Effusive Badi Silicic Volcano (Central Afar, Ethiopian Rift); Sparse Evidence for Pyroclastic Rocks

We report field observation, textural description (thin section and scanning electron microscope (SEM)) and mineral chemistry (backscattered electron imaging and dispersive X-ray analysis) for rhyolitic obsidian lavas from previously under described effusive Badi volcano, central Afar within the Ethiopian rift. These rhyolitic obsidian lavas are compositionally homogeneous and contain well developed flow bands. Textural analysis is undertaken to understand the formation of flow band, and to draw inferences on the mechanism of emplacement of this silicic volcano. Flow band arises from variable vesicularity (i.e., alternating domains of vesicular, light glass and non-vesicular, brown glass). Such textural heterogeneities have been developed during distinct cooling and degassing of the melt in the conduit.

The Model Analysis of Inclusion Moving in the Swirl Flow Zone Sourcing from the Inner-Swirl-Type Turbulence Controller in Tundish

In order to improve the inclusion removal property of the tundish, the mathematic model for simulation of the flow field sourced from inner-swirl-type turbulence controller (ISTTC) was developed, in which there were six blades arranged with an eccentric angle (θ) counterclockwise. Based on the mathematical and water model, the effect of inclusion removal in the swirling flow field formed by ISTTC was analyzed. It was found that ISTTC had got the better effect of inhibiting turbulence in tundish than traditional turbulence inhibitor (TI). As the blades eccentric angle (θ) of ISTTC increasing, the intensity of swirling flow above it increased. The maximum rotate speed of fluid in swirling flow band driven by ISTTC (θ=45°) was equal to 25 rmp. Based on the force analysis of inclusion in swirling flow sourced from ISTTC, the removal effect of medium size inclusion by ISTTC was attributed to the centripetal force (Fct) of swirling flow, but removal effect of ISTTC to small size inclusion was more depend on its better turbulence depression behavior.

OBSIDIAN SUB-SOURCES AT THE ZARAGOZA-OYAMELES QUARRY IN PUEBLA, MEXICO: SIMILARITIES WITH ALTOTONGA AND THEIR DISTRIBUTION THROUGHOUT MESOAMERICA

We present data produced through archaeological and geological survey, as well as geochemical analysis of the Zaragoza-Oyameles obsidian source area located on the northern and western flanks of the Los Humeros Caldera in eastern Puebla, Mexico. One result of the intensive archaeological surface survey of this obsidian source area was the identification of 117 obsidian flow-band exposures. Geologic samples from 40 of these were submitted for instrumental neutron activation analysis. Eighty-five projectile points collected from the surface were characterized using portable X-ray fluorescence. These analyses identified three sub-sources: Z-O1, Potreros Caldera, and Gomez Sur. The Gomez Sur sub-source appears chemically similar to the previously identified Altotonga source, located 25 km to the northeast. Results of the geological survey help elucidate the relationship of Altotonga obsidian with the Zaragoza-Oyameles source area. The data from the three sub-sources are compared to all consumer site data attributed to the Zaragoza-Oyameles source in the Missouri University Research Reactor database. Results indicate that the majority of consumer samples throughout Mesoamerica match the Z-O1 sub-source, while 4 percent match the Potreros Caldera sub-source. This information, combined with the Gomez Sur data, is discussed in terms of economic relations with the regional center of Cantona. Obsidian procurement and distribution may have been more nuanced than previously modeled. We suggest that a number of potentially independent communities in addition to Cantona may have been involved in distributing this obsidian throughout Mesoamerica.

Sliding Wear of Copper Against Alumina

OFHC copper pins with 10 ppm oxygen were slid against alumina at a load of 50 N and sliding speeds of 0.1 ms−1 to 4.0 ms−1. The wear characteristics of copper were related to the strain rate response of copper under uniaxial compression between strain rates of 0.1 s−1 and 100 s−1 and temperatures in the range of 298 K to 673 K. It is seen that copper undergoes flow banding at strain rates of 1 s−1 up to a temperature of 523 K, which is the major instability in the region tested. These flow bands are regions of crack nucleation. The strain rates and temperatures existing in the subsurface of copper slid against alumina are estimated and superimposed on the strain rate response map of copper. The superposition shows that the subsurface of copper slid at low velocities is likely to exhibit flow band instability induced cracking. It is suggested that this is the reason for the observed high wear rate at low velocities. The subsurface deformation with increasing velocity becomes more homogeneous. This reduces the wear rate. At velocities >2 ms−1 there is homogeneous flow and extrusion of thin (10 μm) bands of material out of the trailing edge. This results in the gradual increase of wear rate with increasing velocity above 2.0 ms−1.

Mass-Balance Studies of Ice Streams A, B, and C, West Antarctica, and Possible Surging Behavior of Ice Stream Β

Recent airborne radar sounding has made it possible to map accurately three of the West Antarctic ice streams that flow into Ross Ice Shelf. In previous work we have shown that ice streams A and Β have negative mass balances, whereas inactive Ice Stream C has a strongly positive balance. In this paper we examine in more detail the balance of ice streams A and Β by constructing several gates across them where velocities and ice thicknesses have been measured. We then examine the net fluxes in blocks of the ice streams delimited by successive pairs of gates.Ice Stream A as a whole is apparently discharging more ice than is being accumulated in the catchment area, and currently thinning at the rate of 0.08 ± 0.03 m a−1. The situation on Ice Stream Β is more complex. We have calculated separately the fluxes from tributary ice streams Bl and B2, and examined their individual fluxes within Ice Stream Β by tracing the suture zone between them down-stream of their confluence. The flow band that is the farthest up-stream (girdle), encompassing both Ice Stream Bl and Ice Stream B2, shows a strongly negative net flux that we attribute to lateral and headward expansion of the ice streams within the band. Such expansion can occur by lateral movement of an ice-stream boundary, by temporally accelerating ice flow at the head of the ice stream, or by activation of formerly slowly moving “island” or “peninsula” ice.The imbalance in this flow band, 8 ± 2 km3 a−1 (equivalent mean rate of change in ice thickness, is nearly half of the total excess outflow for the Ice Stream Β system (20 ± 4 km3 a−1), — the remainder is mostly the difference between flow through the uppermost gate and mass input to the catchment area .When for the whole of Ice Stream Β is plotted against the distance along the entire Ice Stream B, the overall pattern appears to be of mild thinning in the catchment, intense thinning in the girdle, and thickening in the main body of the ice stream, which decreases with distance from the girdle. This global behavior is suggestive of a major transient response, resulting from either a change in the internal dynamics or an internal adjustment to a change in the external forcings. We argue that there are a number of conditions which could lead to this type of response pattern. One possibility is a surge. Although the distribution of the changes in thickness is one characteristic of a surge, we caution that this alone is not sufficient to classify the behavior as a surge. Several other possibilities that support a picture of Ice Stream Β as a system in the process of dynamic change and in unsteady state are discussed.At present, Ice Stream C and its catchment area are thickening over their entire area The present surface elevation does not suggest that Ice Stream Β has captured part of Ice Stream C. Moreover, the shut-down of Ice Stream C and the large mass imbalance of Ice Stream Β are not related.