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Yujiro Ogawa Ryota Mori Toshiaki Tsunogae Yildirim Dilek Ron Harris 《International Geology Review》2015,57(5-8):824-842
Many concepts and interpretations on the formation of the Franciscan mélange have been proposed on the basis of exposures at San Simeon, California. In this paper, we show the distribution of chaotic rocks, their internal structures and textures, and the interrelationship between the chaotic rocks and the surrounding sandstones (turbidites). Mélange components, particularly blueschists, oceanic rocks, including greenstone, pillow lava, bedded chert, limestone, sandstone, and conglomerate, have all been brecciated by retrograde deformation. The Cambria Slab, long interpreted as a trench slope basin, is also strongly deformed by fluidization, brecciation, isoclinal folding, and thrusting, leading us to a new interpretation that turbiditic rocks (including the Cambria Slab) represent trench deposits rather than slope basin sediments. These rocks form an accretionary prism above mélanges that were diapirically emplaced into these rocks first along sinistral-thrust faults, and then along dextral-normal faults. Riedel shear systems are observed in several orders of scale in both stages. Although the exhumation of the blueschist blocks is still controversial, the common extensional fractures and brecciation in most of the blocks in the mélanges and further mixture of various lithologies into one block with mélange muddy matrix indicate that once deeply buried blocks were exhumed from considerable depths to the accretionary prism body, before being diapirically intruded with their host mélange along thrust and normal faults, during which retrograde deformation occurred together with retrograde metamorphism. Recent similar examples of high-pressure rock exhumation have been documented along the Sofugan Tectonic Line in the Izu forearc areas, in the Mineoka belt in the Boso Peninsula, and as part of accretionary prism development in the Nankai and Sagami troughs of Japan. These modern analogues provide actively forming examples of the lithological and deformational features that characterize the Franciscan mélange processes. 相似文献
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A mooring observation of current velocity, temperature and bottom pressure was carried out approximately 30 km off the coast
of Monbetsu, between August 7 and September 2, 2005, to investigate the characteristics of bottom boundary layer (BBL) off
the Soya Warm Current (SWC). We succeeded in measuring the Ekman veering and bottom Ekman transport in the BBL. On comparing
the observed current velocity with that represented by the classical theoretical equation, the observed alongshore current
velocity in BBL disagreed with that represented by the classical theoretical equation, but the cross-shore one agreed well.
However after applying a linear extrapolation for the alongshore current velocity to estimate the alongshore geostrophic current
velocity above the bottom, we could explain the alongshore current velocity by that represented in the classical theoretical
equation. Consequently, our observations strongly support one of the proposed formation mechanisms of the cold-water belt
observed off the SWC, that is, the convergence of bottom Ekman transport. The volume transport of vertical pumping velocity
was estimated to be (0.12–0.25) Sv. In addition, the vertical profile of average temperature in all observation periods shows
that slightly warmer water lies beneath the homogenous temperature layer, in the BBL. The result is considered to imply that
the down-slope advection due to bottom Ekman transport supplies the SWC water in BBL and the eddy diffusivity of order of
10−3 m2s−1 maintains the oceanic structure in the bottom mixed layer. 相似文献
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The vertical mixing process induced by internal tides was investigated by repeated conductivity, temperature, and depth (CTD)
measurements and bottom-mounted acoustic Doppler current profiler (ADCP) in Uchiura Bay from July 24 to 25, 2001. Internal
tides were observed with a wave height of 40 m and a horizontal current of 0.3 ms−1. Density inversions were found in the CTD data, and the method of Galbraith and Kelley (1996) was applied to the data to
identify overturns and to calculate Thorpe scale. Most of the overturns distributed in the region of low Richardson number,
so that they were considered to be caused by shear instability associated with the internal tides. Thorpe scale was calculated
to be 0.48 m. From the Thorpe scale, the vertical eddy diffusivity due to internal tides in Uchiura Bay was estimated as K
ρ ∼ 10−4 m2s−1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Kazuaki Nakamura Vincent Renard Jacques Angelier Jacques Azema Jacques Bourgois Christine Deplus Kantaro Fujioka Yozo Hamano Philippe Huchon Hajimu Kinoshita Pierre Labaume Yujiro Ogawa Tetsuzo Seno Akira Takeuchi Manabu Tanahashi Akinori Uchiyama Jean-Louis Vigneresse 《Earth and Planetary Science Letters》1987,83(1-4)
Leg 2 of the French-Japanese 1984 Kaiko cruise has surveyed the Suruga and the Sagami Troughs, which lie on both sides of the northwestward moving and colliding Izu-Bonin Ridge, the northernmost part of the Philippine Sea plate. The transition from the Nankai Trough to the Suruga Trough is characterized by northward decrease in width of the accretionary prism, in good agreement with the increasing obliquity between the through axis and the direction of the convergence, as the strike of the convergent boundary changes from ENE-NNE to south-north. South of the area, the southern margin of the Zenisu Ridge shows contractional deformations. This supports the interpretation made by the team of Leg 1 who studied the western extension of the area we studied, that it is an intra-oceanic thrusting of the ridge over the Shikoku Basin. In the Sagami Trough, where the relative motion is highly oblique to the plate boundary, active subduction is mostly confined in the east-west trending portions of the trough located south of the Boso Peninsula and along the lower Boso Canyon, near the TTT triple junction. In between, the present motion is mainly right-lateral along the northwest trending Boso escarpment. However, an inactive but recent (Pliocene to lower Pleistocene) accretionary prism exists south of the Boso escarpment, which suggests that the relative motion was more northerly than at present before about 1 Ma ago. 相似文献
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Tomofumi Kozono Hideki Ueda Taku Ozawa Takehiro Koyaguchi Eisuke Fujita Akihiko Tomiya Yujiro J Suzuki 《Bulletin of Volcanology》2013,75(3):1-13
We present precise geodetic and satellite observation-based estimations of the erupted volume and discharge rate of magma during the 2011 eruptions of Kirishima-Shinmoe-dake volcano, Japan. During these events, the type and intensity of eruption drastically changed within a week, with three major sub-Plinian eruptions on January 26 and 27, and a continuous lava extrusion from January 29 to 31. In response to each eruptive event, borehole-type tiltmeters detected deflation of a magma chamber caused by migration of magma to the surface. These measurements enabled us to estimate the geodetic volume change in the magma chamber caused by each eruptive event. Erupted volumes and discharge rates were constrained during lava extrusion using synthetic aperture radar satellite imaging of lava accumulation inside the summit crater. Combining the geodetic volume change and the volume of lava extrusion enabled the determination of the erupted volume and discharge rate during each sub-Plinian event. These precise estimates provide important information about magma storage conditions in magma chambers and eruption column dynamics, and indicate that the Shinmoe-dake eruptions occurred in a critical state between explosive and effusive eruption. 相似文献
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Roger Antabe Kilian N. Atuoye Vincent Z. Kuuire Yujiro Sano Godwin Arku Isaac Luginaah 《社会与自然资源》2020,33(3):368-385
AbstractDespite the impact of mining-induced environmental change on community livability, we know little about how disparities in knowledge of health risks associated with mining influence residents’ response, especially in an already environmentally stressed context. Guided by theoretical insights from solastalgia, we examined residents’ decision to relocate due to increasing gold mining activities in the fragile Northern Savannah Ecological Zone of Ghana. Fitting complementary log-log regression models to cross-sectional data from the Upper West Region (UWR) of Ghana, we found that residents with limited knowledge of potential health impacts of mining and those who believe mining activities were not meeting environmental standards were more likely to consider relocating. Given the centrality of land in community health and wellbeing in the UWR, Ghana’s mining guidelines should promote local participation in the regulation of mining activities and guarantee the rights of indigenes to livable native lands. 相似文献