Geotectonic evolution of the Himalaya: Wiping out a century-old hangover

The author proposes a transformative model for the evolution of the Himalaya, not in the ideal Cenozoic Alpine way of subduction and back-thrusting, arguing that the fundamental structure of the Mountain belt is rooted in the old structural-cum- stratigraphic fabric, not merely the Cenozoic India-Eurasia collision. His work refutes the ”century-old concept” that the Lesser Himalayan structures (the inner Lesser Himalayan Zone, iLHS) are purely products of Cenozoic back-thrusting. The core of the transformative thesis is ”Sans Cenozoic Hangover” (Chakrabarti, 2023). The iLHS zone has a consistent stratigraphy across Pakistan to Arunachal, representing a Paleoproterozoic folded (F1) mosaic (with later imprints) rather than the backthrustnappe-klippe-thrust scenario over the iLHS portrayed over the past century! The 500 Ma Granitoid belt is identified as a distinct overprint of the late Proterozoic-Cambrian orogeny on the Paleoproterozoic one, with the evolution of the ‘Cambrian’ belt carrying both old and Neoproterozoic-Cambrian signatures. The Main Central Thrust (new MCT) is not a ubiquitous Cenozoic penetration; it is a Cenozoic preference in a long stretch in the higher levels below the exhumed Central Himalayan Crystallines (HHC), coinciding with an older susceptible zone (the PUD zone: Chakrabarti, 2024, 2026). The PUD is a protolith (P), regional unconformity (U) and decollement (D) zone representing a Mesoproterozoic sedimentation gap (<1600–1000 Ma) rather than just a Cenozoic feature; definitely post-Paleoproterozoic impact in varying degrees bewildered workers to consider this old zoneof tectonic susceptibility as an MCT zone everywhere. The NNE/NE–SSW/SW trending mineral lineation, long thought tobe associated with the Cenozoic thrusting (designated a lineation), is actually a mimetically superposition on an earlier lineation parallel to the Paleoproterozoic F1 fold axis (L1: b lineation). Long years of habitat in Alpine (Cenozoic) mode failed to recognise this old b lineation also as an intersection lineation (F1 fold and its axial planar schistosity) ultimately help define and construct the Paleoproterozoic F1 mega-folds in sections across the F1 axis (NNE-SSW). The common NE-SW geological sections drawn over a century displayed the Cenozoic (and in belts the late Palaeozoic--Cambrian) deformation (F2). The so-called bi-generation garnet and Cenozoic hangover of Naha and Ray (1971a,b, 1972) are discussed: the upper greenschist to lower amphibolite facies ILHS exhibits such an apparent bi-generation (in garnet) feature (volume diffusion in higher metamorphic levels: M1) and the evidence of overthrusting across the “ Jutogh Thrust” is considered redundant.