Earth Materials Lecture 15: Intrusions Flashcards
Define and Describe a Hypabyssal intrusion
Igneous rock formations that occur at shallow depths in the Earth’s crust.
- Shallow crustal levels.
- Often minor intrusions.
- Dykes, sills, cone sheets and ring dykes
Define and Describe an Plutonic intrusion
Igneous rocks that solidify deeper underground.
- Deep crustal levels,
- Large scale, major intrusions.
- Stocks, batholiths; lopoliths and ~laccoliths.
Define and Describe a Dyke (hypabyssal intrusion)
A large slab of (igneous) rock that cuts through another type of rock
Dyke swarms - collection of radiating, arcuate, or linear mafic dikes
Associated with continental rifting.
May radiate. Ancient to recent.
Define rifting/continental rifting
Cause to break away through faulting caused by plate tectonics.
Continental rifting is a thinning process of the lithosphere ultimately leading to the rupture of the continent and the formation of a mid-oceanic ridge
Define:
Funnel dyke
Ring dyke
Cone sheet
A funnel dyke appears as a dyke in outcrop, but has a V-shaped cross-section that narrows towards the bottom. It looks like a funnel
E.g. Muskox, Canada/ Jimberlana, Australia /Great Dyke, Zimbabwe.
A ring dyke is a dyke that is circular or oval. Forms around a collapsed magma chamber.
The Loch Ba Ring Dyke, Mull, NW Scotland.
A cone sheet is a thin, inclined sheet of igneous rock that forms a downward-pointing cone shape/shape of an “inverted cone” .Form when magma exerts upward pressure.
Ardnamurchan, NW Scotland
Define and describe sills
Tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or along the direction of foliation in metamorphic rock
Sills can look like a line/ linear chunk of different rock in a cliff or mountain face (E.g. Finger mountain sill). Or can just look like an uplift of different rock in the ground/sediment (e.g. the Whin sill at Hadrian’s wall)
Describe the two types of Plutonic intrusions
Felsic:
* Stocks, bosses, and batholiths.
* Laccoliths.
Basic – ultrabasic:
* Lopoliths and funnel shaped intrusions
Define and Describe a Batholith
Batholiths are largest type of intrusive igneous intrusion.
surface area over 100 square kilometers
Typically formed from the crystallization of large volumes of magma.
giant underground mountains of granite, diorite, or other felsic (silica-rich) rocks.
Often form during mountain building events due to the melting of continental crust.
E.g. The Cornubian Batholith,
SW England
Define and Describe a Stock/Boss
Stocks similar to batholiths but smaller
- Typically less than 100 square kilometers.
Stocks often resemble the exposed tops of larger
batholiths
They can form independently as smaller, isolated magma bodies.
Stocks may become visible through erosion
frequently found in association with larger intrusive bodies.
E.g. the Henry Mountains of Utah and the Shiprock in New Mexico.
A boss is a small stock
Define and Describe a Laccolith
Laccolith is a lens-shaped or mushroom-shaped igneous intrusion. Some are more strangely shaped , e.g. Square Butte Laccolith, NW Montana
Forms when magma is injected between layers of sedimentary rock, forcing the overlying strata to dome upward.
Laccoliths are concordant, aligning with the layering of the surrounding rock.
often made of felsic to intermediate rocks like granite or diorite, though syenite can also occur.
Define and Describe a Lopolith and Basic layered intrusions
Saucer to funnel-shaped.
large, basin-shaped or lens-shaped intrusive body that is typically concave, where the center dips lower than its edges.
Forms when magma intrudes into the crust and spreads laterally, the weight of the injected magma itself or the overlying strata causes it to sag forming a bowl-like structure.
Lopoliths are concordant with the rock layers into which they intrude, lying parallel to the strata.
Commonly associated with mafic or ultramafic magmas, leading to compositions like gabbro or norite
Mostly basic to ultrabasic:
Peridotite, pyroxenite,
gabbro, norite, anorthosite.
e.g. Skaergaard Intrusion, East Greenland
