Canadian Journal of Earth Sciences

Permanent URI for this communityhttps://hdl.handle.net/1807/67561

Published since 1964, this monthly journal reports current research in all aspects of earth science, including geomatics, geophysics, and geology.

Below is a collection of manuscripts accepted for publication in CJES. These manuscripts have not undergone copy editing or page composition.

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Evolution of the Hazelton arc near Terrace, British Columbia: Stratigraphic, geochronological, and geochemical constraints on a Late Triassic-Early Jurassic arc and Cu-Au porphyry belt
(Canadian Science Publishing, 2015-04-07) Barresi, Tony ; Nelson, JoAnne L. ; Dostal, Jaroslav ; Friedman, Richard M.
Understanding the development of island arcs that accreted to the North American craton is critical to deciphering the complex geological history of the Canadian Cordillera. In the case of the Hazelton arc (part of the Stikine terrane, or Stikinia) in northwestern British Columbia, understanding arc evolution also bears on the formation of spatially associated porphyry Cu-Au, epithermal, and volcanogenic massive sulfide deposits. The Hazelton Group is a regionally extensive, long-lived and exceptionally thick Upper Triassic to Middle Jurassic volcano-sedimentary succession considered to record a successor arc that was built upon the Paleozoic and Triassic Stikine and Stuhini arcs. In central Stikinia, near Terrace, British Columbia, the lower Hazelton Group (Telkwa Formation) comprises three volcanic-intrusive complexes (Mt. Henderson, Mt. O’Brien, and Kitselas) which, at their thickest, constitute almost 16 km of volcanic stratigraphy. Basal Telkwa Formation conglomerates and volcanic rocks were deposited unconformably on Triassic and Paleozoic arc-related basement. New U-Pb zircon ages indicate that volcanism initiated by ca. 204 Ma (latest Triassic). Detrital zircon populations from the basal conglomerate contain abundant 205-233 Ma zircons, derived from regional unroofing of older Triassic intrusions. Eleven kilometres higher in the section, ca. 194 Ma rhyolites show that arc construction continued for >10 My. Strata of the Nilkitkwa Formation (upper Hazelton Group) with a U-Pb zircon age of 178.90 ± 0.28 Ma represent waning island arc volcanism. Telkwa Formation volcanic rocks have bimodal silica concentrations ranging from 48.1 - 62.8 and 72.3 - 79.0 wt.%, and display characteristics of subduction-related magmatism (i.e. calc-alkaline differentiation with low Nb and Ti and high Th concentrations). Mafic to intermediate rocks form a differentiated suite that ranges from high-Al basalt to medium-high K andesite. They were derived from hydrous melting of isotopically juvenile spinel lherzolite in the mantle wedge and from subsequent fractional crystallization. Compared to basalts and andesites (εNd = +5 to +5.5), rhyolites have higher positive εNd values (+5.9 - +6.0) and overlapping incompatible element concentrations, indicating that they are not part of the same differentiation suite. Rather, the rhyolites formed from anatexis of arc crust, probably caused by magmatic underplating of the crust. This study documents a temporal and spatial co-occurrence of Hazelton Group volcanic rocks with a belt of economic Cu-Au porphyry deposits (ca 205 – 195 Ma) throughout northwestern Stikinia. The coeval relationship is attributed to crustal underplating and intra-arc extension associated with slab rollback during renewed or reconfigured subduction beneath Stikinia, following the demise of the Stuhini arc in the Late Norian.
Slipstream: an Early Holocene Slump and Turbidite Record from the Frontal Ridge of the Cascadia Accretionary Wedge off Western Canada and Paleoseismic Implications
(Canadian Science Publishing, 2015-04-07) Hamilton, T.S. ; Enkin, Randolph J ; Riedel, Michael ; Rogers, Garry C ; Pohlman, John W ; Benway, Heather M.
Slipstream Slump, a well-preserved 3 km wide sedimentary failure from the frontal ridge of the Cascadia accretionary wedge 85 km off Vancouver Island, Canada, was sampled during CCGS Tully cruise 2008007PGC along a transect of five piston cores. Shipboard sediment analysis and physical property logging revealed 12 turbidites interbedded with thick hemipelagic sediments overlying the slumped glacial diamict. Despite the different sedimentary setting, atop the abyssal plain fan, this record is similar in number and age to the sequence of turbidites sampled farther to the south from channel systems along the Cascadia Subduction Zone, with no extra ones present in this local record. Given the regional physiographic and tectonic setting, megathrust earthquake shaking is the most likely trigger for both the initial slumping and subsequent turbidity currents, with sediments sourced exclusively from the exposed slump face of the frontal ridge. Planktonic foraminifera picked from the resedimented diamict of the underlying main slump have a disordered cluster of 14C ages between 12.8 and 14.5 ka. For the post-slump stratigraphy, an event-free depth scale is defined by removing the turbidite sediment intervals and using the hemipelagic sediments. Nine 14C dates from the most foraminifera-rich intervals define a nearly constant hemipelagic sedimentation rate of 0.021 cm/yr. The combined age model is defined using only planktonic foraminiferal dates and Bayesian analysis with a Poisson-process sedimentation model. The age model of ongoing hemipelagic sedimentation is strengthened by physical properties correlations from Slipstream events to the turbidites for the Barkley Canyon site 40 km south. Additional modelling addressed the possibilities of seabed erosion or loss and basal erosion beneath turbidites. Neither of these approaches achieves a modern seabed age when applying the commonly used regional marine 14C reservoir age of 800 years (ΔR=400 years). Rather the top of the core appears to be 400 years in the future. A younger marine reservoir age of 400 years (ΔR=0 years) brings the top to the present and produces better correlations with the nearby Effingham Inlet paleo-earthquake chronology based only on terrestrial carbon requiring no reservoir correction. The high resolution dating and facies analysis of Slipstream Slump in this isolated slope basin setting demonstrates that this is also a useful type of sedimentary target for sampling the paleoseismic record in addition to the more studied turbidites from submarine canyon and channel systems. The first 10 turbidites at Slipstream Slump were deposited between 10.8 and 6.6 ka, after which the system became sediment-starved and only 2 more turbidites were deposited. The recurrence interval for the inferred frequent Early Holocene megathrust earthquakes is 460 ± 140 years, compatible with other estimates of paleoseismic megathrust earthquake occurrence rates along the subduction zone.
A GIS-BASED METHOD FOR DEPICTING THE CHARACTERISTICS OF MESOSCALE EDDIES: A CASE STUDY IN THE NORTHERN SOUTH CHINA SEA
(Canadian Science Publishing, 2015-04-27) Li, Ce; Du, Yunyan; Liang, Fuyuan; Yi, Jiawei; Lakhan, V. Chris
The paper presents a Geographical Information System (GIS)-based method for depicting the characteristics, particularly the internal structures and evolutionary processes, of mesoscale eddies. This was done by examining topologic relations among closed Sea Surface Height (SSH) contours which were reconstructed from the Naval Research Laboratory (NRL) Layered Ocean Model (NLOM). Different scenarios of the topological relations among the contour lines permitted the identification of the outermost outline of eddies and the depiction of the number of cores in each mesoscale oceanic eddy. With full consideration of the internal structure of the eddies, we then reconstructed the evolutionary processes of these eddies and the results were compared with empirical observations on three long-lived mesoscale eddies in the northern South China Sea (SCS). Tracking results were similar, thereby validating our method as being efficient and robust in reconstructing mesoscale ocean eddies, especially their evolutionary processes based on their internal structures.
Geological setting of vertebrate microfossil localities across the Cretaceous-Paleogene boundary in southwestern Saskatchewan, Canada
(Canadian Science Publishing, 2015-05-01) Redman, Cory Martin; Gardner, James D.; Scott, Craig S.; Braman, Dennis R.
The Frenchman and Ravenscrag formations of southwestern Saskatchewan, Canada, record an apparently continuous sequence of nonmarine clastic sediments across the Cretaceous-Paleogene (K-Pg) boundary. Extensive exposures of these fossil-rich sediments occur in the Frenchman River Valley, near the towns of Ravenscrag, Eastend, and Shaunavon, and have been a focus of study since the 1970s. Despite this long history of investigation, a comprehensive account of the geographic and stratigraphic positions of many of the significant fossil localities has yet to be published. Given this state of affairs, the goals of this paper are to 1) document the geographic locations, stratigraphic positions, and lithologies of eleven key vertebrate microfossil localities, including several new localities that have been recently discovered and 2) provide an update on the status of these fossil localities, the majority of which have not been sampled in the last 20 years. Four fossil localities are known from the lower Paleocene Ravenscrag Formation, all of which are Puercan in age: Rav W-1 (Pu2), French Fry (Pu1), Croc Pot (?Pu2), and Pine Cree (?Pu2). With the exception of Rav W-1, which has since been lost as a consequence of quarry reclamation, all of the Ravenscrag Formation localities remain accessible and continue to be productive. Seven vertebrate microfossil localities from the upper Maastrichtian Frenchman Formation are reported here, all of which are Lancian in age: Long Fall, Fr-1, By Gar Gap, Hairpin, Wounded Knee, Wounded C, and Gryde. With the exception of Long Fall and Wounded Knee, which have been lost through reclamation or construction, all of the Frenchman Formation localities are accessible and remain productive.
SHRIMP U-Pb and REE data pertaining to the origins of xenotime in Belt Supergroup rocks: Evidence for ages of deposition, hydrothermal alteration, and metamorphism
(Canadian Science Publishing, 2015-05-05) Aleinikoff, John N.; Lund, Karen; Fanning, C. Mark
The Belt-Purcell Supergroup, northern Idaho, western Montana, and southern British Columbia, is a thick succession of Mesoproterozoic sedimentary rocks with an age range of about 1470-1400 Ma. Stratigraphic layers within several sedimentary units were sampled to apply the new technique of U-Pb dating of xenotime that sometimes forms as rims on detrital zircon during burial diagenesis; xenotime also can form epitaxial overgrowths on zircon during hydrothermal and metamorphic events. Belt Supergroup units sampled are the Prichard and Revett Formations in the lower Belt, and the McNamara and Garnet Range Formations, and Pilcher Quartzite in the upper Belt. Additionally, all samples that yielded xenotime were also processed for detrital zircon to provide maximum age constraints for the time of deposition and information about provenances; the sample of Prichard Formation yielded monazite that was also analyzed. Ten xenotime overgrowths from the Prichard Formation yielded a U-Pb age of 1458 ± 4 Ma. However, because SEM-BSE imagery suggests complications due to possible analysis of multiple age zones, we prefer a slightly older age of 1462 ± 6 Ma derived from the three oldest samples, within error of a previous U-Pb zircon age on the syn-sedimentary Plains sill. We interpret the Prichard xenotime as diagenetic in origin. Monazite from the Prichard Formation, originally thought to be detrital, yielded Cretaceous metamorphic ages. Xenotime from the McNamara and Garnet Range Formations, and Pilcher Quartzite formed at about 1160-1050 Ma, several hundred m.y. after deposition, and probably also experienced Early Cretaceous growth. These xenotime overgrowths are interpreted as metamorphic/diagenetic in origin (i.e., derived during greenschist facies metamorphism elsewhere in the basin, but deposited in sub-greenschist facies rocks). Several xenotime grains are older detrital grains of igneous derivation. A previous study on the Revett Formation at the Spar Lake Ag-Cu deposit provides data for xenotime overgrowths in several ore zones formed by hydrothermal processes; herein, those results are compared to data from newly analyzed diagenetic, metamorphic, and magmatic xenotime overgrowths. The origin of a xenotime overgrowth is reflected in its REE pattern. Detrital (i.e., igneous) xenotime has a large negative Eu anomaly and is HREE-enriched (similar to REE in igneous zircon). Diagenetic xenotime has a small negative Eu anomaly and flat HREE (Tb to Lu). Hydrothermal xenotime is depleted in LREE, has a small negative Eu anomaly, and decreasing HREE. Metamorphic xenotime is very LREE-depleted, has a very small negative Eu anomaly, and is strongly depleted in HREE (from Gd to Lu). Because these characteristics seem to be process related, they may be useful for interpretation of xenotime of unknown origin. The occurrence of 1.16-1.05 Ga metamorphic xenotime, in the apparent absence of pervasive deformation structures, suggests that the heating may be related to poorly understood regional heating due to broad regional underplating of mafic magma. These results may be additional evidence (together with published ages from metamorphic titanite, zircon, monazite, and garnet) for an enigmatic, Grenville-age metamorphic event that is more widely recognized in the southwestern and eastern United States.
Modelling Seabed Shear Stress, Sediment Mobility and Sediment Transport in the Bay of Fundy
(Canadian Science Publishing, 2015-05-15) Li, Michael Z.; Hannah, Charles G.; Perrie, William A.; Tang, Charles C. L.; Prescott, Robert H.; Greenberg, David A.
Information about seabed stability and sediment dynamics is part of the fundamental geoscience knowledge required for the extraction of tidal energy in the Bay of Fundy, and for the integrated management of the Bay. Waves, tidal currents and wind-driven and circulation currents were obtained from oceanographic models to assess the wave and current processes for the broader Bay of Fundy. The wave and current outputs were coupled with observed grain size in a sediment transport model to predict, for the first time, the seabed shear stresses, sediment mobility, and sediment transport patterns for the entire Bay. The root mean square tidal current, highest in the upper Bay (> 1.4 m s
Implementation of a rigorous least-squares modification of Stokes formula to compute a gravimetric geoid model over Saudi Arabia (SAGEO13)
(Canadian Science Publishing, 2015-05-21) Abdalla, Ahmed; Mogren, Saad S
A precise gravimetric geoid model (SAGEO13) is computed for the Kingdom of Saudi Arabia using a rigorous stochastic computational method. The computational methodology is based on a combination of least-squares (LS) modification of Stokes formula and the additive corrections for topographic, ellipsoidal, atmospheric and downward continuation effects on the geoid solution. In this study, we used the terrestrial gravity data, digital elevation model (SRTM3) and seven geopotential models (GGMs) to compute the a new geoid model for Saudi Arabia. The least-squares coefficients are derived based on the optimisation of the input modification parameters. The gravimetric solution and its additive corrections are computed based on the optimum LS coefficients. Comparing to GPS-levelling data, SAGEO13 shows a fit of 18 cm (RMS) after using the 4-parameter fitting model.
Geophysical models of the Montresor metasedimentary belt and its environs, central Nunavut, Canada
(Canadian Science Publishing, 2015-05-22) Tschirhart, Victoria; Percival, John A.; Jefferson, Charlie W.
Recent identification of hydrothermally altered rocks and breccia in the underexplored Montresor belt of Paleoproterozoic metasedimentary rocks suggests the possible presence of undiscovered mineralization. This study examines potential field data from the region with the goal of identifying subsurface features that could be associated with or serve as vectors to mineralization (subsurface alteration zones, faulting and/or igneous intrusions). Gravity data were used to model regional and local geological features using known geology and physical properties from the study area and environs as constraints, and documents dense intrusive bodies underlying the Paleoproterozoic sequences. Maps of transformed apparent magnetic susceptibility values outline corridors of weak magnetization that correspond to observed zones of non-magnetic breccia and epidote-hematite-quartz alteration. Imputing the apparent susceptibility and rock property information into a magnetic forward model defines the geometry of this alteration zone, which is best explained as a northerly dipping non-magnetic or demagnetized, metasomatized intrusive sheet. The presence of previously undocumented igneous intrusions, their association with demagnetized hydrothermal breccia, and the continuity of the demagnetized zone suggests additional prospective areas within the region. This geological-geophysical framework for the nature and geometry of the Montresor belt and its surrounds highlights the importance of integrated modelling for areas with limited data.
The Black Rock Coatings in Rouyn-Noranda, Québec: Fingerprints of Historical Smelter Emissions and the Local Ore
(Canadian Science Publishing, 2015-06-09) Caplette, Jaime N.; Schindler, Michael; Kyser, T. Kurtis
Smelting of base-metal-sulfide rich ore in Rouyn-Noranda, Québec have resulted in the formation of black rock coatings on exposed rocks to a maximum distance of 6 km from the smelter centre. This study has shown that these coatings are excellent mineralogical and chemical fingerprints of smelter emissions, ore types, and elemental partitioning into mineral phases. The black coatings are composed of a silica-rich matrix that formed due to the intense chemical weathering of exposed silicate rocks interacting with acidic meteoric waters. They contain metal-sulfate rich layers along the atmosphere-coating interface (ACI) and rock-coating interface (RCI) formed by the in situ dissolution and precipitation of metal(loid)-bearing phases. Entombed within the silica matrix are spherical particulates and particles composed of Cu- and Zn- bearing Fe-oxides (e.g., spinels), Fe-oxides (e.g., hematite), Pb-silicates (e.g., alamosite), sulfates (anglesite (PbSO4) and minerals of the jarosite group), amphiboles, pyroxenes, micas, Na-feldspar and clinochlore. Concentrations of elements are low in proximity to the smelter but drastically increase around 2 km from the stack, most likely the result of a shadow effect of the smelter. This shadow effect is more pronounced if an element is highly compatible with minerals of the jarosite and spinel groups, and is thus called the smelter-compatibility effect. Elements displaying a high smelter-compatibility effect are Ag, Cu, Se and As whereas elements such as Hg, incompatible with the jarosite and spinel structure, show a low smelter-compatibility effect. High δ
Comparing global and local calibration schemes from a differential split-sample test perspective
(Canadian Science Publishing, 2015-07-05) Gaborit, Étienne T.É.M.; Ricard, Simon; Lachance-Cloutier, Simon; Anctil, Francois; Turcotte, Richard
This work explores the performances of the hydrologic model Hydrotel applied to 36 catchments located in the Province of Québec, Canada. A local calibration (each catchment taken individually) and a global calibration (a single parameter set sought for all catchments) schemes are compared in a differential split-sample test perspective. Such a methodology is useful to gain insights on a model's skills under different climatic conditions, in view of its use for Climate-Change (CC) impact studies. The model was calibrated using both schemes on five non-continuous dry and cold years and then evaluated on five dissimilar humid and warm years. Results indicate that, as expected, local calibration leads to better performances than the global one. However, global calibration achieves satisfactory simulations while producing a better temporal robustness (i.e. model transposability to periods with different climatic conditions). Global calibration, in opposition to local calibration, thus imposes spatial consistency to the calibrated parameter values, while locally adjusted parameter sets can significantly vary from one catchment to another due to equifinality.. It is hence stated that a global calibration scheme represents a good trade-off between local performance, temporal robustness, and the spatial consistency of parameter values, which is for example of interest in the context of ungauged catchments' simulation, climate-change impact studies, or even simply large-scale modeling.
GIS-analyses of ice-sheet erosional impacts on the exposed shield of Baffin Island, eastern Canadian Arctic
(Canadian Science Publishing, 2015-07-19) Ebert, Karin
The erosional impacts of former ice sheets on the low-relief bedrock surfaces of Northern Hemisphere shields are not well understood. This paper assesses the variable impacts of glacial erosion on a part of Baffin Island, eastern Canadian Arctic, between 68 and 72°N and 66 and 80°W. This tilted shield block has been covered repeatedly by the Laurentide Ice Sheet during the late Cenozoic. The impact of ice-sheet erosion is examined by GIS-analyses using two geomorphic parameters: lake density and terrain ruggedness. The resultant patterns generally conform to published data from other remote sensing studies, geological observations, cosmogenic exposure ages and the distribution of the Chemical Index of Alteration for tills. Lake density and terrain ruggedness are thereby demonstrated to be useful quantitative indicators of variable ice-sheet erosional impacts across Baffin Island. Ice-sheet erosion was most effective in the lower western parts of the lowlands, in a west-east oriented band at around 350-400 m a.s.l. and in fjord onset zones in the uplifted eastern region. Above the 350-400 m a.s.l band and between the fjord onset zones, ice-sheet erosion was not sufficient to create extensive ice-roughened or streamlined bedrock surfaces. The exception where lake density and terrain ruggedness indicate that ice sheet erosion had a scouring effect all across the study area was in an area from Foxe Basin to Home Bay that does not exceed elevations of 400 m a.s.l.. These morphological contrasts link to former ice sheet basal thermal regimes through the Pleistocene. The zone of low glacial erosion surrounding the cold-based Barnes Ice Cap probably represents its greater extent during successive Pleistocene cold stages. Inter-fjord plateaus with few ice sheet bedforms remained cold-based throughout multiple Pleistocene glaciations. In contrast, zones of high lake density and high terrain ruggedness are a result of the repeated development of fast-flowing, erosive ice in warm-based zones beneath the Laurentide Ice Sheet. These zones are linked to greater ice thickness over western lowland Baffin Island. Adjacent lowland surfaces with similar elevations, however, of non-eroded, weakly eroded, and ice-scoured shield bedrock indicate that even in areas of high lake density and terrain ruggedness the total depths of ice-sheet erosion did not exceed 50 m.
Chronostratigraphy of the Hottah terrane and Great Bear magmatic zone of Wopmay orogen, Canada, and exploration of a terrane translation model
(Canadian Science Publishing, 2015-07-25) Ootes, Luke; Davis, William J; Jackson, Valerie Ann; van Breemen, Otto
The Paleoproterozoic Hottah terrane is the western-most exposed bedrock of the Canadian Shield, and a critical component for understanding the evolution of the Wopmay orogen. Thirteen new high-precision U-Pb zircon crystallization ages are presented and support field observations of a volcano-plutonic continuum from Hottah terrane through to the end of the Great Bear magmatism; from >1950 Ma to 1850 Ma. The new crystallization ages, new geochemical data, and newly published detrital zircon U-Pb data, are used to challenge hitherto accepted models for the evolution of the Hottah terrane as an exotic arc and micro-continent that arrived over a west-dipping subduction zone and collided with the Slave craton at ca. 1.88 Ga. While the Hottah terrane does have a tectonic history that is distinct from that of the neighbouring Slave craton, it shares a temporal history with a number of domains to the south and east, domains that were tied to the Slave craton by ca. 1.97 Ga. It is interpreted herein that Hottah terrane began to the south of its current position and evolved in an active margin over an always east-dipping subduction system that began prior to ca. 2.0 Ga and continued to ca. 1.85 Ga, and underwent tectonic switching and migration. The stratigraphy of the ca. 1913 to 1900 Ma Hottah plutonic complex and Bell Island Bay Group comprises a subaerial rifting arc sequence, followed by basinal opening that is represented by marginal marine quartz arenite and overlying ca. 1893 Ma pillowed basalt flows and lesser rhyodacites. We interpret this stratigraphy to record Hottah terrane rifting off its parental arc crust, in essence the birth to the new Hottah terrane. This model is similar to rapidly rifting arcs in active margins, for example modern Baja California. These rifts generally occur at the transition between subduction zones (e.g., Cocos-Rivera plates) and transtensional shear zones (e.g., San Andreas fault) and we suggest that extension driven transtensional shearing, or more simply terrane translation, was responsible for the evolution of Bell Island Bay Group stratigraphy and that it transported this newly born Hottah terrane laterally (northward in modern coordinates), arriving adjacent to the Slave craton at ca. 1.88 Ga. Renewed east-dipping subduction led to the Great Bear arc flare-up at ca. 1876 Ma, continuing to ca. 1869 Ma. This was followed by voluminous Great Bear plutonism until ca. 1855 Ma. The model implicates that it was the westerly Nahanni terrane and its subducting oceanic crust that collided with this active margin, shutting down the > 120 million year old, east-dipping subduction system.
An Upper Jurassic ichthyosaur (Ichthyosauria: Ophthalmosauridae) from the Bowser Basin, British Columbia
(Canadian Science Publishing, 2015-08-14) Sissons, Robin L.; Caldwell, Michael W.; Evenchick, Carol A.; Brinkman, Donald B.; Vavrek, Matthew J.
Although the Jurassic was a period of high diversity in ichthyosaurs, only a small number of specimens have been recorded from Canada to date. We describe here a new occurrence of an ophthalmosaurid ichthyosaur from a shallow marine depositional environment within the Bowser Basin of northern British Columbia. Based on vertebral diameters and the size of the humerus, the ichthyosaur was relatively large compared to other contemporaneous forms, yet possessed teeth that were small for its body size. As well, the height to length ratio of the preserved vertebrae suggest it may have had a more elongate, less regionalized body shape. Although indeterminate at a generic level, the presence of Late Jurassic ichthyosaurs in nearshore waters of northwestern North America further demonstrates their cosmopolitan distribution.
The tectonic significance of the Early Cretaceous forearc-metamorphic assemblage in south-central Alaska based on detrital zircon U-Pb dating of sedimentary protoliths
(Canadian Science Publishing, 2015-08-27) Labrado, Amanda; Pavlis, Terry L.; Amato, Jeffrey M.; Day, Erik M.
A complex array of faulted arc rocks and variably metamorphosed forearc accretionary complex rocks form a mappable arc-forearc boundary in southern Alaska known as the Border Ranges fault (BRF). We use detrital U-Pb zircon dating of metasedimentary rocks within the Knik River terrane in the western Chugach Mountains to show that a belt of Early Cretaceous amphibolite-facies metamorphic rocks along the BRF was formed when older mélange rocks of the Chugach accretionary complex were reworked in a sinistral-oblique thrust reactivation of the BRF during a period of forearc plutonism. The metamorphic subterrane of the Knik River terrane has a maximum depositional age of 156.5 ± 1.5 Ma and a detrital zircon age spectrum that is indistinguishable from the Potter Creek assemblage of the Chugach accretionary complex, supporting correlation of these units. These ages contrast strongly with new and existing data that show Triassic to Earliest Jurassic detrital zircon ages from metamorphic screens in the plutonic subterrane of the Knik River terrane, a fragmented Early Jurassic plutonic assemblage generally interpreted as the basement of the Peninsular terrane. Based on these findings, we propose new terminology for the Knik River terrane. We propose the terms: (1) “Carpenter Creek metamorphic complex” for the Early Cretaceous “metamorphic subterrane”; (2) “western Chugach trondhjemite suite” for the Early Cretaceous forearc plutons within the belt; (3) “Friday Creek assemblage” for a transitional mélange unit that contains blocks of the Carpenter Creek complex in a chert-argillite matrix; and (4) “Knik River metamorphic complex” in reference to metamorphic rocks engulfed by Early Jurassic plutons of the Peninsular terrane that represent the roots of the Talkeetna arc). The correlation of the Carpenter Creek metamorphic complex with the Chugach mélange indicates that the trace of the Border Ranges fault lies ~1–5 km north of the map trace shown on geologic maps, although like other segments of the Border Ranges fault, this boundary is blurred by local complexities within the Border Ranges fault system. Ductile deformation of the mélange is sufficiently intense that few vestiges of its original mélange fabric exist, suggesting the scarcity of rocks described as mélange in the cores of many orogens may result from misidentification of rocks that have been intensely overprinted by younger, ductile deformation.
A new elasmobranch assemblage from the early Eocene (Ypresian) Fishburne Formation of Berkeley County, South Carolina, USA
(Canadian Science Publishing, 2015-09-02) Case, Gerard R.; Cook, Todd D.; Wilson, Mark V. H.
A rich elasmobranch assemblage was recovered from the early Eocene (Ypresian) Fishburne Formation in a limestone quarry at Jamestown, Berkeley County, South Carolina, USA. Reported herein are 22 species belonging to eight orders, at least 15 families, and 21 genera. It includes the first occurrence of Protoginglymostoma from North America. Many of the reported species have large palaeobiogeographical ranges and inhabited waters on both sides of the Atlantic, whereas others endemic to the east coast of North America. The paucity of sizeable dentition from several of the larger species in this assemblage, and the apparent absence of relatively large macrophagous species found in contemporaneous deposits elsewhere, suggests the Jamestown site may represent a nursery ground and refuge for young and smaller individuals.
Sedimentology of the lower Serpukhovian (upper Mississippian) Mabou Group in the Cumberland Basin of eastern Canada; tectonic, halokinetic and climatic implications
(Canadian Science Publishing, 2015-09-02) Jutras, Pierre; McLeod, Jason R.; Utting, John
The Visean-Serpukhovian transition in Atlantic Canada was marked by a general humidification of the climate as the region drifted towards equatorial latitudes. It also corresponds to a time when ice volume was increasing on Gondwana, which marked the end of Mississippian marine incursions in the region. Glacioeustatic fluctuations of greater magnitude are thought to have increased the response of the regional climate to third-order cyclicity from orbital forcing. In the Cumberland Basin, fluvial grey beds of the lower Serpukhovian Shepody Formation were deposited in sub-humid conditions during highstands, whereas red playa deposits of the same unit were deposited under semi-arid conditions during lowstands. Basin reconstruction suggests that this unit was sourced from the fault-bounded Cobequid and Caledonia highlands and deposited in two separate salt-withdrawal minibasins. This fluvial system was seemingly discharging to the north into the broad lake that deposited the contemporaneous Hastings Formation. A disconformity separates the Shepody Formation from mid-Serpukhovian red beds of the Claremont Formation and is tentatively associated with another increase in ice volume on Gondwana followed by a recrudescence of fault activity and basin subsidence. A prolonged time of aridity, floral crisis, non-deposition, deep weathering and karstification in late Serpukhovian to early Bashkirian times is contemporaneous with abundant glacial deposits in higher latitudes, suggesting that globally low sea-levels may have been at play in creating a situation of greater continentality in the study area. La transition du Viséen au Serpukhovien dans le Canada atlantique fût marquée par une humidification générale du climat alors que la région dérivait en direction des latitudes équatoriales. Cette époque correspond à un temps durant lequel le volume des glaces était croissant sur Gondwana, mettant ainsi fin aux incursions marines mississippiennes dans la région. L’amplitude croissante des fluctuations glacioeustatiques à l’époque aurait rendu le climat régional plus sensible aux cycles orbitaux de troisième ordre. Dans le bassin de Cumberland, les lits fluviaux gris de la formation de Shepody (Serpukhovien inférieur) se seraient déposés dans des conditions sub-humides durant des temps de hauts niveaux marins, tandis que les dépôts de playa de la même unité se seraient déposés dans des condition semi-arides durant des temps de bas niveaux marins. Cette unité se serait déposée à partir des hautes-terres de Cobéquid et de Calédonia à l’intérieur de deux mini-bassins distincts. Ce système fluviatile aurait connecté au nord à un grand lac dans lequel se serait déposée la formation contemporaine de Hastings. Une discordance d’érosion sépare la formation de Shepody des lits rouges de la formation de Claremont (Serpukhovien moyen) et corresponderait à une autre recrudescence des glaces sur Gondwana suivie par une augmentation des taux de subsidence et d’activité de failles. Des temps prolongés d’aridité, de crise florale, de non-déposition, d’altération profonde et de karstification durant le Serpukhovien supérieur et le Bashkirien inférieur sont contemporains à des dépôts glaciaires abondants en hautes latitudes, suggérant qu’un bas niveau marin global aurait pu aggraver les conditions de continentalité dans la région étudiée.
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, Zhensheng
We 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.
Cenozoic uplift of the Central Andes in northern Chile and Bolivia - reconciling paleoaltimetry with the geological evolution
(Canadian Science Publishing, 2015-09-16) Lamb, Simon
The 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 (over
Geology of the orogenic Cheminis gold deposit along the Larder Lake-Cadillac deformation zone, Ontario
(Canadian Science Publishing, 2015-10-01) Lafrance, Bruno
The Larder Lake - Cadillac deformation zone (LLCDZ) is one of two major, auriferous, deformation zones in the southern Abitibi subprovince of the Archean Superior Province. It hosts the Cheminis and the giant Kerr Addison – Chesterville deposits within a strongly deformed band of Fe-rich tholeiitic basalt and komatiite of the Larder Lake Group (ca. 2705 Ma). The latter is bounded on both sides by younger, less deformed, Timiskaming turbidites (2674 Ma - 2670 Ma). The earliest deformation features are F1 folds affecting the Timiskaming rocks, which formed either during D1 extensional faulting or during early D2 north-south shortening related to the opening and closure, respectively, of the Timiskaming basin. Continued shortening during D2 imbricated the older volcanic rocks and turbidites and produced regional F2 folds with an axial planar S2 cleavage. D2 deformation was partitioned into the weaker band of volcanic rocks, producing the strong S2 foliation, L2 stretching lineation, and south-side-up shear sense indicators, which characterize the LLCDZ. Gold is present in quartz-carbonate veins in deformed fuchsitic komatiites (carbonate ore) and turbiditic sandstone (sandstone-hosted ore), and in association with disseminated pyrite in altered Fe-rich tholeiitic basalts (flow ore). All host rocks underwent strong mass gains in CO2, S, K2O, Ba, As, and W, during sericitization, carbonatization, and sulphidation of the host rocks, suggesting that they interacted with the same hydrothermal fluids. Textural relationships between alteration minerals and S2 cleavage indicate that mineralization is syn-cleavage. Thus, gold was deposited as hydrothermal fluids migrated upward along the LLCDZ during contractional, D2 south-side-up shearing. The gold zones were subsequently modified during D3 reactivation of the LLCDZ as a dextral transcurrent fault zone.
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, Pamela
Abstract 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.

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