Thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya, central Nepal: The composite orogenic system

The Himalayan orogen represents a ‘‘Composite Orogenic System’’ in which channel flow, wedge extrusion, and thrust stacking operate in separate ‘‘Orogenic Domains’’ with distinct rheologies and crustal positions. We analyze 104 samples from the metamorphic core (Greater Himalayan Sequence, GHS) and bounding units of the Annapurna-Dhaulagiri Himalaya, central Nepal. Optical microscopy and electron backscatter diffraction (EBSD) analyses provide a record of deformation microstructures and an indication of active crystal slip systems, strain geometries, and deformation temperatures. These data, combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the GHS. The profiles define a three-stage thermokinematic evolution from midcrustal channel flow (Stage 1, >7008C to 550–6508C), to rigid wedge extrusion (Stage 2, 400–6008C) and duplexing (Stage 3, <280–4008C). These tectonic processes are not mutually exclusive, but are confined to separate rheologically distinct Orogenic Domains that form the modular components of a Composite Orogenic System. These Orogenic Domains may be active at the same time at different depths/positions within the orogen. The thermokinematic evolution of the Annapurna-Dhaulagiri Himalaya describes the migration of the GHS through these Orogenic Domains and reflects the spatial and temporal variability in rheological boundary conditions that govern orogenic systems

Tracking the Growth of the Himalayan Fold‐and‐Thrust Belt From Lower Miocene Foreland Basin Strata: Dumri Formation, Western Nepal

New data from the lower Miocene Dumri Formation of western Nepal document exhumation of the Himalayan fold-thrust belt and provenance of the Neogene foreland basin system. We employ U-Pb zircon, Th-Pb monazite, Ar-40/Ar-39 white mica, and zircon fission track chronometers to detrital minerals to constrain provenance, timing, and rate of exhumation of Himalayan source regions. Clusters of Proterozoic-early Paleozoic (900-400 Ma) Th-Pb monazite and Ar-40/Ar-39 white mica detrital ages provide evidence for erosion of a Greater Himalayan sequence protolith unaffected by high-grade Eohimalayan metamorphism. A small population of similar to 40 Ma cooling ages in detrital white mica grains shows exhumation of low-grade metamorphic Tethyan Himalayan sequence through the similar to 350 degrees C closure temperature along the Tethyan Frontal thrust (proto-South Tibetan detachment) during the late Eocene. Dumri Formation detritus shows a similar to 12 Myr time difference between cooling of its source rocks through the similar to 350 and similar to 240 degrees C closure temperatures as recorded by similar to 40-38 Ma youngest peak cooling ages in Ar-40/Ar-39 detrital white mica and similar to 28-24 Ma youngest populations in detrital zircon fission track. Exhumation between circa 40 and 28 Ma is consistent with slip and exhumation along the Main Central Thrust. Combined with similar data from northwestern India, our study suggests west-to-east spatially variable exhumation rates along strike of the Main Central Thrust. Our data also show an increase in exhumation during middle Miocene-Pliocene time, which is consistent with growth of the Lesser Himalaya duplex.U.S. National Science Foundation (NSF) [Tectonics-EAR-1140068]; Conoco Fellowship scholarship (2016); Chevron Texaco Geology Fellowship (2016); University of Arizona Galileo Circle Scholarship (2017); U.S. National Science Foundation (NSF) [NSF EAR-1338583, EAR1649254]6 month embargo; published online: 29 August 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Dose‐ and time‐dependent effects of an immune challenge on fish across biological levels

Abstract Due to global changes, fish are increasingly exposed to immune challenges associated with disease outbreaks in aquatic ecosystems. Adjustments in physiology and behavior are generally critical to maintaining homeostasis after an immune challenge, but there is limited knowledge on the specific thresholds and dynamics of responses across levels of biological organization in fish. In this study, we tested how different concentrations of an antigens mixture (phytohemagglutinin and lipopolysaccharide) affected innate immunity with potential consequences on oxidative stress, energy reserves, body condition, and behavior across time, using the common gudgeon ( Gobio sp.) as model species. The immune challenge induced a transitory increase in lytic enzyme activity (i.e., lysozyme) and local immune response (i.e., skin swelling) 2 days after the antigen injection. The available energy stored in muscle was also reduced 4 days after injection, without inducing oxidative stress at the cellular level. Overall, the immune challenge induced limited costs at the molecular and cellular levels but had strong effects at the whole organism level, especially on behavior. Indeed, fish swimming activity and sociability were affected in a dose- and time-dependent manner. These results suggest that immune challenges have dose-dependent effects across levels of biological organization and that behavior is a key response trait to cope with pathogen-induced immune costs in the wild, although fitness consequences remain to be tested. , Highlights The costs induced by immune challenge vary in fish in a dose- and time-dependent manner. Medium and high doses of antigens mostly affected immune and behavioral traits with limited effects on fish condition, likely due to energy reallocation

Developmental temperature affects phenotypic means and variability: A meta‐analysis of fish data

Fishes are sensitive to their thermal environment, and face an uncertain future in a warming world. Theoretically, populations in novel environments might express greater levels of phenotypic variability to increase the chance of surviving – and eventually thriving – in the new conditions. Most research on the effect of the early thermal environment in fish species focuses on average phenotypic effects rather than phenotypic variability, but to understand how fishes will respond to rising temperatures we need to consider both the average response of the population, as well as the breadth of individual responses. Here we present the first meta-analysis on the effects of developmental temperature in fishes. Using data from 43 species and over 6,000 individual fish, we show that a change in developmental temperature induces a significant change in phenotypic means and variability, but differently depending on whether the temperature is increased or decreased. Decreases in temperature (cool environments) showed a significant decrease in phenotypic means and no change in phenotypic variability. Increases in temperature (warm environments) showed a non-significant increase in phenotypic means, and a marginally significant increase in phenotypic variability. Larger increases in temperature saw greater increases in phenotypic variability, but no increase in the mean phenotypic response. Together, our results suggest that fishes exhibit both directed and stochastic developmental plasticity in response to warming temperatures, which could facilitate or accelerate adaptation to a changing environment