Russian Journal of Earth Sciences
Vol. 6, No. 2, April 2004
Provenance and tectonic settings of accretionary
wedge sediments on northeastern Karaginski Island
(Kamchatka, Russian Far East)
G. V. Ledneva, J. I. Garver,
M. N. Shapiro, J. Lederer,
M. T. Brandon, and K. T. Hollocher
Abstract
The provenance and tectonic setting of the sediments
and rare cobbles from the accretionary wedge on Karaginski Island
were examined. This study provides a picture of the nature of the
NE Asian paleomargin in the middle Eocene to early Miocene. The
trace element geochemistry of shale from the flysch and mélange
indicates (a) their common provenance with the quartzofeldspathic
and arkosic sandstones, and (b) derivation of these sediment types
from active continental and island arcs with partially dissected
basement rocks. Previous studies of the sandstones [Shapiro et al.,
2000] showed that they dominate in debris whose
composition is very similar to those of the felsic extrusive and
intrusive rocks in cobbles and boulders embedded in the sediments.
Fission-track (FT) ages from detrital zircon from sandstones, and
felsic cobbles show their derivation from sources with several
cooling histories in the Late Cretaceous and Early Tertiary. The
youngest detrital component probably represents continuous
younging population from active volcanism in the source that is
nearly the same age of deposition. The felsic cobbles represent
the essentially random selection of the older material component.
They include three distinct types: (a) subduction-related low-K
tonalites and trondhjemites and their extrusive analogues;
(b) crustally-derived med-K two-mica leucogranites, and
(c) crustally-derived high-K biotite leucogranites. The felsic
rock cobbles of all types have a narrow range of zircon FT grain
ages that indicate cooling in the source in the Late Cretaceous to
Early Paleogene. Tonalites and trondhjemites (low-K) cooled at
53.8 ( - 3.5/+3.8) Ma and 78.5 ( - 6.7/+7.6) Ma. The rhyolites
(med-K) cooled at 70.1 ( - 3.7/+3.9) Ma. The biotite leucogranites
(high-K) cooled between 59.1 Ma ( - 3.3/+3.9) and 58.6
( - 3.2/+3.3) Ma (two clasts). The Late Cretaceous cooling ages
(70-78 Ma) probably reflect original magmatic activity whereas
the Early Eocene cooling ages may indicate timing of exhumation.
The chemical and age data obtained on the felsic cobbles suggest
derivation of the accretionary wedge sediments from a source
formed either by: (a) subduction in the Late Cretaceous and
collision/exhumation in the Early Paleogene; or by (b) continuous
subduction. The closest petrochemical and age intrusive and
extrusive analogues of the felsic cobbles occur only locally in
the Olyutorsky Peninsula subterrane. Nonetheless, this structure
is too small and too remote from Karaginski Island to supply
enough material for the middle Eocene-early Miocene
accretionary wedge sediments. We speculate that the structure of
the Olyutorsky Peninsula subterrane might be extended in the shelf
where several highs exist.