The Siang antiform which forms the southern portion of the Eastern Himalayan Syntaxis is a massive subaerial duplex comprised of Paleogene rocks. The specifics of growth and deformation of the Siang duplex remain ambiguous due to limited studies in the region. Using multi-thermochronometry and Raman spectroscopy of carbonaceous matter (RSCM), this study place temporal depth constraints on the formation of the duplex. Results show that the cooling history of the northern part of the Siang antiform is separate from the central and proximal zone. The study utilises 09 new biotite $^{40}$Ar/$^{39}$Ar and 05 zircon (U–Th)/He (ZHe) ages. The new data is complemented with our earlier published (Salvi et al. in Geomorphology 284:238–249, 2017) 09 ZHe and 11 AFT ages and 02 ZHe ages of Liebke et al. (Geol. Soc. London, Spec. Publ. 353:71–97, 2011). Biotite $^{40}$Ar/$^{39}$Ar cooling ages suggest that the distal end of the MCT zone in the Siang window was active at least till ca. 11 Ma. The ZHe cooling ages ca. 10–8 Ma intimate exhumation due to Lesser Himalayan duplexing on a shallower (${\sim}$7–8 km) MHT. The creation of several duplexed antiforms by the Paleogene rocks on the emplaced MBT thrust sheet led to doming up of the roof sheet. Erosion through the roof sheets exposed the Paleogene rocks presently seen in the Siang window. The peak metamorphic temperatures decrease from 650–400$^{\circ}$C in the lower LHS to 250–300$^{\circ}$C in the upper LHS, and < 200$^{\circ}$C in the sub-Himalaya. The RSCM results corroborate thermochronological ages and inform that the northern part of the metamorphosed lower LHS rocks exhumed from greater depths, >20 km during early-middle Miocene. While in the central and southern regions, the rocks exhumed from comparatively shallower depths of ${\sim}$7–8 km since the late Miocene. We suggest ${\sim}$3–4 km of the cover rocks have been removed since Pleistocene.

$\bf{Highlights}$

$\bullet$ First multi-thermochrometry studies suggest distal end of MCT zone in the Siang window was active till ca. 11 Ma.

$\bullet$ ZHe cooling ages ca. 10–8 Ma intimate exhumation due to Lesser Himalayan Duplexing on a shallower (${\sim}$ 7–8 km) MHT.

$\bullet$ The creation of several duplexed antiforms by the Paleogene rocks on the emplaced MBT thrust sheet led to doming up of the roof sheet.

$\bullet$ RSCM peak metamorphic temperatures furnish 650–400 $^{\circ}$C in the lower LHS to 250–300 $^{\circ}$C in the upper LHS, and < 200 $^{\circ}$C in the sub-Himalaya.

$\bullet$ Average exhumation rate post Late Pliocene is ${\sim}$ 1.6–3.3 mm/a in the Siang window, increases to 4.0–6.6 mm/a in the last 1.0 Ma, north of Tuting.