A groupe of plutonic rocks intermediate in composition between
acidic and basic, characteristically composed of hornblende, oligoclase, or andesine,
pyroxene, and sometimes a little quartz.
A stable area marginal to an orogenic belt, toward which the rocks of the belt were
thrust or overfolded. Generally the foreland is a continental part of the crust, and is
the edge of the craton or platform area.
Study of time in relationship to the history of the Earth, esp. by the absolute age
determination and relative dating systems developed for this purpose.
A name that is widely used for a major plutonic, metamorphic, and deformational event
during the Precambrian which affected a broad province along the southeastern border of
the Canadian Shield.
A Canadian national Earth science research project to investigate the 3-dimensional
structural evolution of Canada's landmass and continental margins. Research is conducted
in a coordinated, integrated, multidisciplinary fashion, with seismic techniques
spearheading the research. The
LITHOPROBE Home Page.
A layer of strength relative to the underlying asthenosphere. It includes the crust and
part of the upper mantle and is of the order of 100 km in thickness.
The mineralogical, chemical, and structural adjustment of solid rocks to physical and
chemical conditions imposed at depth below the surface zones of weathering and
cementation, whcih differs from the conditions under which the rocks originated.
The boundary surface or sharp seismic-velocity discontinuity that separates the Earth's
crust from the subjacent mantle. It marks the level in the Earth at which the P-wave
velocities change abruptly from 6.7-7.2 km/sec to 7.6-8.6 km/sec on average.
A linear or arcuate region that has been subjected to folding and other deformation
during an orogenic cycle. Orogenic belts are mobile belts during their formative stages,
and most of them later became mountain belts by postorogenic processes.
A theory in which the surface of the Earth is made up of a number of rigid plates moving
relative to each other, separating at mid-oceanic ridges where new ocean-floor is produced
and converging at subduction zones, where one plate descends beneath another,
Calculating an age in years for geologic materials by measuring the presence of a
radioactive element; based on nuclear decay of naturally occurring radioactive isotopes.
A tabular zone of rock that as been crushed and brecciated by many parallel fractures
due to shear strain. Such an area is often mineralized by ore-forming solutions.
A branch of geology dealing with the broad architecture of the outer part of the earth,
that is, the major structural or deformational features and their relations, origin, and
historical evolution. It is closely related to structural geology, but tectonics generally
deals with larger features.