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Anomalous Seismic Structure beneath the Klyuchevskoy Group,
Kamchatka, as Indicated by Receiver Function Analysis
Alex Nikulin (Rutgers University), Vadim Levin (Rutgers University), Ashley Shuler (LDEO, Columbia University), Michael
West (AVO, University of Alaska - Fairbanks)
The Klyuchevskoy Group (KG) of volcanoes in Kamchatka, Russia is among the largest volcanic features on the planet, yet
its position within the Kamchatka subduction zone is hard to explain with a simple tectonic mechanism. Geochemical evidence
(Ishikawa et al., 2010) indicates that lavas of the KG are typical products of subduction-induced flux melting, yet the depth to
the subducting Pacific plate beneath this volcanic center is much larger than the average depth of subduction associated with arc
volcanism (Syracuse and Abers, 2006). We present new seismological constraints on the upper mantle structure beneath the KG,
based on receiver function analysis of data collected by the PIRE project (Nikulin et al., 2010). We identify a sharply bounded
zone of anomalous velocities in the mantle wedge beneath the KG (Figure 1), which we refer to as the Klyuchevskoy Upper
Mantle Anomaly (KUMA). The presence of a sharp velocity deviation in the mantle wedge does not conform to our understanding
of the standard subduction model, where a homogeneous velocity profile is expected in the mantle wedge. We contend that
the observed anomaly is essential for understanding the location and the exceptional nature of the volcanic activity at the KG.
Located at the typical depth of volatile release within the mantle wedge, this feature is a likely source of melts erupting at the KG.
Presence of this heterogeneity in the upper mantle beneath the KG may explain the elevated level of volcanic activity of the KG
and its position relative to the subducting Pacific Plate.
References
Ishikawa T., F Tera, and T. Nakazawa (2001), Boron Isotope and trace element systematics of the three volcanic zones in the Kamchatka arc.
Geoch. Cosm. A., 65, 4523-4537
Nikulin, A., V. Levin, A. Shuler, and M. West (2010), Anomalous seismic structure beneath the Klyuchevskoy Group, Kamchatka, Geophys.
Res. Lett., in press.
Syracuse, E. M., and. G.A. Abers (2006), Global compilation of variations in slab depth beneath arc volcanoes and implications, Geochem.
Geophys. Geosyst., 7, Q05017
Acknowledgements: The authors would like to aknowledge the support of the Partnership In Research and Education (PIRE) project, funded
by the National Science foundation and the support of the Graduate School of Rutgers University, New Brunswick.
Position of the KUMA (red-blue bar) with respect to the subducting Pacific plate outlined by seismicity and the CKD volcanoes. Vertical cross-sections show earthquakes
(circles) located over 10 years (2000-2009) by the Kamchatka Branch of the Geophysical Service of Russian Academy of Sciences. The online catalog (www.
emsd.ru) includes events with M=3.5 and larger. Cross-sections are centered on the Tolbachik volcano, aligned along A-A’ and normal B-B to the Pacific plate motion
direction, and include events within 25 km of the profile. Crosses on the map correspond to 50 km tick marks on the distance axes of cross-sections, red circles denote
100 km depth pierce points of 166 individual rays from earthquakes used to construct RF gather in Figure 2. CKD volcanoes marked by triangles: BZ – Bezymianny,
K – Klyuchevskoy, T – Tolbachik, SHShiveluch.
II-214 | 2010 IRIS Core Programs Proposal | Volume II | Upper Mantle Structure and Dynamics