May 2016 LIP of the Month

Large Igneous Provinces record of reconstructed southern Siberia and northern Laurentia from 1.9 to 0.7 Ga

Richard E Ernst

Scientist in Residence, Dept. of Earth Sciences, Carleton U., 1125 Colonel By Drive, Ottawa, Canada K1S 5B6;

Faculty of Geology and Geography, Tomsk State University, 36 Lenin Ave, Tomsk, 634050, Russia; and

Ernst Geosciences, 43 Margrave Ave., Ottawa, Canada K1T 3Y2

Email: Richard.Ernst@ErnstGeosciences.com

Based on Ernst, R.E., Hamilton, M.A., Söderlund, U., Hanes, J.A., Gladkochub, D.P., Okrugin, A.V., Kolotilina, T., Mekhonoshin, A.S., Bleeker, W., LeCheminant, A.N., Buchan, K.L., Chamberlain, K.R., & Didenko , A.N. (2016) Long-lived connection between southern Siberia and northern Laurentia in the Proterozoic. Nature Geoscience (in press), doi: 10.1038/NGEO2700. http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2700.html

Introduction

An expanded Large Igneous Province (LIP) record can expedite progress toward robust Precambrian continental reconstructions (Bleeker and Ernst 2006; Ernst et al. 2013). LIPs and especially their dolerite dyke and sill swarms represent targets of choice for paleomagnetic studies to test proposed reconstructions. In addition the LIP record is useful on its own:

1. For comparison of the LIP ‘barcode’ record between crustal blocks, thereby identifying those blocks which were likely to have been nearest neighbors in past supercontinents; and
2. For restoration of the primary geometry (radiating or linear) of regional mafic dyke swarms (the plumbing system of LIPs) which offers another reconstruction criterion.

A consortium of companies has been funding U-Pb dating of regional dyke swarms and sill provinces around the world toward completion of the global LIPs barcode record. Approximately 220 new U-Pb ages were produced so far in the course of this 2009-2017 Industry-NSERC CRD funded project (e.g. Ernst et al. 2013; 2015).

Northern Laurentia – Southern Siberia Reconstruction Based on LIP Record

This present LIP of the Month contribution is focused on our recent paper (Ernst et al., 2016) that demonstrates a close fit of southern Siberia and northern Laurentia over the interval 1.9-0.7 Ga based on matching of LIP events between the two blocks.  Nine LIP events are found to closely match or approximately match between the two blocks. Figures 1 and 2 show the barcode comparison and the proposed reconstruction, respectively.

Implications of the Reconstruction

The reconstruction in Ernst et al. (2016) and also shown here (Fig. 2) provides a framework for integrating the geology/tectonics of southern Siberia and northern Laurentia over the period 1.9-0.7 Ga. It predicts that all the matched (and at present unmatched) LIP events (in Fig. 2) have a wider distribution across both southern Siberia and northern Laurentia--to be tested by further U-Pb dating of LIP units, particularly in southern Siberia, where precise dating remains limited. Furthermore, the many new LIP events that we have recognized in Siberia based on our new U-Pb and Ar-Ar dating now become important palaeomagnetic targets.

Given the large scale of these shared LIP events, it is likely that many Proterozoic ore deposits (for example, Ni-Cu-PGE and hydrothermal types) scattered across northern Laurentia and southern Siberia are directly, or indirectly, associated with magmatism, heat and fluids from the LIP events (Ernst and Jowitt, 2013). In Fig. 2, the ca. 720 Ma Ni-Cu-PGE bearing intrusions (Polyakov et al. 2013) of the Irkutsk region are juxtaposed opposite 720 Ma Franklin units in northern Laurentia, highlighting the economic prospectivity of the Franklin LIP. 

Mantle Plume Centres

Another thematic aspect relates to the inferred location of mantle plume centres (see stars in Figure 2).  In some cases a single plume centre is inferred for the entire reconstructed LIP.  For instance, the separately identified plume centres for the c. 725-715 Ma Franklin LIP (Laurentia) and Irkutsk LIP (Siberia) are superimposed in the reconstruction (Fig.  2a), representing a single plume centre for the combined Franklin-Irkutsk LIP.  Similarly, the 1260 Ma Srednecheremshanskii dyke (Siberia) trends toward the well-defined plume centre for the 1270 Ma Mackenzie LIP (Laurentia) (Fig. 2d).  On the other hand, at c. 1750 Ma (Fig. 2j), although the age match between units in Siberia and Laurentia suggests a genetic link, there must be at least two distinct 1750 Ma magmatic (plume?) centres.  The Timpton plume centre (Siberia) is located at the focus of a radiating swarm (see also Gladkochub et al. 2010).  However, according to Peterson et al. (2015) the Kivalliq magmatism of Laurentia was linked to a thermal pulse associated with lithospheric delamination.  The ideas (two magmatic centres, mantle plume origin and delamination) can be integrated as follows:  1) Şengör (2001) emphasizes the importance of lithospheric delamination in association with a mantle plume, and 2) it is possible for a mantle plume to spread along the base of thick lithosphere and ascend in widely separated lithospheric thinspots (e.g. Sleep, 2006; Ernst, 2014; Bright et al. 2014). In the 1750 Ma case, the Kivalliq thinspot is caused by delamination, and the Timpton centre thinspot is located along an older enigmatic structure that has been termed the Akitkan belt (Pisarevsky et al. 2008).  Such a scenario could explain the presence of the two distinct magmatic centres (stars) dated as 1,750 Ma in reconstructed Siberia and Laurentia (Fig. 2j) or the two widely-separated nodes of 1,380 Ma magmatism in Laurentia (see Fig. 2f).

Acknowledgements

The research in Ernst et al. (2016), on which this webpage is based, is part of the Large Igneous Provinces - Supercontinent Reconstruction - Resource Exploration Project which has been funded by an industry consortium and Canadian grant NSERC CRDPJ 419503-11 (www.supercontinent.org; www.camiro.org/exploration/ongoing-projects CAMIRO Project 08E03).