Taking the Pulse of Planet Earth / Completing the Plate Tectonic Revolution
Reconstruction of Supercontinents Back To 2.7 Ga Using The Large Igneous Province (LIP) Record, With Implications For Mineral Deposit Targeting, Hydrocarbon Resource Exploration, and Earth System Evolution
Paleocontinental reconstructions are critical to providing a tectonic context for major ore deposits, the tracing of metallogenic belts between blocks, and identifying new prospective regions for mineral deposits of a wide variety of types. They are equally important to understanding the full context of sedimentary basins, their evolution, and their hydrocarbon reserves and potential.
Unfortunately, the state of understanding of pre-Pangea reconstructions and their specific paleogeography is tentative at best. There is good evidence, based for instance on the episodic nature of orogenic belts, that there have been several Precambrian supercontinents, specifically, in the late Archean (e.g. Kenorland, or perhaps three supercratons, Superia, Sclavia, Vaalbara), the late Paleoproterozoic (supercontinent Nuna; also referred to as Columbia), and the Neoproterozoic (Rodinia). Beyond these general concepts, the exact reconstructions are poorly constrained. The high-quality information content of the LIP record (precise ages, trends, precise piercing points, paleomagnetic information; see Fig. 1 for LIP record) can resolve these issues unambiguously. With a global team of collaborators, we have organized an Industry-Government-University consortium for a 5-year project to constrain paleocontinental reconstructions back to 2.6 Ga using the LIP record. This is an ambitious but realistic goal, given recent breakthroughs in correlation techniques using LIPs.
Large Igneous Provinces (LIPs)
LIPs and their dyke swarms (www.largeigneousprovinces.org), typically preceding and accompanying the breakup of continents, can now be dated routinely with high precision and accuracy using U-Pb baddeleyite and zircon methods. Continental breakup typically leaves remnants of sharply-timed LIP events on conjugate margins. Dating multiple events precisely produces, in effect, a high-fidelity ‘barcode’ for a craton or terrane that can be compared to that of other cratons or terranes (e.g., Fig. 2). Originally contiguous crustal fragments will share essential parts of their barcodes. Any precise barcode match beyond just a single event indicates an original ‘nearest neighbour’ relationship (Bleeker and Ernst 2006; see also http://www.largeigneousprovinces.org/06may.html).
Figure 2: Hypothetical ‘barcodes’ for five cratons. Individual ‘bars’ are the age range of short-lived magmatic events on vertical timelines. Partially matching barcodes (e.g. between cratons A and D) from time T4 to T7, and possibly from as early as T2) are a strong indication that the two cratons were contiguous (i.e. ‘nearest neighbours’) in an ancestral supercraton. Cratons C and E are unrelated to A and D, but may have shared a common history as part of another supercraton; more precise age data would be required to test this correlation. Craton B, with no matches, must represent a distant, if not unrelated, fragment of crust (after Bleeker and Ernst 2006).
Not only do short-lived magmatic LIP events contain precise temporal information, they also contain structural and paleomagnetic information, and much more. Dyke swarms extending far into cratonic hinterlands provide very precise piercing points that are relatively insensitive to collision and uplift. Critical progress in all these fields has quickly made this integrated method using LIPs (precise barcodes, precise piercing points, key paleomagnetic poles, etc.) a highly powerful and robust correlation tool (Bleeker and Ernst 2006).
Examples of Paleocontinental Reconstruction Questions Being Solved Using The LIP Record
The pattern of the opening of the Labrador Sea is constrained by pre-breakup dyke swarms of the same age on both the Greenland and Canadian sides, which represent precise piercing points (Fig. 3)—a fit further strengthened by paleomagnetic and geochemical comparisons of the swarms (Buchan et al., 1996).
A major stage of development of the Arctic ocean can be linked to the initiation of the 130-90 Ma HALIP (High Arctic Large Igneous Province) affecting northern Canada, northern Greenland, Svalbard and Franz Josef Land (Maher 2001; Buchan and Ernst 2006). Given the hydrocarbon potential of the Arctic, the location of an interpreted mantle plume (associated with HALIP) has implications for oil maturation (and over maturation).
The 723 Ma Franklin LIP event of northern Canada (extending over 2 million km2) can now be linked with magmatism in southern Siberia because of a single new, preliminary, U-Pb age (725+/-8 Ma; dated by M. Hamilton, sample collected by Alexay Lygin and supplied by BHP Billiton) on the Dovyren layered intrusion of the Lake Baikal region. This critical age match, in addition to several older LIP barcode matches, confirms that the southern Siberian craton was adjacent to northern Canada at 725 Ma and perhaps back to ca. 1800 Ma, the time of amalgamation of supercontinent Nuna. Integration of Franklin magmatism across arctic Canada and equivalent magmatism in Siberia into a single LIP will permit a system-scale analysis of the plumbing system of this giant LIP and assist in the targeting of associated ore deposits.
The ca. 1590 Ma Olympic Dam deposit and associated Gawler Range volcanics of the Gawler craton can be linked with northwest Laurentia on the basis of an age match with the coeval Wernecke Breccias (Thorkelson et al., 2001), and with the newly dated Western Channel Diabase (WCD; Hamilton and Buchan 2007). The precise dates on WCD and resulting paleomagnetic comparison with the Gawler Range volcanics represent evidence for a Gawler – northwest Laurentia link at this time.
The ca. 2055 Ma Bushveld intrusion is linked with a number of other smaller coeval layered intrusions, sills, volcanics and a carbonatite intrusion (Phalaborwa) into a single LIP that is widespread throughout the Kaapvaal craton. The mutual absence of 2057 Ma Bushveld magmatism in the adjacent Zimbabwe craton, and of 2575 Ma Great Dyke magmatism from the Kaapvaal craton, requires that the Zimbabwe and Kaapvaal cratons did not dock until after Bushveld time (e.g. Bleeker 2003). This insight from the LIP record alone cuts through the complicated structural analysis of the intervening Limpopo belt which has failed to yield a clear consensus regarding timing of collision.
The LIP record has been used to suggest a Paleoproterozoic reconstruction (>2500 Ma to about 2100 Ma) of Karelia-Kola, Hearne and Wyoming cratons against the southern margin of the Superior craton (Fig. 4; after Bleeker and Ernst 2006). A resulting unique fit juxtaposes the 2500 Ma Mistassini and 2450-2480 Ma Matachewan-East Bull Lake events of the Superior craton against the Baltic Large Igneous Province (BLIP) of Karelia-Kola into a common LIP, allowing this magmatism (and its metallogeny) to be studied at a system-wide scale (e.g. Ernst 2007).
The 2750-2700 Ma Abitibi greenstone belt of the Superior craton contains proven economic mineral wealth. Specifically, the E-W trending Abitibi belt has historically produced ~200 million ounces of Au, hosts the two largest massive sulphide deposits in the world (Kidd Creek and Horne), and has significant base metal and Ni-Cu deposits. The Abitibi belt is truncated, however, on the eastern side, by a probable Paleoproterozoic breakup margin. New U-Pb baddeleyite age determinations (2512, 2470 and 2408 Ma) from dykes in the Zimbabwe craton (Soderlund et al. submitted) provide barcode matches with eastern Superior craton suggesting that the Abitibi greenstone belt and the 2700 Zimbabwe greenstone belts should be linked and furthermore that the Great Dyke of Zimbabwe event may graze the eastern Superior craton margin.
Constraining paleocontinental reconstructions back to 2.6 Ga requires a dramatic expansion of precise dating of mafic units. It has been estimated that there are about 35 major Archean cratonic fragments (‘pieces of the puzzle’, see Bleeker 2003) and for each we ideally need about 10 events in order to define a unique barcode. So far, we have abundant geochronological information (and a relatively robust barcode) for Superior, Slave, Karelia, and parts of Australia, but for most blocks the data are poor or nonexistent. Once the precise barcode for each cratonic block or fragment has been defined, the global paleogeographic puzzle will quickly resolve itself with robust configurations for all major continental aggregations prior to Pangaea.
Fortunately, there is a vast reservoir of units, especially dyke swarms, sill provinces and layered intrusions available through time and on most cratonic blocks to be dated. To complete the barcodes for all major pieces of the puzzle and achieve paleocontinental reconstructions back to 2.6 Ga will require approximately 250 precise age determinations from targeted units around the world. We hope to achieve this goal through a 5 year project being funded by industry with anticipated matching government funds, and involving links with universities and government surveys around the world.
For more information about the project or to consider becoming involved, please contact us through the email addresses below. If you are already a participant in the project you can access further information through the "Login" (using the username and password assigned to you).
Sponsors of the Project are: Anglo American Exploration (Canada) Ltd, Gold Fields Exploration Inc., Minerals and Metals Group, Nor-West Rotors, Shell Products and Technology, Vale Exploration Canada Inc.
Bleeker, W. 2003. The late Archean record: a puzzle in ca. 35 pieces. Lithos, v.71, pp. 99-134.
Bleeker W, and Ernst R. 2006. Short-lived mantle generated magmatic events and their dyke swarms: The key unlocking Earth's paleogeographic record back to 2.6 Ga. In Dyke Swarms - Time Markers of Crustal Evolution. Edited by E. Hanski, S. Mertanen, T. Rämö, and J. Vuollo. Taylor and Francis/Balkema, London, pp. 3-26.
Buchan, K.L., and Ernst, R. 2006. Giant dyke swarms and the reconstruction of the Canadian Arctic islands, Greenland, Svalbard and Franz Josef Land. In: Dyke Swarms: Time Markers of Crustal Evolution. Edited by E. Hanski, S. Mertanen, T. Rämö, and J. Vuollo. Taylor and Francis/Balkema, London, pp. 27-48.
Buchan, K.L., Hodych, J.P., Roddick, J.C., Emslie, R.F., and Hamilton, M.A. 1996. Paleomagnetism and U-Pb geochronology of Mesoproterozoic dykes of Labrador and correlations with dykes of Southwest Greenland. Abstract for COPENA/ESCOOT/IBTA conference on Proterozoic Evolution in the North Atlantic realm, Goose Bay, Labrador, Canada, Program and Abstracts, p. 37.
Ernst, R.E. 2007. Large Igneous Provinces (LIPs) in Canada Through Time and Their Metallogenic Potential. In: Mineral Deposits of Canada: A Synthesis of Major Deposit-Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods, Edited by W.D. Goodfellow. Geological Association of Canada, Mineral Deposits Division, Special Publication 5, pp. 929-937.
Ernst, R.E., Buchan, K.L., and Campbell, I.H., 2005. Frontiers in Large Igneous Province research. Lithos, v. 79, pp. 271-297.
Hamilton, M.A., and Buchan, K.L. 2007. Precise 1.59 Ga age for Western Channel Diabase, Wopmay orogen: implications for Laurentia APWP and reconstruction of Laurentia, Baltica and Gawler craton. Abstracts with Programs, Geological Society of America Annual Meeting, v. 39, pp. 285-286.
Maher, H.D. 2001. Manifestation of the Cretaceous High Arctic Large Igneous Province in Svalbard. Journal of Geology, v. 109, pp. 91-104.
Söderlund, U., Hofmann, A., Klausen, M.B., Olsson, J.R., Ernst, R., Persson, P.-O., 2010. Towards a complete magmatic barcode for the Zimbabwe craton: Baddeleyite U-Pb dating of regional dolerite dyke swarms and sill complexes. Precambrian Research Special volume “High precision dating of Precambrian magmatic provinces, especially their dyke swarms”, in press.
Thorkelson, D.J., Mortensen, J.K., Davidson, G.J., Creaser, R.A., Perez, W.A., and Abbott, J.G. 2001. Early Mesoproterozoic intrusive breccias in Yukon, Canada: the role of hydrothermal systems in reconstructions of North America and Australia. Precambrian Research, v.111, pp. 31-55.