The chemical compositions of primary magmas of olivine tholeiite (OTB), high‐alumina basalt (HAB), and alkali olivine basalt (AOB) are obtained by the olivine maximum fractionation model for Quaternary magnesian basalts from the Northeastern Japan arc. These basalts are assumed to have fractionated only olivine crystals before eruption. The melting phase relations for three primary basalt compositions have been determined under both anhydrous and water‐undersaturated conditions. The AOB melt coexists with olivine, orthopyroxene, and clinopyroxene at 17 kbar and 1360°C under anhydrous conditions and at 23kbar and 1320°C in the presence of 3wt % water. The HAB melt also coexists with the above three phases at 15 kbar and 1340°C under anhydrous conditions and at 17 kbar and 1325°C in the presence of 1.5 wt % water. The OTB melt, on the other hand, coexists with olivine and orthopyroxene at 11 kbar and 1320°C under anhydrous conditions. The water contents in arc basalt magmas are estimated to be about 3, 1.5, and nearly O wt % for the AOB, HAB, and OTB, respectively, on the basis of the solubility limit of water in silicate melts. Based on these estimates and the experimental results, the AOB, HAB, and OTB magmas are suggested to segregate from the mantle at about 1320°C and at 23, 17, and 11 kbar, respectively. As the temperatures at the segregation of the magmas given above appear to be too high for a stable mantle geotherm, the mantle diapir is the most probable mechanism for the magma production in a subduction zone. Considering the heat of formation of melt in the diapir, the region with temperatures higher than 1400°C has to be present in the mantle wedge.

The anelastic properties of compressional waves in a peridotite have been determined in the laboratory at sufficiently high temperatures (to 1280°C) and pressures (to 0.73 GPa) to warrant comparison with seismic measurements of the Earth. A substantial decrease of Qp is observed at temperatures well below the onset of partial melting. Qp systematically increases with increasing pressure over the entire temperature range. Of major significance is the finding that Qp is dependent on the ratio of the temperatures to the melting (solidus) temperature; i.e., Qp depends on the homologous temperature. The pressure dependence of Qp appears through the pressure dependence of the solidus of the peridotite. Within the uncertainties of measurement of both Qp and the phase diagram, it appears that melting and high‐temperature anelastic properties have a common origin in peridotite. The homologous temperature dependence of Qp suggests that we may estimate the temperature and pressure dependence of Qp for peridotites of different compositions and possibly even for hydrous peridotites, if solidus temperatures are known as a function of pressure (a far easier measurement than elastic and anelastic properties). The activation volume of Qp is greatly reduced at high pressure, since the slope of solidus versus pressure rapidly decreases with increasing pressure. Pressure dependence of seismic velocity and melt fraction in peridotite also appears to be related to the homologous temperature. The Qp‐homologous temperature relation suggests a connection between Qp and the properties of the grain boundaries; that is, the major loss of seismic energy occurs at the grain boundaries. Grain boundary relaxation or high‐temperature background attenuation is a possible mechanism for the grain boundary damping. No frequency dependence of Qp is resolved (0<α<0.2 in Qp ∝ fα) over the pressure, temperature and frequency ranges of the measurement. The present results and the model of grain boundary relaxation suggest that an appropriate choice of grain size may give an ultrasonic Q that is applicable to the Earth. Experimentally determined anelastic properties of a peridotite are critical for modeling mechanical properties of the upper mantle. Implications of the results are as follows: (1) Seismic data commonly interpreted as indicating a partially molten asthenosphere may instead reflect a hot solid asthenosphere at 90–100% of the solidus temperature. (2) Partial melting may not produce any abrupt change of seismic velocity and Q; rather, elastic and anelastic properties of the upper mantle will change gradually at the boundary where the geotherm crosses the solidus. (3) There may be no sharp mechanical boundary between the lithosphere and the asthenosphere.

Abstract--A technique has been developed to determine attenuation in rocks at high temperature using a gas-media, high-pressure apparatus. A pulse transmission technique and a spectral ratio method are used to study compressional seismic properties of rocks. Seismic waves are transmitted to and from the sample through buffer rods of mullite. The effect of seismic wave reflections within the sample assembly are cancelled out by taking ratios of the spectra measured at different temperatures. In order to obtain good signal-to-noise ratio for resolving the attenuation at high pressure and temperature, special care is taken in the sample assembly and the ultrasonic coupling between the sample, buffer rods and transducers. A very tight connection of the sample-buffer rod-transducer is essential for obtaining high frequency signals ( > 300 kHz) at high temperature. A small mass is attached to each outside end of the transducer to drive low frequency signals ( < 250 kHz) into the sample. Before attenu~:tion measurements, the sample and the buffer rods are tightly compacted in a platinum tube at high pressure and room temperature to ensure pressure seal of the sample assembly. The frequency range of measurement covers 50 to 450 kHz for the sample. Attenuation is very small in the buffer rod compared to the sample for the entire temperature range of the study. Because of the small attenuation, a wide frequency band of 50 kHz to 3.2 MHz can be covered for investigating the attenuation in the buffer rod. The technique has been used to measure attenuation at high confining pressure, and temperatures including sub-and hyper-solidus of upper mantle rocks. Therefore, effects of partial melting on attenuation can be studied.The method is applied to the attenuation measurement in a peridotite as a function of temperature to 1225~ at 200 MPa confining pressure. At high temperature, signal amplitude decays more rapidly at high frequency than at low frequency, from which attenuation (and Q) can be determined using a spectral ratio method. No frequency dependence of Q is resolved for both the sample and the buffer rod over the entire temperature and frequency ranges of the measurement. The results show that Q decreases rapidly with increasing temperature even in the temperature range below the solidus of peridotites. Such temperature sensitivity of Q is probably more useful to probe thermal structure in the upper mantle than that of conductivity at temperatures below the solidus. The results in this study are compared with available seismic velocity, electrical conductivity and solidus data for peridotites, suggesting that there is no discontinuous change in both mechanical and electrical properties of peridotites at the solidus temperature. PAGEOPH,Even at hypersolidus temperatures, it appears that velocity drops and conductivity increases continuously (not abruptly) with increasing melt fraction. This implies that mechanical and electrical properties of the upper mantle will gradually change at the boundary where the geotherm cross...

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The normal spectral emissivity ε of four compositions in the Al-Ti binary liquid system was measured in dependence of the wavelength and temperature. It was found that all compositions show negligible temperature dependence. At a wavelength of 940 nm, the emissivity amounts to 0.37, 0.40, 0.32, and 0.31 for Ti, Al20Ti80, Al50Ti50, and Al70Ti30, respectively. The dependence of the emissivity on composition is in good agreement with literature data of binary and multi-component Al-Ti-based alloys. Using the classical Drude model, electrical resistivities are predicted for the Al-Ti system from the measured emissivities. Comparison with existing data from literature for Al show reasonable agreement.

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