Early Neoproterozoic (~0.95–1.0 Ga) HT-HP Metamorphism in the Sandmata Complex and Its Implications for Rodinia Assembly in the Aravalli Craton (NW India)

The Paleoproterozoic Sandmata Complex (SC) of the Aravalli Craton (NW India) is traditionally regarded as a reworked Archean crustal terrane. It also preserves exhumed granulite-facies rocks that record high-grade metamorphic events. In the westernmost part of the complex, the dominant lithology comprises garnet-bearing, migmatitic quartzo-feldspathic gneisses (MS30A) that host mafic microgranular enclaves (MME; MS30B) and leucosomes (MS30C). This study presents new insights based on integrated structural, metamorphic, geochemical, and geochronological analyses of rocks from the western Sandmata Complex. The migmatitic gneisses preserve evidence for at least two deformation events (D₁ and D₂). The early fabric (S₁) is a centimetre-scale, gently dipping gneissic foliation, which is overprinted by a spaced, NNE-striking, steeply dipping axial-planar foliation (S₂). The peak metamorphic assemblage in the migmatitic gneisses consists of Grt(core) + Pl₂ + Kfs + Qz + Amp + Ilm + Ttn ± Bt₁ ± Mt. In contrast, the MMEs record the peak assemblage Grt(core) + Pl₂ + Kfs + Amp₁ + Ep₂ + Ttn₂ + Qz + Ilm ± Mt, whereas the leucosomes contain Grt(core) + Pl₂ + Qz + Amp₁ + Ep₂ + Ttn₂ + Ilm ± Mt. The MME and leucosomes are characterized by symplectitic coronas around garnet, defined by Grt-rim + Pl₃ + Qz + Amp₂ + Ep₃ + Ttn₃ ± Mt ± Ilm ± Bt. Pseudosection modelling constrains peak metamorphic conditions at ~9.7 kbar and ~820 °C. The symplectite assemblages reflect post-peak re-equilibration at ~7.6 kbar and 580–610 °C. Prograde conditions, estimated using the melt-reintegration approach, indicate temperatures of ~600 °C at ~10.3 kbar. Together, the prograde, peak, and retrograde P–T estimates define a clockwise P–T path involving isobaric heating to peak conditions, followed by cooling and decompression. U–Pb dating of magmatic zircon cores from the migmatitic gneiss yields concordant age of 1720 ± 13 Ma (MSWD = 0.97; n = 15), which are interpreted as the crystallization ages of the parental magmatic protolith. In contrast, U–Pb analyses of titanite associated with the peak metamorphic assemblages produce a discordant age of 969 ± 7 Ma (MSWD = 1.7; n = 49). This younger age constrains the timing of partial melting and migmatization of the gneisses. These results provide the first robust evidence for ~0.97 Ga high-grade metamorphism in the Sandmata Complex, a metamorphic event not previously documented in this terrain. Combined with earlier records of 1.78–1.90 Ga granulite-facies metamorphism, the data indicate that the SC experienced two distinct high-grade metamorphic episodes during its geological history. Regionally, the ~0.95–1.0 Ga event corresponds to a major tectonothermal phase associated with the accretion and amalgamation of the Aravalli Orogen and the Central Indian Tectonic Zone. This younger metamorphic overprint, thus, reflects the development of a high-grade orogenic belt during the assembly of Rodinia, linking the evolution of the Sandmata Complex to broader Neoproterozoic continental-scale processes.