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On predicting mantle mushroom plumes

Geoscience Frontiers 2011年第2期2卷 223-235,235+233-234页

作者： Ka-Kheng Tan Rex B. Thorpe Zhidan Zhao Global Environment Centre HELP University College BZ-2 Pusat Bandar Damansara 50490 Kuala Lumpur Malaysia Department of Chemical and Process Engineering University of Surrey Guildford GU2 7XH U School of Earth Sciences and Resources China University of Geosciences Beijing 100083 China

This study investigates the mechanism of formation of convection plumes of mushroom shape in sub-solidus mantle and their prediction. The seismic-tomographic images of columnar structures of several hundreds kilometers in diameter have been reported by several researchers, while the much cherished mushroom-shaped plume heads could only be found in computational geodynamics （CGD） models and simple small-scale laboratory analogue simulations. Our theory of transient instability shows that the formation of convection plumes is preceded by the onset of convection caused by unsteady-state heat conduction at the boundaries, from which filamentous plumes first appear. The plumes generated at the Core Mantle Boundary （CMB） and lithosphere rising and falling through the mantle have been pre- dicted simply with our theory for various heat fluxes and viscosities, which still remain uncertain amongst geoscientists. The sizes of mushroom plumes in the sub-solidus mantle caused by heat fluxes of 20 and 120 mW/m2 at the CMB are found to be 1842 km and 1173 km with critical times over 825 Myr and 334 Myr respectively. They are comparable to some large continental flood basalt provinces, and they number between 17 and 41. The thickness of the thermal boundary layers at the CMB from which convection plumes evolved are found to be 652 km and 415 km for 20 and 120 mW/m^2 respectively. Top cooling may produce plunging plumes of diameter of 585 km and at least 195 Myr old. The number of cold plumes is estimated to be 569, which has not been observed by seismic tomograpby

关键词： Mantle mushroom plumesSizes critical times Transient Reynoldsnumber

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