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Character and tectonic setting of plutonic rocks in the Gällivare area, northern Norrbotten, Sweden
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering. Luleå University of Technology. (Malmgeologi)ORCID iD: 0000-0002-7413-4461
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering. (Malmgeologi)
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering. (Malmgeologi)
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering. (Malmgeologi)
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2018 (English)In: GFF, ISSN 1103-5897, E-ISSN 2000-0863Article in journal (Refereed) Epub ahead of print
Abstract [en]

Petrographical and lithogeochemical investigations in combination with mapping in the Gällivare area, northern Norrbotten, Sweden, have led to the identification of several igneous intrusive rock types. These include: (1) ultramafic-mafic complexes, (2) mafic-intermediate rocks, (3) dolerites and (4) felsic plutons. The ultramafic-mafic rocks include the ca. 1.88 Ga Dundret complex and ca. 1.80 Ga Vassaravaara complex. The Dundret complex has tholeiitic to calc-alkaline affinity, shows a primitive mineral content and was formed in an extensional tectonic setting. The Vassaravaara complex has a similar chemical signature as the Dundret complex. The mafic-intermediate plutons vary in composition from gabbro to diorite. The chemical signature of the dioritic rocks indicate formation in a volcanic arc setting. Dolerites occur as solitary dikes and have calc-alkaline affinity. The felsic plutons include granite and syenite of ca. 1.88, 1.80 and 1.78 Ga age. The felsic plutons have calc-alkaline to shoshonitic affinity and mostly show a metaluminous I-type character. Results indicate subduction at 1.90 Ga resulting in a volcanic arc system, and including extensional events generating back-arc environments leading to mafic, intermediate and felsic magmatism in the Gällivare area. Subduction at 1.80 Ga is suggested to have caused a similar process generating mafic and felsic magmatic rocks in the same area. A subsequent collision event finally generated 1.78 Ga granitic rocks.

Place, publisher, year, edition, pages
2018.
Keywords [en]
Gällivare area, mafic layered intrusions, petrography, lithogeochemistry, back-arc environment
National Category
Natural Sciences
Research subject
Ore Geology
Identifiers
URN: urn:nbn:se:ltu:diva-69190DOI: 10.1080/11035897.2018.1526209OAI: oai:DiVA.org:ltu-69190DiVA, id: diva2:1215500
Available from: 2018-06-08 Created: 2018-06-08 Last updated: 2018-12-04
In thesis
1. Timing and Origin of Igneous Rocks in the Gällivare area, Northern Sweden
Open this publication in new window or tab >>Timing and Origin of Igneous Rocks in the Gällivare area, Northern Sweden
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Gällivare area is one of Europe’s top mining regions. The area is located in the northern Norrbotten ore district which hosts ore deposits such as the Malmberget underground iron ore mine, the Aitik open pit Cu-Au mine and the currently explored Nautanen Cu-Au deposit. In addition, several small, mineralized bodies are found. These deposits are hosted by volcanic and volcanosedimentary rocks intruded by intrusive rocks. Previous studies of intrusive and volcanic rocks have often been of local scale and restricted to the major deposits, or of regional scale including entire northern Norrbotten. Minor attention has been paid to rocks of the Gällivare area on a semi-regional scale, especially the intrusive rocks. Very few studies have presented radiometric data of the intrusive and volcanic rocks. In addition, the choice of radiometric method or the re-sults have been lacking confidence. A multidisciplinary approach combining structural geology, geochemistry, geochronology and geophysics is commenced to understand the geological history, crustal geometries and geological evolution of the Gällivare area. This forms basis for future exploration of ore deposits. This study presents geochemical, geochronological and Hf-isotope results with the purpose to characterize and classify major intrusive and volcanic rocks, their timing, source magmas and tectonic environment.

Petrographical and geochemical investigations reveal that the intrusive rocks range in composition from ultramafic-mafic to felsic. The ultramafic-mafic rocks comprise dominantly gabbroic layered complexes with peridotitic sequences and have tholeiitic to calc-alkaline affinity. The intermediate and felsic intrusive rocks show calc-alkaline to shoshonitic affinity. Volcanic rocks of the Malmberget deposit show alkali to alkali-calcic character. The geochemical character of the intrusive and volcanic rocks favors a continental arc, transitional to extensional setting (late- to post-collisional).

Radiometric in situ U-Pb zircon analyses indicate that mafic and felsic intrusive rocks were generated during magmatic episodes at 1.88, 1.80 Ga and 1.78 Ga. Volcanic rocks hosting the Malmberget deposit belong to the 1.88 Ga magmatic episode. Hydrothermal overgrowth rims from the analyzed zircon crystals indicate extensive reworking and high-T metamorphism of the area around 1.81-1.78 Ga.

The mafic-intermediate rocks show minor internal variations in Hf-isotopic signature as well as minor variations inbetween the samples indicative of relatively homogenous source regions beneath the Archean basement. The felsic rocks show a wider range in their Hf-isotopic signature suggesting multiple sources with contribution from old Archean crust.

It is here suggested that a subduction process active at 1.9 Ga resulted in a volcanic arc system and ex-tensional environments (back-arc environments) leading to mafic, intermediate and felsic magmatism in the Gällivare area at 1.88 Ga. The mafic-intermediate rocks were extracted from a rather homogenous source reservoir. The c. 1.80 Ga and 1.78 Ga intrusive rocks indicate a complex tectonic evolution of the area at that time. The early 1.80 Ga mafic rocks are suggested to have been generated as a result of extensional magmatism related to an east-directed 1.80 Ga subduction system. Subsequent compression followed by uplift, resulted in the generation of 1.78 Ga felsic rocks.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Natural Sciences Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-69186 (URN)978-91-7790-171-6 (ISBN)978-91-7790-172-3 (ISBN)
Public defence
2018-09-14, C305, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2018-06-21 Created: 2018-06-08 Last updated: 2018-09-06Bibliographically approved

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