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For archaeologists, the task of processing large terrestrial laser scanning (TLS)-derived point cloud data can be difficult, particularly when focusing on acquiring analytical and interpretive outcomes from the data. Using our TLS lidar data collected in 2013 from two compositionally different, low Arctic multi-component hunter-gatherer sites (LdFa-1 and LeDx-42), we demonstrate how a manual point cloud classification approach with open source software can be used to extract natural and archaeological features from a site’s surface. Through a combination of spectral datasets typical to TLS (i.e., intensity and RGB values), archaeologists can enhance the visual and analytical representation of archaeological huntergatherer site surfaces. Our approach classifies low visibility Arctic site point clouds into independent segments, each representing a different surface material found on the site. With the segmented dataset, we extract only the surface boulders to create an alternate characterization of the site’s prominent features and their surroundings. Using surface point clouds from Paleo-Inuit sites allows us to demonstrate the value of this approach within hunter-gatherer research as our results illustrate an effective use of large TLS datasets for extracting and improving our analytical capabilities for low relief site features.

Over the last 30 years, through Lithoprobe and other programmes, modern, high-quality magnetotelluric (MT) measurements probing deep into the lithosphere and underlying asthenosphere have been made at over 6000 sites across Canada in all provinces and territories, except Nova Scotia. Some regions are well covered, particularly Alberta, southern British Columbia, and western Ontario, whereas others remain poorly covered, such as Quebec and large swaths of Nunavut. Prior publications from individual studies have added significantly to the wealth of Canada's geoscience knowledge, and have demonstrated that MT can contribute significantly to understanding of the tectonic processes that have shaped Canada. However, to date no continent-scale maps of lithospheric electrical parameters have been constructed from the extensive MT database. Herein we review the contributions made by the MT components of Lithoprobe, and present new continental-scale maps of various electrical parameters at crustal and upper mantle depths for the whole of Canada. From those maps, combined with regional estimates of temperature, we develop derivative information on petrological- geophysical properties, including predictions of temperature and water content. We find that at 100 km depth the Canadian Shield is cold and dry, and the Cordillera is warmer but mostly dry, i.e., little water is present in the peridotite. Exceptions are beneath the Prairies, the Wopmay Orogen, and northeast Nunavut where there does appear to be water in the nominally anhydrous minerals. Also, southwest British Columbia appears colder than the rest of the Cordillera due to the subducting Juan de Fuca plate. In contrast, at 200 km depth almost all of Canada is dry. Au cours des trente dernieres annees, grace a Lithoprobe et a d'autres programmes, des mesures magnetotelluriques (MT), modernes et de grande qualite, ont ete prises a plus de 6000 sites a travers le Canada, dans toutes les provinces et territoires sauf en Nouvelle-Ecosse; ces mesures sondaient profondement dans la lithosphere et l'asthenosphere sous- jacente. Certaines regions sont bien couvertes, surtout l'Alberta, le sud de la Colombie-Britannique et l'ouest de l'Ontario, alors que d'autres sont mal couvertes, par exemple le Quebec et de grandes parties du Nunavut. Des publications anterieures, basees sur des etudes individuelles, ont grandement contribue a enrichir les connaissances geoscientifiques canadiennes et elles ont demontre que les mesures MT peuvent grandement contribuer a la comprehension des processus tectoniques qui ont forme le Canada. Toutefois, a ce jour, aucune carte des parametres electriques lithospheriques, a l'echelle du continent, n'a ete construite a partir de la vaste base de donnees MT. Dans le present article, nous revoyons les contributions des composantes MT de Lithoprobe et nous presentons de nouvelles cartes a l'echelle du continent de divers parametres electriques aux profondeurs de la croute et du manteau superieur pour l'ensemble du Canada. A partir de ces cartes, combinees a des estimes regionaux de temperature, nous derivons de l'information sur les proprietes petrologiques-geophysiques, incluant les predictions de temperature et de teneur en eau. Nous avons trouve qu'a une profondeur de 100 km, le Bouclier canadien est froid et sec et que la Cordillere est plus chaude mais surtout seche, c.-a-d. la peridotite contient peu d'eau. Les exceptions sont sous les Prairies, l'orogene de Wopmay et le nord-est du Nunavut oU il semble y avoir de l'eau dans les mineraux supposement anhydres. De plus, le sud-ouest de la Colombie-Britannique semble plus froid que le reste de la Cordillere en raison du plongement de la plaque Juan de Fuca. Par contre, a une profondeur de 200 km presque tout le Canada est sec. [Traduit par la Redaction], Introduction During its five funded phases spanning two decades, the Lithoprobe project (Clowes 2010a) accomplished an astounding amount on its 10 transects (Fig. 1a), and generated geoscientific data that were [...]

Magnetotelluric (MT) measurements were made in southern Manitoba, Canada, as part of the Portable Observatories for Lithosphere Analysis and Research Investigating Seismicity (POLARIS) project, to image the northeastern part of the Williston basin and underlying Precambrian lithosphere. Data collected at 21 sites along a 400 km east-west profile at 49.5°N and a 300 km north-south profile at 100°W were analyzed using robust spectral analysis, tensor decomposition, and two-dimensional inversion. The resulting resistivity models allow subdivision of the Williston basin into three layers: an upper layer of 1-5 Ωm corresponding to Mesozoic and upper Paleozoic rocks, a 20-50 Ωm layer corresponding to lower Paleozoic carbonate rocks, and a 2-3 Ωm layer corresponding to the Ordovician Winnipeg Formation. Deeper penetrating MT responses, interpreted with other MT data, reveal a region in the westernmost Superior craton with a southwest-northeast geoelectric fabric that is oblique to subprovince boundaries. The observations can be explained by Proterozoic deformation extending several hundred kilometres east of the Superior boundary zone or by a separate Archean terrane adjacent to the boundary. The Thompson belt (TOBE) conductor in the south of the study area has previously been interpreted as part of the Superior boundary zone (SBZ). However, MT results show that the conductor does not extend continuously along the margin of the zone and MT studies to the north define conductors on the margin of the Sask craton. The results suggest the TOBE conductor is associated with the Sask craton margin. The MT results indicate significant along-strike variation of the SBZ in southern Manitoba. Des mesures magnetotelluriques ont ete effectuees dans le Sud du Manitoba, Canada, dans cadre du Projet POLARIS ('Portable Observatories for Lithosphere Analysis and Research Investigating Seismicity '); le but etait de former une image de la partie nord-est du basin Williston et de la lithosphere precambrienne sous-jacente. Des donnees recueillies a 21 sites le long d'un profil est-ouest de 400 km de long a une latitude 49,5 [degre]N et le long d'un profil nord-sud de 300 km de long a une longitude de 100 [degre]O ont ete etudiees par analyse spectrale robuste, par decomposition des tenseurs et par inversion bidimensionnelle. Les modeles de resistivite qui en decoulent permettent une subdivision du basin Willistonen trois couches : une couche superieure de 1 a 5Ωm, correspondent a des roches datant du Mesozoique et du Paleozoique superieur; une couche de 20 a 50 Ωm correspondent aux carbonates du Paleozoique inferieur et une couche de 2 a 3 Ωm, correspondent a la Formation de Winnipeg (Ordovician). Des reponses magnetotelluriques a plus grande profondeur,interpretees avec d'autres donnees magnetotelluriques, revelent une region, dans la partie la plus a fouest du craton du Superieur, qui a une texture geoelectrique sud-ouest--nord-est, oblique aux limites de la sous-province. Les observations peuvent etre expliquees par une deformation au Proterozoique qui s'etend sur plusieurs centaines de kilometres a Pest de la zone limite du Superieur ou par un terrane archeen independant adjacent a la bordure. Le conducteur TOBE (ceinture de Thompson) dans le sud du secteur a 1'etude avait ete anterieurement interprete comme une partie de la zone de la limite du Superieur. Toutefois, les resultats de la magnetotellurique montrent que le conducteur ne s'etend pas de maniere continue le long de la limite de la zone; des etudes au nord definissent des conducteurs le long de la bordure du craton Sask. Selon les resultats, le conducteur TOBE serait associe a la bordure du craton Sask; ils indiquent aussi une variation importante le long de la direction de la zone limite du Superieur dans le Sud du Manitoba. [Traduit par la Redaction], Introduction In this study, which forms part of the Canadian POLARIS (Portable Observatories for Lithosphere Analysis and Research Investigating Seismicity) project, the magnetotelluric (MT) method is used to image the [...]

Extraction of gold from quartz-carbonate shear zones has left a barren deposit of tailings at Central Manitoba mine, which remains unchanged after 70 years. In this study, the shape of the basin, the groundwater and surface water flow regime, and the electrical conductivity of the tailings have been delineated using a combination of geotechnical, geophysical, and geochemical techniques. Groundwater and surface water flow from the north-south-fractured bedrock outwards to the east and west. A component of upward groundwater movement in the deposit is due to evaporation in hot, dry summers, limited recharge from precipitation, and the tailings basin being a local groundwater discharge zone. Electromagnetic surveys indicate that the thickness of the tailings and underlying peat bog material increases from ~1 m at the south of the tailings to ~5 m at the north. The surveys provided an effective way of mapping the spatial distribution of acidic pore fluids and associated increased salinity. Zones of acidification, occurring mainly on the south side of the tailings, support the hypothesis that acidification is due to differential settling during the initial discharge of carbonate and sulfide minerals. Key words: gold mine tailings, hydrology, electrical conductivity, geochemistry, acidity. L'extraction d'or provenant de zones de cisaillement de quartz--carbonate a produit un depot de residus sans valeur economique a la mine Central Manitoba, qui est en place depuis 70 ans. Dans cette etude, la forme du bassin, les regimes d'ecoulement de surface et souterrain et la conductivite electrique des residus ont ete definis a l'aide d'une combinaison de methodes geotechniques, geophysiques et geochimiques. Les eculements souterrains et de surface partent du roc fracture d'orientation nord--sud vers l'est et l'ouest. Une composante verticale (vers le haut) de l'ecoulement souterrain dans les residus est causee par l'evaporation lors des etes chauds et secs, la recharge limitee par les precipitations, et le fait que le parc a residu se trouve dans une zone de decharge locale de l'eau souterraine. Une campagne de mesures electromagnetiques a revele que l'epaisseur des residus et de la tourbiere sous les residus est d'environ 1 m au sud des residus et augmente jusqu'a environ 5 m au nord. Les mesures ont permis de cartographier de facon efficace la distribution spatiale de l'eau interstitielle acide et l'augmentation de salinite associee. Les zones d'acidification, presentes surtout dans la partie sud des residus, supporte l'hypothese que l'acidification est due au tassement differentiel durant la periode initiale de decharge des mineraux carbonates et sulfureux. Mots-cles: residus miniers auriferes, hydrologie, conductivite electrique, geochimie, acidite. [Traduit par la Redaction], Introduction The production of acid by the oxidation of sulfide minerals in mine tailings can cause the mobility of potentially toxic metals (Blowes 1997; Plumlee et al. 1999; Nordstrom and [...]

Magnetotelluric data acquired across the Paleoproterozoic Trans-Hudson orogen, northern Saskatchewan, image one of the world's longest crustal features, the North American Central Plains conductivity anomaly. Modeling shows the anomaly at this latitude to comprise two distinct, westward-dipping bodies of high conductivity lying structurally above a late collisional feature, the Guncoat thrust. The shallower of these bodies correlates with the western part of the La Ronge belt; the deeper body at mid-crustal depths underlies the Wathaman batholith, and its western boundary is close to the inferred subsurface extension of the subvertical Needle Falls shear zone. The anomaly is identified with interleaved, biotitic, metasedimentary rocks of the Nemeiben zone and Cree Lake belt and is interpreted to have been thrust beneath the margin during collision of the La Ronge arc with the Rae-Hearne continent via westward-directed subduction.

Frasnian reef complexes along the northern margin of the Canning Basin in northwestern Australia evolved during rifting of the Fitzroy Trough. Geological investigations of the Frasnian Hull platform, which developed on an active tilted fault‐block, reveal significant lateral and vertical facies variations superimposed on prominent metre‐scale cyclicity. This study uses numerical analyses of facies and magnetic susceptibility data from three measured sections along the Hull platform to test whether a tectonic signal can be distinguished from eustatic and other signals. Geostatistical analysis of facies variations reveals an exponential distribution of thin (<3 m) facies, characteristic of stochastic depositional processes. Thick subtidal facies predominate in the Guppy Hills (GH) and southeastern Hull Range (SHR) sections near the hangingwall margin, and thick shallow‐subtidal to intertidal facies dominate the Horse Springs drillcore (HD 14) section near the footwall margin. Power and wavelet spectral analyses indicate a strong periodic component; Average Spectral Misfit and spectral optimisation methods confirm the presence of Milankovitch eccentricity signals and suggest the presence of obliquity and precession signals. However, the results also expose strong temporal and spatial variation providing evidence for tectonic control. Spectral analyses show strongest periodicity is recorded in short intervals that are not correlated across the platform and provide evidence of variations in sedimentation rate and hiatuses. Time series for the neighbouring GH and SHR sections show no overall statistical correlation, and Markov analysis indicates weakly ordered vertical facies transitions that do not correlate across the platform. Subtidal to intertidal facies data from HD 14 core suggest that at least 35% of the section is absent, almost obscuring the Milankovitch signal. The results indicate a complex set of controls on deposition on the Hull platform with local tectonic effects having produced spatio‐temporal moderation of the underlying eustatic signals and autogenic processes adding a localised stochastic response. [ABSTRACT FROM AUTHOR]

The Archean Slave craton in northwestern Canada is an ideal natural laboratory for investigating lithosphere formation and evolution, and has become an international focus of broad geoscientific investigation following the discovery of economic diamondiferous kimberlite pipes. Three deep-probing magnetotelluric surveys have recently been carried out on the craton using novel acquisition procedures. The magnetoteiluric responses reveal an unexpected and remarkable anomaly in electrical conductivity, collocated with the kimberlite field that is modeled as a spatially confined upper mantle region of low resistivity ([is less than] 30 [Omega] [multiplied by] m) at depths of 80-100+ km, and is interpreted to be due to dissolved hydrogen or carbon in graphite form. This geophysically anomalous upper mantle region is also spatially coincident with a geochemically defined ultradepleted harzburgitic layer. The tectonic processes that emplaced this structure are possibly related to the lithospheric subduction and trapping of overlying oceanic mantle at 2630-2620 Ma. Keywords: Slave Province, magnetotelluric surveys, electromagnetic, Archean, electrical conductivity, plate tectonics.

The resistivity structure of the lithospheric mantle beneath the Proterozoic Grenville Province in southern Ontario, Canada is investigated using 84 magnetotelluric (MT) sites divided into four profiles. Depth-based regional geoelectric dimensionality analyses of the MT responses indicate that the mantle lithosphere north of Lake Ontario can be subdivided into upper (45- 150 km) and deeper (>200 km) lithospheric mantle layers with regional strike azimuths of N85°E (±5°) and N65°E (±5°), respectively. MT responses from the Grenville Front and the northwest part of the Central Gneiss Belt are compatible with the presence of 2-D resistivity structures but farther to the southeast, in the southeast part of the Central Gneiss Belt and Central Metasedimentary Belt, they suggest the presence of localized 3-D structures. 2-D inversion of distortion-free MT responses images a large scale very resistive (>20 000 Ω m) region that extends 300 km southeast of the Grenville Front and for at least 800 km alongstrike in the lithospheric mantle beneath the Grenville Province. This feature is interpreted to be Superior Province lithosphere and the corresponding N85°E geoelectric strike to be associated with the fabric of the Superior Province. The base of the resistor reaches depths of 280 km on two of the three MT profiles north of Lake Ontario and this depth is interpreted to be the base of the lithosphere. A large region of enhanced conductivity in the lower lithosphere, spatially correlated with decreased seismic velocity, is bounded to the northwest by a subvertical resistivity anomaly located near the Kirkland Lake and Cobalt kimberlite fields. The enhanced conductivity in the lower lithosphere is attributed to refertilization by fluids associated with Cretaceous kimberlite magmatism and can be explained bywater content in olivine of 50 wt ppm in background areas with higher values in a localized anomaly beneath the kimberlite fields. Farther to the southeast the resistivity models include a lithospheric conductor between 100 and 150 km depth beneath the Central Metasedimentary Belt. The enhanced conductivity is attributed to grain boundary graphite films, associated with the Cretaceous kimberlitic magmatic process, or to water and carbon, introduced into the mantle during the pre-Grenvillian tectonism. [ABSTRACT FROM AUTHOR]

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Magnetotelluric (MT) soundings were made along a transect in northern Canada crossing the Proterozoic Wopmay Orogen, Fort Simpson basin, and adjacent parts of the Slave craton and the Nahanni terrane. The results are used to define the geoelectric structure and constrain the crustal and lithospheric structure and evolution. Across the Wopmay Orogen, geoelectric strikes at crustal depths average N34°E and are interpreted to be related to transcurrent faulting that occurred during late distal collisions at the western margin of the orogen. Weak two-dimensionality in the Fort Simpson basin is interpreted to be due to the sedimentary rocks in the basin. At longer periods, geoelectric strikes across the Wopmay Orogen rotate from ∼N43°E at uppermost mantle penetration to ∼N62°E at a depth of 100 km. The uppermost mantle strikes are interpreted to be due to ductile shearing linked to the transcurrent faulting in the overlying crust. The deeper strikes may be caused by shearing at the base of the present-day lithosphere. Within the Wopmay Orogen, the MT results image a conductor at the margin of the Fort Simpson and Hottah terranes interpreted to be related to the collision of these terranes. Conductive crust beneath the western margin of the Great Bear magmatic arc suggests correlative rocks of the Coronation margin extend south of the Slave craton. Lastly, decreased resistivity in the Hottah terrane at mantle depths is interpreted to be caused by the introduction of graphitic or sulphidic rocks during subduction prior to the Hottah–Slave and Fort Simpson – Hottah collisions. [ABSTRACT FROM AUTHOR]