2015
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Item Wenlock-Ludlow boundary interval revisited: New insights from the off-shore facies of the Prague Synform, Czech Republic(Canadian Science Publishing, 2015-12-22) Storch, Petr; Manda, Štěpán; Slavík, Ladislav; Tasáryová, ZuzanaAbstract: Wenlock-Ludlow boundary beds exposed near NesvaÄ ily in the Prague Synform are documented in terms of their lithology, faunal content, high-resolution record of 19 graptolite species, graptolite biostratigraphy and conodont record. This is the first time in Bohemia and peri-Gondwanan Europe that a continuous graptolite-bearing section through upper ludensisâ middle nilssoni biozones is described in detail in order to refine high-resolution biostratigraphy and correlation of the Wenlock-Ludlow boundary. Organic-rich shale, relatively rare non-graptolite fauna and absence of bioturbation indicate a stable deep-water off-shore setting with sporadic, low level bottom oxygenation. The uninterrupted succession revealed a series of origination events of principal graptolite taxa employed in determination of the Wenlock-Ludlow boundary strata world-wide. Bohemograptus represented by B. praecox appeared as early as in the uppermost Wenlock ludensis Biozone. B. praecox is later accompanied and replaced by B. bohemicus associated with Uncinatograptus uncinatus. The lowest Neodiversograptus nilssoni marked the base of the Ludlow nilssoni Biozone. Speciation within Bohemograptus continued in the middle nilssoni Biozone when the robust B. butovicensis evolved from B. bohemicus. Colonograptus colonus shows its lowest occurrence in the middle part of the nilssoni Biozone together with the latest C. gerhardi. The monograptids are associated with abundant and diverse plectograptids that are at present mostly known from Baltica. B. praecox sp. nov. and B. butovicensis (BouÄ ek, 1937) are described in the systematic part. The conodont Kockelella ortus absidata, found in the lower-middle part of the nilssoni Biozone, is consistent with a stratigraphic interval within Oz. bohemica and K. crassa conodont biozones.Item Paleolatitudinal morpho-gradient of the early Silurian brachiopod Pentameroides in Laurentia(Canadian Science Publishing, 2015-12-22) Gushulak, Cale Anthony Camille; Jin, Jisuo; Rudkin, David M.Pentameroides is a large-shelled pentameride brachiopod, which was widespread throughout Laurentia in the early Silurian (Telychian). Evolving from Pentamerus in the early Telychian, it dispersed from its subtropical/high tropical origin to sub-equatorial intracratonic seas by the late Llandovery. In this study large collections of reef-dwelling Pentameroides septentrionalis from the Attawapiskat Formation, Akimiski Island, Nunavut and level-bottom-inhabiting Pentameroides subrectus from the Fossil Hill Formation, Manitoulin Island, Ontario, and the Jupiter Formation, Anticosti Island, Quebec, were biometrically analyzed for seven external morphological features. Bivariate and ordination analysis (PCA) revealed that P. septentrionalis has a more globose, more biconvex shell with a larger ventral umbo than P. subrectus. These morphological differences, coupled with their excellent preservation in shallow-water reefal environments, suggest that P. septentrionalis was adapted to a relatively low-turbulence, hurricane-free, nutrient stressed environment near the equator (Item Propagation of a strike slip plate boundary within an extensional environment: the westward propagation of the North Anatolian Fault(Canadian Science Publishing, 2015-10-18) Le Pichon, Xavier; Şengör, Celâl; Kende, Julia; İmren, Caner; Henry, Pierre; Grall, Céline; Karabulut, HayrullahThe Sea of Marmara marks a key point in the propagation of the North Anatolian Fault (NAF) toward the northern extremity of the Aegean subduction during the last 12-11 Myr. There is no indication that a localized plate boundary existed to the west of it, north of the Aegean portion of the Anatolia plate, before 2 Ma. Prior to 2 Ma, the shear produced by the motion of Anatolia-Aegea with respect to Eurasia was distributed over the whole width of the Aegean-West Anatolian western portion. This was most probably related to the presence there of a N/S component of extension produced by the southward migration of the Aegean-West Anatolian subduction. Fast subduction of the oceanic Ionian lithosphere had been initiated 15 Ma ago, a few million years before the Anatolia westward motion began 11 Ma ago. These two processes are obviously tightly linked. We document the establishment of the Aegea-Anatolia/Eurasia plate boundary in Plio-Pleistocene time in this geodynamic context. We show that the beginning of the formation of a localized plate boundary occurred between 4.5 and 3.5 Ma ago at the location of the present Sea of Marmara by the initiation of a shear zone comparable to the Gulf of Corinth one in Central Greece. Thus the first part of the formation of the Sea of Marmara was purely extensional. We discuss the transition from the initial extensional basins to the present strike-slip system, that today cuts across the whole Sea of Marmara and that is called Main Marmara Fault (MMF). We show that the beginning of its development is not earlier than 2.5 Ma ago. Shortly after, the plate boundary migrated west of the Sea of Marmara along the northern border of Aegea from the North Aegean Trough, to the Gulf of Corinth area and to the Kefalonia fault. There, it finally linked with the northern tip of the Aegean subduction zone, completing the system of plate boundaries delimiting the Anatolia-Aegea plate. We have related the remarkable change in the distribution of shear over the whole Aegea from Miocene to Pliocene to the formation of a relatively undeforming block in Pliocene that forced the shear to be distributed over a narrow plate boundary to the north of it. We attribute the formation of this relatively undeforming Aegean block to the northeastward progression of the cold oceanic Ionian slab. We propose that the slab cuts the overlying lithosphere from asthenospheric sources and induces a shortening environment over it.Item Neo-Tethys geodynamics and mantle convection: from extension to compression in Africa and a conceptual model for obduction(Canadian Science Publishing, 2015-12-12) Jolivet, Laurent; Faccenna, Claudio; Agard, Philippe; Frizon de Lamotte, Dominique; Menant, Armel; Sternai, Pietro; Guillocheau, FrançoisSince the Mesozoic, African has been under extension with shorter periods of compression associated with obduction of ophiolites on its northern margin. Less frequent than “normal” subduction, obduction is a first order process that remains enigmatic. The closure of the Neo-Tethys Ocean, by the Upper Cretaceous, is characterized by a major obduction event, from the Mediterranean region to the Himalayas, best represented around the Arabian Plate, from Cyprus to Oman. These ophiolites were all emplaced in a short time window in the Late Cretaceous, from ~100 to 75 Ma, on the northern margin of Africa, in a context of compression over large parts of Africa and Europe, across the convergence zone. The scale of this process requires an explanation at the scale of several thousands of kilometres along strike, thus probably involving a large part of the convecting mantle. We suggest that alternating extension and compression in Africa could be explained by switching convection regimes. The extensional situation would correspond to steady-state whole-mantle convection, Africa being carried northward by a large-scale conveyor belt, while compression and obduction would occur when the African slab penetrates the upper-lower mantle transition zone and the African plate accelerates due to increasing plume activity, until full penetration of the Tethys slab in the lower mantle across the 660 km transition zone during a 25 Myrs-long period. The long-term geological archives on which such scenarios are founded can provide independent time constraints for testing numerical models of mantle convection and slab/plume interactions.Item Connemara:its position and role in the Grampian Orogeny(Canadian Science Publishing, 2015-10-19) Dewey, John Frederick; Ryan, Paul DesmondIn the Irish and British Caledonides, the early Ordovician Grampian Orogeny was the result of collision between the Laurentian rifted margin and an oceanic island arc. The Connemara terrain in western Ireland differs in position and character from all other parts of the exposed Dalradian rocks of the Grampian Orogen in lying south of the collided arc and fore-arc, and in having north-verging fold nappes that developed synchronously with the intrusion of huge volumes of calc-alkaline magmas that provided the heat for regional Barrovian metamorphism. We have tested this hypothesis with a numerical model, which demonstrates its admissablity. Connemara is not a terrane, displaced with respect to the remainder of the Grampian Orogen but was overridden, northwards, by the arc and its fore-arc basin (South Mayo Trough), frontal ophiolite complex (Deer Park) and accretionary complex (Killadangan). Deposition in the South Mayo Trough occurred below sea level and above the evolving Grampian Orogen, which developed on a hyper-extended rifted margin bounded to the north by the Clew Bay Line.Item Dynamic Cause of Marginal Lithospheric Thinning and Implications for Craton Destruction: A Comparison of the North China, Superior and Yilgarn Cratons(Canadian Science Publishing, 2015-09-07) Wang, Xu; Zhu, Peimin; Kusky, Timothy; Zhao, Na; Li, Xiaoyong; Wang, ZhenshengWe present a comparative tectonic analysis of the North China craton (NCC), which has lost parts of its root, with the Yilgarn and Superior cratons, which preserve their roots. We compare the geophysical structure and tectonic histories of these cratons to search for reasons why some cratons lose their roots, while others retain them. Based on the comparison and analysis of geological, geophysical and geochemical data, it is clear that the lithospheric thinning beneath craton margins is a common phenomenon, which may be caused by convergence between plates. However, craton destruction is not always accompanied by lithospheric thinning, except for cratons that suffered subduction and collision from multiple sides. The western block (also known as the Ordos Block) of the NCC, Yilgarn and Superior cratons have not experienced craton destruction; the common ground among them is that they are surrounded by weak zones (e.g., mobile belts or orogens) that sheltered the cratons from deformation, which contributes greatly to the long-term stability of the craton. Subduction polarity controlled the water released by the subducting plate, and if subducting plates dip underneath the craton, they release water which hydroweakens the overlying mantle, and makes it easy for delamination or sub-continental lithospheric mantle (SCLM) erosion to take place in the interior of the craton. Thus, subduction polarity during convergence events is an important element in determing whether a craton retains or loses its root.Item Plate-tectonic evolution of the Earth: bottom-up and top-down mantle circulation(Canadian Science Publishing, 2015-10-14) Ernst, W. G.; Sleep, Norman H.; Tsujimori, TatsukiIntense devolatilization and chemical-density differentiation attended accretion of planetesimals on the primordial Earth. These processes gradually abated after cooling and solidification of an early magma ocean. By 4.3 or 4.2 Ga, water oceans were present, so surface temperatures had fallen far below low-pressure solidi of dry peridotite, basalt, and granite, ~1300, ~1120, and ~950 °C, respectively. At less than half their T solidi, rocky materials existed as thin lithospheric slabs in the near-surface Hadean Earth. Stagnant-lid convection may have occurred initially but was at least episodically overwhelmed by subduction because effective, massive heat transfer necessitated vigorous mantle overturn in the early, hot planet. Bottom-up mantle convection, including voluminous plume ascent, efficiently rid the Earth of deep-seated heat. It declined over time as cooling and top-down lithospheric sinking increased. Thickening and both lateral extensional + contractional deformation typified the post-Hadean lithosphere. Stages of geologic evolution included: (a) 4.5-4.4 Ga, magma ocean overturn involved ephemeral, surficial rocky platelets; (b) 4.4-2.7 Ga, formation of oceanic and small continental plates were obliterated by return mantle flow prior to ~4.0 Ga; continental material gradually accumulated as largely sub-sea, sialic crust-capped lithospheric collages; (c) 2.7-1.0 Ga, progressive suturing of old shields + younger orogenic belts led to cratonal plates typified by emerging continental freeboard, increasing sedimentary differentiation, and episodic glaciation during transpolar drift; onset of temporally limited stagnant-lid mantle convection occurred beneath enlarging supercontinents; (d) 1.0 Ga-present, laminar-flowing asthenospheric cells are now capped by giant, stately moving plates. Near-restriction of komatiitic lavas to the Archean, and appearance of multicycle sediments, ophiolite complexes ± alkaline igneous rocks, and high-pressure/ultrahigh-pressure (HP/UHP) metamorphic belts in progressively younger Proterozoic and Phanerozoic orogens reflect increasing negative buoyancy of cool oceanic lithosphere, but decreasing subductability of enlarging, more buoyant continental plates. Attending supercontinental assembly, density instabilities of thickening oceanic plates began to control overturn of suboceanic mantle as cold, top-down convection. Over time, the scales and dynamics of hot asthenospheric upwelling versus lithospheric foundering + mantle return flow (bottom-up plume-driven ascent versus top-down plate subduction) evolved gradually, reflecting planetary cooling. These evolving plate-tectonic processes have accompanied the Earth’s thermal history since ~4.4 Ga.Item Cenozoic uplift of the Central Andes in northern Chile and Bolivia - reconciling paleoaltimetry with the geological evolution(Canadian Science Publishing, 2015-09-16) Lamb, SimonThe Cenozoic geological evolution of the Central Andes, along two transects between ~17.5°S and 21°S, is compared with paleo-topography, determined from published paleo-altimetry studies. Surface and rock uplift are quantified using simple 2-D models of crustal shortening and thickening, together with estimates of sedimentation, erosion and magmatic addition. Prior to ~25 Ma, during a phase of amagmatic flat-slab subduction, thick skinned crustal shortening and thickening (nominal age of initiation ~40 Ma) was focused in the Eastern and Western Cordilleras, separated by a broad basin up to 300 km wide and close to sea level, which today comprises the high Altiplano. Surface topography at this time in the Altiplano and the western margin of the Eastern Cordillera appears to be ~1 km lower than anticipated from crustal thickening, which may be due to the pull-down effect of the subducted slab, coupled to the overlying lithosphere by a cold mantle wedge. Oligocene steepening of the subducted slab is indicated by the initiation of the volcanic arc at ~27 - 25 Ma, and widespread mafic volcanism in the Altiplano between 25 and 20 Ma. This may have resulted in detachment of mantle lithosphere and possibly dense lower crust, triggering 1 – 1.5 km of rapid uplift (overItem Olympia Interstadial: Vegetation, landscape history and paleoclimatic implications of a mid Wisconsinan (Stage 3) nonglacial sequence from southwest British Columbia, Canada(Canadian Science Publishing, 2015-12-16) Hebda, Richard J.; Lian, Olav B.; Hicock, StephenLithostratigraphic,Item Recovery brachiopod associations from the lower Silurian of South China and their paleoecological implications(Canadian Science Publishing, 2015-12-22) HUANG, Bing; Zhan, Renbin; Wang, GuangxuA recovery brachiopod fauna occurs in the lower Niuchang Formation (upper Rhuddanian-lower Aeronian, Llandovery) of the Xinglongchang section, Meitan County, northern Guizhou Province, South China. Nine collections were made at the section, all of which are dominated by brachiopods, and three associations are recognized here and their paleoecology is discussed. Paleoenvironmental analysis shows a shallowing upward trend for the lower Niuchang Formation although a global transgression was happening at that time. The balance between the global transgression and the regional Qianzhong Uplift guaranteed a stable environment for the formation of the Niuchang Formation and the recovery of brachiopods in South China after the end-Ordovician mass extinction. In addition to the traditional methods of PCA and CA, a relatively new technique to paleontology, “Network Analysis” (NA), is applied successfully in this study. It is suggested that Network Analysis could be used as one of the supporting methods in investigating brachiopod paleoecology.Item New data on Hirnantian (latest Ordovician) postglacial carbonate rocks and fossils in northern Guizhou, Southwest China(Canadian Science Publishing, 2015-12-22) Wang, Guangxu; Zhan, Renbin; Percival, Ian G.The Kuanyinchiao Formation (Hirnantian, Upper Ordovician), yielding the typical Hirnantia fauna, has commonly been accepted as representing cool-water sediments deposited during the glacial interval in the Hirnantian GSSP region of South China. Recent investigation reveals that the uppermost carbonate-dominated part of this formation yields a warm-water rugose coral fauna with Silurian affinities at many localities of northern Guizhou Province, which substantially differs from the underlying cool-water fauna. This suggests that these carbonates were probably postglacial warm-water sediments, rather than having formed during the Hirnantian glacial interval as previously thought. Such a conclusion is consistent with the evidence from the associated brachiopod fauna, i.e., the Dalmanella testudinaria-Dorytreta longicrura community, which is similarly distinct from the underlying typical Hirnantia fauna. The sedimentological data show warm-water features at the same level (e.g., the presence of oolitic grains), also supporting this new interpretation.Item Aeronian (Llandovery, Silurian) conodonts from the Densmore Creek Phosphate Bed and the Budd Road Phosphate Bed, Clinton Group, western New York State(Canadian Science Publishing, 2015-11-25) Waid, Christopher Bradley; Over, Jeff J.Conodonts from the Densmore Creek Phosphate Bed at the base of the Maplewood Shale in Irondequoit, NY, include Panderodus unicostatus, Pranognathus tenuis, and Icriodella discreta. The taxa Ozarkodina cf. Oz. hassi, Pranognathus tenuis, Oulodus panuarensis, Panderodus unicostatus, Panderodus recurvatus, and Pseudooneotodus beckmanni were recovered from the overlying Budd Road Phosphate Bed at the base of the Reynales Formation near Lockport, NY. The specimens from both beds are indicative of the Pranognathus tenuis Zone, which correlates to the lower to middle Aeronian, and indicate that the Budd Road Phosphate Bed at Lockport was deposited in a more offshore environment than the Densmore Creek Phosphate Bed at Irondequoit.Item 10Be ages of flood deposits west of Lake Nipigon, Ontario: evidence for eastward meltwater drainage during the early Holocene Epoch(Canadian Science Publishing, 2016-01-04) Kelly, Meredith A.; Fisher, Timothy G.; Lowell, Thomas V.; Barnett, Peter J.; Schwartz, RoseanneThe Nipigon channels, located to the west and northwest of Lake Nipigon, Ontario, are thought to have enabled the eastward drainage of meltwater from glacial Lake Agassiz during the last deglaciation. Here we present the first direct ages of flood deposits in two of these channels using 10Be surface exposure dating. Five 10Be ages of a coarse-grained deposit near the Roaring River in the Kaiashk channel complex indicate deglaciation and cessation of water flow by ~11,070±430 yr. To test for inherited nuclides in boulder samples, we also measured the 10Be concentrations of the undersides of two boulders at the Roaring River site. Five 10Be ages of boulders atop a large bedform near Mundell Lake in the Pillar channel complex indicate deglaciation and cessation of water flow by ~10,770±240 yr. Two 10Be ages of nearby bedrock are slightly younger (10,340±260 and 9,860±270 yr). The 10Be ages from the two sites are statistically indistinguishable and indicate that Laurentide Ice Sheet recession occurred rapidly in the region. We used clast diameters and channel dimensions at the Mundell Lake site to estimate paleo-discharge and evaluate the possibility that meltwater drainage influenced climate conditions. We estimate a large maximum discharge of 119,000–159,000 m3s-1 at the site. However, the timing of meltwater discharge at both Roaring River and Mundell Lake is not contemporaneous with abrupt climate events.Item Geologic Interpretation of Aeromagnetic and Chemical Data from the Oaks Belt, Wabigoon Subprovince, Minnesota: Implications for Au-rich VMS Deposit Exploration(Canadian Science Publishing, 2015-12-12) Hendrickson, MichaelThe Oaks Belt (OB) is a Neoarchean volcanic complex located in northwestern Minnesota, USA. It is part of the Wabigoon granite-greenstone terrane that hosts the world-class Rainy River gold deposit in nearby Ontario, Canada. Rocks in the OB form a north-dipping homocline in the fault-bounded pressure shadow of a sigma-shaped volcano-plutonic wedge that spans E-W for 220 km across the Minnesota-Canada border. Exploration drilling in the area delineated pyrrhotite-pyrite massive sulfide deposits, iron formation, chert and semi-massive sphalerite mineralized zones. High-resolution aeromagnetic data indicate a large (~60 km2) composite subvolcanic intrusion underlies these iron-rich strata in the OB. The position of this inferred intrusion elucidates the low base metal content of known massive sulfide deposits, as they were too far away (6-10 km) from a heat source to have been favorable sites for base metal deposition. The relative abundance of Au and Zn in the OB, alongside correlation coefficients between metals in massive sulfide deposits, iron formation, and chert, indicates the rocks were affected by a low-temperature hydrothermal system under relatively shallow water conditions (Item Further studies on the focal mechanism and the source rupture process of the 2012 Haida Gwaii, Canada, MW 7.8 earthquake(Canadian Science Publishing, 2015-11-25) Motazedian, Dariush; Zhang, Yong; Ma, Shutian; Chen, Yun-taiThe 28 October 2012 Haida Gwaii, British Columbia, Canada MW 7.8 earthquake occurred along an east-dipping poorly known thrust fault beneath the Queen Charlotte Terrace. It was the largest thrust event ever recorded in this dominated by strike-slip motion region. We studied the focal mechanism and the source rupture process for the event. The retrieved geometric parameters of the fault plane were a strike of 329°, dip of 24°, and slip of 114°. The isotropic moment was negative and its value was about one fifth of the total seismic moment released. The earthquake ruptured an area of about 160 km × 60 km, and major slip occurred in an area of about 100 km × 60 km. The maximum slip was about 5.8 m. The slip distribution on the fault plane was highly heterogeneous, with four slip patches. The main slip lay on a large zone above the hypocentre to the sea floor. The maximum and average stress drops calculated using the Brune model were 16.5 and 4.6 MPa, respectively. The major rupture occurred about 10 s after the rupture initiation, and lasted about 25 s. During a subducting earthquake the leading edge of the overriding plate is assumed to spring seaward and upward, while the landward portion is assumed to extend and drop down, and the generated rapid motions set off a tsunami. The falling-down process seems to be consistent with a negative isotropic moment. Key words: Haida Gwaii earthquake, moment tensor, negative isotropic moment, source rupture model, tsunami.Item A 2169 Ma U-Pb baddeleyite age for the Otish Gabbro, Quebec: Implications for correlation of Proterozoic magmatic events and sedimentary sequences in the eastern Superior Province(Canadian Science Publishing, 2015-11-25) Hamilton, Michael A.; Buchan, Kenneth L.Otish Gabbro sills intrude sedimentary rocks in the Otish Basin of the southeastern Superior Province. Here, deposition of Otish Supergroup sediments had previously been thought to be older than K-Ar and Sm-Nd ages of ca. 1750-1710 Ma for Otish Gabbro sills, and younger than ca. 2515-2500 Ma U-Pb ages of underlying Mistassini dykes. However, a much older U-Pb baddeleyite age of 2169.0 ± 1.4 Ma is presented here for an Otish sill, indicating that they are coeval with, and likely genetically related to, the giant 2172-2167 Ma Biscotasing dyke swarm to the southwest and (or) the Cramolet sills and Payne River dykes to the north. The new date also indicates that the age of the Otish Supergroup falls between ca. 2515 Ma and ca. 2169 Ma, only a little different from the ca. 2450-2217 Ma bracket for the Huronian Supergroup of the Southern Province, and is consistent with both supergroups spanning the oxy-atmo inversion. The Otish Supergroup could also be coeval with the Sakami Formation to the north, but is likely older than the Richmond Gulf Group on the east coast of Hudson Bay. Early paleomagnetic study of Otish sills yielded a remanence ~20° from that expected for Biscotasing-aged intrusions. This may indicate that too few distinct sills were studied to average out paleosecular variation, that demagnetization techniques failed to fully remove unstable magnetization components, or that the remanence is a stable secondary overprint, perhaps acquired during a fluid event related to uranium mineralization at ca. 1720 Ma.Item Secondary Migration of Hydrocarbons in the Zhujiang Formation in the Huixi Half-graben, Pearl River Mouth Basin, South China Sea(Canadian Science Publishing, 2016-01-04) Peng, Junwen; Pang, Xiongqi; Xiao, Shuang; Peng, Huijie; Li, Qianwen; Song, Shuang; Wu, Luya; Chen, Di; Hu, TaoThe process and mechanisms of secondary hydrocarbon migration in the Huixi half-graben, Pearl River Mouth Basin, were investigated on the basis of geological analysis of the strata and study of the porosity and permeability of the reservoir rocks, fluid potential, oil properties, and geochemistry of oil-source correlation. The results suggest that the hydrocarbons of the Zhujiang Formation in the Huixi half-graben were derived from source rocks of the Eocene Wenchang Formation and the Eocene–Oligocene Enping Formation in the Huizhou Sag. The hydrocarbons migrated laterally from northeast to southwest. The sandstone in the upper member of the Zhujiang Formation exhibited superior physical properties (porosity and permeability) and connectivity than the lower member. Thin sandstone beds with good physical properties and stable distribution in the upper member of the Zhujiang Formation were the main carrier beds for lateral hydrocarbon migration.Item Peridotite and Pyroxenite xenoliths from the Muskox kimberlite, northern Slave craton, Canada(Canadian Science Publishing, 2015-10-03) Newton, David Edward; Kopylova, Maya G; Burgess, Jennifer; Strand, PamelaAbstract We present petrography, mineralogy and thermobarometry for 53 mantle-derived xenoliths from the Muskox kimberlite pipe in the northern Slave craton. The xenolith suite includes 23% coarse peridotite, 9% porphyroclastic peridotite, 60% websterite and 8% orthopyroxenite. Samples primarily comprise forsteritic olivine (Fo 89-94), enstatite (En 89-94), Cr-diopside, Cr-pyrope garnet and chromite spinel. Coarse peridotites, porphyroclastic peridotites, and pyroxenites equilibrated at 650-1220 °C and 23-63 kbar, 1200-1350 °C and 57-70 kbar, and 1030-1230 °C and 50-63 kbar, respectively. The Muskox xenoliths differ from the neighboring and contemporaneous Jericho kimberlite by their higher levels of depletion, the presence of a shallow zone of metasomatism in the spinel stability field, a higher proportion of pyroxenites at the base of the mantle column, higher Cr2O3 in all pyroxenite minerals, and weaker deformation in the Muskox mantle. We interpret these contrasts as representing small scale heterogeneities in the bulk composition of the mantle, as well as the local effects of interaction between metasomatizing fluids and mantle wall rocks. We suggest that asthenosphere-derived pre-kimberlitic melts and fluids percolated less effectively through the less permeable Muskox mantle resulting in lower degrees of hydrous weakening, strain and fertilization of the peridotitic mantle. The fluids tended to concentrate and pool in the deep mantle causing partial melting and formation of abundant pyroxenites.Item Geochemistry, geochronology, and fluid inclusion study of the Late Cretaceous Newton epithermal gold deposit, British Columbia(Canadian Science Publishing, 2015-10-30) Liu, Lijuan; Richards, Jeremy P.; DuFrane, S. Andrew; Rebagliati, MarkNewton is an intermediate-sulfidation epithermal gold deposit related to Late Cretaceous continental arc magmatism in south-central British Columbia. Disseminated gold mineralization occurs in quartz-sericite-altered Late Cretaceous felsic volcanic rocks, and feldspar-quartz-hornblende porphyry and quartz-feldspar porphyry intrusions. The mineralization can be divided into 3 stages: (1) disseminated pyrite with microscopic gold inclusions, and sparse quartz-pyrite ± molybdenite veins; (2) disseminated marcasite with microscopic gold inclusions and minor base metal-sulfides; and (3) polymetallic veins of pyrite-chalcopyrite-sphalerite-arsenopyrite. Re-Os dating of molybdenite from a stage 1 vein yielded an age of 72.1 ± 0.3 Ma (McClenaghan 2013). The age of the host rocks has been constrained by U-Pb dating of zircon: Late Cretaceous felsic volcanic rocks: 72.1 ± 0.6 Ma (Amarc Resources Ltd., unpublished data, reported in McClenaghan 2013); feldspar-quartz-hornblende porphyry: 72.1 ± 0.5 Ma; quartz-feldspar porphyry: 70.9 ± 0.5 Ma (Amarc Resources Ltd., unpublished data, reported in McClenaghan 2013). The mineralized rocks are intruded by a barren diorite, with an age of 69.3 ± 0.4 Ma. Fluid inclusions in quartz–pyrite ± molybdenite ± gold veins yielded an average homogenization temperature of 313° ± 51°C (n = 82) and salinity of 4.8 ± 0.9 wt.% NaCl equiv. (n = 46), suggesting that a relatively hot and saline fluid likely of magmatic origin was responsible for the first stage of mineralization. Some evidence for boiling was also observed in the veins. However, the bulk of the gold mineralization occurs as disseminations in the wallrocks, suggesting that wallrock reactions were the main control on ore deposition. Keywords: Newton, Intermediate-sulfidation, Epithermal, Gold, British ColumbiaItem Modelled Nearshore Sediment Transport in Open-Water Conditions, Central North Shore of Prince Edward Island, Canada(Canadian Science Publishing, 2015-10-13) Manson, Gavin K.; Davidson-Arnott, Robin A.; Forbes, Donald L.The central north shore of Prince Edward Island comprises embayments separated by subtle headlands that may constrain nearshore sediment transport. The study area includes two such embayments informally known as Brackley and Tracadie Bights, both of which are sand-rich onshore and sand-starved between 20 and 50 m water depth. Storm winds and waves from the northwest and northeast are common in autumn and winter. The hydrodynamic model Delft3D is used to simulate waves, currents, water levels, and sediment transport in Brackley and Tracadie Bights during 23 autumn seasons between 1955 and 2005. When compared to wave and current measurements from a field experiment in the autumn of 1999, the model successfully simulates conditions during storms and fair weather periods. Results from the simulations show that, in autumn, the weighted mean direction of transport is to the southeast (133