Isovolumetric weathering of granite in Wake County, North Carolina.

摘要

This dissertation examined the influence of joint orientation on isovolumetric weathering of saprolite developed on the Rolesville granitic batholith at Knightdale, North Carolina. Rock density (rhos) (mu alpha 0.05) was 2.62 +/- 0.01 g cm-3. Mass altered per unit volume (mA/VT) of saprolite was taken as the difference between rhos and primary mineral mass remaining per unit volume (m10R/VT). Altered mass lost per unit volume (mAL/VT) was taken as the difference between rhos and bulk density (rho b). Altered mass retained per unit volume (mAR /VT) was taken as (mA/VT) - (m AL/VT).; Saprolite with steeply-dipping joints showed a uniformly sandy texture. The distribution (mass percent) of sand-, silt-, and clay-sized particles (mu alpha 0.05) was 82.4 +/- 2.7, 10.3 +/- 1.8, and 2.3 +/- 2.5, respectively, on a whole saprolite basis, and rhob (mu alpha 0.05) was 1.66 +/- 0.06 g cm-3. Saprolite with horizontally-oriented unloading joints was extensively altered and occurred between horizontal slabs of unweathered rock. The saprolite was composed of sandy layers alternating with clayey layers on the scale of approximately 1 to 2 cm. The distribution of sand-, silt-, and clay-sized particles (mu alpha 0.05) in the saprolite was 50.1 +/- 10.4, 3.1 +/- 0.5, and 46.8 +/- 10.5, respectively, on a whole saprolite basis. Bulk density (mu alpha 0.05) was 1.55 +/- 0.01 g cm -3. The mean content of sand-, silt-, and clay-sized particles in the two saprolites differed statistically at alpha = 0.001, and mean bulk density differed at alpha = 0.01.; Density of unweathered granite (mu 0.05) was 2.62 +/- 0.01 g cm-3. Calculated mean (mu alpha 0.05 ) values of mA/VT, mAL/VT, and mAR/VT (all in g cm-3) in saprolite with steeply-dipping joints were 1.17 +/- 0.12, 0.96 +/- 0.06 and 0.21 +/- 0.05, respectively. Corresponding values in saprolite with horizontal joints were 1.85 +/- 0.15, 1.08 +/- 0.02 and 0.77 +/- 0.17, respectively. Calculated mean (mu alpha 0.05) values of m AL/MA were 0.82 +/- 0.03 for the former saprolite and 0.58 +/- 0.06 for the latter, indicating greater leaching losses in the former. Differences in the calculated means of mA/VT, mAR/VT, mAR/mA and mAL/m A in the two saprolites are statistically significant at alpha = 0.001, and mAL/VT differed at alpha = 0.05.; Saprolite with steeply dipping joints was composed predominantly of plagioclase and potassium feldspar. Saprolite with horizontal joints contained approximately equal proportions of potassium feldspar and kaolinite (or halloysite). Nordstrandite occurred in both types of saprolite.; Saprolite was classified based on the relative proportions of (m1 0R/VT) 100/rhos, (mAR/V T) 100/rhos, and (mAL/VT) 100/rho s. Saprolite with steeply-dipping joints classified as 'moderately altered, highly leached', and saprolite with horizontal joints classified as 'severely altered, moderately leached'.; Joint orientation appears to be a significant variable in saprolite formation. (Abstract shortened by UMI.)