Petrology of amphibolite‐facies mafic and ultramafic rocks from the Catalina Schist, southern California: metasomatism and migmatization in a subduction zone metamorphic setting

Sorensen, Sorena S.

doi:10.1111/j.1525-1314.1988.tb00431.x

Cited by 98 publications

(41 citation statements)

References 28 publications

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“…Experimental work on water-saturated or dehydration melting of amphibolites has produced adakite melt [43][44][45][46][47][48][49] . Adakitic glass inclusions in arc lavas, mineralogy of xenoliths within subduction related lavas [36,50] and migmatitic veins with intermediate to felsic compositions in ophiolites [51][52][53][54] have also been observed. Finally, ion probe analyses of clinopyroxene phenocrysts in primitive Aleutian magnesian andesites show atypical correlation between Mg # and Sr and Nd/Yb, suggesting a slab melt that equilibrated with mantle olivine is necessary to generate the archetypal adakite [55] .…”

Section: Adakite From Slab Meltingmentioning

confidence: 92%

An overview of adakite petrogenesis

2006

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Section: Adakite From Slab Meltingmentioning

confidence: 92%

An overview of adakite petrogenesis

2006

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“…They typically have Zr/Y ratios of 20 or more and Zr/Sm ratios of 60 or more, which would explain the trends in Figure 10. Moreover, amphibolite melting has been observed in metamorphic soles beneath ophiolitic slabs (e.g., Pearce, 1989) and subduction zone metamorphic terranes (Sorensen, 1988). Note, however, that component B is more radiogenic than PMM.…”

Section: Isotope-trace Element Covariationsmentioning

confidence: 99%

Isotopic Evidence for the Origin of Boninites and Related Rocks Drilled in the Izu-Bonin (Osagawara) Forearc, Leg 125

Pearce¹,

Thirlwall²,

Ingram³

et al. 1992

Proceedings of the Ocean Drilling Program

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Twenty-six samples representing the wide range of lithologies (low-and intermediate-Ca boninites and bronzite andesites, high-Ca boninites, basaltic andesites-rhyolites) drilled during Leg 125 at Sites 782 and 786 on the Izu-Bonin outer-arc high have been analyzed for Sr, Nd, and Pb isotopes. Nd-Sr isotope covariations show that most samples follow a trend parallel to a line from Pacific MORB mantle (PMM) to Pacific Volcanogenic sediment (PVS) but displaced slightly toward more radiogenic Sr. Pb isotope covariations show that all the Eocene-Oligocene samples plot along the Northern Hemisphere Reference Line, indicating little or no Pb derived from subducted pelagic sediment in their source. Two young basaltic andesite clasts within sediment do have a pelagic sediment signature but this may have been gained by alteration rather than subduction. In all isotopic projections, the samples form consistent groupings: the tholeiites from Site 782 and Hole 786A plot closest to PMM, the boninites and related rocks from Sites 786B plot closest to PVS, and the boninite lavas from Hole 786A and late boninitic dikes from Hole 786B occupy an intermediate position. Isotope-trace element covariations indicate that these isotopic variations can be explained by a three-component mixing model. One component (A) has the isotopic signature of PMM but is depleted in the more incompatible elements. It is interpreted as representing suboceanic mantle lithosphere. A second component (B) is relatively radiogenic (εNd = ca 4-6; 206 Pb/ 204 Pb = ca 19.0-19.3; εSr = ca -10 to -6)). Its trace element pattern has, among other characteristics, a high Zr/Sm ratio, which distinguishes it from the "normal" fluid components associated with subduction and hotspot activity. There are insufficient data at present to tie down its origin: probably it was either derived from subducted lithosphere or volcanogenic sediment fused in amphibolite facies; or it represents an asthenospheric melt component that has been fractionated by interaction with amphibole-bearing mantle. The third component (C) is characterized by high contents of Sr and high εSr values and is interpreted as a subducted fluid component. The mixing line on a diagram of Zr/Sr against ε Sr suggests that component C may have enriched the lithosphere (component A) before component B. These components may also be present on a regional basis but, if so, may not have had uniform compositions. Only the boninitic series from nearby Chichijima would require an additional, pelagic sediment component. In general, these results are consistent with models of subduction of ridges and young lithosphere during the change from a ridge-transform to subduction geometry at the initiation of subduction in the Western Pacific.

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“…The most comprehensive studies to date come from the Catalina schist within a blueschist-bearing subduction complex in Southern California (Sorensen and Barton, 1987;Sorensen, 1988;Sorensen and Grossman, 1989). The conditions of melting and metamorphism in the Catalina schist (8-11 kb and 640° C-750° C) are probably at higher pressure and lower temperature than we envisage at the initiation of subduction, and the presence of both metabasalts and metasediments in the Catalina schists is a complicating factor.…”

Section: Possible Observed Amphibolite Melt Compositionsmentioning

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

288

265

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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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Petrology of amphibolite‐facies mafic and ultramafic rocks from the Catalina Schist, southern California: metasomatism and migmatization in a subduction zone metamorphic setting

Cited by 98 publications

References 28 publications

An overview of adakite petrogenesis

An overview of adakite petrogenesis

Isotopic Evidence for the Origin of Boninites and Related Rocks Drilled in the Izu-Bonin (Osagawara) Forearc, Leg 125

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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