The noble gas and halogen composition of the hydrated oceanic crust

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Author(s): Chavrit, Deborah; Burgess, R.; Ballentine, C.; Weston, B.; Teagle, D.
Author Affiliation(s): Primary:
University of Manchester, School of Earth, Atmospheric and Environmental Sciences, Manchester, United Kingdom
University of Southampton, United Kingdom
Volume Title: Goldschmidt 2011 abstract volume
Source: Mineralogical Magazine, 75(3), p.648; Goldschmidt2011, Prague, Czech Republic, Aug. 14-19, 2011. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X CODEN: MNLMBB
Note: In English. 2 refs.
Summary: Mantle heavy noble gases have a remarkable similarity to those found in marine pore fluids. This implies a significant contribution of these gases into the mantle recycled through subduction zones. In order to better constrain the quantity and character of noble gases available for subduction, we are reassessing the major host phases of noble gases in pre-subducted material. We have acquired, from different ODP sites, a sample suite that is representative of the altered oceanic crust. Noble gas (He, Ne, Ar, Kr and Xe) isotopes and abundances are being determined using crushing release measured with an upgraded VG5400 mass spectrometer. Preliminary results from four altered basalts (ODP sites 504B and 1256D in the Southeast Pacific Ocean, respectively 5.9 and 15 Ma) show Ne to Xe isotopically identical to air. 3He/4He ratios are uniform at 6.82±0.42 (R/Ra). Heavy noble gas elemental ratios fall within a narrow range, with 130Xe/36Ar and 84Kr/36Ar ratios varying between seawater values and values enriched in Xe and Kr and indistinguishable from mantle values. The range of 130Xe/84Kr, varying by up to a factor 2.5, suggests that different trapping or fixation sites could control such compositions. This is supported by an observed correlation of increase of the 132Xe/36Ar ratio relatively to 84Kr/36Ar with crushing step in the same sample, which does not seem related to air contamination. This could be representative of the different phases retaining different amounts of heavy nobles gases. These measurements will be extended to include halogen determinations which are tracers of marine pore fluids and seawater interaction. Analysing noble gases and halogens in basalts characterized by different alteration patterns and in gabbros and sediments will allow the identification of the noble gas host phases, as well as the controls of the seawater noble gases interaction with the oceanic crust.
Year of Publication: 2011
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 05 Petrology, Igneous and Metamorphic; Basalts; Chemical composition; Crust; DSDP Site 504; East Pacific; Equatorial Pacific; Halogens; Igneous rocks; Lithosphere; Mantle; Noble gases; North Pacific; Northeast Pacific; ODP Site 1256; Ocean Drilling Program; Oceanic crust; Oceanic lithosphere; Pacific Ocean; Pore water; Volcanic rocks
Coordinates: N064400 N064400 W0915600 W0915600
N011335 N011338 W0834348 W0834357
Record ID: 2013078570
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland