© Left-Lateral Transpressive Deformation And Its Tectonic Implications, Svecononwegian Orogen, Baltic Shield, Southwestern Sweden Stephens, MB; Wahlgren, CH; Weijermars, R; Cruden, AR ELSEVIER SCIENCE BV, PRECAMBRIAN RESEARCH; pp: ; Vol: 79 King Fahd University of Petroleum & Minerals Summary The Mylonite Zone (MZ) is a major, ductile deformation zone in the Sveconorwegian orogen (Baltic Shield) of southwestern Sweden and southeastern Norway which has a strike length of over 400 km and an across-strike width which often exceeds 5 km. It is an orogen-parallel deformation zone which formed under retrogressive metamorphic conditions relative to the higher-grade structures in the surrounding crustal units. The MZ marks a conspicuous metamorphic break in the area south of lake Vanern and a distinct lithological break in the area north of this lake. Regional metamorphic considerations suggest that its surface exposure represents an oblique section through the crust with deeper levels exposed along the southern parts of the zone and shallower levels exposed farther north. Structural studies in three areas north of lake Vanern (Varmlandsnas, Kil and Torsby-Charlottenberg) suggest that the MZ displays coeval, left-lateral, strike-slip and reverse, dip-slip senses of shear characteristic of a transpressive tectonic regime active under upper greenschist-facies conditions. In the northernmost Torsby-Charlottenberg area, at relatively shallow crustal levels, the MZ splays out to form two left-lateral, contractional strike-slip duplexes which together define a positive flower structure. Regionally, the MZ defines the western flank of an east-verging thrust system which formed in the eastern part of the Sveconorwegian orogen. The structures within this thrust system preceded the MZ, contain a subordinate, left-lateral strike-slip component of movement and were rotated into the Sveconorwegian Frontal Deformation Zone (SFDZ) in the frontal part of the orogen. The MZ is inferred to have formed in an extrusive Copyright: King Fahd University of Petroleum & Minerals;

© (dispersive) tectonic environment which developed in connection with a slightly oblique collision and crustal shortening in a WNW-ESE direction. The initial stages of this collision produced the east-verging thrust system and shortening was absorbed, at this stage, by crustal thickening. Late, possibly out-of-sequence thrusting with a right-lateral, strike-slip sense of shear along the SFDZ marked the waning stages of crustal shortening in the Sveconorwegian orogen. References: 1988, TECTONOPHYSICS, V150, P253 BERTHELSEN A, 1978, TECTONIC GEOLOGY HIM, P287 BERTHELSEN A, 1980, INT GEOL C PARIS C, V6, P5 BERTHELSEN A, 1987, ANATOMY MOUNTAIN RAN, P31 DAHLJENSEN T, 1991, TECTONOPHYSICS, V195, P209 EISBACHER GH, 1970, GEOL SOC AM BULL, V81, P2009 FALKUM T, 1980, GEOL RUNDSCH, V69, P622 GORBATSCHEV R, 1988, GEOL FOREN STOCKHOLM, V110, P392 GREEN CM, 1988, TECTONOPHYSICS, V150, P349 HANMER S, 1991, 9017 GEOL SURV CAN P HARDING TP, 1985, AAPG BULL, V69, P582 HARRISON TM, 1992, SCIENCE, V255, P1663 HEYBROEK P, 1949, GEOL FOREN STOCKHOLM, V71, P425 HOGBOM AG, 1910, B GEOL I UPSALA, V10, P1 HOLDSWORTH RE, 1991, GEOLOGY, V19, P510 HOWELL DG, 1989, TECTONICS SUSPECT TE JARL LG, 1992, GEOL FOREN STOCKHOLM, V114, P349 JOHANSSON L, 1991, J METAMORPH GEOL, V9, P283 JOHANSSON L, 1993, GEOL FOREN STOCKHOLM, V115, P1 JUHLIN C, 1989, GEOPHYS J INT, V99, P567 LARSON SA, 1986, PRECAMBRIAN RES, V31, P237 LINDH A, 1974, GEOLOGISKA FORENINGE, V96, P183 LINDH A, 1984, GEOL RUNDSCH, V73, P881 LINDH A, 1988, GEOL FOREN STOCKHOLM, V110, P15 MAGNUSSON NH, 1937, EOL FOREN STOCKHOLM, V59, P205 PAGE L, 1996, IN PRESS J GEOL SOC PARK RG, 1991, PRECAMBRIAN RES, V49, P245 PARK RG, 1992, GEOLOGY, V20, P725 SAMUELSSON L, 1985, SVER GEOL UNDERS AF, V136 TAPPONNIER P, 1986, GEOL SOC LOND SPEC P, V19, P115 TORNEBOHM AE, 1983, GEOL FOREN STOCKHOLM, V6, P622 WAHLGREN CH, 1977, GEOL FOREN STOCKHOLM, V99, P291 WAHLGREN CH, 1994, PRECAMBRIAN RES, V70, P67 WEIJERMARS R, 1984, GEOLOGY, V12, P603 Copyright: King Fahd University of Petroleum & Minerals;

© WOODCOCK NH, 1986, J STRUCT GEOL, V8, P725 ZECK HP, 1974, B GEOLOGICAL SOC DEN, V23, P159 For pre-prints please write to: Copyright: King Fahd University of Petroleum & Minerals;