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Two billion years of mantle evolution in sync with global tectonic cycles
Copyright policy )Abstract The continental crust and sub-continental lithospheric mantle (SCLM) are co-dependent reservoirs in terms of their geochemistry, tectonics, and long-term evolution. Obtaining insight into the mechanisms of lithosphere formation and differentiation requires robust constraint on the complex petrological history of mantle rocks. This has proven difficult as samples from the deep mantle are rare and, although many may have formed in the Archean, no such age has been obtained directly from mantle-derived silicate minerals. Lutetium-hafnium geochronology of garnet has the potential of overcoming this limitation. In this study, this technique was applied on fragments of the SCLM exposed in the Norwegian Caledonides. The chronologic record of these rocks is rich and extensive, yet it is difficult to interpret and is, in part, inconsistent. Our Lu–Hf results from supersilicic pyrope in dunite provide the first Archean internal isochron ages for mantle rocks. These ages are consistent with a period of juvenile crust formation worldwide and provide a record of deeply sourced mantle upwellings from >350 km depth. Results from fertile rock types indicate that melting and isotope re-equilibration occurred in sync with two Proterozoic supercontinent break-up events that are recorded in the Laurentian and Baltic lithospheres. Together, the results indicate that since its extraction during a period of rapid Archean crustal growth, the SCLM appears to have largely been at petro-physical and chemical stasis, with the exception of major episodes of continental break-up. The evolution of the SCLM is thus, highly punctuated and ultimately controlled by the Wilson cycle.
Microsoft Academic Graph classification: Lithosphere Proterozoic Geochemistry Continental crust Supercontinent Geology Archean Geochronology Tectonics Mantle (geology)
Space and Planetary Science, Earth and Planetary Sciences (miscellaneous), Geochemistry and Petrology, Geophysics
Space and Planetary Science, Earth and Planetary Sciences (miscellaneous), Geochemistry and Petrology, Geophysics
Microsoft Academic Graph classification: Lithosphere Proterozoic Geochemistry Continental crust Supercontinent Geology Archean Geochronology Tectonics Mantle (geology)
- Utrecht University Netherlands
- University of Stuttgart Germany
- Swedish Museum of Natural History Sweden
- University of British Columbia Canada
- Natural Sciences and Engineering Research Council of Canada (NSERC)
- Utrecht University Netherlands
- University of Stuttgart Germany
- Swedish Museum of Natural History Sweden
- University of British Columbia Canada
Abstract The continental crust and sub-continental lithospheric mantle (SCLM) are co-dependent reservoirs in terms of their geochemistry, tectonics, and long-term evolution. Obtaining insight into the mechanisms of lithosphere formation and differentiation requires robust constraint on the complex petrological history of mantle rocks. This has proven difficult as samples from the deep mantle are rare and, although many may have formed in the Archean, no such age has been obtained directly from mantle-derived silicate minerals. Lutetium-hafnium geochronology of garnet has the potential of overcoming this limitation. In this study, this technique was applied on fragments of the SCLM exposed in the Norwegian Caledonides. The chronologic record of these rocks is rich and extensive, yet it is difficult to interpret and is, in part, inconsistent. Our Lu–Hf results from supersilicic pyrope in dunite provide the first Archean internal isochron ages for mantle rocks. These ages are consistent with a period of juvenile crust formation worldwide and provide a record of deeply sourced mantle upwellings from >350 km depth. Results from fertile rock types indicate that melting and isotope re-equilibration occurred in sync with two Proterozoic supercontinent break-up events that are recorded in the Laurentian and Baltic lithospheres. Together, the results indicate that since its extraction during a period of rapid Archean crustal growth, the SCLM appears to have largely been at petro-physical and chemical stasis, with the exception of major episodes of continental break-up. The evolution of the SCLM is thus, highly punctuated and ultimately controlled by the Wilson cycle.