The Upper Carboniferous porphyritic microgranite of Altenberg-Frauenstein,

formerly known as Granitporphyr (Dalmer 1896) and here abbreviated as GP, forms a 36 km long and up to 18 km wide complex of ring dykes related to the Teplice-Altenberg caldera in the German–Czech border region of the Eastern Erzgebirge/Kruvsné Hory. The microgranites are characterized by the occurrence of plagioclase-mantled K-feldspar phenocrysts. The microgranite varieties rep-resent two main stages of intrusion evolved from acid (GP I) to intermediate rocks (GP II) within the intrusion. The most acid rock (GP Icum) occurs as en-claves in GP I and GP II and is interpreted as a cumulate of K-feldspar and quartz phenocrysts. The porphyritic microgranites show field, textural and geochemi-cal evidence suggesting that some of them have formed as a result of interac-tion between felsic and mafic magmas. Mixing features are abundant in the por-phyritic quartz-feldspar-hornblende microgranite (GP II) interpreted as a hybrid rock. They are less discrete in the early phase (GP I) and not obvious in the acid enclaves (GP Icum). This trend seems to reflect a continuous deflation of the magma chamber from the top to the bottom. According to the definition o