Geochemistry and fractal analysis of enclaves in the Dehe Bala granodioritic pluton in order to investigate magma hybridization processes

The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with ellipsoidal and rounded shapes and varying sizes (from a few centimeters up to 30 cm). The MMEs are composed of diorite, monzodiorite and diorite-gabbro while the host rocks comprise mainly granodiorite. The presence of disequilibrium textures in enclaves, such as plagioclase phenocrysts with repeated resorption surfaces and sieve texture, quartz ocelli and acicular apatite, suggest a varity of magma mixing processes affecting the Dehe Bala pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMEs and the felsic host rocks. Unusual REE enrichment of the enclaves compared to the country rocks can be attributed to significant differences in their parent magma compositions. The complexity of the morphology of the enclaves (fractal dimension) caused by magma mixing processes. Fractal dimensions of the enclaves vary between 1.14 to 1.29. The frequencies of Dbox = 1.29 is the highest frequency in histogram. According to the fractal dimensions of enclaves, the logarithm of the viscosity ratio between the host granodiorite and the enclave ranges between 0.56 to0.96 with most values clustering around 0.96. The most of enclaves in the Dehe Bala pluton characterized by silica content around 56 w% and a high fractal dimension. These evidence confirmed the occurrence of slight hybridization between the mafic enclave magma and surrounding felsic magma, causing increasing of viscosity difference between the host granodiorite and the enclave magmas.