Crystal Size Distribution (CSD) as a proxy of granitoid magmatic processes in southern Mexico

Magmatic differentiation is a key process behind the diversity of continental crust rocks. Crystal Size Distribution (CSD) is a stereological-textural method that provides insights into nucleation and crystal growth, especially when integrated with geochemical and petrological data. While most CSD studies focus on igneous textures in volcanic rocks, particularly in K-feldspar and plagioclase crystals, fewer address granitoid textures. This study presents CSD analyses of eight plutonic bodiesfrom Michoac & aacute;n, southern Mexico, supported by geochemical, chronological, and thermobarometric data. These granitoids range in composition from tonalite to granite and display calcalkaline arc signatures in major and trace elements. U-Pb zircon ages span from the Jurassic to the Miocene (164.8-20.6 Ma), suggesting long-term magmatic activity. CSD plots of plagioclase crystals indicate open magmatic systems with variable conditions, inconsistent with simple cooling. Granitoids hosting mafic microgranular enclaves show concave-up CSD trends and abrupt slope changes, implying magma mixing. Estimated average residence times (tau) range from 17 to 67 years for crystals <0.5 mm and 86 to 187 years for larger crystals (>0.5 mm), aligning with theoretical diffusion times during magma mixing and assimilation in intermediate to silicic systems. Combined CSD and thermobarometric data propose an inverse relationship between magma temperature, silica content, and crystal residence time at shallow emplacement levels. These findings provide new insights into the dynamics of crustal magma chambers and the physical parameters influencing pluton emplacement in arc-related settings.