The second stage of isotopic exchange with O fractionation and a marked decrease in the δD values of biotite.These kinetic effects have been recorded in the finer-grained granites of Groups III and IV.
On the basis of these data the Aral batholith is considered to be late- or post-orogenic emplaced during the late Hercynian., late Hercynian granite.
The circle and the nearby number show the sampling location and sample number with the prefix XG omitted.
Megacrysts become less abundant (1 kg, were collected from the four petrographic units. Rock samples were crushed into grains with sizes ranging between 0·5 and 0·2 mm.
Quartz, feldspar and biotite were separated using the standard separation procedure of panning, flotation, magnetic dressing, separation by heavy liquid, corrosion in hot dilute HCl solution and hand-picking under the binocular microscope (Liu , 1996).
The batholith is dated at 250·9 Ma by the whole-rock Rb–Sr isochron method (Liu, 1990), with an initial Sr ratio of 0·7085 ± 0·0005.