Metamorphic history of a syn-convergent orogen-parallel detachment: The South Tibetan detachment system, Bhutan Himalaya

摘要: The South Tibetan detachment system (STDS) in the Himalayan orogen is an example of normal-sense displacement on orogen-parallel shear zone during lithospheric contraction. Here, situ monazite U(-Th)-Pb geochronology combined with metamorphic pressure and temperature estimates to constrain pressure-temperature-time ( P-T-t ) paths for both hangingwall footwall rocks a Miocene ductile component STDS (outer STDS) now exposed eastern Himalaya. outer located south younger, ductile/brittle (inner STDS), characterized by structurally upward decreasing grade corresponding transition from sillimanite-bearing Greater sequence garnet that preserves diffusive chemical zoning staurolite-bearing Chekha Group hangingwall, records prograde zoning. Monazite ages indicate growth occurred prior partial melting at 22.6 ± 0.4 Ma, peak temperatures were reached following c. 20.5 Ma. In contrast, 22 Ma. Normal-sense (top-to-the-north) shearing followed metamorphism 23 Ma until least 16 Ma. Retrograde are compatible modelled analogue isolated inner intervening extrusion dome mid-crustal material.