Mylonitization events bracketing a granitoid intrusion--A Proterozoic example from the Manzano Mts. , New Mexico
- New Mexico Inst. of Mining and Tech., Socorro, NM (United States). Dept. of Geoscience
- New Mexico Bureau of Mines and Mineral Research, Socorro, NM (United States)
- Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Geology
Resolution of the timing of plutonism relative to deformation and metamorphism is critical to an understanding of crustal evolution. All of the elements necessary to address this topic in the southwestern US exist in the Manzano Mts., where metamorphic tectonites are intruded by the ca. 1.45 Ga Priest pluton. Structures adjacent to the Priest pluton record three phases of deformation. Phase 1 is characterized by a layer-parallel schistosity (S1). Although no Phase 1 folds or faults are found, some supracrustal rocks were overturned prior to Phase 2. Phase 2 structures dominate at all scales. Upright, shallowly north-plunging folds (F2) are associated with a mylonitic axial planar foliation (S2). Sense-of-shear indicators within the relatively high-temperature (amphibolite facies) S2 record west-side-up motion. Inclusion trails in garnets are oriented at a high angle to S2 and locally preserve crenulations, indicating that garnets grew early in Phase 2. F2 folds are truncated by the Priest pluton. The Phase 3 mylonitic foliation (S3), which is locally developed and similar in orientation to S2, exhibits microstructures that suggest relatively low-temperature (greenschist facies) deformation. S3, the only solid-state fabric found in the pluton, records east-side-up shearing. Observations indicate that most of the deformation occurred prior to the ca. 1.45 Ga plutonism. Regional relationships suggest that these early deformation phases resulted from crustal shortening. The regional significance of the Phase 3 low-grade mylonites is unknown.
- OSTI ID:
- 5880113
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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