Petrography, geochemistry and Fractal analysis of Mafic Enclaves in the Alvand Plutonic to investigate magma mixing processes

Abstract

The Alvand plutonic complex is located in Sanandaj- Sirjan Zone in south and west of Hamedan. Petrographic studies indicate that this body is composed of mafic intrusive rocks, porphyry granitoids and leoucocratic granitoids with various enclaves such as surmicaceous, mafic microgranular and felsic microgranular enclaves. Field, petrography and geochemical studies show that the enclaves, the host and the mafic rocks have calc-alkaline affinity and aluminum saturation index of the host rock is peraluminous and mafic microgranular enclaves and mafic rocks are metaluminous and in the boundary between metaluminous and peraluminous fields. On the base of spider diagrams, all rocks are depleted in HFSE and enriched in LILE, which is particular of rocks of the subdution zones. The complexity of the morphology of the enclaves (fractal dimension) confirms the importance of magma mixing in this body. Fractal dimensions of the enclaves vary between 1.08 to 1.21 and the frequency of Dbox=1.1 is the highest one in histogram. According to the fractal dimensions of enclaves, the logarithm of viscosity ratio of the host rock and the enclave ranges from 0.48 to 0.74 with most values clustering around 0.51. The different forms of the studied microgranular mafic enclaves suggest that the effect of magma mingling (mechanical mixing) on the enclaves and the host have been various in different parts of the Alvand body so that from the border of mafic body to the center of granitoid body enclaves become smaller, fewer; and their fractal dimensions decrease.

Keywords

• enclave
• geochemistry
• fractal analysis
• magma mixing
• the alvand plutonic complex
• sanandaj – sirjan