2018

Permanent URI for this collectionhttps://hdl.handle.net/1807/81043

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Forearc strike-slip displacement as an alternative to subduction erosion, with examples from Mexico and California (sinistral Nacimiento fault)
(Canadian Science Publishing, 2018-11-04) Ingersoll, Raymond Vail
Slip on the Nacimiento fault of the central Coast Ranges of California has been variably interpreted as dextral, sinistral, or reverse. The currently prevailing interpretation is that the Nacimiento fault represents subduction erosion, by which the central to eastern part of the Cretaceous California batholith was thrust over the western part of the batholith and forearc basin, resulting in juxtaposition of the Salinian batholithic block against the Franciscan Complex, concurrently with Laramide flat-slab subduction (75–55 Ma) and underplating of the Pelona-Orocopia-Rand schist. No modern convergent plate margin includes such overthrusting. The closest modern analog to the likely configuration of the Salinian continental margin near the end of the Laramide deformation is southern Mexico, where arc plutons are exposed near the trench. Although commonly considered an example of subduction erosion, this margin is “missing” parts of the plutonic arc and forearc because they have been displaced to the southeast by sinistral slip. By analogy, the Nacimiento forearc was modified as a trench-trench-transform triple junction migrated southeastward along the continental margin during flat-slab subduction. This model makes testable predictions involving northwest-to-southeast younging of deep-marine deposits on batholithic crust underlain by contemporaneous schist. Correct restoration of later Cenozoic primarily dextral slip and Maastrichtian – Early Eocene primarily sinistral slip must result in realignment of north–south-trending belts of the Sierra Nevada – Salinia – Peninsular Ranges batholith, Great Valley forearc, and Franciscan Complex. These modern and ancient examples suggest that several “erosional” subduction zones are more plausibly explained by strike-slip truncation of forearcs.
Timeline of the South Tibet – Himalayan belt: the geochronological record of subduction, collision, and underthrusting from zircon and monazite U–Pb ages
(Canadian Science Publishing, 2018-10-17) Burg, Jean-Pierre; Bouilhol, Pierre
The “exact timing” of collision between India and Eurasia is a recurring theme. Careful dating is critical for all tectonic events. With the example of the South Tibet – Himalaya collision system, a short review of arguments from different approaches suggests that this pursuit is in vain, but that our knowledge is already sufficient to provide an acceptably “precise” timing of the main events. We reviewed U–Pb ages of zircons and monazites, recognizing that major tectonic events can produce thermal effects strong enough to be recognized in high-temperature geochronology. This review also shows that precise timing is beyond the precision of the methods and the rock record. General consistency between geologic and thermochronologic records strengthens previous interpretations of the collisional orogenic system. We argue that the Tsangpo Suture in South Tibet results from two merged subduction zones and that island arcs may be part of the root of the Eurasian paleoactive margin, which is at variance with most tectonic interpretations. The two main collisional events closely followed each other at ca. 50 and 40 Ma.
The sources of metamorphic heat during collisional orogeny: The Barrovian enigma.
(Canadian Science Publishing, 2018-10-09) Ryan, Paul Desmond; Dewey, John Frederick
The problem of the observed very rapid advection of heat into metamorphic thrust stacks is reviewed. Conductive models relying on the thermal relaxation of a thickened crust will not produce the observed Barrovian (medium temperature, medium pressure) assemblages within some short-lived orogens (e.g., western Ireland and Timor). Studies of the rate and timing of metamorphic mineral growth suggest that this is commonly faster than predicted by thermal relaxation. Barrovian assemblages are localised in some orogens (e.g., the Alps) but extensive in others (e.g., the Himalayas). Metamorphic mineral growth brackets deformation; consequently, slow growth is inconsistent with the rapid uplift of many orogens. Thus, no single mechanism can account for the development of Barrovian assemblages during collisional orogeny. The only mechanisms that can supply large amounts of heat for regional metamorphism quickly (<10 Myr) are: rapidly thinning the lithosphere without stretching it (e.g., by plume thermal erosion, slab drop-off, or delamination); by emplacing magma into the crust (modest deep mafic underplate and (or) very large amounts of mafic and silicic magma emplaced into the middle and upper crust); or obducting hot nappes of arc with a thin ophiolite forearc (“hot iron” mechanism). Frictional and viscous heating produces local rapid heating but not fast regional heating. Back-arc or any kind of lithospheric extension increases the geothermal gradient and heat flow but does not heat rocks up. We suggest that magmatic advection of heat-associated lithospheric thinning or “hot iron” overthrusting of an arc/ophiolite are the primary sources of heat in short-lived orogens.
A new approach to the opening of the Eastern Mediterranean Sea and the origin of the Hellenic Subduction Zone Part 1: The eastern Mediterranean Sea
(Canadian Science Publishing, 2018-12-15) Le Pichon, Xavier; Şengör, Celâl; İmren, Caner
We identify long transform faults that frame the eastern Mediterranean Sea and that were active during Jurassic and probably the Early Cretaceous, during the opening of the central Atlantic Ocean. We show that the African margin of the eastern Mediterranean Sea is an 1800 km long transform fault that absorbed the Africa/Eurasia Jurassic left-lateral motion during the opening of the central Atlantic. We call this transform fault the Eastern Mediterranean South Transform fault (EMST). We identify two other transform faults that were active simultaneously and framed the eastern Mediterranean Sea during its formation. These are the Apulia Transform fault (AT) and the Eastern Mediterranean North Transform fault (EMNT). The AT, three hundred km north of the EMST, followed the southern boundary of the Apulia block. Still 300 km farther north, the EMNT formed the northern boundary of this eastern Mediterranean shear zone. This last fault has been destroyed over a large portion by the Hellenic subduction. We relate these transform faults to the kinematics of the Jurassic Africa/Eurasia motion. We conclude that the eastern Mediterranean Sea is a long pull-apart created by left-lateral shearing of the Adria block as it was structurally linked to Africa.
Testing of Permian-Lower Triassic stratigraphic data in half-graben/tilt-block system: evidence for the initial rifting phase in Antalya Nappes
(Canadian Science Publishing, 2018-11-05) ŞAHİN, Nazif; ALTINER, Demir
Testing of Middle Permian-Lower Triassic stratigraphic data from the Antalya Nappes in a half- graben/tilt-block system has revealed the presence of episodic rifting events separated by periods of tectonic quiescence. Following a period of uplift during the Permian (late Artinskian to Roadian), the basement rocks have been activated by displacement faults and several depocenters in half-graben like asymmetrical basins began to be filled with Roadian to Wordian continental clastic deposits intercalated with coal and marine rocks. The early Capitanian time was a period of tectonic quiescence. The second event occurred in middle to late Capitanian times and produced basaltic volcanic rocks intercalated in the shallow marine fossiliferous carbonate successions. Following the Lopingian (Wuchiapingian and Changhsingian) and Permian-Triassic boundary interval representing a long tectonic quiescence, the last rifting episode started with an abrupt facies change in the late Griesbachian. Variegated shales, limestones, volcanics, talus breccia and debris flow deposits were laid down in a half-graben/tilt-block system. As normal faulting has become active the deposition continued on the subsiding hanging wall side. The stratigraphic gap increased in magnitude as the erosional truncation has incised deeply the footwall side. This initial rifting phase in the Antalya Nappes is prior to the onset of a stronger and more continuous rifting event which occurred in the Anisian-Carnian interval including a variety of deep water clastic and carbonate deposits, radiolarites containing sometimes blocks and clasts derived from the basin margins and volcanic rocks carrying intra-oceanic setting character.
Testing of Permian-Lower Triassic stratigraphic data in half-graben/tilt-block system: evidence for the initial rifting phase in Antalya Nappes
(Canadian Science Publishing, 2018-11-05) ŞAHİN, Nazif; ALTINER, Demir
Testing of Middle Permian-Lower Triassic stratigraphic data from the Antalya Nappes in a half- graben/tilt-block system has revealed the presence of episodic rifting events separated by periods of tectonic quiescence. Following a period of uplift during the Permian (late Artinskian to Roadian), the basement rocks have been activated by displacement faults and several depocenters in half-graben like asymmetrical basins began to be filled with Roadian to Wordian continental clastic deposits intercalated with coal and marine rocks. The early Capitanian time was a period of tectonic quiescence. The second event occurred in middle to late Capitanian times and produced basaltic volcanic rocks intercalated in the shallow marine fossiliferous carbonate successions. Following the Lopingian (Wuchiapingian and Changhsingian) and Permian-Triassic boundary interval representing a long tectonic quiescence, the last rifting episode started with an abrupt facies change in the late Griesbachian. Variegated shales, limestones, volcanics, talus breccia and debris flow deposits were laid down in a half-graben/tilt-block system. As normal faulting has become active the deposition continued on the subsiding hanging wall side. The stratigraphic gap increased in magnitude as the erosional truncation has incised deeply the footwall side. This initial rifting phase in the Antalya Nappes is prior to the onset of a stronger and more continuous rifting event which occurred in the Anisian-Carnian interval including a variety of deep water clastic and carbonate deposits, radiolarites containing sometimes blocks and clasts derived from the basin margins and volcanic rocks carrying intra-oceanic setting character.
Southeast Anatolian Orogenic Belt Revisited (Geology and Evolution)
(Canadian Science Publishing, 2018-09-27) Yilmaz, Yücel
The Southeast Anatolian Orogenic Belt consists of the Arabian Platform, a zone of imbrication, and a nappe zone. The Arabian Platform is represented by a thick marine succession. The zone of imbrication is a narrow belt sandwiched between the Arabian Platform and the nappes. The nappes are the highest tectonic unit. They consist of two continental slivers separated by ophiolitic associations representing oceanic environments. They were involved in the orogenic development and formed two metamorphic belts. The oceanic environment survived by the end of Middle Eocene. A northward subduction began in this ocean and generated the Elbistan–Yüksekova arc built above the Göksun ophiolite. Development of the Southeastern Anatolian Orogenic Belt began in the north, where the Binboğa–Malatya metamorphic massif, collided with the Elbistan volcanic arc to the end of Early Eocene period. Later new tectonic entities were accreted to this progressively growing and southerly transporting nappe stack. In the lower plate, the southern continental sliver that was attached to the oceanic slab subducted together and underwent high-pressure metamorphism. The subducting oceanic slab retreated. Asthenospheric inflow caused high-temperature metamorphism, which superimposed on the previous high-pressure metamorphism. The oceanic and continental fragments formed the Bitlis Massif and the Berit metaophiolite when exhumed. A younger volcanic arc was built on the ocean floor to the south. Accretion of the volcanic arc to the nappe pile occurred during the Late Eocene period. The orogenic belt was formed when the nappes collided with the Arabian plate during the Late Miocene.
The History of the Core Dynamos of Mars and the Moon Inferred From Their Crustal Magnetization: A Brief Review
(Canadian Science Publishing, 2018-06-16) Arkani-Hamed, Jafar
The core dynamos of Mars and the Moon have distinctly different histories. Mars had no core dynamo at the end of accretion. It took ~100 Myr for the core to create a strong dynamo that magnetized the martian crust. Giant impacts during 4.2-4.0 Ga crippled the core dynamo intermittently, until a thick stagnant lithosphere developed on the surface and reduced the heat flux at the core-mantle boundary, killing the dynamo at ~3.8 Ga. On the other hand, the Moon had a strong core dynamo at the end of accretion that lasted ~100 Myr and magnetized its primordial crust. Either precession of the core, or thermo-chemical convection in the mantle, or chemical convection in the core created a strong core dynamo that magnetized the sources of the isolated magnetic anomalies in later times. Mars and the Moon indicate dynamo reversals and true polar wander. The polar wander of the Moon is easier to explain compared to that of Mars. It was initiated by the mass deficiency at South Pole Aitken basin which moved the basin southward by ~68o relative to the dipole axis of the core field. The formation of mascon maria at later times introduced positive mass anomalies at the surface, forcing the Moon to make an additional ~52o degree polar wander. Interaction of multiple impact shock waves with the dynamo, the abrupt angular momentum transfer to the mantle by the impactors, and the global overturn of the core after each impact were probably the factors causing the dynamo reversal.
Pargasite-bearing vein in spinel lherzolite from the mantle lithosphere of the North America Cordillera
(Canadian Science Publishing, 2018-12-07) Ghent, Edward D.; Edwards, Benjamin R.; Russell, James K.
Basanite lavas near Craven Lake, British Columbia, host a spinel lherzolite xenolith containing cross-cutting veins with pargasitic amphibole (plus minor apatite). The occurrence of vein amphibole in spinel lherzolite is singular for the Canadian Cordillera. The vein crosscuts foliated peridotite and is itself cut by the basanite host. The amphibole is pargasite, which is the most common amphibole composition in mantle peridotite. Rare earth element concentrations in the pargasite are similar to those for mafic alkaline rocks across the northern Cordilleran volcanic province (light rare earth elements ∼50× chondrite and heavy rare earth elements ∼5× chondrite). Two-pyroxene geothermometry suggests that the vein and host peridotite were thermally equilibrated prior to sampling by the basanite magma. Calculated temperature conditions for the sample, assuming equilibration along a model steady-state geotherm, are between 990 and 1050 °C and correspond to a pressure of 0.15 GPa (∼52 ± 2 km depth). These conditions are consistent with the stability limits of mantle pargasite in the presence of a fluid having XH2O < ∼0.1. The pargasite vein and associated apatite provide direct evidence for postaccretion fracture infiltration of CO2–F–H2O-bearing silicate fluids into the Cordilleran mantle lithosphere. Pargasite with low aH2O is in equilibrium with parts per million concentrations of H2O in mantle olivine, potentially lowering the mechanical strength of the lithospheric mantle underlying the Cordillera and making it more susceptible to processes such as lithospheric delamination. Remelting of Cordilleran mantle lithosphere containing amphibole veins may be involved in the formation of sporadic nephelinite found in the Canadian Cordillera.
Late Pleistocene age, size, and paleoenvironment of a caribou antler from Haida Gwaii, British Columbia
(Canadian Science Publishing, 2018-12-16) Mathewes, Rolf W.; Richards, Michael; Reimchen, Thomas E.
The basal portion of a fossil caribou antler from Graham Island is the only evidence of large terrestrial vertebrates older than the Fraser (late-Wisconsin) glaciation on Haida Gwaii. This antler has been radiocarbon-dated three times by different laboratories and all ages fall within the mid-Wisconsin Olympia Interglaciation (Marine Isotope Stage 3, MIS 3). We suggest that the latest date, using ultrafiltration of bone collagen is closest to the true age at 43,200 Âą 650 BP (48,200-45,200 cal BP). Previous paleoecological analysis from Graham Island reconstructed a vegetation cover during MIS 3 consisting of mixed coniferous forest with non-forested openings, similar to cool subalpine forests of today. These conditions are consistent with environments that support Woodland Caribou and the related extinct Dawson caribou. Morphometric comparison of antlers from Woodland and Dawson Caribou suggest that they are more similar than previously interpreted, and raise questions about the inferred differences between the mainland and island subspecies.
Petrography, geochemistry and Nd isotope systematics of metaconglomerates and matrix-rich metasedimentary rocks: Implications for the provenance and tectonic setting of the Labrador Trough, Canada
(Canadian Science Publishing, 2018-11-20) Henrique-Pinto, Renato; Guilmette, Carl; Bilodeau, Carl; Stevenson, Ross R.; Carvalho, Bruna Borges
The New Quebec Orogen consists of a supracrustal belt that was reworked when the Superior craton collided with the Core Zone terrane during the Paleoproterozoic Trans-Hudson Orogeny. Within the New Quebec Orogen, the Kaniapiskau Supergroup can be divided into four terrigenous lithotypes metamorphosed at low-grade: one set with greater compositional and textural sedimentary maturity classified as quartz arenites and subarkoses, and another set with lower textural maturity classified as feldspathic wackes and mudrocks. In contrast, the Laporte Group includes homogeneous lithotypes represented by feldspathic and lithic wackes with a range of matrix contents metamorphosed at low to medium-grade. The Kaniapiskau Supergroup rocks have a wide range of SiO2 and Al2O3 contents (SiO2/Al2O3 = 3.7-51) compared to the restricted compositional range of the Laporte Group rocks (SiO2/Al2O3 = 4.4-6.8). In general, the geochemical variations in both formations of the Laporte Group are within the range of the main clast varieties from basal metaconglomerates, although the Deborah Formation (top unit), records higher TiO2, P2O5, MgO and Ni contents and high Cr/Th, Co/Ba, Th/U and Rb/Sr ratios indicating additional mafic sources. Our results support the hypothesis that the Kaniapiskau Supergroup was deposited along an intraplate continental margin with predominantly recycled (ɛNd(1.87Ga) -12) Paleoarchean sources (TDM 3.2 Ga). In contrast, the Laporte Group marks the transition from a continental forearc (Grand Rosoy Fm.) with a typical juvenile source, including granitic clasts (ɛNd(1.83Ga) -0.1 to +3.1), to a wedge-top depozone (Deborah Fm.) in the context of a collisional pro-foreland basin. This syn-collisional sedimentary environment is characterized by the presence of old crustal components (ɛNd(1.83Ga) -4.4 to -9.1).
Conditions and Timing of LP-HT Metamorphism in the Montresor Belt, Rae Province, Nunavut
(Canadian Science Publishing, 2018-11-17) Dziawa, Carolyn; Gaidies, Fred; Percival, John
P-T-t estimates for the Montresor Belt, obtained using phase equilibria and geospeedometry modelling integrated with in-situ U-Th-Pb monazite geochronology, shed new light on the tectono-metamorphic effects of the Snowbird phase of the Trans-Hudson orogeny. Typical metapelitic assemblages of the lower Montresor group consist of white mica, biotite, plagioclase, quartz, and andalusite, which in some rocks is partly or completely pseudomorphed by white mica. The observed assemblages reflect peak P-T conditions centering at ca. 575 °C and 3 kbar. Rocks with high bulk Fe/Mg contents contain compositionally zoned garnet, permitting the addition of further constraints on the conditions of metamorphism in the Montresor Belt: Core compositions of earliest-grown garnets indicate initial garnet crystallization at ca. 535 °C and 2.3 kbar suggesting a nearly isobaric P-T path of prograde metamorphism with a gradient of ca. 50 °C/kbar. Chemical age-dating of monazite inclusions in garnet yields ages of ca. 1870 ± 9 to 1837 ± 9 Ma. Retrograde, pseudomorphic andalusite replacement by white mica at ca. 540 °C is inferred to have been controlled by variations in bulk rock chemistry. Morphologically corroded and chemically heterogeneous monazite adjacent to white mica pseudomorphs suggest that andalusite replacement took place at ca. 1792 ± 10 Ma, possibly associated with extension and movement along the detachment fault separating the upper and lower Montresor groups. Simulations of diffusion across chlorite- and biotite-filled cracks in garnet assumed to be coeval with andalusite replacement suggest that the rocks have experienced the retrograde event for at least 20 My.
Makran continental margin sedimentation during Late Holocene
(Canadian Science Publishing, 2018-08-30) Alizadeh Ketek Lahijani, Hamid; Amjadi, Sedigheh; Pourkerman, Majid; Naderi-Beni, Abdolmajid; Hosseindost, Mona; Habibi, Parisa
Sedimentation in the Makran active margin is governed by complex interaction of atmospheric, tectonics and hydrodynamic setting of northern flank of the Gulf of Oman. The mixed clastic carbonate sediments in tectonically and hydrodynamically active environment have complicated distribution pattern. The region is suffering from basic sedimentological data and specifically the sedimentation history of the Holocene deposits was rarely studied in Iranian coast. To deal with this deficiency, surface and core sediment samples from the Iranian continental shelf and upper slope of the Gulf of Oman have been studied using standard sedimentological techniques. The overall sediment distribution pattern demonstrates that the grain size gradually decreases from shoreline to the deeper zones. However, some medium to coarse grained sand patches can be found in deeper parts specially in the middle part of the studied area that can be related to sediment supply of ephemeral rivers discharging in to the sea in rainy seasons and/or high energy events i.e. turbidites and tsunamis during the Holocene. Several horizons of the coarse grained detrital sediments are detectable in upper slope sediment cores. The coarse grained materials are received from hinterland during flashfloods and could be accumulated due to mass wasting events. The elevated amount of organic materials in the upper slope indicates deficit of dissolved oxygen that leads to preservation of organic materials in the bottom sediments.
Fluid compartmentalization of Devonian and Mississippian dolostones, Western Canada Sedimentary Basin: petrologic and geochemical evidence from fracture mineralization
(Canadian Science Publishing, 2018-11-18) Al-Aasm, Ihsan S.; Mrad, Carole; Packard, Jeffrey
Integrated petrographic, geochemical and fluid inclusion study of fracture mineralization and associated host rock in selected Mississippian and Devonian carbonates extending from southeast Alberta to northwest British Columbia, Canada, aims at quantifying the type and nature of fluids precipitated saddle dolomite and late calcite cement and their origin. Petrographic and isotopic evidence from both the Devonian and Mississippian fracture-filling carbonates indicate the presence of a hydrothermal fluid source. The δ18O isotopic values for the Devonian saddle dolomite (-14.62 to -3.75‰ VPDB; average -11.12 ‰) combined with enriched 87Sr/86Sr isotopic ratios (0.70827 to 0.71599; average 0.71006) and higher homogenization temperatures (Th=74-194.6oC; average 126.8oC) and salinity values (7.7 to 26.6, average 16.2wt% NaCl eq.) show significant differences from the Mississippian saddle dolomite, which is characterized by less negative δ18O isotopic values (-12.53 to -7.82‰ VPDB; average -9.14‰), less radiogenic 87Sr/86Sr isotopic ratios (0.70859 to 0.70943; average 0.70887) and lower homogenization temperatures (Th) and salinity values of fluid inclusions (87.6-214.2oC; average 136.3oC;2.0 to 13.2, average 9.6wt% NaCl eq.). Later fracture- and vug-rimming blocky calcite cement records comparable or slightly lower values of oxygen (-16.31 to -4.08 ‰ VPDB; average -9.76 ‰) and Sr isotopes (0.70784 to 0.709743; average 0.70868) and much lower salinity values (0 to 22.5 wt. % NaCl; average: 2.86 wt. % NaCl) for samples mostly from the Mississippian age group. These results suggest possibly two different hydrothermal episodes related to early (Antler) and late (Laramide) tectonic events that affected the Western Canada Sedimentary Basin with possible compartmentalization of hydrothermal systems and their associated brines in the basin.
Three-dimensional stochastic assimilation of gravity data in Lalor volcanogenic massive sulphide, Manitoba, Canada
(Canadian Science Publishing, 2018-12-14) Tirdad, Shiva; Gloaguen, Erwan; Bouchedda, Abderezzak; Dupuis, Christian
We propose a new numerical workflow based on stochastic data integration where we merge a conceptual geological model, the drillhole geophysical and geological logs as well as surface geophysical data to compute a unified numerical model of a VMS deposit. The first step of the workflow consists in building a 3D numerical conceptual model of the geology. This conceptual model as well as geological logs are then used to generate multiple equiprobable scenarios of the geology by means of multiple point simulation (MPS). The MPS method studies high-order statistics in the space of a numerical conceptual model making it possible to reproduce complex geological structures. We then use conventional conditional sequential Gaussian simulation, which is a method based on a node-by-node sequential process to stochastically populate the geological grid with densities. For this purpose we use available density logs to simulate multiple equiprobable spatial distributions of the density at high spatial resolution within each geological unit separately. The stochastic high-resolution density models are iteratively combined by the gradual deformation method in order to minimize the difference between measured Bouguer anomaly data and the data computed on the combined realizations of density. Application of the proposed method to the Lalor deposit, a volcanogenic massive sulphide deposit in Manitoba, Canada, produces a density model that honours the geology of the deposit and the Bouguer anomaly data. This unified model has the advantage to include all the available information (geological and density logs and surface geophysics) at scales appropriate for mining applications.
The Bathurst Mining Camp, New Brunswick: Data Integration, Geophysical Modelling and Implications for Exploration
(Canadian Science Publishing, 2018-09-22) Ugalde, Hernan; Morris, William A.; van Staal, Cees
The Bathurst Mining Camp (BMC) is one of Canada's oldest mining districts for volcanogenic massive sulfide (VMS) deposits. Most of the 46 known deposits were discovered in the 1950s using a combination of geological and geophysical methods. However, renewed exploration efforts over the past 15 years have not been as successful as one would expect for the level of expenditure the camp has gone through. Nevertheless, this has created a large database of high resolution airborne geophysical data (magnetics, electromagnetics, radiometrics, full tensor gravity gradiometry) which makes Bathurst a unique case. We show data compilation and map view interpretation, followed by 2.5D gravity and magnetic modelling. From this, we provide constraints on the folded structure of the mafic and felsic volcanic units, and we interpret a large gravity anomaly in the south-east as a possible ophiolite or a dense thick package of basaltic rocks. Finally, we show an example of 3D modelling in the northwestern part of the camp, where we combine map view interpretation with section-based modelling and 3D geophysical inversion.
Musings in structure and tectonics
(Canadian Science Publishing, 2018-09-05) Dewey, John Frederick
I outline and discuss my career in the context of the history of structural geology and tectonics, the progressive developments that led to plate tectonics, the people who have encouraged and influenced me, the events that changed my life, my fifty six doctoral students who have taught me so much, and my principal interests in tectonics. I discuss, in particular, nine topics of special current interest: the evolution of Tibet, the geomorphology of the British Isles, transtension, the Precambrian, the complexities of plate boundary evolution, Appalachian–Caledonian evolution, ophiolites, the structure and strength of the lithosphere, and the subducting slab.
Microsedimentological evidence of vertical fluctuations in subglacial stress from the northwest sector of the Laurentide Ice Sheet, Northwest Territories, Canada.
(Canadian Science Publishing, 2018-11-08) Rice, Jessey; Menzies, John; Paulen, Roger C.; McClenaghan , M. Beth
The past-producing Pine Point lead-zinc mining district, Northwest Territories, Canada, provides a unique opportunity to study the role of glacial dynamics in a thick, continuous till succession that has not been influenced by the underlying bedrock topography. Parts of the Pine Point mining district are covered by >20 m of subglacial Quaternary sediments (till) associated with the former Laurentide Ice Sheet. Till facies exposed in unreclaimed open-pit K-62 have been classified into four separate units. Micro- and macro-sedimentological analyses were undertaken to identify the change in subglacial stress during sediment deposition and across till unit boundaries. An analysis of high- and low-angle microshears (lineations) in thin sections produced from these till units indicate that there is a noticeable decrease in the abundance of low-angle shear features immediately below till unit boundaries. The deformation of low-angle shears in the underlying tills was likely caused by remobilization of the overlying till unit. This remobilization is consistent with aggradation-constant entrainment decay mechanisms for subglacial till emplacement/accretion and subglacial dispersion models.
Geology, Lithogeochemistry and Petrogenesis of Intrusions Associated with Gold Mineralization within the Timmins-Porcupine Gold Camp, Canada
(Canadian Science Publishing, 2018-11-19) MacDonald, Peter J.; Piercey, Stephen J.
The Timmins-Porcupine gold camp, Abitibi greenstone belt, is host >60 Moz of Au with many gold deposits spatially associated with porphyry intrusions and the Porcupine-Destor deformation zone (PDDZ). Porphyry intrusions form three suites. The Timmins porphyry suite (TIS) consists of high-Al tonalite-trondjhemite-granodiorite (TTG) with calc-alkalic affinities and high La/Yb ratios and formed during ~2690 Ma D1-related crustal thickening and hydrous partial melting of mafic crust where garnet and hornblende were stable in the residue. The Carr Township porphyry intrusive suite (CIS) and the granodiorite intrusive suite (GIS) also have high-Al TTG, calc-alkalic affinities, but were generated 10-15 m.y. after the TIS; the CIS were generated at shallower depths (during post-orogenic extension?) with no garnet in the crustal residue, whereas the GIS formed during D2 thrust-related crustal thickening and partial melting where garnet was stable in the residue. Gold mineralization is preferentially associated with the TIS, and to a lesser extent the GIS, proximal to the PDDZ. Intrusions near mineralization have abundant sericite, carbonate, and sulphide alteration. These intrusions exhibit low Na2O and Sr, and high Al2O3/Na2O, K2O, K2O/Na2O, Rb, and Cs, (i.e., potassic alteration); sulfide- and carbonate-altered porphyries have high (CaO+MgO+Fe2O3)/Al2O3 and LOI values. While porphyries are not genetically related to gold mineralization, they are spatially related and are interpreted to reflect the emplacement of intrusions and subsequent Au-bearing fluids along the same crustal structures. The intrusive rocks also served as structural traps, where gold mineralization precipitated in dilatant structures along the margins of intrusions during regional (D3?) deformation.
Deep mineral exploration using multi-scale electromagnetic geophysics: The Lalor massive sulphide deposit case study
(Canadian Science Publishing, 2018-08-08) Yang, Dikun; Fournier, Dominique; Kang, Seogi; Oldenburg, Douglas W.
The Lalor deposit in Snow Lake, central Manitoba is one of the most significant mineral discoveries in Canada in the past decade. Buried 600 m below the surface, the deposit remained undiscovered until a deep penetrating geophysical electromagnetic (EM) system was employed. Since then, the deposit has been a test site for many modern geophysical systems. This paper presents a comparative study of four data EM sets acquired at Lalor. We image the electrical conductivity structure of the subsurface by carrying out independent 3D inversions of the data. The four datasets are acquired through airborne, surface and borehole systems, including airborne natural source EM (ZTEM), airborne time-domain EM (HELITEM), surface large loop EM (SQUID) and borehole EM (PULSE-EM). ZTEM has good depth of penetration, but its inversion model may be biased if the background model is not properly chosen. The HELITEM system can complement ZTEM by validating the actual conductivity of the deposit. With the information provided by airborne surveys, surface EM can better define the geometry of the ore body at a local scale and help in defining drilling targets. Once boreholes are drilled, sensors can be sent downhole, possibly probing the ore lenses that are interbedded at a greater depth. Our 3D imaging experiments demonstrate that modern geophysical technology is capable of making deep exploration and assisting a more informed process throughout the entire workflow from reconnaissance to drilling and development.

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