Universität zu Köln

Hasenstab-Duebeler, Eric, Tusch, Jonas, Hoffmann, J. Elis, Fischer-Goedde, Mario, Szilas, Kristoffer ORCID: 0000-0002-5541-306X and Muenker, Carsten (2022). Temporal evolution of 142Nd signatures in SW Greenland from high precision MC-ICP-MS measurements. Chem. Geol., 614. AMSTERDAM: ELSEVIER. ISSN 1872-6836

Full text not available from this repository.

Abstract

Measurements of Nd-142 isotope signatures in Archean rocks are a powerful tool to investigate the earliest silicate differentiation events on Earth. Here, we introduce a new analytical protocol that allows high precision radio -genic and mass-independent Nd isotope measurements by MC-ICP-MS. To validate our method, we have measured well-characterized-3.72 to-3.8 Ga samples from the Eoarchean Itsaq Gneiss Complex and associated supracrustal belts, as well as Mesoarchean greenstones and a Proterozoic dike in SW Greenland, including lithostratigraphic units that were previously analyzed for Nd142-143 isotope systematics, by both TIMS and MC-ICP-MS. Our mu Nd-142 values for-3.72 to-3.8 Ga rocks from the Isua region range from +9.2 +/- 2.6 to +13.2 +/- 1.1 ppm and are in good agreement with previous studies. Using coupled Nd-142,Nd-143/Nd-144 isotope systematics from our data for-3.8 Ga mafic-ultramafic successions from the Isua region, we can confirm previous age constraints on the earliest silicate differentiation events with differentiation age of 4.390(-0.060)(+0.045) Ga. Moreover, we can resolve a statistically significant decrease of Nd-142/Nd-144 isotope compositions in the ambient mantle of SW Greenland that already started to commence by Eoarchean time, between-3.8 Ga (mu Nd-142 = +13.0 +/- 1.1) and -3.72 Ga (mu Nd-142 = +9.8 +/- 1.0). Even lower but homogeneous mu Nd-142 values of +3.8 +/- 1.1 are found in-3.4 Ga mantle-derived rocks from the Ameralik dike swarms. Our study reveals that epsilon Nd-143(i) and epsilon Hf(i) values of Isua rocks scatter more than it would be expected from a single stage differentiation event as implied from nearly uniform mu Nd-142 values, suggesting that the previously described decoupling of Hf and Nd isotopes is not a pri-mordial magma ocean signature. Instead, we conclude that some of second stage processes like younger mantle depletion events or recycling of subducted material affected the (Sm-143Nd)-Sm-147 isotope systematics. The preser-vation of pristine whole-rock isochrons largely rules out a significant disturbance by younger alteration events. Based on isotope and trace element modelling, we argue that the temporal evolution of coupled Nd-142,Nd-143/Nd-144 isotope compositions in the ambient mantle beneath the Isua rocks is best explained by the progressive admixture of material to the Isua mantle source that must have had present-day-like mu Nd-142 compositions. In contrast, Mesoarchean mafic rocks from the-3.08 Ga Ivisaartoq greenstone belt and the 2.97 Ga inner Ameralik Fjord region as well as a 2.0 Ga Proterozoic dike within that region all have higher mu Nd-142 values as would be expected from our simple replenishment model. This argues for reworking of older Isua crustal material that carried elevated mu Nd-142 compositions.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Hasenstab-Duebeler, Eric UNSPECIFIED UNSPECIFIED UNSPECIFIED Tusch, Jonas UNSPECIFIED UNSPECIFIED UNSPECIFIED Hoffmann, J. Elis UNSPECIFIED UNSPECIFIED UNSPECIFIED Fischer-Goedde, Mario UNSPECIFIED UNSPECIFIED UNSPECIFIED Szilas, Kristoffer UNSPECIFIED orcid.org/0000-0002-5541-306X UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-673086
DOI:	10.1016/j.chemgeo.2022.121141
Journal or Publication Title:	Chem. Geol.
Volume:	614
Date:	2022
Publisher:	ELSEVIER
Place of Publication:	AMSTERDAM
ISSN:	1872-6836
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language ITSAQ GNEISS COMPLEX; SOUTHERN WEST GREENLAND; ISUA SUPRACRUSTAL BELT; ND-ISOTOPE HETEROGENEITY; HADEAN MANTLE; SILICATE DIFFERENTIATION; EOARCHEAN ROCKS; GREENSTONE-BELT; ND-142 EVIDENCE; LU-HF Multiple languages Geochemistry & Geophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/67308