Integrated analysis of multiple mineral reactions

The minerals present in magmatic and/or metamorphic rocks combined with their microstructures and textures observed under the microscope provide an important window into the deep portions of the Earths crust and mantle, where these rocks are formed and which are otherwise inaccessible to us. In this context, reading the information engraved in the rocks constituent minerals, including their chemical compositions as well as their microstructures and textures is of key importance. Rock-forming silicate minerals often contain numerous ultra-fine micrometre to sub-micrometre sized micro-inclusions of oxide minerals, which impart a dusty cloudy appearance to them. Extant works indicate complex formation pathways of clouding that hold crucial information about the evolution of the rock. In this project, clouding of two of the most abundant rock-forming minerals, plagioclase and orthopyroxene by spinel will be investigated in a Precambrian rock from the Dharwar craton, India. In addition to clouding, the rock also features a rich inventory of metamorphic and magmatic mineral-reaction textures. This offers unique possibility to make use of clouding coupled with other micro-structures for determining the relative timing, absolute rate and potential interplay among the different mineral reactions, which are pivotal for inferring the rates of geological processes operating in the deep crust. The samples will be subjected to an integrated mineralogical, crystallographic and petrographical analysis with the state-of-the-art microscopic and analytical techniques. This involves Optical Microscopy, Scanning Electron Microscopy including crystal orientation analysis by Electron Backscatter Diffraction, Transmission Electron Microscopy, Electron Probe Micro Analyser and Laser Ablation Inductively Coupled Plasma Mass Spectrometry. This will provide crucial information on the mineralogy, major and trace element composition, and orientation of sub-micron sized phases present within the rock. The obtained dataset will be further used for mass balance calculations, theoretical analysis and numerical simulations. This will elucidate and quantify the physico-chemical controls (pressure-temperature-oxidation state-fluid composition) and the rates under which geological processes proceeded in the deep portions of the Precambrian Earths crust.