The Swansea Plutonic Suite: Synextensional magmatism in the Buckskin and Rawhide Mountains, west-central Arizona
Conference
·
· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5291411
- Geological Survey, Denver, CO (United States). Denver Federal Center
- Geological Survey, Menlo Park, CA (United States)
About 200 km[sup 2] of the crystalline rocks exposed below the Buckskin-Rawhide detachment fault in west-central Arizona consists of gabbro to granite of the 20--30 Ma Swansea Plutonic Suite. Gabbro is only locally mylonitized and is intruded by more felsic rocks of the suite. The felsic rocks have a well-developed mylonitic texture and northeast-trending mineral lineation formed by ductily deformed quartz grains and aggregates. The felsic rocks are generally fine to medium grained except for a distinctive porphyritic phase, in which K-feldspar phenocrysts (now porphyroclasts) are as much as 3 cm in diameter. The suite is calcic to alkali calcic, metaluminous to weakly peraluminous (A/CNK = 0.7--1), and has average Th/U of 4.8 and Rb/Sr of 0.11. It shows a wide range in total rare-earth abundances (REE = 132--393 ppm), light to heavy REE enrichment (chondrite normalized [CN] La/Yb = 3--52), and heavy REE enrichment (CN Yb = 2.6--24.5). Intermediate and silicic members are depleted in HREE compared with mafic members, indicating magmatic control by clinopyroxene with or without amphibole or garnet. The porphyritic phase has the highest total REE and HREE abundances. Lead isotope ratios cluster in tight groups between reference lines for the Mohave and central Arizona crustal provinces. Lead in the porphyritic phase is distinctly less radiogenic than in the other phases. U-Pb zircon age of a granite in the suite is 21 [+-] 1.5 Ma. Upper intercept of the discordia line is 1,420 [+-] 54 Ma, indicating that 1,400-Ma rock dominates the source region for at least the felsic rocks of the suite. The suite was emplaced during the beginning and early phases of crustal extension and was probably pulled southwest out from beneath the Colorado Plateau transition zone as extension progressed. Thus the suite may represent roots of subaerial volcanic centers at the margin of the transition zone, which chemically resemble rocks of the suite in major-element chemistry.
- OSTI ID:
- 5291411
- Report Number(s):
- CONF-9305259--
- Conference Information:
- Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
- Country of Publication:
- United States
- Language:
- English
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