Polyphase Proterozoic metamorphism and deformation at Four Peaks, southern Mazatzal Mountains, Arizona
- Univ. of Massachusetts, Amherst, MA (United States). Dept. of Geology and Geography
Proterozoic rocks at Four Peaks may have been deformed in the 1.65 Ga. Mazatzal Orogeny and again at ca. 1.4 Ga. Metamorphic and ductile deformation events occurred before and after emplacement of the ca. 1.4 Ga. Four Peaks granite. The granite cuts a metamorphosed supracrustal package tentatively correlated with the rocks of the Alder and Mazatzal Groups. Exposed rocks include (from oldest to youngest): rhyolite, massive quartzite (30m), a thinly-bedded sequence of schist and immature micaceous quartzite (300m), vitreous orthoquartzite (300m), and a green-black slate of unknown thickness. In addition to the K-feldspar megacrystic ca. 1.4 Ga. Granite, plutonic rocks include a large body of coarse-grained hornblende granodiorite, and several smaller, fine grained granitoids. The syncline folds an early foliation (S1) and is cut by a heterogeneous axial plane cleavage (S2). South of the syncline is a major NE-striking shear zone, more than 500 meters wide. North, west, and east of the syncline the 1.4 Ga. granite cuts the syncline and has no deformational fabric, indicating that folding and thrusting are older. Adjacent to the shear zone, the generally unfoliated. Four Peaks granite has an anastomosing steeply SE-dipping foliation, parallel to, but apparently less intense than that in the shear zone, suggesting a reactivation of the shear zone after emplacement. The two phase history is supported by microfabric evidence and phase relationship. Regionally, porphyroblasts that preserve S1 are present in rocks dominated by a younger foliation (S2). Rocks proximal to the 1.4 Ga. granite contain pseudomorphs after earlier porphyroblasts and new porphyroblasts that overgrow both foliations. The authors interpret the older deformation and metamorphism to be related to the ca 1.6 Ga.
- OSTI ID:
- 5976292
- Report Number(s):
- CONF-9303212-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:1; Conference: 27. annual Geological Society of America (GSA) South-Central Section meeting, Fort Worth, TX (United States), 15-16 Mar 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ARIZONA
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
PETROGENESIS
DEFORMATION
GRANITES
GRANODIORITES
METAMORPHISM
OROGENESIS
PRECAMBRIAN ERA
QUARTZITES
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGY
IGNEOUS ROCKS
METAMORPHIC ROCKS
NORTH AMERICA
PETROLOGY
PLUTONIC ROCKS
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USA
580000* - Geosciences