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We performed ultrasonic pulse echo measurements on high-purity polycrystalline cerium across the isostructural γ to α-fcc-to-fcc transition, up to 13 kbar and then back down to 0.3 kbar. Our results confirm the anomalous decrease of the longitudinal sound velocity in the γ-phase approaching the transition, a significant hysteresis loop, and definitively highlight the strong difference in the long wavelength limit of the lattice dynamics of the γ and α phases. We have also studied the kinetics of the transition, which is well described by an Arrhenius behavior, with an activation volume of 10 cm3/mol. [ABSTRACT FROM AUTHOR]

To date, most research utilizing the diamond anvil cell (DAC) at very high pressure has been conducted with polycrystalline samples, thus the results are limited to addressing average bulk properties. However, experiments on single crystals can yield data on a range of orientation-dependent properties such as thermal and electrical conductivity, magnetic susceptibility, elasticity and plasticity. Here, we report new procedures to produce extremely high-quality metallic single crystal samples of size compatible with DAC experiments in the Mbar range. So far, we have produced samples of zinc, Al 2 O 3 , cobalt, molybdenum and cerium, and have evaluated the quality of the finished samples with white-light interferometry, synchrotron X-ray diffraction and inelastic X-ray scattering. [ABSTRACT FROM AUTHOR]

Abstract: Along the San Juan de Marcona Bay of southern Peru, two spectacular sequences of preserved marine terraces record net Quaternary uplift. Previous geomorphic analysis of these paleo-shorelines has revealed evidence of upper plate deformation and regional uplift. However, in the absence of a robust absolute dating method, these studies contain substantial uncertainties concerning the numerical dating of these marine markers and thus the corresponding calculated surface uplift rates. However, field mapping, surveying the neotectonic features and 10Be dating of abraded surfaces contained within two sequences of marine terraces along this margin should allow for the robust calculation of Pleistocene uplift rates. The San Juan de Marcona Bay lies on the southern flank of the subducting and south-migrating aseismic Nazca Ridge where the maximum rates of coastal uplift are expected. In this locality, we measure high uplift rates ranging from 0.4m/ka to 0.9m/ka during the Pleistocene. Margin-parallel normal faults displace several marine terraces and influence the development of bays, thereby contributing to the configuration of paleo- and present-day coastlines. The faults have relatively low slip rates, <0.1m/ka over 400ka, and have been inactive for the last 80ka. The presence and activity of these normal faults can be directly linked to subduction zone processes, with the release and accommodation of short-term coseismic compression during megathrust subduction-zone events. In contrast, the regional permanent uplift is probably controlled by post-seismic and/or interseismic strain accumulation over longer time-scales due to inelastic behavior of the upper plate. Since at least the latest Pliocene, the San Juan de Marcona area has experienced long-term regional tectonic uplift that has increased since about 800ka due to the southward migration of the subducting Nazca Ridge. Based on migration velocity and geometry of the ridge, the influence of the Nazca Ridge on the uplift of the forearc should account for ~0.4m/ka within 145km south of the ridge axis. Hence, most of the post-400ka mean uplift rate of the San Juan de Marcona area could be explained by the Nazca Ridge subduction. [Copyright &y& Elsevier]

Abstract: Pleistocene uplift of the Chilean coast is recorded by the formation of wave-cut platforms resulting from marine erosion during sea-level highstands. In the Altos de Talinay area (~31°S), we have identified a sequence of 5 wave-cut platforms. Using in situ produced 10Be exposure ages we show that these platforms were formed during interglacial periods at 6, 122, 232, 321 and 690 ka. These ages correspond to marine isotopic stages (MIS) or substages (MISS) 1, 5e, 7e, 9c and 17. Shoreline angle elevations used in conjunction with our chronology of wave-cut platform formation, illustrate that surface uplift rates vary from 103±69 mm/ka between 122 and 6 ka, to 1158±416 mm/ka between 321 and 232 ka. The absence of preserved platforms related to the MIS 11, 13 and 15 highstands likely reflects slow uplift rates during these times. We suggest that since 700 ka, the Altos de Talinay area was predominantly uplifted during 2 short periods following MIS 17 and MISS 9c. This episodic uplift of the Chilean coast in the Pleistocene may result from subduction related processes, such as pulses of tectonic accretion at the base of the forearc wedge. [Copyright &y& Elsevier]