Viscosity of peridotite liquid up to 13 GPa: Implications for magma ocean viscosities

The viscosity of synthetic peridotite liquid has been investigated at high pressures using in-situ falling sphere viscometry by combining a multi-anvil technique with synchrotron radiation. We used a newly designed capsule containing a small recessed reservoir outside of the hot spot of the heater, in which a viscosity marker sphere is embedded in a forsterite + enstatite mixture having a higher solidus temperature than the peridotite. This experimental setup prevents spheres from falling before a stable temperature above the liquidus is established and thus avoids difficulties in evaluating viscosities from velocities of spheres falling through a partially molten sample.

Experiments have been performed between 2.8 and 13 GPa at temperatures ranging from 2043 to 2523 K. Measured viscosities range from 0.019 (± 0.004) to 0.13 (± 0.02) Pa s. At constant temperature, viscosity increases with increasing pressure up to  8.5 GPa but then decreases between  8.5 and 13 GPa. The change in the pressure dependence of viscosity is likely associated with structural changes of the liquid that occur upon compression. By combining our results with recently published 0.1 MPa peridotite liquid viscosities [D.B. Dingwell, C. Courtial, D. Giordano, A. Nichols, Viscosity of peridotite liquid, Earth Planet. Sci. Lett. 226 (2004) 127–138.], the experimental data can be described by a non-Arrhenian, empirical Vogel-Fulcher-Tamman equation, which has been modified by adding a term to account for the observed pressure dependence of viscosity. This equation reproduces measured viscosities to within 0.08 log₁₀-units on average. We use this model to calculate viscosities of a peridotitic magma ocean along a liquid adiabat to a depth of  400 km and discuss possible effects on viscosity at greater pressures and temperatures than experimentally investigated.     

High-reliability zircon separation for hunting the oldest material on Earth: An automatic zircon separator with image-processing/microtweezers-manipulating system and double-step dating

Despite the recent development in radiometric dating of numerous zircons by LA-ICPMS, mineral separation still remains a major obstacle, particularly in the search for the oldest material on Earth. To improve the efficiency in zircon separation by an order of magnitude, we have designed/developed a new machine-an automatic zircon separator(AZS). This is designed particularly for automatic pick-up of100 μm-sized zircon grains out of a heavy mineral fraction after conventional separation procedures. The AZS operates in three modes:(1) image processing to choose targeted individual zircon grains out of all heavy minerals spread on a tray,(2) automatic capturing of the individual zircon grains with microtweezers, and(3) placing them one-by-one in a coordinated alignment on a receiving tray. The automatic capturing was designed/created for continuous mineral selecting without human presence for many hours. This software also enables the registration of each separated zircon grain for dating, by recording digital photo-image, optical(color) indices, and coordinates on a receiving tray. We developed two new approaches for the dating; i.e.(1) direct dating of zircons selected by LA-ICPMS without conventional resin-mounting/polishing,(2) high speed U-Pb dating, combined with conventional sample preparation procedures using the new equipment with multiple-ion counting detectors(LA-MIC-ICPMS).With the first approach, Pb-Pb ages obtained from the surface of a mineral were crosschecked with the interior of the same grain after resin-mounting/polishing. With the second approach, the amount of time required for dating one zircon grain is ca. 20 s, and a sample throughput of 150 grains per hour can be achieved with sufficient precision(ca. 0.5%).We tested the practical efficiency of the AZS, by analyzing an Archean Jack Hills conglomerate in Western Australia with the known oldest(4.3 Ga) zircon on Earth. Preliminary results are positive; we were able to obtain more than 194 zircons that are over 4.0 Ga out of ca. 3800 checked grains, and 9 grains were over 4300 Ma with the oldest at 4371 ± 7 Ma. This separation system by AZS, combined with the new approaches, guarantees much higher yield in the hunt for old zircons.     

Cause and countermeasure of long-period oscillations of moored ships and the quantification of surge and heave amplitudes

Long-period oscillations of moored ships whose periods are about 1 or 2 min cause many troubles in many ports and harbours. It is necessary to investigate these phenomena and verify their causes and countermeasures in each case because they are strongly dependent on the environment of each port and harbour. From this point of view, long-period oscillations of moored ships in the Port of Shibushi in Japan were investigated by means of wave observations, the image processing of moored ship motions using the video camera and motion-capture software and numerical simulations. From observation results, the relationship between offshore long-period waves and long-period oscillations of moored ships was recognized and surge and heave amplitudes were quantified by using wave data in order to forecast moored ship motions. Furthermore, from observation and numerical results, it was revealed that long-period waves with the peak period of 120 s from the offshore typhoon kept or exaggerated the local harbour oscillation of 60–70 s and it caused long-period oscillations of moored ships. Numerical results in case of reducing the reflection coefficient of the target berth implied that it ceased the local harbour oscillation and it would give an effective countermeasure to reduce long-period oscillations of moored ships in the Port of Shibushi.     

Heterogeneous shock-induced thermal radiation in minerals

A 500 channel optical imaging intensifying and spectral digital recording system is used to record the shock-induced radiation emitted from 406 to 821 nm from transparent minerals during the time interval that a shock wave propagates through the sample. Initial results obtained for single crystals of gypsum, calcite and halite in the 30 to 40 GPa (300 to 400 kbar) pressure range demonstrate greybody emission spectra corresponding to temperatures in the 3,000 to 4,000 K range and emissivities ranging from 0.003 to 0.02. In the case of gypsum and calcite, distinctive line spectra, are superimposed on the thermal radiation. The observed color temperatures are a factor of 2 to 10 greater than the Hugoniot temperature, calculable on the basis of continuum thermodynamics and equation of state models for the shock states achieved in the three minerals. These observed high temperatures are believed to be real. We conclude that we are detecting a large number of closed spaced high temperature shear-band regions immediately behind the shock front. A shear instability model, such as proposed independently by Grady (1977, 1980), Ananin et al. (1974), and Horie (1980), in which small zones of highly deforming and melted material are produced which are the source of the detected thermal radiation and have a fractional effective area approximately numerically equal to the measured emissivity, can be used to predict an effective emissivity of 0.0065 directly behind the shock front. If shear band instability arises from viscous flow processes, Grady's model and mineral thermal properties yield for the shocked mineral viscosities values in the range of 10⁹ to 10¹⁵ P immediately behind the shock front.     

Anatomy of a subduction complex: architecture of the Franciscan Complex,California, at multiple length and time scales

The Franciscan Complex of California records over 150 million years of continuous E-dipping subduction that terminated with conversion to a dextral transform plate boundary. The Franciscan comprises mélange and coherent units forming a stack of thrust nappes, with significant along-strike variability, and downward-decreasing metamorphic grade and accretion ages. The Franciscan records progressive subduction, accretion, metamorphism, and exhumation, spanning the extended period of subduction, rather than events superimposed on pre-existing stratigraphy. High-pressure (HP) metamorphic rocks lack a thermal overprint, indicating continuity of subduction from subduction initiation at ca. 165 Ma to termination at ca. 25 Ma. Accretionary periods may have alternated with episodes of subduction erosion that removed some previously accreted material, but the complex collectively reflects a net addition of material to the upper plate. Mélanges (serpentinite and siliciclastic matrix) with exotic blocks have sedimentary origins as submarine mass transport deposits, whereas mélanges formed by tectonism comprise disrupted ocean plate stratigraphy and lack exotic blocks. The former are interbedded with and grade into coherent siliciclastic units. Palaeomegathrust horizons, separating nappes accreted at different times, appear restricted to narrow zones of <100 m thickness. Exhumation of Franciscan units, both coherent and mélange, was accommodated by significant extension of the hanging wall and cross-sectional extrusion. The amount of total exhumation, as well as exhumation since subduction termination, needs to be considered when comparing Franciscan architecture to modern and ancient subduction complexes. Equal dextral separation of folded Franciscan nappes and late Cenozoic (post-subduction) units across strands of the (post-subduction) San Andreas fault system shows that the folding of nappes took place prior to subduction termination. Dextral separation of similar clastic sedimentary suites in the Franciscan and the coeval Great Valley Group forearc basin is approximately that of the San Andreas fault system, precluding major syn-subduction strike-slip displacement within the Franciscan.     

The impact of the Tokyo Metropolitan Emissions Trading Scheme on reducing greenhouse gas emissions: findings from a facility-based study

This paper provides a detailed analysis of the Tokyo Metropolitan Emissions Trading Scheme (Tokyo ETS), Japan’s first emissions trading scheme with mandatory cap initiated by the government of Tokyo. Unlike trading schemes in other countries, the Tokyo ETS covers indirect emissions from the commercial sector. It is well known that a variety of market barriers impede full realization of energy efficiency opportunities, especially in the commercial sector. Experiences with the Tokyo ETS should therefore provide important lessons for the design of climate change mitigation policies, especially when targeting the commercial sector. The emissions from covered entities have been drastically reduced from those at the scheme’s outset, with an average 14% reduction as of the end of the first commitment period of five years (2010–2014) compared with 2009 levels. This paper shows that the Tokyo ETS alone did not cause these reductions; there were other drivers. Among them, the energy savings triggered by the Great East Japan Earthquake in 2011 were crucial. The contribution of credit trading, in contrast, was limited since most of the covered entities reduced emissions by themselves. Through an investigation of official reports, an assessment of the emissions data from the covered entities compared to those of uncovered entities and in-depth interviews with firms covered by the scheme, this paper confirms that the main drivers of emissions reductions by covered entities were separate from the ETS. In fact, the advisory aspect of the scheme seems to be much more important in encouraging energy-saving actions.

Key policy insights

• Most of the observed emission reductions were not caused by the Tokyo ETS alone.

• An advisory instrument was crucial to the effectiveness of the Tokyo ETS.

• The experience of the Tokyo ETS suggests that making full use of the advantages of emissions trading is difficult in the case of the commercial sector.

• Price signals have not provided a stimulus to climate change mitigation actions, which implies that establishing a cap to yield effective carbon prices poses a challenge.

     

Diabatic heating and the low frequency dynamics in the tropics

Summary Using a General Circulation Model developed at FSU (FSUGCM), the role of the diabatic heating on the 30–60-day oscillation is investigated. To concentrate on the radiation and the moist convection processes, an aqua planet model is employed in this paper. We have obtained a 40-day oscillation with relatively lower frequency than other GCMs without strong heating in the lower troposphere. Unlike some GCMs and simple models, the convective area does not move eastward along with the oscillation. Adiabatic cooling due to the upward motion is mostly compensated by diabatic heating. This implies that Kelvin CISK theory might not explain our 40-day oscillation. We have also examined the impact of radiative heating on the low frequency oscillation. When we reduce the radiative cooling rate, our 40-day mode does not appear and a Kelvin CISK mode appears with a faster phase speed. The impact of the different convection schemes is also investigated. With an enhanced convection scheme, zonal wave number two with a 40-day period is generated.With 12 FiguresOn leave from Japan Meteorological Agency.     

Observation of Sea-Ice Thickness Using ENVISAT Data From LÜtzow-Holm Bay, East Antarctica

To investigate the suitability of synthetic aperture radar (SAR) polarization data to estimate the sea-ice thickness in early summer in Lutzow-Holm Bay, Antarctica, we compared in situ ice thicknesses with the corresponding backscattering co-efficient for each polarization and the VV-to-HH backscattering ratio. The VV-to-HH backscattering ratio was derived from data acquired by ENVISAT Advanced SAR (ASAR). This ratio is related to the near-surface dielectric constant of the sea ice, which is, in turn, related to the developing process of ice and, thus, its thickness via changes in the near-surface sea-ice salinity. The sea ice encountered in the study area is close first-year pack ice and fast ice. For these old and relatively rough sea-ice types, the VV-to-HH backscattering ratio can be expected to depend on salinity-driven changes in the near-surface dielectric constant rather than changes of the surface roughness. We applied the empirical relationships between the ice thickness and the VV-to-HH backscattering ratio with the linear and logarithm fits to ASAR data. The linear fit gave the reliable result, with an rms error being 0.08 m and a correlation coefficient being 0.91, when compared to in situ fast-ice thickness.     

Paleomagnetism of the middle Cretaceous Iritono granite in the Abukuma region, northeast Japan

We have studied the paleomagnetism of the middle Cretaceous Iritono granite of the Abukuma massif in northeast Japan together with ⁴⁰Ar–³⁹Ar dating. Paleomagnetic samples were collected from ten sites of the Iritono granite (102 Ma ⁴⁰Ar–³⁹Ar age) and two sites of its associated gabbroic dikes. The samples were carefully subjected to alternating field and thermal demagnetizations and to rock magnetic analyses. Most of natural remanent magnetizations show mixtures of two components: (1) H component, high coercivity (B_c > 50–90 mT) or high blocking temperature (T_b > 350–560 °C) component and (2) L component, relatively low B_c or low T_b component. H component was obtained from all the 12 sites to give a mean direction of shallow inclination and northwesterly declination (I = 29.9°, D = 311.0°, α₉₅ = 2.7°, N = 12). This direction is different from the geocentric axial dipole field at the present latitude (I = 56.5°) and the typical direction of the Cenozoic remagnetization in northeast Japan. Since rock magnetic properties indicate that the H component of the Iritono granite is carried mainly by magnetite inclusions in plagioclase, this component probably retains a primary one. Thus the shallow inclination indicates that the Abukuma massif was located at a low latitude (16.1 ± 1.6°N) about 100 Ma and then drifted northward by about 20° in latitude. The northwesterly deflection is attributed mostly to the counterclockwise rotation of northeast Japan due to Miocene opening of the Japan Sea. According to this model, the low-pressure and high-temperature (low-P/high-T) metamorphism of the Abukuma massif, which has been well known as a typical location, would have not occurred in the present location. On the other hand, the L component is carried mainly by pyrrhotite and its mean direction shows a moderate inclination and a northwesterly declination (I = 42.8°, D = 311.5°, α₉₅ = 3.3°, N = 9). Since this direction is intermediate between the H component and early Cenozoic remagnetization in northeast Japan, some thermal event would have occurred at lower temperature than pyrrhotite Curie point ( 320 °C) during the middle Cretaceous to early Cenozoic time to have resulted in partial remagnetization.