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Pre-Andean Uplift and Exhumation as a Source of Carboniferous Reservoir Rocks in Eastern Bolivia

Ryan Anderson
Nevada Bureau of Mines and Geology/Geology, University of Nevada Reno, Reno, NV, USA
[email protected]

Abstract

The majority of hydrocarbon resources in Bolivia are hosted within Carboniferous sedimentary rocks in the eastern part of the Andean fold-thrust belt and the Chaco foreland basin. It has been suggested on the basis of structural/stratigraphic relationships that these Carboniferous rocks were deposited in a foreland basin system that subsided as sediment eroded off a pre-Andean orogenic high. One proposed highland from which this sediment may have been derived is to the west, in the present-day Eastern Cordillera of southern Bolivia, where deeply-exhumed, low-grade metamorphic Ordovician sedimentary rocks are unconformably overlain by un-metamorphosed Mesozoic rocks. K-Ar ages of synkinematic illite in Ordovician rocks indicate that metamorphism occurred in the late Carboniferous (310-290 Ma); however, the timing of their exhumation is presently unconstrained. Our objective is to constrain the timing of this pre-Andean exhumation event, and to see how it relates temporally to deposition of Carboniferous hydrocarbon host rocks. Geologic mapping and a balanced cross-section through the eastern part of the thrust belt will be extended westward into the Eastern Cordillera. Raman spectroscopy on carbonaceous material and (U-Th)/He dating of zircon will be utilized to determine peak metamorphic temperatures and exhumation timing of Ordovician rocks in the Eastern Cordillera, and detrital (U-Th)/He zircon thermochronology will be performed on Carboniferous rocks from the frontal part of the thrust belt. We predict that if a regional, pre-Andean erosion event in the Eastern Cordillera was the source of Carboniferous rocks, then detrital thermochronologic ages from Carboniferous rocks should match the Ordovician bedrock cooling ages.

AAPG Search and Discovery Article #90199 © 2014 AAPG Foundation 2014 Grants-in-Aid Projects