BOLIVAR: Deformation History of the Villa de Cura Blueschist Belt, Venezuela

Alastair M. John 1
Hans G. Avˆ© Lallemant 1
Armando Altamira-Areyan 2

1Rice University, Department of Earth Science-MS126, 6100 Main Street, Houston, TX 77005, United States
2University of Houston, Department of Geosciences, Houston-SR1, 4800 Calhoun Road, TX 77204, United States

As part of the BOLIVAR project ("Broadband Ocean-Land Investigations of Venezuela and the Antilles arc Region") we conducted an on-land geological study of the high pressure-low temperature (HP-LT) Villa de Cura blueschist belt (VdC) in Venezuela The belt is part of the Caribbean Mountain system (CMS) that dominates the South American-Caribbean plate boundary zone in central Venezuela The CMS is characterized by south-vergent thrust faults and east trending dextral strike-slip faults. We performed a structural analysis in the western and central parts of the VdC belt. The Villa de Cura Group consists of coherent blueschist-facies meta-volcanic and meta-sedimentary rocks that display island-arc affinities. It overlies middle- to upper-greenschist facies meta-volcanics of the Las Hermanas Formation. The VdC belt is in fault contact with non- to lower-greenschist facies metamorphosed lithologies of the Paracotos belt to the north and with the non-metamorphosed sedimentary units of the Serranía del Interior foreland fold-thrust belt to the south. Most authors consider the VdC belt to be a klippe that in Cenozoic times was thrust over the Venezuelan passive margin and foreland basin during the diachronous collision (progressively younger plate interaction from west to east) of the Antilles arc terrane with the South American plate. The main objectives of this research are: (1) to test the hypothesis that diachronous collision of the island arc with the continent lead to diachronous deformation, uplift and exhumation of HP-LT metamorphic rocks, and (2) to provide a full deformation-time path for the VdC to test previous geothermobarometric, geochronological, and geochemical studies.

Meso- and microstructural analysis and petrography have led to the recognition of three ductile, two brittle-ductile and at least two brittle deformation phases. Samples were collected for 40Ar/39Ar radiometric age dating and for fluid inclusion microthermometry. In most active margins around the world studies of HP-LT metamorphosed rocks have provided constraints on the development of the margin, both in structural styles as well as age. We propose that the ductile deformation at near peak-metamorphic conditions took place during the final stages of subduction and early uplift of these rocks under a volcanic arc. The brittle-ductile folding and faulting is then associated with the collision of the arc with the South American continental margin and early stages of thrust emplacement of the CMS. The brittle structures are associated with deformation of the margin and final emplacement and exhumation of the VdC.