New Mexico Geological Society Annual Spring Meeting — Abstracts

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.