A geochemical perspective of mafic enclaves in the Deccan Traps Continental Flood Basalts reveals magma chamber dynamics

Trachytes of the Deccan Traps from the Manori–Gorai area of Mumbai host numerous mafic enclaves which record magma chamber processes in continental flood basalt (CFB) settings. In this study, we undertook a comprehensive study, including petrography, mineral chemistry, whole-rock Sr-Nd isotope, in-situ trace elements and Sr isotopic analysis of the host trachyte (SiO₂ = 65-72 wt.%) and the mafic enclaves (SiO₂ = 45-52 wt.%) to understand magma chamber processes. A sharp-to-transitional hybrid mixed zone is evident between the host trachyte and enclaves, indicating mixing and mingling of two different magmas. Plagioclase and clinopyroxene are the major phenocrysts residing within a glassy groundmass. Plagioclase occurs as euhedral to anhedral grains, as inclusions, and within the groundmass across different zones. Clinopyroxene is predominantly augitic in composition throughout these zones. The wide compositional range from bytownite to sanidine indicates fractional crystallization coupled with heterogeneous magma mixing. Light rare earth element (LREE) enriched patterns (La_N/Sm_N = 3.4–5.4; Sm_N/Yb_N= 4.2–5.3), incompatible trace element enrichment, and whole-rock Sr–Nd isotopic compositions of both the enclaves (⁸⁷Sr/⁸⁶Sr_i = 0.70524–0.70536; ε_Ndi = +1.8 to +2.3) and trachyte (⁸⁷Sr/⁸⁶Sr_i = 0.70506–0.70511; ε_Ndi = +0.5 to +0.6) suggest derivation from a common parental magma, with minor crustal contamination recorded in the trachyte. In-situ trace element analyses and Sr isotopic ratios in feldspar (⁸⁷Sr/⁸⁶Sr_i = 0.7039–0.7056) further support a shared source affected by heterogeneous mixing. The observed geochemical trends in both the mafic enclaves and trachyte indicate recharge of mafic melt into an evolved, fractionated magma chamber, followed by buoyancy-driven ascent forming mafic enclaves at the interface.