Emplacement and deformation of the ca. 1.45 Ga Karlshamn granitoid pluton, southeastern Sweden, during ENE-WSW Danopolonian shortening

Abstract

Anisotropy of magnetic susceptibility and structural geology of the ca. 1.45 Ga Karlshamn pluton (southern Sweden) are used to study its emplacement and structural evolution. The Karlshamn pluton is one of the largest metaluminous A-type granitoid intrusions in southern Sweden. It is a multiphase body made up of two suites that differ in composition but which have similar crystallization ages. The magmatic foliation, ductile shear zones and granite-pegmatite filled fractures were mapped as well as the metamorphic foliation and extension lineation in the metamorphic host rocks. The anisotropy of magnetic susceptibility was used to map the magnetite petrofabric of the pluton, providing a larger data set for both the magmatic foliations and lineations, which could not be mapped in the field. The fabrics within the pluton are continuous with the metamorphic fabrics in the country rocks. Both the pluton and the country rock fabrics were folded during ENE-WSW compression, while the pluton was still a magma mush. The stress field orientation during cooling of the pluton is determined on the basis of magmatic, ductile and brittle structures in the Karlshamn pluton that formed successively as the pluton cooled. The compressional event is referred to as the Danopolonian orogeny and therefore the Karlshamn granitoids, and other plutons of similar composition and age in central and southern Sweden, on the Danish Island of Bornholm, and in Lithuania, may be considered as syntectonic intrusions and not as anorogenic, as was previously thought.

In situ Rb-Sr dating of slickenfibres in deep crystalline basement faults

“…3c and 6) both coincide with known tectonic events. The 1438 ± 33 Ma www.nature.com/scientificreports www.nature.com/scientificreports/ age is similar to 40 Ar/ 39 Ar muscovite ages found further south (Laxemar area, SE Sweden) of altered wall rocks adjacent to veins and greisen related to adjacent Mesoproterozoic A-type granites 41 associated with the Danopolonian-Hallandian orogenies, which in the south featured WSW-ENE-directed crustal shortening 42 . If the Rb-Sr closure temperature of adularia is similar to that for 40 Ar/ 39 Ar (150 ± 30 °C 43 ;), the regional temperature regime of >200-225 °C 35,36 recorded in the Paleo-Mesoproterozoic of the Fennoscandian shield may have been high enough to reset grains grown at an earlier stage.…”

U–Pb SIMS dating of some granitoids from eastern Blekinge, southern Sweden

“…Titanite from several rocks analyzed by TIMS by the same authors yielded a cluster of 207 Pb/ 206 Pb ages at 1431 ± 6 Ma. Thus, the combined evidence seems to favour two separate metamorphic events, one encompassing pervasive deformation under relatively dry conditions in close connection with the formation of these rocks at 1.76-1.75 Ga, and a second episode, possibly of more static character, with heating and migmatization related to the intrusion of the Karlshamn granitoid suite at ca 1.45 Ga (Åberg 1988;Čečys & Benn 2007) and, more generally, to the so-called Danopolonian event of Bogdanova (2001). Movements along the Karlskrona Deformation Zone are envisaged to have occurred in close connection with the first event, while uplift along the SBDZ may have occurred somewhat later, but prior to the intrusion of the Karlshamn suite (Kornfält 1999a;Kornfält & Bruun 2002).…”

Danopolonian migmatization of Mesoproterozoic sedimentary rocks in southernmost Sweden: a SIMS zircon study

“…1), the Västanå metavolcanic rocks and quartzites, their stronger metamorphosed and migmatized equivalents in the "coastal gneisses" and various granitoids were all formed within a narrow time interval between 1.77 and 1.75 Ga (Johansson et al 2006). At c. 1.46 Ga, these rocks were intruded by the Karlshamn group of granites (Kornfält & Bergström 1983;Å berg 1988;Kornfält 1993Kornfält , 1999 during the Danopolonian orogeny within a general NE -SW compression (Č ečys & Benn 2007;Bogdanova et al 2008). During the late, extensional stages of the Sveconorwegian orogeny at 0.98-0.95 Ga, extensive mafic dyking took place to the east of the Sveconorwegian orogen (Blekinge -Dalarna dyke swarm; Söderlund et al 2005).…”