Preliminary geophysical interpretation of the McKeand River area, southern Baffin Island, Nunavut: insights from gravity, magnetic and geological data

The recently completed McKeand River and Amittok Lake aeromagnetic surveys on southern Baffin Island, Nunavut pro- vide a new high-resolution magnetic dataset over an area with no previous coverage. Complemented by regional gravity data, newly acquired rock-property information and geological-mapping products, the aeromagnetic dataset yields qualita- tive and quantitative information on the structure and geology of the underlying bedrock. This paper presents a preliminary interpretation of these datasets that delineates three gravimetric and five magnetic domains. The gravity data outline a broad negative anomaly associated with a plutonic-intrusive suite, as well as several isolated gravity highs associated with metasedimentary strata. Magnetic domains are defined on the basis of anomaly amplitude, wavelength and texture, and are correlated to the mapped geology and magnetic properties. Associations between potential-field anomalies, physical prop- erties and mineral occurrences help define the regional distribution of economically significant horizons

Basement-cover relations and internal structure of the Cape Smith klippe: A 1.9 Ga greenstone belt in northern Quebec, Canada

The Cape Smith Belt is a 380x60 km tectonic klippe composed of greenschistto amphibolite-grade mafic and komatiitic lava flows and fine-grained quartzose sediment, intruded by minor syn- to post-tectonic granitoids. Previously studied transects in areas of relatively high structural level show that the belt is constructed of seven or more north-dipping thrust sheets which verge toward the Superior Province (Archean) foreland in the south and away from an Archean basement massif (Kovik Antiform) external to the Trans-Hudson Orogen (Early Proterozoic) in the north. A field project (mapping and structural-stratigraphic-metamorphic studies) directed by MRS was begun in 1985 aimed at the structurally deeper levels of the belt and underlying basement, which are superby exposed in oblique cross-section (12 km minimum structural relief) at the west-plunging eastern end of the belt. Mapping now complete of the eastern end of the belt confirms that all of the metavolcanic and most of the metasedimentary rocks are allochthonous with respect to the Archean basement, and that the thrusts must have been rooted north of Kovik Antiform. The main findings follow

Record of modern-style plate tectonics in the Palaeoproterozoic Trans-Hudson orogen

The Trans-Hudson orogen of North America is a circa 1,800 million year old, middle Palaeoproterozoic continental collisional belt. The orogen may represent an ancient analogue to the Himalayan orogen, which began forming 50 million years ago and remains active today. Both mountain belts exhibit similar length scales of deformation and timescales of magmatism and metamorphism. A notable divergence in this correlation has been the absence of high-pressure, low-temperature metamorphic rocks in the Trans-Hudson compared with the Himalaya. It has been debated whether this absence reflects a secular tectonic change, with the requisite cool thermal gradients precluded by warmer ambient mantle temperatures during the Palaeoproterozoic, or a lack of preservation. Here we identify eclogite rocks within the Trans-Hudson orogen. These rocks, which typically form at high pressures and cool temperatures during subduction, fill the gap in the comparative geologic record between the Trans-Hudson and Himalayan orogens. Through the application of phase equilibria modelling and in situ U–Pb monazite dating we show that the pressure–temperature conditions and relative timing of eclogite-facies metamorphism are comparable in both orogenies. The results imply that modern-day plate tectonic processes featuring deep continental subduction occurred at least 1,830 million years ago. This study highlights that the global metamorphic rock record (particularly in older terrains) is skewed by overprinting and erosion

Completing the bedrock mapping of southern Baffin Island, Nunavut; plutonic suites and regional stratigraphy

This paper summarizes the field observations and initial interpretations following eight weeks of regional and targeted bed- rock mapping on south-central Baffin Island, Nunavut. The 2015 field campaign completes a two-decade mission to update the geoscience knowledge for the whole of Baffin Island south of latitude 70°N. The bedrock in the area is dominated by a Paleoproterozoic metaplutonic suite, ranging in composition from gabbro to syenogranite, with crosscutting relations indi- cating a progression from mafic to silicic magmatism. Phase-equilibria modelling reveals that the prevailing upper-amphi- bolite– to lower-granulite–facies metamorphic conditions overlap the stability limits of magnetite and orthopyroxene for a typical granitoid bulk composition, which is consistent with field observations of the discontinuous presence of both phases throughout the map area. This result is also consistent with regional aeromagnetic data that show complex structures within relatively homogeneous map units, which are primarily attributed to variations in the abundance of magnetite. The granitoid rocks are interpreted as part of the middle Paleoproterozoic Cumberland Batholith. Metasedimentary rocks, including quartzite, pelite, marble and metagreywacke, are present as enclaves and screens within and between plutonic bodies. An examination of the ‘ghost’stratigraphy suggests that the metasedimentary rocks through- out most of the map area can be correlated with the middle Paleoproterozoic Lake Harbour Group, except in the northeast, where the unique presence of greywacke suggests a middle Paleoproterozoic Piling Group affinity. This transition in strata is consistent with the proposal that a middle Paleoproterozoic tectonic suture (the Baffin suture) associated with the Trans- Hudson Orogen runs through Cumberland Sound. Completion of the bedrock mapping in southern Baffin Island indicates that the region offers a world-class exposure of a reworked Paleoproterozoic convergent margin, which affords valuable in- sight into a variety of magmatic and tectonic processes that can be applied to younger collisional belt

Early anterior cingulate involvement is seen in presymptomatic MAPT P301L mutation carriers

BACKGROUND: PET imaging of glucose metabolism has revealed presymptomatic abnormalities in genetic FTD but has not been explored in MAPT P301L mutation carriers. This study aimed to explore the patterns of presymptomatic hypometabolism and atrophy in MAPT P301L mutation carriers. METHODS: Eighteen asymptomatic members from five families with a P301L MAPT mutation were recruited to the study, six mutation carriers, and twelve mutation-negative controls. All participants underwent standard behavioural and cognitive assessment as well as [18F]FDG-PET and 3D T1-weighted MRI brain scans. Regional standardised uptake value ratios (SUVR) for the PET scan and volumes calculated from an automated segmentation for the MRI were obtained and compared between the mutation carrier and control groups. RESULTS: The mean (standard deviation) estimated years from symptom onset was 12.5 (3.6) in the mutation carrier group with a range of 7 to 18 years. No differences in cognition were seen between the groups, and all mutation carriers had a global CDR plus NACC FTLD of 0. Significant reduction in [18F] FDG uptake in the anterior cingulate was seen in mutation carriers (mean 1.25 [standard deviation 0.07]) compared to controls (1.36 [0.09]). A similar significant reduction was also seen in grey matter volume in the anterior cingulate in mutation carriers (0.60% [0.06%]) compared to controls (0.68% [0.08%]). No other group differences were seen in other regions. CONCLUSIONS: Anterior cingulate hypometabolism and atrophy are both apparent presymptomatically in a cohort of P301L MAPT mutation carriers. Such a specific marker may prove to be helpful in stratification of presymptomatic mutation carriers in future trials

Ptarmigan Fiord basement-cover thrust imbricates, Baffin Island, Nunavut

The rocks at Ptarmigan Fiord on the Hall Peninsula of Baffin Island underwent midcrustal deformation during the formation of the Paleoproterozoic Trans-Hudson Orogen. The structural style in the region is dominated by imbricate panels of Archean basement orthogneiss and Paleoproterozoic supracrustal strata, interpreted to have been deformed by thick- skinned ductile thrusting. Basement rocks comprise amphibolite-facies metatonalite, metagranodiorite, metaquartz-diorite and metamonzogranite, and cover rocks comprise amphibolite-facies migmatitic pelitic and semipelitic schist, psammitic schist, amphibolite, calcsilicate and quartzite. The S 1a penetrative foliation is variably present in basement rocks and consis- tently present in cover rocks, and is defined by alignment of biotite, sillimanite and leucogranite that formed before and dur- ing the thermal metamorphic peak. The S 1a foliation was deformed by F 1b isoclinal folds with an amplitude of 100 m. These structures are interpreted as forming during a D 1 east-west crustal shortening event. Basement and cover imbrication oc- curred after the thermal metamorphic peak and is interpreted as D 2 thick-skinned ductile thrusting. Ductile thrust faults at the base of seven basement-cover slices are identified on the basis of repetition of units and strain localization, and are inter- preted as predominantly south-to-southeast verging on the basis of shear-sense indicators. There are two structural panels of D 2 thrust imbricates, one in the northwestern part of the map area and one in the eastern part of the map area. Map-scale crosscutting relationships indicate that the northwestern panel overthrusted the eastern panel on a southeasterly T 2c -di- rected thrust fault, following a F 2b folding event that folded the T 2a basement-cover thrust imbricates in the eastern panel. The Ptarmigan Fiord area contains a world-class exposure of thick-skinned structures as they are spectacularly delineated by belts of distinctive grey-weathering Archean basement rocks and brown- to black-weathering Paleoproterozoic supra- crustal rocks

Quantifying Water Diffusivity and Metamorphic Reaction Rates Within Mountain Belts, and Their Implications for the Rheology of Cratons

Abstract: The distribution of rheologically strong cratons, and their weakening by metamorphic hydration reactions, is of fundamental importance for understanding first‐order strength contrasts within the crust and the resulting controls on the tectonic evolution of the continents. In this study, the Douglas Harbor structural window within the Paleoproterozoic Trans‐Hudson orogen of Canada is used to study the hydration of the footwall Archean Superior craton basement by water released from the overlying Paleoproterozoic Cape Smith thrust‐fold belt. Phase equilibria modeling is applied to quantify the Archean and Paleoproterozoic metamorphic conditions, and to determine the effect of hydration on basement mineralogy. The amount of structurally bound water within the basement is calculated and shown to decrease as a function of distance below the basal décollement of the thrust‐fold belt. Applying a reactive fluid transport model to these results, the rate coefficient for fluid‐rock reaction is constrained to be 10 − 19 m o l − 1 m 3 s − 1 , and the diffusivity of water through the grain boundary network to be 10 − 9 m 2 s − 1 at the ambient metamorphic conditions of 570 ° C and 7.5 kbar. This newly documented rate of water diffusion is three orders of magnitude slower than thermal diffusion, implying that hydration by diffusion may be the rate‐limiting factor in the weakening of cratons, and therefore plays an important role in their geological persistence. This conclusion is consistent with field observations that Paleoproterozoic strain in the Douglas Harbor structural window is restricted to hydrated portions of the Archean Superior craton basement

New linear stability parameter to describe low-β\beta electromagnetic microinstabilities driven by passing electrons in axisymmetric toroidal geometry

In magnetic confinement fusion devices, the ratio of the plasma pressure to the magnetic field energy, $\beta$, can become sufficiently large that electromagnetic microinstabilities become unstable, driving turbulence that distorts or reconnects the equilibrium magnetic field. In this paper, a theory is proposed for electromagnetic, electron-driven linear instabilities that have current layers localised to mode-rational surfaces and binormal wavelengths comparable to the ion gyroradius. The model retains axisymmetric toroidal geometry with arbitrary shaping, and consists of orbit-averaged equations for the mode-rational surface layer, with a ballooning space kinetic matching condition for passing electrons. The matching condition connects the current layer to the large scale electromagnetic fluctuations, and is derived in the limit that $\beta$ is comparable to the square root of the electron-to-ion-mass ratio. Electromagnetic fluctuations only enter through the matching condition, allowing for the identification of an effective $\beta$ that includes the effects of equilibrium flux surface shaping. The scaling predictions made by the asymptotic theory are tested with comparisons to results from linear simulations of micro-tearing and electrostatic microinstabilities in MAST discharge #6252, showing excellent agreement. In particular, it is demonstrated that the effective $\beta$ can explain the dependence of the local micro-tearing mode (MTM) growth rate on the ballooning parameter $\theta_0$ -- possibly providing a route to optimise local flux surfaces for reduced MTM-driven transport.Comment: 29 pages, 14 figure

Monitoring of Manufacturing Changes and Formulation Excipients on Solid Oral Dosage Forms of Furosemide Using Chemometrics and Laser-Induced Breakdown Spectroscopy (LIBS)

Peer reviewed: NoNRC publication: Ye

Age and anatomy of the Gongga Shan batholith, eastern Tibetan Plateau, and its relationship to the active Xianshui-he fault

The Gongga Shan batholith of eastern Tibet, previously documented as a ca. 32–12.8 Ma granite pluton, shows some of the youngest U-Pb granite crystallization ages recorded from the Tibetan Plateau, with major implications for the tectonothermal history of the region. Field observations indicate that the batholith is composite; some localities show at least seven crosscutting phases of granitoids that range in composition from diorite to leucocratic monzogranite. In this study we present U-Pb ages of zircon and allanite dated by laser ablation–inductively coupled plasma–mass spectrometry on seven samples, to further investigate the chronology of the batholith. The age data constrain two striking tectonic-plutonic events: a complex Triassic–Jurassic (ca. 215–159 Ma) record of biotite-hornblende granodiorite, K-feldspar megacrystic granite and leucogranitic plutonism, and a Miocene (ca. 14–5 Ma) record of monzonite-leucogranite emplacement. The former age range is attributed to widespread Indosinian tectonism, related to Paleo-Tethyan subduction zone magmatism along the western Yangtze block of south China. The younger component may be related to localized partial melting (muscovite dehydration) of thickened Triassic flysch-type sediments in the Songpan-Ganze terrane, and are among the youngest crustal melt granites exposed on the Tibetan Plateau. Zircon and allanite ages reflect multiple crustal remelting events; the youngest, ca. 5 Ma, resulted in dissolution and crystallization of zircons and growth and/or resetting of allanites. The young garnet, muscovite, and biotite leucogranites occur mainly in the central part of the batholith and adjacent to the eastern margin of the batholith at Kangding, where they are cut by the left-lateral Xianshui-he fault. The Xianshui-he fault is the most seismically active strike-slip fault in Tibet and is thought to record the eastward extrusion of the central part of the Tibetan Plateau. The fault obliquely cuts all granites of the Gongga Shan massif and has a major transpressional component in the Kangding-Moxi region. The course of the Xianshui Jiang river is offset by ∼62 km along the Xianshui-he fault and in the Kangding area granites as young as ca. 5 Ma are cut by the fault. Our new geochronological data show that only a part of the Gongga Shan granite batholith is composed of young (Miocene) melt, and we surmise that as most of eastern Tibet is composed of Precambrian–Triassic Indosinian rocks, there is no geological evidence to support regional Cenozoic internal thickening or metamorphism and no evidence for eastward-directed lower crustal flow away from Tibet. We suggest that underthrusting of Indian lower crust north as far as the Xianshui-he fault resulted in Cenozoic uplift of the eastern plateau