Occurrence of chloritoid and pyrophyllite in metaclastic rocks of Morava Zone

Abstract

Metaclastics of the Morava Zone (eastern part of the Serbo-Macedonian Massif) occur in one, or two or more successive discontinuous levels, up to several tens of meters in thickness. The investigated metaclasites were determined as primary conglomerates and sandstones deposited in shallow water environments at a continental margin. Chloritoid, pyrophyllite and biotite formed during the last metamorphic event indicate that metamorphic temperature reached 350°C, ±50°C. Pressure conditions are less well constrained, 2-3 Kb being inferred. The mentioned estimates indicate that metamorphic conditions were of lower grade than in other investigated areas. Chloritoid and pyrophyllite are present also in virtually all rocks in the Morava Zone. The occurrence of these minerals is attributed to basin-wide alteration by infiltrating hydrothermal fluid during metamorphism. Their formation do not require unusual conditions for the sedimentation of weathering products, diagenesis or epithermal activity to produce the alumina rich assemblage, and timing constrains appear incompatible with such explanations.