HR: 1340h
AN: V13B-1467    [Abstracts]
TI: Parental Magmas to the Alaskan-Type Platinum-Bearing Plutons: Evidence From Galmoenan Massif (Far East, Russia).
AU: * Batanova, V G
EM: batanova@mpch-mainz.mpg.de
AF: Max-Planck-Institut fur Chemie, Abt. Geochemie, Postfach 3060, Mainz, 55020 Germany
AU: * Batanova, V G
EM: batanova@mpch-mainz.mpg.de
AF: Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin str. 19, Moscow, 117975 Russian Federation
AU: Pertsev, A
EM: alexei_n@igem.ru
AF: Institute of Ore Deposits Geology, Petrography, Mineralogy and Geochemistry, Staromonetnyi, 35, Moscow, 109017 Russian Federation
AU: Kamenetsky, V
EM: Dima.Kamenetsky@utas.edu.au
AF: Max-Planck-Institut fur Chemie, Abt. Geochemie, Postfach 3060, Mainz, 55020 Germany
AU: Kamenetsky, V
EM: Dima.Kamenetsky@utas.edu.au
AF: School of Earth Sciences and Centre for Ore Deposit Research, University of Tasmania, GPO BOX 252-79, Hobart, 7001 Australia
AU: Ariskin, A
EM: ariskin@geokhi.ru
AF: Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin str. 19, Moscow, 117975 Russian Federation
AU: Mochalov, A
AF: Institute of Precambrian Geology and Geochronology (IGGD RAS), Makarov nab. 2, St. Petersburg, 199034 Russian Federation
AU: Sobolev, A
EM: asobolev@mpch-mainz.mpg.de
AF: Max-Planck-Institut fur Chemie, Abt. Geochemie, Postfach 3060, Mainz, 55020 Germany
AU: Sobolev, A
EM: asobolev@mpch-mainz.mpg.de
AF: Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin str. 19, Moscow, 117975 Russian Federation
AB: Alaskan-type platinum-bearing plutons and potassium-enriched mafic to ultramafic volcanic rocks are temporally and spatially associated within the Late Cretaceous-Paleocene Achaivayam-Valaginskii intraoceanic paleo-arc terrain, allochthonously present in the Koryak Highland and Kamchatka Peninsula (Far East Russia). The compositions of magmas parental to the Alaskan-type complexes were estimated using the Galmoenan plutonic complex as an example. This intrusive, composed of dunites, pyroxenites and minor gabbros, is the largest (~20 km3) in the system and best studied owing to associated platinum placer deposits. The compositions of principal mineral phases in the Galmoenan massif, olivine Fo$_{79-92}$, clinopyroxene (1-3.5 wt% Al2O3, 0.1-0.5 wt% TiO2, and incompatible trace element abundances) and Cr-spinel (5-15 wt% Al2O3 and 0.3-0.7 wt% TiO2), are typical of liquidus assemblage in primitive island arc magmas in the intraoceanic settings, and closely resembles the mineral compositions in the Achaivayam-Valaginskii ultramafic volcanic rocks. Temporal and spatial association of intrusive and extrusive units and remarkable similarity of their mineral compositions provide evidence that both suites were formed from the same parental magma. The composition of parental magmas for the Galmoenan plutonic rocks was defined using previously reported data on the Achaivayam-Valaginskii ultramafic volcanic rocks and their melt inclusions. The quantitative simulation of crystallisation in the Galmoenan magma chamber from the parental magma shows that the compositions of cumulate units are best modelled by fractional crystallisation with periodic magma replenishment. This model accounts reasonably well for large amounts of dunite present in the intrusive, extensive interval of co-crystallisation of olivine and clinopyroxene, and also explains the observed range of mineral compositions. Given estimated parameters of the parental magmas and their mantle sources, we can envisage that fluxing of highly refractory "boninite-type" mantle wedge by chlorine-rich aqueous fluids is primarily responsible for both extensive melting and geochemical characteristics of magmas, including their enrichment in platinum-group elements (PGE). Such ultramafic PGE-bearing magmas are proposed to be common in the formation of Alaskan-type intrusive complexes.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3640 Igneous petrology
DE: 3655 Major element composition
DE: 3670 Minor and trace element composition
DE: 1010 Chemical evolution
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting