GEOLOGICAL HIGHLIGHTS - JUDD'S DYKES

Along the western shore of Arran, between Tormore and Blackwaterfoot, a series of dykes and sills can be seen. Known collectively as Judd’s Dykes, after the geologist who first studied them in the late 1800’s, these rocks are a classic example of composite intrusions.

The variable compositional nature of these dykes and sills reflect the simultaneous availability of basic and acidic magmas. The original magma would have been a differentiate of mantle melt, which later became altered by contamination from crustal material. Magmatic fractionation processes could have produced the acidic and basic magmas which may have existed in a stratified magma chamber.

This reservoir would have been tapped on various occasions to release the different types of magma. Often, the magma would exploit the zones of weakness provided by previous intrusions. This process juxtaposes intrusions of strikingly different composition, hence the name composite intrusion.