Evaluating the influence of aseismic ridge subduction and accretion(?) on detrital modes of forearc sandstone: an example from the Kronotsky Peninsula in the Kamchatka Forearc

The Kronotsky Peninsula, in the forearc region of the Kamchatka magmatic ar e, lies on trend with the Emperor Seamount chain situated on the currently subducting Pacific tectonic plate. Detrital modes of volcaniclastic sandsto ne interbedded with mafic Eocene(?) basement rocks and within the overlying sedimentary sequence provide insight into the late Cenozoic geologic histo ry of this area. Eocene(?) and basal Miocene sandstones are primarily compo sed of variably altered mafic volcanic debris. Their detrital modes are sim ilar to those of Emperor Seamount sandstones and Hawaiian beach sands. Alth ough aspects of the stratigraphy and volcaniclastic sand composition an con sistent with a seamount setting, there is no physical evidence for an accre tion event, and the suggested Eocene age for this unit makes an Emperor Sea mount origin unlikely. A seamount origin cannot be ruled out for older Kron otsky basement complexes, however. A Miocene lull in Kronotsky volcanism wa s followed by rapid basin subsidence and influx of ace-derived turbidites f rom the west. Detrital modes of these sandstones are typical of a moderatel y evolved continental or micro-continental are. An anomalously high proport ion of sedimentary lithic fragments is the only possible compositional fing erprint attributable to seamount or ridge subduction. (C) 1999 Elsevier Sci ence B.V. All rights reserved.