Ellesmerian Orogeny Research Articles

Some issues related to the Svalbardian tectonic event (Ellesmerian Orogeny) in Svalbard

Some issues related to the Svalbardian tectonic event (Ellesmerian Orogeny) in Svalbard

Redbed diagenesis links district-scale mineralising fluids to Cu source rock in the Polaris Zn-Pb(-Cu) district, Arctic Canada

Red sandstone of the Proterozoic Aston Formation (Nunavut, Canada) is exposed in the same geographic area as the Storm Cu showing in the Paleozoic-carbonate-hosted Polaris Zn-Pb district (Arctic Canada). The ∼800-m-thick Aston Formation experienced successive burial and exhumation episodes, with maximum burial (>3 km) at the time of the Devonian Ellesmerian orogeny. A petrographic and in situ SIMS oxygen isotope study identified redbed diagenetic events, associated fluid types and temperatures, and their relative timing. The first hematite coat (Hem1) developed in the Proterozoic. Intrusion of Proterozoic dykes and sills heated local formation water to high temperatures (130–223 °C), resulting in precipitation of patchy Qz1 cement in a shallow-burial environment. The Fe and Si were probably derived through alteration of non-quartz silicate detritus. In the Paleozoic, a bleaching (reducing) event removed most Hem 1; the reduced fluid may have been related to regional Zn mineralisation throughout the Polaris district during the mid-Paleozoic Ellesmerian orogeny. Ensuing pressure-solution during maximum burial was probably also Ellesmerian. A second hematisation episode (Hem 2) encloses the pressure-solved quartz-grain contacts. Coeval with Hem 2 was pervasive Qz2 cementation from a low- to mid-latitude, meteoric-derived, oxidised hydrothermal (140–180 °C) fluid that supplied externally derived Si and Fe, probably in the Early Carboniferous. The nature and timing of the fluid events indicated by the Aston Formation’s diagenetic history closely match the fluid history recorded in both Cu and Zn mineralisation in the Polaris district. This relationship strongly supports the concept that Cu in sedimentary-rock-hosted ore deposits can be sourced from redbeds, even those whose depositional age and environment is much older than, and geodynamically unrelated to, the fluid event(s) that caused diagenetic reddening and Cu transfer from source rock to mineralising site.

Phanerozoic Tectonic and Sedimentation History of the Arctic: Constraints From Deep‐Time Low‐Temperature Thermochronology Data of Ellesmere Island and Northwest Greenland

AbstractRocks exposed along both sides of the Smith Sound in Ellesmere Island and NW Greenland record the tectono‐sedimentary evolution of the whole Phanerozoic, including two periods of mountain building—the Palaeozoic Ellesmerian Orogeny and the Palaeogene Eurekan Orogeny—and the formation of two major sedimentary basins, the Franklinian and the Sverdrup Basins. We used geo‐ and thermochronology and apatite chemistry data to unravel this evolution. Apatite fission track and (U‐Th)/He dates vary strongly from >600 to <100 Ma. We present internally consistent thermal history models, which allow to explain the data variations by a unitized exhumation and burial history. Our models suggest that the cratonic areas were buried beneath a several km‐thick succession of Franklinian Basin deposits. During the Ellesmerian Orogeny, the craton acted as sediment source, as also suggested by the composition of apatite and by U‐Pb ages of zircon contained in Devonian foreland sediments. The Ellesmerian foreland was buried by up to 4–5 km thick strata on top of the preserved sedimentary rocks. During the Triassic, the Sverdrup Basin strongly widened and extended at least ∼370 km further toward the east, as compared with previous reconstructions of the basin based on the preservation of Triassic deposits. Thermal history modeling suggests Late Cretaceous to early Cenozoic reheating, which may be caused by deposition associated with the Eurekan Orogeny and/or enhanced heat flow associated with continental breakup. Our data also show that low‐temperature thermochronology is not suitable for resolving potential strike‐slip movements along the Wegener Fault.

Franklinian Composite Tectono-Sedimentary Element, Canadian Arctic Islands

Abstract The Neoproterozoic–Devonian strata of the Canadian Arctic Islands record three Tectono-Sedimentary Elements (TSEs): (i) the Neoproterozoic Synrift TSE; (ii) the Neoproterozoic–Late Devonian Franklinian Margin TSE composed of Cambrian–Ordovician carbonate-dominated passive-margin strata and latest Ordovician, Silurian and Lower Devonian mixed carbonate and clastic strata deposited on an unstable margin; and (iii) Middle–Upper Devonian Foreland Basin TSE deposited in an expanding foreland basin. These three TSEs comprise the Franklinian Composite Tectono-Sedimentary Element (CTSE). In the southern parts of the Arctic Islands, strata are flat lying but there is localized faulting and folding in the central Arctic Islands and towards the northern end of the Franklinian CTSE. These strata of the Franklinian Margin and Foreland Basin TSEs were broadly folded over deeply seated reverse faults localized along Late Silurian–Early Devonian contractional uplifts or deformed by widespread Late Devonian thin-skin folds and thrusts related to the Ellesmerian Orogeny. The parts of the CTSE overprinted by Late Silurian–Early Devonian north–south-trending structures are grouped as Boothia Structural Domains, and the area of the CTSE overprinted by Ellesmerian structures is termed the Ellesmerian Structural Domain. The major hydrocarbon source rock is Upper Ordovician–Lower Silurian shale but maximum thermal maturity over much of the area was achieved by the Late Devonian, prior to the formation of large folds. The complex geological history of the area since the Late Devonian reduces the chances of hydrocarbon preservation.

Geochemical Evidence for a Topographically Driven Regional Mineralizing Fluid in the Polaris Zn District, Arctic Canada

AbstractThe Polaris district in Canada’s Arctic Archipelago contains numerous carbonate rock-hosted Zn + Pb showings and rare, anomalous Cu showings in a 450- × 130-km area. As in many metallogenic districts, a genetic relationship between the mined deposit and surrounding showings has been assumed but not tested. This study uses an in situ, multianalytical approach combining optical and scanning electron microscopy petrography, fluid inclusion microthermometry, evaporate mound analysis, trace element analysis, and in situ stable isotope analysis on sphalerite and carbonate gangue to characterize the fluid histories of individual showings and the district as a whole. Results indicate that a regional, marine-derived fluid dissolved subsurface evaporite minerals, interacted with their connate brines, and transported metals and sulfate to sites of mineralization. Initial fluid mixing with local reduced sulfur accumulations resulted in precipitation of sulfides with lower δ34S values; after exhaustion of the local reduced sulfur pool, thermochemical sulfate reduction (TSR) of transported sulfate became dominant, resulting in higher δ34S. Differences in main-stage δ34S values among different showings indicate a variable extent of TSR among sites. The mineralized volume of each showing is predominantly a function of local fluid flux and availability of a local reductant. The nature and consistency of geochemical characteristics throughout the district confirm the genetic relationship between the large deposit (Polaris) and surrounding showings and indicate that a uniform mineralizing fluid, topographically mobilized during the mid-Paleozoic Ellesmerian orogeny, was responsible for the main, district-wide mineralization, after initially mixing at a smaller scale with local, on-site fluids.

Franklinian Composite Tectono-Sedimentary Element, North Greenland

Abstract The Franklinian Composite Tectono-Sedimentary Element (CTSE) in North Greenland is dominated by Neoproterozoic–lowermost Devonian sedimentary strata and includes early synrift through to passive-margin TSEs of mixed carbonate and siliciclastic facies. The sedimentary successions are well exposed in much of northern Greenland, but in parts were strongly affected by the Ellesmerian Orogeny, resulting in a fold and thrust belt that deformed the northernmost exposures. An exposed palaeo-oilfield attests to the petroleum potential of the basin. Several formations have good source potential and several others have good reservoir properties. Palaeoheat-flow indicators show that temperatures increase to the north, where much of the basin is over-mature. Because of the remoteness of the area and the restricted locations where there is likely to remain petroleum potential, the basin is not currently a target for exploration.

Mackenzie–Peel Platform and Ellesmerian Foreland Composite Tectono-Sedimentary Element, northwestern Canada

Abstract The Mackenzie–Peel Platform Tectono-Sedimentary Element (TSE), and the overlying Ellesmerian Foreland TSE, consist of Cambrian–Early Carboniferous shelf and slope sedimentary deposits in Canada's northern Interior Plains. In this chapter, these elements are combined into the Mackenzie–Ellesmerian Composite TSE. The history of the area includes early extensional faulting and subsidence in the Mackenzie Trough, passive-margin deposition across the Mackenzie–Peel Platform, local uplift and erosion along the Keele Arch, subsidence and deposition in the Ellesmerian Foreland, possible minor folding during the Ellesmerian Orogeny, and folding and faulting in Cretaceous–Eocene time associated with the development of the Canadian Cordillera. Recorded petroleum discoveries are within Cambrian sandstone (Mount Clark Formation), Devonian carbonate strata (Ramparts and Fort Norman formations) and Devonian shale (Canol Formation). Additional oil and gas shows are documented from Cambrian–Silurian carbonate units (Franklin Mountain and Mount Kindle formations), Devonian carbonate units (Arnica, Landry and Bear Rock formations) and Late Devonian–Early Carboniferous siliciclastic units (Imperial and Tuttle formations). Petroleum exploration activity within the area has occurred in several phases since 1920, most of it associated with the one producing oilfield at Norman Wells.

Small carbonaceous fossils (SCFs) from North Greenland: new light on metazoan diversity in early Cambrian shelf environments

AbstractThe Sirius Passet Lagerstätte of North Greenland is one of the oldest records of soft‐bodied metazoan‐dominated ecosystems from the early Cambrian. The Lagerstätte site itself is restricted to just a singlec. 1‐km‐long outcrop located offshore from the shelf margin, in an area affected by metamorphic alteration during the Ellesmerian Orogeny (Devonian – Early Carboniferous). The recent recovery of small carbonaceous fossils (SCFs) to the south, in areas that escaped the effects of this deformation, has substantially expanded the known coverage of organic preservation into shallower water depositional settings in this region. Here, we describe additionalSCFassemblages from the siliciclastic shelf succession of the Buen Formation (Cambrian Series 2, stages 3–4;c. 515 Ma), expanding the previously documentedSCFbiota. Newly recovered material indicates a rich diversity of non‐mineralizing metazoans, chiefly represented by arthropod remains. These include the filtering and grinding elements of a sophisticated crustacean feeding apparatus (the oldest crustacean remains reported to date), alongside an assortment of bradoriid sclerites, including almost complete, 3D valves, which tie together a number ofSCFs previously found in isolation. Other metazoan remains include various trilobite cuticles, diverse scalidophoran sclerites, and a range of metazoan fragments of uncertain affinity. This shallower water assemblage differs substantially from the Sirius Passet biota, which is dominated by problematic euarthropod stem‐group members and sponges. Although some of these discrepancies are attributable to taphonomic or temporal factors, these lateral variations in taxonomic composition also point to significant palaeoenvironmental and/or palaeoecological controls on early Cambrian metazoan communities.

Deciphering late Devonian–early Carboniferous P–T–t path of mylonitized garnet‐mica schists from Prins Karls Forland, Svalbard

AbstractQuartz‐in‐garnet inclusion barometry integrated with trace element thermometry and calculated phase relations is applied to mylonitized schists of the Pinkie unit cropping out on the island of Prins Karls Forland, western part of the Svalbard Archipelago. This approach combines conventional and novel techniques and allows deciphering of the pressure–temperature (P–T) evolution of mylonitic rocks, for which the P–T conditions could not have been easily deciphered using traditional methods. The results obtained suggest that rocks of the Pinkie unit were metamorphosed under amphibolite facies conditions at 8–10 kbar and 560–630°C and mylonitized at ~500 to 550°C and 9–11 kbar. The P–T results are coupled with in‐situ Th–U‐total Pb monazite dating, which records amphibolite facies metamorphism at c. 359–355 Ma. This is the very first evidence of late Devonian–early Carboniferous metamorphism in Svalbard and it implies that the Ellesmerian Orogeny on Svalbard was associated with metamorphism up to amphibolite facies conditions. Thus, it can be concluded that the Ellesmerian collision between the Franklinian margin of Laurentia and Pearya and Svalbard caused not only commonly accepted brittle deformation and weak greenschist facies metamorphism, but also a burial and deformation of rock complexes at much greater depths at elevated temperatures.

Pre-mid-Frasnian angular unconformity on Kotel’ny Island (New Siberian Islands archipelago): evidence of mid-Paleozoic deformation in the Russian High Arctic

We present detailed structural studies which reveal for the first time the existence of an angular unconformity at the base of the Middle Frasnian deposits across the western part of Kotel’ny Island (New Siberian Islands, Russian High Arctic). Pre-Mesozoic convergent structures are characterized by sublatitudinal folds and south-verging thrusts. Based on the age of the rock units above and below the unconformity, the age of the deformation event can be described as post-Givetian but pre-mid-Frasnian. Based on the vergence direction of thrusts deforming pre-Frasnian deposits on Kotel’ny Island, shortening occurred from north to south (in the present day coordinates). The small scale of the structures suggests that this part of the New Siberian Islands formed a distal part of an orogenic belt in the Middle Paleozoic. The angular unconformity described on Kotel’ny Island can be tentatively correlated with the Ellesmerian Orogeny. However, due to a paucity of detailed geological data from the neighboring broad Arctic continental shelves, a precise correlation with known tectonic events of the circum-Arctic cannot be achieved. The subsequent Mesozoic tectonic structures with NW-trending folds and faults were superimposed on pre-existing Paleozoic and older structures. Thus, the data presented here provide additional constraints on the Paleozoic geodynamic affinity of the New Siberian Islands and provide a regional link to other Arctic regions, aiding future tectonic reconstructions of the circum-Arctic.

Atypical Cu mineralisation in the Cornwallis carbonate-hosted Zn district: Storm copper deposit, Arctic Canada

The metallogenetically important Cornwallis Zn district, in Canada’s Arctic islands, includes the past-producing Polaris mine and numerous base-metal showings, including Storm copper. Storm is unusual because it is near the southern limit of the district, is Cu- versus Zn-dominated, is overlain and underlain by red sandstone, and is hosted by Silurian strata (rather than Ordovician strata, as at Polaris). Mineralisation styles are primarily carbonate replacement and breccia, and consist of geerite, covellite, bornite, and chalcopyrite, all of which are associated with calcite and dolomite gangue. Multiple in situ micro-analytical techniques (fluid inclusion microthermometry, evaporate mound SEM-EDS, LA ICP-MS, SIMS), plus conventional Cu isotopic analysis were integrated to characterise the nature of the mineralising fluids and events. Fluid inclusions yielded low-temperature (Th <130 °C), moderate- to low-salinity (17.0 to 0.4 wt% NaCl equiv.) fluids. Evaporate mound SEM-EDS analysis, which quantified the solute chemistry, show a change from bimodal Na- and Na+K-dominated fluid mixture to a Na+K-dominated fluid. The δ18OH2O signature of the mineralising fluid involved reservoirs reflecting involvement of meteoric (<0%) and rock-equilibrated (8%) fluids, respectively. The δ34S values are nearly homogeneous for pre-ore and second generation sulphides at 0% and 10%, respectively, whereas the third generation (recrystallised) sulphides are more variable, with values from 8.8 to 23.4%. The majority of Cu sulphides have δ65Cu values near 0%, but second-generation chalcopyrite shows elevated δ65Cu values from +1.31% in the north to +3.44% in the south, suggesting a probable southward fluid flow. Positive Eu PAAS-normalised anomalies in early dolomite cements, which indicate basement involvement, are absent in succeeding cements, suggesting a change in fluid pathways and hence the mineralogical nature of the reservoir. Negative CeSN anomalies in main-stage calcite cement indicate an oxidised fluid, but the lack of similar Ce anomalies in the dolomite cements indicates reduced fluids. These data suggest that Storm copper mineralisation is related to basement-equilibrated fluids mobilised during the Ellesmerian orogeny (Devonian), which acquired heat and leached Cu from underlying Proterozoic red sandstone (Aston Formation) and were then focussed up faults where Cu sulphides precipitated. Prolonged meteoric fluid movement from the north, with intermittent episodes of basin-equilibrated fluid influx, produced hypogene and supergene mineralisation. Fluid movement resumed in the Cenozoic, when high-latitude fluids altered Cu minerals to atacamite. Storm copper mineralisation shares characteristics with both red-bed and Irish-type Cu deposit sub-types, but may also highlight a relationship with carbonate-replacement Zn-Pb deposits. Timing of mineralisation is comparable to that of Zn ore precipitation at Polaris, suggesting that Storm may be an integral part of the Cornwallis district, in spite of its unusual composition.

Correction to: U–Pb geochronology of Paleoproterozoic gneiss from southeastern Ellesmere Island: implications for displacement estimates on the Wegener fault

The Wegener fault is a sinistral transform in Nares Strait, which lies between Greenland and Ellesmere Island; it connects the opening of the Eurasian Basin with spreading in Baffin Bay after ≈ 56 Ma (magnetic anomaly 24) and before 36 Ma (magnetic anomaly 13). The amount of horizontal slip on the Wegener fault system can be estimated from the offset of the boundary between the Archean Rae craton to the south and Paleoproterozoic gneisses of the Thelon Tectonic Zone to the north. This boundary is best defined in Greenland due to recent U–Pb zircon geochronology, but is less well known on Ellesmere Island. We have dated zircon in five samples of Precambrian granitic to tonalitic gneiss from southeastern Ellesmere Island using secondary ion mass spectrometry. Cathodoluminescence images reveal complex zircons with oscillatory zoning that lack evidence of xenocrystic cores and are commonly overprinted by recrystallization and surrounded by homogeneous rims. Trace-element patterns show the range of disturbance in zircon. The intrusive age is Paleoproterozoic and ranges from 2007 ± 14 to 1958 ± 14 Ma. In one sample, a well-defined lower intercept age of 357 ± 16 Ma on late overgrowths corresponds to a disturbance during the Ellesmerian orogeny. The results enhance the sparse data set of U–Pb ages in southeast Ellesmere Island and corroborate the previous placement of the boundary with Archean gneiss to the south near Devon Island. The boundary is offset by a minimum of 215 km across Nares Strait, corresponding to the minimum offset on the Wegener fault.

Proterozoic to Cretaceous evolution of the western and central Pearya Terrane (Canadian High Arctic)

The Proterozoic to early Palaeozoic Pearya Terrane at the northern margin of Ellesmere Island is composed of several crustal fragments and is built up by five tectono-stratigraphic successions. This study focusses on parts of Successions 1–3 and related intrusions, including the Cape Fanshawe Martin Pluton (CFMP). Petrographical, geochemical, and geochronological data reveal a protracted, complex with in parts different geological history of these Pearya segments.Succession 1 is dominated by c. 1000–950 Ma old orthogneisses, which are part of a Stenian-Tonian magmatic arc. The arc was later intruded by mafic dykes probably related to the opening of the Iapetus Ocean. Post-tectonic leucogranite bodies were emplaced at c. 360 Ma.Succession 2 comprises Neoproterozoic to early Ordovician clastic sediments. It is subdivided in different units, for which the detrital zircon U–Pb ages reveal different source areas. Unit W with main ages at c. 1800–1050 Ma, and a youngest population at 1067 Ma, older than the biostratigraphic maximum depositional age of <600 Ma, was sourced from a continent that experienced the Grenvillian Orogeny. Unit A with ages mainly in the range of 1800–1000 Ma, and a maximum depositional age at 920 Ma, and Unit M2 with numerous age peaks between 2940 and 570 Ma and the maximum depositional age at 572 Ma received detritus from both the continental source and the Stenian-Tonian magmatic arc, and Unit M2 additionally from a Timanian island arc. Unit A was intruded by A-type granites at c. 485 Ma, which were migmatised at 454 Ma. The ultramafic to felsic CFMP at the coast of the Arctic Ocean northeast of Unit A comprises charnockites intruded at 458–456 Ma and granites emplaced at 441 Ma. The boundary with Unit A is probably tectonic.Succession 3 includes volcaniclastic sediments with detrital zircon ages of 621–492 Ma peaking at 573 Ma, which are dominantly sourced from an intra-oceanic Timanian island arc, and two genetically different igneous suites, an ophiolitic E-MORB suite of unknown age and a subduction-related suite formed at c. 500–470 Ma (Thores Suite). Both suites were juxtaposed during the M'Clintock Orogeny at c. 470–454 Ma.After the probably stepwise accretion of Pearya blocks to the northern margin of Laurentia during the Devonian to early Carboniferous Ellesmerian Orogeny, the Pearya Terrane was affected by thermal events during the Mesozoic, such as the intrusion of Triassic/Jurassic alkali-basaltic dykes and the Cretaceous magmatism of the High Arctic Large Igneous Province (HALIP). This study supports previous models that the Pearya Terrane is composed of crustal fragments, which are exotic to the Canadian Arctic margin.

Detrital zircon (U-Th)/He ages from Paleozoic strata of the Severnaya Zemlya Archipelago: Deciphering multiple episodes of Paleozoic tectonic evolution within the Russian High Arctic

Combined (U-Th)/He and U-Pb detrital zircon geochronological data are reported from Ordovician to Devonian strata of the Severnaya Zemlya archipelago to address the paleogeography of the Kara Terrane in the Russian High Arctic. (U-Th)/He ages from all six samples analyzed were not reset after sediment deposition, indicating that detrital zircons carry information on the exhumation history in the source region of the clastic material. In Ordovician-Silurian strata, (U-Th)/He ages range from 583.8 ± 46.7 to 429.0 ± 34.3 Ma. These ages nicely coincide with significant regional exhumation during the Caledonian and Timanian orogenies. In addition, combined U-Pb and (U-Th)/He dating show that within the source region, zircons that were crystalized during the Timanian Orogeny (U-Pb ages 680–560 Ma) were likely exhumed during younger Caledonian events ((U-Th)/He ages of 455–495 Ma), suggesting potential overlap of these orogens within the source region. In Devonian strata, detrital zircon (U-Th)/He ages range from 517.2 ± 41.38 to 332.9 ± 26.6 Ma, with a peak age of ca. 375 Ma. This 375 Ma event may be correlated with either the Ellesmerian Orogeny or the terminal Solundian/Svalbardian stages of the Caledonian Orogeny.

Structural transect through Ellesmere Island (Canadian Arctic): superimposed Palaeozoic Ellesmerian and Cenozoic Eurekan deformation

Abstract The 400 km long transect through Ellesmere Island is located perpendicular to the North American continental margin between the Arctic Ocean in the NNW and the Greenland–Canadian Shield in the SSE. It provides an insight into the structural architecture and tectonic history of the upper parts of the continental crust. The northernmost segment of the transect is dominated by the composite Pearya Terrane, which amalgamated with the Laurentian margin during the Late Devonian–Early Carboniferous Ellesmerian Orogeny. The Neoproterozoic to Devonian Franklinian Basin is exposed south of the terrane boundary and most probably overlies the crystalline basement of the Greenland–Canadian Shield. The structures along the transect in this area are dominated by kilometre-scale Ellesmerian folding of the Franklinian Basin deposits above a deep-seated detachment, which is suggested to be located at the boundary between the basement of the Canadian Shield and the overlying &gt;8 km thick Franklinian Basin. Following the development of the Late Mississippian–Palaeogene Sverdrup Basin, the complex Eurekan deformation reactivated Ellesmerian thrust faults and probably parts of the associated deep-seated detachment. In addition, large Eurekan strike-slip faults affected and displaced pre-Eocene deposits and tectonic structures, particularly in the northern part of the transect.

Timing and metal sources for carbonate-hosted Zn-Pb mineralization in the Franklinian Basin (North Greenland): Constraints from Rb-Sr and Pb isotopes

Carbonate-hosted Zn-Pb (± barite, fluorite) occurrences in the Franklinian Basin of North Greenland were studied using the Rb-Sr method, applied to sphalerite, and combined Sr and Pb isotope analysis of ore and gangue minerals, to place constraints on their age and genesis. The occurrences are located in the easternmost part of the basin in Peary Land and Kronprins Christian Land, and are hosted by Upper Ordovician to lowermost Silurian dolostones of the Turesø Formation.Sphalerite samples from the Zn-Pb occurrence at Børglum, in Peary Land, reflect undisturbed Rb-Sr systems and return an isochron age of 388±4Ma (MSWD=1.6, 87Sr/86Sri=0.70930±1). Sphalerites and their fluid inclusion fractions from an adjacent Zn-Pb occurrence, at Tvilum, exhibit various degrees of isotopic disturbance caused by secondary fluid overprint. They yield no age, however, reconstructive modelling of their Rb-Sr and Pb-Pb signatures indicates original isotope systematics consistent with the Børglum data. Likewise, due to a lack of suitable samples, no Rb-Sr age could be determined for a third occurrence in southeastern Peary Land at Løgum, however, the time-integrated Pb isotopic evolution of fluorite and calcite from this mineralization over c. 390Ma is compatible with modelled initial signatures for Tvilum and Børglum ores. Consequently, a contemporaneous formation at c. 390Ma can be assumed for all studied locations in Peary Land. For the Zn-Pb occurrence in Kronprins Christian Land farther east, a Rb-Sr sphalerite age of c. 360–365Ma has been obtained through a combined isochron and paleomixing line approach.The absolute ages obtained at the studied occurrences, corresponding to Middle to Upper Devonian ages, are in no conflict with the age of the host dolostones of the Turesø Formation, which placed a maximum age limit for the mineralization. Actually, the fact that mineralization was emplaced at least 50Ma after deposition of the host rocks, which would have been completely lithified by then, warrants the classification of the studied occurrences as epigenetic Mississippi Valley-Type, rather than diagenetic Irish-type. Furthermore, the obtained ages are contemporaneous to the Middle or Upper Devonian to the Lower Carboniferous Ellesmerian Orogeny, indicating that the mineralization likely formed from basinal brines expelled by tectonism and/or hydraulic head caused by Ellesmerian orogenic uplift, as previously suggested for the Polaris carbonate-hosted Zn-Pb deposit (Cornwallis Island, Canada).Pb isotope systematics of base metal mineralization in the Franklinian Basin point to principal metal sources located in the crystalline basement and in basement-derived clastic sediments. These two reservoirs define radiogenic and unradiogenic end components from which lead was mobilized and mixed in different proportions during discrete periods of hydrothermal activity. Distinct thorogenic Pb isotope signatures indicate that specific local sources (lower crustal basement, carbonate rocks and possibly organic-rich shales) were also involved in mineralization.

Evidence for Timanian-age basement rocks in North Greenland as documented through U-Pb zircon dating of igneous xenoliths from the Midtkap volcanic centers

Igneous xenoliths have been identified within the Paleozoic Midtkap volcanic centers of North Greenland that cut through Cambrian-Ordovician deep water trough sedimentary rocks that were subsequently deformed during the south-verging Ellesmerian Orogeny. The xenoliths were characterized geochemically and their zircons dated through the U-Pb technique. This provided ages ranging from 628 to 570 Ma, for xenoliths with granitic and monzonitic compositions, the former apparently older than the latter. These ages, coupled with the geochemical signature compatible with an arc setting, provide evidence for the presence of Timanian like basement in North Greenland. The structural setting suggests that the dated xenoliths belong to an allochthonous unit emplaced during the Caledonian Orogeny and deformed during the Ellesmerian Orogeny. Furthermore, this data provides new evidence for a northwestern extension (through continuation and/or through dispersal) of the late Neoproterozoic Timanide belt, from its type locality, in the Timan-Pechora region in Russia, through Svalbard, into North Greenland, to the Pearya Terrane on Ellesmere Island.

Tectonic map of the Ellesmerian and Eurekan deformation belts on Svalbard, North Greenland, and the Queen Elizabeth Islands (Canadian Arctic)

The tectonic map presented here shows the distribution of the major post-Ellesmerian and pre-Eurekan sedimentary basins, parts of the Caledonian orogen, the Ellesmerian fold-and-thrust belt, structures of the Cenozoic Eurekan deformation, and areas affected by the Eurekan overprint. The present continental margin of North America towards the Arctic Ocean between the Queen Elizabeth Islands and Northeast Greenland and the present west margin of the Barents Shelf are characterized by the Palaeozoic Ellesmerian fold-and-thrust belt, the Cenozoic Eurekan deformation, and, in parts, the Caledonian orogen. In many areas, the structural trends of the Ellesmerian and Eurekan deformations are more or less parallel, and often, structures of the Ellesmerian orogeny are affected or reactivated by the Eurekan deformation. While the Ellesmerian fold-and-thrust belt is dominated by orthogonal compression and the formation of wide fold-and-thrust zones on Ellesmere Island, North Greenland, and Spitsbergen, the Eurekan deformation is characterized by a complex network of regional fold-and-thrust belts (Spitsbergen, central Ellesmere Island), large distinct thrust zones (Ellesmere Island, North Greenland), and a great number of strike-slip faults (Spitsbergen, Ellesmere Island). The Ellesmerian fold-and-thrust belt was most probably related to the approach and docking of the Pearya Terrane (northernmost part of Ellesmere Island) and Spitsbergen against the north margin of Laurasia (Ellesmere Island/North Greenland) in the earliest Carboniferous. The Eurekan deformation was related to plate tectonic movements during the final break-up of Laurasia and the opening of Labrador Sea/Baffin Bay west, the Eurasian Basin north, and the Norwegian/Greenland seas east of Greenland.

Geochemistry of Phanerozoic diagenesis on Victoria Island, NWT, Canada

Victoria Island, in Arctic Canada, is one of the largest islands in the world, but its geology has remained largely unmapped and unstudied owing to its remoteness. Base-metal and hydrocarbon showings have been reported from the island, but the origin and prospectivity of these showings remain enigmatic. Regionally extensive, void-filling Phanerozoic diagenetic phases (dolomite, calcite, quartz) are conspicuous in two of the most widespread carbonate units, the Neoproterozoic Wynniatt Formation and the Cambro–Ordovician Victoria Island formation, recording repeated post-depositional movement of fluid through the rocks. These phases were studied to (a) determine whether they could have been associated with movement of metalliferous or petroliferous fluids, (b) establish a diagenetic base-line for a very large and economically unexplored area, and (c) determine whether the fluid-flow events could have been related to known episodes of deformation and mineralisation elsewhere in the Canadian Arctic archipelago. Using an innovative protocol combining in situ SIMS analysis of O and S isotopes with LA-ICP-MS trace-element analysis, the geochemical conditions attending the diagenetic evolution of host dolostone and cement phases were determined. The Wynniatt Formation dolostone contains four Phanerozoic cements: saddle dolomite, brown dolomite, replacive calcite and late calcite. Average δ18O (SMOW) values of Wynniatt Formation saddle and brown dolomite, replacive calcite, and late calcite cements are 24.7‰, 7.7‰, and 6.9‰, respectively. The PAAS-normalised rare earth element patterns of the dolostone, dolomite, and replacive calcite are smooth and flat with slightly positive Ce and Y anomalies and MREE-enrichment; late calcite cement, in contrast, has negative Ce and positive Y anomalies. Recrystallisation of the host dolostone by a reduced, saddle-dolomite-precipitating fluid in a fluid-dominated system altered the isotopic and REE pattern of the dolostone to saddle-dolomite values. This fluid had interacted with shale at depth and then mixed with a relatively high-salinity fluid. Brown dolomite precipitated from this fluid after a decrease in salinity, and oxygenated meteoric water later infiltrated the system and precipitated the calcite cements.The Victoria Island formation dolostone contains two cements: quartz and dolomite. Host dolostone, quartz, and dolomite have average δ18O (SMOW) values of 31.7‰, 18.7‰, and 18.6‰, respectively, whereas δ34S (V-CDT) for framboidal pyrite in the quartz cement averages −7.5‰. The host dolostone has flat PAAS-normalised REE patterns with a positive Eu anomaly, no Ce anomaly, and a zig-zag HREE pattern, whereas the dolomite cements have two REE patterns: one similar to the dolostone (flat) and the other with LREE-enrichment, and negative La and Eu anomalies. These data suggest that a reduced, hydrothermal fluid altered and partially silicified the host dolostone. Quartz precipitated from a seawater-sourced fluid that had incorporated metals at depth and mixed with bacterially reduced sulphur at the site of precipitation. The dolomite cement records the change from a rock-dominant system to a fluid-dominant system. This fluid was sourced from seawater and interacted with REE-phosphate minerals.The results suggest that precipitation of the diagenetic cements took place before peak burial associated with the Ellesmerian Orogeny (late Devonian–early Carboniferous). The most probable cause of fluid migration, therefore, is the Ellesmerian Orogeny for the majority of the diagenetic phases. High-latitude meteoric fluid then infiltrated the system at some time after the Ellesmerian Orogeny. Similar ages, temperatures, compositions, and precipitation mechanisms as those associated with the Cornwallis zinc district (Polaris mine), highlight a possible relation to known base-metal mineralising fluids.The results of this study provide much needed baseline knowledge of the post-depositional history of Victoria Island. It also illustrates that a “less-is-more” approach, using detailed micro-analytical methods on carefully selected and well-constrained samples, allows one to decipher a complex diagenetic history involving the mixing of fluids from different reservoirs and frequent changes in redox state, both of which may be overlooked using conventional macro-scale approaches.

Late Paleozoic granitic rocks of the Chukchi Peninsula: Composition and location in the structure of the Russian Arctic

An Early Carboniferous (352–359 Ma) U-Pb (TIMS, SIMS) age is established for granitic rocks of the Kibera pluton, quartz sienites of the Kuekvun pluton, and granites from the pebbles in the basement of Carboniferous rocks of the Kuul and Kuekvun uplifts in the Central Chukotka region. These data support the suggestion of granitic magmatism to occur in the region in the Late Paleozoic. The petrogeochemistry of most granitic rocks of the Kibera and Kuekvun plutons is similar to that of I-type granites, and their age coincides with tectonic events of Ellesmerian Orogeny in the Arctic region at the Late Devonian-Early Carboniferous boundary. The Devonian-Early Carboniferous granitic complexes extend to the territories of the Arctic Alaska, Yukon, and Arctic Canada, which indicates a common geological evolution within the Chukotka-Arctic Alaska block, which experienced a motion away from Arctic Canada.