An investigation of the petrogenesis of the Buddusò I-type granites and its mafic enclaves in Sardinia, Italy.

There is still great debate surrounding the petrogenesis of I-type granites with mafic enclaves.The granite controversy indulges three prevalent processes/models surrounding the typical range in chemistry portrayed by common I-type granites; 1) magma mixing/mingling, 2) differential entrainment of material from the source and 3) fractional crystallisation from the source.There are three predominant theories which describe the petrogenesis of mafic enclaves: 1) they represent cumulate fragments, 2) blobs of hybrid magma representing a mixture of a mafic magma mixing with a felsic host magma and 3) fragments of recrystallized metamorphic rocks inherited from the source during partial melting from a parent magma.Mafic enclaves are widely considered to represent evidence for magma mixing/ mingling of a mafic magma and felsic host magma in I-type granites.The Buddus Pluton is a perfect example of a common I-type granitic body with mafic enclaves.This study aims to; 1) explain the origin of the compositional variation seen in the granitic units as well as the mafic enclaves, 2) constrain the most consistent model for the petrogenesis of the Buddus pluton.This study will make use of a blend of geo-analytical techniques; field relations, whole rock geochemistry, petrography, mineral chemistry, zircon geochronology and Lu-Hf and U-Pb isotopic analysis of the zircons from both mafic enclaves and granites to aid in meeting the aims of the study.The Buddus pluton is comprised of three units; an inner unit comprised of leucogranites, a middle unit comprised of granite compositions and an outer unit comprised of granodiorites.Mafic enclaves exist throughout the pluton, increasing in abundance from the inner to outer units.Granites from all units show negative correlations for all major elements except K2O with respect to SiO2.They show an increase in Al2O3, CaO, FeO, MgO, TiO2 and, P2O5 with decreasing SiO2 from the inner unit through to the outer unit.Granites show tighter correlations with respect to the major and trace elements vs. SiO2 with trends portrayed by the mafic enclaves.Mafic enclaves show a similar mineral assemblage to the granites (sensu lato) with a higher proportion of mafic minerals, both contain complexly zoned plagioclase crystals.U-Pb isotope data indicated a crystallisation age of 2942Ma for both granites and mafic enclaves and revealed that the age of the source was fairly close in age to that of the pluton (2925Ma (Del Moro et al., 1975)).Hf(t) values from Lu-Hf isotope analyses suggest that both the granites and mafic enclaves have crustally derived isotopic signatures and showed small scale isotopic