Magmatic arc structure around Mount Rainier, WA, from the joint inversion of receiver functions and surface wave dispersion
Abers, Geoffrey A.
Date of Issue2014
Earth Observatory of Singapore
The deep magmatic processes in volcanic arcs are often poorly understood. We analyze the shear wave velocity (VS) distribution in the crust and uppermost mantle below Mount Rainier, in the Cascades arc, resolving the main velocity contrasts based on converted phases within P coda via source normalization or receiver function (RF) analysis. To alleviate the trade-off between depth and velocity, we use long period phase velocities (25–100 s) obtained from earthquake surface waves, and at shorter period (7–21 s) we use seismic noise cross correlograms. We use a transdimensional Bayesian scheme to explore the model space (VS in each layer, number of interfaces and their respective depths, level of noise on data). We apply this tool to 15 broadband stations from permanent and Earthscope temporary stations. Most results fall into two groups with distinctive properties. Stations east of the arc (Group I) have comparatively slower middle-to-lower crust (VS = 3.4–3.8 km/s at 25 km depth), a sharp Moho and faster uppermost mantle (VS = 4.2–4.4 km/s). Stations in the arc (Group II) have a faster lower crust (VS = 3.7–4 km/s) overlying a slower uppermost mantle (VS = 4.0–4.3 km/s), yielding a weak Moho. Lower crustal velocities east of the arc (Group I) most likely represent ancient subduction mélanges mapped nearby. The lower crust for Group II ranges from intermediate to felsic. We propose that intermediate-felsic to felsic rocks represent the prearc basement, while intermediate composition indicates the mushy andesitic crustal magmatic system plus solidified intrusion along the volcanic conduits. We interpret the slow upper mantle as partial melt.
Geochemistry, geophysics, geosystems
© 2014 American Geophysical Union. This paper was published in Geochemistry, Geophysics, Geosystems and is made available as an electronic reprint (preprint) with permission of American Geophysical Union. The paper can be found at the following official DOI: [article DOI: http://dx.doi.org/10.1002/2014GC005581]. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.