Igneous intrusions and lava flows Flashcards
Dyke
A discordant sheet like intrusion
Transgressive sill
A sheet like intrusion that cuts across the bed
Sill
A concordant sheet like intrusion
Country rock
The rock into which an igneous rock has been intruded
Chilled margin
Where the igneous rock has cooled rapidly so has fine crystals
Intrusion
Composed of igneous rock formed below the earth’s surface, where magma is forced into pre-existing rocks
Batholith
A large igneous intrusion which may be an aggregate of plutons
Hypabyssal
When igneous rocks form at relatively shallow depths below the earth’s surface
Plutonic
When igneous rocks form deep below the earth’s surface
Concordant
Intrusions are parallel to the existing beds
Discordant
Intrusions cut across the existing beds
Baked margin
In the country rock where it was heated by the intrusion and altered
Assimilation
The melting process that incorporates blocks of country rock, freed by stoping, into the magma
Xenolith
Pieces of rock within an igneous rock which have not been derived from the original but have been introduced from elsewhere. These are usually from the surrounding country rock.
Stoping
The process that accommodates the magma, as it moves upwards into the country rock, by the mechanical fracturing of the surrounding country rock.
Partial melting
It occurs when only a portion of rock is melted. When a rock is heated, those minerals with lower melting temperatures will melt. Those with higher melting temperatures will remain solid
Diapir
A body of relatively low density material that pierces and rises up through overlying material of higher density.
Volcanic plug
An intrusion formed when magma crystallises in the conduits or vent of the volcano.
Ring dykes
Roof collapses when the magma pressure decrease in the underlying pluton or magma chamber. Magma oozes out into the fractures surrounding the collapse and produces dykes that dip away from the centre of the underlying pluton or magma chamber.
Cone sheets
Magma pressure pushes up and fractures the overlying roof rocks. Magma is forcibly injected into the fractures producing a conical emplacement with the dykes dipping toward the buried centre of the magma source.
Cumulate
An igneous rock produced by gravity settling of crystals in a magma
Palaeosol
A soil horizon that was formed in a past geological age
What’s the difference between sills and lava flows?
Lava flows cool at the earth’s surface and are extrusive igneous rocks whilst sills cool below the earth’s surface and are intrusive igneous rocks.
How can baked margins be used to distinguish sills form lava flows?
Sills have two baked margins where as lava flows only have one
