Magmatic evolution of the Karmoy ophiolite complex, SW Norway; relationships between MORB-IT-boninitic-calc-alkaline and alkaline magmatism

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Authors:Pedersen, R. B.; Hertogen, J.
Author Affiliations:Primary:
Univ. Bergen, Inst. Geol., N-5007 Bergen, Norway
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 104(3), p.277-293. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1990
Note:In English. 79 refs.; illus. incl. 41 anals., block diag., 5 tables, geol. sketch map
Summary:The polyphasal magmatic evolution of the Caledonian Karmoy ophiolitic complex includes: 1) formation of an axis sequence from island-arc tholeiitic (IAT) and more MORB-like magmas (493 +7/+4 m.y.); 2) intrusion of magmas of boninitic affinity (485 +- 2 m.y.); 3) intrusion of MORB- and IAT-like magmas; 4) intrusion and extrusion of calc-alkaline magmas (470+9/+5 m.y.); and 5) intrusion and extrusion of basalts with alkaline trace-element affinity. Repeated intrusion of MORB and IAT-like magmas may be explained by intermittent magmatism involving magma-chamber solidification and remelting of a source characterized by initial epsilon Nd of +6.5. The boninitic rocks may have formed from two LREE-depleted sources: the primary source of the axis- sequence magmas and the residual source left after extraction of these magmas. These sources have been enriched in LREE, Th and Zr from subducted material exhibiting a continental Nd-isotope signature with initial epsilon Nd less than -8. Covariation between epsilon Nd and Th, Zr, Nd, Y and Yb may be explained by metasomatic enrichment of a LREE-depleted mantle source by a LREE-enriched subduction component, followed by partial melting during which the degree of melting of the metasomatized mantle source increased linearly with the amount of subduction component added to the mantle source. The calc-alkaline magmas may have formed by remelting of a highly depleted source, which became enriched in some trace elements derived from the source of the subsequent alkaline magmatism. The geology and geochemistry of the Karmoy complex suggest growth of an island-arc upon newly-formed oceanic crust, followed by arc-splitting and the development of a new basin. [Authors' abstract] [P.Br.]
Subjects:Alkalic composition; Andesites; Basalts; Boninite; Calc-alkalic composition; Chemical composition; Extrusive rocks; Igneous rocks; Isotope ratios; Isotopes; Magmas; Metals; Mid-ocean ridge basalts; Nd-144/Nd-143; Neodymium; Ophiolite; Petrology; Plutonic rocks; Rare earths; Sm/Nd; Stable isotopes; Ultramafics; Volcanic rocks; Europe; Norway; Scandinavia; Southern Norway; Western Europe; Igneous activity; Karmoy ophiolite complex; Ratios; Southwestern Norway
Abstract Numbers:90M/4789
Record ID:1993039385
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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