DEEP-STRUCTURE OF THE METAN-GUACHIPAS REGION - TECTONIC INVERSION IN NORTHWESTERN ARGENTINA

New deep seismic-reflection data obtained by reprocessing an industria l line from the eastern sector of the Salta rift system, Northwestern Argentina, are examined. An oil well located along the line provides s tratigraphic control for the seismic interpretation. The corresponding synthetic seismogram extends this interpretation through the Met;in t rough. The data show the deep structure of the rift, consisting of a s eries of half-grabens, filled with Cretaceous red beds of the Pirgua S ubgroup. The sag phase deposits consist of limestones, marls, shales a nd evaporites of the Balbuena and Santa Barbara Subgroups, deposited i n a transitional marine to lacustrine environment. Several oblique eas t-dipping reflectors at 10 to 20-24 km depth, are interpreted as maste r shears that control the extensional mechanics of the rift system, pa rtially reactivated during Andean compression. The structure of this e astern sector of the rift is integrated through a regional cross-secti on through the entire rift system. The section clearly shows that trou ghs and highs may be related to flats and ramps of a regional master s hear dipping to the east. (C) 1998 Elsevier Science Ltd. All rights re served.