AUTHOR=Baruah Amiya , Roy Manas Kumar , Mandal Nibir , Misra Santanu 

TITLE=Reaction-diffusion modelling of petrological mixing mechanisms in the evolution of continental crusts

JOURNAL=Frontiers in Earth Science

VOLUME=11

YEAR=2023

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2023.1115103

DOI=10.3389/feart.2023.1115103

ISSN=2296-6463

ABSTRACT=<p>Petrological assimilation is a key process in the evolution of high-grade metamorphic terrains in the continental crusts. This study examines the mechanisms of such macroscopic assimilation between felsic (<italic>F</italic>) and mafic (<italic>M</italic>) constituents as two petrologically interacting continuum phases, as observed in the Chotanagpur Granite Gneissic Complex (CGGC), India, which underwent amphibolite to granulite facies metamorphism (∼775 to 900°C and 7 to 11 kb) between from the Paleoproterozoic to the late Mesoproterozoic. From field investigation we could recognized four interface patterns: planar, wavy, fingering and incoherent, which are generated at the interface between the <italic>F</italic> and <italic>M</italic> units. We have adopted the Turing type reaction-diffusion (RD) approach, which is a well established theoretical model to interpret any complex auto-regulatory pattern in natural and physical sciences, to understand the physics of the self-organizing interface geometries observed across the CGGC. The RD model findings suggest that these patterns are constrained by a combination of: diffusion coefficients (<italic>D</italic><sub><italic>F</italic></sub>, <italic>D</italic><sub><italic>M</italic></sub>) of <italic>F</italic> and <italic>M</italic>, a linear or non-linear reaction term (<italic>R</italic>) that describes phase interactions and a pinning field (<italic>W</italic>) that introduces microscale heterogeneity. For linear interactions, <italic>F</italic> − <italic>M</italic> undergo homogeneous mixing and show planar/wavy interfaces, when <italic>D</italic><sub><italic>F</italic></sub> = <italic>D</italic><sub><italic>M</italic></sub> and <italic>W</italic> = 0. The mixing turns heterogeneous as <italic>D</italic><sub><italic>F</italic></sub> ≠ <italic>D</italic><sub><italic>M</italic></sub> and <italic>W</italic> &gt; <italic>0</italic>, resulting in phase boundary migration with a fingering pattern. Non-linear reaction coupling enhances heterogeneous mixing and produces incoherent phase boundaries where <italic>F</italic>-phases host relics of <italic>M</italic>-phases, following a power-law size distribution. Striking similarities of interface patterns and fractal dimensions estimated from model and CGGC validate the proposed mechanism of macroscopic petrological assimilation. We argue that RD model provides a new insight into the genesis of hybrid rocks in metamorphic terrains.</p>