A peculiar feature of the Himalaya is the occurrence of a system of low‐angle normal faults and shear zones, the South Tibetan Detachment System (STDS), at the mountain crests. The STDS was active during synconvergent tectonics. We describe the STDS‐related sheared rocks along the Dhauli Ganga valley, in the Garhwal Himalaya (NW India), where the Malari granite, reported as an undeformed igneous body crosscutting the STDS, occurs. A detailed multidisciplinary study, integrating field‐based, microstructural, petrographic, and geochronological analyses, was carried out on rocks along this valley. We demonstrate how the noncoaxial ductile portion of the STDS affected the upper part of the Greater Himalaya Sequence migmatite, which experienced peak pressure (P)‐temperature (T) conditions of 0.9–1.1 GPa and ≥750°C at ≥24 Ma. This migmatite has been reworked structurally upward leading to the formation of high‐T sillimanite‐bearing mylonites. Further upward, medium‐T shearing deformed the Malari granite and leucogranite dykes, forming medium‐T mylonites. Ductile shearing was temporally constrained, based on new in situ monazite datings and previously published Ar‐Ar geochronology, between ~20 and 15 Ma. We demonstrate that a preserved ductile to brittle spatial and temporal transition of the STDS deformation exists, with the brittle features overprinting ductile ones. Our data shed new light on the geological evolution of the STDS in the NW Himalaya with implications for the relationship and relative timing of partial melting, granite emplacement, and deformation along low‐angle normal faults.

Vorticity estimates based on porphyroclasts analysis are limited by the extrapolation to three dimensions of two‐dimensional data. We describe a 3D approach based on the use of X‐ray micro‐computed tomography that better reflects the real 3D geometry of the porphyroclasts population. This new approach for kinematic vorticity analysis in the Munsiari Thrust mylonites, the lower boundary of the Main Central Thrust zone (MCTz) in Indian Himalaya, indicates a large pure shear component during non‐coaxial shearing. 40Ar/39Ar ages of micas along the mylonitic foliation of the Munsiari and Vaikrita thrusts (the upper boundary of the MCTz) constrain thrust activity to 5–4 and 8–9 Ma, respectively. Available kinematic vorticity analyses of the Vaikrita mylonites suggest the dominance of a simple shear component. Combining these data, we suggest that the southward and structurally downward shift of deformation along the MCTz was accompanied by a progressive increase in the pure shear component in a general shear flow.

The timing of shearing along the Vaikrita Thrust, the structurally upper boundary of the Main Central Thrust zone (MCTz), was constrained by combined microstructural, microchemical and geochronological investigations. Three different biotite-muscovite growth and recrystallisation episodes were observed: a relict mica-1; mica-2 along the main mylonitic foliation; mica-3 in coronitic structures around garnet during its breakdown. Analyses of biotite by electron microprobe show chloritization, and bimodal composition of biotite-2 in one sample. Muscovite-2 and muscovite-3 differ in composition from each other. Biotite and muscovite 39 Ar-40 Ar age spectra from all samples give both inter-sample and intrasample discrepancies. Biotite step ages range between 8.6 and 16 Ma, muscovite step ages between 3.6 and 7.8 Ma. These ages cannot be interpreted as "cooling ages", as samples from the same

Low-Angle Normal Faults (LANFs) represent in the central Southern Alps area (N Italy) the main structures along which the Variscan basement is in contact with the Upper Carboniferous-Permian volcanic-sedimentary succession. Tourmalinites frequently occur along LANFs, usually replacing former cataclasites. The mineralogy and chemical composition of tourmalinites point to a metasomatic origin. LANFs, together with high-angle faults, controlled the opening of the Permian Orobic Basin and likely acted as a preferred pathway for hydrothermal fluids that triggered the Boron-metasomatism. Along the Aga-Vedello LANF, tourmalinites appear to have formed after the cessation of fault activity, as no brittle post-metasomatism deformation overprint has been observed. These relationships suggest that the circulation of B-rich fluids occurred after the opening of the Orobic Basin that is broadly constrained to the Early Permian. At the same time, ca. 285–270 Ma, a strong magmatic activity affected all the Southern Alps, ranging in composition from mafic to acidic rocks and from intrusions at deep crustal levels to effusive volcanic products. The Early Permian magmatism was likely the source of the late-stage hydrothermal fluids that formed the tourmalinites. The same fluids could also have played a significant role in the formation of the Uranium ore deposit of the Novazza-Vedello mining district, as the ore bodies in the Vedello valley are concentrated along the basement-cover contact.

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