Crust–mantle decoupling and the growth of the Archaean Zimbabwe craton

https://doi.org/10.1016/S0899-5362(02)00015-5Get rights and content

Abstract

Based on the Zimbabwe craton, it is suggested that, during the Archaean, full decoupling between a strong upper crust and a strong upper mantle across a weak detachment zone at the Moho allowed the independent development of crustal and mantle geometries in response to lithospheric shortening. This is an effective way to explain the field observations made in the Zimbabwe craton, which suggest a late-Archaean interplay between lateral accretionary processes through low angle thrust stacking and underplating and deep seated lineament zones with a possible mantle origin. The lineament zones play an important role in the localisation of mineral deposits such as base metals, gold, and possibly diamonds. Thickening of the mantle lithosphere occurred independently from the crust, through early Archaean melt segregation and/or lithospheric underplating.

Introduction

The nature of tectonic processes resulting in the formation of Archaean cratons remains a poorly understood topic in earth sciences. We know that at some stage during the Archaean the change occurred from vertical melt segregation leading to formation of early crust, to the emergence of strong plates affected by plate margin processes similar to modern-day plate tectonics. What is less obvious is how and when this transition took place, whether it was gradual or sudden, or separated by a period dominated by entirely different tectonic processes.

In this paper we present a summary of the geological, geochronological and geochemical data for the Zimbabwe craton, which can be used to build a convincing case for lateral continental growth through obduction/thrusting, and low-angle underplating and remelting of crustal fragments, which is similar to scenarios described for the Superior Province, Kaapvaal craton and Yilgarn Block (de Wit et al., 1992; Myers, 1995; Kusky and Polat, 1999). However, such a scenario of crustal thickening through shortening must be paralleled by corresponding shortening of the mantle lithosphere, a point generally not addressed in literature. At the high geotherms prevailing in the Archaean, decoupling of crust and mantle lithosphere is expected, allowing strain to be accommodated independently in both layers. Accretionary geometries in the Zimbabwe craton display large scale spatial alignments indicative of deep seated linear controls that can be used to infer Crust–mantle delamination.

With this paper we would like to start a discussion regarding the interplay between crust and mantle lithosphere during the Archaean, by offering some possible tectonic scenarios based on the Zimbabwe craton example.

Section snippets

Growth of the Zimbabwe craton: a case study

The Zimbabwe craton is a granite-greenstone terrain in southern Africa that formed during a timespan of almost 1000 Ma (3.55–2.58 Ga; Fig. 1). The evolution of this terrain is explained with a series of crustal growth stages that added greenstones and granitoids to a ≈3.5 Ga old nucleus (Wilson et al., 1995). These stages are commonly linked to the emplacement of mantle plumes below existing continental crust, causing intracontinental rifting and crustal melting (e.g. Bickle et al., 1994;

And what about the mantle lithosphere?

Geochronological, geochemical and structural observations on the formation of the Zimbabwe craton are all consistent with lateral growth, centred on old proto-cratonic nuclei, through processes that resemble active continental margin and collisional processes like subduction and thrust stacking in active orogens. In spite of such similarities, a uniformitarian application of modern-day accretion–subduction–collision models to Archaean terrains cannot be made. For example, crustal stacking in

The strength of the Archaean lower crust

The Archaean represents the time period during which Earth transformed from a hot, seething ball of molten lava covered by a thin crust, to something resembling a modern-day tectonic scenario with plate boundaries and plates strong enough to transmit stresses. Throughout the Archaean, but especially during the earlier parts, Earth was characterised by a far less differentiated and evolved mantle-crust architecture, and by much higher geothermal gradients than today. This was partly due to

Conclusion

Considering all of the above points we would like to suggest the following scenario for the evolution of the Zimbabwe craton, which may also be applied to other cratons. In the early Archaean thick mantle lithosphere was formed after segregation of a basaltic melt, which accumulated as oceanic crust. At the prevailing geotherms a thin layer of strong upper crust was separated from a much thicker layer of strong mantle lithosphere by highly ductile lower crust. Total decoupling between the crust

Acknowledgements

We would like to thank Stichting Schurmannfonds for financially supporting this research (grants 1996–2001/13). Dr. Kurt Stuewe and Dr. Henri Kampunzu are thanked for their supportive reviews.

References (69)

  • M.L. Vinyu et al.

    First U–Pb zircon ages from a craton-margin Archaean orogenic belt in northern Zimbabwe

    Precambrian Research

    (1999)
  • N.J. Vlaar

    Continental emergence and growth on a cooling earth

    Tectonophysics

    (2000)
  • N.J. Vlaar et al.

    Cooling of the Earth in the Archaean: consequences of pressure-release melting in a hotter mantle

    Earth Planetary Science Letters

    (1994)
  • K.R. Wilks et al.

    Rheology of some continental lower crustal rocks

    Tectonophysics

    (1990)
  • J.F. Wilson

    The geology of the country around Mashaba

    Rhodesia Geological Survey Bulletin

    (1968)
  • J.F. Wilson

    A craton and its cracks: some of the behaviour of the Zimbabwe block from the late Archaean to the Mesozoic in response to horizontal movements and the significance of some of ist mafic dyke patterns

    Journal African Earth Sciences

    (1990)
  • D.H. Abbott et al.

    Archaean plate tectonics revisited. 1. Heat flow, spreading rate and the age of subducting lithosphere and their effects on the origin and evolution of continents

    Tectonics

    (1984)
  • C.M. Barton et al.

    The geology of the country around Rushinga and Nyamapanda

    Zimbabwe Geological Survey Bulletin

    (1991)
  • M.J. Bickle et al.

    Archaean greenstone belts are not oceanic crust

    Journal Geology

    (1994)
  • T.G. Blenkinsop et al.

    The Zimbabwe Craton

  • S.A. Bowring et al.

    3.96 Ga gneisses from the Slave province, Northwest Territories, Canada

    Geology

    (1989)
  • Brake, C., 1996. Tholeiitic magmatism in the Belingwe greenstone belt, Zimbabwe. Ph.D. thesis, University of...
  • Buchholz, P., 1995. Gold minineralization in the Kwekwe district, Midlands greenstone belt, Zimbabwe. Ph.D. thesis,...
  • J.D. Byerlee

    Friction of rocks

    Pure Applied Geophysics

    (1978)
  • S.D.G. Campbell et al.

    Structural controls of gold mineralization in the Zimbabwe Craton––Exploration guidelines

    Zimbabwe Geological Survey Bulletin

    (1994)
  • Chenjerai, K.G., 1995. The Mutare greenstone belt, Zimbabwe: geology, geochemistry and gold mineralisation. Ph.D....
  • P.N. Chopra et al.

    The role of water in the deformation of dunite

    Journal Geophysical Research

    (1984)
  • G.F. Davies

    On the emergence of plate tectonics

    Geology

    (1992)
  • M.J. de Wit et al.

    The onset of interaction between the hydrosphere and oceanic crust, and the origin of the first continental lithosphere

  • M.J. de Wit et al.

    Formation of an Archaean continent

    Nature

    (1992)
  • P.H.G.M. Dirks et al.

    Horizontal accretion and stabilization of the Zimbabwe Craton

    Geology

    (1998)
  • Dirks, P.H.G.M., Mikhailov, A., 1999. Tectonic controls on gold mineralisation in the Zimbabwe craton: the use of large...
  • P.H.G.M. Dirks et al.

    Early duplexing in an Archaean greenstone sequence and its control on gold mineralisation

    Journal African Earth Sciences

    (1997)
  • Dirks, P.H.G.M., Jelsma, H.A., Hofmann, A., 2001. Thrust-related accretion of an Archaean greenstone belt in the...
  • Cited by (23)

    • Diamond growth from C–H–N–O recycled fluids in the lithosphere: Evidence from CH<inf>4</inf> micro-inclusions and δ<sup>13</sup>C–δ<sup>15</sup>N–N content in Marange mixed-habit diamonds

      2016, Lithos
      Citation Excerpt :

      If these diamonds are peridotitic then they could be as old as Palaeoarchaean, given the evidence from the southern Zimbabwe lithosphere for extensively depleted Archaean components (Smith et al., 2009a). If eclogitic, diamond formation could be related to numerous subduction events recorded in the Zimbabwe lithosphere, such as during Archaean amalgamation of the craton (Dirks and Jelsma, 2002) or Proterozoic subduction along the western margin of the craton (Magondi Belt; Jacobs et al., 2008; Stowe, 1989). This study is based on thirteen diamond plates, ranging in diameter from 5 to 9 mm and all less than 1 mm thick.

    • Precambrian crustal structure in Africa and Arabia: Evidence lacking for secular variation

      2013, Tectonophysics
      Citation Excerpt :

      The major sub-terranes include the Kimberly (3.0–2.8 Ga), Pietersburg (3.0–2.8 Ga), Witwatersrand (3.6–3.1 Ga), and Swaziland (3.6–3.1 Ga) blocks. The Tokwe terrane forms the core of the Zimbabwe Craton and consists of granite-greenstone belts that formed between 3.6 and 2.5 Ga (Dirks and Jelsma, 2002). The Limpopo Belt consists of highly metamorphosed granite-greenstone and granulite terranes that underwent a series of orogenic events between 2.0 and 3.0 Ga during the collision of the Kaapvaal and Zimbabwe Cratons (Krammers et al., 2006; McCourt and Armstrong, 1998).

    • A re-appraisal of the Epoch nickel sulphide deposit, Filabusi Greenstone Belt, Zimbabwe: A hydrothermal nickel mineral system?

      2013, Ore Geology Reviews
      Citation Excerpt :

      The Upper Greenstones are widespread throughout the Zimbabwe Craton and contain the most important NiS deposits of Zimbabwe, such as Trojan, Shangani, Madziwa, Epoch (e. g. Baglow, 1986; Chimimba, 1986; Chimimba and Ncube, 1986; Maier, 2005; Prendergast, 2003). Most of the greenstone lithologies in the Zimbabwe Craton were formed during the 2.75–2.58 Ga events (Dirks and Jelsma, 2002; Kusky, 1998; Prendergast, 2004). Following cratonization, the Great Dyke was emplaced at ~ 2.6 Ga (e.g., Mukasa et al., 1998; Wilson, 1990; Wingate, 2000).

    • Magmatic nickel sulfide mineralization in Zimbabwe: Review of deposits and development of exploration criteria for prospectivity analysis

      2010, Ore Geology Reviews
      Citation Excerpt :

      The Archean granite–greenstone terrain accumulated between 3.5 to approximately 2.6 Ga. Greenstone belts are scattered throughout the craton in various directions and significant komatiite-hosted magmatic nickel sulfide deposits such as Empress, Hunters Road, Trojan, and Shangani, developed between 2.8 and 2.7 Ga, and they are also associated with major rift events (Dirks and Jelsma, 2002, and references therein; Prendergast, 2003). Given the similarity in age and tectonic setting, the komatiites of the Zimbabwe craton could potentially host similar deposits of nickel sulfides.

    View all citing articles on Scopus
    View full text