U-Pb Zircon Geochronology of Hermit's Peak Batholith Granite, Northern New Mexico: Implications for Tectonic Quiescence at 1.4 GA
Abstract
The Hermit's Peak batholith, a Proterozoic metamorphic-plutonic massif in the southern Sangre de Cristo Mountains, is located in the transition zone between the Yavapai and Mazatzal Precambrian provinces. We conducted zircon geochronology at the University of Arizona's LaserChron Center on granitic phases within the Hermit's Peak batholith to establish the timing of granite magmatism relative to Proterozoic orogenesis. Two analyses (core and rim) of more than 20 zircon crystals were incorporated into a final age calculation for each sample. Within the batholith, early granitoid intrusions form centimeter- to meter-wide coarse-grained tabular sheets and layers within Paleoproterozoic host rock gneisses. The intrusions were deformed during isoclinal folding along with their host rocks, suggesting that the early granites are pre- or syntectonic with contractional deformation associated with Yavapai-Mazatzal collision. These granites show a fine- to medium-grained anhedral granular texture with quartz microstructures indicative of dynamic strain and solid state deformation, including undulose extinction, subgrain development, and serrated grain boundaries. All zircon crystals are euhedral with aspect ratios of 2:1 to 3:1 and lengths ranging from 100-300 μm. Cathodoluminescence imaging shows that most crystals have oscillatory zonation indicating they are igneous in origin. Elemental U/Th ratios are all low (<10) indicating an igneous origin as well. Most crystals show a bright rim (high U) suggesting a late-stage fluid interaction. However, there was no discordance between core and rim age analyses. The granitic gneiss yielded a weighted mean 207Pb/206Pb age of 1.705 ± 0.017 Ga placing its emplacement prior to or early in the Mazatzal orogeny. A small (< 1.0 km2) nonfoliated coarse-grained anhedral granular granite intrudes the granitic gneiss. All zircon crystals are euhedral with aspect ratios of 2:1 to 3:1 and lengths ranging from 100-300 μm. Cathodoluminescence imaging shows that most crystals have oscillatory zonation. The nonfoliated granite yielded a weighted mean 207Pb/206Pb age of 1.448 ± 0.012 Ga. The 1.4 Ga granite shows no mineral alignment, chemical segregation, or microstructures indicative of deformation which suggests that 1.4 Ga granite magmatism in the Hermit's Peak batholith did not accompany deformation. Further structural and geochronology studies are aimed at determining the extent and influence of 1.4 granite magmatism on the construction of the Hermit's Peak batholiths and the tectonic setting for Mesoproterozoic granite emplacement.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.T23B2672L
- Keywords:
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- 1100 GEOCHRONOLOGY;
- 8178 TECTONOPHYSICS / Tectonics and magmatism;
- 9622 INFORMATION RELATED TO GEOLOGIC TIME / Proterozoic