ALBERT

Description: Was the Yukon-Tanana Terrane (YTT), a California-sized part of south-central Yukon, an autochthonous or para-autochthonous part of northern British Columbia in the Early Cretaceous or was it part of a proposed allochthonous ‘Baja B.C.’ continent offshore of southern California? To answer this fundamental question, a paleomagnetic study has been completed on 347 specimens from 24 sites in the 114.7 ± 1.1 Ma Quiet Lake batholith. This 1300 km 2 pluton is composed mostly of massive medium-to-coarse grained biotite quartz monzonite that exhibits no evidence of either deformation or metamorphism, and that intrudes metamorphosed pre-Cretaceous basement rocks of the YTT in southern Yukon. The paleomagnetic analysis utilized thermal and alternating field step demagnetization, and saturation isothermal remanence methods. A well-defined characteristic remanent magnetization (ChRM) direction was isolated throughout the 500–585 °C temperature range at Decl. = 340.6°, Incl. = 77.4° ( N = 14 sites, k = 51.2, A 95 = 5.6°). The ChRM resides in magnetite with a low titanium content and is interpreted to be a primary thermoremanent magnetization. After correction for 490 km of geologically demonstrable dextral displacement on the inboard Tintina fault zone, the Quiet Lake batholith's paleopole is not significantly different at 95 per cent confidence from the co-eval 115 Ma reference paleopole for North America, giving non-significant translation and rotation estimates of 1.4° ± 5.1° (1) northwestwards and 10° ± 13° (1) clockwise, respectively. Thus, this is the first Early Cretaceous paleopole to show clearly that the YTT in Yukon is a para-autochthon that was part of North America's continental margin at that time. Further, after correction for Tintina fault displacement, the eight available Mesozoic YTT paleopoles agree closely with the North American apparent polar wander path (APWP). In contrast, the 22 paleopoles from the Intermontane Belt show the expected behaviour of an allochthonous thin-skin of terranes (i.e. ‘Baja B.C.’ behaviour) and record ~8° of northward translation and ~50° of clockwise rotation relative to both the YTT and North American APWPs during the Mesozoic and Paleogene.

Description: Climate change affects agriculture by altering not only output quantity, but also crop quality. We quantify the economic impacts of climate change on agriculture through changes in both quantity and quality, where quality is measured by crop grades. Our model controls for methodological issues regarding sample selection, aggregation, phenology, and nonlinearity. The empirical application to Japanese rice production indicates that temperature effects are asymmetric: quantity is especially vulnerable to cold, whereas quality is vulnerable to extremely high temperature. Using these results, we simulate the effect of global warming, and we find that warming (a 3 °C increase) increases farm revenues by improving yield but decreases revenues as a result of deteriorating quality. The net effect is negative, suggesting that quality matters more than quantity. The negative effect, however, can be mitigated by shifting cultivation periods and/or regions. Overall, our results suggest that the estimated impacts of climate change and adaptation strategies could be severely misleading unless quality is considered.

Description: In this article, we describe an improved method to assign the projection angle for averaged images using tilt-pair images for three-dimensional reconstructions from randomly oriented single-particle molecular images. Our study addressed the so-called ‘initial volume problem’ in the single-particle reconstruction, which involves estimation of projection angles of the particle images. The projected images of the particles in different tilt observations were mixed and averaged for the characteristic views. After the ranking of these group average images in terms of reliable tilt angle information, mutual tilt angles between images are assigned from the constituent tilt-pair information. Then, multiples of the conical tilt series are made and merged to construct a network graph of the particle images in terms of projection angles, which are optimized for the three-dimensional reconstruction. We developed the method with images of a synthetic object and applied it to a single-particle image data set of the purified deacetylase from archaea. With the introduction of low-angle tilt observations to minimize unfavorable imaging conditions due to tilting, the results demonstrated reasonable reconstruction models without imposing symmetry to the structure. This method also guides its users to discriminate particle images of different conformational state of the molecule.

Description: 〈span〉〈div〉Summary〈/div〉The extensive Yukon-Tanana terrane of the northern Canadian Cordillera has been considered controversially to be part of the allochthonous ‘Baja B.C.’ microcontinent or of the para-autochthonous North American cratonic margin during the Mesozoic. Paleomagnetic methods have isolated a very-stable Early Jurassic thermochemical remanent remagnetization in the terrane's felsic Tatlmain batholith and mafic Ragged stock after correction for: 1) rotation from northeast-plunging anticlinal deformation; 2) northerly dipping tectonic tilt of the host rocks; and, 3) northwestward regional translation on the adjacent Tintina transcurrent fault zone. The resulting 196 ± 6 Ma Tatlmain and Ragged paleopoles are 64.9° N, 44.8° E (A〈sub〉95〈/sub〉 = 5.9°) and 64.2° N, 58.5° E (A〈sub〉95〈/sub〉 = 7.7°), respectively. The YTT paleopoles support para-autochthonous tectonic models that have the YTT: 1) accreting to North America by the Early Jurassic; 2) undergoing non-significant orogen-perpendicular shortening by mid-Early Cretaceous from thrust-faulting; and, then 3) undergoing significant orogen-parallel northward translation of ∼500 km from mid-Early Cretaceous to the Eocene. In contrast, the paleopoles for Stikinia and Quesnellia of the Intermontane Belt show progressive northwestward translation relative to North America by ∼1000 km and a rotation of ∼55° cw since mid-Early Cretaceous. We speculate that ∼500 km of the northward translation is related to dextral motion on the Tintina and Northern Rocky Mountain Trench fault in British Columbia, and that the clockwise rotation is related to upper crustal tectonics in both Yukon and southern British Columbia.〈/span〉

Description: 〈span〉〈div〉SUMMARY〈/div〉The extensive Yukon-Tanana terrane (YTT) of the northern Canadian Cordillera has been considered controversially to be part of the allochthonous ‘Baja BC’ microcontinent or of the para-autochthonous North American cratonic margin during the Mesozoic. Palaeomagnetic methods have isolated a very-stable Early Jurassic thermochemical remanent remagnetization in the terrane's felsic Tatlmain batholith and mafic Ragged stock after correction for: (1) rotation from northeast-plunging anticlinal deformation, (2) northerly dipping tectonic tilt of the host rocks and (3) northwestward regional translation on the adjacent Tintina transcurrent fault zone. The resulting 196 ± 6 Ma Tatlmain and Ragged palaeopoles are 64.9°N, 44.8°E (〈span〉A〈/span〉〈sub〉95〈/sub〉 = 5.9°) and 64.2°N, 58.5°E (〈span〉A〈/span〉〈sub〉95〈/sub〉 = 7.7°), respectively. The YTT palaeopoles support para-autochthonous tectonic models that have the YTT: (1) accreting to North America by the Early Jurassic, (2) undergoing non-significant orogen-perpendicular shortening by mid-Early Cretaceous from thrust-faulting, and, then (3) undergoing significant orogen-parallel northward translation of ∼500 km from mid-Early Cretaceous to the Eocene. In contrast, the palaeopoles for Stikinia and Quesnellia of the Intermontane Belt show progressive northwestward translation relative to North America by ∼1000 km and a rotation of ∼55° cw since mid-Early Cretaceous. We speculate that ∼500 km of the northward translation is related to dextral motion on the Tintina and Northern Rocky Mountain Trench fault in British Columbia, and that the clockwise rotation is related to upper crustal tectonics in both Yukon and southern British Columbia.〈/span〉

Description: The 69 Ma Prospector Mountain stock is located in southwestern Yukon in the northern Canadian Cordillera. This massive monzonite-syenogranite stock is thought to be the intrusive volcanic centre for the surrounding coeval Carmacks Group volcanics. Anomalous palaeomagnetic data from these volcanics have provided the only evidence for the commonly posited hypothesis that the Yukon-Tanana terrane (YTT) was part of the far-travelled (1950 ± 600 km northward) ‘Baja BC’ terrane from 70 to 50 Ma. All other geologic evidence and averaged palaeomagnetic data support a northward displacement of ~415 ± 15 km. This study provides a direct test of the Carmacks volcanics’ estimate and examines the possible causes of its anomalous results. Both the stock and volcanics are unmetamorphosed and rest unconformably on metamorphosed basement rocks of the YTT. Palaeomagnetic and mineral magnetic results from 17 of 19 tested sites (218 specimens) in the Prospector stock and its peripheral skarn isolated a stable thermoremanent magnetization (TRM) in magnetite or low-Ti titanomagnetite that was mostly determined on demagnetization between temperatures of 500 and 580 °C. The TRM has a direction of Decl. = 8.3°, Incl. = 82.4° ( N = 17, k = 71.9, α 95 = 4.2°), providing a non-significant northwards translation estimate of 70 ± 880 km for the YTT. The normal-polarity TRM direction at Prospector Mountain provides a highly significant palaeomagnetic reversals test with the reversed-polarity TRM of the 70 Ma Swede Dome stock, another volcanic centre of the Carmacks Group about 190 km to the north. The test affirms to a high probability that both stocks carry primary TRMs and have not been tectonically tilted significantly since emplacement. Combining the palaeopoles for these two stocks with that for the 75 Ma Mount Lorne volcanic centre stock about 210 km south of Prospector Mountain yields a combined northward translation estimate of 330 ± 400 km for the YTT since ~71 Ma. This estimate agrees closely with the 415 ± 15 km estimate from geological constraints on strike-slip motion along the inboard Tintina fault zone since ~70 Ma, and with the palaeomagnetic estimate of 650 ± 450 km northward since ~108 Ma from four mid-Cretaceous batholiths. In contrast, the palaeomagnetic directions from four areas of the ~70 Ma Carmacks volcanics are poorly clustered. Nonetheless their estimates of ~1900 km northward have been used for a quarter of a century to support a far-travelled ‘Baja BC’ tectonic model for the YTT. This paper discusses and concludes that the anomalous far-travelled estimates from the Carmacks volcanics are attributable to the unfortunate additive effects of inadequate averaging of secular variation, dipole offset error, unrecognized primary dip and other possible causes.

Description: Author(s): Q. Shi, M. A. Zudov, J. Falson, Y. Kozuka, A. Tsukazaki, M. Kawasaki, K. von Klitzing, and J. Smet We report on nonlinear magnetotransport in a two-dimensional electron gas hosted in a MgZnO/ZnO heterostructure. Upon application of a direct current, we observe pronounced Hall field–induced resistance oscillations (HIRO), which are well known from experiments on high-mobility GaAs/AlGaAs quantum w… [Phys. Rev. B 95, 041411(R)] Published Mon Jan 30, 2017