Cenozoic volcanism of the
Fedorov P.I.*, Koloskov A.V.**
1. At the northeast
edge of Asia (Penzhina-Anadyr-Koryak and
The Maastrichtian-Mid-Eocene stage consists of high-Ti, low- and moderate-K tholeiites and alkaline olivine basalts erupted in pull-apart systems and are connected with the most early rifting stage [Fedorov, Filatova, 1999, Fedorov, Koloskov, 1999]. Basalts are laterally heterogeneous. The lateral zoning of rocks is expressed in the replacement of K–Na compositions by potassic subalkaline and alkaline rocks going from southeast to northwest, i.e., toward the continent. The tholeiites have high Ti, Hf and low Ta and Nb concentrations. They are characterized by fractionated REE distribution (Lan/Ybn=1,3-8,7). The isotope ratios of strontium, neodymium and lead are low (87Sr/86Sr=0,702930-0,704215; εNd=3,8-5,7; 206Pb/204Pb=18,167-18,340; 207Pb/204Pb=15, 462-15,531; 208Pb/204Pb=37,798-38,073; D8/4Pb=20-28). The alkaline olivine basalts are enriched in titanium (2,0-2,4% TiO2), and are characterized by a strong LREE enrichment and a fractionated REE spectrum (Lan/Smn=1,9-3,9; Lan/Ybn=6,5-19,4).
Eocene-Oligocene stage is linked to the formation of the Koryak sector of the
West Kamchatka-Koryak volcanic-plutonic belt. The belt is made up of rocks of a
continuously differentiated andesite-basalt-rhyolite, moderately potassic
calcalkaline series and comagmatic intrusive granitoids. The rocks are
characterized by a low titanium content (TiO2=0,1-1,2%),
high aluminum, and a strong Ta-Nb minimum. The 87Sr/86Sr and
εNd ratios have strong lateral
variability (from 0,70447-0,70709 and 0,9-
The Miocene areals of the Koryak highland are composed of lava flows of tholeiitic basalts, extrusives and dacite dikes, typical of radiative continental margin rift formation. The basalts are high in titanium (TiO2=1,3-1,9%), with a highly fractionated distribution of REE (Lan/Smn=1,9-3,9;š Lan/Ybn=3,8-11,8) and a clear, negative Ta-Nb anomaly. The isotope ratios of strontium, neodymium and lead are moderately depleted (87Sr/86Sr=0,703289-0,703669; εNd=3,8-6,0; 206Pb/204Pb=18,20-18,42; 207Pb/204Pb=15,495-15, 524; 208Pb/204Pb=37,877-38,059; D8/4Pb=16-30).
The late Miocene-early Pliocene melanephelinites of the eastern Chukotka Peninsula are characterized by high titanium and potassium contents (TiO2=2,6-5%; 2,3-4% K2O with Na2O/K2O=0,8-2,1), strongly fractionated REE (Lan/Smn=6; Lan/Ybn=35), moderately low isotope ratios of strontium (87Sr/86Sr=0,7031080-0,7032970) and lead (206Pb/204Pb=18,32-18,43; 207Pb/204Pb=15,474-15,509; 208Pb/204Pb= 38,03-38,19; D8/4Pb=23-29) with high neodymium ratios (εNd=7,3-7,9) [Apt et al., 1998]. šIn the northern Priokhotsk area, mid- to late-Miocene melanephelinites are distinguished by higher concentrations of Ta and Nb and a less fractionated REE distribution (Lan/Smn=3,5; Lan/Ybn=17,8) with more depleted isotope ratios of strontium, neodymium and lead (87Sr/86Sr=0,703036-0,703079; 143Nd/144Nd=0,513052-0,513054; εNd=8,1; 206Pb/204Pb=17,907-17,925; 207Pb/204Pb=15,42-15,47; 208Pb/204Pb=37,505-37,693; D8/4Pb=34-40) [Apt et al., 1998].
stage of volcanism consists of individual lava flows, small cinder cones, necks
and dikes making up the
2. The data
presented on the composition of the Cenozoic volcanic complexes of the
3. Study of mantle reservoirs for the late-Cenozoic volcanic rocks of the Bering Sea region using Sr-Nd-Pb isotope systematics (Zou et al., 2000) and the ratios 87Sr/86Sr–206Pb/204Pb allows identificdation of three relatively separate trends, linked at the baseline by comparable values of 87Sr/86Sr=0,70275-0,70295. This baseline may be thought of as evidence for a common asthenospheric source. The lead isotope ratios define two sets of points, separated by 206Pb/204Pb @ 18,5 and reflecting the influence of two compositionally heterogeneous lithospheric blocks of different ages: the Asiatic and Alaskan [Koloskov, Fedorov, 2008]. Evidence for a primary role of decompression melting of the Pacific asthenospheric mantle in this volcanism is given in a number of studies [Portnyagin et al., 2005, Flower et al., 1998, Koloskov, 2008].
Yu. E., Akinin V. V., Wright J. E. Sr, Nd, and Pb Isotopes in
Neogene Melanephelinites and Deep-Seated Xenoliths from
P.I., Koloskov A.V. Cenozoic volcanism of southeastern Koryak Highland (
P.I., Filatova N.I. Geochemistry and Petrology of Late Cretaceous and Cenozoic
Basalts from Extensional Zones at the Continental Margin of Northeastern
Tamaki K., Hoang N. Mantle extrusion: a model for dispersed volcanism and
DUPAL-like asthenosphere in
Sr-isotope anomaly on the
Koloskov A.V., Fedorov P.I. Bering Sea region in the Last Cenizoic: Sr-Nd-Pb isotope systematics of volcanic rocks // Geochemistry of magmatic rocks-2008. School «Geochemistry of Alkaline rocks». St.-Peterburg, 23-26 May, 2008. P. 76-77.
Portnyagin M., Hoernle K., Avdeiko G. et al. Transition from arc to oceanic magmatism at the Kamchatka-Aleutian junction // Geology. 2005. Vol. 33. P. 25-28.