This is probably the first question that comes in mind when looking at feldspar megacrysts in rapakivi granites. This is a bit of a mystery and we are determined to study the 'locus classicus' rapakivi suites in South-Finland to get a clear understanding why some of the mega-crysts are 'like a cube of ice dissolving in a whiskey on the rocks!" However, the path to dissolving that round piece of the puzzle is not straight forward and includes many research areas of petrology and geochemistry.
Prof. Tapani O. Rämö
Dr. Aku Heinonen
Dipl.-Min. Radoslaw M. Michallik
Heinonen A., Kivisaari, H. & Michallik, R.M. 2019. High-aluminum orthopyroxene megacrysts (HAOM) in the Ahvenisto complex, SE Finland and the polybaric crystallization of massif-type anorthosites. Contributions to Mineralogy and Petrology (submitted).
Heinonen, A., Mänttäri, I., Rämö, O.T., Andersen, T. & Larjamo, K. 2017. Zircon as a proxy for the magmatic evolution of Proterozoic ferroan granites; the Wiborg rapakivi granite batholith, SE Finland. Journal of Petrology vol 58, issue 12, pp. 2493-2517. doi: 10.1093/petrology/egy014
Heinonen, A., Andersen, T., Rämö, O.T. & Whitehouse, M. 2015. The source of Proterozoic anorthosite and rapakivi granite magmatism: Evidence from combined in situ Hf–O isotopes of zircon in the Ahvenisto complex, southeastern Finland. Geological Society. Journal, vol. 172, no. 1, pp. 103-112. doi: 10.1144/jgs2014-013
Rämö, O.T., Turkki, V., Mänttäri, I., Heinonen, A., Larjamo, K.M. & Lahaye, Y. 2014. Age and isotopic fingerprints of some plutonic rocks in the Wiborg rapakivi granite batholith with special reference to the dark wiborgite of the Ristisaari Island. Bulletin of the Geological Society of Finland, vol 86, no. 2, pp. 71-91.