TY - JOUR

T1 - Late-Svecofennian transpressive deformation in SW Finland - evidence from late-stage D3 structures

AU - Levin, Thomas

AU - Engström, Jon

AU - Lindroos, Alf

AU - Baltybaev, Shauket

AU - Levchenkov, Oleg

N1 - Funding Information: Acknowledgements. – This study was supported financially by the Foundation for Research of Natural Resources in Finland, the Magnus Ehrnrooth Foundation, the Åbo Akademi Foundation and the Finnish Society of Sciences and Letters (the Sohlberg foundation). Professor Carl Ehlers gave profound and critical comments on the manuscript. The authors express their thanks to reviewers Timo Kilpeläinen, Karin Högdahl and Markku Väisänen for their useful comments on the original manuscript. We are grateful to A.F. Makeev and S.Z. Yakoleva (IPGG RAS) for their help in the analytical investigation of the monazites. Juha Kauhanen prepared the thin sections. All the contributions are gratefully acknowledged.

PY - 2005

Y1 - 2005

N2 - Late-Svecofennian deformation was investigated in the Bjensböle area of SW Finland. The deformation history was revealed by following marker horizons of amphibolite, marble and black schist, in addition to microscopic studies and U-Pb monazite geochronology. The D1 structures are transposed and overprinted by D2 structures. The mesoscopic F2 folds are tight to isoclinal with fold axes plunging 20-40°NE-ENE. Regional large-scale open F3 folds formed during the main D3 phase, and the macroscopic structure in Bjensböle is an F2-F3 interference pattern formed by N-S compression. The area consist of low P/high T amphibolite facies sillimanite gneiss and low P/low T amphibolite facies quartz schist, separated by a low P/low T amphibolite horizon in the central part of the area. The sillimanite gneiss yielded a U-Pb monazite age of 1824±5 Ma. This age gives a timing for the peak metamorphism and the D3 folding on the Kemiö Island. After the peak metamorphism some deformational structures developed. A NE-SW directed crenulation cleavage in the quartz schist and the amphibolite, small open folds in the marble, a foliation in the sillimanite gneiss and a muscovite orientation in the quartz schist all have the same direction. These structures are interpreted as late-stage D3 (D3L). The angle between the NE-SW directed D3L structures and the locally predominant S0 + S1 + S2 schistosity is ca. 25°. The structural evidence related to the D3L point to a dextral sense of shearing along roughly E-W directed zones with a NW-SE compression. This is related to a regional ductile shearing signifying the vaning stages of the late-Svecofennian transpressive deformation in SW Finland.

AB - Late-Svecofennian deformation was investigated in the Bjensböle area of SW Finland. The deformation history was revealed by following marker horizons of amphibolite, marble and black schist, in addition to microscopic studies and U-Pb monazite geochronology. The D1 structures are transposed and overprinted by D2 structures. The mesoscopic F2 folds are tight to isoclinal with fold axes plunging 20-40°NE-ENE. Regional large-scale open F3 folds formed during the main D3 phase, and the macroscopic structure in Bjensböle is an F2-F3 interference pattern formed by N-S compression. The area consist of low P/high T amphibolite facies sillimanite gneiss and low P/low T amphibolite facies quartz schist, separated by a low P/low T amphibolite horizon in the central part of the area. The sillimanite gneiss yielded a U-Pb monazite age of 1824±5 Ma. This age gives a timing for the peak metamorphism and the D3 folding on the Kemiö Island. After the peak metamorphism some deformational structures developed. A NE-SW directed crenulation cleavage in the quartz schist and the amphibolite, small open folds in the marble, a foliation in the sillimanite gneiss and a muscovite orientation in the quartz schist all have the same direction. These structures are interpreted as late-stage D3 (D3L). The angle between the NE-SW directed D3L structures and the locally predominant S0 + S1 + S2 schistosity is ca. 25°. The structural evidence related to the D3L point to a dextral sense of shearing along roughly E-W directed zones with a NW-SE compression. This is related to a regional ductile shearing signifying the vaning stages of the late-Svecofennian transpressive deformation in SW Finland.

KW - Crenulation cleavage

KW - Kemiö

KW - Late-stage D

KW - Late-svecofennian

KW - Monazite

KW - Quartz schist

KW - Sillimanite gneiss

KW - Sw finland

KW - U-pb

UR - http://www.scopus.com/inward/record.url?scp=24344478140&partnerID=8YFLogxK

U2 - 10.1080/11035890501272129

DO - 10.1080/11035890501272129

M3 - Article

AN - SCOPUS:24344478140

VL - 127

SP - 129

EP - 137

JO - GFF

JF - GFF

SN - 1103-5897

IS - 2

ER -