Multivariate analysis of feldspar exsolution lamellae morphology: Insights from the Koraput Alkaline Complex, India

Magmatic crystallization and cooling within alkaline complexes located in the Eastern Ghats Granulite Belt (EGGB) frequently trigger feldspar exsolution, yet the exact mechanisms governing how these resulting textures morphologically evolve remain poorly understood. In this study we quantify the microtextural (perthite and mesoperthite) evolution to understand the macro-evolutionary rhythm of the region through petrography, multivariate methods including principal component analysis (PCA), redundancy discriminant analysis (RDA), and non-metric multi-dimensional scaling (NMDS) combined with numerical simulations and generalized additive models (GAM). These statistical and computational approaches were integrated to objectively isolate competing multi-variable controls and mathematically validate the physical drivers of texture development. We investigate the influence of composition, formation temperature of plagioclase lamellae, and nucleation density within host alkali feldspar on plagioclase lamellae morphology, and evaluate the role of lithological formation and cooling history. Petrographic evidence shows that coarse, coherent plagioclase lamellae within perthite and mesoperthite reflect slow cooling under subsolidus conditions, whereas localized patchy and incoherent intergrowths likely formed during later deuteric alteration. The results further demonstrate that: (1) feldspar composition is the primary control on perthite and mesoperthite lamellar morphology, whereas formation temperature exerts only a secondary influence; (2) numerical simulations indicate that the nucleation sites of plagioclase lamellae within alkali feldspar have minimal influence on lamellar morphology; and (3) lamellar morphology preserves a record of the formation history, cooling evolution, and spatial position of the host rocks within the alkaline complex.