Browsing by Author "Ostos Rosales, Marino"

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    Structural interpretation of the Tinaquillo peridotite and its country rock, Cojedes State, Venezuela
    (1984) Ostos Rosales, Marino; Lallemant, Hans G. Avé; Oldow, John S.; Stormer, J. C.
    The Tinaquillo Complex is bordered to the south by the Tinaco Complex, and to the north is separated by a thrust fault from the Cordillera de la Costa belt. The Tinaquillo Complex, consisting mainly of harzburgite and metagabbro, was formed at high temperature (up to 14°C) and presumably at great depth in the upper mantle. The Tinaco Complex consists of meta-igneous and metasedimentary rocks. The Tinaquillo Complex was juxtaposed onto the Tinaco Complex at intermediate crustal levels at temperatures of about 65°C. Structures in the Tinaquillo harzburgites indicate that the juxtaposition was caused by northwesterly directed thrusting. The metamorphism in the Tinaco Complex is clearly not of the contact type, as has been suggested previously, but is a regional metamorphism. Although good age dates are not available, it is suggested that the juxtaposition of the two complexes occurred during Late Paleozoic times, probably related to collision of a volcanic island arc with South America. The juxtaposition of both complexes onto the Cordillera de la Costa belt is probably a Late Cretaceous or Tertiary event and may be related to a collision of another volcanic island arc with South America.
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    Tectonic evolution of the south-central Caribbean based on geochemical data
    (1990) Ostos Rosales, Marino; Avé Lallemant, Hans G.
    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.