THE GEOCHEMISTRY OF A METAVOLCANIC HORIZON IN THE MARACAS FORMATION, NORTHERN RANGE, TRINIDAD

TREVOR A. JACKSON
Department of Geology,
University of the West Indies
Kingston 7, JAMAICA
and
TERRENCE E. SMITH
Department of Geology, University of Windsor,
Windsor, Ontario N9B 3P4, CANADA


A lower greenschist fades metavolcanic horizon is exposed near the base of the Maracas Formation along the North Coast Road, Northern Range. The horizon is distinguished from other units in the Maracas Formation by its predominantly green colour due to the presence of chlorite, epidote and actinolite. The metavolcanics are characterised by a pervasive foliation defined by lepidoblastic chlorite and granoblastic quartz. Pretectonic crystals of plagioclase and pyroxene are also present in the assemblage.
Major and trace element analysis of the metavolcanic horizon confirm that it is a metabasite. FeO/MgO ratios with respect to Si02 indicate a tholelitic affinity and the discrimination diagrams suggest that the metavolcanic originated from the eruption of an ocean floor basalt.
The chemical analyses of the metavolcanics of the Maracas Formation differ from the metavolcanics of the Parlatuvier Formation, Tobago, but compare closely to the Sans Souci volcanics in the eastern section of the Northern Range.

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