Structure, Petrography and Emplacement of Plutonic Rocks

The two-phase Ballachulish pluton is composed of a zoned monzodiorite - quartz diorite envelope with distinct flow- and deformation-foliation, surrounding a core of porphyritic granite with hybrid margins. Mesotype members of this suite are constituted of alkaline hypersthene diorites. This provides an unique opportunity to quantify the magmatic crystallization sequence within a relatively “dry” plutonic environment at upper crustal level, in terms of $$ T - X - {f_{{o_2}}} $$ evolution (Weiss and Troll, Chap. 4, this Vol.). The present chapter starts with a gross megascopic description of the igneous rocks. Section 3.2 deals with contact relationships, xenoliths and foliation structures, followed by a modal classification of the igneous units (Sect. 3.3.1). A detailed petrography of index minerals, their texture and areal distribution (Sect. 3.3.2) precede the synoptical Sect. 3.4 on magma emplacement and intrusion mechanics.