Age constraints on basalt samples from a transect across the Lau Basin: supporting evidence for modification by multiple mantle sources.

Thursday, 18 December 2014
Christopher Scott Conatser1, Anthony A P Koppers1, Matthew G Jackson2, Jasper G Konter3, Allison A Price2 and Kevin Konrad4, (1)Oregon State University, Corvallis, OR, United States, (2)University of California Santa Barbara, Department of Earth Sciences, Santa Barbara, CA, United States, (3)University of Texas at El Paso, El Paso, TX, United States, (4)Oregon State University, Salem, OR, United States
The tectonic activity of the Lau and North Fiji backarc basins in the South Pacific is complex and not well delimited. Rapid subduction of the Pacific plate at the Tonga trench, together with rifting between the Tonga and Australian plates and Niuafo'ou microplate, has created multiple types of volcanic activity as a function of this complex tectonic setting (1). In addition to extensional volcanism producing depleted mantle melt (2), a number of hotspots (Samoa, Rurutu, Rarotonga, Macdonald and Louisville) have passed near the area, each at distinct time periods, possibly contributing mantle plume components to the magmatism of the Lau Basin. During the summer of 2013, three transects in the Lau Basin and southwest of Samoa were dredged onboard the R/V Roger Revelle (Expedition RR1310). We present here the results of 10 new step heating experiments by the 40Ar/39Ar method using the ARGUS-VI multi-collector mass spectrometer, comprising groundmass and plagioclase separates from 9 basalt samples. These high-precision 40Ar/39Ar ages will allow us to determine whether some of the volcanic activity in the Lau Basin correlates with known ages of hotspot transits through the area, clarifying evidence from corresponding geochemical analyses for a subset of these samples, which support incorporation of Samoan (EMII), Rurutu (HIMU), and Rarotonga (EMI) mantle components into spreading center volcanism across a larger area than previously reported (presented by Price et al., this volume). These ages thus provide insights into the complex construction of the Lau Basin through time.

1. Zellmer, K.E.; Taylor, B. (2001). "A three-plate kinematic model for Lau Basin opening." Geochem., Geophys., Geosyst. 2 (5): 1020

2. F. and B. Taylor. 2002. "Mantle Wedge Control on Back-Arc Crustal Accretion." Nature 416 (6879): 417-420.