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

The Protogine Zone comprises a system of anastomosing deformation zone s which approximately parallel the eastern boundary of the Sveconorweg ian (1200-900 Ma) province in south-west Sweden. Ages of granulite fac ies metamorphism in the Sveconorwegian province require exhumation fro m c. 30 to 35 km crustal depths after 920-880 Ma. Ar-40/Ar-39 cooling ages are presented for muscovite from high-alumina rocks formed by hyd rothermal leaching associated with the Protogine Zone. Growth of fabri c-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 i n zones of intense alteration indicates that temperatures>375 +/- 25 d egrees C were maintained until c. 940 Ma. Textural relations of Al2SiO 5 polymorphs and chloritoid suggest that dated fabrics formed during e xhumation. The process of exhumation, brittle overprint on ductile str uctures and hydrothermal activity along faults within the Protogine Zo ne tentatively are interpreted as the peripheral effects of initial Ne oproterozoic exhumation of the granulite region of south-western Swede n. Muscovite in phyllonites associated with the 'Sveconorwegian thrust system' cooled below argon retention temperatures at c. 927 Ma. Exhum ation associated with this cooling could have been related to extensio n and onset of brittle-ductile deformation superimposed on Sveconorweg ian contraction.