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

Abstract

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

Pressure–temperature–time–deformation path of kyanite-bearing migmatitic paragneiss in the Kali Gandaki valley (Central Nepal): Investigation of Late Eocene–Early Oligocene melting processes

“…Schärer, 1984), even if this should be rather minor (e.g. Kellett et al, 2010). As it can be seen from Fig.…”

Petrochronologic record of metamorphism and melting in the upper Greater Himalayan sequence, Manaslu–Himal Chuli Himalaya, west-central Nepal

“…Previous geochronologic studies have noted a correlation between monazite chemical zonation and U-Th-Pb age (e.g., Foster et al, 2002;Gibson et al, 2004;Kohn et al, 2005;Cottle et al, 2009a;Kellett et al, 2010). These studies have shown that individual grains are capable of recording evidence of multiple growth and resorption events and that the relative abundance of yttrium within the different zones can be linked to processes controlling the yttrium budget of the rock.…”

Exhumation of (ultra-)high-pressure terranes: concepts and mechanisms

“…For a system subducting material of heterogeneous strength, the plunger model predicts episodic exhumation during the subduction of the stronger units. Based on geophysical evidence for a midcrustal ramp, this mechanism has been suggested for the exhumation of cryptic lower-crustal granulitized eclogites in Solid Earth, 4, 75-92, 2013 www.solid-earth.net/4/75/2013/ C. J. Warren: Exhumation of (ultra-)high-pressure terranes 85 the eastern Himalaya (Kellett et al, 2010;Grujic et al, 2011;Warren et al, 2011), but its operation may be difficult to prove in ancient collisional settings.…”