Eight new U-Pb zircon ages are reported for volcanic and plutonic rocks from the Paleoproterozoic Flin Flon Domain. The shoshonitic Vick Lake tuff crystallized at 1885 +/- 3 Ma, marking a late phase of arc-related volcanism. Synvolcanic diabase of the Ocean Floor Assemblage at Athapapuskow Lake is poorly dated at ca. 1.9 Ga, but nevertheless is the first direct age constraint on mafic rocks of the Ocean Floor Assemblage. Tonalite from the West Arm of Athapapuskow Lake crystallized at 1903 +6/-4 Ma, an age that supports a correlation with the dated Mystic Lake tonalite to the northwest, places a minimum age on the volcanic rocks it intrudes, and a maximum age for its deformation. Porphyritic granodiorite and marginal gabbro from the Reynard Lake pluton crystallized at 1850 +/- 3 Ma and 1849 +3/-2 Ma, respectively. As the pluton is larely undeformed, these results place a minimum age on an early foliation that we attribute to amalgamation of the Ocean Floor, Mystic Lake, and Arc assemblages. A felsic dyke, interpreted as having intruded during terrane amalgamation, crystallized at 1869 +/- 1 Ma. Thus, deformation associated with terrane accretion commenced after 1903 Ma, was in progress by 1869 Ma, and was complete by 1850 Ma. Amphibolite-facies quartz diorite from the sub-Paleozoic Namew Gneiss Complex crystallized at 1880 +/- 2 Ma. An improved age of 1831 +5/-4 Ma was obtained for the Cormorant Batholith, marking the last major phase of plutonism in the Flin Flon Domain.
Abundant granitic plutons intruded the eastern Meguma terrane of Nova Scotia in the middle- to late Devonian. Less voluminous diorite–tonalite and gabbro intrusions are associated with the granitic plutons along the northern margin of the terrane adjacent to the Cobequid–Chedabucto fault zone. All plutons contain metasedimentary xenoliths, and the mafic plutons show magma mingling textures with their adjacent granitic plutons. New U–Pb zircon data from autocrystic zircon in 13 samples indicate coeval emplacement of mafic and granitic plutons between ca. 382 and 368 Ma. However, the zircon grains contain numerous inherited domains that range in age from Palaeoproterozoic to Devonian. These inherited ages correspond to detrital zircon U–Pb dates from the Cambrian to Ordovician metasedimentary host rocks. Zircon oxygen isotopic data (δ 18 O) are between +7.4 ± 0.2‰ and +9.3 ± 0.3‰ indicating significant involvement of the crust as the magma source or contaminant. If the high δ 18 O zrn values are a result of contamination, the contaminant was likely the metasedimentary rocks of the Meguma terrane. Hafnium isotopic data from autocrystic zircon have ε Hf ( t) between −6.0 ± 1.5 and +2.1 ± 2.5. The new zircon U–Pb, O, and Hf isotopic data from plutons in the eastern Meguma terrane are indistinguishable from published data from the South Mountain Batholith. The data suggest that Devonian magmatism in the Meguma terrane post-dated the main orogenic event that caused folding and regional metamorphism and involved the same magma source and/or contaminants throughout the terrane.
The dependence on azimuthal angle of acoustic sea-surface reverberation is investigated at 60 kHz, utilizing a three-axis rotationally stabilized conical-beam transducer. Measurements of backscattering strength in the upwind and crosswind directions are compared for a range of grazing angles from 10° to 40°. Polar plots of scattering strength versus azimuthal angle are presented for wind speeds from 4 to 13 kt. An attempt is made to correlate the backscattering measurements with swell and local wind-driven waves by means of aerial sea-state photographs taken during the test. Data indicate that surface reverberation has a pronounced dependence on azimuthal angle at wind speeds below about 9 kt, but becomes independent of azimuthal angle at higher wind speeds.
The change in the attenuation of sound and in the elastic constant ${c}_{33}$ of gadolinium has been measured at 5 MHz as a function of applied magnetic fields to 13 kOe in the temperature range 270-320 \ifmmode^\circ\else\textdegree\fi{}K. The minimum in the elastic constant at the Curie point moved upwards in temperature and tended to diminish and broaden with increasing field. Studies of the change in attenuation due to magnetic field in the same region revealed sharp $\ensuremath{\lambda}$-shaped increases up to a field of 1. 8 kOe. At higher fields this peak split into two diminishing maxima, one moving upwards and the other downwards with increasing field. The zero-field-attenuation data decreased as $\ensuremath{\Delta}\ensuremath{\alpha}\ensuremath{\sim}{\ensuremath{\epsilon}}^{y}$, where $\ensuremath{\epsilon}=|\frac{(T\ensuremath{-}{T}_{c})}{{T}_{c}}|$ and $y=\ensuremath{-}1.8\ifmmode\pm\else\textpm\fi{}0.2$ in the paramagnetic region. In the presence of a magnetic field, the changes in the velocity are attributed to changes in the spin-correlation function.
The Ashuanipi complex and Minto block of the Superior Province are large regions that have been classified as "high-grade gneiss" terranes on the basis of the presence of orthopyroxene-bearing units. Like the granite–greenstone and metasedimentary subprovinces of the southern Superior Province, the two terranes consist predominantly of intrusive rocks, but are distinguished by their primary magmatic orthopyroxene. Both "high-grade" and "gneiss" are misnomers because granulite-facies gneisses are only sparingly present and the regions consist dominantly of massive, unmetamorphosed plutonic rock.The Ashuanipi complex consists of a deformed, metamorphosed package of metasedimentary rocks and primitive, early tonalite cut by widespread orthopyroxene ± garnet granodiorite (diatexite), as well as plutons of tonalite, granite, and syenite. Based on its lithological and chronological similarity and on-strike position, the complex appears to be the continuation of metasedimentary subprovinces such as the Quetico. Its evolution involved deposition of immature greywacke in an accretionary prism, early arc (tonalitic) magmatism and deformation, followed by widespread intracrustal magmatism in the period 2700–2670 Ma. Both metamorphic and igneous rocks record equilibration under granulite-facies conditions (700–835 °C; 0.35–0.65 GPa; [Formula: see text] ~0.3) and indicate exposure levels of ~20 km.The Minto block at the latitude of Leaf River consists of several north-northwest-trending domains of similar scale and diversity to the east-trending subprovinces of the southern Superior Province. The central Goudalie domain is dominantly amphibolite-facies tonalitic rocks including some with ages >3 Ga, with small belts of volcanic and sedimentary origin. Lake Minto domain contains poorly preserved supracrustal remnants in a plutonic complex comprising hornblende granodiorite, clinopyroxene ± orthopyroxene granodiorite, orthopyroxene–biotite diatexite, and granite. The hornblende granodiorite suite constitutes most of the Utsalik and Tikkerutuk domains and is thought to represent continental arc magmatism. On the basis of their distinct aeromagnetic and lithological character, two additional domains are evident north of the Leaf River area, the Inukjuak domain in the west and the Douglas Harbour domain in the east.The northerly grain of the Minto block appears to have been established in situ with respect to the easterly belts of the southern Superior Province (i.e., no large-scale block rotation) during the same interval of time (3.0–2.7 Ga). Modification of the tectonic framework for the Superior Province is required to explain Minto arc magmatism. In the interval ~2730–2690 Ma ago, a continental magmatic arc built the Berens River and Bienville subprovinces and Minto block on the southern and eastern edges, respectively, of a northern protocratonic foundation. In the same period, primitive volcanic arcs and accretionary prisms developed outboard on oceanic crust and were accreted to form a southern tectonic regime.
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