semiconformable alteration zone

^{GLOSSARY OF VOLCANIC TERMS}

A regional zone of hydrothermal alteration typically characterized by a sheet-like or cloud-like geometry. Semiconformable alteration zones are generally quite extensive in permeable rock units (e.g. tuffs, medium- to coarse-grained clastic sediments and sedimentary rocks), and are generally patchy in less permeable rock units (e.g. lavas, intrusions). These zones commonly are found along the periphery of "pipe-like" alteration zones, which are generally confined to regions in close proximity to synvolcanic structures (e.g. synvolcanic faults zones) (Morton and Franklin, 1987).