Universität zu Köln

Bast, Rebecca, Scherer, Erik E., Sprung, Peter ORCID: 0000-0003-4862-1415, Mezger, Klaus ORCID: 0000-0002-2443-8539, Fischer-Goedde, Mario, Taetz, Stephan, Boehnke, Mischa, Schmid-Beurmann, Hinrich, Muenker, Carsten, Kleine, Thorsten ORCID: 0000-0003-4657-5961 and Srinivasan, Gopalan (2017). Reconciliation of the excess Hf-176 conundrum in meteorites: Recent disturbances of the Lu-Hf and Sm-Nd isotope systematics. Geochim. Cosmochim. Acta, 212. S. 303 - 324. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD. ISSN 1872-9533

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Abstract

The long-lived (176) Lu-(176) Hf and Sm-147-Nd-143 radioisotope systems are commonly used chronometers, but when applied to meteorites, they can reveal disturbances. Specifically, Lu-Hf isochrons commonly yield dates up to similar to 300 Myr older than the solar system and varying initial Hf-176/Hf-177 values. We investigated this problem by attempting to construct mineral and whole rock isochrons for eucrites and angrites. Meteorites from different parent bodies exhibit similar disturbance features suggesting that a common process is responsible. Minerals scatter away from isochron regressions for both meteorite classes, with low-Hf phases such as plagioclase and olivine typically being most displaced above (or left of) reference isochrons. Relatively Hf-rich pyroxene is less disturbed but still to the point of steepening Lu-Hf errorchrons. Using our Lu-Hf and Sm-Nd data, we tested various Hf and Lu redistribution scenarios and found that decoupling of Lu/Hf from Hf-176/Hf-177 must postdate the accumulation of significant radiogenic Hf-176. Therefore early irradiation or diffusion cannot explain the excess Hf-176. Instead, disturbed meteorite isochrons are more likely caused by terrestrial weathering, contamination, or common laboratory procedures. The partial dissolution of phosphate minerals may predominantly remove rare earth elements including Lu, leaving relatively immobile and radiogenic Hf behind. Robust Lu-Hf (and improved Sm-Nd) meteorite geochronology will require the development of chemical or physical methods for removing unsupported radiogenic Hf and silicate-hosted terrestrial contaminants without disturbing parent-daughter ratios. (C) 2017 Elsevier Ltd. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Bast, Rebecca UNSPECIFIED UNSPECIFIED UNSPECIFIED Scherer, Erik E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Sprung, Peter UNSPECIFIED orcid.org/0000-0003-4862-1415 UNSPECIFIED Mezger, Klaus UNSPECIFIED orcid.org/0000-0002-2443-8539 UNSPECIFIED Fischer-Goedde, Mario UNSPECIFIED UNSPECIFIED UNSPECIFIED Taetz, Stephan UNSPECIFIED UNSPECIFIED UNSPECIFIED Boehnke, Mischa UNSPECIFIED UNSPECIFIED UNSPECIFIED Schmid-Beurmann, Hinrich UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED Kleine, Thorsten UNSPECIFIED orcid.org/0000-0003-4657-5961 UNSPECIFIED Srinivasan, Gopalan UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-221260
DOI:	10.1016/j.gca.2017.05.043
Journal or Publication Title:	Geochim. Cosmochim. Acta
Volume:	212
Page Range:	S. 303 - 324
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 EARLY SOLAR-SYSTEM; GLOBAL CRUSTAL METAMORPHISM; THERMAL METAMORPHISM; GARNET GEOCHRONOLOGY; DIFFUSION KINETICS; AGE-DETERMINATION; CORE FORMATION; EARLY HISTORY; PB AGE; EUCRITE Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/22126