Neogene Kinematics in the Japan Sea Region and Volcanic Activity of the Northeast Japan Arc

Abstract

Deep sea drilling in the Japan Sea during ODP Legs 127 and 128 brought new constraints to the timing and dynamics of backarc opening. The nature and age of the oceanic basement as well as the recovered lithology allow us to present new reconstructions from 25 Ma to the present. On-land deformation data as well as the offshore crustal structure and timing of volcanic events are the major constraints we use. The Japan Sea opened as a complex pull-apart basin in a dextral shear zone that extends more than 2000 km from Central Japan to Northern Sakhalin. Oceanic crust was emplaced in the northern part of the Japan Basin, and highly extended arc crust in the Tsushima and Yamato basins. Westward propagation of oceanic spreading was active in the early Miocene. Our reconstructions give a minimum estimate for the finite dextral displacement of about 400 km. We observe correlations between volcanic events and tectonic phases, and we explore the hypothesis that variations in the character of volcanism during the Neogene in Northeast Japan can be due to changes in the tectonic status of the arc crust other than deep-seated variations in the mantle: (1) starvation of the volcanic activity in the late Miocene (10-7 Ma) is correlated with a reorganization of the stress field over the whole region from a dextral transtensional field during the Japan Sea opening to the present compressional field, and this period of inversion did not allow the ascent of magma through the upper brittle crust; (2) correlation is also seen between the formation of the incipient subduction zone at 1.8 Ma along the eastern margin of the Japan Sea and the transition from acidic to andesitic volcanism in Northeast Japan. Compression between 7 and 2 Ma is associated with the formation of large calderas and eruptions of acidic products, after which the present-day andesitic volcanism began at 2 Ma. During the compressive period the magma could not easily make its way up to the surface and stayed longer in the deep crust, where it could differentiate until the formation of a caldera. After localization of strain along the eastern margin of the Japan Sea and inception of the new subduction zone, which partly released the stress across the arc, the ascent of magma became much easier and the character of surface eruptions thus changed to less explosive. We also discuss the migration of the volcanic front through time from 30 Ma to the present with respect to tectonic processes.

Tectonic regime of the southern Kurile Trench as revealed by multichannel seismic lines

“…After a period of transpressional dextral strike-slip crustal faulting, from the Oligocene to the Middle Miocene, a drastic change to transtensional deformation occurred at 10 m.y., which is contemporaneous with the end of the opening of the Japan Sea and Kurile Basin (Jolivet and Tamaki, 1992). If both events are related, then about 400 km of dextral displacement are expected .…”

Paleomagnetism of Miocene Sedimentary Rocks in the Kakegawa Area and Implication for Tectonic Rotation in Central Japan.

“…Hayashida et al (1991) suggested a possibility that the drifting process of Southwest Japan involved a southward translation before 16 Ma and clockwise rotation of about 50° between 16 and 14 Ma. Jolivet and Tamaki (1992) inferred that coherent rotation of Southwest Japan of about 30° occurred in transtensional drift of the Japanese Islands to the south, assuming additional clockwise rotation of local small blocks within Southwest Japan.…”

Geochronology of alkali volcanism in Oki-Dogo Island, Southwest Japan: Geochemical evolution of basalts related to the opening of the Japan Sea.

“…Recent studies on Cenozoic stratig raphy of the Japanese Islands , 40Ar -39Ar dating of submarine volcanic rocks from the Japan Sea (Kaneoka et al, 1990(Kaneoka et al, , 1992, and results of Ocean Drilling Project (Jolivet and Tamaki, 1992) The outline of geology of Oki-Dogo Island (Fig. 2), combined with previous works and cur rent age determinations, is as follows: Basement rocks of Oki-Dogo Island are Prot erozoic metamorphic rocks whose Nd-Sm whole rock ages are about 2 Ga (Tanaka and Hoshino, 1987), and granitic rocks of Palaeozoic and Neo gene age (Tainosho et al, 1991).…”