Nucleation and Growth of Pyroxene in the Hypersthene Diorites

Abstract

For a detailed textural study on intermediate igneous rocks of Ballachulish complex, an area in the southeastern part of the pluton was selected, where hypersthene-bearing monzodiorites are nearest to the contact. These relatively ‘dry’ diorites are least affected by late- to post-magmatic hydration southeast of Sgorr Dhonuill, where a very fine-grained chilled marginal facies bordered quartzitic country rocks, before the emplacement of granitic rocks partially separated the diorites from the metasediments. The term ‘chilled margin’ is used here in a general sense, defined as a zone of “fine-grained rock, enclosing and grading into the relatively coarser inner parts of an intrusion” (Cox et al. 1979). Figure 5.1 attempts a reconstruction of the monzodiorite main zone before the emplacement of younger granites, omitting the large ring-dyke granite apophysis and correcting for later sinistral fault displacement (compare Fig. 3.13c).