Landsat studies of the central Andes

Randle, Jane de Grey (1989). Landsat studies of the central Andes. MPhil thesis The Open University.



An area of the Central Andes where major features such as the crustal thickness, subduction angle and tectonic regime vary is the subject of this large scale remote sensing survey. 514 volcanoes were classified into 25 groups using a relative dating method and simple size analysis from ten Landsat multispectral scanner (MSS) images.
Models of magma generation (Marsh 1975,1982), segmented subduction (Swift and Carr 1974, Carr et al. 1982), development of silicic magma chambers (Hildreth 1981), are all relevant to the volcanism of the region and the data, derived from study of volcanic density, spacing and alignment, presented herein are used to evaluate the models and to investigate the relation between the tectonic fabric and volcanism.
The major segment boundary at 24°30'S (Swift and Carr 1974) divides the survey area. In the north, the Altiplano forms an asymmetric basin (Coward 1986) with high cone density near the vertically-faulted volcanic front in the west, and lesser density associated with low-angle thrusted blocks in the east. In the south a more random regional distribution is seen with arcate patterns in the more rugged terrain of the narrower Argentine Puna. These two distinct distributions of volcanoes suggest that subduction angle controls the surface pattern of volcanism.
In the north, using variation in size against volcanic density and alignment of volcanoes, several smaller segments are recognised; but since they do not coincide, the simple relationship of crustal thickness, regional elevation, gravity, size and alignment of volcanoes described by Carr et al (1982) for Central America is more complicated in the Central Andes.
Relative dating against density studies proved less useful for plotting migration of volcanism within the province, but it demonstrates that the smaller younger volcanoes are secondary features often associated with silicic complexes.

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