally associated with the arc tholeiite series. These are overlain by an unusual series of pyroxene (bronzite) andesites with relatively high Mg, Ni, and Cr and very low Ti, Zr, Y, and REE contents. Lavas with similar characteristics from the Bonin Islands have been called boninites. Because the Site 458 samples show a wider range of textures than is commonly attributed to boninites, the term "boninite series" is suggested for the purpose of discussion. These lavas probably derived from wet partial melting of very depleted mantle materials overlying the Palau-Kyushu-Mariana subduction zone. In Hole 459B, 50 km west of the trench, all the lavas recovered have the general chemical characteristics of arc tholeiite series andesites. Petrographically, volcanic cobbles recovered in sedimentary deposits on the lower trench slope at Sites 460 and 461 (Holes 460, 460A, 461, and 461 A) 23 and 11 km, respectively, from the trench axis are similar to Hole 459B lavas. Chemical data for samples from these sites are compatible with this association.All the volcanic rocks recovered show evidence of secondary alteration. Secondary minerals include clays, carbonate, zeolite, cristobalite, quartz, tridymite, celadonite, chlorite/clay, Fe-hydroxides, and other minor phases. In spite of the alteration, primary phases including pyroxenes, Plagioclase, Fe-Ti-oxides, and glass remain unaltered in some samples. This type of alteration is similar to that observed in typical seafloor volcanic sections in the major ocean basins. No evidence of high P, low T metamorphic conditions has been uncovered.The proximity of arc-related volcanic rocks to the trench axis is difficult to explain in terms of current models of subduction complexes. Possible causes include magma generation at shallow depths along the Eocene-Oligocene subduction zone and tectonic erosion of the lower trench slope.

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Section: Discussionmentioning

confidence: 99%

Petrology of Volcanic Rocks from the Fore-Arc Sites

Meijer¹,

Anthony²,

Reagan³

1982

Initial Reports of the Deep Sea Drilling Project

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“…The average SD value for these basalts is -67 ± 4%o and water content is 2.8 ± 0.3 wt.%. Dehydration above 400°C, when the subducting slab is deep beneath the volcanic front (Toksoz et al, 1971;Delaney and Helgeson, 1978;Van den Benkel and Wortel, 1987) should be accompanied by <20%o fractionation (Graham et al, 1984;Cole et al, 1987). Thus, if we assume that the sub ducted slab beneath the modern Kamchatka-Kurile arc was altered to a similar extent as the Kamchatsky Cape basalts, the hydrogen isotopic composition of water released from the subducted oceanic slab (but not from sediments) can be esti mated to have a SD value --50%0.…”

Section: Isotopic and Chemical Composition Of Mineralsmentioning

confidence: 99%

“…Aqueous fluids derived from the dehydration of subducted oceanic crust play an important role in the process of magma generation (Delaney and Helgeson, 1978;Tatsumi et al, 1986;Tatsumi, 1989;Othman et al, 1989;Peacock, 1990;Avdeiko et al, 1992;Giggenbach, 1992;Stolper and Newman, 1994). The participation of recycled oceanic water in the generation of arc magmas is suggested by the following observations: (1) There is an enrichment in deuterium of high-temperature magmatic gases from island arc volcanoes (Sakai and Matsubaya, 1977;Mizutani, 1978;Taran et al, 1987Taran et al, , 1989Taran et al, , 1995Symonds et al, 1990; *Present address: Instituto de Geofisica, UNAM, 04510, Coyocan, Mexico Giggenbach, 1992;Chiodini et al, 1995) over that commonly ascribed to mantle-derived water (e.g., Taylor and Sheppard, 1986); (2) there is also an enrichment in deuterium in amphiboles from is land arc volcanic rocks (Graham et al, 1982;Taran et al, 1989;Deloule et al, 1991;Miyagi and Matsubaya, 1992); and (3) there is a high pre eruptive water content in subduction zone mag mas (Harris and Anderson, 1984;Johnson et al, 1994) and high initial D/H ratios as estimated for closed or open system degassing models (Taylor et al, 1983;Taylor, 1986;Newman et al, 1988).…”

Section: Introductionmentioning

confidence: 99%

Hydrogen isotopes in hornblendes and biotites from Quaternary volcanic rocks of the Kamchatka-Kurile arc.

Taran¹,

Pokrovsky

Volynets³

1997

Geochem. J.

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“…Delaney and Helgeson (1978) examined the thermodynamics of many of the possible dehydration reactions in sediment and serpentinite associated with subduction. They did not, however, consider the most important reactions for the dehydration of oceanic crust, which involves chlorite breakdown and hornblende formation.…”

Section: Composition Of the Subducted Slabmentioning

confidence: 99%

Boninite and Harzburgite from Leg 125 (Bonin-Mariana Forearc): A Case Study of Magma Genesis during the Initial Stages of Subduction

Pearce¹,

Laan²,

Arculus³

et al. 1992

Proceedings of the Ocean Drilling Program

289

273

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Holes drilled into the volcanic and ultrabasic basement of the Izu-Ogasawara and Mariana forearc terranes during Leg 125 provide data on some of the earliest lithosphere created after the start of Eocene subduction in the Western Pacific. The volcanic basement contains three boninite series and one tholeiite series. (1) Eocene low-Ca boninite and low-Ca bronzite andesite pillow lavas and dikes dominate the lowermost part of the deep crustal section through the outer-arc high at Site 786. (2) Eocene intermediate-Ca boninite and its fractionation products (bronzite andesite, andesite, dacite, and rhyolite) make up the main part of the boninitic edifice at Site 786. (3) Early Oligocene intermediate-Ca to high-Ca boninite sills or dikes intrude the edifice and perhaps feed an uppermost breccia unit at Site 786. (4) Eocene or Early Oligocene tholeiitic andesite, dacite, and rhyolite form the uppermost part of the outer-arc high at Site 782. All four groups can be explained by remelting above a subduction zone of oceanic mantle lithosphere that has been depleted by its previous episode of partial melting at an ocean ridge. We estimate that the average boninite source had lost 10-15 wt% of melt at the ridge before undergoing further melting (5-10%) shortly after subduction started. The composition of the harzburgite (<2% clinopyroxene, Fo content of about 92%) indicates that it underwent a total of about 25% melting with respect to a fertile MORB mantle. The low concentration of Nb in the boninite indicates that the oceanic lithosphere prior to subduction was not enriched by any asthenospheric (OIB) component.The subduction component is characterized by (1) high Zr and Hf contents relative to Sm, Ti, Y, and middle-heavy REE, (2) light REE-enrichment, (3) low contents of Nb and Ta relative to Th, Rb, or La, (4) high contents of Na and Al, and (5) Pb isotopes on the Northern Hemisphere Reference Line. This component is unlike any subduction component from active arc volcanoes in the Izu-Mariana region or elsewhere. Modeling suggests that these characteristics fit a trondhjemitic melt from slab fusion in amphibolite facies. The resulting metasomatized mantle may have contained about 0.15 wt% water. The overall melting regime is constrained by experimental data to shallow depths and high temperatures (1250°C and 1.5 kb for an average boninite) of boninite segregation. We thus envisage that boninites were generated by decompression melting of a diapir of metasomatized residual MORB mantle leaving the harzburgites as the uppermost, most depleted residue from this second stage of melting. Thermal constraints require that both subducted lithosphere and overlying oceanic lithosphere of the mantle wedge be very young at the time of boninite genesis. This conclusion is consistent with models in which an active transform fault offsetting two ridge axes is placed under compression or transpression following the Eocene plate reorganization in the Pacific. Comparison between Leg 125 boninites and boninites and related rocks e...

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Calculation of the thermodynamic consequences of dehydration in subducting oceanic crust to 100 kb and > 800 degrees C

Cited by 202 publications

References 0 publications

Petrology of Volcanic Rocks from the Fore-Arc Sites

Petrology of Volcanic Rocks from the Fore-Arc Sites

Hydrogen isotopes in hornblendes and biotites from Quaternary volcanic rocks of the Kamchatka-Kurile arc.

Boninite and Harzburgite from Leg 125 (Bonin-Mariana Forearc): A Case Study of Magma Genesis during the Initial Stages of Subduction

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