Universität zu Köln

Reifenroether, Ramon, Muenker, Carsten and Scheibner, Birgit (2021). Evidence for tungsten mobility during oceanic crust alteration. Chem. Geol., 584. AMSTERDAM: ELSEVIER. ISSN 1872-6836

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Abstract

Being a mobile element, the budget of W in the oceanic crust, an important geochemical reservoir, may be severely affected by hydrothermal alteration, but W data for altered oceanic crust (AOC) have not been available so far. In this study, we present the first high precision W concentration data obtained by isotope dilution and MC-ICPMS, along with high precision Th, U, Ta, Zr, Nb, Lu, and Hf data, for a complete section of altered upper oceanic crust (IODP-Borehole 1256D) down to the basal gabbros. As W, Th, U and Ta are similar melt incompatible, the latter were selected as framework to study W enrichment. In the studied section of altered oceanic crust, preserved alteration styles range from low temperature (< 150 degrees C) seawater altered lavas to high temperature (> 400 degrees C) altered granoblastic dikes. Tungsten is systematically enriched over Th, U, and Ta in the whole depth succession. Uranium is also hydrothermally enriched locally, whereas Th and Ta both behaved entirely immobile over the entire depth succession. Based on U-series data, most alteration activity can be confined in age to >350 kyrs. The strongest W enrichments were found in contact zones between the different lithological units, at the sites of extreme fluid alteration. Generally, the elemental ratios of W/Th, Ta/VV and W/U show only minor overlap with pristine MORB ratios and may even exceed the values reported for global arc lavas with respect to W enrichment. The selective enrichment of W in many arc lavas may therefore be partially inherited from altered oceanic crust. Nevertheless, there are examples of arcs where subducted oceanic crust dominates the trace element budget, but the lavas do not show pronounced W enrichment. We propose three models to explain this conundrum, (a) retention of W in accessory phases, (b) selective enrichment of subduction zone fluids in U and Th relative to W, and (c) incomplete sampling of AOC by hole 1256D, leaving W depleted portions in the oceanic crust unsampled.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Reifenroether, Ramon UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED Scheibner, Birgit UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-563991
DOI:	10.1016/j.chemgeo.2021.120504
Journal or Publication Title:	Chem. Geol.
Volume:	584
Date:	2021
Publisher:	ELSEVIER
Place of Publication:	AMSTERDAM
ISSN:	1872-6836
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language SUBDUCTION-ZONE FLUIDS; PARTITION-COEFFICIENTS; TRACE-ELEMENTS; RIDGE BASALTS; ARC LAVAS; ISOTOPE; MANTLE; GEOCHEMISTRY; RUTILE; SR Multiple languages Geochemistry & Geophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/56399