METAMORPHIC ZONATION IN LOWER CRETACEOUS ISLAND-ARC DEPOSITS OF REBUNISLAND (JAPAN)

The Lower Cretaceous Rebun Group is part of the Lower Cretaceous volca nic are of northern Japan. It consists of an alternation of volcanocla stic rocks and subordinate lava flows and sills. Clasts and lavas are mainly tholeiitic andesitic basalts. The group has been affected by ve ry low grade metamorphism that probably results from the conjunction o f burial and a thermal event. This metamorphism is characterized by a vertical zonation of the mineral assemblages (zeolite and prehnite-pum pellyite facies), that indicates an increasing metamorphic grade with depth, and by the predominance of a metastable equilibrium.