34. DISTRIBUTION AND CHEMISTRY OF SECONDARY MINERALS (ZEOLITES AND CLAY MINERALS) FROM HOLE 917A, SOUTHEAST GREENLAND MARGIN¹

Alain Demant,² Philippe Münch,³ Nathalie Romeuf,³ and Diego Morata⁴

ABSTRACT

The Paleocene basalts recovered at Hole 917A, Leg 152, suffered very low grade metamorphism as indicated by the presence of zeolites and clay minerals. Chabazite, heulandite-group zeolites, thomsonite, analcite, and natrolite occur as vesicle fillings and in the groundmass, whereas chlorite, interlayered chlorite/smectite, and saponite/smectite were identified in the same microdomains; saponite is restricted to olivine pseudomorphs. These mineralogical assemblages indicate that the temperature of the metamorphic transformations did not exceed 170°C. The regular increase of cationic Na toward the top of the volcanic pile indicates that the zeolites formed during a hydrothermal process in an open system clearly influenced by seawater. This metamorphism was therefore a late post-emplacement event that affected the whole volcanic pile and occurred after the opening of the North Atlantic Ocean.

¹Saunders, A.D., Larsen, H.C., and Wise, S.W., Jr. (Eds.), 1998. Proc. ODP, Sci. Results,152: College Station, TX (Ocean Drilling Program).
²Laboratoire de Pétrologie Magmatique, URA CNRS 1277 et FU 17, CEREGE BP 80, 13545 Aix-en-Provence Cedex 04, France. ADEMANT@ARBOIS.CEREGE.FR
³Centre de Sédimentologie Paléontologie, URA CNRS 1208, Université de Provence, 3 Place Victor Hugo, 13331 Marseille Cedex 3, France.
⁴Departamento de Mineralogía Petrología y Geoquímica, Facultad de Ciencias del Mar, Universidad de Cadiz, 11510 Puerto Real (Cadiz), Spain.