Tectonic evolution of the south-central Caribbean based on geochemical data
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- Geologic Map: Chichiriviche, D.F. La Victoria, Aragua State
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- Geologic Map: La Victoria - San Sebastian, Aragua State
Ostos Rosales, Marino
Avé Lallemant, Hans G.
Doctor of Philosophy
Northern Venezuela consists of seven east-west trending tectonostratigraphic belts which are from north to south: Dutch and Venezuelan islands (DVI), Venezuelan platform, Cordillera de la Costa-Margarita terrane (CCMT), Cordillera de la Costa belt (CCB), Caucagua-El Tinaco belt (CTB), Paracotos belt (PB), and Villa de Cura belt (VCB). Geochemical, metamorphic, and structural data were collected in several transects through these belts. Major- and trace-element abundances in mafic and felsic rocks were determined to find the tectonic affinity of these rocks. The Precambrian basement of the CCB appears to consist of within-plate granites. The Paleozoic basement of the CTB consists of MORB's, Andean-type tholeiites, and arc granites. The mafic rocks of Mesozoic age have variable affinities: the DVI, CCMT, and VCB are underlain by MORB's, but part of the VCB has volcanic arc affinity. All felsic rocks of Mesozoic age in the DVI and CCMT are arc granites. Several periods of metamorphism have occurred in Venezuela in Precambrian and Paleozoic time. An important metamorphic event occurred in the Cretaceous. The CCMT and VCB underwent high P/low T metamorphism and subsequently low to intermediate P/T metamorphism. These events may be related to subduction and subsequent uplift, respectively. The CCB underwent an intermediate P/T metamorphism, because it probably has never been buried as deeply. The PB underwent very low-grade metamorphism possibly related to the obduction of ophiolitic thrust sheets. Four generations of folds and three generations of faults were recognized. The first two phases of folding occurred probably in the Permian and the last two during a Late Cretaceous-Tertiary orogeny. Kinematic indicators suggest that the entire system underwent dextral shear parallel to the belts during the Late Cretaceous-Tertiary. Based on the available geologic data, a plate tectonic model is proposed. In the model the east-west trending belts of northern South America are allochthonous and deformed as a result of collision of a microcontinent (Sebastopol block) with northwestern South America. The belts were initially coupled to the overriding South American plate, but because of the large obliquity of plate convergence were transported easterly since the Late Cretaceous.