The U–Pb age of the Finse batholith, a composite bimodal Sveconorwegian intrusion

Abstract

The Sveconorwegian autochthonous basement in the Finse area, South Norway, comprises a c. 900 km 2 bimodal batholith, dominated by K-feldspar megacrystic granite. The granite is locally intermingling with gabbroic rocks, and cut by different generations of pegmatite and aplite dykes. Zircon U-Pb geochronological data obtained by ID-TIMS demonstrate that granite, granodiorite and gabbro are coeval, as they define a common upper intercept age of 985.6 ± 1.6 Ma, dating emplacement of the batholith. Titanite is variously disturbed by later Sveconorwegian events. Pegmatites cross-cutting all structures yield zircon and titanite ages of 976 ± 8 Ma, 939 ± 2, and possibly 958 ± 2 Ma, reflecting the latest stages of the evolution of the batholith. The Finse batholith is one of the earliest members of the widespread ferroan hornblende-biotite-granitoid (HBG) suite, in the western part of the Sveconorwegian orogen.

Magma-driven, high-grade metamorphism in the Sveconorwegian Province, southwest Norway, during the terminal stages of Fennoscandian Shield evolution

“…In our study we recorded mafic magmatism at 1031 ± 5, 1025 ± 13 and 990 ± 12 Ma; along with earlier studies (Jensen and Corfu, 2016;Vander Auwera et al, 2011;Wiest et al, 2018), this suggests geographically widespread mafic magmatism during Sveconorwegian orogenesis.…”

“…Most studies on the mechanisms of long-lived UHT metamorphism invoke mantle-derived heat in the form of mafic magmatism resulting from extensional and/or compressional tectonics in arc and/or backarc settings (e.g., Brown, 2006;Currie and Hyndman, 2006;Walsh et al, 2015), similar to the tectonic-switching model of Collins (2002). Emerging evidence from the Sveconorwegian Province, including this study and that of Wiest et al (2018) near Bergen, and Jensen and Corfu (2016) at Finse, show that the Sveconorwegian orogeny was accompanied by geographically widespread mafic magmatism. A marked increase in Ti-in-zircon temperatures ca.…”

“…930 Ma, in association with the Rogaland Igneous Complex (Vander Auwera et al, 2011) and in the northern part of the Sveconorwegian Province, near Finse, ca. 986 Ma, in association with ferroan hornblende-biotite granites (Jensen and Corfu, 2016) has been documented. The new data presented here (Table 1; Fig.…”

“…1020 Ma, and was succeeded by widespread, long-lived granitic and bimodal magmatism between ca. 990 and 920 Ma (e.g., Jensen and Corfu, 2016;Slagstad et al, 2013a;Vander Auwera et al, 2003). The granites of the latter age range constitute relatively large, seemingly isolated bodies throughout the orogen, except farthest east, in the Eastern Segment.…”

Geochronological constraints for a two-stage history of the Sveconorwegian rare-element pegmatite province formation

“…Highpressure (at c. 1045 Ma) and upper-amphibolite-facies metamorphism (at c. 1025 Ma) in the Idefjorden lithotectonic unit (Söderlund et al, 2008) coincided with the emplacement of the Sirdal Magmatic Belt. The last major magmatic event in the Sveconorwegian orogen occurred when the hornblende-biotite granite suite was emplaced 1000-920 Ma (Granseth et al, 2020;Høy,2016;Jensen and Corfu, 2016;Slagstad et al, 2013Slagstad et al, , 2018Vander Auwera et al, 2003, 2011. The heat source for the hornblende-biotite granite magmatism is thought to be related to the underplating of mafic magmas due to crustal extension and mantle upwelling during this last orogenic stage (Andersen et al, 2007b;Granseth et al, 2020).…”