Isotopic constraints on the timing of crustal accretion of the Bamble Sector, Norway, as evidenced by coronitic gabbros

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doi: 10.1016/0301-9268(93)90090-O
Authors:de Haas, Geert-Jan L. M.; Verschure, Rob H.; Maijer, Cornelis
Author Affiliations:Primary:
University of Utrecht, Department of Geochemistry, Utrecht, Netherlands
Free University Amsterdam, Amsterdam, Netherlands
Volume Title:Baltic Shield
Volume Authors:Gorbatschev, Roland, editor
Source:Precambrian Research, 64(1-4), p.403-417; 2nd symposium on the Baltic Shield, Lund, Sweden, June 1990, edited by Roland Gorbatschev. Publisher: Elsevier, Amsterdam, International. ISSN: 0301-9268
Publication Date:1993
Note:In English. 45 refs.Special volume; illus. incl. 3 tables, sketch maps
Summary:This paper presents the first Sm-Nd data for coronitic gabbros (hyperites) from the high-grade Proterozoic Bamble Sector, Norway. Sm-Nd whole-rock isochron ages of the Vestre Dale Gabbro, 1.11±0.14 Ga, the Jomasknutene Gabbro, 1.77±0.19 Ga, and the Flosta Gabbro, 1.64±0.23 Ga indicate that, contrary to earlier ideas, intrusion of these gabbros is not exclusively bound to the Sveconorwegian orogeny (1.2-0.9 Ga). Some of the gabbros were already emplaced at the onset of or during the Gothian Orogeny (1.75-1.5 Ga). Initial εNd values of about +5.5 of Jomåsknutene and Flosta Gabbros provide clear evidence of a depleted mantle reservoir beneath this part of the Southwest Scandinavian Domain. This highly positive value differs from the Nd-isotope evolution curve for the Southwest Scandinavian mantle as postulated by Mearns et al. (1986), which assumes that depletion of the mantle beneath this part of Scandinavia started at c. 1.74 Ga. However, the initial εNd value of the Vestre Dale Gabbro plots close to this curve, whereas 143Nd/144Nd ratios of the mantle sources of the Tromöy and Arendal Gabbros evolved with approximately chondritic 147Sm/144Nd ratios; their εNd (1.1 Ga) values range from +5.1±0.3 to +6.0±0.3. Gothian metasomatism of a depleted mantle source by LILE- and LREE-bearing fluids provides a mechanism to obtain low Nd-isotope ratios in magmas represented by the Vestre Dale Gabbro. Examples of low Nd-isotope magmas have also been found in the Telemark Sector, and in southern Sweden. The marked depletion in Nb indicates that the metasomatic fluids were possibly related to Gothian subduction.
Subjects:Absolute age; Accretion; Crust; Dates; Gabbros; IGCP; Igneous rocks; Isochrons; Isotope ratios; Isotopes; Magmas; Mantle; Mass spectra; Mechanism; Metals; Metasomatism; Nd-144/Nd-143; Neodymium; Orogeny; Plate tectonics; Plutonic rocks; Precambrian; Rare earths; Sm/Nd; Spectra; Stable isotopes; Subduction; Sveconorwegian Orogeny; Whole rock; Bamble Norway; Europe; Fennoscandian Shield; Norway; Scandinavia; Telemark Norway; Western Europe; Arendal Gabbro; Tromoy Gabbro; Vestre Dale Gabbro
Abstract Numbers:94M/4821
Record ID:1994014134
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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