Mineralogical control on the chlorine isotope composition of altered oceanic crust

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doi: 10.1016/j.chemgeo.2012.07.022
Author(s): Barnes, Jaime D.; Cisneros, Miguel
Author Affiliation(s): Primary:
University of Texas at Austin, Department of Geological Sciences, Austin, TX, United States
Volume Title: Chemical Geology
Source: Chemical Geology, Vol.326-327, p.51-60. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541 CODEN: CHGEAD
Note: In English. Includes appendices. 86 refs.; illus., incl. 2 tables
Summary: Bulk chlorine concentrations and chlorine stable isotope compositions were determined for hydrothermally altered basalt (extrusive lavas and sheeted dikes) and gabbro samples (n=50) from seven DSDP/ODP/IODP drill sites. These altered oceanic crust (AOC) samples span a range of crustal ages, tectonic settings, alteration type, and crustal depth. Bulk chlorine concentrations range from <0.01 wt.% to 0.09 wt.%. In general, higher chlorine concentrations coincide with an increase in temperature of alteration and amphibole content. δ37Cl values of whole rock AOC samples range from -1.4 to +1.8 ppm. High δ37Cl values (≥ ∼0.5 ppm) are associated with areas of higher amphibole content. This observation is consistent with theoretical calculations that estimate amphibole should be enriched in 37Cl compared to co-existing fluid. Negative to near zero δ37Cl values are found in areas dominated by clay minerals. Chlorine geochemistry is a rough indicator of metamorphic grade and mineralogy. AOC is a major Cl host in the subducting oceanic lithospheric slab. Here we show that bulk chlorine concentrations are ∼3 times higher than previous estimates resulting in a greater contribution of Cl to the mantle. Abstract Copyright (2012) Elsevier, B.V.
Year of Publication: 2012
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 05 Petrology, Igneous and Metamorphic; Atlantic Ocean; Atlantis II fracture zone; Basalts; Bermuda Rise; Chemical composition; Chlorine; Chromatograms; Cl-37/Cl-35; Crust; DSDP Site 418; East Pacific; Equatorial Pacific; Expeditions 309/312; Gas chromatograms; Guatemala Basin; Halogens; Hydrothermal alteration; Igneous rocks; Indian Ocean; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Lithosphere; Metasomatism; Mineral composition; North Atlantic; North Pacific; Northeast Pacific; Northwest Pacific; ODP Site 1256; ODP Site 735; ODP Site 801; Ocean Drilling Program; Oceanic crust; Oceanic lithosphere; Pacific Ocean; Pigafetta Basin; Southwest Indian Ridge; Stable isotopes; Volcanic rocks; West Pacific; X-ray diffraction data
Coordinates: N064400 N064400 W0915600 W0915600
S324327 S324318 E0571618 E0571557
N183831 N183835 E1562136 E1562134
N250205 N250207 W0680326 W0680327
Record ID: 2012095595
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands