Structural and metamorphic history of precambrian rocks, Upper Gallinas Creek area, San Miguel County, New Mexico



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Texas Tech University


Precambrian rocks in the upper Gallinas Creek area of the southern Sangre de Cristo Mountains, New Mexico, display two metamorphic and two deformational events and at least two episodes of igneous intrusion. The first metamorphic event (M1) reached at least the biotite zone of the epidote-amphibolite facies. It was associated with a progressive, penetrative deformation, which formed a foliation (S1) that was folded into tight to isoclinal folds (F1). This folding involved partial transposition of the foliation into a second s-surface (S2), an axial-plane schistosity. Accompanying the M1 metamorphism was the initial intrusion of the Embudo Granite and related pegmatite sills. Subsequent intermittent intrusion of Embudo Granite and pegmatite dikes and sills is associated with a second metamorphic event (M2), which is characterized by static recrystallization that probably reached the kyanite-staurolite zone in some areas. The static M2 recrystallization is most pronounced in contact area of a large granitic stock. Part of this episode of metamorphism and granitic intrusion is associated with a second deformation, which is characterized by northeast-southwest trending, open flexure-slip folds (F2) that are superposed on the earlier F1 isoclinal folds. Still later, axes of the F2 flexure-slip folds were rotated by a post-Precambrian deformation that is recorded as gentle, flexure-slip folds (F3) in the Paleozoic rocks. The latter folds are associated with the faulting of probable Laramide age.



Stratigraphic -- Precambrian, Geology, Geology -- New Mexico -- San Miguel County