|Title:||Archean xenocrysts in modern volcanic rocks from Kamchatka: Insight into the basement and paleodrainage|
|Authors:||I.N. Bindeman, L.P. Anikin, and A.K. Schmitt|
|Publication:||Jour. Geol., v. 124, p. .|
|Publish Date:||March 2016|
We report U‐Pb zircon ages and in situ δ18O values for crystals of zircon, rutile, and corundum erupted in the course of a March 2009 phreatomagmatic explosion of Koryaksky volcano, Eastern Volcanic Front, Kamchatka, Russia. Zircon crystals display a wide spectrum of crystallization ages ranging from Cenozoic to Archean, including single grains and grain‐age clusters, ca. 1.7, 11, 37‐56, 89‐99, 152, 1461, 1946, 2584‐2734, and 3314 Ma. The older end of this spectrum represents the oldest known zircon ages from Kamchatka. Oxygen isotopic values span from normal to low δ18O in zircon (3.3‰ to 5.5‰), corundum (4.3‰ to 5.5‰), and rutile (2‰ to −2.8‰). As Koryaksky volcano is built over Cretaceous−Eocene and younger crust, the presence of older zircon crystals requires that these accessory minerals with their diverse ages and δ18O values were derived from heterogeneous detrital components in sediment that contaminated the magma shortly before or during the phreatomagmatic eruption. We also present a compilation of published U‐Pb zircon ages in Kamchatka for detrital and metamorphic grains for comparison purposes. We propose that sediment was delivered from the metamorphic Ganal and Sredinny Massifs along the Petropavlovsk fracture zone via a paleodrainage system whose remnants are now covered by the modern edifices of the Eastern Volcanic Front volcanoes. The termination of this paleodrainage system connecting to the modern north‐flowing Kamchatka River postdates 1.7 Ma, on the basis of the age of the youngest detrital zircon present.