Textural and mineralogical features in the high-K calc-alkaline Kozárovice granodiorite (Hercynian Central Bohemian Pluton, Bohemian Massif) and associated small quartz monzonite masses imply that mixing between acid (granodioritic) and basic (monzonitic/ monzogabbroic) magmas was locally petrogenetically significant. Net veining, with acicular apatite and numerous lath-shaped plagioclase crystals present in the quartz monzonite, and abundant mafic microgranular enclaves (MME) in the granodiorite, indicate that as the monzonitic magma was injected into the granodioritic magma chamber, it rapidly cooled and was partly disintegrated by the melt already present. Evidence from cathodoluminescence suggests that the two magmas exchanged early-formed plagioclase crystals. In the quartz monzonite, granodiorite-derived crystals were overgrown by narrow calcic zones, followed by broad, normally zoned sodic rims. In the granodiorite, plagioclase crystals with calcic cores overgrown by normally zoned sodic rims are interpreted as xenocrysts from the monzonite. After thermal adjustment, crystallisation of the monzonitic magma ceased relatively slowly, forming quartz and K-feldspar oikocrysts. Although the whole-rock geochemistry of the quartz monzonite and the MME support magma mixing, major- and trace-element based modelling of the host granodiorite has previously indicated an origin dominated by assimilation and fractional crystallisation. Magma mixing therefore seems to represent a local modifying influence rather than the primary petrogenetic process.

Abstract The Lewisian complex, formed before the deposition of the Torridonian sedimentary sequence, contains remnants of at least two sedimentary groups and shows evidence of polyphase deformation and polymetamorphism in at least three orogenic episodes—Scourian, Inverian, and Laxfordian—dated at about 2,600+ to 2,460 m.y. ago, 2,200 to ?2,000 m.y. ago, and 1,600 to 1,300 m.y. ago, respectively. The dominant foliation in a supracrustal assemblage of quartzo-feld- spathic gneiss, hornblende schist, amphibolite, and distinctive sedimentary types, which occurs both in a northern belt (Rhiconich group) and a southern belt (Loch Maree Series), formed as the result of deformation early in the Laxfordian orogeny. The regional ESE-WNW trend of this banded sequence is controlled by major asymmetric folds, such as the Strath Dionard antiform in the northern belt and the Tollie antiform and Letterewe synform in the southern belt. These large-scale structures were formed during a second deformational phase of the Laxfordian orogeny and deform the dominant foliation and banding. The central belt shows evidence of basement deformation during both the Laxfordian and Inverian orogenies, and the disposition of the structural elements was influenced by structures formed during the Scourian orogeny. These earlier-formed structures deform the lithologically layered, supracrustal Kylesku group, which includes metasedimentary relics. The dominant banding shown by the rocks of this group was formed coevally with granulite-facies metamorphism during an early deformational phase of the Scourian orogeny. The largest structure recognized in the central belt, the Kylesku fold, formed during a later (third) deformational phase of the Scourian orogeny. orogenic

The banded Lewisian gneisses of Mingulay, with minor amphibolites, show the effects of at least five phases of folding and related deformation. The formation of the banding in the gneisses is associated with the earliest recognized phase of deformation during which the main metamorphic reconstitution took place, with the strong linear (L 1 ) and planar (S 1 ) fabric elements related to tight isoclinal folds (F 1 ). The largest folds (F 2 ), which exercise strong control on the gross attitude of the banding, were formed during a second phase of deformation. They are asymmetrical in form with secondary axial planar foliation (S 2 ) and their axial planes controlled the uprise of locally derived quartzo-feldspathic pegmatitic material. Pseudotachylite formation preceded the three subsequent phases of deformation in which the folds (F 3 , F 4 , F 5 ) were formed. These folds are generally open with little or no related mineral reconstitution. Interference structures resulting from the superimposition of these sets of open folds on the asymmetrical folds are common and account for the variation in attitudes of the lithological layering. The most common and largest pegmatitic veins, derived from deeper crustal levels, are situated in the hinge zones of the fourth fold set. Major- and trace-element proportions are consistent with a derivation of the amphibolites from basic igneous rocks. Metamorphic segregation resulted in the formation of hornblendite pods and balls and associated quartzo-feldspathic material. The gneisses are generally comparable to granodiorite in chemical composition and in parts show gradations to more potassium-rich quartzo-feldspathic veins of pegmatitic aspect which are largely concordant. Many of the discordant pegmatites have abundant potassium feldspar. The genesis of the different types of quartzo-feldspathic rock is related to the varying roles of extraction and redeposition of the most soluble substance under conditions of heterogeneous pressure, partial melting, and potassium metasomatism.