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Timing of plutonism in the Gällivare area: mplications for Proterozoic crustal development in the northern Norrbotten ore district, Sweden
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.ORCID-id: 0000-0002-7413-4461
Luossavaara-Kiirunavaara AB, SE-981 86 Kiruna.
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.ORCID-id: 0000-0003-1627-7058
Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.ORCID-id: 0000-0003-4711-7671
Visa övriga samt affilieringar
2018 (Engelska)Ingår i: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 155, nr 6, s. 1351-1376Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Zircon ion probe (secondary-ion mass spectrometry or SIMS) data from a set of intrusive rocks emplaced in the vicinity of major ore bodies, as well as from large igneous intrusions in the Gällivare area, gave the following results: (1) the Dundret ultramafic–mafic layered complex (1883±5 Ma), the Aitik granite (1883±5 Ma), the Nautanen diorite (1870±12 Ma), the Vassaravaara ultramafic–mafic layered complex (1798±4 Ma), the Aitik dolerite (1813±9 Ma), the Bergmästergruvan and Sikträsk syenites (1795±4 Ma and 1801±3 Ma, respectively) and the Naalojärvi granite (1782±5 Ma). These data broadly fall within the ranges 1.89–1.87 Ga (early Svecofennian) and 1.80–1.78 Ga (late Svecofennian), but geochronologically allow further subdivision into pulses at 1885–1880, 1875–1870, 1800 and 1780 Ma. During these events, large layered ultramafic–mafic and felsic plutonic rocks were generated with distinct overlap in time suggesting coeval felsic–mafic magmatism. Results also indicate the presence of inherited c. 1.87 Ga zircon crystals in the plutonic rocks at 1.78 Ga, supporting reworking of the previous crust. These data indicate the importance of mantle-derived mafic underplating in the process of crustal magma generation in the region. The c. 1.88 Ga event that generated ultramafic–mafic layered complexes is tentatively suggested to have played an important role in the formation of the Aitik Cu–Au porphyry system. The later event at c. 1.80 Ga, generating voluminous mafic–felsic units, is suggested to be coupled to the regional iron-oxide-copper-gold (IOCG) overprint.

Ort, förlag, år, upplaga, sidor
Cambridge University Press, 2018. Vol. 155, nr 6, s. 1351-1376
Nationell ämneskategori
Geologi
Forskningsämne
Malmgeologi
Identifikatorer
URN: urn:nbn:se:ltu:diva-63390DOI: 10.1017/S0016756817000280ISI: 000439690800008Scopus ID: 2-s2.0-85018356169OAI: oai:DiVA.org:ltu-63390DiVA, id: diva2:1096100
Anmärkning

Validerad;2018;Nivå 2;2018-07-26 (inah)

Tillgänglig från: 2017-05-17 Skapad: 2017-05-17 Senast uppdaterad: 2018-08-15Bibliografiskt granskad
Ingår i avhandling
1. Timing and Origin of Igneous Rocks in the Gällivare area, Northern Sweden
Öppna denna publikation i ny flik eller fönster >>Timing and Origin of Igneous Rocks in the Gällivare area, Northern Sweden
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2018
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nationell ämneskategori
Naturvetenskap Geologi
Forskningsämne
Malmgeologi
Identifikatorer
urn:nbn:se:ltu:diva-69186 (URN)978-91-7790-171-6 (ISBN)978-91-7790-172-3 (ISBN)
Disputation
2018-09-14, C305, Luleå, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2018-06-21 Skapad: 2018-06-08 Senast uppdaterad: 2018-09-06Bibliografiskt granskad

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