Use of porphyroblast-matrix relationships to solve a complex polyphase geologic history in Middle Proterozoic rocks of central New Mexico
- Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences
Porphyroblast-matrix textural relationships are often ambiguous and, used in isolation, can lead to conflicting interpretations of the geologic history of an area because deformation and metamorphism are generally heterogeneous in both space and time. This is true in Proterozoic rocks in southwestern North America where the debate about an orogenic versus an orogenic Middle Proterozoic geologic history continues. For example, the emplacement of the 1.43 Ga Priest quartz monzonite in central New Mexico is here interpreted to have post-dated most of the region (D[sub 2]) deformation and some amphibolite-facies metamorphism, to have been synchronous with continued or renewed NW-SE shortening and development of a 1--2 km wide metamorphic aureole, and to have been overprinted by low-temperature deformation after cooling. Apparently conflicting porphyroblast-matrix assemblages and disequilibrium mineral assemblages can be reconciled with this polyphase history. Evidence that a major component of the NW-SE shortening pre-dated pluton emplacement is; (1) the pluton cross-cuts the regional, subvertical S[sub 2] fabric and isoclinal F[sub 2] folds; (2) the pluton is generally unfoliated compared to intensely deformed country rocks; (3) most contact-metamorphic minerals (75%) epitaxially overgrow a differentiated S[sub 2] cleavage. Pre-pluton metamorphism may be represented by kyanite, rare staurolites that are included in contact-metamorphic garnets, and cloudy, anhedral garnets that are locally overgrown by contact-metamorphic garnets.
- OSTI ID:
- 5130052
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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