High-resolution, garnet-based pressure-temperature (P-T) paths were obtained for nine rocks across the Himalayan Main Central Thrust (MCT) (Marsyangdi River transect, central Nepal). Paths were created using garnet and whole rock compositions as input parameters into a semiautomated Gibbs free-energy-minimization technique. The conditions recorded by the paths, in general, yield similar T but lower P compared to estimates from mineral equilibria and quartz-in-garnet Raman barometry. The paths are used to modify a model based on a two-dimensional finite difference solution to the diffusion-advection equation. In this model, P-T paths recorded by the footwall garnets result from fault motion at specified times, thermal advection, and alteration of topography. The best fit between the high-resolution P-T paths and model predictions is that from 25 to 18 Ma, samples within the MCT footwall moved at 5 km/Ma, while those in the hanging wall moved at 10 km/Ma. Under these conditions, topography grew to 3.5 km. A pause in activity along the MCT between 18 and 15 Ma allows heat to advect and may be due to a transfer of tectonic activity to the structures closer to the Indian subcontinent. During this time, the topography erodes at a rate of 1.5 km/Ma. Thrusting within the MCT footwall reactivates between 8 and 2 Ma with exhumation rates up to 12 mm/yr since the Pliocene. The results suggest the potential for the highestresolution garnet-based P-T paths to record both the thermobarometric consequences of fault motion and large-scale erosion.Plain Language Summary The Main Central Thrust (MCT) is a major Himalayan fault system largely responsible for the generation of its high topography. Garnets across the MCT record their growth history in the crust through changes in their chemistry. These chemical changes can be extracted and modeled. Here we report detailed pressure-temperature paths recorded by garnets collected across the MCT along the Marsyangdi River in central Nepal. The paths track evolving conditions in the Earth's crust when the MCT was active during the growth of the Himalayas. The results suggest that the MCT formed as individual rock packages moved at distinct times. Further modeling makes predictions about how the Himalayas developed, including that the MCT may have ceased motion 18-15 million years ago, as other faults closer to the Indian subcontinent became active, and that it reactivated 8-2 million years ago, leading to the generation of high topography. The modeling also suggests that very high erosion rates occurred within the range after reactivation. Although garnets have long been used to understand how fault systems evolve, we provide details of an approach that allows higher-resolution data to be extracted from them and show how they could be used to track large-scale erosion.

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The Menderes Massif (Turkey) is a metamorphic core complex that records Alpine crustal shortening and extension. Here, nine garnet-bearing schist samples in the Central Menderes Massif (CMM) from below the Alaşehir detachment (AD) were studied to reconstruct their growth history. P-T estimates made using a chemical zoning approach, and petrological observations, indicate garnet grew between ~6 kbar and 550°C and 7.5-9 kbar and 625-650°C. Two P-T path shapes from two samples emerged (isobaric and burial), suggesting that either separate garnet-growth events occurred, or different garnet generations from the same metamorphic event were sampled. Despite observable diffusional modification in most garnets, thermobarometric estimates for crystal-rim growth yield P-T estimates similar to those reported elsewhere in the region. Ion microprobe monazite ages, paired with textural observations, from three of the samples time early retrograde metamorphism (~36-28 Ma). To better understand Neogene extension/exhumation, K-feldspar 40Ar/39Ar ages were obtained from two synextensional granites (Salihli and Turgutlu) exposed along the AD and two from the northern Simav detachment (Koyunoba and Eğrigöz). This data suggests the Simav detachment footwall rapidly exhumed at ~20 Ma, whereas the AD experienced two periods of exhumation/cooling (~14 Ma and~5 Ma). AD ages support a pulsed exhumation model for the massif.

The Menderes Massif, Turkey, is a type locality for deciphering the plate tectonic response from collision‐ to extension‐driven exhumation. Conventional thermobarometry and garnet pressure‐temperature (P‐T) paths from isochemical phase diagrams were calculated across a major fault (Selimiye Shear Zone, SSZ) bounding the southern edge of the Menderes Massif. Both approaches yield similar garnet rim temperatures (from 555 to 671 °C), but estimated P differs by between 8 and 15 kbar. Three garnets north of the SSZ reveal N‐shaped P‐T paths, whereas paths from three samples south of the SSZ show a simple increase in P‐T. Monazite and zircon were dated in thin section from the same rocks using Secondary Ion Mass Spectrometry and Laser Ablation Inductively Coupled Plasma‐Mass Spectrometry, respectively. Textural relationships of monazite within garnet appears indicative of post‐garnet growth. The amount of monazite common 204Pb and 137Ba+/Th+ significantly exceeds what is observed for the monazite age standard, suggesting their ages mark fluid‐driven events, loosely constrained to Late Eocene‐Early Miocene. Some zircon ages are consistent with Cambro‐Ordovician ages reported elsewhere in the region, and other ages are Neoproterozoic and Permian‐Triassic, a period not previously recognized in this area. Despite the lack of age constraints for the duration of garnet growth, we present a thermal model to understand the meaning of the N‐shaped path. These paths are best reproduced by thermal models incorporating SSZ thrusting before and after denudation. This paper presents an example of the insight from high‐resolution P‐T paths, and an example of denudation within a prograde metamorphic event.

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