Автор(ы):Ayalon A., Summer N.S.
Издание:Pergamon, 1995 г., 14 стр.
Dike intrusion into unconsolidated sandstone and the development of quartzite contact zones

Shallow, near-surface magma emplacement into a porous, unlithified sandstone occurred by forceful dike dilation and was accompanied by a localized hydrothermal event. Petrographic fabric, authigenic mineralogy and petrophysical data, grade smoothly through the quartzite contact zone outward into the friable Inmar sandstone of Makhtesh Ramon, Israel. Quartz grain deformation, fracturing and rehealing of grains, and pressure solution constitute overwhelming evidence of a compressive environment adjacent to dike margins, albeit with temperatures and pressures insufficient to fully recrystallize detrital grains. Dikes were accommodated primarily by the repacking of the sandstone with both brittle and elastic grain interaction. Post emplacement heating together with elastic compressive stress dissipation, lead to fracture healing and pressure solution. The occasional columnar-jointing must be related to thermal contraction of the quartzite during later cooling and resulting mode I cracks. The alteration of both contact zone and dike material occurred via a transitory and confined hydrothermal seepage up dike margins. Elsewhere around the world highly altered intrusions bordered by indurated sometimes uniformly jointed sediments, may also be the result of forceful magma emplacement and hydrothermal alteration at near-surface levels.

ТематикаРегиональная геология
Автор(ы):Bas Den Brok
Издание:Journal of Structural Geology, 1996 г., 2 стр.
The effect of crystallographic orientation on pressure solution in quartzite

By measuring the degree of flattening and the orientation of the c-axis of single quartz grains in a naturally deformed ("cleaved") sandstone, Becker (1995) showed that: "quartz grains with a small angle between c-axis and the Z-axis of shortening exhibit the least amount of pressure solution, whereas grains with c-axes oriented at about 50° to Z manifest the highest degree of pressure solution". I briefly present some experimental results that show exactly the same. <...>

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