Geological Constraints on the Origin of the Mantle Root beneath the Canadian Shield

摘要: Cratonic North America is composed of a cluster Archaean microcontinents centred on the Canadian shield, and juvenile Proterozoic crust that lies mainly buried beneath sedimentary cover western southern interior platforms. The shield underlain by an anomalous low-temperature mantle root absent platform. As there appears to be no systematic difference in crustal thickness or density between platform, long-lived arching implies intrinsic buoyancy imparted more than offsets its colder temperature. Isotopic seismic anisotropy data indicate age for root, close time formation overlying crust. preferential development consistent with origin imbrication partly subducted slabs highly depleted oceanic lithosphere, assuming buoyant subduction was common Archaean. Formation not dependent collisional orogenesis, as has been suggested, but cratonic sufficiently refractory survive later tectonic thickening. persists transected mafic dyke swarms subjected short-lived episodes post-orogenic melting, reduced at plume initiation sites. partitioning Proterozic respectively, causes misrepresent Precambrian whole. Studies falsely conclude high percentage formed Archaean, characterized epicontinental volcanism sedimentation, `reworking'. Furthermore, isotopic ratios detritus eroded from craton may tend overestimate mean continental