The magnitude of contraction, or shortening, accommodated in active mountain ranges is a critical observation for understanding how mountain belts evolve over geologic time. Shortening is often estimated from cross-section models that are constrained by geologic map patterns and fault geometries at scales of kilometers or greater. In addition, micro-scale strain data from several ranges show that regionally significant amounts of shortening can also occur at the grain-scale (millimeters or less). Here, Nathan Eichelberger and Nadine McQuarrie present new micro-scale strain data from the Bolivian Andes that indicates that micro-scale shortening was a negligible part of the deformation budget. By comparing variables such as deformation temperature and rock strength between mountain ranges, Eichelberger and McQuarrie explore what factors may have limited grain-scale shortening in the Bolivian Andes. It appears that low deformation temperatures and abundant-but-weak shale favored the development of faults rather than grain-scale shortening. Globally, this implies that pre-deformation basin sedimentology of may later influence mountain belt evolution.
Age and provenance of the Cryogenian to Cambrian passive margin to foreland basin sequence of the northern Paraguay Belt, Brazil
B. McGee et al., Centre for Tectonics, Resources and eXploration (TRaX), School of Earth and Environmental Sciences, B09, Mawson Building, The University of Adelaide, Adelaide, SA 5005, Australia. Published online on 30 July 2014; '/>"/>
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Geological Society of America