TECTONOTHERMAL EVOLUTION OF HIGH-ALUMINA ROCKS WITHIN THE PROTOGINE ZONE, SOUTHERN SWEDEN

The Protogine Zone comprises a system of anastomosing deformation zones which approximately parallel the eastern boundary of the Sveconorwegian (1200-900 Ma) province in south-west Sweden. Ages of granulite facies metamorphism in the Sveconorwegian province require exhumation from c. 30 to 35 km crustal depths after 920-880 Ma. 40Ar/39Ar cooling ages are presented for muscovite from high-alumina rocks formed by hydrothermal leaching associated with the Protogine Zone. Growth of fabric-defining minerals was associated with a ductile deformational event; muscovite from these rocks cooled below argon retention temperatures (c. 375 +/- 25 degrees C) at c. 965-955 Ma. Muscovite from granofels in zones of intense alteration indicates that temperatures>375 +/- 25 degrees C were maintained until c. 940 Ma. Textural relations of Al2SiO5 polymorphs and chloritoid suggest that dated fabrics formed during exhumation. The process of exhumation, brittle overprint on ductile structures and hydrothermal activity along faults within the Protogine Zone tentatively are interpreted as the peripheral effects of initial Neoproterozoic exhumation of the granulite region of south-western Sweden. The Protogine Zone comprises a system of anastomosing deformation zones which approximately parallel the eastern boundary of the Sveconorwegian (1200-900 Ma) province in south-west Sweden. Ages of granulite facies metamorphism in the Sveconorwegian province require exhumation from c. 30 to 35 km crustal depths after 920-880 Ma. 40Ar/39Ar cooling ages are presented for muscovite from high-alumina rocks formed by hydrothermal leaching associated with the Protogine Zone. Growth of fabric-defining minerals was associated with a ductile deformational event; muscovite from these rocks cooled below argon retention temperatures (c. 375 +/- 25 degrees C) at c. 965-955 Ma. Muscovite from granofels in zones of intense alteration indicates that temperatures>375 +/- 25 degrees C were maintained until c. 940 Ma. Textural relations of Al2SiO5 polymorphs and chloritoid suggest that dated fabrics formed during exhumation. The process of exhumation, brittle overprint on ductile structures and hydrothermal activity along faults within the Protogine Zone tentatively are interpreted as the peripheral effects of initial Neoproterozoic exhumation of the granulite region of south-western Sweden.