HIGH-PRESSURE METAMORPHISM ALONG THE SOUTHERN MARGIN OF THE
CARIBBEAN-WHEN, WHY, AND WHERE?

W.V. MARESCH, B. STOCKHERT,
R. KLUGE, G. KROCKHANS,,
and A. TOETZ
(Inst. fur Mineralogie, Univ. Munster, 4400 Munster, F.R.G., and Inst. Fur Geologie, Ruhr-Univ.
Bochum, 4630 Bochum, F.R.G.)


Plate tectonic tenets allow the present-day geodynamic regime of the Caribbean to be understood and interpreted with a high degree of confidence. The situation in the Late Mesozoic and Early Tertiary, prior to and contemporaneous with the introduction of an oceanic plateau from the Pacific into the Caribbean gap, is much less clear. Short-lived, constantly evolving island arcs and their collision with each other and with continental margins appear to play a major role. High-pressure metamorphism accompanied these collisions. Two end-member hypotheses are currently being debated to explain a major belt of high-pressure metamorphics along the northern margin of South America:
A) The high-pressure rocks originated in the Late Cretaceous during a collision along the western margin of South America. They were subsequently tectonically dispersed along the 1000km strike slip zone representing the plate boundary along the present-day northern margin. The high-pressure rocks are thus part of the Caribbean plate.
B) Oblique collision of an island arc situated on the prow of the Pacific oceanic plateau wIth the northern margin of South America led to In Situ high pressure metamorphism. The hi-P rocks are then part of the South American plate. In this case an Early Tertiary metamorphic age must be invoked, In accord with the timing of eastward progress of the plateau.
Although presently available data yield no unequivocal support for either of the two hypotheses, the high-pressure metamorphic rocks of the island Margarita, and their correlative sequences on mainland Venezuela, are superbly suited to test these models. The nature, interdependence and timing of metamorphism and deformation, both viewed as continuous processes, allow the necessary constraints for a resolution of the problem to be outlined.

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