HR: 0800h
AN: T41C-1224    [Abstracts]
TI: Changes in Plate Boundary Conditions Along the NW Pacific Rim as Recorded in the Tertiary Mineoka Ophiolite (Central Japan)
AU: Ogawa, Y
EM: yogawa@arsia.geo.tsukuba.ac.jp
AF: Earth Evolution Sciences, University of Tsukuba, Tsukuba, Iba 305-8572 Japan
AU: * Dilek, Y
EM: dileky@muohio.edu
AF: Department of Geology, Shideler Hall, Miami University, Oxford, OH 45056 United States
AB: The Tertiary Mineoka ophiolite, which occurs in a fault zone at the intersection of the Honshu and Izu forearcs in central Japan, displays structural and geochemical evidence for its multi-stage evolution in various tectonic settings that attests to rapid changes in plate boundary conditions along the NW Pacific Rim throughout the late Cenozoic. The Mineoka ophiolite first developed as a mid-ocean ridge crust (49-45 Ma) on the Mineoka plate (counterpart of the New Guinea plate). A change in the regional stress regime around 43 Ma resulted in the initiation of a west-dipping subduction zone, which produced island arc tholeiitic magmatism and subsequently backarc basin rift magmatism superimposed on the earlier-formed _eMineoka_f oceanic crust. Eruption of Ocean Island Basalt (OIB)-like alkali-basalts on the Mineoka plate occurred near the paleo-Japan continental arc, around 20-19 Ma, after the cessation of backarc rifting. These alkali basalts and the _eMineoka_f oceanic crust were covered with Paleogene to Miocene pelagic sediments on the way to the oblique convergent margin of Eurasia (paleo-Japan arc). Much of the _eMineoka_f ocean floor was subducted beneath the paleo-Japan continental arc (Eurasian plate) by 14 Ma. With southward migration of the unstable TTT-triple junction between the Pacific and Mineoka plates, the northern tip of the Izu volcanic arc collided with the Honshu Arc (continental arc) and fragments of the _eMineoka_f oceanic crust were incorporated as an ophiolite into the upper plate of the subduction-accretion system of this continental arc. After the consumption of the Mineoka plate and the emplacement of the Mineoka ophiolite, the Boso triple junction was established with the E-W-trending transpressional Sagami Trough adjoining the Izu-Bonin and Japan Trenches. Around 2 Ma, a change in the relative motion of the Philippine-Eurasian plates resulted in the development of a dominantly dextral strike-slip stress regime within the Sagami Trough, part of which has occupied today_fs Boso Peninsula and the Mineoka fault zone. This stress regime initiated a broad zone of dextral strike-slip deformation between the Boso triple junction and the recently established Fuji triple junction further to the west that is still active today.
DE: 9355 Pacific Ocean
DE: 8158 Plate motions--present and recent (3040)
DE: 8168 Stresses--general
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting