Alkali-feldspar and Fe-Ti oxide exsolution textures as indicators of the distribution and subsolidus effects of magmatic ‘water’ in the Klokken layered syenite intrusion, South Greenland

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Abstract
The layered syenites in the Klokken intrusion consist of horizons of fine-grained, granular-textured ferroaugite syenite showing inverted cryptic layering, interleaved with coarser, laminated, more fractionated hedenbergite syenite. Distribution of hydrous mafic phases indicates build-up of water in parallel with magmatic evolution, and druses and pegmatitic segregations in the laminated syenites are evidence for late development of a gas phase. Feldspar bulk compositions are close to the minimum on the Ab-Or binary, with An decreasing from An7 to An1 with fractionation, and normal zoning in cryptoperthite crystals. Feldspars in granular syenites are transparent coherent cryptoperthites or braid microperthites; An-content is probably the main control of fine-perthite coarseness. Laminated syenite feldspars are turbid, coarse patch microperthites with rare relics of braid textures. This non-coherent coarsening was caused by interactions between feldspars and water entrapped at magmatic temperatures which was retained within the original lithologies to low subsolidus temperatures. Fe-Ti oxides reflect this water distribution, with regular trellis ilmenite-titanomagnetite intergrowths in less fractionated rocks and ragged granule exsolution in more advanced syenites. The sharp change in exsolution textures at granular-laminated syenite boundaries implies steep water-gradients within these interleaved rock types. Water was unable to penetrate the granular layers and did not circulate freely in the cooling intrusion.