Thomas A. Wickham1 and K. E. Karlstrom1
New mapping (1:6000), compilation of previous mapping (Long, 1973; McCarty, 1983; Bauer, in press), and structural analysis of the south central Picuris Mountains has led to new structural interpretations. The Vadito Group is folded into km-wavelength (F2) folds (McCarty, 1983) that are cored by the deformed Rana (1.67 Ga) and Puntiagudo (1.68 Ga) granites. These folds refold a complex tectonite layering involving interleaved amphibolites and pelitic schists. Fold overprinting results in map-scale types 2 and 3 fold interference patterns. The F2 folds plunge moderately (20°-40°) to the northeast based on map pattern of folds and on stereonet analysis. Axial surfaces dip 60°-80° southeast.
F2 folds and S2 axial plane cleavage are cross cut at right angles by pegmatites, including the 1.4 Ga Harding and the 1.48 Ga Penasco-derived pegmatites. These dikes show local, weak cuspate-lobate folding and boundinage, but are interpreted to have post-dated the main S2 shortening. Thus regional penetrative northverging contraction was pre-1.45 Ga. However, there was also weak syn-and post-1.4 Ga deformation that is recorded in 1.4 Ga plutonic rocks. Syn-emplacement deformation is recorded by northeast striking subvertical magmatic foliation concentrated near the margins of the Penasco pluton. Post-emplacement deformation resulted in discrete shear bands in the Penasco and cuspate-lobate folds in the Harding Pegmatite. This deformation took place at relatively low temperatures, after 1.4 Ga.
1993 New Mexico Geological Society Annual Spring Meeting April 16, 1993, Macey Center Online ISSN: 2834-5800
Pages: 17