THERMAL HISTORY OF THE PAN-AFRICAN BRASILIANO BORBOREMA PROVINCE OF NORTHEAST BRAZIL DEDUCED FROM AR-40/AR-39 ANALYSIS/

Detailed step heating Ar-40/Ar-39 analyses were performed on different minerals from magmatic and metamorphic rocks of the Borborema Provinc e. This region, located in northeast Brazil, belongs to the Pan-Africa n/Brasiliano belt which is about 1000 km wide and 600 km long. Twenty- six single grains of amphibole, muscovite and biotite were extracted f rom eighteen samples selected in an area of about 17,500 km(2) (250 km by 70 km) in the Patos region. This region has been affected by a con tinental-scale shear zone system. Well-defined Ar-40/Ar-39 plateau age s and an U-Pb analysis on zircon [Leterrier, J., Jardim de Sa, E.F, Be rtrand, J.M. and Pin, C., 1994. Ages U-Pb sur zircon de granitoides br asilianos de la ceinture du Serido (Province Borborema, NE bresil). C. R. Acad. Sci., Paris, 318: 1505-1511] allow the definition of a homoge neous and unusual slow cooling history (3-4 degrees C/Ma) and suggest a rather slow uplift rate between 580 and 500 Ma, followed by a fast c ooling of the whole studied area around 500 Ma. Rapid cooling is sugge sted by concordant plateau ages on muscovite and biotite. The existenc e of such an event at the end of the belt history is in agreement with data obtained on other major belts such as the Alpine-Himalayan syste m or the Hercynian belt. (C) 1998 Elsevier Science B.V. All rights res erved.