Analyses confirm that the change in alkali composition is also relatively sharp at these interfaces. In places, the homogenisation interfaces have shapes reflecting the local arrangements of nanotunnels or pull-aparts. Homogenisation of lamellae appears to proceed in an unexpected manner: two smooth interfaces, microstructurally sharp, advance from the original interfaces toward the mid-line of each twinned, semicoherent lamella. Homogenisation T is in agreement with experimentally determined solvi for coherent ordered intergrowths, when a 50–100☌ increase in T for An1 is applied. Subgrains in patch perthite homogenised more slowly than coherent lamellae and chemical gradients in patches persisted for >5,000 h at 700☌. A lamella which homogenised after 6,800 h at 600☌, therefore, would have required only 0.6 s to do so in the melting interval at 1,100☌. Changes in lamellar thickness with time at different T point to an activation energy of ~350 kJmol-1. A typical unheated phenocryst from Shap is composed of about 70 vol% of tweed orthoclase with strain-controlled coherent or semicoherent micro- and crypto-perthitic albite lamellae, with maximum lamellar thicknesses 700☌, and after >48 h at 700☌, all such regions were essentially compositionally homogeneous, as indicated by X-ray analyses at fine scale in the transmission electron microscope. Microtextural changes brought about by heating alkali feldspar crystals from the Shap granite, northern England, at atmospheric pressure, have been studied using transmission and scanning electron microscopy. The maximum temperature from hornblende-plagioclase thermometer is $816 C, which probably reflects late-stage crystallisation of the magma. The highest temperature for the rocks comes from orthopyroxene-clinopyroxene solvus thermometry, and is $1000 C this is interpreted to reflect the initial crystallisation of the diorite magma immediately after its em-placement. Several geothermometers have been applied to the Quarry Diorite, the outermost intrusion of the complex. Thermometry, using ternary and binary feldspar systems, yields low temperatures, which probably reflect late-stage, post-magmatic re-equilibration of these minerals. Application of Al-in-hornblende barometry and crossite contents of amphiboles indicates a pressure <3 kbar for the intrusion, in good agreement with published independent pressure estimates of $2 kbar from mineral equilibria in metasedimentary hornfelses in the Etive thermal aureole. Six samples, representing the major rock units in the southern parts of the Etive complex were chosen for mineral chemical studies and for estimation of the pressure and temperature conditions of magmatic crystallisation.

The Etive complex, one of the Caledonian 'Newer Granites' of Scotland, is a ring complex of Devonian age, ranging in composition from pyroxene-diorite to leucogranite.

Plagioclase feldspar ternary diagram