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Mosquera, Alfonso1 
(1) Tecpetrol S. A, Buenos Aires, Argentina

ABSTRACT: Basement Control in Southern Subandean Thrust Belt Development and its Implications in Hydrocarbon Trapping. Northern Argentina and Southern Bolivia

Presently, the northern Argentina - southern Bolivia Subandean thrust belt holds the largest gas accumulations in Southamerica (EUR: 50 tcf), stored mainly in naturally fractured tight sandstone Devonian reservoirs 
It is an active thin-skinned fold and thrust belt (500 by 200km) characterized by a series of parallel large scale narrow anticlines (5 by 100 km.) and detached in the Silurian Kirusillas Fm. and in the Devonian Los Monos Fm shales, basal and upper decollements. 
Widespread lateral continuity of these units provides a very homogeneous mechanical stratigraphy. 
Despite its subtle surface expression, basement control in the Subandean can clearly be seen on seismic lines, especially in the southern plunge of the three easternmost trends (Aguaragüe, Campo Duran and Mandeyapecua). 
Basement influence results in the east-west, northeast southwest bending and wrenching of these north – south striking trends. 
The Aguaragüe trend (EUR: 1 tcf) bends northeast southwest, as a result of the interference of a Cretaceous age rift fault that passively controls the position of the lower ramp corner of the Aguaragüe thrust. 
The Campo Duran – Madrejones (EUR: 5 tcf) thrust is cut by a dextral tear fault that displaces eastward (2 km) the central and northern portion of the trend. This tear fault separates two mayor gas accumulations, the Campo Duran-Madrejones (5tcf) gas and condensate fields (Tupambi – Las Peñas Fms, Carboniferous) from the Madrejones gas field (EUR: 1tcf) (Huamampampa Fm, Devonian). 
Finally, the southern plunge of Mandeyapecua is controlled by a dextral strike-slip fault, where Palo Marcado field is located.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.