Evidence for fourth generation structures in the Piedra Lumbre region, Western Picuris Mountains, New Mexico

Conference · Mon Feb 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6138785

Chernoff, C B; Helper, M A; Mosher, S ^[1]

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1. Univ. of Texas, Austin, TX (United States). Dept. of Geological Sciences

Mid-Proterozoic Hondo Group metasediments in the western Picuris Mountains, New Mexico clearly display 3 generations of previously recognized penetrative, synmetamorphic structures and a previously undocumented forth generation of overprinting folds with an associated axial planar foliation. The earliest structures include: (1) a bedding-parallel S[sub 1] foliation and rare, rootless, intrafolial F[sub 1] folds; (2) north-verging, west-trending F[sub 2] folds and an axial planar metamorphic foliation (S[sub 2]); (3) a steeply dipping, N-S striking crenulation cleavage (S[sub 3]). In the Piedra Lumbre region, southwest-plunging, open, upright chevron and box folds (F[sub 4]) locally reorient F[sub 2], S[sub 2] and S[sub 3] crenulations. The largest F[sub 4] folds in the Piedra Lumbre region have half-wavelengths of 500 meters. An associated nearly vertical foliation (S[sub 4]) overprints the first three foliations. The S[sub 4] foliation is a crenulation cleavage in micaceous layers and a discontinuous alignment of biotite laths in quartzose layers. Crystallization of biotite during S[sub 4] and chloritoid after S[sub 4], along with static recrystallization and mineral replacement by chlorite, suggests this deformation occurred during the waning stages of mid-Proterozoic metamorphism. The orientation of F[sub 2] and F[sub 4] folds are similar and both appear to occur on a regional scale. Interference of open upright F[sub 4] folds and tight, north-verging, overturned F[sub 2] folds produces a geometry that resembles that of the kilometer-scale Copper Hill Anticline of the western Picuris Mountains, previously interpreted to be solely the result of F[sub 2] folding.

• OSTI ID: 6138785
• Report Number(s): CONF-9303212--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:1
• Country of Publication: United States
• Language: English

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