This project builds upon the work Alex Nikulin did in the framework of the Kamchatka PIRE project.

Data used to detect the odd feature in the mantle beneath Klyuchevskoy volcanic group   and were published in GRL in 2010.

NOTE: published article had a mistake in the figure, this site shows a correct version, GRL will publish a correction shortly (02/2012)

Position of the Klyuchevskoy Upper Mantle Anomaly (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. Crosssections 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 the figure above. CKD volcanoes marked by triangles: BZ, Bezymianny; K, Klyuchevskoy; T, Tolbachik; SH, Shiveluch.

ABOVE:

Map of the Kamchatka subduction zone showing major geological and geographical features and the plate motion direction. Dashed lines mark the geographical orientation of volcanic clusters. White arrow represents the direction of subduction and red triangles mark active volcanoes. CKD, Central Kamchatka Depression; EVB, Eastern Volcanic Front; SR, Sredinny Range.

RIGHT:

Backazimuthal RF gather and predicted delay times for P‐to‐S converted phases. Blue lines show expected times for conversions from horizontal interfaces at 30, 40 and 50 km. A positive phase at ∼3.5 s likely originates at the 30 km deep Moho discontinuity. Green lines show P‐to‐S converted phases expected from interfaces at 90, 100, 110 and 120 km, dipping 35° to the south. Closely spaced negative and positive pulses between 9 and 13 s follow the predicted pattern, and are matched well by the interface at ~100 km. Red lines show expected arrivals from the top of the Pacific slab, represented by interfaces at 180, 190 and 200 km, dipping 35° towards N310°W.

A subsequent study (published in EPSL in early 2012) used more data, and resulted in an image shown below (to be compared with a schematic rendition of the anomaly above). Also, the followup study explored geochemical signatures of the lavas erupted in the Central Kamchtka Depression, and reached a conclusion that the likely origin of KUMA is a concentration of pyroxenite-rich melt, likely initially formed through fluid-rock reaction above the descending Pacific slab.

Migrated RF profile images, showing the location of the upper mantle anomaly. Right panel shows profile orientations. Black circles indicate hypocenters of local earthquakes within 20km of the profile. Letters indicate volcano names (K -  Klyuchevskoy, T – Tolbachik, B – Bezymianny, S – Shiveluch).

A schematic presentation of the model for Klyuchevskoy group volcanism built on the basis of geophysical and petrological constraints. Arguments in favor of this model are presented below, with links to full published papers.

Light blue lines ascending from the subducting Pacific Plate indicate high-H2O fluid flux.

Kamchatka Upper Mantle Anomaly (KUMA, purple rectangle) is the proposed concentration of pyroxenite and its melts, labeled as dark blue lines. Green lines indicate peridotite melts. Both melt types undergo mixing prior to eruption at Central Kamchatka Depression (CKD) volcanoes.

Plate geometry of NUVEL1 is used in this cartoon and the map below, so Kamchatka belongs to the North American plate.