The Baltica–lapetus passive margin dyke complex in the Sarektjåkkå Nappe, northern Swedish Caledonides

Abstract

The polymetaphoric Seve Nappe Complex (SNC) of the Scandinavian Caledonides contains sequences representing the passive margin between continenral Baltica and the lapetus Ocean. The Sarektjikki Nappe in the SNC consists of sedimentary rocks intruded by mafic dykes that constitute 70-80 per cent of the nappe and frequently form sheeted dyke complexes. The internal parts of the Sarektjikki Nappe escaped pecetrative deformation and metamorphism during Caledonian nappe transport and primary igneous relations are preserved. A sequence of nine dyke generations have been identified in a sheeted dyke complex in one well exposed area (Favorithallen). The alteration in this dyke complex was triggered by heat in connection with the dyke emplacement; overprint from Caledonian regional metarnorphism cannot be demonstrated. Neither the relative age of a dyke in the dyke complex, nor the contact metamorphism caused by the emplacement of subsequent dykes had any detectable effect on the chemical composition of the dykes.The chemical composition of the diabases thus reflects the composition of the magma. Xenoliths of diabase and various types of gabbro are not uncommon and represent wallrock sampling during intrusion. Irregular patches of static alteration reveal the presence of fluids (brines), probably derived from metaevaporites in the wallrock, during the period of dyke intrusion. Scapolite rich dioritic-quartz dioritic inclusions and veins formed by partial or complete melting of wallrock xenoliths. A Sm-Nd age determination indicates a crystallization age of 573 It 74 Ma for the Sarek diabase, coinciding with the Vendian-Early Cambrian period of global continental break-up. Geophysical data from continent-ocean transitions at modern passive margins agree well with the structure of the Sarektjikki Nappe. I t is suggested that the Sarek dyke complexes were intruded during the initial stages of seafloor spreading in the Iapetus or pre-Iapetus Ocean.

Detrital zircon signatures of the Baltoscandian margin along the Arctic Circle Caledonides in Sweden: The Sveconorwegian connection

“…The Särv and Seve nappes at 66-67 • N, are comparable with their correlatives in northern Jämtland; they pass northwards into thrust sheets with more than 80% dykes (Sarektjåkkå Nappe, SA in Fig. 1; Andréasson, 1986;Svenningsen, 1994;Andréasson et al, 1998) and in the area around Sweden's highest mountain, Kebnekaise (K in Fig. 1; Andréasson and Gee, 1989;Baird et al, 2014).…”

“…The sample (CKS10) collected from directly above the Akkajaure Nappe Complex is a mica schist from what Kirkland et al inferred is the Skarja Nappe, by some authors (Rehnström et al, 2002) treated as lower Seve, by other authors interpreted as equivalent to the Särv nappes (Andréasson et al, 1992;Svenningsen, 1994;Rehnström, 1998;Thelander, 2009). Kirkland et al (2011) obtained a unimodal Paleoproterozoic (c. 1800 Ma) detrital zircon population from the mica schist, i.e.…”

Root zone of a continental rift: the Neoproterozoic Kebnekaise Intrusive Complex, northern Swedish Caledonides

“…(i) The KIC has a higher dyke density than that documented in other dyke complexes of the Seve Nappes (Svenningsen, 1994;Stølen, 1994;Kathol, 1989;Bingen et al, 1998). Across dyke swarms of other continental rifts, an increased density of dykes has been observed toward the central rift axis (e.g.…”

“…-In order to evaluate their regional significance, the KIC rocks are compared to correlative riftrelated igneous rocks occurring at the western margin of Baltica, either intruding the crystalline basement, or contained in the Middle Allochthon (Särv and Kalak Nappes) and the Upper Allochthon (Seve Nappes), respectively. These include (1 -Basement): the Egersund dykes (Bingen et al, 1998;Bingen and Demaiffe, 1999), and the Alnö Alkaline Complex (Vuorinen, 2005); (2 -Särv Nappes): the Ottfjället dykes (Solyom et al, 1979(Solyom et al, , 1985, the Sørli dykes (Beckholmen and Roberts, 1999); (3 -Kalak Nappes): the Corrovarre dykes (Roberts, 1990), the Seiland Igneous Province (Roberts, 2007;Roberts et al, 2010); (4 -Seve Nappes): the Tsäkokk basalts (Kullerud et al, 1990), the Sarek (Andréasson et al, 1992;Svenningsen, 1994) and Indre Troms dykes (Rohkunborri; Stølen, 1994), as well as mafic rocks from the Grapesvare Sun and McDonough (1989). Other Seve mafic rocks include values from Sarek (Andréasson et al, 1992;Svenningsen, 1994), Indre Troms (Stølen, 1994), Grapesvare (Andréasson and Albrecht, 1995) and Sylarna (Solyom et al, 1985;Pettersson, 2003).…”

Noble gas and halogen evidence for the origin of Scandinavian sandstone-hosted Pb-Zn deposits

“…These metadolerite dykes are preserved in the Late Precambrian metasedimentary rocks of the Middle and lowermost Upper Allocthons (Solyom et al, 1979;Zwaan and Roermund, 1990;Stølen, 1994;Svenningsen, 1994) and also in the basement in SW Norway (Bingen et al, 1998). Such a volatile source implies an even earlier, late Precambrian, origin for this component of the mineralizing brine and means that the involvement of original pore fluids from the lowermost glaciogenic parts of the autochthonous cover sequence (Fig.…”