Scenes from Catamarca and La Rioja Provinces in the Flat Subduction Region
All photos by Jim Reynolds
Upper Miocene sandstones are exposed along the northern flank of the Sierra de Famatina in La Rioja and Catamarca Provinces. These rocks, in the Quebrada de la Troya, Catamarca record the uplift history of the northwestern Sierras Pampeanas.

Contamination from the tailings pond of an abandoned gold mine gives the Río Amarillo its name (Yellow River). The water is used for irrigation on the lower slopes between Santa Florentina and Chilecito. The Sierra de Famatina in the background is the highest range in the Sierras Pampeanas, rising more than 6,200 m (20,500') above sea level. A large porphyry copper deposit is exposed above 5,000 m but has never been exploited because of the extreme conditions. The range began to rise in the latest Miocene.

The Sierra de Velasco rises to the east of the Sierra de Famatina. Chronostratigraphic data suggest that it began to rise about 12 million years ago. Unlike the Sierra de Famatina, which is composed of Lower Paleozoic granite, the Sierra de Velasco is made up of Proterozoic gneisses and schists.

The Cadena de Paiman (middle distance) and the Sierra de Velasco (far distance) expose Precambrian basement of Grenville affinity. The ranges are in the northern central Sierras Pampeanas to the east of the Sierra de Famatina. The Cadena de Paiman runs through the city of Chilecito.

The road from Chilecito to Villa Unión crosses the Cuesta de Miranda on the southern flank of the Sierra de Famatina. Triassic continental strata of the Paganzo Group overlie the Ordovician granite that constitutes range. This photo was taken in the middle of winter. The paucity of snow on the peaks attests to the aridity of this part of the Andean foreland.

Middle Miocene strata of the Río Mañero Formation were gently tilted during uplift of the westernmost ranges of the Sierras Pampeanas (Sierra Morada and Sierra de los Tarjados) less than 6 million years ago. The strata were deposited in a mudflat/playa lake environment. These strata are located at the southern end of the Campo de Talampaya. They contain a distal record of the middle Miocene rise of the Precodillera, located to the west of the section.

Sand flat deposits of the Desencuentro Formation overlie the Río Mañero Formation. These beds record the rise of the Sierra de Velasco, about 90 km to the east.

Cerro Rajado is one of a series of discontinuous ranges that form the western side of the Campo de Talampaya. These ranges are all northern extensions of the Sierra de Valle Fértil located in eastern San Juan Province. They make up the western boundary of the Sierras Pampeanas.

The road from Villa Unión to Jáchal passes through the western Sierras Pampeanas giving a view of the structure exposed in Cerro Bola, another northern extension of the Sierra de Valle Fertil. The Bermejo Basin lies at the western base of the range. The Precordillera bounds the western side of the basin.

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Last updated October 4, 2005