The gyroscopic Earth and its role in supercontinent and metallogenic cycles

摘要

Compilation and analysis of the paleomagnetically constrained plate tectonic reconstructions for the last 2.5 Ga of Earth's history reveal that continental and oceanic hemispheres are principal and stable first order divisions on the Earth, with cyclical breakup and reassembly of the continental crust into supercontinents. Although the breakup of the supercontinent Rodinia at 0.75 Ga marked important reorganization of the plate tectonic pattern, the movements of large continental masses, both before and after the breakup of Rodinia, show remarkable synchronism, albeit in significantly rearranged combinations. The patterns with disassembled continents coincided with periods when substantially more than 50% of the continental masses occurred either in the northern (during Palaeoproterozoic and Cenozoic times) or southern (during Neoproterozoic to middle Palaeozoic times) hemispheres, whereas the reassembled supercontinents were always symmetrically centred near the Equator. It is proposed that such regularity might be governed by a convection-driven move of the continental fragments towards a pole after the breakup of the supercontinent, followed by gyroscopic rebalancing (or shift) of all earth's solid shells (e.g., entire mantle+lithosphere) towards the Equator relative to the more stable-oriented magnetic currents in the liquid core. This process is somewhat similar to the true polar wander concept, but it takes into account the spinning forces of the Earth. Mantle convection is considered as an important force, constantly driving the plates in the oceanic hemisphere and keeping the continental hemisphere intact. The periods of gyroscopic rebalancing correspond to the reassembly of the supercontinents at 2.7-2.5 Ga (Kenorland), 2.0-0.75 Ga (Columbia and its modification into Rodinia), and 0.32-0.18 Ga (Pangaea). The main reassembly mechanism, in addition to rifting, spreading and collision, is large-scale strike-slip translation of not only relatively small lithotectonic terranes, but also of major cratons. These cycles govern changes from the dominantly extension- to collision- and plume-related mineral deposit types in the internal orogens in the continental hemisphere, whereas subduction-related to collision-related mineral deposit types remain persistent through the metallogenic cycles at the oceanic/continental hemisphere transition zone, just migrating oceanward in time.