Tham khảo tài liệu 'earth as an evolving planetary system part 8', khoa học tự nhiên, địa lý phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | The Supercontinent Cycle and Mantle-Plume Events 9 Introduction Supercontinents have aggregated and dispersed several times during geologic history although our geologic record of supercontinent cycles is only well documented for the last two cycles Gondwana-Pangea and Rodinia Hoffman 1989 Rogers 1996 . It is generally agreed that the supercontinent cycle is closely tied to mantle processes including both convection and mantle plumes. However the role that mantle plumes may play in fragmenting supercontinents is still debated. Condie 1998 and Isley and Abbott 1999 have presented arguments that mantleplume events have been important throughout the Earth s history and may account for the episodicity of continental growth as described in Chapter 8. Although the meaning of mantle-plume event varies in the scientific literature I shall constrain the term to refer to a short-lived mantle event 100 My during which many mantle plumes bombard the base of the lithosphere. During a mantle-plume event plume activity may be concentrated in one or more mantle upwellings as during the mid-Cretaceous mantle-plume event some 100 Ma when activity was focused mainly in the Pacific mantle upwelling. However as I have pointed out Condie 1998 Condie 2000 alleged Precambrian mantle-plume events at and Ga correlate with maxima in worldwide production rate of juvenile crust thus these events may not have been confined to one or two mantle upwellings. One of the first models presented to explain episodic continental growth was that of McCulloch and Bennett 1994 . They proposed a nonrecycling model involving three reservoirs continental crust depleted mantle and primitive mantle. It assumes that the volume of depleted mantle increases with time in a stepwise manner which is linked to major episodes of continental crust formation at and Ga. The isotopic and trace element composition of the upper mantle is buffered by the progressive extraction of continental crust and the
