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.