. Bulletin of the British Museum (Natural History), Mineralogy. FROM THE BORRALAN COMPLEX, SCOTLAND 329. Fig. 15. The distribution of the major rock types of the Borralan Complex in the system Qz - Ne - Ks. I, pseudoleucite suite ; II, ledmorites ; III, hybrid rocks of the lower suite, South-eastern Tract; IV, later syenites and quartz syenites - based on data of Parsons (1972). The squares are the least hybridized pyroxene group rocks (n and 18), which plot in the ledmorite field, and the biotite syenite (hornblende group) and pyroxene- microcline xenolith which have undergone potash metasoma
. Bulletin of the British Museum (Natural History), Mineralogy. FROM THE BORRALAN COMPLEX, SCOTLAND 329. Fig. 15. The distribution of the major rock types of the Borralan Complex in the system Qz - Ne - Ks. I, pseudoleucite suite ; II, ledmorites ; III, hybrid rocks of the lower suite, South-eastern Tract; IV, later syenites and quartz syenites - based on data of Parsons (1972). The squares are the least hybridized pyroxene group rocks (n and 18), which plot in the ledmorite field, and the biotite syenite (hornblende group) and pyroxene- microcline xenolith which have undergone potash metasomatism. The triangles are ledmorite dykes of the Assynt area. Field of leucite (L) etc. as on Text-fig. 10. (3) The relationship to the ledmorites The four principal groups of rocks which comprise the Borralan intrusion, ex- cluding certain ultramafic rocks, are defined in Text-fig. 15 in terms of Qz - Ne - Ks. The nepheline syenites of the complex have been shown by Tilley (1958) to include two types, a foyaite type and a juvite (juvet) type, and these plot in Text-fig. 15 in the ledmorite and pseudoleucite suite fields respectively. In a similar plot to Text-fig. 15 Tilley (1958, Fig. 1), combining the data then available for the Bor- ralan and nearby Loch Ailsh complexes, together with data for the minor intrusions of the Assynt region, defined four groups, which correspond in Text-fig. 15 to the borolanite part of group I, group II and group IV which Tilley subdivided into two separate groups. No data corresponding to group III were then available. He concluded that ' Consideration of this analytical plot raises many problems relating to the differentiation and evolution of alkali complexes of the Assynt type '. A mechanism for the production of group III rocks involving hybridiza- tion between II and IV has been outlined above, but the direct genetic relationship between the later syenites and the highly undersaturated groups I and II, a prob- lem which arises in many syenit
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