The Main Central Thrust (MCT) juxtaposes the high‐grade Greater Himalayan Crystallines over lower‐grade Lesser Himalaya Formation; an apparent inverted metamorphic sequence characterizes shear zone that underlies thrust. Garnet‐bearing assemblages sampled along Marysandi River and Darondi Khola in Annapurna region of central Nepal show striking differences garnet zoning Mn, Ca, Mg, Fe above below MCT. Thermobarometry MCT footwall rocks yields temperature pressure gradients ∼18°C km −1 ∼0.06...

The origin of the paired granite belts and inverted metamorphic sequences Himalaya has generally been ascribed to development Main Central Thrust (MCT). Although a variety models have proposed that link early Miocene anatexis with metamorphism, recent dating studies indicate recrystallization elements MCT footwall occurred in central as recently ∼6 Ma. recognition hanging wall magmatism metamorphism are not spatially temporally related renders unnecessary need for exceptional physical...

The Lesser Himalaya (LH) consists of metasedimentary rocks that have been scrapped off from the underthrusting Indian crust and accreted to mountain range over last ∼20 Myr. It now forms a significant fraction Himalayan collisional orogen. We document kinematics thermal metamorphism associated with deformation exhumation LH, combining thermometric thermochronological methods structural geology. Peak metamorphic temperatures estimated Raman spectroscopy carbonaceous material decrease...

Research Article| April 01, 2003 Kinematic model for the Main Central thrust in Nepal D.M. Robinson; Robinson 1Department of Geosciences, University Arizona, Tucson, Arizona 85721, USA Search other works by this author on: GSW Google Scholar P.G. DeCelles; DeCelles C.N. Garzione; Garzione 2Department Earth and Environmental Sciences, Rochester, New York 14627, O.N. Pearson; Pearson 3Department T.M. Harrison; Harrison 4Research School Australian National University, Canberra ACT 0200,...

Research Article| January 01, 2002 U-Th-Pb Dating of Phosphate Minerals T. Mark Harrison; Harrison School Earth Sciences, The Australian National University, Canberra, A.C.T. 0200 Australia Search for other works by this author on: GSW Google Scholar Elizabeth J. Catlos; Catlos Geology, Oklahoma State Stillwater, 74078 Jean-Marc Montel LMTG-Minéralogie UMR, CNRS 5563, 39 allées Guesde, 31000 Toulouse, France Reviews in Mineralogy and Geochemistry (2002) 48 (1): 524–558....

Abstract In the Sikkim region of north‐east India, Main Central Thrust (MCT) juxtaposes high‐grade gneisses Greater Himalayan Crystallines over lower‐grade slates, phyllites and schists Lesser Himalaya Formation. Inverted metamorphism characterizes rocks that immediately underlie thrust, large‐scale South Tibet Detachment System (STDS) bounds northern side Crystallines. situ Th–Pb monazite ages indicate MCT shear zone in was active at c. 22, 14–15 12–10 Ma, whereas zircon from a slightly...

Research Article| July 01, 2001 Pressure-temperature-time path discontinuity in the Main Central thrust zone, central Nepal Matthew J. Kohn; Kohn 1Department of Geological Sciences, University South Carolina, Columbia, Carolina 29208, USA Search for other works by this author on: GSW Google Scholar Elizabeth Catlos; Catlos 2Department Earth and Space California, Los Angeles, California 90095, Frederick Ryerson; Ryerson 3Institute Geophysics Planetary Physics, Lawrence Livermore National...

Allanite, which is a common accessory mineral in wide variety of rock types, typically contains high concentrations Th and U; thus, an in-situ method U-Th-Pb dating this phase would have broad application. We describe to permit Th-Pb ages allanite be determined with approximately ±10% accuracy using high-resolution ion microprobe. Knowledge the composition substitution mechanisms complex key understanding relative ionization efficiencies Th+ Pb+. The chemical compositions three samples used...

With the advent of techniques that preclude mineral separation, ages from specific compositional domains in monazite [(Ce,La,Th)PO4] have provided a wealth information regarding timing geologic evolution numerous regions. However, confusion can arise when single grains show large differences age fail to correlate chemistry or location within monazite. Generalizations lead incorrect interpretations include zoning Y, Th, and/or rare earth elements (REE) always identify: (1) distinct tectonic...

The oldest-known air-breathing land animal is the millipede Pneumodesmus newmani, found in Cowie Harbour Fish Bed at Stonehaven, Scotland. Here we report youngest, most concordant 238U-206Pb zircon age from ash below fish bed of 413.7±4.4 Ma (±2σ), whereas youngest a tuffaceous sandstone above statistically indistinguishable 414.3±7.1 Ma. thus appears to be lowermost Devonian (Lochkovian), contrary previously accepted mid-Silurian based on palynomorphs adjacent exposures. This has...

Abstract 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 created using garnet and whole rock compositions as input parameters into a semiautomated Gibbs free‐energy‐minimization technique. The conditions recorded by paths, in general, yield similar T but lower P compared to estimates from mineral equilibria quartz‐in‐garnet Raman barometry. are used...

Subduction recycles aqueous fluids from slab and sediment to the mantle. zones are long-lived, but time scales for fluid-rock interaction within subduction complexes uncertain. Large-ion lithophile elements (potassium barium) were added eclogite (subducted basalt) during high pressure/temperature metamorphism via phengite crystallization zone fluids. Phengite grains blocks their metasomatic selvages yielded 40Ar/39Ar ages across between samples that indicate 25 60 million years of in Samana...