TECTONIC ANALYSIS OF THE GUARICO MOUNTAIN FRONT, VENEZUELA, SOUTH AMERICA

A 1:150,000-scale tectonic map of the east-trending Guarico Mountain Front prepared in this study includes the topographic transition across the margin of the Cordillera Central and the Llanos Centrales to the south. Based on lithology and potential tectonic setting of deposition, seven lithotectonic packages are defined in four tectonic domains. 1. Cretaceous Passive Margin Platform Sequence (carbonate and shale) 2. Middle Cretaceous Blueschist Metavolcanic Sequence (meta-basalt) 3. Late Cretaceous Volcanic Arc Sequence (basalt flows, serpentine and tuff) 4. Late Cretaceous Volcanic Arc Turbiditic Sequence (greywacke and shale) 5. Paleogene Foredeep Sequence (lithic arenite, shale and limestone olistoliths) 6. Late Eocene-Miocene Foredeep Marginal Sequence (limestone and shale) 7. Oligocene-Pliocene Synorogenic Sequence (continental clastics and coal)

Structural cross sections, seismic data interpretation, styles of deformation and stereonet analysis of these lithotectonic units enable the definition of four tectonic domains, which from north to south are: A. Villa de Cura Allochthon Domain (units 2,3) B. Fold Thrust Domain: Steep Dips (units 1,3,4,5) C. Fold Thrust Domain: Gentle Dips (units 5,6) D. Tuy Depression Strike Slip and Normal Faulting Domain (unit 7)

Dominant structures of Domains A, B, and C are E-NE trending, south-vergent, fault-bend and fault-propagation folds. Cross-cutting relationships indicate Late Cretaceous to Late Miocene-Pliocene deformation coincident with a transpressional regime related to oblique convergent interaction between the Caribbean and South American Plates. Initiation of deformation is younger eastward. Subsequently, the regional stress field changed to one of transtension along this plate boundary, focused north of the mountain front. W-NW and NE-trending faults (with negative flower structures) comprise the boundaries of Domain D and oblique movement along dominantly normal, NW-trending faults affected strata within the basin. Crosscutting relationships indicate structural development during and after the Miocene-Pliocene (probably still active). Fault geometries and orientations indicate maximum horizontal E-NE extension and counter-clockwise rotation of faulted blocks.