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Published September 1995 | public
Book Section - Chapter

"Hotspots"; Uppermantle or Deep-Mantle Phenomena?

Abstract

Large igneous provinces (LIPs) such as continental flood basalt (CFB) and oceanic plateau basalt (OPB) provinces are usually attributed to the arrival of giant plume heads from deep mantle thermal plumes. Thermal instability in D" is the usually mentioned mechanism. The difficulties with this mechanism include the effects of internal heating, background mantle convection, upper mantle phase changes, pressure dependent thermodynamic properties (low a, high lattice conductivity in D"), cold downwellings and lack of a mechanism for fixing locations. In the mantle, upwellings are expected to be broad and to be seriously affected by both endothermic and exothermic phase changes, plate motions and by dense cold downwellings., The ability of the mantle to generate narrow, hot, low viscosity, fixed plumes, independent of plate motions and convection, has not been demonstrated. Furthermore, the chemistry of so-called hotspot or plume magmas does not favor a deep source, particularly one at the core-mantle boundary (D"). The strongest evidence against a plume origin in a thin layer in contact with the core is the high and chondritic siderophile chemistry of "plume" basalts. Other components of hotspot magmas are fairly convincingly due to recycled material (oceanic and continental sediments, dehydrated slab, slab fluids) of various ages. All of the chemical components of hotspot magmas are found in island arc magmas and xenoliths, suggesting that the enriched components of hotspots can be provided by the shallow mantle. In fact, it is difficult to conceive how any recycled material (sediments, altered oceanic crust components) can be carried beyond the dehydration, ecologitization fronts.

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© 1995 Elsevier Science B.V.

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August 20, 2023
Modified:
October 20, 2023