Triaxial stress state deep in orogenic belts: an example from Turkey

A rare metachert pebble containing amphibole grains with microboudin structures in a wide range of orientations provides an opportunity to perform stress analysis in two orthogonal orientations on the foliation surface. The sample was analysed by the microboudin method to infer the triaxial stress state during microboudinage. Stress parameters proportional to the far-field differential stress were determined for sodic amphibole grains in the two orientations. The ratio of the stresses in the two orthogonal orientations (σ₁−σ₂)/(σ₁−σ₃) was calculated to be 0.64, indicating that σ₂ lies closer to the midpoint between σ₁ and σ₃ than to σ₃.     

Summary of the fossil record of pinnipeds of Japan, and comparisons with that from the eastern North Pacific

Abstract The fossil pinniped record of the North Pacific Ocean includes both Phocidae and Otariidae ( sensu lato ), extends from the Late Oligocene to the Late Pleistocene, is taxonomically diverse, and is constantly becoming more complete owing to additional important discoveries. The earliest and most diverse fossil pinnipeds in the North Pacific are otariids, the phocids not appearing until the latest Pliocene. The theoretical center of otariid pinniped evolutionary history has been considered by some to be in the eastern North Pacific. New materials from the western North Pacific, however, including representatives of the subfamilies Enaliarctinae, Imagotariinae, Odobeninae and Otariinae, indicate that pinniped evolutionary patterns were basin-wide phenomena, and that a more complete record undoubtedly would reveal numerous trans-Pacific distributions. This would be expected considering the distributions of living species. The paucity of fossil Phocidae and their absence from pre-Pliocene deposits are consistent with theories that the family primarily evolved outside the North Pacific.     

Classification and distribution of Oligocene Aetiocetidae (Mammalia; Cetacea; Mysticeti) from western North America and Japan

Abstract Fossil whales in the very rare, primitive, extinct cetacean family Aetiocetidae are small, relict, toothed mysticetes that persisted into Late Oligocene time after more highly derived baleen-bearing mysticetes had already evolved. No known aetiocetid could be ancestral to baleen-bearing mysticetes, but aetiocetid morphology is in many ways intermediate between archaeocetes and baleen-bearing mysticetes, demonstrating the probable transitional steps passed through in the evolution of baleen-bearing mysticetes. Their discovery indicates that mysticetes evolved from Archaeocetes, and supports theories of the monophyly of Cetacea. Late Oligocene aetiocetids have been found on both sides of the North Pacific Ocean: on Vancouver Island, British Columbia, Canada; in Oregon and Washington, USA; in Baja California Sur, México; and the islands of Kyushu and Hokkaido, Japan. The most primitive North American aetiocetid, Chonecetus sookensis Russell, 1968, is from the early Late Oligocene Hesquiat Formation on Vancouver Island, British Columbia, Canada. A more derived, Late Oligocene species, Chonecetus goedertorum Barnes and Furusawa, new species, from the Late Oligocene Pysht Formation, Olympic Peninsula, Washington, has the primitive placental mammalian tooth count of 11/11. The type genus of the family, Aetiocetus Emlong, 1966, has as its type species, A. cotylalveus Emlong, 1966, known only from the Late Oligocene Yaquina Formation on the coast of Oregon. It has 11 upper teeth on each side of the rostrum. A more derived species, Aetiocetus weltoni Barnes and Kimura, new species, from a higher stratigraphic level in the Yaquina Formation, has a more posteriorly positioned cranial vertex and a tooth count of 11/12. We describe four new species of aetiocetids in three genera from the Late Oligocene Morawan Formation near Ashoro, Hokkaido, Japan. The most primitive, Ashorocetus eguchii Barnes and Kimura, new genus and species, has a primitive stage of cranial telescoping, and is closely related to Chonecetus Russell, 1968. Another, Morawanocetus yabukii Kimura and Barnes, new genus and species, in some ways intermediate between Chonecetus and Aetiocetus, has a suite of unique derived characters, including a much foreshortened brain case. The third, Aetiocetus tomitai Kimura and Barnes, new species, is the most primitive species of Aetiocetus yet discovered. The fourth, Aetiocetus polydentatus Sawamura, new species, the most derived species of Aetiocetus known, has a highly telescoped cranium, homodonty, polydonty and a dental count of 13–14/14–15. The fossil record now indicates considerable diversity in the family, with several different contemporaneous lineages in three new subfamilies: Chonecetinae, Morawanocetinae and Aetiocetinae. Aetiocetids are not known outside the North Pacific. Many Recent mysticetes are essentially cosmopolitan, and aetiocetids might have also been relatively widely dispersed. We suspect that with time their remains will be found around other ocean basins also. If so, then they may be potentially useful in trans-oceanic geological correlations.     

Natural and anthropogenic aquatic environmental changes reconstructed by paleolimnological analyses in Lake Kitaura,central Japan

In order to assess the recent anthropogenic environmental changes in Lake Kitaura, central Japan, changes during the past few centuries were reconstructed from results of radiometric and tephrochlonological age determination, magnetic susceptibility measurements, total organic carbon analyses, total nitrogen analyses and fossil diatom analyses on a sediment core from the lake. A total of six major and sub-zones are recognized according to the diatom fossil assemblages, and we discuss aquatic environmental change in Lake Kitaura mainly based on these diatom assemblage change. Zone Ia and Zone Ib (older than AD 1707) are marine to brackish. In Zone IIa (AD␣1707–AD 1836), most of the brackish diatoms disappeared, and were replaced by freshwater species indicating a decrease in salinity. We interpret the salinity decrease in Zone I–IIa as a sea-level fall during the Little Ice Age. The salinity of the lake decreased to near freshwater conditions in Zone IIb (AD 1836–AD 1970), which could arise from alteration in River Tone or development of a sandspit in the mouth of River Tone in addition to sea-level change. In Zone IIIa (AD 1970–AD 1987), the diatom assemblage indicates a freshwater environment, and sedimentation rates increase rapidly. These changes reflect sedimentary environment change and an ecosystem transition due to the construction of the tide gate. In Zone IIIb (AD 1987–AD 2002), the diatom flux (valves cm⁻² y⁻¹) increased and species composition changed. The changes in Zone IIIb show a good agreement with limnological monitoring data gathered from the lake. These paleolimnological data suggest that the recent human-induced changes of the aquatic environment of the lake after the 1970s exceed rates during the period concerned in this study.     

A Simple Single-Layer Urban Canopy Model For Atmospheric Models: Comparison With Multi-Layer And Slab Models

We developed a simple, single-layer urban canopy model, and comparedit to both multi-layer and slab models. Our single-layer model has thefollowing features: (a) It is a column model of energy and momentumexchange between an urban surface and the atmosphere, (b) it includesthe influence of street canyons, which are parameterized to representthe urban geometry, (c) it includes shadowing from buildings andreflection of radiation, and (d) it estimates both the surfacetemperatures of, and heat fluxes from, three surface types: roof, wall,and road. In the simulation of the single-layer model, the roof washottest during the daytime, but coolest from midnight to early morning.This is consistent with output from the multi-layer model and fieldobservations at a residential area on a clear, summer day. The diurnalvariation of the energy budget from the single-layer model agrees wellwith that from the multi-layer model. Our single-layer model'sperformance is nearly that of a multi-layer model for studyingmesoscale heat islands. Nevertheless, it is simply parameterized,and thus easily included in larger-scale atmospheric models. The slabmodel has the largest nighttime cooling rate of the three models. Toovercome this, it needs more adjustments than for the canopy models.     

Collision orogeny at arc-arc junctions in the Japanese Islands

Abstract In the Japanese Islands, collision tectonics are operating at arc-arc junctions in three regions: Hokkaido, Central Japan and Kyushu. Hokkaido is situated at the junction of the Kuril and Northeast Japan Arcs. The Kuril fore arc sliver collides with the Northeast Japan Arc, and the lower crust of the Kuril Arc thrusts upon the fore arc of the Northeast Japan Arc in Hokkaido. Outcrops of the lower crust are observed in the Hidaka Mountains in the fore arc of the junction area. Central Japan is in the juncture area among the Northeast Japan, Izu-Bonin, and Southwest Japan Arcs. The Izu-Bonin arc is colliding against the Honshu mainland, which has been bent by the collision. Kyushu is a juvenile collision area between the Southwest Japan and Ryukyu Arcs. The fore arc of the Southwest Japan Arc is starting to underthrust beneath the Kyushu islands along the Bungo Strait, where shallow seismicity within the crust is active in terms of the collision. Collision tectonics are observed at most of the arc-arc junctions in the circum-Pacific orogenic belts and may be an important process contributing to the relatively rapid growth of new continental crust in subduction zones.     

Ca, Al-rich inclusions in Yamato 791717 (CO3) carbonaceous chondrite: Formation and alteration

In three polished thin sections of Yamato 791717 (CO3). fifty-five Ca, Al-rich inclusions were found, which include two hibonite-bearing, eight melilite-rich and forty-five spinel-pyroxene inclusions. Based on the petrography and mineral chemistry of the inclusions, it is proposed that the melilite-rich inclusions and spinel-pyroxene inclusions condensed in the solar nebula, and the hibonite-bearing inclusions crystallized from melts. The heavy alteration of the inclusions in Yamato 791717, which probably took place under a very oxidizing condition in the solar nebular, is also confirmed. Project supported by the National Natural Science Foundation of China (Grant No. 49673200). and by the Japanese Society for Promotion of Sciences (JSPS).     

Distribution of gold and rhenium between nickel-iron and silicate melts: implications for the abundance of siderophile elements on the Earth and Moon

The distribution equilibrium of Au and Re between nickel-iron and basaltic melts was studied at 1400–1600°C, using radioactive tracers. Metal/silicate distribution coefficients were 1–3 orders of magnitude higher than earlier estimates, as follows. Mauna Loa basalt—Fe₁₀Ni₉₀: D_Au = 3.3 × 10⁴, D_Re = (2.4?89) × 10⁴. Gorda Ridge basalt—Fe₁₀Ni₉₀: D_Au = (18?75) × 10⁴. Synthetic lunar basalt—Fe₇₀ Ni₃₀: D_Au≥ 2 × 10⁴, D_Re ≥ 2 × 10³. The experimental ΔG₁₈₀₀^° for the distribution of Au between nickel-iron and Mauna Loa basalt is ?40 kcal/mole, compared to a calculated value of about ?110 kcal/mole for a reaction involving simple Au³⁺ ions. Presumably the difference represents stabilization of Au(III) by complex formation with ligands such as Cl^?, H₂O, etc.Gold abundances in lunar basalts are roughly consistent with the measured D_Au, but those in terrestrial basalts are two orders of magnitude too high. This discrepancy may reflect complexing by volatiles in the Earth's upper lithosphere, as well as oxidative destruction of metal in the final stages of accretion. In the absence of a metal phase, siderophile trace elements would remain trapped in the upper mantle and crust.     

Primary melt from Sannome-gata volcano,NE Japan arc: constraints on generation conditions of rear-arc magmas

The conditions under which rear-arc magmas are generated were estimated using primary basalts from the Sannome-gata volcano, located in the rear of the NE Japan arc. Scoriae from the volcano occur with abundant crustal and mantle xenoliths, suggesting that the magma ascended rapidly from the upper mantle. The scoriae show significant variations in their whole-rock compositions (7.9–11.1 wt% MgO). High-MgO scoriae (MgO > ~9.5 wt%) have mostly homogeneous ⁸⁷Sr/⁸⁶Sr ratios (0.70318–0.70320), whereas low-MgO scoriae (MgO < ~9 wt%) have higher ⁸⁷Sr/⁸⁶Sr ratios (>0.70327); ratios tend to increase with decreasing MgO content. The high-MgO scoriae are aphyric, containing ~5 vol% olivine microphenocrysts with Mg# [100 × Mg/(Mg + Fe²⁺)] of up to 90. In contrast, the low-MgO scoriae have crustal xenocrysts of plagioclase, alkali feldspar, and quartz, and the mineralogic modes correlate negatively with whole-rock MgO content. On the basis of these observations, it is inferred that the high-MgO scoriae represent primary or near-primary melts, while the low-MgO scoriae underwent considerable interaction with the crust. Using thermodynamic analysis of the observed petrological features of the high-MgO scoriae, the eruption temperature of the magmas was constrained to 1,160–1,220 °C. Given that the source mantle was depleted MORB-source mantle, the primary magma was plausibly generated by ~7 % melting of a garnet-bearing spinel peridotite; taking this into consideration, and considering the constraints of multi-component thermodynamics, we estimated that the primary Sannome-gata magma was generated in the source mantle with 0.5–0.6 wt% H₂O at 1,220–1,230 °C and at ~1.8 GPa, and that the H₂O content of the primary magma was 6–7 wt%. The rear-arc Sannome-gata magma was generated by a lower degree of melting of the mantle at greater depths and lower temperatures than the frontal-arc magma from the Iwate volcano, which was also estimated to be generated by ~15 % melting of the source mantle with 0.6–0.7 wt% H₂O at ~1,250 °C and at ~1.3 GPa.