Petrochemistry of Abyssal Oceanic Basalts and Dolerites, and Their Secondary Alterations, Sites 469, 470, 471, 472, 473

Grechin, V.I.; Eroshchev-Shak, Vadim A; Zoloratev, B.P.

doi:10.2973/dsdp.proc.63.127.1981

Cited by 3 publications

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References 2 publications

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“… Projection of XRF‐derived bulk compositions (GM9, GM13, GM15 B , GM18, GM21) and actual mineral compositions (garnet, omphacite, jadeite and chlorite in GM13) onto the jadeite (NaAlSi 2 O 6 )–diopside [Ca(Mg, Fe, Mn)Si 2 O 6 ]–chlorite [(Mg, Fe, Mn) 4.8 Al 2.4 Si 2.8 O 10 (OH) 8 ] plane from lawsonite, phengite (Si = 3.5 apfu), quartz and H 2 O. Data of eclogitized oceanic crust from the Zermatt Saas ophiolite (ZSO) (Angiboust & Agard, 2010), altered oceanic basalt and dolerite (Grechin et al. , 1981; Kelley et al.…”

Section: Sample Petrographymentioning

confidence: 99%

“…This sample is a fine-grained eclogite with a welldefined schistosity and stretching lineation. Garnet grains ($17 vol.%) exhibit a well-defined rhombic dodecahedral habit with little variation in size (Angiboust & Agard, 2010), altered oceanic basalt and dolerite (Grechin et al, 1981;Kelley et al, 2003) and fresh normal MORB (Hofmann, 1988) are also plotted. Dashed arrow indicates the trend for spilitization ⁄ albitization.…”

Section: Gm18mentioning

confidence: 99%

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Metamorphic evolution of lawsonite eclogites from the southern Motagua fault zone, Guatemala: insights from phase equilibria and Raman spectroscopy

Endo

Wallis

Tsuboi

et al. 2011

Journal Metamorphic Geology

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Lawsonite eclogite (metabasalt and metadolerite) and associated metasedimentary rocks in a serpentinite me´lange from an area just south of the Motagua fault zone (SMFZ), Guatemala, represent excellent natural records of the forearc slab-mantle interface. Pseudosection modelling of pristine lawsonite eclogite reproduces the observed predominant mineral assemblages, and garnet compositional isopleths intersect within the phase fields, yielding a prograde P-T path that evolves from 20 kbar, 470°C (M1) to 25 kbar, 520°C (M2). The dominant penetrative foliation within the eclogite blocks is defined by minerals developed during the prograde evolution, and the associated deformation, therefore, took place during subduction. Thermometry using Raman spectra of carbonaceous material in metasedimentary rocks associated with the SMFZ eclogites gives estimates of peak-T of $520°C. Barometry using Raman spectroscopy shows unfractured quartz inclusions in garnet rims retain overpressures of up to $10 kbar, implying these inclusions were trapped at conditions just below the quartz ⁄ coesite transition, in agreement with the results of phase equilibrium analysis. Additional growth of Ca-rich garnet indicates initial isothermal decompression to 20 kbar (M3) followed by hydration and substantial cooling to the lawsonite-blueschist facies (M4). Further decompression of the hydrated eclogite blocks to the pumpellyite-actinolite facies (3-5 kbar, 230-250°C) is associated with dehydration and veining (M5). The presence of eclogite as m-to 10 m-sized blocks in a serpentinite matrix, lack of widespread deformation developed during exhumation and derived prograde P-T path associated with substantial dehydration of metabasites within the antigorite stability field suggest that the SMFZ eclogites represent the uppermost part of the forearc slab crust sampled by an ascending serpentinite diapir in an active, moderate-T subduction zone.

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