INTERACTION BETWEEN ACID AND BASITE MAGMAS IN THE HAMMARUDDA COMPLEX,SW FINLAND - P-T CONDITIONS OBTAINED BY MINERALOGICAL THERMOMETRY ANDBAROMETRY

Indicative rock-forming minerals from a variety of textural components of mafic hybrid labradorite-bearing enclaves and their host quartz-fe ldspar rapakivi porphyry of the Hammarudda Complex, Aland Massif, sout hwestern Finland, were studied to determine the interaction conditions of the basite and acid magmas. Comparing the composition of the pyrox enes and hornblende from mafic hybrid enclaves and granitoids, on the one hand, and from basites in various individual intrusions of the Ala nd Massif and the Aland-Aboland dike swarm, on the other, we came to t he conclusion that the enclaves and gabbro-anorthosite-monzodiorite se ries were produced by the same parental melt. Mineralogical thermomete rs were employed to determine the crystallization conditions of a seri es of subsequent mineral assemblages that originated in the course of basite and acid magma mixing. The basite and acid magmas began interac ting at a pressure of no less than 5-5.5 kbar and a temperature of at least 1050-1120 degrees C. The most active hybridization of basite mag ma fragments occurred at pressures from similar to 4.5 to 1.5-2 kbar a nd a temperature decreasing from 820-880 to 680-700 degrees C during t he ascent of the basite and acid magmas along the common conduit. The acid magma ascended under subisothermal conditions at a temperature of approximately 730 degrees C or at insignificant heating, which was ca used by the energy released by crystallizing enclaves in the basite an d acid magmas. The Hammarudda quartz-feldspar porphyries finished crys tallizing at P congruent to 1 kbar and T = 630-670 degrees C. The fina l crystallization of the most hybridized mafic enclaves in the granito ids proceeded at similar conditions. This was caused by the notable de crease in the solidus temperatures of the hybrid melts with their incr easing mixing with acid liquids and simultaneous saturation in volatil es, which were released by the quartz-feldspar porphyry melt at the de pth of the intrusion emplacement.