Metamorphic amphibolite from mountain roots, Cairn Bannoch скачать в хорошем качестве

Metamorphic amphibolite from mountain roots, Cairn Bannoch

Amphiboles are common metamorphic minerals which form at temperatures around 550-750 Centigrade. There are two ways to heat rocks to these temperatures - burial deep in the crust (in which case the rock is called an amphibolite), or contact with igneous intrusions (when it is called a hornblende hornfels - hornblende is a common amphibole mineral). Here in the White Mounth we are at the heart of the Barrovian (burial type metamorphism) metamorphic zones and sitting right on top of a granite intrusion, so either is possible. On balance, the large grain size, and the way that the metamorphic grade is consistent with the regional variations (called the metamorphic field gradient) lead me to think this is an amphibolite produced by burial rather than a contact metamorphic rock.