RELATIONSHIP AMONG SUPERCONTINENT ASSEMBLY, SUPERPLUME EVENTS, AND SECULAR TRENDS IN VMS AND IRON FORMATIONS

Recurrent association in the Precambrian between superplume events and Iron Formation deposition has been known for some time (Isley and Abbott, 1995; Condie et al., 2001; Barley et al., 2005). Recently, their temporal relationship in the Precambrian and Phanerozoic with VMS deposits was also established (Bekker et al., 2010). The link is obvious: hydrothermal systems are more extensive, vigorous, reducing, and metal-rich during LIP emplacement. As a result, larger volumes of metals were released from volcanic rocks and vented to the ocean floor, where massive sulfide deposits formed; ocean redox state was lowered by enhanced flux of reductants (e.g., Fe, Mn, and H₂); and Fe with Mn were delivered by plumes to shallow-water settings where they precipitated forming iron- and manganese-rich sediments. However, peaks in tonnage of VMS deposits are typically also associated with time intervals when supercontinents were assembled since VMS mineralization hosted by bimodal volcanic rocks in back-arc basins has a higher preservation potential in the rock record. Considering that mantle plumes are relatively common throughout the Earth history, it remains uncertain why superplumes and associated mineralization are genetically linked with the early stages in the supercontinent assembly. The association is however striking and repetitive at ~2.74-2.69 Ga, 2.5-2.45 Ga, 2.05-2.06 Ga, 1.88 Ga, 1.1 Ga, and 0.5 Ga when Kenorland, Vaalbara, Nuna, Zimvaalbara-São Fransisco, Rodinia, and Gondwana supercontinents were assembled (cf., Huston et al., 2010). It is proposed herein that external ocean closure during the early stage of supercontinent amalgamation dramatically changed the heat budget of the mantle, leading to mantle overturn, superplume events, and eventually development of new mantle convection pattern. As a result, superplume-initiated rifting at the time when external oceans contracted allows for plate tectonics to persist without interruption in the aftermath of the supercontinent assembly.