GEOLOGY OF THE LOS TEQUES–CUA REGION, VENEZUELA

Abstract

The Los Teques-Cua portion of the Coast Range of north-central Venezuela consists essentially of a granitic basement overlain by two metasedimentary and metaigneous complexes of probable Cretaceous age, locally covered by unmetamorphosed volcanic and Tertiary sedimentary rocks. The Sebastopol orthogneiss forms the basement, overlain unconformably by the Caracas metasedimentary series. Although now gneissic, the Sebastopol was probably unmetamorphosed, coarse-grained granite when the sediments of the Caracas series were deposited. The Older Metamorphic Complex, the Caracas series, is chiefly metamorphosed sediments seemingly deposited on a stable platform in a transgressing early Cretaceous sea. This sequence of arkoses, conglomerates, orthoquartzites, dolomitic and reef limestones, and calcareous and noncalcareous shales was metamorphosed to microcline dolomite rocks, and schists and marbles of the Las Brisas formation, the Antimano limestone, and the Las Mercedes formation. An amphibolite layer, possibly representing a metamorphosed basaltic flow, occurs interbedded in the sequence. Well-defined schistosity and lineation were developed during the folding and metamorphism. The sediments of the Younger Metamorphic Complex, the Paracotos formation, lie unconformably above the Older Complex and represent rapid deposition under eugeosynclinal conditions. They consist of a mixture of graywackes, conglomerates, and cherts, interbedded with tuffaceous and limy layers. Most of the clastic material for the graywackes was derived from the already exposed Caracas series schists and the Sebastopol basement. The Paracotos sediments were intruded by peridotitic igneous rocks and a hornblende diorite with related dikes of soda granite. Metamorphism of this complex to the muscovite-chlorite subfacies of the green-schist facies shortly after the emplacement of the igneous rocks converted the sediments to phyllites and metagraywackes and imparted a slight schistosity and microfold lineation to all the rocks affected. The ultramafic intrusives were also partly altered to antigorite in the northern outcrops. In neither this nor the earlier metamorphism of the Caracas series was a thick cover of sediments present. The Tiara volcanics consist of gabbroic dikes and sills and basaltic flows emplaced immediately after the metamorphism of the Younger Complex. These, together with the earlier metamorphics, were being eroded by Coniacian time, supplying material to the Late Cretaceous, Tertiary, and Quaternary sediments. Structurally the region lies on the southern limb of the major anticline which trends N.75°E. across the northern part of the area. All magnitudes of folding occur in these rocks, from the large isoclinal folds to the microscopic fold lineation. Faulting is also prominent chiefly as N.80°E. transcurrent faults and their accompanying N.60°W. normal faults. Thrust faults, probably older than the transcurrent faults, occur locally. The region is rugged. Youthful streams are cutting rapidly into an uplifted erosion surface.