Size evolution of micropyrite from diagenesis to low-grade metamorphism
Published:April 17, 2019
Víctor Cárdenes, Raúl Merinero, Aurora López-Mungira, Álvaro Rubio-Ordoñez, Iain K. Pitcairn, Veerle Cnudde, 2019. "Size evolution of micropyrite from diagenesis to low-grade metamorphism", Metamorphic Geology: Microscale to Mountain Belts, Silvio Ferrero, Pierre Lanari, Philippe Goncalves, Eugene G. Grosch
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Size distribution and evolution of framboidal and euhedral microscopic crystals of pyrite (micropyrites, MPy) have been used for the last thirty years to deduce palaeo-redox conditions. The analysis of the MPy distributions can give valuable information about these palaeo-redox conditions. However, other information can also be retrieved from this type of analysis. In this work, we propose that the formation of new populations of MPy is a proxy of the transition from the anchizone to the epizone. High-resolution X-ray tomography (micro-CT) was used to determine the size distributions of MPy hosted in pelitic rocks subjected to different grades of low temperature metamorphism. These data were filtered and statistically analysed, which allowed us to find a statistical representative size distribution of the MPy present in the samples. The metamorphic grade was determined using the Kübler Index in combination with petrological and scanning electron microscopy (SEM) examination. The results show a relationship between metamorphic grade and MPy size distributions, and that new populations of MPy formed due to the effects of metamorphism. This new methodology for MPy size distribution has different potential applications in some fields of Earth sciences, such as palaeoenvironment reconstruction, ore mining or metamorphic petrology.
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Metamorphic Geology: Microscale to Mountain Belts
CONTAINS OPEN ACCESS
In Earth evolution, mountain belts are the loci of crustal growth, reworking and recycling. These crustal-scale processes are unravelled through microscale investigations of textures and mineral assemblages of metamorphic rocks. Multiple episodes of metamorphism, re-equilibration and deformation, however, generally produce a complex and tightly interwoven pattern of microstructures and assemblages. Over the last two decades, the combination of advanced computing and technological capabilities with new concepts has provided a vast array of novel petrological tools and high-resolution/high-sensitivity techniques for microanalysis and imaging. Such novel approaches are proving fundamental to untangling the enigma represented by metamorphism with an unprecedented level of detail and confidence. As a result, the first decade and a half of this century has already seen the tumultuous development of new research avenues in metamorphic petrology. This book aims to provide a timely overview of the state of the art of this field, of newly developed petrological techniques, future advancements and significant new case studies.