Abstract

The geochemistry and geochronology of the igneous rocks from the Venezuelan islands in the southern Caribbean, the Netherlands Leeward Islands, and the Caribbean Mountains of northern Venezuela were studied in an effort to test plate tectonics models for the evolution of that part of the Caribbean region. The continental platform north of Venezuela is underlain by an igneous and metamorphic complex that crops out on the Venezuelan islands. The older metamorphic rocks (lower to upper greenschist facies) are similar to those found in the Caribbean Mountains. These rocks were intruded by basic and granitic igneous rocks and andesitic to basaltic volcanic rocks during Early Cretaceous to early Tertiary time.

Geochemically, the igneous rocks can be divided into two suites, a calc-alkaline suite consisting of quartz diorite, granodiorite, trondhjemite, and granite, and an olivine and ocean-floor tholeiitic suite consisting of gabbro, diabase, lamprophyre, and orthoamphibolite. The calc-alkaline affinity is shown by high Al2O3 and K2O, and low MgO and TiO2 contents. The K2O content increases southward from the Venezuelan islands toward the Caribbean Mountains. The tholeiitic affinity is shown by low Fe2O3/MgO ratios, low K2O and Sr contents, and high K/Rb ratios. K-Ar age determinations on these rocks show that the tholeiitic rock suite is the oldest, which confirms field relations, ranging between 114 m.y. and 130 m.y. (Early Cretaceous). The K-Ar ages of the calc-alkaline rock suite range between 30 m.y. and 84 m.y. (Late Cretaceous to Oligocene). These ages are interpreted to represent a Late Cretaceous–early Tertiary time of intrusion and later metamorphism and also support a late Eocene–Oligocene erogenic event that resulted in the present structural configuration of the central Caribbean Mountains. A dacite in the Carúpano area (Araya-Paria Península) yielded a K-Ar age of 5 m.y., or late Pliocene, which is the youngest evidence of igneous activity in northern Venezuela. The dacite is possibly related to the younger volcanic province of the Lesser Antilles.

Our data support the hypothesis that the Aves Ridge represents a presently inactive volcanic arc prior to the Lesser Antilles arc.

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