Universität zu Köln

Kurzweil, Florian, Muenker, Carsten, Tusch, Jonas and Schoenberg, Ronny (2018). Accurate stable tungsten isotope measurements of natural samples using a W-180-W-183 double-spike. Chem. Geol., 476. S. 407 - 418. AMSTERDAM: ELSEVIER SCIENCE BV. ISSN 1878-5999

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Abstract

Tungsten is a moderately siderophile element and, thus, enriched in the Earth's core. Moreover, W behaves incompatibly during partial melting, causing relative enrichment in the Earth's crust compared to the mantle. However, little is known about the geochemical cycle of the redox-sensitive element W in the crust-mantle system and in modern to ancient low-temperature environments. High resolution stable W isotope measurements of rock samples from different geochemical reservoirs might be a powerful tool to better constrain this cycle. So far, low relative mass differences between the different W isotopes and analytical challenges hampered such high-resolution measurements. Notably, some pioneering studies on the stable W isotope composition of geological reference material show inconsistent results, calling for further verification of the true compositions of these materials. This study presents an analytical protocol for stable W isotope measurements including the calibration of a W-180-W-183 double-spike as well as W isotope and W concentration data of several geological reference materials (BHVO-2, AGV-2, SDC-1, W-2a, ScO-2, NOD-A-1, NOD-P-1). The reproducibility of stable W isotope measurements (+/- 0.018% in delta(186)/W-184; 2 s.d.) is significantly improved compared to previous studies, which allows resolving between the stable W isotope compositions of various rock reservoirs on Earth. Relative to the NIST SRM 3163 standard, the highest delta W-186/184 value was observed for the Pacific Mn crust NOD-P-1 (+ 0.154 +/- 0.013%; 2 s.d.; n = 6), which is significantly different from the delta(186)/W-184 value of the Atlantic Mn crust NOD-A-1 (+ 0.029 +/- 0.014%; 2 s.d.; n = 6). Considering equilibrium fractionation between seawater WO42- and slowly growing Mn oxides, this indicates an isotopically heterogeneous distribution of W in the modern oceans. Igneous rocks also show a resolvable range in delta(186)/W-184 values. Magmatic reference materials range in d(186)/W-184 between + 0.016 +/- 0.032% (andesite AGV-2; 2 s.d.; n = 5) and + 0.082 +/- 0.010% (basalt BHVO-2; 2 s.d.; n = 5) showing relative enrichment of light isotopes in more evolved magmatic rocks. These isotopic differences might result from isotope fractionation during magmatic differentiation. Alternatively, the mobilization of W by hydrothermal and/or magmatic fluids might be accompanied by isotope fractionation.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Kurzweil, Florian UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED Tusch, Jonas UNSPECIFIED UNSPECIFIED UNSPECIFIED Schoenberg, Ronny UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-199082
DOI:	10.1016/j.chemgeo.2017.11.037
Journal or Publication Title:	Chem. Geol.
Volume:	476
Page Range:	S. 407 - 418
Date:	2018
Publisher:	ELSEVIER SCIENCE BV
Place of Publication:	AMSTERDAM
ISSN:	1878-5999
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language EARLY CORE FORMATION; HF-W CHRONOMETRY; ICP-MS; RAPID ACCRETION; PACIFIC-OCEAN; SOLAR-SYSTEM; MC-ICPMS; METEORITES; MOLYBDENUM; MO Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/19908