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Zhang S.,Canada Nunavut Geoscience Office | Mirza K.,Geological consultant | Barnes C.R.,University of Victoria
Canadian Journal of Earth Sciences | Year: 2016

The conodont biostratigraphy for the Upper Ordovician – Upper Silurian carbonate shelf (Irene Bay and Allen Bay formations) and interfingering basinal (Cape Phillips Formation) facies is established for parts of Devon and Ellesmere islands, central Canadian Arctic Islands. Revisions to the interpreted regional stratigraphic relationships and correlations are based on the stratigraphic distribution of the 51 conodont species representing 32 genera, identified from over 5000 well-preserved conodonts recovered from 101 productive samples in nine stratigraphic sections. The six zones recognized are, in ascending order, Amorphognathus ordovicicus Local-Range Zone, Aspelundia fluegeli Interval Zone, Pterospathodus celloni Local-Range Zone, Pt. pennatus procerus Local-Range Zone, Kockelella patula Local-Range Zone, and K. variabilis variabilis – Ozarkodina confluens Concurrent- Range Zone. These provided a more precise dating of the members and formations and, in particular, the range of hiatuses within this stratigraphic succession. The pattern of regional stratigraphy, facies changes, and hiatuses is interpreted as primarily related to the effects of glacioeustasy associated with the terminal Ordovician glaciation and smaller Early Silurian glacial phases, the backstepping of the Silurian shelf margin, and the geodynamic effects of the collision with Laurentia by Baltica to the east and Pearya to the north. Conodont colour alteration index values (CAI 1–6.5) from the nine sections complement earlier graptolite reflectance data in providing regional thermal maturation data of value in hydrocarbon exploration assessments. © 2016, Canadian Science Publishing. All rights reserved.

Pell J.,Peregrine Diamonds | Russell J.K.,University of British Columbia | Zhang S.,Canada Nunavut Geoscience Office
Earth and Planetary Science Letters | Year: 2015

Kimberlites are mantle-derived ultramafic rocks preserved in volcanic and sub-volcanic edifices and are the main primary source of diamonds. The temperatures of formation, transport, eruption and deposition remain poorly constrained despite their importance for understanding the petrological and thermodynamic properties of kimberlite magmas and styles of volcanic eruption. Here, we present measured values of Colour Alteration Indices (CAI) for conodonts recovered from 76 Paleozoic carbonate xenoliths found within 11 pipes from the Chidliak kimberlite field on Baffin Island, Nunavut, Canada. The dataset comprises the largest range of CAI values (1.5 to 8) and the highest CAI values reported to date for kimberlite-hosted xenoliths. Thermal models for cooling of the Chidliak kimberlite pipes and synchronous heating of conodont-bearing xenoliths indicate time windows of 10-20 000 h and, for these short time windows, the measured CAI values indicate heating of the xenoliths to temperatures of 225 to >925 °C. We equate these temperatures with the minimum temperatures of the conduit-filling kimberlite deposit (i.e. emplacement temperature, TE). The majority of the xenoliths record CAI values of between 5 and 6.5 suggesting heating of xenoliths to temperatures of 460 °C-735 °C. The highest CAI values are consistent with being heated to 700 °C-925 °C and establish the minimum conditions for welding or formation of clastogenic kimberlite deposits. Lastly, we use TE variations within and between individual pipes, in conjunction with the geology of the conduit-filling deposits, to constrain the styles of explosive volcanic eruption. © 2014 Elsevier B.V.

Zhang S.,Canada Nunavut Geoscience Office | Pell J.,Peregrine Diamonds
Canadian Journal of Earth Sciences | Year: 2014

Hall Peninsula, located on southeastern Baffin Island, Nunavut, hosts the newly discovered Chidliak kimberlite province. Presently, this area lacks Phanerozoic sedimentary cover, except for the unconsolidated glacial deposits; however, Late Ordovician and Early Silurian microfossil conodonts have been recovered from carbonate xenoliths preserved in the Late Jurassic - Early Cretaceous kimberlites. Over 1300 conodont specimens were recovered, among which 32 species representing 23 genera are recognized, with four elements indeterminate. The well-preserved conodont faunas provide reliable evidence on the Hall Peninsula for (i) reconstructing the Lower Paleozoic stratigraphic units, including the Upper Ordovician Frobisher Bay, Amadjuak, Akpatok, and Foster Bay formations, and the Lower Silurian Severn River Formation, (ii) estimating a total of 270-305 m in thickness of Lower Paleozoic sedimentary cover prior to the emplacement of the kimberlites, (iii) tracing the erosion history after the emplacement of the kimberlites, and (iv) calculating a minimum erosion rate of 2 m/Ma. The conodonts have a wide range of conodont Color Alteration Index (CAI) values between 1.5 and 8, which is the largest range recorded in any known suite of xenoliths entrained in kimberlites.

Sanborn-Barrie M.,Geological Survey of Canada | Davis W.J.,Geological Survey of Canada | Berman R.G.,Geological Survey of Canada | Rayner N.,Geological Survey of Canada | And 3 more authors.
Canadian Journal of Earth Sciences | Year: 2014

Integrated mapping, structural analysis, and U-Pb geochronology of the Committee Bay area, Nunavut, establish a record of Neoarchean crustal growth followed by penetrative Paleoproterozoic deformation. Supracrustal rocks include a lower ca. 2.73 Ga mafic-ultramafic volcanic-dominated sequence, a middle, economically significant 2.71 Ga intermediate volcanicbearing sequence with intercalated sulphidized, gold-bearing iron formation, and an upper <2.69 Ga clastic ± komatiite- quartzite sequence. Following an 80 million year hiatus, this succession was intruded by voluminous ca. 2.61-2.57 Ga granodiorite-tonalite-granite ± diorite, which do not appear to have thermally or tectonically affected the supracrustal belt. Instead, three generations of structures record polyphase Paleoproterozoic deformation of the region. D1 structures are consistent with a doubly vergent structural fan developed at ca. 2.35 Ga in response to the Arrowsmith orogeny that affected the western Rae margin. Penetrative D2 structures dominate the map pattern and include northeast-trending, southeast-dipping folds and fabrics within which gold is localized. The general southeast dips of S2 and inclined, northwest-vergent attitude of F2 reflect northwest-directed shortening at 1.84-1.82 Ga. The absence of syn-D2 plutonic rocks in the west and central Committee Bay belt support amphibolite-facies metamorphism as a response to crustal thickening, which, in turn, led to syn-D2 crustal melting in the east. Regionally extensive upright to northwest-vergent D2 structures and associated ca. 1.85-1.82 Ga tectonometamorphism across the Rae craton are attributed to an early stage of the Hudsonian orogeny involving microcontinent collision(s) with its southeastern margin. D3 folds and dextral shearing at ca. 1780 Ma accommodated localized, late-stage compressional strain during final amalgamation of Laurentia.

Zhang S.,Canada Nunavut Geoscience Office
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2011

Conodonts from the Slave Craton of the Canadian Shield provide solid evidence for estimating the timing and extent of the maximum transgression across Laurentia during the Late Ordovician. Upper Ordovician limestone xenoliths and a continuous limestone interval have been recovered from the Middle Jurassic Jericho kimberlite pipe piercing into the central Slave Craton of the Canadian Shield, an area that lacks Phanerozoic sedimentary cover nowadays. All fourteen limestone xenolith samples contain diverse conodonts, among which seventeen species belonging to twelve genera are recognized. This fauna is represented by Plegagnathus dartoni (Stone and Furnish). , indicating an early Richmondian (Late Ordovician) age. In general, the fauna is characteristic of deposition in a shallow and open marine environment. This newly discovered fauna, in addition to those previously found on Canadian Shield and vicinity, provides reliable evidence that 1) the Ordovician inundation on the now-exposed Slave Craton by shallow seas occurred in the early Richmondian; 2) the previous recognized transgression during the second phase of Taconian orogeny, the Taconic tectophase, in the southeastern Laurentia in the early Chatfieldian (Late Ordovician) was only the initiation of the Taconic transgression; 3) the Taconic transgression reached its maximum extent and much of Laurentia was submerged in the early Richmondian. © 2011.

Zhang S.,Canada Nunavut Geoscience Office
Canadian Journal of Earth Sciences | Year: 2011

Southampton Island was located on the north margin of the Hudson Bay Basin, one of the largest Paleozoic sedimentary basins in North America. The Upper Ordovician sequence on the island includes the Bad Cache Rapids and Churchill River groups and the Red Head Rapids Formation; the latter contains three oil shale intervals in its lower part, which may have significant potential as hydrocarbon source rocks, but their precise biostratigraphic position remains unclear. Numerous conodont elements from 14 localities allow establishment of four interval zones throughout the Upper Ordovician on Southampton Island: the Belodina confluens and Pseudobelodina v. vulgaris zones in the Bad Cache Rapids Group, which are correlative to the upper Edenian lowest Richmondian Stage; the Amorphognathus ordovicicus Zone from the uppermost Bad Cache Rapids Group to the top of Churchill River Group to the lower Richmondian Stage; and the Rhipidognathus symmetricus Zone in the Red Head Rapids Formation to the upper Richmondian Stage. The oil shale intervals in the lower Red Head Rapids Formation exposed at Cape Donavan, Sixteen Mile Brook, and Boas River on Southampton Island are correlated with the lower R. symmetricus Zone of the upper Richmondian Stage, not the Maysvillian-Richmondian Stage as previous interpreted. The "Boas River shale" and "Sixteen Mile Brook shale" biostratigraphically and lithostratigraphically equate to the Cape Donovan lower and middle oil shale intervals, respectively. The conodont data and continuous sections across the boundaries between the different lithostratigraphic units have proved the presence of Maysvillian strata on Southampton Island, rather than absence as previously interpreted.

Zhang S.,Canada Nunavut Geoscience Office
Canadian Journal of Earth Sciences | Year: 2013

Northeastern Melville Peninsula, Nunavut, Canada, preserves the stratigraphic record of the northwestern margin of the Foxe Basin. The Ordovician sequence on the peninsula includes the Lower Ordovician Ship Point Formation and Upper Ordovician Frobisher Bay, Amadjuak, Akpatok, and Foster Bay formations. Their biostratigraphic ages and correlations are poorly understood; in particular it is unclear whether the organic-rich "Boas River Formation" exists on the peninsula. Following extensive sampling of these stratigraphic units, studies of numerous conodont elements from both outcrops and rubble at about 60 localities have established five conodont assemblages through the five lithostratigraphic units on the peninsula. Oepikodus communis - Jumudontus gananda Assemblage in the Ship Point Formation is correlated to the Reutterodus andinus Zone in the uppermost Ibexian, Lower Ordovician. The other four assemblages from the Upper Ordovician are as follows: Appalachignathus delicatulus - Polyplacognathus ramosus - Belodina confluens in the Frobisher Bay Formation correlated to lower B. confluens Zone in the upper Chatfieldian; Belodina confluens - Periodon grandis in the Amadjuak Formation to the upper B. confluens, Oulodus velicuspis, O. robustus, and lower Aphelognathus grandis zones from Edenian to lowest Richmondian; Amorphognathus ordovicicus - Plegagnathus and Rhipidognathus symmetricus - Aphelognathus cf. A. divergens in the Akpatok and Foster Bay formations to the lower and upper Richmondian. The biostratigraphy is combined with geographical information systems (GIS) and Google Earth technologies in estimating the thickness of Paleozoic strata, which reduces the likelihood of "Boas River Formation" existing on Melville Peninsula to minimum.

Sherlock R.L.,Canada Nunavut Geoscience Office | Sherlock R.L.,Miramar Mining Corporation | Shannon A.,University of British Columbia | Hebel M.,University of British Columbia | And 8 more authors.
Economic Geology | Year: 2012

The Archean Hope Bay greenstone belt is located in the Bathurst Block of the northeastern part of the Slave Structural Province, a predominantly Archean, granite-greenstone-metasedimentary terrane. The greenstone belt is dominated by mafic volcanic rocks with less common felsic volcanic and volcaniclastic products and subordinate ultramafic bodies and metasedimentary rocks. Three main Au deposits have been defined in the greenstone belt, with a cumulative resource of over 10 million ounces (Moz) of Au, as of April 2007. The Hope Bay greenstone belt can be divided into a series of coherent panels of strata that tend to be fault bounded and collectively are used to construct a composite stratigraphic column of the belt constrained by U-Pb geochronology on felsic suites. The oldest felsic suite, the Flake Lake suite (ca. 2700 Ma), is a succession of felsic volcanic rocks that has a tholeiitic geochemical affinity, interpreted as a product of rift-related volcanism. Overlying this suite is a series of well-constrained calc-alkaline, mainly felsic volcanic rocks, which have ages of ca. 2690 Ma (Square Lake suite), ca. 2686 Ma (Windy felsic suite), ca. 2677 Ma (Koignuk suite), and ca. 2662 Ma (Clover Lake suite), all of which are interpreted as products of arc volcanism. The transition from rift-to arc-related volcanism divides the greenstone belt into upper and lower volcanic cycles with the transition occurring at about ca. 2690 Ma. The older cycle of volcanic rocks has a distinctive group of mafic rocks consisting of mafic pillowed flows which have an Fe-rich tholeiitic geochemical affinity which is not recognized in the younger volcanic cycle. These Fe-rich tholeiitic mafic volcanic rocks commonly show a spatial relationship to Au mineralization acting as host strata to the main Au deposits in the greenstone belt. The younger cycle (

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