Definitions and images to illustrate geological terms, links to images and website articles

igneous structures

Magma is molten (igneous) rock formed when Earth's radioactivity heats rocks – because of Earth's geothermal gradient, the deeper in the Earth, the greater the temperature.

◙◙ Rock Index: Igneous Rocks ◙◙

Magma that is emplaced below the surface when molten rock intrudes into or across strata of country rock cools and crystallizes in a variety of intrusive structures, including large plutonic and small hypabassal structures:

intrusive emplacement / structures: ▪ aplite, aplite dike (◙ aplite) ▪ batholithboudinbysmalithconcordantconformablediapirdiatremedikediscordantenclaveshypabassallaccolithslopolithsplutonsillsstratavolcanovein

structures reflecting flow/crystallization within magma chambers: ▪ cumulatesenclavesschlierenxenoliths

magmatic processes: ▪ anatexisassimiliationexchange of volatilesfractional crystallizationigneous rocksigneous structuresmagmamagmatic differentiationmagmatic mixingophiolite complexestectonics

When melted rock flows extrusively or erupts explosively at the surface is called lavaHawaii's and Iceland's basalt lavas fountain or flow freely, while other lavas are sticky and explosive, producing deadly pyroclastic flows (Mount St. Helens, Vesuvius, Pinatubo).

extrusive: ▪ aphanitic texturelavatectonismvolcanoesvulcanism

Links: Maps of North American rock types : rock types - metamorphic, plutonic, sedimentary, volcanic; tapestry of time and terrain, terrain.

Labels: , , , , , ,

. . . evolving since 01/07/07