Duration of Louisville Hotspot Volcanism at IODP 330 Sites Canopus, Burton, and Rigil via 40Ar/39Ar Geochronology

Cohen, B.E. , Vasconcelos, P.M., Koppers, A.A.P. and Thiede, D.S. (2013) Duration of Louisville Hotspot Volcanism at IODP 330 Sites Canopus, Burton, and Rigil via 40Ar/39Ar Geochronology. In: AGU Fall Meeting, San Francisco, CA USA, 09-13 Dec 2013,

Abstract

The Louisville seamount trail is a chain of intraplatevolcanoes constructed over the past ~80 million years, as the Pacific plate moved 4300 km over a long-lived mantle melting anomaly. During IODP Expedition 330, over 800 m of alkaline mafic volcanic lavas, as well as interbedded and overlying sediments, were recovered from five of these seamounts in the older (~80-50 Ma) part of the chain. In this study we have undertaken geochronology of the volcanic units to provide time constraints for the magmatic evolution of the volcanoes. Sixteen of these drilled lava flows have been successfully dated using MAP-215-50 spectrometers, with six samples analyzed at Oregon State University (Koppers et al. 2012) and 12 flows analyzed at The University of Queensland. To check for consistency, two lava flows were dated at both laboratories; both samples yielded results within 2σ error. To minimize the effects of seawater alteration, only samples with well-crystallized groundmass were picked, and material cleaned via HNO3 and HCl acid pretreatment. Plateaus comprise 61 to 87% of the 39Ar released, and 40Ar/36Ar vs. 39Ar/36Ar correlation diagrams reveal all samples contained trapped argon within error of modern-day atmosphere. All ages determined are consistent with stratigraphic constraints, and we interpret the results to be reliable estimates of eruption ages. Units from Burton Guyot (site U1376A) yield ages from 70.8 ± 0.5 to 64.1 ± 0.5 Ma (2σ, using the atmospheric argon ratio and decay constants from Steiger & Jäger (1978) and a Fish Canyon sanidine age of 28.02 (Renne et al. 1998)). This long (~7 Ma) duration is consistent with petrologic evidence for substantial post-shield volcanic activity at this site. Meanwhile, at Canopus (site U1372A) and Rigil (sites U1373A and U1374A), lavas from the base, middle, and top of the respective volcanic piles yielded ages within analytical error. At the two deepest sites (U1372A and 1374A) 187 and 505 m of volcanic rocks were drilled; the 2σ errors on the 40Ar/39Ar results constrain eruptions to less than 1.2 and 1.7 Ma respectively, indicating minimum eruption rates of ~200-300 m/Ma. These eruption rates are an order of magnitude lower than observed on Mauna Kea and Mauna Loa (2000-8000 m/Ma: Sharp & Renne 2005;Jourdan et al. 2012) and are consistent with the largely alkalic shield-building eruptions on Louisville versus tholeiitic shield stage observed on the Hawaii-Emperor chain.

• Item Type: Conference Proceedings
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Cohen, Dr Benjamin
• Authors: Cohen, B.E., Vasconcelos, P.M., Koppers, A.A.P., and Thiede, D.S.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences

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