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Diversity of 1.8 Ga potassic granitoids along the edge of the Archaean craton in northern Scandinavia: a result of melt formation at various depths and from various sources
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
Laboratory for Isotope Geology. Swedish Museum of Natural History, Stockholm.
1994 (English)In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 33, no 4, p. 265-283Article in journal (Refereed) Published
Abstract [en]

The edge of the Archaean craton in northern Scandinavia had been intensively reworked during the Svecofennian orogeny 1.93-1.86 Ga ago and was subsequently intruded by potassic granitoids of 1.79–1.80 Ga age. Despite similar or even identical ages and overlapping areas of occurrence, these rocks belong to two different groups, the Edefors and Lina granitoids, which have contrasting geochemistries and Sm---Nd isotopic characteristics. The Edefors granitoids range from syenites to granites, and are alkali-rich and distinctly metaluminous. They crystallized from dry magmas. This is indicated by the scarcity of pegmatites and aplites. The contacts to older rocks are often distinct, but gradual transitions to Lina-type granitoids are common. The Edefors granitoids have high contents of Zr but not of elements such as Y, REE, Ta and Nb, and have low Mg/Mg+Fe ratios. They also frequently have positive Eu anomalies, even in the quartz rich varieties. Initial εNd values range from −2.1 to +1.4, indicating that the Edefors granitoids were formed by the mixing of mantle-derived magmas and continental crustal materials. The amount of crustal component was probably less than 35% in most cases. The Lina granitoids are accompanied by abundant pegmatites and aplites. Ghost structures and remnants of country rock are common. True granites predominate, but also quartz monzonites occur. The content of HFS elements is low and the Mg/Mg+Fe ratios are higher than in the Edefors granitoids. Initial εNd values range from −9.3 to −3.7, reflecting a significant portion of Archaean Nd in the source materials. The Lina granitoids are largely the result of remobilisation of continental crust with a small input of juvenile material. However, the dominant source for these crustally derived granitoids are c. 1.9 Ga old granitoids. These carry a large proportion of Archaean Nd. The most probable environment of the formation of potassic migmatite granitoids, such as the Lina type, is a collision zone between two masses of felsic crust (e.g. arc-continent or continent-continent), but the details of such a collision in the Baltic Shield remain to evaluated. The formation of the Edefors granitoids could have been associated with an extensional zone developed due to delamination caused by separation of the down-dip oceanic lithosphere from the continental lithosphere.

Place, publisher, year, edition, pages
1994. Vol. 33, no 4, p. 265-283
National Category
Geochemistry
Research subject
Applied Geology
Identifiers
URN: urn:nbn:se:ltu:diva-8338DOI: 10.1016/0024-4937(94)90033-7ISI: A1994QA51000003Scopus ID: 2-s2.0-0028576586Local ID: 6d72d7e0-dd1b-11db-9cae-000ea68e967bOAI: oai:DiVA.org:ltu-8338DiVA, id: diva2:981230
Note
Godkänd; 1994; 20070328 (pafi)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved

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Öhlander, Björn

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