The
Grenville in Western Quebec - Glossary
Grenville Glossary
- accretion
- A theory of continental growth by the addition
of successive geosynclines to the craton.
- allocthon
- A mass of rock that has been moved a long distance
from its place of origin, commonly by a tectonic process such as overthrusting.
- Archean
- Said of the rocks of the Archeozoic.
- Archeozoic
- The earlier part of two great divisions of the
Precambrian time.
- autochthon
- A body of rocks that remains at its site of origin,
where it is rooted to its basement. Rocks of an autochthon may be mildly
to considerably deformed.
- craton
- A part of the earth's crust that has attained
stability and has been little deformed for a long time. The term is restricted
to continents.
- cross-section
- A diagram showing the features transected by a
vertical plane, e.g. a vertical section through an orebody, an anticline,
or a fossil.
- diorite
- 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.
- footwall
- The mass of rock beneath a fault.
- ductile
- Said of a rock that is able to sustain, unde a
given set of condition, 5-10% deformation before fracturing or faulting.
- foreland
- 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.
- geochronology
- 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.
- geophone
- A seismic detector, placed on or in the ground,
that responds to ground motion at its point of location.
- granite
- Broadly applied,any quartz-bearing plutonic rock
composed entirely of crystals, i.e. having no glassy part.
- greenstone
- A field term for any compact dark-green altered
or metamorphosed basic igneous rock that owes its color to chlorite, actinolite,
or epidote.
- Grenville orogen
- 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.
- Grenville province
- A series of the Precambrian of Canada and New
York.
- impricate
- Overlapping, as shingles or tiles on a roof.
- klippe
- An isolated rock unit that is an erosional remnant
or outlier nof a nappe.
- Lithoprobe
- 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.
- lithosphere
- 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.
- mafic
- Said of an igneous rock composed chiefly of one
or more ferromagnesian, dark-colored minerals in its mode; also said of
those minerals.
- metamorphism
- 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.
- metamorphic grade
- The intensity of metamorphism, measured by the
degree of difference between the parent rock and the metamorphic rock.
- meteorite
- Any solid object from interplanetary space that
has fallen to the earth's surface without being vaporized during its passage
through the atmosphere.
- Mohorovicic discontinuity
- 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.
- para-autochthon
- Said of a rock unit that is intermediate in tectonic
character between autochthon and allocthon.
- parautochthonous
- Said of a rock unit that is intermediate in tectonic
character between autochthonous and allochthonous.
- plutonic
- Pertaining to rocks formed by any process at great
depth.
- orogenic belt
- 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.
- plate tectonics
- 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,
- Proterozoic
- The more recent of two great divisions of the
Precambrian.
- Precambrian
- All geologic time, and its corresponding rocks,
before the beginning of the Paleozoic; it is equivalent to about 90% of
geologic time.
- radiometric dating
- 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.
- seismic
- Pertaining to an earth vibration, including those
that are artificially induced.
- seismic record
- In geophysical exploration, a photographic or
magnetic record of reflected or refracted seismic waves.
- shear zone
- 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.
- tectonics
- 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.
- tonalite
- A group of plutonic rocks having the composition
of diorite but with an appreciable amount of quartz, i.e. between 5 and
20 percent.
- underthrust
- A thrust fault in which the footwall was the active
element.
