Absaroka Sequence - A sequence of Permian-Pennsylvanian sediments bounded by both above and below by a regional unconformity and recording an episode of marine transgression over an eroded surface, full flood level of inundation, and regression from the craton.
Abyssal plains – Broad and very flat submarine plains of the ocean covered with a layer of pelagic (deep sea) sediment between the depths of 3 km to 5 km.
Acadian Orogeny - An episode of mountain building in the northern Appalachians during the Devonian Period.
Acanthodians - The earliest known vertebrates(fishes) with a movable, well-developed lower jaw, or mandible; hence, the first jawed fishes.
Accommodation zones – A region where two rift segments interact and connect containing complex deformation from strike slip, dip slip and oblique slip faulting.
Accretionary Complexes – At subduction zones it is the fraction of the subducting plate that gets left behind and accumulates at the leading edge of the overriding plate.
Accretionary prism or accretionary wedge – the accumulation of slivers of oceanic crust and mantle from thrusting and deformation resulting from plate convergence.
Accretionary terrane - A block of continetal crust having fault boundaries that is geologically distict from surrounding terranes.
Achondrites – a class of meteorite known as stones (made up of silicate minerals) that do not contain chondrules.
Adriatic Plate – A small tectonic plate in the middle of the orogens Apennines, Alps and Dinarides carrying primarily continental crust that broke away from the African plate in the Cretaceous period. The term Adriatic plate usually refers to the northern part of the Apulian Plate. The Adriatic/Apulian plate contain the eastern part of the Italian Peninsula and the Adriatic Sea.
Advection – The process in which moving fluid brings or removes heat to or from a solid. Example – Hot magma passes through fractures or faults and heats the surrounding rock. Cooling by advection can occur when cool seawater makes its way into the oceanic crust absorbs the heat rises and carries the heat back to the sea.
African Plate – A major tectonic plate that includes the continent of Africa and ocean crust that lies between the continent and surrounding ocean ridges.
Amorphous – lacks a crystalline structure.
Amphibolite – A metamorphic rock consisting mainly of hornblende and plagioclase and can be foliated or non-foliated. The protolith for this rock is either a mafic igneous rock or greywacke.
a b James Furman Kemp: A handbook of rocks for use without the microscope : with a glossary of the names of rocks and other lithological terms. 5. Aufl., New York: D. Van Nostrand, 1918, pp. 180 , 240 : C. E. Dutton, 4th Annual Report U.S. Geological Survey, 1883, S. 95; Bulletin of the Geological Society of America, Volume 25 / Geological Society of America. 1914, p. 639
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