REE, Th, Hf, Ta in Bamble gabbros (southern Norway) and their amphibolitized equivalents; implications for gabbro tectonic setting

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doi: 10.1016/0301-9268(91)90073-J
Authors:Smalley, P. C.; Field, D.
Author Affiliations:Primary:
Inst. Energy Technol., Kjeller, Norway
Other:
Univ. Nottingham, United Kingdom
Volume Title:Precambrian Research
Source:Precambrian Research, 53(3-4), p.233-242. Publisher: Elsevier, Amsterdam, International. ISSN: 0301-9268
Publication Date:1991
Note:In English. Presented at Dennis Field mem. symp., Nottingham, May 1987. 31 refs.; illus. incl. 3 tables
Summary:These gabbros are a group of partly metamorphosed Proterozoic basic intrusions which are discordant to structures formed during the Kongsbergian (1540 m.y.) high-grade metamorphism, yet are themselves partially amphibolitized. A previous study of closely- spaced gabbro-amphibolite sample pairs revealed that amphibolitization was accompanied by increases in K, Fe3+, P, H2O, Rb, Cl +- Zr and decreases in Ca, Fe2+, S, Zn +- Si +- Co. New data for REE, Th, Hf, Ta in the same samples indicate that the only possible metamorphic modification of these elements is a barely significant increase in La in one locality. Eu/Eu* ratios are preserved. The combined chemical data fingerprint the gabbros as similar to present-day destructive plate-margin-related basic rocks, which is surprising as it had previously been supposed that they are an expression of the tensional alkaline magmatism that was widespread in the N Atlantic province at approx 1250 m.y. It thus seems more likely that the Bamble gabbros are related to renewed subduction after the approx 1250 m.y. anorogenic period. The geochemistry of these widespread gabbros must be accounted for in future Proterozoic Scandinavian tectonic reconstructions. [R.E.S.]
Subjects:Actinides; Amphibolites; Amphibolitization; Gabbros; Hafnium; Igneous rocks; Intrusions; Mafic composition; Metals; Metamorphic rocks; Metasomatism; Petrology; Plutonic rocks; Rare earths; Reconstruction; Structural geology; Subduction; Tantalum; Tectonics; Thorium; Europe; Norway; Scandinavia; Southern Norway; Western Europe; Bramble Sector; Kragero; Valberg
Abstract Numbers:92M/2999
Record ID:1991057968
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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