Microstructural evidence of melt-present deformation and its effect on zircon modification

The Earth’s structure, chemistry, and the formation of mineral resources, require significant transfer of mass through the crust. Though pathways are identified such as dykes and shear zones, the recognition of these pathways can be improved and the effects of melt migration n zircon geochronology studied. This project examines a suite of variably strained outcrops associated with a m– scale shear zone in the Pembroke Granulite, Fiordland, New Zealand. This project shows an improved understanding of the signatures and processes associated with mass transfer by identifying five key microstructures indicative of the former presence of melt within intermediate to high strain zones in the Pembroke Granulite; 1) small dihedral angles of interstitial grains including plagioclase, clinozoisite, rutile and ilmenite; 2) veinlets/melt films pseudomorphed by plagioclase, clinozoisite and rutile; 3) melt pseudomorphs including biotite; 4) cuspate grains; & 5) quartz – amphibole symplectites. Further development of this tool is the recognition on how melt-present deformation can modify zircons within a melt-fluxed system. This thesis proposes that microstructures indicative of the former presence of melt, and zircon modification, may be used as a tool for identifying rocks that formed during melt present deformation at variable strain intensities and potential shortfalls to interpretation.