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Thermobarometric data and compositional zoning of garnet show the discontinuities of both metamorphic pressure conditions at peak-T and P-T paths across the Main Central Thrust (MCT), which juxtaposes the high-grade Higher Himalayan Crystalline Sequences (HHCS) over the low-grade Lesser Himalaya Sequences (LHS) in far-eastern Nepal. Maximum recorded pressure conditions occur just above the MCT (11 kbar), and decrease southward to 6 kbar in the garnet zone and northward to 7 kbar in the kyanite ± staurolite zone. The inferred nearly isothermal loading path for the LHS in the staurolite zone may have resulted from the underthrusting of the LHS beneath the HHCS. In contrast, the increasing temperature path during both loading and decompression (i.e. clockwise path) from the lowermost HHCS in the staurolite to kyanite ± staurolite transitional zone indicates that the rocks were fairly rapidly buried and exhumed. Exhumation of the lowermost HHCS from deeper crustal depths than the flanking regions, recording a high field pressure gradient (1.2-1.6 kbar km )1 ) near the MCT, is perhaps caused by ductile extrusion along the MCT, not the emplacement along a single thrust, resulting in the P-T path discontinuities. These observations are consistent with the overall scheme of the model of channel flow, in which the outward flowing ÔHHCSÕ and inward flowing ÔLHSÕ are juxtaposed against each other and are rapidly extruded together along the ÔMCTÕ. A rapid exhumation by channel flow in this area is also suggested by a nearly isothermal decompression path inferred from cordierite corona surrounding garnet in gneiss of the upper HHCS. However, peak metamorphic temperatures show a progressive increase of temperature structurally upward (570-740°C) near the MCT and roughly isothermal conditions (710-810°C) in the upper structural levels of the HHCS. The observed field temperature gradient is much lower than those predicted in channel flow models. However, the discrepancy could be resolved by taking into account heat advection by melt and ⁄ or fluid migration, as these can produce low or nearly no field temperature gradient in the exhumed midcrust, as observed in nature.

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Metamorphic P–T conditions, monazite chemical ages and zircon U–Pb ages from the gneisses exposed in the Oki belt, Japan, were integrated to unravel the multi‐stage metamorphic history of the belt. Microstructural observations combined with obtained P–T conditions and metamorphic ages reveal three distinct stages of metamorphism: M1, M2 and M3. The M1 stage occurred c. 1.85 Ga with high‐T granulite‐facies metamorphism (793–803°C and 9.8–12.3 kbar and 738–755°C and 9.1–12.0 kbar in the southwestern and southeastern Oki gneisses, respectively). The age of the M1 stage is well recorded in monazites included in large garnet porphyroblasts and low Th/U metamorphic rims in zircons from the Oki gneisses. The M1 metamorphism was overprinted by c. 230 Ma metamorphism (M2), which occurred at granulite‐facies conditions (817–829°C and 9.0–10.3 kbar) in the southwestern Oki gneisses and at upper amphibolite‐facies conditions (693°C and 5.3 kbar) in the southeastern Oki gneisses. Monazites in small garnets, euhedral zircons and outermost rims of zircons crystallized during this stage. The final metamorphism occurred as retrograde amphibolite‐facies recrystallization (M3) at conditions of 558–638°C and 3.7–4.8 kbar. The inherited cores in zircons yield ages from Paleoarchean to Paleoproterozoic but lack Palaeozoic ages. The detrital zircon distribution and the Paleoproterozoic metamorphic event in the Oki belt support the idea that the Oki gneisses are fragments of a Precambrian terrane rather than Palaeozoic sediments derived from the terrane. Combined with previous studies, we concluded that the c. 1.85 Ga M1 high‐T granulite‐facies metamorphism in the Oki belt could be related to that of the Jiao‐Liao‐Ji belt in the eastern North China block via the northern Gyeonggi and Nangrim Massifs on the Korean Peninsula, whereas the c. 250–230 Ma M2 stage could be associated with collision between the North and South China blocks. The Oki belt geologically corresponds to the northern Gyeonggi Massif in South Korea due to their similar Paleoproterozoic and Triassic tectonothermal events.