Basalts Dredged from the Northeastern Pacific Ocean
Volcanic rocks dredged from seamounts, fault ridges, and other major geological features of the northeast Pacific Ocean include a wide variety of basalts. Most of these are vesicular, porphyritic types with near analogues in the Hawaiian and other oceanic islands. In addition, aluminous basalts and diabasic theoleiites impoverished in potassium also occur. There is no simple correlation of composition, degree of oxidation, vesiculation, or hydration of these basalts with texture, or depth of dredge site. Most samples appear to have been extruded at much shallower depths than those now pertaining at the dredge site. The distribution of these basalts suggests that the andesite line coincides with or lies on the continent side of the foot of the continental slope.
Dredged Basalt from Giacomini Seamount
DURING the cruise in July 1965 of the RV Acona of the University of Alaska Institute of Marine Science, two angular blocks of basalt (15×12×5 cm3 and 20×15×9 cm3) were dredged from the summit area of Giacomini Seamount (56° 24′ N, 146° 34′ W), at a depth of 790 m (Fig. 1). Several hundred igneous, metamorphic and sedimentary pebbles, cobbles and boulders were also recovered in the dredge haul; they showed a wide range of rounding and a very thin coating of manganese oxide, and were very similar to those recovered from the summit areas of Gilbert, Miller, Pratt and Ga-3 Seamounts in the Gulf of Alaska Seamount Province, as previously reported by Menard1 and others. Menard concluded that these gravels were ice-rafted glacial drift, an interpretation which is strongly supported by the presence of faceted and striated rocks among the Giacomini erratics.
The micro-mechanical behaviour of artificially cemented sand particles under compression and shear
The mechanical behaviour of cemented sands at macro-scale has been widely studied in the past, while there is still a lack of laboratory test data for the micro-mechanical response. Therefore, a series of uniaxial compression and tangential shear tests on artificially cemented sand particles have been conducted using a microscope to observe their behaviour. First, the consistency of cemented particles with different cementing agents is discussed. Three breakage modes are proposed according to the images taken using a microscope camera. A new parameter named ‘local roundness at contact’ is introduced to emphasise the effect of contact morphology on sample strength. Moreover, the effect of bond thickness on the mechanical response of cemented particles has been investigated. Finally, the shear strength parameters of artificially cemented sand samples have been determined for two different sample diameters.