The origin of silicic domes in the vicinity of the Makiling Stratovolcano in the Macolod Corridor, Luzon, Philippines: Evidence from bulk chemistry, mineralogy and oxygen isotopes.

摘要

The origin of high-silica magmas in areas lacking continental crust is not well-understood. The Macolod Corridor an Luzon Island of the Philippines provides an ideal area to study to this problem. Two end-member models, partial melting of previously emplaced magma batches and fractional crystallization, have been developed to explain the formation of high-silica magmas. The silicic domes (Bulalo, Bijang, Olila and Colombo) examined in this study are located near the Makiling Stratavolcano. The mineralogy and chemical composition of Bulalo, Bijang and Olila are very similar, while Colombo shows some slight differences. Most of the evidence developed in this study supports partial melting of discrete batches of previously emplaced crystallized magma as the likely source for the high-silica magmas composing the domes. The composition of domes can only be produced through the partial melting of an andesitic/dacitic source. The Sr concentration in the domes is too high to indicate the fractionation of large amounts of plagioclase. Neither the An content of plagioclase phenocrysts nor the Sr/Ba ratio indicates that fractional crystallization could have produced the chemistry of the domes. The observed difference in REE patterns of Calamba may be due to a larger degree of partial melting. The oxygen isotope values are similar for the three domes analyzed, indicating a similar source for the dome magmas. The high-silica Mt. Makiling samples most likely originated from a different source magma than the dome samples.