Crustal melting and deformation are intrinsically linked processes governing the evolution of continental crust and the generation of tonalite–trondhjemite–granodiorite (TTG) suites and granitic magmas. This study investigates the structural, petrological and geochronological evolution of partially molten amphibolites from the Nellore Schist Belt, India, integrating detailed field observations, microstructural analysis (EBSD), mineral chemistry, phase equilibria modelling and U–Pb geochronology to reconstruct the evolution of a melt-bearing shear zone.
Melt-reintegrated phase equilibria modelling indicates that fluid-assisted partial melting initiated under amphibolite-facies conditions, followed by peak metamorphism and progressive melt segregation. Geochemical modelling demonstrates that melts escaped the system in two distinct stages, evolving from hydrous tonalitic–granodioritic melts to more differentiated granitic compositions consistent with TTG-like magmas. U–Pb zircon and titanite geochronology constrain two major tectonothermal events at ~1673 Ma and ~1448 Ma, linking deformation, partial melting and crustal reworking over more than 200 million years.
EBSD analyses reveal strong crystallographic preferred orientations in amphibole but weak fabrics in plagioclase and quartz, indicating strain partitioning and deformation under melt-present conditions rather than dominantly solid-state deformation. These findings demonstrate that deformation:
- Localised fluid-assisted melting
- Controlled melt extraction along structurally favourable pathways
- Promoted rheological weakening
- Facilitated the generation of TTG-like magmas during Paleoproterozoic crustal reworking
By integrating structural geology with quantitative petrology and geochronology, the study provides new insights into the mechanisms controlling melt generation, fluid pathways and deformation in high-grade terranes. The results highlight how multi-scale geological observations — from mineral-scale deformation fabrics to regional structural architecture — can be combined to unravel complex geological histories and develop robust geological models.
