Morgan,J.P., Reston,T.J. and Ranero,C.R.(2004): Contemporaneous mass extinctions, continental flood basalts, and ‘impact signals’: are mantle plume-induced lithospheric gas explosions the causal link? Earth and Planetary Science Letters, 217, 263-284.


 Contemporaneous occurrences of the geologic signals of ‘large impacts’, craton-associated continental flood basalts, and mass extinctions have occurred far too often during the past 400 Myr to be plausibly attributed to random coincidence. While there is only a 1 in 8 chance that even one synchronous large impact within the interval of a continental flood basalt and mass extinction event should have happened during this period, there is now geologic evidence of four such ‘coincidences’, implying causal links between them. The 〜66 Ma (K-T) evidence suggests that impacts do not trigger flood basalts, since the Deccan flood basalt had started erupting well before the Chicxulub impact event. If extraterrestrial impacts do not trigger continental flood basalt volcanism, then we are really only left with two possible resolutions to the dilemma posed by these mega-coincidences: either the reported ‘impact signals’ at the times of great mass extinctions are spurious or misleading, or - somehow - a terrestrial process linked to continental rifting and the eruption of cratonic flood basalts is sometimes able to generate the shocked quartz, microspherules, and other geologic traces commonly attributed to large extraterrestrial impacts, while also triggering a mass extinction event. Here we explore a promising mechanistic link: a large explosive carbon-rich gas release event from cratonic lithosphere, triggered by mantle plume incubation beneath cratonic lithosphere, and typically associated with the onset phase of continental rifting. Sudden CO2/CO and SO2 release into the atmosphere would provide the primary killing mechanism of the induced extinction event. Such explosive deep-lithospheric blasts could create shock waves, cavitation, and mass jet formation within the venting region that could both create and transport a sufficiently large mass of shocked crust and mantle into globally dispersive super-stratospheric trajectories. We suggest these be called ‘Verneshot’ events.

Keywords: mass extinctions; flood basalts; large impacts; cryptoexplosions』

1. Introduction
2. Do two (or more) synchronous CFB/bolide impact events imply a causal link?
3. Can large bolide impacts initiate CFBs and their subsequent long-lived hotspot activity?
4. Do subcratonic mantle plumes cause ‘impact signals’ and CFBs?
5. Cratonic lithospheric gas explosions - the great extinctions' missing terrestrial link?
6. Carbon-rich plume melts can bring significant mantle carbon into cratonic lithosphere
7. Cratonic lithosphere incubation - a possible mechanism for CO2 buildup
8. Energetics of a large lithospheric gas explosion
9. Recognizing a preserved Verneshot pipe
10. Kimberlites - byproducts of ‘micro’-Verneshots?
11. Ecological effects of a Verneshot
12. Was the Chicxulub crater caused by the impact of a Verneshot mass jet?
13. Unresolved problems of the Verneshot hypothesis
14. Summary

Table 1. ‘Impact signals’ found at the four most recent great Phanerozoic mass extinctions and their interpretation in terms of the Verneshot hypothesis

Fig. 1. Known correlations between the timing of the five great Phanerozoic mass extinctions, CFBs, and the geologic ‘impact signals’ associated with these mass extinctions.

Fig. 2. Map of CFBs known to have occurred in the past 400 Myr and their present-day hotspot traces (where known). The Deccan Traps (K-T flood basalts, 〜66 Ma) are linked by a chain of volcanism to the presently active Reunion plume. The Central Atlantic Magmatic Province (CAMP) Traps (Tr-J, 〜201 Ma) in Guyana can be rotated back using Morgan’s [94] reconstruction for the opening of the Atlantic to the site of the present-day Trindade hotspot. Although poorly known this appears to be a fairly strong hotspot because it has recently created a chain of volcanism on old, 〜120 Ma, thick oceanic lithosphere. It is not known whether the Siberian Traps (P-Tr, 〜251 Ma) or Emeishan Traps (〜257 Ma) were created above any presently active hotspot. The Pripyat-Dniepr-Donets (FF, 〜364 Ma) CFB is an almost entirely buried structure with scarce surface outcrop. The spatial extent of almost all flood basalt provinces is likely to be underestimated because of their subsequent erosion above now high-standing cratons and burial beneath the rifting-related sedimentary basins to which their formation is closely tied. Stars show the sites of the Chicxulub (K-T), Siljan (〜FF), and Great Tunguska Depression (P-Tr) structures.

〔Morgan,J.P., Reston,T.J. and Ranero,C.R.(2004): Contemporaneous mass extinctions, continental flood basalts, and ‘impact signals’: are mantle plume-induced lithospheric gas explosions the causal link? Earth and Planetary Science Letters, 217, 263-284.から〕