HR: 0800h
AN: V51D-1516    [Abstracts]
TI: Late Cretaceous modification of deep continental crust in the NE Paleo Pacific: additional evidence from Viliga lower crust xenoliths
AU: * Akinin, V V
EM: akinin@neisri.magadan.ru
AF: North East Interdisciplinary Science Research Institute FEB RAS, 16 Portovaya, Magadan, 685000 Russian Federation
AU: Miller, E L
EM: miller@pangea.stanford.edu
AF: Stanford University, Dep. Geol. and Envir. Science, Stanford, CA 94305 United States
AU: Layer, P
EM: player@gi.alaska.edu
AF: University of Alaska, Geophysical Institute, Fairbanks, AK 99775 United States
AB: The Viliga volcanic field is located ~200 km NE of Magadan, Russia, near the junction of North America-Eurasia-Okhotsk Sea plates. 40Ar/39Ar dating of whole rock olivine melanephelinite samples indicates two magmatic pulses at 8.5 and 10.8 Ma. Volcanism of this age in NE Russia (outside of Kamchatka) is not common but the ages obtained from this newly dated volcanic field are similar to reported ages from intraplate alkali basalts located far to the north (Enmelen volcanoes on the Chukotka Peninsula) and to the south in Primorie (Vladivostok area). The volcanism at Viliga and in Primorie could be controlled by NE trending, leaky strike-slip like faults related to geologically recent plate boundary interactions. The Viliga olivine melanephelinites are highly depleted in radiogenic isotopes (Sr, Nd, Pb) but are quite enriched in incompatible trace elements. The generation of an alkaline magma in such depleted sources requires a relatively recent metasomatic even, which occurred less than 200 Ma and led to an enrichment of incompatible elements but of insufficient time elapsed to shift isotopic ratios. The lavas contain peridotite mantle xenoliths mainly with fertile major element signatures that lead to the conclusion that the lithospheric mantle beneath Viliga has not been affected by Late Cretaceous subduction of the paleo - Pacific plate as it was suggested for region. Viliga lower crustal xenoliths, however, contain zircons with U-Pb SHRIMP ages ranging from 63 to 100 Ma (24 dated zircon grains from two samples). These ages of lower crustal xenoliths are the same as those obtained from lower crustal xenoliths collected from Enmelen and St. Lawrence Island basalts located 1500 km to the NE in the Bering Strait area. This remarkable similarity in lower crustal ages suggests that the lower crust beneath a very wide portion of the continental margin of NE Russia and western Alaska has been affected by a similar Late Cretaceous magmatic/metamorphic event that modified the deep crust across the region.
DE: 1020 Composition of the continental crust
DE: 1040 Radiogenic isotope geochemistry
DE: 1115 Radioisotope geochronology
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005