Contamination of Tris(4-Chlorophenyl) Methane and Tris(4-Chlorophenyl) Methanol in Marine Mammals from Russia and Japan: Body Distribution, Bioaccumulation and Contamination Status

Four seal species (Phoca caspica, Phoca sibirica, Phoca hispida and Phoca largha) and one whale (Orcinus orca) from Russia and Japan were examined to determine the body distribution, bioaccumulation and contamination status of tris(4-chlorophenyl) methane (TCPMe) and tris(4-chlorophenyl) methanol (TCPMOH). Lipid normalized concentrations of TCPMe and TCPMOH were comparable in various organs and tissues, implying that their body distribution is followed to the lipid-dependent accumulation, similar to that for other organochlorines. The highest body burden of these compounds was found in the blubber. Bioaccumulation potential of TCPMe and TCPMOH was high and comparable to PCBs and DDTs. Relatively higher concentrations of TCPMe and TCPMOH were observed in Caspian seal than in other seal species examined. TCPMOH concentration in killer whale was the highest of the marine mammals examined. Another peak detected had similar mass spectrum to TCPMOH, however, at a different retention time, suggesting the presence of an isomer of TCPMOH.     

Continuous GPS Array and Present-day Crustal Deformation of Japan

—A GPS array with about 1,000 permanent stations is under operation in Japan. The GPS array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the Japanese islands. Based on daily coordinate data of the GPS stations, strain rate distribution is estimated. Most regions with a large strain rate are related to plate boundaries and active volcanoes. In addition, the Niigata-Kobe Tectonic Zone (NKTZ) is recognized as a region of large strain rate along the Japan Sea coast and in the northern Chubu and Kinki districts. This newly found tectonic zone may be related to a hypothetical boundary between the Eurasian (or Amurian) and the Okhotsk (or North America) plates. Precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities. Appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations.     

Timescale of material circulation in subduction zone: U–Pb zircon and K–Ar phengite double‐dating of the Sanbagawa metamorphic complex in the Ikeda district,central Shikoku,southwest Japan

We have estimated the timescale of material circulation in the Sanbagawa subduction zone based on U–Pb zircon and K–Ar phengite dating in the Ikeda district, central Shikoku. The Minawa and Koboke units are major constituents of the high‐P Sanbagawa metamorphic complex in Shikoku, southwest Japan. For the Minawa unit, ages of 92–81 Ma for the trench‐fill sediments, are indicated, whereas the age of ductile deformation and metamorphism of garnet and chlorite zones are 74–72 Ma and 65 Ma, respectively. Our results and occurrence of c. 150 Ma Besshi‐type deposits formed at mid‐ocean ridge suggest that the 60‐Myr‐old Izanagi Plate was subducted beneath the Eurasian Plate at c. 90 Ma, and this observation is consistent with recent plate reconstructions. For the Koboke unit, the depositional ages of the trench‐fill sediments and the dates for the termination of ductile deformation and metamorphism are estimated at c. 76–74 and 64–62 Ma, respectively. In the Ikeda district, the depositional ages generally become younger towards lower structural levels in the Sanbagawa metamorphic complex. Our results of U–Pb and K–Ar dating show that the circulation of material from the deposition of the Minawa and Koboke units at the trench through an active high‐P metamorphic domain to the final exhumation from the domain occurred continuously throughout c. 30 Myr (from c. 90 to 60 Ma).     

Rb-Sr and Sm-Nd Mineral Isochron Ages of the Metamorphic Rocks in the Namaqualand Metamorphic Complex, South Africa

Rb-Sr and Sm-Nd isotopic studies were carried out for metamorphic rocks in the Namaqualand Metamorphic Complex, South Africa. The metamorphic rocks give the Rb-Sr mineral isochron ages (whole-rock - biotite - felsic fractions) of 844±85 Ma and 811.6±6.6 Ma for the lower granulite zone and of 776.5±5.4 Ma for the upper granulite zone. The rocks yield the Sm-Nd mineral isochron ages of 1071±18 Ma (whole-rock - garnet - felsic fractions) and 1067±158 Ma (whole-rock - hornblende - biotite rich fraction - felsic fractions) for the lower granulite zone and of 1052.0±3.6 Ma and 1002.5±1.4 Ma (whole-rock - garnet - felsic fractions) for the upper granulite zone. These age data suggest that the granulite facies metamorphism took place at 1060-1000 Ma, and that the rocks cooled down at 850-780 Ma. The Sr and Nd isotopic compositions of metamorphic rocks are different between the lower and upper granulite zones.     

Subduction erosion and accretion in the Solomon Sea region

The Solomon Sea region is an area of intense tectonic activity characterized by structural complexity, a high level of seismicity and volcanism, and rapid evolution of plate boundaries. There is little accretion in the eastern New Britain Trench. Accretion gradually increases westward with thick accretion in the western New Britain Trench and in the Trobriand Subduction System. The thick accretion in the western part of the New Britain Trench may be a result of collision from the north of Finisterre-Huon block with New Guinea mainland. The present boundary of the collision is along the Ram-Markham fault. Deformation structures and present day seismicity suggest that the northern block is under compression.

Accretion has occurred in the sediment filled trenches in the Solomon Sea. The scale of the accretionary wedge depends on the amount of trench-fill sediment available. It is unlikely that there is no sediment supply to the eastern part of the New Britain Trench where no accretion is observed and subduction erosion may be occurring. There are two possible mechanisms for subduction erosion of sediment; either a rapid rate of subduction relative to the supply of sediment inhibiting sediment accumulation in the trench; or horizontal tensional force superimposed on both the forearc and backarc regions of the arc. Seafloor spreading in both the Manus and Woodlark basins is fan-like with nearby poles in the western margins of the basins. This may be a reflection of a horizontally compressional field in the western part and a tensional field in the eastern part of the Solomon Sea. Therefore it is possible to conclude that the consumption of sediment in the eastern New Britain Trench is related to the horizontal tensional field superimposed on both the forearc and backarc regions of the subduction system.

Imbricated thrust and overthrust faults in the western New Britain Trench and Trobriand Trough are not linear over long distance, but form wavy patterns in blocks with unit distance of approximately 10 km.     

Three-dimensional mapping of red stingray (Dasyatis akajei) movement with reference to bottom topography

Most demersal fishes maintain strong relations with bottom substrates and bottom depths and/or topography during their lives. It is important to know these relations to for understand their lives. In Tokyo Bay, red stingray, Dasyatis akajei, classified as near-threatened species by IUCN, has increased since the 1980s. It is a top predator and engages in ecosystem engineer by mixing the sand bed surface through burring behavior, and greatly influences a coastal ecosystem. It is reported that this species invades in plage and tidal flats and has sometimes injured beachgoers and people gathering clams in Tokyo bay. Thus, it is necessary to know its behavior and habitat use to avoid accidents and to better conserve the biodiversity of ecosystems. However, previous studies have not examined its relationship with the bottom environment. This study aims to describe its behavior in relation to the bottom environment. We sounded three dimensional bottom topography of their habitat off Kaneda Cove in Tokyo Bay with interferometric sidescan sonar system and traced the movement of red stingrays by attaching a data logger system to survey their migration. The results revealed that red stingray repeated vertical movement between the surface and bottom, and used not only sand beds but also rocky beds.

     

The basement geology of Japan from A to Z

The Precambrian and lower Paleozoic units of the Japanese basement such as the Hida Oki and South Kitakami terranes have geological affinities with the eastern Asia continent and particularly strong correlation with units of the South China block. There are also indications from units such as the Hitachi metamorphics of the Abukuma terrane and blocks in the Maizuru terrane that some material may have been derived from the North China block. In addition to magmatism, the Japanese region has seen substantial growth due to tectonic accretion. The accreted units dominantly consist of mudstone and sandstone derived from the continental margin with lesser amounts of basaltic rocks associated with siliceous deep ocean sediments and local limestone. Two main phases of accretionary activity and related metamorphism are recorded in the Jurassic Mino–Tanba–Ashio, Chichibu, and North Kitakami terranes and in the Cretaceous to Neogene Shimanto and Sanbagawa terranes. Other accreted material includes ophiolitic sequences, e.g. the Yakuno ophiolite of the Maizuru terrane, the Oeyama ophiolite of the Sangun terrane, and the Hayachine–Miyamori ophiolite of the South Kitakami terrane, and limestone‐capped ocean plateaus such as the Akiyoshi terrane. The ophiolitic units are likely derived from arc and back‐arc basin settings. There has been no continental collision in Japan, meaning the oceanic subduction record is more complete than in convergent orogens seen in intracontinental settings making this a good place to study the geological record of accretion. Hokkaido lacks most of the Paleozoic history recognized in Honshu, Shikoku, Kyushu, and the Ryukyu Islands to the south and its geology reflects the Cenozoic development of two convergent domains with volcanic arcs, their approach, and eventual collision. The Hidaka terrane reveals a cross section through a volcanic arc and the main accretionary complex of the convergent system is represented by the Sorachi–Yezo terrane.     

Thermal modelling in shallow subduction: an application to low P/T metamorphism of the Cretaceous Shimanto Accretionary Complex, Japan

This paper presents the results of numerical modelling to investigate the regional occurrence of prehnite‐bearing metamorphic rocks at shallow levels in subduction zones. The modelling assumes a simple geometrical configuration in which the thermal structure in a prism is controlled by boundary conditions at the top and base of the prism. It is expected that the predominant metamorphic facies in a prism will change with decreasing age of the descending slab. The results of thermal modelling show that the facies boundary between pumpellyite–actinolite and prehnite–actinolite facies (including prehnite–pumpellyite facies) overlaps with an array of P–T conditions in the prism when the age of a descending slab is younger than 10 Myr. This implies that the change of the predominant metamorphic facies from pumpellyite–actinolite to prehnite–actinolite facies will switch drastically. The critical age of the switch depends on subduction parameters. In particular, the critical age of the descending slab is <5 Myr in the case of no shear heating, with a subduction rate of v=75–200 mm y^?1 and subduction angle of θ=5–15°. For shear heating (constant shear stress=30 MPa) with a subduction rate of v=75 mm y^?1 and subduction angle of θ=10° the critical age is 7 Myr. To test this switching behaviour in the development of prehnite–actinolite facies in the prism, petrologic data from the Cretaceous Shimanto Accretionary Complex (CSAC) in Kyushu, Japan were compiled. The regional occurrence and mineral assemblages of prehnite‐bearing metamorphic rocks suggest that the most of CSAC was metamorphosed under prehnite–actinolite facies. This conclusion is consistent with subduction of a young, hot slab, as has been proposed based on other geological observations. This suggests that the regional extent of the prehnite–actinolite facies metamorphic rocks may be a unique evidence for the subduction of a young, hot slab.