Geology of Proterozoic outcrops in Dead Man and Little San Nicolas Canyons, southern San Andres Mountains, New Mexico
Pamela J. Roths

Abstract:

Proterozoic outcrops in the southern San Andres Mountains generally consist of large granitic plutons. However, isolated areas, such as Dead Man and Little San Nicolas Canyons, contain other rock types. A sequence of interbedded schists and fine-grained quartzites overlain by a crossbedded, micaceous quartzite is exposed in Dead Man Canyon. Three generations of folding have been identified: (1) early isoclinal folds perhaps synchronous with the metamorphism; (2) open to tight folds with a well-developed axial planar cleavage that strikes northwest; and (3) east-trending reclined folds that reorient the earlier structures into broad kinks. A foliated pluton dated at 1632 ± 24 Ma (U-Pb zircon) defines a maximum age for the second phase of deformation. Little San Nicolas Canyon, approximately 32 km south of Dead Man Canyon, contains highgrade gneiss, amphibolite and non-foliated granitic rock. The gneiss displays a foliation, defined by bands of dark and light minerals, that has been folded into tight to isoclinal east-trending folds. This unit is exposed along high-angle reverse faults. Zircons from the gneiss are highly discordant, but yield an age of 1730± 130 Ma. The protolith of this gneiss is unknown, but is most likely plutonic. One post-orogenic granite has been dated at 1460 ± 65 Ma. Although both study areas display similar east-west structural trends, they are markedly dissimilar.


Citation:

  1. Roths, Pamela J., 1991, Geology of Proterozoic outcrops in Dead Man and Little San Nicolas Canyons, southern San Andres Mountains, New Mexico, in: Geology of the Sierra Blanca, Sacramento and Capitan Ranges, New Mexico, Barker, James M.; Kues, Barry S.; Austin, George S.; Lucas, Spencer, G., New Mexico Geological Society, Guidebook, 42nd Field Conference, pp. 91-96.

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