Universität zu Köln

Fonseca, Raul O. C. ORCID: 0000-0002-0897-4884, Kirchenbaur, Maria, Ballhaus, Chris, Muenker, Carsten, Zirner, Aurelia, Gerdes, Axel ORCID: 0000-0003-3823-2125, Heuser, Alexander ORCID: 0000-0003-3772-5534, Botcharnikov, Roman and Lenting, Christoph ORCID: 0000-0001-8374-5857 (2017). Fingerprinting fluid sources in Troodos ophiolite complex orbicular glasses using high spatial resolution isotope and trace element geochemistry. Geochim. Cosmochim. Acta, 200. S. 145 - 167. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD. ISSN 1872-9533

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Abstract

The Troodos igneous complex (Cyprus) is a ca. 90 Ma old, well preserved supra-subduction zone ophiolite. Troodos is unique in that it shows evidence of fluid-saturation throughout the complex, from its base (i.e. podiform chromitites) to its uppermost units-the upper pillow lavas (UPL). However, it is unclear what the source of dissolved water in UPL tholeiites is, with possibilities including shallow seawater infiltration, assimilation of altered Troodos oceanic crust, recycled serpentinized oceanic crust, or subducted pelagic sediments. In order to identify and characterize these components we have carried out a detailed high-resolution study on tholeiitic lavas on orbicular structures and glasses from the UPL in Troodos. Basaltic orbicules were measured for their Sr-Nd-Hf-Pb isotope compositions, and in situ for their B isotopes using LA-MC-ICP-MS. UPL orbicules display a very narrow range in Nd-is an element of and Hf-is an element of (+ 7 to + 8 and + 13 to + 15, respectively) indicating melting of a depleted mantle source. Lead isotopes, specifically Pb-207/(204) Pb vs. Pb-206/Pb-204, form a mixing array with pelagic sediments. Furthermore, high-resolution characterization of individual orbicules revealed that UPL tholeiites display strong variability in Sr-87/Sr-86 (0.7039-0.7060) at the outcrop scale. Samples display delta B-11 between -8.2 (+/- 0.5)% and + 5.9 (+/- 1.1)% with an average B content of ca. 5 mu g/g. Contrary to expectation, altered orbicules and their associated hyaloclastite matrixes display lower delta B-11 (down to -10%) and higher B contents (max. 200 mu g/g) when compared to fresh glass. Furthermore, the orbicules studied here show little or no evidence of interaction with seawater, which is supported by their trace element contents and isotope compositions. When all isotope systems are taken into account, UPL lavas reflect melting of a depleted mantle source that was overprinted by hydrous sediment melts, and potentially, fluid-like subduction components that in part originate from serpentinized oceanic crust. Subsequent low-temperature alteration then drove d delta B-11 to lower values coupled with increased B uptake due to its adsorption into palagonite. (C) 2016 Elsevier Ltd. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Fonseca, Raul O. C. UNSPECIFIED orcid.org/0000-0002-0897-4884 UNSPECIFIED Kirchenbaur, Maria UNSPECIFIED UNSPECIFIED UNSPECIFIED Ballhaus, Chris UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED Zirner, Aurelia UNSPECIFIED UNSPECIFIED UNSPECIFIED Gerdes, Axel UNSPECIFIED orcid.org/0000-0003-3823-2125 UNSPECIFIED Heuser, Alexander UNSPECIFIED orcid.org/0000-0003-3772-5534 UNSPECIFIED Botcharnikov, Roman UNSPECIFIED UNSPECIFIED UNSPECIFIED Lenting, Christoph UNSPECIFIED orcid.org/0000-0001-8374-5857 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-237634
DOI:	10.1016/j.gca.2016.12.012
Journal or Publication Title:	Geochim. Cosmochim. Acta
Volume:	200
Page Range:	S. 145 - 167
Date:	2017
Publisher:	PERGAMON-ELSEVIER SCIENCE LTD
Place of Publication:	OXFORD
ISSN:	1872-9533
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language RARE-EARTH-ELEMENTS; BORON ISOTOPE; OCEANIC-CRUST; SUBDUCTION ZONES; ORIGIN; SYSTEMATICS; SEAWATER; LAVAS; WATER; EXCHANGE Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/23763