Precambrian structural and metamorphic history of the Rociada Area, New Mexico

Precambrian rocks are exposed in the eastern foothills of the southern Sangre de Cristo Mountains in the Rociada area of north-central New Mexico. These rocks, overlain by Paleozoic sedimentary rocks, are divided into an amphibolite and a schist unit, the latter consisting of quartz-mica schist and mica-quartz schist sub-units. These units are interpreted as being primarily of sedimentary origin, with some amphibolites of probable igneous origin.

These Precambrian rocks were subjected to three periods of deformation and two metamorphic episodes. The first deformation is characterized by east-west trending, tight to isoclinal folds and a pervasive foliation. This deformational event was accompanied by synkinematic metamorphism of middle greenschist facies. Late in the first deformation, a few small quartz and granitic dikes were intruded.

The second deformation reoriented early structural trends, and produced northeast trending, doubly plunging, open to gentle flexure folds. Some small-scale axialplane cleavage developed in second generation fold crests This deformational event was followed by a static metamorphic episode of the hornblende-hornfels facies of contact metamorphism. Following thermal activity, pegma tite dikes were intruded.

A third deformational event of Post-Pennsylvanian age is characterized by gentle to open folds in Paleozoic sedimentary rocks.