Microcracks and energy. Progress report, April 1, 1980-February 28, 1981

The study of the microcracks in granites from Redstone Quarry (NH), Granite Mountains (WY), and Sherman Mountain area (WY) shows the following: microcracks are abundant; most microcracks are sealed; common sealing phases are carbonate minerals, quartz, magnetite, hematite, Nb-bearing phosphate, a Ca and REE-bearing mineral, quartz, and feldspar; and many microcracks contain U. It is concluded that microcracks were the channels through which U migrated; that REEs are mobile; and that the mobilities of U and REEs may be related. It is suggested that sealed microcracks can be dated absolutely with modified fission track techniques. Cracks that contain U and cut quartz and also cracks that contain quartz and cut uraniferous minerals can be dated. Heat flow and heat generation in several provinces were examined and the data used to constrain models of the distribution of U, Th, and K in the crust. Seismic velocity was measured as a function of direction in several locations in New Hampshire where other researchers have mapped joints. Anisotropies in the velocities were found that correlate roughly with the joint distributions. The sealed fractures associated with a dike penetrated by the corehole at Redstone Quarry were examined. It is concluded tentatively that the cooling of rock in-situ from 600 to 1000C produced a significant volume of open fractures