Date of pluton emplacement: ~ 570 millions years ago
The northernmost section of the Channel Island of Guernsey comprises several large igneous complex outcrops, which are built from multiple intrusions. Of particular interest are the Bordeaux Diorite Complex and the Cobo Granite. The Bordeaux Diorite Complex consists of three rock types which are broadly contemporaneous and all display a range of mixing and mingling textures. In the North East at Beaucette Battery there are layers of leucocratic and melanocratic diorites. The melanocratic diorites contain pipes and dikes of more felsic material, sometimes pegmatic, which are continous with a vein system in the more leucocratic layers. Further round the coast at Chouet, there are more mixing textures such as enclaves and irregular margins. The Cobo granite is exposed in the North West of the island and it intruded into the Diorite Complex. A transitional zone exists between the two intrusions which shows a gradational change in rock composition. The granite contains enclaves that have been captured from the diorite and the enclaves themselves contain orthoclase feldspar xenocrysts that have been captured from the granite.