Department of Earth Sciences
The University of Queensland

Andes Projects

1995-1998

Structure, tectonics, and metallogenesis of the San Juan-La Rioja area in northern Argentina
Tim Coughlin (PhD project); R J Holcombe (supervisor) [and see list of publications].

 

Project to define the major structural and tectonic elements and tectonic history of the eastern Andes in central northern Argentina and their controls on mineralisation. The project arose out of a discrepancy (noted by Dr. Vic Wall) between observed tectonic patterns in the Argentine Andes and the generally accepted simple models of "Andean" margins. Effectively the project has examined the timing and inter-relationships between the Andean Cordillera, Precordillera, Altiplano/Puna plateau, and the Sierras Pampeanas, a young, dominantly westward-verging, fold-thrust belt in the Andean foreland (see map). Eventually the project has focussed on the role of major cross-orogen lineaments and structures and we have concentrated much of our mapping. Our work has shown that these crustal/lithospheric scale features have had persistent structural and sedimentologic signatures, probably since the Palaeozoic, and this inherited crustal architecture strongly controls the development of this part of the Andean Orogen. Slight differences in the lithospheric response and kinematics between these crustal "blocks" are reflected in strongly diachronous orogenic events in the upper crust, and control major metallogenic patterns.

We have supplemented structural mapping in key areas with Ar-Ar geochronology and Apatite Fission Track Analysis over a wide area. In particular we have concentrated on an area where a NE-trending dextral transpressive lineament/fault zone (the Tucuman Zone) links with a SE-trending sinistral transpressive fault zone (the Valle Fertil Fault) in a very complex transfer zone. These two structures effectively define a crustal-scale indentor that, since ~5-7Ma, has been translated slightly westward against the earlier Andean Cordillerra/Precordillera and Altiplano/Puna orogen (forming the Sierras Pampeanas in the process).

Publications...