uu.seUppsala University Publications
Change search
ReferencesLink to record
Permanent link

Direct link
Petrogenesis and geotectonic setting of early Svecofennian arc cumulates in the Roslagen area, east-central Sweden
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2012 (English)In: Geological Journal, ISSN 0072-1050, E-ISSN 1099-1034, Vol. 47, no 6, 557-593 p.Article in journal (Refereed) Published
Abstract [en]

Several intrusions of ultrabasic to basic composition occur in the Roslagen area of east-central Sweden in close spatial and temporal association with the surrounding 1.90-1.87Ga old early orogenic Svecofennian granitoids. An imprecise Sm-Nd WR errorchron yields an age of 1895±71Ma. In spite of the penetrative deformation in the granitoids, the basic-ultrabasic rocks mostly appear undeformed and largely preserve magmatic textures with plagioclase, olivine (in some rock types), orthopyroxene and clinopyroxene, and amphibole as major constituents. The plagioclase is typically very anorthitic (ca. An 90). The Roslagen intrusions range in composition from primitive to evolved (Mg# 80 to 49) but contain only 40-50wt% SiO 2. Many samples are highly elevated in Al 2O 3 (up to 30wt%), CaO (up to 16wt%) and Sr (up to 800ppm), with strongly positive Eu and Sr anomalies, in line with being plagioclase cumulates. Although masked by cumulus effects, the relative trace element contents indicate a volcanic arc signature. The initial Nd isotope composition is homogeneously 'mildly depleted', with ε Nd of +0.3 to +1.1, and the initial Sr isotope composition 'mildly enriched', with ε Sr of +8 to +15. Non-cumulus rocks with small Eu and Sr anomalies can be used to deduce the composition of the parental magma. This LILE- and LREE-enriched and HFSE-depleted high-alumina basalt magma, with Mg# of ca. 50-60 and Ca# of ca. 80, most likely formed by partial melting of mantle material, enriched by fluids in a subduction environment, at 1.9Ga. The cumulate rocks apparently crystallized from a somewhat more evolved water-rich magma with Mg# of ca. 40. Crystallization was followed by the development of late-magmatic to post-magmatic coronas between olivine and plagioclase in the presence of H 2O-rich fluids. The subduction-related setting would make these intrusions Palaeoproterozoic counterparts of Alaskan-type ultramafic intrusions, but they differ from those in being plagioclase enriched, possibly reflecting different levels of exposure.

Place, publisher, year, edition, pages
2012. Vol. 47, no 6, 557-593 p.
Keyword [en]
Anorthite, Arc magmas, High-Al basalt, Olivine-plagioclase reaction coronas, Plagioclase cumulates, Roslagen gabbros, Svecofennian, Sweden
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-186701DOI: 10.1002/gj.2416ISI: 000310685300001OAI: oai:DiVA.org:uu-186701DiVA: diva2:573033
Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2012-12-10Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text
By organisation
Department of Earth Sciences
In the same journal
Geological Journal
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 185 hits
ReferencesLink to record
Permanent link

Direct link