Geology of the Zambales ophiolite, Luzon, Philippines

Rossman, D.L.; Castañada, G.C.; Bacuta, George C.

doi:10.1016/0040-1951(89)90366-1

Cited by 26 publications

(13 citation statements)

References 25 publications

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“…Hawkins & Evans, 1983;Geary et al, 1989;Yumul, 1989). However, some workers have argued that the Acoje and Coto blocks physically belong to a single unit and the compositional difference between the two is due to the variation in the source mantle rocks (Rossman et al, 1989). Previous works have also highlighted the prevalence of podiform chromitites within the mantle peridotites of the ZOC.…”

Section: Geological Settingmentioning

confidence: 99%

Textural Evidence for the Chromite‐Oversaturated Character of the Melt Involved in Podiform Chromitite Formation

et al. 2013

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Well-preserved oval-shaped dunite clots occur within the exceptionally fresh massive podiform chromitites from the Coto Block of the Zambales Ophiolite Complex, the Philippines. The dunite/ chromitite boundary shows an interlocking texture; olivine inclusions in chromites in the podiform chromitites show the same optical extinction with larger adjacent olivines in the dunite clots. This texture was formed by the reaction between chromite-oversaturated melt and its dunite inclusions. The existence of such type of melt was previously only hypothesized to explain the origin of layered and podiform chromitites but is now confirmed by this discovery.

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Section: Geological Settingmentioning

confidence: 99%

Textural Evidence for the Chromite‐Oversaturated Character of the Melt Involved in Podiform Chromitite Formation

et al. 2013

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“…The Zambales ophiolite of Luzon. The Zambales ophiolite in Luzon (Philippines) is the best preserved accessible fragment of Eocene oceanic lithosphere in the Western Pacific and therefore holds important clues to the Eocene evolution of the region (e.g., Hawkins and Evans, 1983;Rossman et al, 1989;Geary et al, 1989). The ophiolite forms two distinct blocks.…”

Section: Oaoga Shima^792mentioning

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

290

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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“…Olivine is the main mineral component in ultramafic rocks such as peridotite and dunite, which are abundant in the mantle, in seafloor crustal accumulates, and in ophiolites which represent sections of oceanic lithosphere obducted onto the continental crust (e.g., Rossman et al, 1989;Albrektsen et al, 1991;Dick et al, 2000;Nicolas and Boudier, 2000;Iyer et al, 2008). Moreover, olivine is abundant in the martian crust in ultramafic accumulates and in picritic ultramafic lavas (Hoefen et al, 2003;Christensen et al, 2005;Mustard et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

The Potential for Low-Temperature Abiotic Hydrogen Generation and a Hydrogen-Driven Deep Biosphere

Hellevang

Huang²,

Thorseth³

2011

Astrobiology

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The release and oxidation of ferrous iron during aqueous alteration of the mineral olivine is known to reduce aqueous solutions to such extent that molecular hydrogen, H2, forms. H2 is an efficient energy carrier and is considered basal to the deep subsurface biosphere. Knowledge of the potential for H2 generation is therefore vital to understanding the deep biosphere on Earth and on extraterrestrial bodies. Here, we provide a review of factors that may reduce the potential for H2 generation with a focus on systems in the core temperature region for thermophilic to hyperthermophilic microbial life. We show that aqueous sulfate may inhibit the formation of H2, whereas redox-sensitive compounds of carbon and nitrogen are unlikely to have significant effect at low temperatures. In addition, we suggest that the rate of H2 generation is proportional to the dissolution rate of olivine and, hence, limited by factors such as reactive surface areas and the access of water to fresh surfaces. We furthermore suggest that the availability of water and pore/fracture space are the most important factors that limit the generation of H2. Our study implies that, because of large heat flows, abundant olivine-bearing rocks, large thermodynamic gradients, and reduced atmospheres, young Earth and Mars probably offered abundant systems where microbial life could possibly have emerged.

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Geology of the Zambales ophiolite, Luzon, Philippines

Cited by 26 publications

References 25 publications

Textural Evidence for the Chromite‐Oversaturated Character of the Melt Involved in Podiform Chromitite Formation

Textural Evidence for the Chromite‐Oversaturated Character of the Melt Involved in Podiform Chromitite Formation

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

The Potential for Low-Temperature Abiotic Hydrogen Generation and a Hydrogen-Driven Deep Biosphere

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