Optical and infrared photometry of the Type IIn SN 1998S: days 11–146

We present contemporaneous optical and infrared (IR) photometric observations of the Type IIn SN 1998S covering the period between 11 and 146 d after discovery. The IR data constitute the first ever IR light curves of a Type IIn supernova. We use blackbody and spline fits to the photometry to examine the luminosity evolution. During the first 2–3 months, the luminosity is dominated by the release of shock-deposited energy in the ejecta. After ∼100 d the luminosity is powered mostly by the deposition of radioactive decay energy from 0.15±0.05 M_⊙ of ⁵⁶Ni which was produced in the explosion. We also report the discovery of an astonishingly high IR excess, K − L '=2.5, that was present at day 130. We interpret this as being due to thermal emission from dust grains in the vicinity of the supernova. We argue that to produce such a high IR luminosity so soon after the explosion, the dust must be pre-existing and so is located in the circumstellar medium of the progenitor. The dust could be heated either by the UV/optical flash (IR echo) or by the X-rays from the interaction of the ejecta with the circumstellar material.     

Evidence for low‐temperature growth of fayalite and hedenbergite in MacAlpine Hills 88107, an ungrouped carbonaceous chondrite related to the CM‐CO clan

Abstract— The carbonaceous chondrite MacAlpine Hills (MAC) 88107 has bulk composition and mineralogy that are intermediate between those of CO and CM chondrites. This meteorite experienced minor alteration and a low degree of thermal metamorphism (petrologic type 3.1) and escaped post‐accretional brecciation. The alteration resulted in the formation of fayalite (Fa_90–100). Al‐free hedenbergite (～Fs₅₀Wo₅₀), phyllosilicates (saponite‐serpentine intergrowths), magnetite, and Ni‐bearing sulfides (pyrrhotite and pentlandite). Fayalite and hedenbergite typically occur as veins, which start at the opaque nodules in the chondrule peripheries, crosscut fine‐grained rims and either terminate at the boundaries with the neighboring fine‐grained rims or continue as layers between these rims. These observations suggest that fayalite and hedenbergite crystallized after accretion and compaction of the fine‐grained rims. Fayalite also overgrows isolated forsteritic (Fa_1–5) and fayalitic (Fa_20–40) olivine grains without any evidence for Fe‐Mg interdiffusion; it also replaces massive magnetite‐sulfide grains. The initial ⁵³Mn/⁵⁵Mn ratio of (1.58 ± 0.26) × 10^?6 in the MAC 88107 fayalite corresponds to an age difference between the formation of fayalite and refractory inclusions in Allende of either ～9 or 18 Ma, depending upon the value of the solar system initial abundance of ⁵³Mn used in age calculations. Formation of secondary fayalite and hedenbergite requires mobilization and transport of Ca, Si, and Fe either through a high‐temperature gaseous phase (Hua and Buseck, 1995) or low‐temperature aqueous solution (Krot et al., 1998a, b). The high‐temperature nebular model for the origin of fayalite (Hua and Buseck, 1995) fails to explain (a) formation of fayalite‐hedenbergite assemblages after accretion of fine‐grained rims that lack any evidence for high‐temperature processing; (b) extreme fractionation of refractory lithophile elements of similar volatility, Ca and Al, in hedenbergite; and (c) absence of Fe‐Mg interdiffusion along fayalite‐forsterite boundaries. We conclude that fayalite and hedenbergite in MAC 88107 formed during late‐stage, low‐temperature (approximately 150–200 °C) aqueous alteration. The data for MAC 88107 extend the evidence for an early onset of aqueous activity on chondrite parent bodies and reinforce the conclusion that liquid water played an important role in the chemical and mineralogical evolution of the first chondritic planetesimals.     

Influence of dissimilatory metal reduction on fate of organic and metal contaminants in the subsurface

Geobacter become dominant members of the microbial community when Fe(III)-reducing conditions develop as the result of organic contamination, or when Fe(III) reduction is artificially stimulated. These results suggest that further understanding of the ecophysiology of Geobacter species would aid in better prediction of the natural attenuation of organic contaminants under anaerobic conditions and in the design of strategies for the bioremediation of subsurface metal contamination. Received, May 1999/Revised, October 1999/Accepted, October 1999     

BAVARIAN LEAVENWORTH AND THE SYMBOLIC ECONOMY OF A THEME TOWN

ABSTRACT. Theme towns are an often‐overlooked but significant form of tourism in rural areas. Many a small town across the United States, faced with a declining resource‐based economy, has turned to “theming” as an economic‐development strategy. In hopes of creating an alluring landscape, the built environment is radically transformed, and a variety of invented traditions are instituted. This article explores one such place‐Leavenworth, Washington‐that “went Bavarian” in the 1960s and is widely viewed as a success story. We examine four interrelated concepts that produce the symbolic economy of Leavenworth: emulation of other theme towns, authenticity, visual difference, and place marketing. After discussing each, we turn to the questions of how residents are affected by tourism and what it is like to live in Leavenworth.     

Using wind run to predict sand drift

Conventional aeolian sand transport models relate mass transport rate to wind speed or shear velocity, usually expressed and empirically tested on a 1-s time scale. Projections of total sand delivery over long time scales based on these models are highly sensitive to any small bias arising from statistical fitting on empirical data. We analysed time series of wind speed and sand transport rate collected at 14 independent measurement stations on a beach during a prior field experiment. The results show that relating total sand drift to cumulative above-threshold wind run yields models which are more statistically robust when fitted on empirical data, generating smaller prediction errors when projected to longer time scales. Testing of different power exponents indicates that a linear relationship between sand drift and above-threshold wind run yields the best results. These findings inspire a speculative novel phenomenological model relating the mass flow of air in the boundary layer to the mass transport of sand over the surface. © 2020 John Wiley & Sons, Ltd.     

Ridge subduction,magmatism, and metallogenesis

Modern oceans contain large bathymetric highs(spreading oceanic ridges, aseismic ridges or oceanic plateaus and inactive arc ridges) that, in total, constitute more than 20–30% of the total area of the world's ocean floor. These bathymetric highs may be subducted, and such processes are commonly referred to as ridge subduction. Such ridge subduction events are not only very common and important geodynamic processes in modern oceanic plate tectonics, they also play an important role in the generation of arc magmatism, material recycling, the growth and evolution of continental crust, the deformation and modification of the overlying plates, and metallogenesis at convergent plate boundaries. Therefore, these events have attracted widespread attention. The perpendicular or high-angle subduction of mid-ocean spreading ridges is commonly characterized by the occurrence of a slab window, and the formation of a distinctive adakite–high-Mg andesite–Nb-enriched basalt-oceanic island basalt(OIB) or a mid-oceanic ridge basalt(MORB)-type rock suite, and is closely associated with Au mineralization. Aseismic ridges or oceanic plateaus are traditionally considered to be difficult to subduct, to typically collide with arcs or continents or to induce flat subduction(low angle of less than 10°) due to the thickness of their underlying normal oceanic crust(6–7 km) and high topography. However, the subduction of aseismic ridges and oceanic plateaus occurred on both the western and eastern sides of the Pacific Ocean during the Cenozoic. On the eastern side of the Pacific Ocean, aseismic ridges or oceanic plateaus are being subducted flatly or at low angles beneath South and Central American continents, which may cause a magmatic gap. But slab melting can occur and adakites, or an adakite–high-Mg andesite–adakitic andesite–Nb-enriched basalt suite may be formed during the slab rollback or tearing. Cu-Au mineralization is commonly associated with such flat subduction events. On the western side of the Pacific Ocean, however, aseismic ridges and oceanic plateaus are subducted at relatively high angles(30°).These subduction processes can generate large scale eruptions of basalts, basaltic andesites and andesites, which may be derived from fractional crystallization of magmas originating from the subduction zone fluid-metasomatized mantle wedge. In addition,some inactive arc ridges are subducted beneath Southwest Japan, and these subduction processes are commonly associated with the production of basalts, high-Mg andesites and adakites and Au mineralization. Besides magmatism and Cu-Au mineralization,ridge subduction may also trigger subduction erosion in subduction zones. Future frontiers of research will include characterizing the spatial and temporal patterns of ridge subduction events, clarifying the associated geodynamic mechanisms, quantifying subduction zone material recycling, establishing the associated deep crustal and mantle events that generate or influence magmatism and Cu-Au mineralization, establishing criteria to recognize pre-Cenozoic ridge subduction, the onset of modernstyle plate tectonics and the growth mechanisms for Archean continental crust.     

The temporal and spatial scales of rocky coast geomorphology: a commentary

Rocky shores are complex landforms that result from marine erosion and subaerial weathering. They are time‐integrated features where their present day form is the result of instantaneous erosion, often on the millimetre to sub‐metre scale, occurring for centuries to millennia. As a result, research on rocky coasts focuses on a range of temporal and spatial scales from granular‐scale swelling of a rock surface and instantaneous wave impact to modelling millennial‐scale sea level drivers. The challenge for rocky coast researchers is either to upscale or to downscale their results to the human‐timescales of greatest interest to managers. The research presented in Earth Surface Processes and Landforms over the past 3 years highlights the range of spatial and temporal approaches to the study of coastal cliffs and shore platforms. We identify a key temporal and spatial gap in current research. Seasonal–annual timeframes over hundreds of metres to kilometre scale studies appear to be lacking and are likely critical in understanding the future evolution of rocky coasts, especially their response to climate change. Copyright © 2017 John Wiley & Sons, Ltd.     

Eocene melting of subducting continental crust and early uplifting of central Tibet: Evidence from central-western Qiangtang high-K calc-alkaline andesites, dacites and rhyolites

Changes in oceanic O–Sr isotopic compositions and global cooling beginning in the Eocene are considered to have been caused by the uplift of the Tibetan Plateau. The specific timing and uplift mechanism, however, have long been subjects of debate. We investigated the Duogecuoren lavas of the central-western Qiangtang Block, which form the largest outcrops among Cenozoic lavas in northern-central Tibet and have widely been considered as shoshonitic. Our study demonstrates, however, that most of these lavas are high-K calc-alkaline andesites, dacites and rhyolites. Moreover, they are characterized by high Sr (367–2472 ppm) and Al₂O₃ (14.55–16.86 wt.%) and low Y (3.05–16.9 ppm) and Yb (0.31–1.48 ppm) contents and high La/Yb (27–100) and Sr/Y (48–240) ratios, similar to adakitic rocks derived by partial melting of an eclogitic source. They can be further classified as either peraluminous and metaluminous subtypes. The peraluminous rocks have relatively high SiO₂ (> 66 wt.%) contents, and low MgO (< 1.0 wt.%), Cr (4.94–23.3 ppm) and Ni (2.33–17.0 ppm) contents and Mg^# (20–50) values, while the metaluminous rocks exhibit relatively low SiO₂ (55–69 wt.%) contents, and high MgO (1.41–6.34), Cr (25.7–383 ppm), Ni (14.13–183 ppm) and Mg^# (46–69) values, similar to magnesian andesites. ⁴⁰Ar/³⁹Ar and SHRIMP zircon U–Pb dating reveal that both peraluminous and metaluminous adakitic rocks erupted in the Eocene (46–38 Ma). Paleocene–Early Miocene thrust faults and associated syn-contractional basin deposits in the Qiangtang Block suggest that this region was undergoing crustal shortening within a continent during the Eocene. The low ε_Nd (− 2.81 to − 6.91) and high ⁸⁷Sr/⁸⁶Sr (0.7057–0.7097), Th (11.2–32.3 ppm) and Th/La (0.23–0.88) values in the Duogecuoren adakitic rocks further indicate that they were not derived by partial melting of subducted oceanic crust. Taking into account tectonic and geophysical data and the compositions of xenoliths in Cenozoic lava in northern-central Tibet, we suggest that the peraluminous adakitic rocks were most probably derived by partial melting of subducted sediment-dominated continent of the Songpan-Ganzi Block along the Jinsha suture to the north at a relatively shallow position (the hornblende + garnet stability field), but the metaluminous adakitic rocks likely originated from the interaction between peraluminous adakitic melts generated at greater depths (the garnet + rutile stability field) and mantle. Because the Duogecuoren adakitic rocks must have originated from a garnet-bearing (namely, eclogite facies) source, Eocene continental subduction along the Jinsha suture caused the thickening of the Qiangtang crust. Given that crustal thickening generally equates with elevation, the uplift of the Central Tibetan Plateau probably began as early as 45–38 Ma, which provides important evidence for tectonically driven models of oceanic O–Sr isotope evolution during global cooling and Asian continental aridification beginning in the Eocene.     

Comment on A.J. Biggin et al., A comparison of a quasi-perpendicular method of absolute palaeointensity determination with other thermal and microwave techniques,Earth and Planetary Science Letters 257 (2007) 564–581

While Biggin et al.'s paper is an important review and critique of palaeomagnetic methods employed at present, we point out here that if the grain size selectivity of microwaves is employed, instead of just using them to heat the sample, alteration can be avoided completely, and previously unavailable grain size dependence of the magnetic moment can be recovered.     

Travel impedance agreement among online road network data providers

ABSTRACT

Online mapping providers offer unprecedented access to spatial data and analytical tools; however, the number of analytical queries that can be requested is usually limited. As such, Volunteered Geographic Information (VGI) services offer a viable alternative, provided that the quality of the underlying spatialtheir data is adequate. In this paper, we evaluate the agreement in travel impedance between estimates from MapQuest Open, which embraces OpenStreetMap (OSM) data–a is based on VGI datasetfrom OpenStreetMap (OSM), and estimates from two other popular commercial providers, namely Google Maps? and ArcGIS? Online. Our framework is articulated around three components, which simulates potentialcalculates shortest routes, estimates their travel impedance using a routing service Application Program Interface (API), and extracts the average number of contributors for each route. We develop an experimental setup with a simulated dataset for the state of North Carolina. Our results suggest a strong correlation of travel impedance among all three road network providers. and that travel impedanceThe agreement is the greatest in areas with a denser road network and the smallest for routes of shorter distances. Most importantly, tTravel estimates from MapQuest Open are nearly identical to both commercial providers when the average number of OSM contributors along the route is larger. The latter finding contributes to a growing body of literature on Linus’s law, recognizing that a larger group of contributors holds the potential to validate and correct inherent errors to the source dataset.