HR: 17:15h
AN: GP44A-06    [Abstracts]
TI: Deeply Exhumed Roots of an Eocene Arc-Continent Collision Zone, Sredinniy Range, Kamchatka
AU: * Hourigan, J K
EM: jeremy.hourigan@yale.edu
AF: Dept. of Geology and Geophysics, P.O. Box 208109 Yale University, New Haven, CT 06520 United States
AU: Soloviev, A V
EM: solov@ilran.ru
AF: Geological Institute - RAS, 7 Pyzhevsky Per., Moscow, 119017 Russian Federation
AU: Brandon, M T
EM: mark.brandon@yale.edu
AF: Dept. of Geology and Geophysics, P.O. Box 208109 Yale University, New Haven, CT 06520 United States
AU: Garver, J I
EM: garverj@union.edu
AF: Department of Geology, Olin Building, Union College 807 Union ST, Schenectady, NY 12308 United States
AU: Palechek, T N
EM: tatiana@ilran.ru
AF: Geological Institute - RAS, 7 Pyzhevsky Per., Moscow, 119017 Russian Federation
AU: Stevenson, J
EM: james.stevenson@yale.edu
AF: Dept. of Geology and Geophysics, P.O. Box 208109 Yale University, New Haven, CT 06520 United States
AB: The Olyutorsky arc-continent collision is marked by the Vatyna Thrust, a regionally extensive suture zone, across which Late Cretaceous-Paleocene Olyutorsky island arc and retro-arc basinal rocks are juxtaposed against the continentally derived Late Cretaceous to Eocene Ukelayat flysch. Geologic relationships in northern Kamchatka and Southern Koryakia are relatively straightforward, and here, the timing of arc obduction is tightly constrained to the Middle Eocene. In southern Kamchatka, within the Sredinniy Range, the major elements of this collision zone are recognized flanking the N-S trending metamorphic core; however, internal structural complexity, old protolith and metamorphic age estimates (Archean to Early Cretaceous) and the high-grade of metamorphism (up to granulite facies) have precluded a straightforward interpretation for the occurrence high P-T metamorphic rocks in the context of this arc-continent collision. Most tectonic models invoke basement-involved thrusting of a previously accreted microcontinental block. We outline a new tectonic model based on recent field, microstructural, thermobarometric and thermochronologic work which demonstrates that the high-grade core of the Sredinniy Range was developed in the Early Eocene during arc-continent collision affecting stratigraphic equivalents of the Ukelayat Flysch and Olyutorsky arc in the absence of microcontinental basement. The Sredinniy Range comprises granulite to amphibolite facies gneiss and schist of continental affinity (Sredinniy Complex) structurally overlain by amphibolite to greenschist facies mafic schists (Malka Complex). The protolith age of the Andrianovka mafic schist within the Malka Complex is problematic with estimates ranging from Precambrian to Cretaceous. Metamorphosed cherts therein contain morphologically well-preserved recrystallized radiolaria. A nearly identical suite of moderately recrystallized radiolaria is found in the low-grade Iruney Group rocks, suggesting that Andrianovka Schist is likely an upgraded analog of the Iruney Group. Similarly, the origin and protolith ages for the Kamchatka Schist and Kolpakova Gneiss are highly debated with estimates ranging from Archean to Early Cretaceous. Our study utilizes minimum detrital zircon U/Pb grain-ages for these metasedimentary units to constrain maximum protolith depositional ages. The Kolpakova Gneiss and Kamchatka Schist give Late Cretaceous and Paleocene stratigraphic age estimates, respectively. Further, a favorable comparison between detrital zircon grain-age probability densities for the Kamchatka Schist and a sample of sub-greenschist facies Ukelayat Flysch suggests that the former is likely a metamorphosed analog of Cretaceous-Paleocene NE Russian marginal strata. U/Pb ages for zircon overgrowths observed in migmatites of the Kolpakova Gneiss and Th/Pb monazite ages indicate that peak metamorphic conditions, including partial melting, occurred at ~52Ma - broadly synchronous with the Olyutorsky arc-continent collision. Taken together, these new correlations suggest that high-grade metamorphic rocks of the Sredinniy Range are best viewed as the metamorphosed, deeply exhumed roots of an Eocene arc continent collision zone.
DE: 8102 Continental contractional orogenic belts
DE: 8105 Continental margins and sedimentary basins
DE: 8158 Plate motions--present and recent (3040)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting