Goban powder3/30/2023 ![]() Don’t wash stones in a metal or glass tub, you risk chipping the stones.Slate/glass is hard, it will scratch clams. Don’t wash white clams with black pieces.Don’t fidget with stones while playing - it puts oil on them and is a bad habit.Don’t use a chlorine bleach, at all, ever.When in doubt, treat them like your teeth: keep them away from water that is too hot or too cold, rub them only with something soft like a plastic brush, and keep them clean! Unlike glass, they have a soft feel and each has a different pattern. Similar weathering could also have reduced the concentrations of radionuclides at Site 900.Clamshell stones are a delight. This result is not surprising as typical mantle peridotites have low concentrations, and these concentrations (particularly U 238) would be further reduced during hydration. The serpentinite samples from Site 897 have negligible radionuclides. ΜW/m 3 for the lower continental crust (Galson, 1983 Ashwal et al., 1987 Fountain et al., 1987 Mareschal et al, 1989). ΜW/m 3 for tholeiitic basalts (Stacey, 1992) and similar to values of 0.4 Values for Site 900 are higher than typical values of 0.08 The average heat production for the Galicia Bank granodiorites are lower than the average for Paleozoic granites observed in Brittany (3.3Ġ.6 µW/m 3 Jolivet el al., 1989) and Wales and Cornwall (3.1Ģ.1 µW/m 3 Richardson and Oxburgh, 1978), as might be expected. ΜW/m 3 for a dolomite sample from Galicia Bank, values can be separated into three distinct groups: Galicia dredge samples, primarily granodiorites (A av = 1.67Ġ.31 µW/m 3) Hole 900A samples, primarily metamorphosed gabbros (A av = 0.21Ġ.19 µW/m 3) and serpentinized peridotites from Holes 897C and 897D (A av < 0.01 µW/m 3). The heat production values are shown as histograms in Figure 3. The overall reproducibility was verified by measuring different aliquots of the same sample and was better than 5%.Ĭoncentrations of the radioelements and the resulting radiogenic heat production are given in Table 1. For some samples, the K concentration was also measured with the standard X-ray spectrometry technique (Schroeder et al., 1980). For K 41, gamma rays at 1525 kev from the disintegration of K 42 (half life 12 hr) were counted. For Th 232, the gamma rays at 312 kev were produced by disintegration of Pa 233 (half life 27 days). For U 238, gamma rays at 277 kev from the disintegration of Np 239 (half life 2.35 days) were counted. Gamma rays were measured with planar low-energy photon scintillometers and coplanar GeLi detectors. ![]() After irradiation, the concentrations of U, Th, and K were measured by gamma-ray spectrometry, following the semi-absolute method of Bergerioux et al. The samples were subjected to a flux ofĥ 10 11 neutrons/cm 2-s for 2 hr. Samples were crushed to a fine powder and neutron activated in the "slowpoke" reactor at École Polytechnique (Montréal). The technique used for measuring the concentrations of radioelements in rocks is described by Mareschal et al. A general description of the sampled rock types and the location of each sample are given in Table 1. ![]() Six samples each from Sites 897 and 900 were analyzed for the concentration of radiogenic heat-producing elements four samples were analyzed from each of the dredge sites GAL 02,07/08, and 11. Also shown are the location of three seismic profiles (Lusigal 12, Resolution 3, and Sonne 16) that have been used to construct a seismic transect along the drill sites (Shipboard Scientific Party, 1993). The location of the Leg 149 sites in the Iberia Basin and dredge sample locations adjacent to Galicia Bank are shown in Figure 2. However, continental heat flow and radiogenic heat production measurements are lacking within the Paleozoic section of northwestern Spain, immediately adjacent to the Leg 149 drill sites and to previous drill sites off Galicia Bank. MW/m 2) to lower oceanic values (generally <60 mW/m 2). Values of radiogenic heat production in the Paleozoic metamorphosed cratons that border these margins are generally high (e.g., Richardson and Oxburgh, 1978 Jolivet et al., 1989), and there is a clear decrease from higher continental values (often >90 This region has the largest number of heat flow measurements relevant to the study of passive margins, with numerous values on land (Lucazeau and Vasseur, 1989) and three detailed transects at sea across Goban Spur, Galicia Bank, and the Amorican Margins (Foucher and Sibuet, 1980 Louden et al., 1991). The location and generalized values for marine and land heat flow are shown in Figure 1 for the regions adjacent to the Leg 149 sites.
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