Geologic field evidence for non-lithostatic overpressure recorded in the North American Cordillera hinterland,northeast Nevada

There is a long-standing discrepancy for numerous North American Cordillera metamorphic core complexes between geobarometric pressures recorded in the exhumed rocks and their apparent burial depths based on palinspastic reconstructions from geologic field data.In particular,metamorphic core complexes in eastern Nevada are comprised of well-documented~12-15 km thick Neoproterozoic-Paleozoic stratigraphy of Laurentia’s western passive margin,which allows for critical characterization of field relationships.In this contribution we focus on the Ruby Mountain-East Humboldt Range-Wood Hills-Pequop Mountains(REWP)metamorphic core complex of northeast Nevada to explore reported peak pressure estimates versus geologic field relationships that appear to prohibit deep burial.Relatively high pressure estimates of 6-8 kbar(23-30 km depth,if lithostatic)from the lower section of the Neoproterozoic-Paleozoic passive margin sequence require burial and or repetition of the passive margin sequence by 2-3×stratigraphic depths.Our observations from the least migmatized and/or mylonitized parts of this complex,including field observations,a transect of peak-temperature(T_(p))estimates,and critical evaluation of proposed thickening/burial mechanisms cannot account for such deep burial.From Neoproterozoic-Cambrian(€)rocks part of a continuous stratigraphic section that transitions~8 km upsection to unmetamorphosed Permian strata that were not buried,we obtained new quartz-in-garnet barometry via Raman analysis that suggest pressures of~7 kbar(~26 km).A T_(p)traverse starting at the same basal€rocks reveals a smooth but hot geothermal gradient of≥40℃/km that is inconsistent with deep burial.This observation is clearly at odds with thermal gradients implied by high P-T estimates that are all≤25℃/km.Remarkably similar discrepancies between pressure estimates and field observations have been discussed for the northern Snake Range metamorphic core complex,~200 km to the southeast.We argue that a possible reconciliation of longestablished field observations versus pressures estimated from a variety of barometry techniques is that the rocks experienced non-lithostatic tectonic overpressure.We illustrate how proposed mechanisms to structurally bury the rocks,as have been invoked to justify published high pressure estimates,are entirely atypical of the Cordillera hinterland and unlike structures interpreted from other analogous orogenic plateau hinterlands.Proposed overpressure mechanisms are relevant in the REWP,including impacts from deviatoric/differential stress considerations,tectonic mode switching,and the autoclave effect driven by dehydration melting.Simple mechanical arguments demonstrate how this overpressure could have been achieved.This study highlights that detailed field and structural restorations of the least strained rocks in an orogen are critical to evaluate the tectonic history of more deformed rocks.

Effect of brazing parameters on fillet size and microstructure of cladded fin-microchannel tube joints

This work concerns the optimization of furnace brazing conditions for joining micro-multiport aluminum tubes and fins made with AA4343/AA3003/AA4343 brazing sheet in mini-assemblies mimicking the core of an automotive heat exchanger.Taguchi method was used for design of experiment,considering five process parameters with two levels of values.The aim was to maximize the fillet size of the brazed joints,which has an important influence on the thermal integrity and mechanical properties.Fillet length measurements of brazed joints were performed with a metallographic microscope.The statistical analysis allowed to obtain the optimum values of process parameters(peak temperature,residence time,heating rate,microchannel tube type and flux).At a 95%confidence level,the variability of fillet length is most significantly affected by the peak brazing temperature(77%),residence time(15%)and heating rate(7%).The predicted maximum fillet length was(152±11)μm,which was corroborated by confirmation trials.The microstructural analysis of tube−fin joints showed that variations in peak temperature and residence time affect only the size of the eutectic zone of fillet formed,but not the nature or composition of the constituent phases.

The effects of humus moisture content on underground fires in a Larix gmelinii plantation

Underground fires are a smoldering combustion with a slow spread rate, low temperatures and no flame. They can last from days to several months, and can even become overwintering fires. They are difficult to find, leading to considerable damage to the forests. The moisture content of combustible fuels is an important factor in the occurrence and persistence of underground forest fires. The Daxing’an Mountains are a hot spot for underground fires in China. This paper looks at the influence of different moisture contents on underground fire characteristics using simulation combustion experiments in the laboratory. The study showed that peak temperature and spread rate fluctuation of humus at different moisture levels increased with humus depth. Peak temperature and spread rate fluctuation of humus at different depths decreased with increased moisture;moisture content and depth of humus had a significant effect on peak temperature and spread rate fluctuation;peak temperature at different depths decreased with increased moisture;the spread rate in upper layers increased with moisture content, while the spread rate in the lower layers decreased with increased moisture content.

Microstructural analysis of the softened zone in the welding joint of 100 kg class hot-rolled extra-high-strength steel

Using the Gleeble 3500 thermal-mechanical system to simulate thermal cycles with different peak temperatures, the hardness and microstructure in the heat-affected zones of two kinds of 100 kg class hot-rolled extra-high-strength steel were compared. When the peak temperature of the thermal cycle was 800℃ ,incomplete transformation occurred during quenching in both steels, and massive martensite and bainite grains were formed. The hardness was determined by the composition and distribution of the microstructure. The concentration of massive martensite was low, and hence the hardness was low,in steel #1. Conversely,the massive martensite content in steel #2 was high and uniformly distributed,resulting in a high hardness. These findings can provide a reference for improving the mechanical properties in the softened zone.

A novel electrical measurement method of peak junction temperature based on the excessive thermotaxis effect of low current

It has been a scientific and technological problem in the field of microelectronics for several decades that the electrical method is used to measure the peak junction temperature of power transistors. Based on the excessive thermotaxis effect of low current, a novel electrical measurement method of the peak junction temperature is presented in this paper. The method is called the thermal spectrum analysis method of transistors, simply designated TSA （thermal spectrum analysis method）. Unlike the common method which uses a single measuring current, TSA uses multi-step currents to measure temperature-sensitive parameters. Based on the excessive thermotaxis effect of low current and the sub-transistor parallel model, the peak junction temperature and non-uniform property of junction temperature distribution are analyzed successfully.

Microstructural Evolution and Softening Behavior of Simulated Heat-Affected Zone in 2219 Aluminum Alloy

The effect of peak temperature （Tp） at 200, 300, 400, 500 and 550 ℃ on the microstructural evolution and softening behavior of the simulated heat-affected zone （HAZ） was studied in the 2219-T87 alloy by electron-backscatter diffraction, transmission electron microscopy, X-ray diffraction, micro-hardness and micro-tensile tests. The results showed that the grain size in the HAZs at 200-500 ℃ was comparable, but the number density of the strengthening precipitates （GP zones/θ′） decreased with increasing Tp. At a Tp of 550 ℃, the grain size significantly decreased and the distribution of the misorientation angles corresponded to the MacKenzie distribution. The GP zones/θ′ phase coarsened and translated into θ phases at Tp values in the range of 200-400 ℃. Increasing the Tp to 500 ℃ and above, some θ′ phases translated into θ phases and others dissolved into the α-Al matrix which led to an increase in the solid solution strengthening. The reduction of the number density of the GP zones/θ′ was responsible for the softening behavior.

Simulation study on heat-affected zone of high-strain X80 pipeline steel

The microstructure evolution and impact-toughness variation of heat-affected zone（HAZ）in X80 highstrain pipeline steel were investigated via a welding thermal-simulation technique,Charpy impact tests,and scanning electron microscopy observations under different welding heat inputs and peak temperatures.The results indicate that when heat input was between 17 and 25kJ·cm^（-1）,the coarse-grained heat-affected zone showed improved impact toughness.When the heat input was increased further,the martensite-austenite（M-A）islands transformed from fine lath into a massive block.Therefore,impact toughness was substantially reduced.When the heat input was 20kJ·cm^（-1） and the peak temperature of the first thermal cycle was between 900 and 1300°C,a higher impact toughness was obtained.When heat input was 20kJ·cm^（-1） and the peak temperature of the first thermal cycle was 1300°C,the impact toughness value at the second peak temperature of 900°C was higher than that at the second peak temperature of 800°C because of grain refining and uniformly dispersed M-A constituents in the matrix of bainite.