February 2014 LIP of the Month
The 1501 ± 3 Ma Kuonamka LIP of northern Siberia
Richard E. Ernst, Department of Earth Sciences, Carleton University, Ottawa, ON, Canada, Richard.Ernst@ErnstGeosciences.com;
Michael A. Hamilton, Jack Satterly Lab., University of Toronto, Toronto, ON, Canada;
Sandra L. Kamo, Jack Satterly Lab., University of Toronto, Toronto, ON, Canada;
Alexander V. Okrugin, Diamond & Precious Metal Geology Institute, RAS, Yakutsk, Russia
Roman Veselovskiy, Lomonosov Moscow State University, Geological Dept., Moscow & Institute of Physics of the Earth, RAS, Moscow, Russia;
Volodia Pavlov, Institute of Physics of the Earth, RAS, Moscow, Russia;
Ulf Söderlund, Department of Earth & Ecosystem Sciences, Lund University, Lund, Sweden;
Kevin Chamberlain, Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, USA
Siberia is best known for the 250 Ma Siberian Trap Large Igneous Province (LIP) which hosts the important Ni-Cu-PGE Noril’sk deposits (e,g., August 2011 LIP of the Month and March 2004 LIP of the Month). However, comparable-scale Proterozoic LIPs are being discovered through a campaign of U-Pb dating of dolerite dykes and sills through the LIPs-Continental Reconstruction-Resource Exploration Project (www.supercontinent.org). Here we profile the 1501 Ma Kuonamka LIP of northern Siberia (Figs. 1 and 2; Ernst et al. 2014), which can also potentially be linked with dykes and sills in the formerly attached São Francisco – Congo craton (Ernst et al. 2013) to produce an event 2000 km across (Fig. 3). (Ages below are by U-Pb TIMS on baddeleyite unless otherwise noted).
The Kuonamka event was originally recognized in the Anabar shield (Fig. 1). An E-trending dyke was dated at 1503+/-5 Ma with additional E-ESE-trending dykes correlated via paleomagnetism (Ernst et al. 2000). A new date (1502+/-6 Ma) allows the swarm to be traced into the Riphean sediments on the western sides of the Anabar shield for a distance of 270 km. A dolerite sill province also cuts these Riphean sediments and yields new ages of 1498+/-2, 1502+/- 6, 1503+/-2, 1502+/-8, and 1493+/-9 Ma. An age of 1466±14 Ma was obtained for a sill by U-Pb SIMS; the meaning of this slightly younger age is being investigated. Several hundred km further east in the Olenek uplift a Sololi sill yielded an imprecise U-Pb SHRIMP age of 1473+/-24 Ma (Wingate et al. 2009) that within uncertainty would match the Kuonamka event further west. Overall these data suggest that the Kuonamka LIP extends E-W for 700 km from the western slopes of the Anabar shield to the Olenek uplift. Convergence of the E-ESE trending Kounamka dykes with SSW-trending dykes in the Olenek uplift would define a ca. 1500 Ma plume centre on the northeastern margin of the Siberian craton. The age of Kuonamka LIP can be summarized as 1501 ± 3 Ma (95% confidence), based on the weighted average of the seven U-Pb TIMs results.
Platinum group minerals have been found in placers along the Anabar River (northeast from the Anabar shield under younger sedimentary cover rocks; see Fig. 1) which are linked to layered intrusions recognized by geophysics along the Anabar River (Okrugin, 1998; Okrugin et al., 2009). Given the prominence of the 1501 Kuonamka LIP in northern Siberia, it should be considered that these unexposed and undated intrusions and also the associated placer PGEs could belong to the Kuonamka LIP.
Figure 1: Distribution of dated dykes and sills superimposed on background map redrafted by R.V. from the original map of Okrugin et al. (1990). Multiple magmatic events were suspected to be present in the Anabar shield based on K-Ar dating (Okrugin et al., 1990), and the timing of some of these event have now been precisely determined by U-Pb geochronology. In addition to the newly recognized Kunonamka LIP which is widespread in the Anabar shield as an E-W dyke swarm and as sills to the west of the Anabar shield (Figs. 2 and 3; blue lines and green polygons), other magmatic events are also present: the 1385 Ma dykes of the Chieress swarm; dated dyke shown in red line), and a ca. 1750 Ma swarm recognized based on Ar-Ar dating (dated dyke shown in orange line) which is part of a proposed giant radiating swarm extending to southern and southwestern Siberia (Ernst et al., 2008; Gladkochub et al., 2010a,b). Dykes belonging to the 250 Ma Siberian Trap event are also likely present. Outside the area of basement rocks (Archean), and overlying Riphean sedimentary cover (Riphean) are younger cover rocks.
Figure 2: Distribution of 1500 Ma magmatic units (in red) in the Anabar shield and environs, and also in the Olenek uplift (several hundred km to the east) in the northern Siberian craton. Basemap after Pisarevsky et al. (2008) with superimposed distribution (in red) of 1500 Ma units: sills located by red-filled areas, dyke swarms located by red lines, and possible mafic-ultramafic intrusions located by the red ellipse. Possible mantle plume centre (star) marked by convergence of E-W dyke swarm of Anabar shield with SSW-NNE swarm of Olenek uplift. See discussion in text.
Figure 3: Reconstruction of northern Siberia with the combined São Francisco-Congo craton. Note age match of 1500 Ma Kuonamka dykes with Curaçá-Chapada dykes of the São Francisco craton and the Humpata sills of the Angolan portion of the Congo craton (Silveira et al. 2013). KAB and KIB are Karagwe-Ankole belt and Kibara belt, respectively, as recently defined by Tack et al. (2010).
References
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Ernst, R.E., Hanes, J.A., Puchkov, V.N., Okrugin, A.V., and Archibald, D.A. (2008). Reconnaissance Ar–Ar dating of Proterozoic dolerite dykes and sills in Siberia and the southern Urals: identification of possible new Large Igneous Provinces (LIPs). In: Common and Regional Problems of Tectonics And Geodynamics, Moscow Tectonics Conference, GEOS, Moscow, extended abstract, p. 492-496.
Ernst, R.E., Pereira, E., Hamilton, M.A., Pisarevsky, S.A., Rodriques, J., Tassinari, C.C.G., Teixeira, W., and Van-Dunem, V. (2013). Mesoproterozoic intraplate magmatic ‘barcode’ record of the Angola portion of the Congo Craton: Newly dated magmatic events at 1505 and 1110 Ma and implications for Nuna (Columbia) supercontinent reconstructions: Precambrian Research, v. 230, p. 103–118,
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