Roger B. Taney, Jacksonian Jurist by Charles W. Smith, Jr.

Review of "Roger B. Taney, Jacksonian Jurist" by Charles W. Smith, Jr

How Lawyers Think -- Clarence Morris

Review of "How Lawyers Think" by Clarence Morri

Short communication : Modeling competing effects of cooling rate, grain size, and radiation damage in low-temperature thermochronometers

Funding Information: Financial support. This research has been supported by the NSERC Discovery, and from the Geological Survey of Canada, Natural Resources Canada. Publisher Copyright: © Copyright:Low-temperature multi-thermochronometry, in which the (U-Th)ĝ€¯/ĝ€¯He and fission track methods are applied to minerals such as zircon and apatite, is a valuable approach for documenting rock cooling histories and relating them to geological processes. Here we explore the behaviors of two of the most commonly applied low-temperature thermochronometers, (U-Th)ĝ€¯/ĝ€¯He in zircon (ZHe) and apatite (AHe), and directly compare them against the apatite fission track (AFT) thermochronometer for different forward-modeled cooling scenarios. We consider the impacts that common variations in effective spherical radius (ESR) and effective uranium concentration (eU) may have on cooling ages and closure temperatures under a range of different cooling rates. This exercise highlights different scenarios under which typical age relationships between these thermochronometers (ZHe>AFT>AHe) are expected to collapse or invert (either partially or fully). We anticipate that these predictions and the associated software we provide will be a useful tool for teaching, planning low-temperature multi-thermochronometry studies, and for continued exploration of the relative behaviors of these thermochronometers in temperature-time space through forward models.Peer reviewe

学会抄録

<p>Confuciusornis, leveled 16bit data, resampled as cubic voxels, resliced in YZ plane</p> <p>265 slices; TIF format; 2.520 Mb each</p> <p>Voxel dimension X = 0.2148 mm</p> <p>Voxel dimension Y = 0.2148 mm</p> <p>Voxel dimension Z = 0.2148 mm</p> <p>These data are 16bit leveled TIF files that are viewable in most viewers (see Usage Notes)</p

Impact-Induced Chondrule Deformation and Aqueous Alteration of CM2 Murchison

Deformed chondrules in CM2 Murchison have been found to define a prominent foliation [1,2] and lineation [3] in 3D using X-ray computed tomography (XCT). It has been hypothesized that chondrules in foliated chondrites deform by "squeezing" into surrounding pore space [4,5], a process that also likely removes primary porosity [6]. However, shock stage classification based on olivine extinction in Murchison is consistently low (S1-S2) [4-5,7] implying that significant intracrystalline plastic deformation of olivine has not occurred. One objective of our study is therefore to determine the microstructural mechanisms and phases that are accommodating the impact stress and resulting in relative displacements within the chondrules. Another question regarding impact deformation in Murchison is whether it facilitated aqueous alteration as has been proposed for the CMs which generally show a positive correlation between degree of alteration and petrofabric strength [7,2]. As pointed out by [2], CM Murchison represents a unique counterpoint to this correlation: it has a strong petrofabric but a relatively low degree of aqueous alteration. However, Murchison may not represent an inconsistency to the proposed causal relationship between impact and alteration, if it can be established that the incipient aqueous alteration post-dated chondrule deformation. Methods: Two thin sections from Murchison sample USNM 5487 were cut approximately perpendicular to the foliation and parallel to lineation determined by XCT [1,3] and one section was additionally polished for EBSD. Using a combination of optical petrography, SEM, EDS, and EBSD several chondrules were characterized in detail to: determine phases, find microstructures indicative of strain, document the geometric relationships between grain-scale microstructures and the foliation and lineation direction, and look for textural relationships of alteration minerals (tochilinite and Mg-Fe serpentine) that indicate timing of their formation relative to deformation event(s). Preliminary Results: Deformed chondrules are dominated by forsterite and clinoenstatite with lesser amounts of Fe-Mg serpentine, sulfides, and low calcium pyroxene. Olivine grains are commonly fractured but generally show sharp optical extinction. The pyroxene, in contrast, is not only fractured but also often displays undulose extinction. In addition, the clinoenstatite is frequently twinned but it is unclear whether the twins are the result of mechanical deformation or inversion from protoenstatite [8]. EBSD work is currently ongoing to determine if areas of higher crystallographic strain can be imaged and mapped, and to determine the pyroxene twin orientations. In regards to alteration, we have found evidence for post-deformation formation of tochilinite and Mg-Fe serpentine indicating that aqueous alteration has indeed post-dated the deformation of the chondrules

Constraining the long-term evolution of the slip rate for a major extensional fault system in the central Aegean, Greece, using thermochronology

The brittle/ductile transition is a major rheologic boundary in the crust yet little is known about how or if rates of tectonic processes are influenced by this boundary. In this study we examine the slip history of the large-scale Naxos/Paros extensional fault system (NPEFS), Cyclades, Greece, by comparing published slip rates for the ductile crust with new thermochronological constraints on slip rates in the brittle regime. Based on apatite and zircon fission-track (AFT and ZFT) and (U–Th)/He dating we observe variable slip rates across the brittle/ductile transition on Naxos. ZFT and AFT ages range from 11.8 ± 0.8 to 9.7 ± 0.8 Ma and 11.2 ± 1.6 to 8.2 ± 1.2 Ma and (U–Th)/He zircon and apatite ages are between 10.4 ± 0.4 to 9.2 ± 0.3 Ma and 10.7 ± 1.0 to 8.9 ± 0.6 Ma, respectively. On Paros, ZFT and AFT ages range from 13.1 ± 1.4 Ma to 11.1 ± 1.0 Ma and 12.7 ± 2.8 Ma to 10.5 ± 2.0 Ma while the (U–Th)/He zircon ages are slightly younger between 8.3 ± 0.4 Ma and 9.8 ± 0.3 Ma. All ages consistently decrease northwards in the direction of hanging wall transport. Most of our new thermochronological results and associated thermal modeling more strongly support the scenario of an identical fault dip and a constant or slightly accelerating slip rate of 6–8 km Myr− 1 on the NPEFS across the brittle/ductile transition. Even the intrusion of a large granodiorite body into the narrowing fault zone at 12 Ma on Naxos does not seem to have affected the thermal structure of the area in a way that would significantly disturb the slip rate. The data also show that the NPEFS accomplished a minimum total offset of 50 km between 16 and 8 Ma

Automated Crack Identification for Cement Paste

The development of an automated procedure for the identification of microcracks in cementitious materials is described. The degree and nature of microcracking is measured using backscattered electron images obtained with an integrated scanning electron microscope/image analysis system. Multiple images for specimens are analyzed using a computer program developed to identify and measure microcracks within the individual phases of cement paste. The procedure is developed to assist in the determination of the roles played by individual phases in cement paste in the formation and propagation of microcracks. Procedures for specimen testing, preparation, imaging, and crack analysis are described, along with a description of the development of the analysis program. The analysis capabilities of the program are demonstrated. The gray level of epoxy-filled cracks in polished cement paste specimens is affected by the atomic number density of underlying and adjacent phases. As a result, cracks cannot be identified based on gray level alone.Epoxy-filled cracks in polished cement paste specimens can be identified based on local changes in gray level and the application of geometric requirements; and combined procedures that establish the floor of a crack, minimum gradient and gray level adjacent to cracks, and minimum differences in gray level between the floor of a crack and adjacent solid phases provide a reproducible and consistent technique for crack identification in cement paste

Evidence for surface uplift of the Atlas Mountains and the surrounding peripheral plateaux: Combining apatite fission-track results and geomorphic indicators in the Western Moroccan Meseta (coastal Variscan Paleozoic basement)

This work represents an initial attempt to link the evolution of the topography in relation to the general tectonic framework of western Morocco. For this purpose, in a section of the Western Moroccan Meseta different tools are combined in order to attain the general objective. Apatite fission-track (AFT) data of granitic rocks of the Rabat–Khenifra area give ages around 200 Ma with track length distributions which are compatible with the thermal models already established for the area. An inverse correlation between AFT ages and elevation is observed which is compatible with previous models indicating northward tilting of the whole Western Moroccan Meseta which is younger than 20–25 Ma. In order to test this possibility a detailed analysis of the topography at different scales in the Western Moroccan Meseta has been performed. Results indicate that two open folds with different amplitudes are recognized and that the one with wider wavelength could correspond to a lithospheric fold as previously stated by other authors on the basis of independent geological arguments. The northward tilting proposed based on the AFT data agrees with the results obtained in the analysis of the topography which reinforces the presence of a very open fold with a wavelength of 200–300 km in the north-western limb of the Western Moroccan Meseta

Comprehensive Non-Destructive Conservation Documentation of Lunar Samples Using High-Resolution Image-Based 3D Reconstructions and X-Ray CT Data

Established contemporary conservation methods within the fields of Natural and Cultural Heritage encourage an interdisciplinary approach to preservation of heritage material (both tangible and intangible) that holds "Outstanding Universal Value" for our global community. NASA's lunar samples were acquired from the moon for the primary purpose of intensive scientific investigation. These samples, however, also invoke cultural significance, as evidenced by the millions of people per year that visit lunar displays in museums and heritage centers around the world. Being both scientifically and culturally significant, the lunar samples require a unique conservation approach. Government mandate dictates that NASA's Astromaterials Acquisition and Curation Office develop and maintain protocols for "documentation, preservation, preparation and distribution of samples for research, education and public outreach" for both current and future collections of astromaterials. Documentation, considered the first stage within the conservation methodology, has evolved many new techniques since curation protocols for the lunar samples were first implemented, and the development of new documentation strategies for current and future astromaterials is beneficial to keeping curation protocols up to date. We have developed and tested a comprehensive non-destructive documentation technique using high-resolution image-based 3D reconstruction and X-ray CT (XCT) data in order to create interactive 3D models of lunar samples that would ultimately be served to both researchers and the public. These data enhance preliminary scientific investigations including targeted sample requests, and also provide a new visual platform for the public to experience and interact with the lunar samples. We intend to serve these data as they are acquired on NASA's Astromaterials Acquisistion and Curation website at http://curator.jsc.nasa.gov/. Providing 3D interior and exterior documentation of astromaterial samples addresses the increasing demands for accessability to data and contemporary techniques for documentation, which can be realized for both current collections as well as future sample return missions