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Early interpretations by WSGS to explain the anomalous occurrence and local abundance of high-quality Wyoming jade were based on the theory that the nephrite was mostly recycled from alluvial units such as the Eocene Ice Point and Crooks Gap conglomerates. Jade with similar characteristics as the type 1 nephrite recently discovered at the Sky Zone—including a lack of inherited mineralogy, the presence of quartz crystals and an extremely fine grain size resulting in high lustre—has been documented from numerous discrete primary occurrences over a wide area of the state. Accretion was followed by the emplacement of the Granite Mountain batholith, a Neoarchean continental arc magmatic event represented in the study area by biotite granite that has been age dated at around 2.60 Ga (Mogk et al. 2023). [...]Laramide uplift and subsequent erosion led to the present exposure of this basement complex.

A thick succession of mafic upper Asbian volcanic rocks is exposed as cap rocks in the Magdalen Islands of eastern Quebec. This succession records peak stages of a Late Devonian to Early Carboniferous magmatic system that regionally developed from transtensional tectonics above a mantle plume. In the upper part of the succession, tholeiitic basalts with enriched mid-oceanic ridge basalt (E-MORB) affinities are tightly interbedded with highly alkaline basalts with ocean island affinities, whereas the lower part is composed of moderately alkaline basalts and pyroclastic deposits that are interpreted as the products of mixing between these two compositionally distinct melts. Based on trace-element contents and geological constraints, the tholeiitic basalts were produced by decompressional melting in depleted uppermost asthenospheric mantle material enriched over the average (E-MORB-type source) at the top of the plume, whereas the highly alkaline basalts were produced subsequently when decompressional melting reached down into the enriched mantle (ocean island basalt–type source). These two primary melts may have been thermally stratified below the lithosphere before being tapped by transtensional structures to feed a thick magmatic underplating that regionally developed at the base of the crust, where magma mixing may have occurred. Interbedding of the two contrasting melts in the upper part of the succession implies that, although the two primary mantle sources were still being tapped into, magma mixing was by then no longer occurring. Above a small gap, the uppermost flow is a fluorine-rich tholeiitic basalt with arc affinities that suggest partial melting of the regional subcontinental lithospheric mantle source, which was previously enriched by nearly continuous subduction below eastern Canada in early to middle Paleozoic times. The latter setting seemingly corresponds to the local waning of the magmatic system in uppermost Asbian times, possibly because of the westward migration of the overridden plume toward New Brunswick, where alkaline volcanism from a sublithospheric source resumed in Brigantian times.

In 2018, a new type of nephrite jade was recognised from the DJ project in Washington State (USA) that exhibits subtle-to-strong directional colour variations when viewed at different orientations. Its colouration ranges from green to blue in light-to-dark tones, and its mineralogical and gemmological properties are consistent with nephrite jade from other localities. The optical phenomenon is related to pleochroism resulting from the internal structure of the tremolite fibres constituting the nephrite. These fibres show high-angle to orthogonal cross-felting, often with variations in chemical composition, and appear to result from more than one generation of formation. The presence of sheen (caused by the scattering of light from fibrous tremolite domains) is sometimes seen in addition to the pleochroic optical effect. This phenomenal material has the toughness required to be cut into cabochons or carved without any stabilising treatment, thus possessing workability that qualifies it as a new and unique variety of nephrite jade. Three other nephrite types--classified here as Ornamental, Carving and Gem--additionally occur at the DJ project, and are also described in this article.

A succession of Lower Carboniferous polymictic conglomerate in eastern Canada is truncated by synsedimentary endokarst conduits, which are clogged by lithified karst infill. Although such rocks do not usually host karst because of their polymineralic and poorly soluble contents, there are contextual and geochemical lines of evidence suggesting that groundwater conditions may have been highly alkaline at the time of karst formation, thus substantially increasing the solubility of common silicate minerals. The succession was deposited in a hyperarid climate and in close proximity to an evaporitic marine body. Because of a combination of high subsidence rates along a basin-bounding normal fault and entrapment within a salt expulsion minibasin, the evaporitic body of water was forced to prograde toward the source area of the sedimentary basin. This restricted sea was also responding to ongoing glacioeustatic variations at the time, which are interpreted to have generated a cyclic progradation of evaporitic groundwater into basin margin fanglomerates, thus favoring their early cementation by calcite. Karstification of the siliciclastic material is interpreted to have occurred during cyclic retreats toward lowstands, when groundwater alkalinity may have been highest.

The quantity, intensity, and quality of urban stormwater runoff are changing as a consequence of urbanization and climate change. Low impact development (LID) techniques (e.g., bioretention systems) are emerging to manage runoff quantity and quality. Street tree pits were used as bioretention units in Montreal, Canada. The concentration and mass flux of contaminants (Na, Cr, Ni, Cu, Zn, Cd, Pb) and dissolved organic carbon (DOC) were measured in soil solution samples from the tree pits. The soil organic matter (SOM) and the permeability of the area nearby the tree pit (sidewalk and front lawn) were tested. The SOM did not affect contaminant concentrations. However, tree pits with higher SOM reduced the mass flux of contaminants more than tree pits with lower SOM. Sidewalk permeability decreased the concentration and mass flux of contaminants observed (e.g., Na and Cr). The estimated water flux in the open part of the tree pit changed from 6.15 to 1.64 mm week−1 from the less permeable units (absence of lawn + impermeable sidewalk) to the more permeable units (presence of lawn + permeable sidewalk). Urban runoff quality and quantity were locally affected by the tree pits. This indicates that the increase in surface permeability and SOM in street tree pits is advisable. Street tree pits have the potential as bioretention units to locally mitigate some of the impacts of urbanization. City planners could consider the use of street tree pits as bioretention units to help the management of urban runoff.

Urban soil amendment with organic matter can increase the steady state concentration of trace metals in urban soil. Different types of organic matter have different abilities to sorb and retain trace metals. The potential of urban soil amended with compost derived from mixed green and table waste and with maple-wood-derived biochar to retain trace metals (Cu, Zn, Cd, Pb) in the presence of de-icing salt (Na) was studied in a leaching test. Soil amended with compost retained significantly higher concentrations of Zn and Pb, as compared to soil amended with biochar, possibly due to the high cation exchange capacity of compost and its positive effect on soil pH. Indicating high ability for retaining trace metals, compost can bind contaminants originating from urban runoff water percolating through urban soil and provide a healthier medium for street tree growth.

Middle to Upper Ordovician volcanic rocks in the Arisaig area of Nova Scotia, Canada, constitute the only known record of volcanism in West Avalonia during that interval. Hence, they have been extensively studied to test paleocontinental reconstructions that consistently show Avalonia as a drifting microcontinent during that period. Identification of volcanic rocks with an intermediate composition (the new Seaspray Cove Formation) between upper Darriwilian bimodal volcanic rocks of the Dunn Point Formation and Sandbian felsic pyroclastic rocks of the McGillivray Brook Formation has led to a reevaluation of magmatic relationships in the Ordovician volcanic suite at Arisaig. Although part of the same volcanic construction, the three formations are separated by significant time-gaps and are shown to belong to three distinct magmatic subsystems. The tectonostratigraphic context and trace element contents of the Dunn Point Formation basalts suggest that they were produced by the high-degree partial melting of an E-MORB type source in a back-arc extensional setting, whereas trace element contents in intermediate rocks of the Seaspray Cove Formation suggest that they were produced by the low-degree partial melting of a subduction-enriched source in an arc setting. The two formations are separated by a long interval of volcanic quiescence and deep weathering, during which time the back-arc region evolved from extension to shortening and was eventually onlapped by arc volcanic rocks. Based on limited field constraints, paleomagnetic and paleontological data, this progradation of arc onto back-arc volcanic rocks occurred from the north, where an increasingly young Iapetan oceanic plate was being subducted at an increasingly shallow angle. Partial subduction of the Iapetan oceanic ridge is thought to have subsequently generated slab window magmatism, thus marking the last pulse of subduction-related volcanism in both East and West Avalonia.

Biochar as a soil amendment in street tree pits can be used to increase the soil’s ability to retain contaminants found in urban runoff. The increased retention can potentially decrease peak concentrations of soluble trace metals and de-icing salts in the soil solution, thereby decreasing the amounts taken up by tree roots or percolated out of the tree pits into the ground water. A leaching test measured the retention of trace metals (Cd, Zn, Cu, and Pb) and deicing salts (Na) by different kinds of biochar. The biochar was produced from hardwood (North American ash tree, Fraxinus americana) under different pyrolysis conditions, with three temperatures (350, 465 and 550 °C) and two residence times (10 and 30 min). Biochar pyrolyzed at 550 °C for 30 min significantly reduced the soluble concentrations of Zn, Cu, and Pb in the column leachate, most likely due to the its higher pH, surface area, and ash content. The pH of each treatment group was measured while the increase in ash content and surface area was inferred according to relevant literature. This biochar was then combined with soil and compost at rates ranging from 0 to 7.5% by dry weight to determine the proportion that optimally sorbed the contaminants. An application rate of 7.5% biochar by dry weight increased the soil mixture’s sorption capacity for Cd and Na while maintaining similar sorption of Cu, Zn, and Pb. The role of organic matter, such as that in compost, was especially important for the sorption of Zn and Cu. Hardwood biochar can thus improve the health of street trees and groundwater quality by sequestering trace metals and de-icing salts. Biochar can also be a useful tool to remediate contaminated soil, especially in urban environments.

The short life span of many street trees in the Montreal downtown area may be due in part to higher than standard concentrations of trace metals in the tree pit soils. The effects of land use, soil organic matter, and time since tree planting in a given tree pit (soil age) were studied with respect to the total concentration of trace metals (Cr, Ni, Cu, Zn, Cd, and Pb) in soil collected from tree pits on commercial and residential streets. Contingency table analysis and multiple linear regression were applied to study how these variables were related to the total concentrations of trace metals in soil. Other variables, such as pH, street width, distance of the tree pit from the curb, and tree pit volume, were also used as input to statistical analysis to increase the analysis’ explanatory power. Significantly higher concentrations of Cu, Cd, Zn, and Pb were observed in soils from commercial streets, possibly as a result of heavier traffic as compared with residential streets. Soil organic matter was positively correlated with the concentrations of Cu and Pb, probably due to the ability of organic matter to retain these trace metals. Nickel, Cu, Zn, Cd, and Pb were positively correlated with the soil age presumably because trace metals accumulate in the tree pit soil over time. This knowledge can be helpful in providing soil quality standards aimed at improving the longevity of downtown street trees.