Intrusive activity Flashcards
What is intrusive activity?
Intrusive activity takes place place beneath the Earth’s surface. It includes the formation of large magma chambers and magma being forced into the crust through cracks in the rock.
Variation in cooling
Magma in intrusive volcanic features cools, crystallizes and solidifies into igneous rocks below the surface.
Slow cooling results in large crystals forming typical of rocks such as granite and dolerite.
How is intrusive activity actually revealed?
Once later erosion removes the overlying rocks.
What are three types of intrusive activity? Scale
Intrusive volcanic activity (batholiths vs dykes and sills) - here it is the scale of the process which results in distinctive landscapes - batholiths create landscapes, whereas dykes and sills are seen more as landforms, but both are created by igneous intrusion.
Which location shows large amounts of intrusive activity?
The Isle of Arran off the west coast of Scotland
What are batholiths?
Batholiths are large masses of intrusive rock that may cause a general doming up of the surface as they are forming.
The heat transferred from the magma to the country rock causes metamorphic rock to be produced around the intruding magma.
What are the dykes at the Isle of Arran?
A series of dykes, 23 m wide, are exposed across the beach at Kildonan.
How are dykes formed?
Dykes are discordant because they cut across the bedding planes of the country rock vertically.
Once exposed, the dykes can appear as linear outcrops of resistant rock.
What are the sills at the Isle of Arran?
At Drumadoon a sill has been exposed on the coast, forming a cliff 50 m high.
How do sills form?
Sills are concordant because they are are formed parallel to bedding planes in the country rock horizontally ,the bedding planes provide a line of weakness along which the magma flows before cooling and solidifying.
As it cools, the magma contracts, producing cracks in the resultant rock.
How was the Isle of Arran formed?
By the intrusion of large granite batholiths that domed the sandstone surface about 60 million years ago as Greenland separated from Scotland during the creation of the Atlantic Ocean.
How was the Isle of Arran been exposed?
The fractured overlying sandstone and metamorphic rock have subsequently been weathered and eroded to expose the resistant granite, peaking at a height of 874 m on Goatfell.
