Ernst Geosciences

Ottawa, Canada

Ernst Geosciences

Ottawa, Canada
SEARCH FILTERS
Time filter
Source Type

Lubnina N.,Moscow State University | Ernst R.,Ernst Geosciences | Ernst R.,Carleton University | Klausen M.,Stellenbosch University | Soderlund U.,Lund University
Precambrian Research | Year: 2010

431 oriented samples were collected from 27 dolerite dykes at 17 sites, belonging to 2.95, 2.65, and 1.90. Ga swarms, that trend SE, E and NE, respectively from the Bushveld Igneous Complex into the eastern Kaapvaal Craton (ages determined by Olsson et al., 2010; Olsson in Söderlund et al., 2010). Samples were analyzed for paleomagnetism and also anisotropy of magnetic susceptibility (AMS). For the 2.95. Ga SE-trending dykes high temperature/coercivity 'P' component has unblocking temperatures up to 590°C and coercivity 40-90. mT and demonstrate SSW declination and intermediate positive inclination. Based on positive contact and conglomerate tests we argue for a primary origin of this component. The paleopole (BAD), calculated from '. P' component, does not correspond to any of the previously obtained Archean-Paleoproterozoic paleopoles for the Kaapvaal Craton, and represents a new key pole for 2.95. Ga. The high-coercivity '. H' component for the 2.65. Ga-old E-trending dykes has a SSW declination and steep positive inclination. Paleomagnetic pole (RYK), recalculated from this component, is close to the paleopoles, obtained by Wingate (1998) and Strik et al. (2007) for 2.78. Ga Ventersdorp volcanics. The third group, NE-trending dykes of the 1.90. Ga Black Hill swarm demonstrate an '. M' component with dual polarity high-coercivity component with SSE-declination and negative intermediate inclination. The paleopole (BHD), calculated from this component is close to the 1.87. Ga pole of the Kaapvaal Craton obtained by Hanson et al. (2004). Overprint directions include a very well developed thermo-chemical overprint (Dec. =329° Inc. =-36°), which is believed to be associated with a ∼0.18. Ga regional 'Karoo' thermal event. © 2010 Elsevier B.V.


Olsson J.R.,Lund University | Soderlund U.,Lund University | Klausen M.B.,Stellenbosch University | Ernst R.E.,Ernst Geosciences
Precambrian Research | Year: 2010

The Archean basement in the northeastern part of the Kaapvaal craton is intruded by a large number of mafic dykes, defining three major dyke swarms, which collectively appear to fan out from the Bushveld Complex. Herein we present U-Pb baddeleyite ages for two of these dyke swarms, the northwest trending Badplaas Dyke Swarm and the east-west trending Rykoppies Dyke Swarm, and infer their correlation with tectonic events in the Kaapvaal craton. We also present a U-Pb baddeleyite age for a noritic phase of the Marginal Zone of the Rustenburg Layered Suite (Bushveld Complex).The age of the Badplaas swarm is determined from two dolerites dated at 2965.9 ± 0.7. Ma and 2967.0 ± 1.1. Ma. These ages coincide with units of the Nsuze Group lavas (2967-2985. Ma), which constitute the world's oldest preserved rift basin, and suggest that dykes of this swarm are feeders to basaltic units of this group. Similarly, the E-W trending Rykoppies swarm has earlier been interpreted as a potential feeder system to the Bushveld Complex. However, the emplacement ages of six dolerites fall in the range 2.66-2.68. Ga, thus ∼600. Myr earlier than the intrusion of the Bushveld Complex (herein dated at 2057.7 ± 1.6. Ma). Rather, these ages coincide with the Allanridge Formation at the uppermost part of the Ventersdorp Supergroup as well as volcanic rocks of the " protobasinal" sequences preserved at the base of the overlying Transvaal Basin. The Rykoppies Dyke Swarm probably marks the initial stages of rifting of the Transvaal Basin and reflects a major shift from a NW-SE to an E-W trending tectonic setting. The origin of the Rykoppies Dyke Swarm can be linked either to prolonged mantle plume activity or to the onset of back-arc extension associated with south-directed subduction of oceanic lithosphere in a compressional setting along the northern margin of the Kaapvaal craton. © 2010 Elsevier B.V.


Nilsson M.K.M.,Lund University | Klausen M.B.,Stellenbosch University | Soderlund U.,Lund University | Ernst R.E.,Ernst Geosciences | Ernst R.E.,Carleton University
Lithos | Year: 2013

Palaeoproterozoic magmatism throughout the North Atlantic Craton (NAC) has produced dyke swarms of diverse orientations and emplacement ages. In southern West Greenland, previously identified swarms include the ca. 2500. Ma Kilarsaarfik dykes, ca. 2215. Ma boninitic norite (BN) dykes, and the abundant ca. 2040. Ma Kangâmiut and coeval 2050-2030. Ma MD3 dykes. Additional insight into the distribution of swarms is provided by new baddeleyite U-Pb ID-TIMS dates interpreted as emplacement ages for six dykes. The geochemistry for a total of 42 samples on 40 dykes (including the dated dykes) provides some constraints on their petrogenesis. Two E-W trending dykes yield ages of 2365. ±. 2. Ma and 2374. ±. 4. Ma, representing a hitherto unknown magmatic event. We propose the name Grædefjord dykes for dykes of this age in southern West Greenland. One NE-SW trending dyke is dated at 2209. ±. 5. Ma, close to a previously published 2214. ±. 10. Ma age for a N-S trending dyke (member of BN dykes). Three dykes yield MD3 ages of 2053. ±. 2. Ma (E-W trending), 2049. ±. 6. Ma (N-S trending) and 2042. ±. 2. Ma (WNW-ESE trending). Ca. 2.21. Ga old and predominantly NE-SE and NNE-SSE trending dolerites (some of which are high-Al basalts) were derived from a relatively depleted mantle and injected during a boninite-dolerite magmatic event, together with nearby BN dykes derived from a harzburgitic, yet highly LREE and LILE enriched, subcontinental lithospheric mantle (SCLM). Ca. 2.05. Ga Kangâmiut-MD3 dolerites were derived from a similar ambient asthenospheric mantle and subsequently experienced crustal assimilation during fractional crystallisation.The ca. 2370. Ma dykes in the NAC are coeval with the Dharwar Giant Dyke Swarm of the Dharwar Craton (DC) and based on this unique age match it is proposed that the Dharwar and NAC were neighbours in the Palaeoproterozoic. Furthermore, both blocks share 2.22-2.21. Ga dykes, and matching the trends of 2.2-2.1 and 2.37. Ga swarms between the two blocks allows several plausible reconstructions. © 2012.


Soderlund U.,Lund University | Hofmann A.,University of KwaZulu - Natal | Klausen M.B.,University of KwaZulu - Natal | Olsson J.R.,Lund University | And 3 more authors.
Precambrian Research | Year: 2010

We present baddeleyite U-Pb ages of Neoarchaean to Palaeoproterozoic dyke swarms and the Mashonaland sill province in Zimbabwe. The 2575.0 ± 1.5. Ma age of the Umvimeela dyke is indistinguishable from the 2575.4 ± 0.7. Ma result (Oberthür et al., 2002) for a pyroxenite layer of the Great Dyke and testifies to synchronous emplacement of the Great Dyke and its satellites. Three samples of WNW- to NNW-trending dykes of the Sebanga swarm yielded ages of 2512.3 ± 1.8. Ma, 2470.0 ± 1.2. Ma and 2408.3 ± 2.0. Ma, the latter of which dates the Sebanga Poort Dyke of this swarm. These results suggest that emplacement took place over a protracted period which involved at least three generations of dykes within the swarm and, more importantly, invalidate previous inferences of a genetic link between the Sebanga swarm and the Mashonaland sills. Crystallisation ages of 1877 ± 2.2. Ma, 1885.9 ± 2.4. Ma and 1875.6 ± 1.6. Ma for three dolerite samples of the extensive Mashonaland sills from different parts of the Zimbabwe craton were also obtained. This is the oldest common igneous event that is recorded in the Zimbabwe and Kaapvaal cratons. Collectively with previous published geochronological and petrological evidence in favour of a major 2.0. Ga event within the Limpopo Belt, these results suggest that the Zimbabwe and Kaapvaal cratons did not form a coherent unit (Kalahari) until ca. 2.0. Ga.In the global barcode record for Archaean cratons, all the three generations of dykes within the Sebanga swarm match exactly events of dyke intrusion and LIPs (Large Igneous Provinces) in the Superior, Hearne and Kola-Karelia cratons, and corroborates the recognition of Superia as a supercontinent in the Neoarchaean. The 2408.3 ± 2.0. Ma result of the Sebanga Poort Dyke also provides a link to Western Australia, i.e. to the giant Widgiemooltha swarm of the Yilgarn craton. We conclude that in the context of the global barcode record, both the Zimbabwe and Yilgarn cratons fit into a Superia reconstruction. © 2009 Elsevier B.V.


Nilsson M.K.M.,Lund University | Soderlund U.,Lund University | Ernst R.E.,Ernst Geosciences | Hamilton M.A.,University of Toronto | And 2 more authors.
Precambrian Research | Year: 2010

The Archaean block of southern Greenland constitutes the core of the North Atlantic craton (NAC) and is host to a large number of Precambrian mafic intrusions and dyke swarms, many of which are regionally extensive but poorly dated. For southern West Greenland, we present a U-Pb zircon age of 2990±13Ma for the Amikoq mafic-ultramafic layered intrusion (Fiskefjord area) and four baddeleyite U-Pb ages of Precambrian dolerite dykes. Specifically, a dyke located SE of Ameralik Fjord is dated at 2499±2Ma, similar to a previously reported 40Ar/39Ar age of a dyke in the Kangâmiut area. For these and related intrusions of ca. 2.5Ga age in southern West Greenland, we propose the name Kilaarsarfik dykes. Three WNW-trending dykes of the MD3 swarm yield ages of 2050±2Ma, 2041±3Ma and 2029±3Ma. A similar U-Pb baddeleyite age of 2045±2Ma is also presented for a SE-trending dolerite (Iglusuataliksuak dyke) in the Nain Province, the rifted western block of the NAC in Labrador. We speculate that the MD3 dykes and age-equivalent NNE-trending Kangâmiut dykes of southern West Greenland, together with the Iglusuataliksuak dyke (after closure of the Labrador Sea) represent components of a single, areally extensive, radiating swarm that signaled the arrival of a mantle plume centred on what is presently the western margin of the North Atlantic craton. Comparison of the magmatic 'barcodes' from the Nain and Greenland portions of the North Atlantic craton with the established record from the north-eastern Superior craton shows matches at 2500Ma, 2214Ma, 2050-2030Ma and 1960-1950Ma. We use these new age constraints, together with orientations of the dyke swarms, to offer a preliminary reconstruction of the North Atlantic craton near the north-eastern margin of the Superior craton during the latest Archaean and early Palaeoproterozoic, possibly with the Core Zone craton of eastern Canada intervening. © 2010 Elsevier B.V.


Bejgarn T.,Lulea University of Technology | Soderlund U.,Lund University | Weihed P.,Lulea University of Technology | Areback H.,Boliden Mineral AB | And 2 more authors.
Lithos | Year: 2013

The Skellefte district, northern Sweden, is known for the occurrence of 1.89Ga Palaeoproterozoic volcanogenic massive sulphide (VMS) deposits. The deposits are hosted by the older part of a volcanosedimentary succession, which was intruded at 1.88-1.86Ga by multiple phases of the syn-volcanic, early orogenic Jörn intrusive complex (JIC). The oldest phase of the JIC hosts different styles of mineralisation, among them porphyry Cu-Mo-Au, intrusion-related Au, and mafic-hosted Fe and Cu-Ni deposits. To discriminate between the different intrusive and ore related events, U-Pb ages of zircons have been obtained for nine intrusive phases and from Na-Ca alteration spatially related to mineralisation, while U-Pb ages of baddeleyite (ZrO2) have been used to constrain intrusive ages of three mineralised and barren mafic-ultramafic intrusive rocks.The two main JIC intrusive phases of a granodioritic-tonalitic composition in the southern study area intruded at 1887±3Ma and 1886±3Ma, respectively, and were succeeded by the intrusion of layered mafic-ultramafic intrusive rocks in the northern and southern study area at 1879±1Ma and 1884±2Ma, respectively. Emplacement of porphyry dykes took place at ca. 1877Ma in the southern, western and northern JIC. The dykes are spatially and temporally associated with formation of porphyry style mineralisation, alteration and Au-mineralisation, as inferred from 1879±5Ma zircons in adjacent Na-Ca alteration zones. High SiO2 and Al2O3 contents together with high Sr/Y ratios, mingling structures, mafic xenoliths and hornblende phenocrysts in the porphyry dykes suggest that the magma originated from hydrated partial melts, possibly from the base of the crust at a mature stage of subduction. Local extension resulted in intrusion of mafic-ultramafic rocks around 1.88Ga prior to and after, the porphyry dykes and associated mineralisation, approximately 10Ma after the formation of the spatially related 1.89Ga VMS deposits in the Skellefte district. This 1.88Ga event correlates with other 1.88Ga mafic-ultramafic units widespread around the world, and could possibly be interpreted as a large scale response to supercontinent formation. © 2012 Elsevier B.V.


Smirnov A.V.,Michigan Technological University | Evans D.A.D.,Yale University | Ernst R.E.,Ernst Geosciences | Ernst R.E.,Carleton University | And 2 more authors.
Precambrian Research | Year: 2013

Original connections among the world's extant Archean cratons are becoming tractable by the use of integrated paleomagnetic and geochronologic studies on Paleoproterozoic mafic dyke swarms. Here we report new high-quality paleomagnetic data from the ∼2.41Ga Widgiemooltha dyke swarm of the Yilgarn craton in western Australia, confirming earlier results from that unit, in which the primary origin of characteristic remanent magnetization is now confirmed by baked-contact tests. The corresponding paleomagnetic pole (10.2°S, 159.2°E, A95=7.5°), in combination with newly available ages on dykes from Zimbabwe, allow for a direct connection between the Zimbabwe and Yilgarn cratons at 2.41Ga, with implied connections as early as their cratonization intervals at 2.7-2.6Ga. The proposed " Zimgarn" supercraton was likely distinct from Vaalbara (Kaapvaal plus Pilbara) at 2.4Ga, but both of those entities independently fragmented at ca. 2.1-2.0Ga, reassembling into the Kalahari and West Australian cratons by 1.95-1.8Ga. © 2012 Elsevier B.V.


Teixeira W.,University of Sao Paulo | D'Agrella-Filho M.S.,University of Sao Paulo | Hamilton M.A.,University of Toronto | Ernst R.E.,Ernst Geosciences | And 4 more authors.
Lithos | Year: 2013

The Tandilia Terrane (southernmost fringe of the Rio de la Plata Craton) is an igneous and metamorphic complex produced by an accretionary orogeny (2.25-2.02Ga). Calc-alkaline acidic dykes with E-W strike and a major shear zone with similar orientation are related with the late orogeny stage, as supported by field relations. In a previous study the acid dykes gave 40Ar-39Ar ages of 2007±24Ma to 2020±24Ma. A N and NW trending tholeiitic dyke swarm (Tandil swarm) is also present in the Tandilia Terrane. One sample from the NW-trending subset previously gave a U-Pb (ID-TIMS) baddeleyite age of 1588±11Ma. New precise U-Pb (ID-TIMS) baddeleyite dating of both N- and NW-trending Tandil dykes yielded crystallization ages of 1589±3Ma, 1588±3Ma and 1588±3Ma. Significantly older tholeiitic dykes known as the Florida swarm occur in the Northern Rio de la Plata Craton, for which a U-Pb (ID-TIMS) baddeleyite age of 1790±5Ma was previously reported. Consequently intermittent rifting (1.79, 1.59Ga) took place after tectonic stabilization of the late Paleoproterozoic lithosphere (proto-Rio de la Plata Craton). The available geochemical data for the 1.59Ga Tandil dykes define low- and high-TiO2 trends, although, only the low-TiO2 subgroup is firmly dated. Both the Tandil and Florida dykes have geochemical and Nd-Sr characteristics consistent with derivation from heterogeneous mantle sources that underwent metasomatic effects.The Tandil dykes may be linked with the 1.57. ±. 0.02. Ga Capivarita anorthosite which occurs to the east of the northern part of the craton. Correlatives on other crustal blocks may include those in Baltica such as bimodal rock association (including the Breven-Hällefors and Åland-Åboland diabase dykes) and in the reconstructed Gawler Craton/NW Laurentia dolerites, bimodal magmatism and IOCG deposits. Contemporary within-plate bimodal associations are also present in the SW Amazonian Craton.Paleomagnetic data for the 1790. Ma Florida dykes allows three possible reconstruction scenarios for the position of Rio de la Plata Craton: i) in the southern hemisphere linked to the Pampia terrane, and the Amazonia. +. Rio Apa landmass as close as they are in present day; ii) in the northern hemisphere, as a nearest neighbor to the reconstructed NW Laurentia and Gawler blocks (proto-Australia); or iii) in the northern hemisphere near the boundary of Amazonia (proto-Amazonian Craton) and Baltica. Positions 2 and 3 are consistent with all three criteria: paleomagnetic poles and proximity to matching ca. 1790. Ma and 1590. Ma mafic magmatism. Our data are consistent with the idea that the Columbia supercontinent started major break up at 1.59. Ga. © 2012 Elsevier B.V.


Ernst R.,Ernst Geosciences | Bleeker W.,Geological Survey of Canada
Canadian Journal of Earth Sciences | Year: 2010

Large igneous provinces (LIPs) are high volume, short duration pulses of intraplate magmatism consisting mainly of flood basalts and their associated plumbing system, but also may include silicic components and carbonatites. Many LIPs have an associated radiating diabase dyke swarm, which typically converges on a cratonic margin, identifies a mantle plume centre, and is linked to breakup or attempted breakup to form that cratonic margin. We hypothesize that every major breakup margin in Canada can be associated with a LIP, and we attempt to identify this LIP. To this end, we focus mainly on high-precision age determinations and the distribution of diabase dyke swarms, which are uniquely valued for preserving the record of magmatic events. The analysis extends from the Phanerozoic to the Neoarchean, but our most complete information is for the Superior craton. There, events at 2.50-2.45, 2.22-2.17, and 2.12-2.08 Ga (LIP and plume) are linked with rifting and breakup or attempted breakup of the south-southeastern, northeastern, and southern margins, respectively. Events at 2.00-1.97 Ga are probably linked with the northern margin (Ungava promontory), while the Circum-Superior event at ca. 1.88 Ga is linked to the north to northwestern margins during a time of Manikewan Ocean closure. Similar linkages for other cratons of North America improve understanding of the breakup history to help identify which blocks were nearest neighbours to Canadian crustal blocks in Precambrian supercontinents. Such interpretations provide a framework for interpreting other geological features of these margins to further test models for the timing and location of breakup.


Kulikov V.S.,Russian Academy of Sciences | Bychkova Y.,RAS Institute of Chemistry | Kulikova V.,Russian Academy of Sciences | Ernst R.,Ernst Geosciences
Precambrian Research | Year: 2010

Ca. 2.5-2.4Ga Sumian magmatism is widespread in the Karelia and Kola cratons of Fennoscandia and probably represents at least two intermixed large igneous provinces (LIPs). It is distinct from other Paleoproterozoic LIPs (Jatulian 2.22-2.1Ga and Ludicovian 2.06-1.96Ga) elsewhere in the Fennoscandian Shield. A poorly understood portion of Sumian magmatism is the Vetreny Poyas (Windy Belt) subprovince, which covers ∼75,000km2 in southeastern Fennoscandia. This subprovince consists of four genetically related complexes which developed at different levels in the crust: a volcanic complex (komatiitic basaltic lava flows on Golets, Levgora and Myandukha hills, and Victoria lava lake on Levgora hill), a subvolcanic complex (mafic-ultramafic sills and lopoliths including Ruiga, Kirichgora, Kozhozero and Undozero), plutonic complexes (Burakovsky and Vyzhiga) and a dyke complex (gabbronoritic Avdeyevo and Shala dykes and peridotitic Vinela and Koppalozero dykes). Similar patterns are present in other Sumian belts elsewhere in Karelia, for instance in southern Lapland and the Kola Peninsula.Negative or near-zero e{open}Nd values for intrusive rocks from the Ruiga massif (-2.0±0.8) and volcanics from Golets Hill (-0.4±0.9) suggest that the mantle source for their melts was enriched or that their parental magmas were contaminated by crustal rocks during intrusion and crystallization. Overall, the petrologic-geochemical study of rocks from the above-mentioned complexes indicates that they were all derived from the same parental primary komatiitic melt (associated with a mantle plume) that experienced crustal contamination. This parental magma for the province is a komatiitic basalt magma type with key petrochemical parameters (9-18% MgO, 0.5-1.0% TiO2, SiO2 <53%), and is contrasted with other high-Mg magmatic types, boninites, komatiites, picrites and meimechites. © 2010 Elsevier B.V.

Loading Ernst Geosciences collaborators
Loading Ernst Geosciences collaborators