The intensity, occurrence, and duration of superplume events and eras over geological time (in Superplume events in Earth history; causes and effects )

Journal of Geodynamics(September 2002), 34(2):265-307

Index Terms/Descriptors: basalts; dike swarms; dikes; flood basalts; geodynamics; igneous rocks; intrusions; layered intrusions; mafic magmas; magmas; magmatism; mantle plumes; Phanerozoic; Precambrian; superplumes; volcanic rocks

Abstract:

We define the characteristics of plume events that can be called superplumes. Using the surface area of the smallest oceanic plateau generated during the Cretaceous superplume era, we define a cutoff surface area for superplume flood basalts of > or =410,000 km ² . We show that the maximum widths of feeder dikes of plume lavas are linearly related to the square root of the surface area covered by their flood basalts. From this we derive a cutoff: the widest feeder dikes of a superplume event must be > or =70+ or -4 m wide. All high Mg rocks as defined by Isley and Abbott [J. Geol. (2001)] are superplume rocks. Layered intrusions formed by superplumes have either high abundances of platinum group elements and/or chromium. We use all of the data from the superplume proxies: flood basalts, dike swarms, high Mg rocks, and layered intrusions to define the duration of superplume eras over Earth history. Over two thirds of the superplume eras last less than 8 million years. We find no significant difference between the average duration of Archean (13+ or -7 Ma) and Phanerozoic (12+ or -3Ma) superplume eras. Finally, we use our data on maximum dike widths and flood basalt surface area to construct estimates of the overall surface area covered by lava during individual superplume events over the last 2.9 Ga. We find that the largest Precambrian superplume events erupted at least 10 times more lava than the largest Phanerozoic superplume event, covering a minimum of 14-18% of the planet. Between 1.7 and 2.9 Ga, there were enough large Precambrian superplume events to completely resurface the planet. We also find evidence for many superplume events earlier than 2.9 Ga, but due to a lack of data on maximum widths of feeder dikes, we cannot estimate the relative sizes of most of these events.