Abbott, D.H. & Isley, A.E. 2002. the Intensity, Occurrence, And Duration of Superplume Events and Eras Over Geological Time

The intensity, occurrence, and duration ofsuperplume events and eras over geological time

Dallas H. Abbotta,*, Ann E. Isleyb

aLamont-Doherty Earth Observatory, Palisades, NY 10964, USAbDepartment of Earth Sciences, State University of New York at Oswego, Oswego, NY 13126, USA

Abstract

We define the characteristics of plume events that can be called superplumes. Using the surface area ofthe smallest oceanic plateau generated during the Cretaceous superplume era, we define a cutoff surfacearea for superplume flood basalts of5410,000 km2. We show that the maximum widths of feeder dikes ofplume lavas are linearly related to the square root of the surface area covered by their flood basalts. Fromthis we derive a cutoff: the widest feeder dikes of a superplume event must be570�4 m wide. All high Mgrocks as defined by Isley and Abbott [J. Geol. (2001)] are superplume rocks. Layered intrusions formed bysuperplumes have either high abundances of platinum group elements and/or chromium. We use all of thedata from the superplume proxies: flood basalts, dike swarms, high Mg rocks, and layered intrusions todefine the duration of superplume eras over Earth history. Over two thirds of the superplume eras last lessthan 8 million years. We find no significant difference between the average duration of Archean (13�7 Ma)and Phanerozoic (12�3Ma) superplume eras. Finally, we use our data on maximum dike widths and floodbasalt surface area to construct estimates of the overall surface area covered by lava during individualsuperplume events over the last 2.9 Ga. We find that the largest Precambrian superplume events erupted atleast 10 times more lava than the largest Phanerozoic superplume event, covering a minimum of 14–18% ofthe planet. Between 1.7 and 2.9 Ga, there were enough large Precambrian superplume events to completelyresurface the planet. We also find evidence for many superplume events earlier than 2.9 Ga, but due to alack of data on maximum widths of feeder dikes, we cannot estimate the relative sizes of most of theseevents.# 2002 Elsevier Science Ltd. All rights reserved.

0264-3707/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.

PI I : S0264-3707(02 )00024-8

Journal of Geodynamics 34 (2002) 265–307

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* Corresponding author. Fax: +1-914-365-8156.

E-mail address: [email protected] (D.H. Abbott).

1. Introduction

We know that the interior of the early Earth had a higher content of radioactive elements. As aresult, the core and mantle were hotter and melted more extensively. Our samples of these highdegree melts are komatiites and other high Mg rocks (Arndt and Nisbet, 1982; Isley and Abbott,2002). Previously, we have shown that these high degree melts had potential temperatures thatdecayed exponentially over time (Abbott et al., 1994), with a decay rate like that predicted inde-pendently from the radioactive element contents of chondritic meteorites (Wasserburg et al.,1964). Overall, the potential temperatures of high Mg rocks (and concurrent mid-ocean ridge typebasalts) have declined about 170�20 �C since the middle Archean (Galer and Metzger, 1998).During the late Phanerozoic, we know that the extrusion of high Mg rocks (e.g. Gorgona andTortugal komatiites) occurred concurrently with greatly increased production of tholeiitic basaltin the form of oceanic plateaus and massive flood basalts (e.g. Caribbean-Columbian province).(Kerr et al., 1996a,b) These episodes of increased production of basaltic extrusives have beendubbed superplumes (Larson, 1991). In between superplumes, the rate of basalt productiondeclines and very few if any high Mg rocks are extruded Plume activity does continue duringthese times, but the plumes are not superplumes. Because the liquidus temperatures of Archeanhigh Mg rocks were much greater than those of the known Phanerozoic high Mg rocks, theaverage degree of melting of the mantle must have been greater. It follows that the volume ofextrusives generated during Archean plume and superplume events must also have been greater.The difficulties lie in using the preserved rock record to quantify the difference in volume and todistinguish between normal plume activity and superplumes.The rock record is by nature incomplete. Oceanic plateaus may be subducted or disaggregated.Continental flood basalts, their feeder dikes, and even their underlying magma chambers may beeroded or deformed. Nonetheless, certain proxies have proven useful in delineating mantle plumeevents (Larson 1991; Ernst and Buchan 1997a,b, 2001). We have previously defined four proxiesof mantle plume activity: komatiites, flood basalts, massive mafic dike swarms and layeredigneous intrusions (Isley and Abbott, 1999). We determined that komatiites are the most robustindicators of the global plume activity that is characteristic of superplumes. We have morerecently suggested that other high-Mg igneous rocks (including meimechites, and some picritesand ankaramites) are the Phanerozoic equivalents of komatiites, and serve as equally strongindicators of global mantle plume volcanism (Isley and Abbott, 2002).However, other plume proxies have yielded more equivocal results. Some Precambrian basaltsequences that lack high-Mg units are of limited areal extent yet have been interpreted as floodbasalts (e.g. the ca. 2.0 Ga. Mugford Group; Barton, 1975). Likewise, there are mafic dikes ofsuch limited areal extent that it is difficult to see how they could have served as feeders to con-tinental flood basalts. While extremely large dike swarms like the Matachewan or CentralAtlantic dikes are suggestive of superplume origin (Ernst and Buchan, 1997a; Heaman, 1997),what areal extent a dike swarm must have to be considered ‘‘massiveø is unclear. Further, manylayered igneous intrusions are emplaced in orogenic provinces, and are unrelated to plume vol-canism. In this paper, we attempt to define the subsets of dikes, flood basalts and layered igneousintrusions that are characteristic of superplume events. We then compile a time-series of indivi-dual superplume events and use it to evaluate which times during Earth history were character-ized by many individual superplume events, thus defining a superplume era.

266 D.H. Abbott, A.E. Isley / Journal of Geodynamics 34 (2002) 265–307

2. Plumes, superplumes events and superplume eras: the importance of the difference

Mantle plumes (or hotspots) were discovered by identifying areas of unusual volcanism thatwere not produced by the dewatering or melting of downgoing plates (Morgan, 1978; Crough,1983). The present-day areas of plume volcanism are sprinkled over the planet, with over 20acknowledged active mantle plumes (Molnar and Stock, 1987; Sleep, 1990). In the ocean basins,ordinary plumes produce hotspot island chains. On land, ordinary plumes produce areas of floodbasalts (e.g. Yellowstone hotspot) or volcanic fields (e.g. Raton hotspot) (Simkin and Siebert,1994).At times, ordinary plumes have order of magnitude increases in their volcanic extrusion rate perunit time (Duncan and Pyle, 1988; Renne, 1995; Hames et al., 2000). These tremendous increasesin volcanic volume result in the production of massive flood basalts, massive dike swarms, andoceanic plateaus. The driving forces for these transitions in plume activity are not known. Somesuggest that large meteorite impacts might trigger such changes (Boslough, 1996; Hagstrom,2000). Others suggest that plume initiation events produce most oceanic plateaus or massive floodbasalts (Richards et al., 1991). Although most ordinary plumes do begin with the formation of alarge igneous province, some large igneous provinces (e.g. Deccan) have formed from ordinaryplumes that suddenly became more active (Bhandari et al., 1993; Courtillot et al., 2000). Thus, thesuperplume/ordinary plume transition can occur at any time in the life of a plume.When many superplume events occur in a short geological period, they constitute a superplumeera. Because they produce massive volumes of basalt in the form of oceanic plateaus and floodbasalts, superplume eras have produced major episodes of continental growth and continentalrifting (White and MacKenzie, 1989; Stein and Hofmann, 1994; Abbott and Mooney, 1995; Steinand Goldstein, 1996). For example, the largest and thickest oceanic plateaus produced by theCretaceous superplume era are unsubductable and constitute new continental blocks (Abbott etal., 1997). A superplume at �202 Ma produced the Central Atlantic Magmatic Province(CAMP) (Sebai et al., 1991; Hames et al., 2000). During the extrusion of the CAMP lavas, a largetriple junction formed that eventually resulted in the divergence of three continental blocks:Africa/Europe, North America, and South America (Ernst and Buchan, 1997a; Marzoli et al.,1999). Thus, superplume events and eras are major drivers of tectonic change on the Earth, bothby building and by disaggregating continents (Condie et al., 2001).Despite the importance of the difference between superplumes and ordinary plumes, the presentmethods of distinguishing between superplumes and ordinary plumes are quite nebulous. Condie(2001) has made a start by defining superplumes as plume heads with a diameter of between 1500and 3000-km. In terms of eruptive volume, he defines superplumes as those producing an eruptivevolume of 5�106 km3 or greater (Condie, 2001). The problem is that both of these definitions arevery difficult to apply to the eroded remnants from ancient plumes. What really constitutes mas-sive flood basalt as opposed to the basalt fields produced by ordinary plumes? How can weidentify events that are distinguished by large increases in igneous extrusion rate as we go back intime and the accuracy of geochronology decreases? When is a dike swarm a massive swarm asopposed to being a simple dike swarm? All of the above methods of distinguishing plumes fromsuperplumes are exceedingly difficult to apply in Precambrian rocks, where the crust is erodedand deformed. We need more quantitative methods of distinguishing superplume events fromplume events, methods that can distinguish superplumes from ordinary plumes using spatially

D.H. Abbott, A.E. Isley / Journal of Geodynamics 34 (2002) 265–307 267

restricted samples. Isley and Abbott (2002) have developed one such method, by defining highMg rocks as characteristic of superplume events. In the following sections, we define more suchquantitative methods.

3. Flood basalts: minimum size indicative of a superplume event

The recent Cretaceous superplume era was characterized by the formation of numerous oceanicplateaus; ten of these have been well dated (Table 1). We assume that the size of the smallest, theWallaby Plateau, 4.1 � 105 km2, is the lower limit for superplume-generated flood basalt pro-vinces. Based on the distribution of high-Mg rocks in flood basalt sequences of known size, weinfer that this is a conservative approach. Neither the Rajmahal flood basalts nor the ColumbiaRiver traps—both of which have areal extents smaller than theWallaby Plateau (Table 2)—containunits with high-Mg character. The total volume of the Columbia River flood basalts is 1.75�105

km3 (Tolan et al., 1989), below the threshold for superplume lava volume proposed by Condie(2001). In comparison, the Caribbean-Columbian basalt province has a surface area of 1,860,000km2, and it contains the Tortugal komatiites (Costa Rica), the Gorgona island komatiites, andthe Curacao picrites (Isley and Abbott, 2002). The North Atlantic basaltic province has an areaof 1,300,000 km2 and contains both picrites and meimechites within parts of Greenland. TheIcelandic plateau covers 800,000 km2, and there are ankaramites on Iceland (Pegram and Allegre,1992). The Caribbean-Columbian, the North Atlantic and the Icelandic provinces all have totallava volumes in excess of 5�105 km3, and thus would fit the definition of a superplume provinceproposed by Condie (2001). Thus, the Phanerozoic data support the decision to consider onlythose flood basalts provinces over 410,000 km2 in area as superplume-generated.Because recent sequences of flood basalts have relatively little erosion compared to ancientones, the original surface areas of recent flood basalt terrains are comparatively well known.However, because of long-term erosion, the present-day outcrop of ancient flood basalts repre-sents only a fraction of their original areal extent. Therefore, we must calculate their original areafrom the remaining outcrop area. We use an erosion correction that was originally developed for

Table 1Cretaceous superplume igneous provinces

Province name Average age (Ma) Error (Ma) Surface area (km2)

Madagascar basalts 87.55 3.8 1 050 000

Rio Grande Rise 88 1 1 670 000Broken Ridge+Naturaliste Plateau 91 2 1 020 000Venezuelan-Colombian Basin 100 20 1 860 000Kerguelen Plateau 100.5 11.5 1 540 000

Hess Rise 107.5 12.5 800 000Alpha Ridge oceanic plateau 111 20 1 650 000Manihiki Plateau 118.5 6.5 1 210 000

Wallaby Plateau 118.5 6.5 410 000Ontong Java Plateau 122.15 3.2 1 860 000


cratonic rocks (Veizer and Jansen, 1985; Condie et al., 2001). The original surface area (Ao) of aflood basalt province is given by the following equation:

Ao ¼ A=e�kT; ð1Þ

where A is the present day surface area, T is time in million years, and k is a decay constant of9.9021E-4 (derived from Condie et al. 2001). If the original surface area of a flood basalt provinceis calculated to be less than 410,000 km2, the flood basalt is not included in our list of superplumegenerated flood basalts (Table 3).Half of the recent flood basalt sequences that we are assuming represent mantle superplumeactivity contain units with rocks containing > 18 wt.% MgO (cf., Isley and Abbott, 2002). Onequarter of the flood basalt sequences are part of an oceanic feature and cannot easily be subjectedto the same sort of scrutiny as continental sequences. Because high-Mg units typically comprise<10% of the total volume of a continental flood basalt (Francis and Hynes, 1979), it is not sur-prising that such units are not known from the oceanic plateaus listed in Tables 1 and 2. There istherefore a generally good agreement between the high-Mg record and the flood basalts that weinfer are proxies of mantle superplume activity.

4. Mafic dikes: minimum size indicative of a superplume event

As a flood basalt province is eroded, its feeder dikes and magma chamber are exposed at thesurface. In ancient terrains, only the feeder dikes and/or magma chamber are left. For example,the Great Dike and satellites of Zimbabwe represent a combination of a layered intrusion (elon-gated magma chamber) and the remnants of a massive dike swarm (Podmore and Wilson, 1987;Ernst and Buchan, 1997b). The edges of this dike swarm have been lost due to lateral erosion anddeformation of the Zimbabwe craton. The problem lies in using the characteristics of the feederdikes to infer whether or not an ordinary plume or a superplume produced the eroded floodbasalt province.

Table 2Large igneous provinces with both mapped feeder dikes and a known value of original surface area of flood basalts

Name Maximumdike width,m

Originalsurface area,km2

References

Deccan province >100 1.50E+06 Karkare and Srivastava, 1990Central Atlantic province 300 7.00E+06 Oliveria et al., 1990; Marzoli et al., 1999Columbia River province 40 1.64E+05 Hooper, 1997

Harrat Hadan 10 5.04E+03 Sebai et al., 1991Parana-Serra Geral and Etendeka 150 1.28E+06 Peate, 1997; Erlank et al., 1984Rajmahal 8 4.10E+03 Kent et al., 1997

Iceland >60 8.60E+05 Gudmundsson, 1990; Schubert and Sandwell, 1989


Table 3Superplume Type Flood Basalt Provinces

Name Location Age Error Surface

area

Reference

age

Reference

width/area

Iceland North Atlantic 7.5 7.5 8.00E+05 Saunders et al., 1997 Schubert and Sandwell, 1989

Rockall Plateau N. Atlantic 57.5 2 6.70E+05 Sinton and Duncan, 1998 Schubert and Sandwell, 1989North AtlanticIgneous Province

N. Atlantic border 59.55 2 1.30E+06 Saunders et al., 1997 Eldholm and Grue, 1994

Deccan Traps India 61.45 4.6 8.00E+05 Baksi, 1994 Duncan and Pyle, 1988

Madagascar basalts(Manajary bas. Kom)

Madagascar 87.55 3.8 1.60E+06 Storey et al., 1997 Ernst and Buchan, 2001

Rio Grande Rise S. Atlantic 88 1 1.67E+06 Schubert and Sandwell, 1989 Schubert and Sandwell, 1989

Broken Ridge Indian Ocean 91 2 5.10E+05 Schubert and Sandwell, 1989 Schubert and Sandwell, 1989Venezuelan-ColombianBasin picrites

Carribbean 100 20 1.86E+06 Schubert and Sandwell, 1989 Schubert and Sandwell, 1989

Kerguelen Plateau Indian Ocean 100.5 11.5 1.54E+06 Schubert and Sandwell, 1989 Schubert and Sandwell, 1989Hess Rise Pacific Ocean 107.5 12.5 8.00E+05 Schubert and Sandwell, 1989 Schubert and Sandwell, 1989Alpha Ridge oceanic plateau Arctic Ocean 111 20 1.65E+06 Embry and Osadetz, 1988 Schubert and Sandwell, 1989Manihiki Plateau Pacific Ocean 118.5 6.5 1.21E+06 Schubert and Sandwell, 1989 Schubert and Sandwell, 1989

Wallaby Plateau Indian Ocean 118.5 6.5 4.10E+05 Schubert and Sandwell, 1989 Schubert and Sandwell, 1989Ontong Java Plateau Pacific Ocean 122.15 3.2 1.86E+06 Coffin and Eldholm, 1994 Schubert and Sandwell, 1989Parana-Serra Geral

and Etendeka

S. America/Africa 128.75 2.8 1.20E+06 Renne et al., 1996a Peate, 1997

Parana-Serra Geraland Etendeka

S. America/Africa 131.35 8.4 1.20E+06 Renne et al., 1996b,Turner et al., 1994

Peate, 1997

Shatsky Rise Pacific Ocean 140 10 1.24E+06 Schubert and Sandwell, 1989 Schubert and Sandwell, 1989Magellan Rise Pacific Ocean 145 5 5.40E+05 Schubert and Sandwell, 1989 Schubert and Sandwell, 1989Ferrar Dolerite Sills Antarctica 183.6 1 4.50E+05 Encarnacion et al., 1996 Fleming et al., 1997

Karoo Province (Lembobo(Letaba) picrites)

Africa 183.7 0.6 2.20E+06 Encarnacion et al., 1996 Marsh et al., 1997

Newark SGp, Merdian Gp N. America 198.5 3.5 7.00E+06 Philpotts, 1998 Ernst and Buchan, 2001Siberian Traps (Bottom 90%) Asia 252.15 3.8 3.40E+05 Renne et al., 1995;

Basu et al., 1995

Sharma, 1997

(continued on next page)

270

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/JournalofGeodynamics34(2002)265–307

Table 3 (continued)

Name Location Age Error Surface

area

Reference

age

Reference

width/area

Emeishan-Song Da-JinpingFlood Basalts (has picrites)

Asia 254.9 5.1 2.50E+05 Chung et al., 1998 Chung et al., 1998

East European Craton Europe 368.75 10.75 3.00E+06 Ernst and Buchan, 2001 Ernst and Buchan, 2001Antrim Plateau Basalts Australia 531.5 18.5 4.50E+05 Bultitude, 1976 Ernst and Buchan, 2001Franklin Sills N. America 724 3 1.27E+05 Heaman et al., 1992 Robertson and Baragar, 1972

Hottah McKenzie mt(inferred from dikes)

N. America 779 2 500000 LeCheminant andHeaman, 1994

LeCheminant andHeaman, 1994

Willouran Volcanics Australia 827 6 2.10E+05 Wingate and Giddings, 2000 Hilyard, 1990

Keweenawan Basalts N. America 1097.7 12.1 1.60E+05 Davis and Paces, 1990,Davis and Green, 1997

Ernst and Buchan, 2001

Umkondo Dolerite FB Africa 1104.7 2.3 2.00E+06 Hanson et al., 1998 Hanson et al., 1998

Coppermine River Basalts N. America 1270 4 2.00E+06 LeCheminant andHeaman, 1989a,b

LeCheminant andHeaman, 1989a,b

Nauyat Plateau Basalt,Mackenzie

N. America 1277 18 2.00E+06 LeCheminant andHeaman, 1989a,b

LeCheminant andHeaman, 1989a,b

Onega Plateau Europe 1975 24 6.00E+06 Puchtel et al., 1999 Puchtel et al., 1999Birrimian thoeliites-Tehini belt Africa 2183.7 6.7 1.26E+04 Hirdes and Davis, 1998 Hirdes and Davis, 1998Nippising diabase flood basalt N. America 2219.05 3.6 4.50E+04 Condie et al., 1987 Buchan et al., 1996

Karelian SGp Sumi-Sariola Gp Baltica 2441.8 1.7 1.00E+04 Amelin et al., 1995 Puchtel et al., 1996Imandra-Varzuga (Strelna) Baltica 2442.8 4.8 1.00E+04 Amelin et al., 1995 Amelin et al., 1995Rampur Flood Basalts

(Gharwar-Mandi)

India 2486 69 1.70E+05 Bhat et al., 1998 Bhat et al., 1998

Klipriveersberg Floodbasalt-Ventersdorp SG

Kaapvaal 2713.3 8.3 2.10E+05 Wingate, 1998 Wingate, 1998

Fortescue-Kylena Pilbara 2725 45 1.12E+05 Wingate, 1998 Blake, 1993

Fortescue-Mt. Roe FB Pilbara 2772 2 1.12E+05 Wingate, 1998 Blake, 1993Derdepoort Flood Basalts Kaapvaal 2782 5 1.00E+04 Wingate, 1998 Wingate, 1998



271

The map area of feeder dike outcrops might be one indicator, but we know from studies of theColumbia River basalts that the map area of the feeder dikes is much less than the map areacovered by basalt flows (Hooper, 1982, 1997). So, the map area of ancient feeder dikes can onlygive, at best, a lower limit on the former areal extent of the flood basalts.Finally, in very old cratons, the small surface areas of the surviving cratons themselves limit ourability to calculate an original extent of plume activity. Cratons are artifacts of the tectonic pro-cesses that formed them and surrounded them with younger, deformed rocks. Their sizes con-stitute an artificial limit on the calculation of dike swarm area and original areal extent of floodbasalt provinces. Additionally, the total surface area covered by dikes is not only poorly pre-served, but what is preserved is usually highly metamorphosed and deformed. So it is necessary tofind another characteristic which may be correlated with areal extent.Theoretical calculations of the total volume of magma passed through a dike (per unit dikeheight) as a function of the dike width at the Earth’s surface shows a nearly linear relationshipbetween the square of dike width and the total magma volume (Fialko and Rubin, 1999). That is,for dikes with widths in excess of about 10 m, the total volume of magma discharged per unit ofdike height (this has units of surface area) ranges from roughly 100 km2 for a dike 10 m wide to10,000 km2 for a dike 100 m wide. This relationship means that a 100-m wide dike has a magmatransport rate that is 100 times the magma transport rate of a 10-m wide dike. Thus, in any givendike swarm, the widest dikes are by far the most important in transporting magma.Erupting flood basalts have very low viscosities and spread out over wide areas, covering hun-dreds of square kilometers in short periods of time. Thus, it has been observed that flood basaltsshow only a small variation in thickness over large areas (Coffin and Eldholm, 1994; Encarnacionet al., 1996; Hooper, 1997). It is reasonable to infer, therefore, that total magma volume and totalsurface area covered are closely related variables. If we could show that total surface area of theflood basalt, S, is equal to some constant A times the square of the maximum dike width, W, wecould then estimate the surface area covered by long eroded flood basalt events. We could furtheruse the maximum widths of the largest feeder dikes to evaluate which past flood basalt eventswere generated by ‘‘normal’’ plume activity and which were generated by superplume activity.It is very difficult at this time to assemble sufficiently reliable data on the areal extent of floodbasalts and the maximum width of their feeder dikes. We have been able to identify just fivePhanerozoic plume and superplume events (Table 2) with accurate data on maximum dike widthand flood basalt area: (1) the Parana-Serra Geral and Etendeka flood basalts of South Americaand West Africa; (2) the Columbia River flood basalts of the northwestern US; (3) the HarratHadan in Ethiopia; (4) the Rajmahal Traps of India; and (5) the Central Atlantic MagmaticProvince (CAMP). (Note that the surface areas listed are the total surface areas covered by floodbasalts before any continental rifting took place.) Data for Iceland and the Deccan Traps are alsolisted in Table 2, but the dike widths for these terrains are not well constrained. Another sequenceof flood basalts, the Ferrar-Karoo Province of South Africa and Antarctica, is not listed becauseit is partly buried under the Antarctic ice cap, so neither dike widths nor total surface area arewell-known.To test for a possible relationship between the maximum dike width and the areal extent of aflood basalt province, we plotted the maximum dike width in each terrain versus the corre-sponding square root of the surface area of flood basalt. Fig. 1 shows that there is a very stronglinear correlation between the two variables, with an R2 value of 0.99 for the correlation. The


relationship is linear for all maximum dike widths in our data set, which range from 8 m wide to300 m wide. To derive our empirical relationships, we made two ‘‘least squares’’ fits to the data,reversing the dependent and independent variables. From our line fits, we were able to derive twosimple predictive equations. The first equation calculates total surface area (A) from the max-imum width (W) of the feeder dikes:

A ¼ 9:0826W2 ð2Þ

The error in the slope of Eq. (2) is �0.527.Conversely, a second least squares fit predicts maximum feeder dike width from the floodbasalts total surface area, so that

W ¼ 0:1093 Að Þ1=2: ð3Þ

The error in the slope of Eq. (3) is �6.67E-3.We can test these relations using the partial data from the other basalt provinces in Table 2.For example, we do not know the maximum width of the Deccan feeder dikes; although it isknown that the widest mapped feeder dikes are over 100 m in width. We use Eq. (3) and the totalsurface area of the Deccan traps (1,500,000 km2) to calculate a maximum dike width of 134�8 m.For the Wallaby plateau, the smallest superplume-generated plateau in Table 1, the equation

Fig. 1. Maximum feeder dike width (meters) versus square root of total surface area (km) covered by flood basalts.Data points: squares. Best-fit line is fit by least squares with a forced zero intercept. Data used to make this plot is in

Table 2.


predicts a maximum dike width of 70�4 m. We therefore assume that superplume activity gen-erates dikes having widths in excess of 70 m (Table 4). Dike swarms with maximum feeder dikewidths less than 70 m are categorized as belonging to ‘‘normal’’ plume events. This definition fitswith the small amount of data listed in Table 2. The Columbia River ‘‘normal’’ plume producedmaximum dike widths of 40 m, consistent with our empirical prediction, while the superplume-generated Deccan traps are known to have dike widths wider than 100 m, consistent with ourdefinition of a superplume event. As better field data for the characteristics of Phanerozoicflood basalt provinces become available in the future, we will be able to refine our boundaryvalues.

5. Superplume layered intrusions

In terranes with high pressure metamorphic rocks exposed at the surface, the dike swarms areeroded and often removed. For example, the areas of the Canadian Shield with granulite faciesrock at the surface have far fewer dike swarms that the adjacent lower grade regions (Fahrig andWest, 1987; Halls, 1987). In the granulite regions, the only remnant of a superplume event may bethe lower part of a magma chamber that fed the eroded dikes. These solidified magma chambersconstitute mafic and ultramafic layered intrusions. The problem is how to differentiate betweenlayered intrusions generated by superplumes and those generated by some other process.The size of a layered intrusion is not a good indicator of the plume magnitude. Instead, the sizesof layered intrusions appear to be dependent on crustal and tectonic factors not necessarily rela-ted to the plume itself. For example, the Rhum intrusion on the isle of Rhum off the coast ofScotland was emplaced during the North Atlantic superplume event. The Rhum intrusion coversan area of only 30 km2 (Hamilton et al., 1998). A much larger feature, the 48.8 Ma Kap EdvardHolm layered intrusion, on the east coast of Greenland, covers 360 km2; but with an age of 48.8Ma, it is too young to have been formed by the North Atlantic superplume (Tegner et al., 1998).Thus, superplumes do not necessarily produce larger intrusions and ‘‘normal’’ plumes do notnecessarily produce smaller intrusions.Superplumes are associated with increased melting in the mantle, so intrusions formed by themwould be expected to have a different mineralogy than those formed by ‘‘normal’’ plumes. Inparticular, we would expect them to have high concentrations of compatible elements such as Crand the platinum group elements (PGEs). The primary magmas, as they crystallized in theintrusion, would be expected to form layers of chromitite or layers enriched in PGEs. The ‘‘GreatDike’’ of Rhodesia, for example, contains extensive chromium deposits (Guilbert and Park,1986).We know that the small Rhum intrusion was formed by a superplume event and therefore wewould expect to find Cr and PGE enrichments. In fact, the Rhum intrusion does contain small,well-defined chromite layers (Hamilton et al., 1998). However, the much bigger Kap EdvardHolm layered intrusion, known to be unrelated to a superplume event, is not enriched in Cr orPGEs and has no chromite layers (Tegner et al., 1998). Other small intrusions along the westcoast of Scotland and east coast of Greenland, known to have been produced by the NorthAtlantic superplume, such as the one on the Isle of Mull and the Skaergaard intrusion, alsocontain chromite and/or show PGE enrichment (Guilbert and Park, 1986).


Table 4Superplume dike swarms

Name Region Width,

m

Age Error Reference

age

Reference:

maximum dike width

Iceland North Atlantic >60 7.5 7.5 Saunders et al., 1997 Gudmundsson, 1990

Peary Land dike swarm Greenland 200 66 6.6 Dawes and Soper, 1971 Nielsen, 1987

Deccan dikes India >100 66.5 4.3 Bhattacharji et al., 1996 Bhattacharji et al., 1996

Parana dikes Brazil 100 132.5 5 Peate, 1997 Druecker and Gay, 1987

Central Atlantic Dike Swarm North America 250 201 2 Dunning and Hodych, 1990 Oliveria et al., 1990

Messejana Dike Spain 300 203 2 Dunn et al., 1998 Dunn et al., 1998

Shelborne Dike Nova Scotia 180 203 2 Dunn et al., 1998 Papezik and Barr, 1981

St Malo dike Swarm Europe 100? 330 10 Aifa et al., 1999 Aifa et al., 1999

Chara Sinsk Dikes Europe 200 377.5 19.5 Tomshin and Koroleva, 1990 Tomshin and Koroleva, 1990

Grenville Dikes Canada 100 590.5 1.5 Kamo et al., 1995 Seymour and Kumarapeli, 1995

Thule dikes Greenland 100 682 25 Dawes and Rex, 1986 Nielsen, 1987

Ganna Kouriep mafic dikes Africa 100* 717 11 Reid et al., 1991 Hunter and Reid, 1987

Borden diabase dikes

(Franklin)

North America 250 724 4 Heaman et al., 1992 Christie and Fahrig,1983

Mundine well dike swarm Australia >300 755 3 Wingate and Giddings, 2000 Wingate and Giddings, 2000

Gairdner Dike Swarm Australia >100 ? 840.5 73.5 Zhao and McCulloch, 1993 Zhao and McCulloch, 1993

Bistjarvi-Laanila diabase dikes Baltica 200 1036.5 55.5 Mertanen et al., 1996 Mertanen et al., 1996

Champ de Mers Australia 130 1058 14 Glikson et al., 1996 Sheraton and Sun, 1997

Guruve Swarm/Deweras dike Zimbabwe 100 1100 270 Hahn et al., 1991 Wilson et al., 1987

Pidgeon river dikes (Logan sill) Canada 500 1110 3 Krogh et al., 1984 Green et al., 1987

Abitibi Dykes Canada 250 1140.6 2 Condie et al., 1987 Ernst et al., 1987

Gardar Giant Dikes-Tugtutoq Greenland 800 1154 16 Upton et al., 1995 Upton and Emeleus,1987

Sundsjo dike Europe 250 1213 18 Patchett, 1978 Patchett, 1978

Sudbury Dikes Canada 100 1238.5 4 Dudas et al., 1994 Condie et al., 1987

Gardar Giant Dikes-older Greenland 200 1259.5 56.5 Patchett, 1978 Upton and Emeleus,1987

Market dolerite Europe 700 1260 10 Suominen, 1991 Suominen, 1991

Muskox Intrusion dikes

(MacKenzie)

Canada 400 1270 4 Barnes and Francis, 1995 Ernst and Buchan, 1997a,b

Harp dolerite dikes/Reid Brook

Intrusion

Canada 400 1277 3 MacKay, 1994 Cadman et al., 1993

Pilanesberg dikes swarm Africa >75 1330 80 Hunter and Reid, 1987 Emerman, 1991

Hallefors dike Europe 1000 1518 38 Patchett, 1978 Aberg and Lopez Montano, 1986

Breven giant dike Europe 1000 1545 26 Patchett, 1978 Wikstrom, 1985

Aland-Aboland dike swarm

(Korso, Foglo)

Europe 400 1558.5 30.5 Suominen, 1991 Lindberg and Eklund, 1990




275

Table 4 (continued)

Name Region Width,

m

Age Error Reference

age

Reference:

maximum dike width

Melville Bugt Dike Swarm Greenland 500 1645 35 Kalsbeek and Taylor, 1986 Nielsen, 1987

Hame olivine dolerite

dikes Ansio

Europe 1000 1646 6 Ramo and Siivola, 1991 Airo, 1999

Tiruvannamali dike

swarm Dharwar

India 100 1650 10 Radhakrishna et al., 1999 Radhakrishna and Joseph, 1996

Hame olivine dolerite

dikes Virmala

Europe 1000 1667 8 Ramo, 1991 Airo, 1999

Dharwar, dolerite-gabbro-

norite, dikes

India 80 1668 31 Radhakrishna and Joseph, 1996 Panganamentula, 1994

Avanavero feeder dikes

(Roraima)

Guiana 51000 1670 28 Teixeira et al., 1998 Gibbs, 1987

Oenpelli dolerite dikes Australia 200 1690 10 Page et al., 1980 Parker et al., 1987

Uruguayan Dikes Rio de la Plata 80 1726 11 Teixeira et al., 1999 Teixeira et al., 1999

Zyzdal-Zalesskaya Dike

Korosten

Europe 51000 1758.8 0.9 Amelin et al., 1993 Shatalov, 1991

Avanavero Suite Sills

(Roraima intrusives)

Guiana 500 1789 2 Norcross et al., 1998 Gibbs, 1987

Dharmapuri dikes India 100 1822 42 Radhakrishna et al., 1999 Radhakrishna and Joseph, 1996

Cuthbert Dikes (younger

Molson) some komatiitic

Superior 120 1882.8 2.3 Heaman et al., 1986 Zhai et al., 1994

Avayalik dikes North America

(Labrador)

>200 1890.5 2.5 Scott and Machado, 1994 Bridgewater et al., 1995

Kennedy dike swarm North America >100 2010 10 Chamberlain et al., 1997 Chamberlain, 2000,written comm.

Lac de Gras dikes Slave >100 2026.5 3.5 LeCheminant et al., 1995 LeCheminant et al., 1995

Kangamuit younger dikes Greenland 100 2039.5 1.5 Nutman et al., 1999 Nielsen, 1987

Ft. Frances, diabase dikes Superior 100* 2076.5 4.5 Hanes et al., 1994 Buchan et al., 1996

Kovero-Koli dikes

(Fe tholeiites)

Europe 100 2113 4 Pekkarinen, 1979;

Pekkarinen

and Lukkarinen, 1991

Nykanen et al., 1994

Marathon diabase, Superior 100* 2114.5 10.5 Buchan et al., 1996 Buchan et al., 1996

Kenora-Kabetogama

komatiitic dikes

Superior 120 2120 67 Beck and Murthy, 1982 Halls, 1987

Pippolanmaki-Kutsu dikes Europe >100 2123 10 Pekkarinen and

Lukkarinen, 1991

Pekkarinen andLukkarinen, 1991

Cauchon (older Molson)-some

komatiitic

Superior 120 2145 25 Heaman et al., 1996a Zhai et al., 1994


276



Table 4 (continued)

Name Region Width,

m

Age Error Reference

age

Reference:

maximum dike width

Biscotasing, qtz. th. dikes Superior 250 2166.7 1.4 Condie et al., 1987 Buchan et al., 1999

Wyoming, Bighorn II Wyoming 150 2200 35 Stueber et al., 1976 Stueber et al., 1976

Klotz basic dikes Superior 100 2209 2 Buchan et al., 1998 Buchan et al., 1998

Sukkertoppen dikes (Pakitsoq,

Sister dikes)

Greenland 200 2214 10 Nutman et al., 1995 Bridgewater et al., 1974

Senneterre, quartz thol., Superior 100 2214.3 12.4 Buchan et al., 1993 Buchan et al., 1993

Kikkertavik Dike Swarm Canada 400 2235 2 Cadman et al., 1993 Cadman et al., 1993

Antarctica, Vestfold Hills II,

high-Mg norites

Antarctica 100 2238 7 Lanyon et al., 1993 Hoek and Seta, 1995

Binneringie/Jimberlana dikes

(Celebration dike/

Widgiemoltha swarm)

Yilgarn 51000 2410.4 2.3 Doehler and

Heaman, 1998

Hatton and Von Gruenewald,

1990

Lewisian, Scourie I, picrites,

norites, pyroxenites

Europe 80 2419.5 5.5 Heaman, 1989 Barooah and Bowes,1990

Koillismaa (Syote, Kussuarvi,

Porttivaara, Narankavaara)

Baltica Craton 51000 2436 5 Vogel et al., 1999 Ernst and Buchan, 1997b

Vinela dike, Vetreny Belt Europe 500 2437 3 Puchtel et al., 1997 Puchtel et al., 1997

Penikat Layered Intrusion

(deformed dike)

(also Kemi and Tornio)

Baltica Craton 51000 2440 10 Alapieti and Lahtinen, 1986 Ernst and Buchan, 1997b

Hearst, Fe-rich qtz. th. dikes Superior 100? 2446 3 Heaman, 1997 Ernst and Halls, 1984

Karelian dikes (near Olango) Baltic 200 2446 5 Vuollo et al., 1999 Mertanen et al., 1999

Matachewan, Fe-rich

qtz tholeiites,

Superior 250 2466 23 Heaman and Tarney, 1989 Condie et al., 1987

Mistassini komatiite and

basaltic dikes

Canada 100 2470 20 Rivers, 1997 Fahrig et al., 1986

Streich gabbro norite dikes

(feeder to Agnew)

Superior 300 2491 5 Krogh et al., 1984 Vogel et al., 1999

Kangamuit older mafic dikes Greenland 100 2528 25 Willigers et al., 1999 Nielsen, 1987

Great Dyke Zimbabwe Craton 1000 2596 14 Mukasa et al., 1997 Podmore and Wilson, 1987

Golden Mile dolerite dike Australia 700 2698 22 Nelson et al., 1994 Parker et al., 1987

Sylvania Inlier dikes Pilbara >200 2747 4 Wingate, 1999 Wingate, 1999

Black Range/Cajuput dike Australia 1000 2771 2 Wingate, 1999 Wingate, 1999

Wyoming Bighorn I Wyoming 150 2826 58 Stueber et al., 1976 Stueber et al., 1976

Ushushuwana Intrusion Kaapvaal Craton 51000 2875 40 Layer et al., 1988 Hunter and Reid, 1987

Tarssartoq-Amerilik dikes Greenland 100 3485 25 Nutman et al., 1996 Nielsen, 1987

Dike width estimated from maximum dike width assuming a 1000:1 ratio of dike length:maximum dike width.



277

Consequently, as our fourth proxy for superplume activity, we use the presence of Cr and/orPGE enrichment in layered intrusions with no arc affinity. Intrusions containing no such enrich-ment are classified as being produced by ‘‘normal’’ plumes. Intrusions containing chromite layers,Cr enrichment, and/or PGE enrichment are classified as being produced by superplumes. Usingthis criterion, we have developed a list of superplume-generated layered igneous intrusions, givenin Table 5.

6. Identification and duration of superplume event and eras

We assembled all the data for each of our superplume proxies into one large data set. Using thegeochronological data, including the errors in age, we generated a time series by making a gaus-sian curve for each age and age error. The area under each gaussian curve is the same for each ageand its error, but the height of the gaussian peak is greater if the age error is small. The result isshown in Fig. 2A where we see a time series generated from the sum of the individual gaussians.The height of the peaks depends on both the numbers of superplume proxies available for a givenevent and the errors in the dating of these events.In Fig. 2A the highest peak is for the next to youngest superplume era, the Cretaceous super-plume era at 84–120 Ma (Larson, 1991). This might suggest that the Cretaceous superplume wasthe largest superplume event in Earth history. However, this is not true. The height of this peak isdue to the very low errors in the rock dates. It is a fact of geochronology that younger rocks aremore precisely dated than older rocks.In order to reduce this bias, we arbitrarily set the minimum age error at 5Ma. That is, all rock unitswith an age error of less than 5 million years were assigned an error of 5 Ma. The result, shown inFig. 2B, shows a smoothed distribution that reduces the peak heights of the best-dated superplumes.This smoothed time series shows that the largest Precambrian superplume era is about as large as thelargest Phanerozoic superplume era. This is more reasonable, but is still rather deceptive.In order to assess the true size of superplume eras, we must quantify the length of time, whichdefines each era. To do this, we must identify the beginning and ending of significant superplumeactivity throughout Earth history. Then we will have more valid information on the relative sizeof Precambrian superplume eras compared to those in the Phanerozoic. To do this, we used acutoff value based on the mean error of the data in the time series in Fig. 2A. The mean error ofthe ages is 17.45 Ma. We added together eight modeled gaussians with the same mean and withan age error of 17.45 Ma. We found that this model time series had a maximum peak height of0.183. Therefore, we define the beginning and end of a superplume era by using the sections of thetime series that have values above 0.183.To obtain the most accurate assessment of the duration of superplume eras, we use the age anderror data as given in the literature (as for the time series shown in Fig. 2A). The resulting list has36 superplume eras occurring throughout recorded Earth history (Table 5). As shown in Fig. 3,most of the superplume eras last a relatively short time, 8 Ma or less. Overall, we find that theaverage duration of superplume eras in the Phanerozoic (12�3Ma) is indistinguishable from theaverage duration of superplume eras in the Archean (13�7 Ma).A few superplume eras are quite long, with durations of over 10 Ma. One superplume era, atabout 2.7–2.8 Ga., lasted about 80 Ma. As the geochronology improves, these longer superplume


Table 5Superplume Type Layered Intrusions

Name Location Mineralization Average

age

Age

error

Age

reference

Mineralization

reference

Skaergaard Intrusion (Sorgenfri

Glerscher Sill)

Greenland PGE-rich 55.55 1.75 Tegner et al., 1998 Guilbert and Park, 1986

Skye Complex (Cuillin

gabbroic complex)

United Kingdom Chromite (accessory

but no bands)

58.91 0.07 Hamilton et al., 1998 Hamilton et al., 1998;

Guilbert and Park, 1986

Rum Intrusion United Kingdom Chromite 60.53 0.08 Hamilton et al., 1998 Hamilton et al., 1998;


Insizwa Complex(MtAyliff)/

Tabankulu

South Africa PGE-rich 178 8 Fitch and Miller, 1984 Guilbert and Park, 1986

Dufek Layered Mafic Intrusion Antarctica Chromite 183.25 0.95 Minor and Mukasa, 1997 Ferris et al., 1998

Norilsk Asia PGEs 250.1 1.5 Renne et al., 1995 Distler, 1994

Talminsky Layered Intrusion

(same age as Norilsk)

Asia Chromite 250.1 1.5 Renne et al., 1995 Dyuzhikov et al., 1984

Laouni Algeria Chromite 565 65 Bertrand et al., 1985 Cottin et al., 1998

Doviren Layered Intrusion Siberia Chromite 699 48 Amelin et al., 1996 Amelin et al., 1996

Rincon del Tigre Complex Brazil Chromite (accessory

but no bands)

992 86 Annells et al., 1986 Annells et al., 1986

Mount Davies (same age as

Giles complex)

Musgrave Block Chromite 1078 5 Glikson et al., 1996 Hoatson, 1998

Duluth Complex USA PGE rich 1098.9 0.75 Paces and Miller, 1993;

Gilbert and Park, 1996

Paces and Miller, 1993;


Muskox Superior Chromite 1270 4 LeCheminant Barnes and Francis, 1995

Mukanda-Buhoro-Musongati

Massif

Burundi PGE-rich 1275.5 10.5 Tack et al., 1994 Tack et al., 1994

Jinchuan layered intrusion China PGE-rich 1508 31 Tang et al., 1992 Fan, 1986

Americano do Brasil Brazil Chromite 1575.5 32.5 Ferreira-Filho et al., 1994 Wirth et al., 1990

Niquelandia/Tocantins Brazil Chromite/PGE 1575.5 32.5 Ferreira-Filho et al., 1994 Wirth et al., 1990

Barro Alto Brazil PGE/Chromite 1729 21 Suita et al., 1994 Wirth et al., 1990

Cana Brava Ultramafic Complex Brazil Chromite 1729 21 Suita et al., 1994 Wirth et al., 1990

Piumhi sill (Piumhi greenstone belt) Brazil Chromite 1840 100 Jahn and Schrank, 1983 Jahn and Schrank, 1983

Sally Malley Australia PGE-rich 1844 3 Sproule et al., 1999 Hoatson, 1998

Sudbury Igneous Complex Superior Craton PGE-rich 1849.5 3.35 Krogh et al., 1994 Deutsch and Grieve,1994

Salt Creek Australia Chromite 1850 50 Wilkinson et al., 1975 Wilkinson et al., 1975;

Ashwal, 1993

Panton Intrusion Australia Chromite 1856 2 Page et al., 1995 Hatton and Von

Gruenewaldt, 1990




279

Table 5 (continued)


age

Age

error

Age

reference

Mineralization

reference

Springvale (Lamboo) Intrusion Australia Chromite 1857 2 Page et al., 1995 Sun et al., 1991

Fox River Sill Superior Craton Chromite,

PGE-rich

1883 1.45 Heaman et al., 1986 Scoates and Eckstrand,1986

Katiniq Sills (Donaldson West) Superior Craton Chromite 1920 8 Parrish, 1989 Hatton and Von

Gruenewaldt, 1990

Bushveld Layered Intrusion Kaapvaal Craton Chromite 2043 11 Schoenberg et al., 1999 Guilbert and Park, 1986

Molopo Farms Kaapvaal Craton Chromite 2043 11 Schoenberg et al., 1999 Hatton and Von

Gruenewaldt, 1990

Kunene Complex Angola-Namibia Chromite 2120.5 73.5 Guilbert and Park, 1986;

Cahen et al., 1984

Guilbert and Park, 1986;

Cahen et al., 1984

Imandra Lopolith Baltica Craton Chromite 2441 1.6 Amelin et al., 1995 Balashov et al., 1993

Olanga Complex Baltica Craton PGE-rich 2441.8 1.7 Amelin et al., 1995 Amelin et al., 1995

Lukkulaisvarra Baltica Craton PGE-rich 2442.1 1.4 Amelin et al., 1995 Balashov et al., 1993

Kivaaka Baltica Craton PGE-rich 2445 2 Balashov et al., 1993 Balashov et al., 1993

Burakovsky Layered

Intrusion

Baltica Craton Chromite 2449 1.1 Amelin et al., 1995 Amelin et al., 1995

East Bull Lake Layered

Intrusion

Superior Craton Chromite 2481 9 Krogh et al., 1984 Hubbard et al., 1998

Agnew Instrusion Superior

Province

Chromite 2491 5 Krogh et al., 1984 Hubbard et al., 1998

Generalskaya Baltica Craton PGE-rich 2505.1 1.6 Amelin et al., 1995 Amelin et al., 1995

Kamiskotia Layered Intrusion Superior Craton PGE-rich 2702 2 Barrie and Davis, 1990 Sutcliffe et al., 1993

Bulong Complex Sills

(Kalgoorlie)

Yilgarn Craton Chromite 2705 4 Nelson et al., 1995 Nelson et al., 1995

Stillwater Layered Complex Wyoming Craton Chromite 2705 5 Premo et al., 1990 Kleinkopf, 1985;

Premo et al., 1990

Mulcahy Lake Layered

Intrusion

Superior Craton Chromite 2733.3 0.95 Morrison et al., 1985 Morrison et al., 1985

Lac des Iles Layered Complex Superior Craton PGE-rich 2736 28 Bruegmann et al., 1997 Bruegmann et al., 1997

Bird River Sill Superior Craton Chromite 2745 5 Ashwal, 1993 Scoates, 1983*

Luanga Brazil Chromite 2763 6 Machado et al., 1991 Diella et al., 1995


280



Table 5 (continued)


age

Age

error

Age

reference

Mineralization

reference

Windimurra+Yoanmi+

Alley+Barambie+

Gabanintha+Narndee

Yilgarn

Craton

Chromite 2800 40 Mathison and

De Laeter, 1994

Hatton and Von

Gruenewaldt, 1990

Fiskanaesset Anorthosite Complex Nain Craton Chromite 2870 70 Ashwal et al., 1989 Hatton and Von

Gruenewaldt, 1990

Bhavani India Chromite 2899 28 Bhaskar Rao et al., 1996 Bhaskar-Rao et al., 1996

Maitland Complex Pilbara Craton Chromite 2925 16 Hoatson et al., 1992 Hoatson et al., 1992

Mount Sholl Pilbara Craton PGE-rich 2925 16 Hoatson et al., 1992 Hoatson et al., 1992

Radio Hill Pilbara Craton PGE-rich 2925 16 Hoatson et al., 1992 Hoatson et al., 1992

Munni Munni Intrusion Pilbara Craton Chromite

PGE-rich

2927 13 Sun and Hoatson, 1992 Barnes and Hoatson,1994

Sittampundi India Chromite 2935 60 Bhaskar-Rao et al., 1996 Baskar-Rao et al., 1996;

Hatton and Von

Gruenewaldt, 1990

Messina Layered Intrusion Limpopo Belt Chromite 3148.8 38.75 Arndt et al., 1991 Jackson, 1996;

Kroener et al., 1999

Selukwe (Shurugwi) Zimbabwe Craton Chromite 3373.5 83.5 Taylor et al., 1991;

Horstwood et al., 1999

Moorbath et al., 1976;

Hatton and Von

Gruenewaldt, 1990

Itsaq Gneiss Complex Greenland Chromite 3811 4 Nutman et al., 1996 Nutman et al., 1996



281

eras may prove to be two or more pulses of superplume activity. For example, the Cretaceoussuperplume era now appears to represent two pulses of superplume activity rather than a singleperiod of continuous superplume magmatism (Table 5).

7. Methodology: extrapolation of superplume sizes from dike widths

The vast majority of flood basalts from past superplume events are nearly completely eroded.At best, only the feeder dikes to these flood basalts remain. We use Eq. (2) to extrapolate the sizeof past flood basalt events. Because the largest of the Phanerozoic flood basalts, the CentralAtlantic Magmatic Province (CAMP) event had maximum feeder dike widths of about 300 m(Marzoli et al., 1999), we are confident that our relationship is valid for maximum dike widths upto 300 m. For feeder dikes less than 300 m in maximum width, we can successfully model theapproximate areal extent of the resulting flood basalt province before it was eroded.Even if only one part of an original plume-generated triple junction has survived in the geologicalrecord, the method is still valid. For example, the plate reconstruction of the initial configuration of

Fig. 2. (A). Time series of superplume events versus time derived from adding gaussians defined by ages and age errors

of individual superplume proxies. This time series uses the errors of ages as they are given in the literature. The result ishigher peak heights for events with very high precision ages. (B) Time series of superplume events versus time derivedfrom adding gaussians defined by ages and age errors of individual superplume proxies. The series is smoothed bysetting all age errors less than 5 my to 5 million years.


the superplume that produced the CAMP flood basalts shows a triple junction in the region thatis now the mid-Atlantic ocean. Four flood basalt provinces on four continents were depositedaround this triple junction before rifting separated them. Now these flood basalts form parts ofNorth America, South America, Europe and Africa. In three out of four of these provinces, thereis a massive feeder dike that has a maximum dike width of 300 m: (1) the Messejana dike inSpain, (2) the Roiraima-Cassipore dikes in South America, and (3) the Ksi-Ksou dike in WestAfrica. In North America, the widest CAMP dike is 180 m wide (the Shelbourne dike in NovaScotia). If we were to wait 1 Ga until only one out of four of these provinces was preserved in thegeological record, there is a 3 out of 4 chance that the widest surviving dikes would be 300 mwide. There is a 25% chance that only the 180-m-wide dike would be preserved. In this example,we would have a 75% chance of closely approximating the actual areal extent and a 25% chanceof seriously underestimating it. Thus, we can feel confident that using the maximum dike widthsin our compilation (Table 5) will produce at least minimum estimates for the sizes of the originalflood basalt provinces and thereby give at least minimum estimates for the size of the plume orsuperplume event.The extrapolation of original superplume size from the maximum feeder dike width is muchmore hazardous when the feeder dikes exceed 300 m in width. It is possible that thermal erosionduring magma transport to the surface artificially increases the width of these large dikes (Wil-liams and Lesher, 1996) and that therefore the linear correlation shown in Fig. 1 is no longervalid. To test this, we used the MacKenzie dike swarm as a test case. The maximum width of thefeeder dikes to the associated Muskox layered intrusion is 400 m. Using our empirical relation-ship shown in Eq. (2), we derive a predicted original surface area for the erodedMacKenzie floodbasalts of 13,200,000 km2.We digitized the boundaries of theMacKenzie dike swarm from the mapof Fahrig and West (1987) and used Stokes theorem to calculate the total surface area covered by

Fig. 3. Histogram of the duration of superplume eras. The distribution has two modes at 2 Ma and at 14 to 18 Ma.


the dike swarm: 2.0E 6 km2. However, in any flood basalt event, the feeder dike swarm covers amuch smaller surface area than the flood basalts. For example, we digitized the boundary of thesurface area covered by the feeder dikes to the Columbia River basalt province (Hooper, 1982)and found that the dike surface area, 8.6E 4 km2, represented 52.4% of the total area of the floodbasalt province. If we scale the MacKenzie dike surface area upward by dividing by 0.524 weget a predicted flood basalt surface area of 3.82E 6 km2. We assume that this represents onlyone third of the original province (LeCheminant and Heaman, 1989a), as would be the case ifthe MacKenzie swarm is analogous to the CAMP event. Therefore, the predicted size of theMacKenzie event is 1.14E 7 km2, about 87% of the prediction of Eq. (2) (Fig. 4). This is wellwithin the error for estimates of the size of the Muskox feeder dikes and for the ratio of feederdike surface area to flood basalt surface area. We also plot the minimum dike widths of thefeeders to Deccan traps and the Iceland basalts, and they plot near the best-fit line. Thus, we feelrelatively confident that for igneous events where the feeder dikes are 400 m or less in maximumwidth, our calculations of flood basalt surface area are reasonable within the known errors of thefield measurements.Using the maximum width of giant feeder dikes (those greater than 400 m in width) to infer thelateral extent of flood basalt provinces has some further problems. When feeder dikes are verywide with very high magma flow rates, local discontinuities in flow can produce irregular thermalerosion of the dike walls. The widest of these irregularities can eventually form funnel shapedlayered intrusions (Ernst and Buchan, 1997b). The width of these funnel shaped layered intru-sions is much wider than the true width of the feeder dike and should not be used to infer the

Fig. 4. Square root of surface area (km) covered by flood basalts versus the maximum width (m) of feeder dikes.Squares: Data points (Table 2) used to fit the line. Best-fit line is fit by least squares with a forced zero intercept. Largecircle: results from MacKenzie dike swarm using the surface area of the dike swarm and the width of the feeder dikes to

the associated Muskox intrusions. Large Triangles with upward arrows: minimum widths of dikes from the Deccantraps and Iceland versus surface area of the superplume lavas.


lateral extent of a flood basalt province. Although most of our dikes do not represent such funnelshaped layered intrusions, a few do. These funnel shaped dikes are the Binneringie/Jimberlanadikes in Australia, the Great Dike in Zimbabwe, the Ushushwana intrusion in South Africa, thePenikat Layered Intrusion in Finland, and the Gardar Giant Dikes in Greenland (Ernstand Buchan, 1997b). Because they are up to two kilometers wide, the Avenavero feeder dikes inSouth America might also be such layered intrusions, but we have not found information indi-cating that the Avenavero dikes have the necessary synformal cumulate layering (Rickwood,1990).The width of the feeder dike to these layered intrusions can be determined from gravity surveysor from along strike studies. For example, the Great Dike of Rhodesia has a maximum width of11 km, but a detailed gravity survey estimates that its feeder dike is about 1 km wide (Podmoreand Wilson, 1987). Therefore, the correct width to use in calculating the original lateral extent ofthe flood basalts emanating from the Great Dike is 1 km, not 11 km. A gravity survey over the 2km wide layered intrusion (dike) at Narankavaara in Finland finds that the feeder dike is 1 kmwide at depth (Alapieti et al., 1979). Because the Great Dike is the widest of the known layeredintrusions, it is unlikely that any of the funnel-shaped intrusions has a feeder dike over 1 km inwidth. (We note that a dike that was 2.6 km wide would, by extrapolation, extrude enough lavato cover the entire surface area of the Earth.) Therefore, we have artificially truncated all esti-mated widths of feeder dikes at 1 km (Table 5). This is the best option we have until more gravitysurveys are performed over funnel shaped layered intrusions.

8. Cumulative extent of eras of superplume magmatism

In the Phanerozoic, superplume eras have occurred over time periods ranging from 4 to 32 Main duration (Table 6). For each of the events listed, we also have information on the total surfacearea covered by the resulting flood basalts that we can use to compare to Precambrian super-plume eras. Because the age resolution of the Phanerozoic events is much better, Phanerozoicsuperplume eras can be resolved much more readily than those in the Precambrian. Nevertheless,most superplume eras are of comparable duration in both the Precambrian and the Phanerozoic.The intensity of magmatic activity during an individual superplume event can only be estimatedfrom the data on flood basalts and maximum dike widths shown in Tables 2 and 6. The geo-chronological data on layered intrusions can be used to define the lengths of superplume eras(Table 5), but their sizes cannot be used to determine the relative intensity of the associatedmagmatism. As a result, our data on cumulative superplume magmatism is incomplete. It is notpossible to estimate the flood basalt surface area of the superplume eras numbered 30, 34, 35, and36 in Table 7.We obtained an estimate for the surface area covered by flood basalt magmatism during eachsuperplume era by adding the estimated surface areas of all the flood basalt provinces associatedwith a particular era [as derived from Eqs. (1) and (2)]. Because our method can estimate totalsurface area from a limited data set (i.e. one-third of a rifted triple junction), we have to avoidcounting a given event more than once. Therefore, we eliminated well-dated events with over-lapping age data on both flood basalts and feeder dikes and/or on more than one set of feederdikes.


Some dike and flood basalt events have ambiguous ages, and it is unclear whether they shouldbe included in a given superplume era. In these cases, the flood basalt surface areas were includedonly in the estimate of the maximum surface area and not in the estimate of the minimum surfacearea. The resulting table (Table 7) shows a list of superplume events and eras through time andthe probable ranges in the surface areas of their associated flood basalts. Of the 36 major super-plume eras we have identified, our data are sufficient to provide a minimum surface area estimatefor 30 eras and a maximum surface area estimate for 32 eras.

Table 6

Duration of major superplume eras

Era number Start, m.y. End, m.y. Duration, m.y.

1 75 53 222 99 82 173 144 112 32

4 185 181 45 206 197 96 259 246 137 379 361 18

8 591 590 19 727 721 610 780 778 2

11 1100 1098 212 1111 1103 813 1142 1139 3

14 1279 1265 1415 1760 1758 216 1790 1788 2

17 1859 1844 1518 1886 1880 619 1891 1890 120 2041 2038 3

21 2116 2111 522 2168 2165 323 2211 2207 4

24 2220 2217 325 2238 2233 526 2413 2409 4

27 2451 2433 1828 2494 2487 729 2506 2504 230 2688 2681 7

31 2775 2696 7932 2787 2784 333 2903 2899 4

34 2932 2924 835 3024 3022 236 3812 3810 2


Table 7Minimum and maximum size of superplume eras and events

Name Age,Ma

Error Area,km2

Eventno

Min. area,km2

Max. area,km2

Iceland flows 7.5 7.5 8.00E+05 NI:0 8.00E+05 8.00E+05North Atlantic flows 59.55 2 1.30E+06 1 5.05E+06 5.05E+06Deccan traps 61.45 4.6 8.00E+05 1Peary Land dikes 66 6.6 2.95E+06 1

Madagascar flows 87.55 3.8 1.60E+06 2 3.78E+06 9.63E+06Rio Grande rise flows 88 1 1.67E+06 2Broken Ridge flows 91 2 5.10E+05 2

Venezuelan-Columbian flows 100 20 1.86E+06 NI:(2)Kerguelen Plateau flows 100.5 11.5 1.54E+06 NI:(2)Hess Rise flows 107.5 12.5 8.00E+05 NI:(2)

Alpha Ridge Plateau flows 111 20 1.65E+06 NI:(2,3)Manihiki Plateau flows 118.5 6.5 1.21E+06 3 5.92E+06 8.11E+06Wallaby Plateau flows 118.5 6.5 4.10E+05 3

Ontong Java Plateau flows 122.15 3.2 1.86E+06 3Parana-Serra Gelal flows/dikes 131.35 8.4 1.20E+06 3Shatsky Rise flows 140 10 1.24E+06 3Magellan Rise flows 145 5 5.40E+05 NI:(3)

Ferrar Dolerite flows 183.6 1 4.50E+05 4 2.65E+06 2.65E+06Karoo Province flows 183.7 0.6 2.20E+06 4CAMP dikes/flows 202 3 7.00E+06 5 7.00E+06 7.00E+06

Siberian traps flows 252.15 3.8 2.00E+06 6 2.32E+06 2.32E+06Emeishan-Song Da flows 254.9 5.1 3.22E+05 6St Malo dikes 330 10 7.37E+05 NI:6a 7.37E+05 7.37E+05

East European craton flows 368.75 10.75 4.33E+06 7 7.28E+06 7.28E+06Chara Sinsk dikes 377.5 19.5 2.95E+06 7Antrim plateau flows 531.5 18.5 7.62E+05 NI:7a 7.62E+05 7.62E+05Grenville dikes 590.5 1.5 7.37E+05 8 7.37E+05 7.37E+05

Thule dikes 682 25 7.37E+05 NI:8a 7.37E+05 7.37E+05Ganna Kouriep dikes 717 11 7.37E+05 NI:(9)Borden dikes 724 4 4.61E+06 9 4.61E+06 5.35E+06

Mundine well dikes 755 3 6.63E+06 NI:9a 6.63E+06 6.63E+06Hottah McKenzie Mt flows 779 2 1.08E+06 10 1.08E+06 1.08E+06Willouran Volcanics flows 827 6 7.37E+05 NI:10a 7.37E+05 7.37E+05

Bistjarvi-Laanilla dikes 1036.5 55.5 2.95E+06 NI:10b 2.95E+06 2.95E+06Champ de Mers dikes 1058 14 1.25E+06 NI:10c 1.25E+06 1.25E+06Keweenawan flows 1097.7 12.1 4.75E+05 11 1.21E+06 1.21E+06

Guruve Deweras dikes 1100 270 7.37E+05 11Umkondo Dolerite flows 1104.7 2.3 2.00E+06 12 2.04E+07 2.04E+07Pidgeon River dikes 1110 3 1.84E+07 12Abitibi dikes 1140.6 2 4.61E+06 13 4.61E+06 5.18E+07

Gardar (Tugtotoq) dikes 1154 16 4.72E+07 NI:(13)Sundsjo dike 1213 18 4.61E+06 NI:13a 4.61E+06 4.61E+06Sudbury dikes 1238.5 4 7.37E+05 NI:13b 7.37E+05 7.37E+05

Older Gardar dikes 1259.5 56.5 2.95E+06 NI:(14)Market dolerite dikes 1260 10 3.61E+07 NI:(14)

(contined on next page)


Table 7 (continued)

Name Age,Ma

Error Area,km2

Eventno

Min. area,km2

Max. area,km2

Muskox/MacKenzie dikes 1270 4 1.18E+07 14 1.18E+07 5.13E+07Pilanesberg dikes 1330 80 4.14E+05 NI:(14)Jinchuan dike 1508 31 9.03E+06 NI:14a 9.03E+06 9.03E+06

Hallefors dike 1518 38 7.37E+07 NI:14b 7.37E+07 7.37E+07Breven dike 1545 26 7.37E+07 NI:14c 7.37E+07 7.37E+07Aland-Aboland dikes(Korso, Foglo) 1558.5 30.5 1.18E+07 NI:14d 1.18E+07 1.18E+07Avanavero dikes II? (Roraima)* 1620 50 1.84E+07 NI:14e 1.84E+07 1.84E+07

Melville Bugt dikes 1645 35 1.84E+07 NI:14f 1.84E+07 1.84E+07Hame dikes (Ansio) 1646 6 7.37E+07 NI:14g 7.37E+07 7.37E+07Tiruvannamali dikes 1650 10 7.37E+05 NI:14h 7.37E+05 7.37E+05

Hame dikes (Virmala) 1667 8 7.37E+07 NI:14i 7.37E+07 7.37E+07Dharwar dikes 1668 31 4.72E+05 NI:14j 4.72E+05 4.72E+05Oenpelli dikes 1690 10 2.95E+06 NI:14k 2.95E+06 2.95E+06

Uruguayan Dikes 1726 11 4.72E+05 NI:14l 4.72E+05 4.72E+05Zyzdal-Zalesskaya Dikes (Korosten)* 1758.8 0.9 7.37E+07 15 7.37E+07 7.37E+07Avanavero dikes I? (Roraima)* 1789 2 7.37E+07 16 7.37E+07 7.37E+07Dharmapuri dikes 1822 42 7.37E+05 NI:(17) 4.10E+05 7.37E+05

Cuthbert Dikes (younger Molson) 1882.8 2.3 1.06E+06 18 1.06E+06 1.06E+06Avayalik dikes 1890.5 2.5 2.95E+06 19 2.95E+06 2.95E+06Onega plateau flows 1975 24 4.26E+07 NI:19a 4.26E+07 4.26E+07

Kennedy dikes 2010 10 7.37E+05 NI:19b 7.37E+05 7.37E+05Lac de Gras dikes 2026.5 3.5 7.37E+05 NI:19c 7.37E+05 7.37E+05Kangamuit younger dikes 2039.5 1.5 7.37E+05 20 7.37E+05 7.37E+05

Ft. Frances dikes 2076.5 4.5 7.37E+05 NI:20a 7.37E+05 7.37E+05Kovero-Koli dikes 2113 4 7.37E+05 21 1.47E+06 3.27E+06Marathon dikes 2114.5 10.5 7.37E+05 21

Kenora-Kabetogama dikes 2120 67 1.06E+06 NI(21)Pippolanmaki-Kutsu dikes 2123 10 7.37E+05 NI(21)Cauchon (older Molson) dikes 2145 25 1.06E+06 NI(22)Biscotasing dikes 2166.7 1.4 4.61E+06 22 4.61E+06 5.67E+06

Birrimian flows 2183.7 6.7 1.10E+05 NI:22a 1.10E+05 1.10E+05Wyoming Bighorn II dikes 2200 35 1.66E+06 NI:(23)Klotz basic dikes 2209 2 7.37E+05 23 7.37E+05 6.08E+06

Sukkertoppen dikes (Pakitsoq, Sister dikes) 2214 10 2.95E+06 NI:(23)Senneterre dikes 2214.3 12.4 7.37E+05 NI:(23)Nippising flows 2219.05 3.6 4.07E+05 24 4.07E+05 4.07E+05

Kikkertavik dikes 2235 2 1.18E+07 25 1.25E+07 1.25E+07Antarctica dikes 2238 7 7.37E+05 25Binneringie/Jimberlana dikes* 2410.4 2.3 7.37E+07 26 7.42E+07 7.42E+07

Lewisian-Scourian dikes 2419.5 5.5 4.72E+05 NI:26a 4.72E+05 4.72E+05Koillismaa dikes* (also Vinela) 2436 5 7.37E+07 27 1.47E+08 1.55E+08Penikat dike*(also Hearst) 2440 10 7.37E+07 27Matachewan dikes 2466 23 4.61E+06 NI:(27,28)

Mistassini dikes 2470 20 7.37E+05 NI:(27,28)Rampur flows 2486 69 2.00E+06 NI:(27,28)Streich dikes(feeder to Agnew) 2491 5 6.63E+06 28 6.63E+06 1.40E+07



However, there are 29 individual superplume events in our data set, which do not fit into any ofthe age ranges of the 36 major superplume eras. The largest problem with the data on these 29events is inadequate geochronology. Many of the 29 superplume events have very large inferredsizes, but their ages are so poorly defined that they overlap with better-defined events. We are certainthat as more geochronological data are published, additional superplume eras will be identified.

9. Relative magnitudes of superplume events and eras over time

Using the methods discussed above and using the data presented in Tables 1–7, we ranked thesuperplume eras in order of size, from the largest yet known (1) to the smallest (36) (Table 8).None of the Phanerozoic superplume eras is in the top 10. Using the calculated surface areas, thethree largest superplume eras apparently occurred in the Archean. There are seven eras whose sizeis indistinguishable, all tied for fourth place. Based on cumulative surface areas, the largest Pre-cambrian superplume era produced enough lava to cover 20 times the surface area covered duringthe largest Phanerozoic superplume era. Based on the ratio of maximum widths of feeder dikes,the largest single Precambrian superplume covered 10 times the surface area of the largest singlePhanerozoic superplume. It is clear that the extent and intensity of both individual Precambriansuperplume events and superplume eras dwarfs that of superplume events and eras occurringduring Phanerozoic time.When the data from Table 7 are plotted in a weighted time series (Fig. 5b), the weightedsuperplume time series has almost no amplitude for the past 1.1 Ga. There are six dominantpeaks in the time series, at �1.65, 1.75, 1.8, 2.4, 2.44, and 2.76 Ga. Overall, it is clear that therehas been a tremendous decrease in superplume intensity and volume since the Archean.

Table 7 (continued)

Name Age,Ma

Error Area,km2

Eventno

Min. area,km2

Max. area,km2

Kangamuit older dikes 2528 25 7.37E+05 NI:(29) 4.10E+05 7.37E+05Great Dyke* 2596 14 7.37E+07 NI:29a 7.37E+07 7.37E+07Golden Mile dike 2698 22 3.61E+07 31 1.18E+08 1.18E+08

Klipriversberg flows 2713.3 8.3 3.10E+06 31Fortescue-Kylena flows 2725 45 1.67E+06 31Sylvania Inlier Dikes 2747 4 2.95E+06 31Black Range/Cajuput dike 2771 2 7.37E+07 31

Derdepoort flows 2782 5 1.58E+05 NI:(32) 4.10E+05 1.82E+06Wyoming Bighorn I dikes 2826 58 1.66E+06 NI:(32)Ushushuwana dikes* 2875 40 7.37E+07 NI:(33) 4.10E+05 7.37E+07

Tarssartoq-Amerilik dikes 3485 25 7.37E+05 NI:35a 7.37E+05 7.37E+05

Possible duplications of the same event have been removed. There is no data for eras 30,34,35, and 36. Events labeledas NI were not included in Table 6 because their amplitudes in the time series in Fig. 1A are too small. If the eventnumber is in parentheses, the age errors allow the superplume event to lie within a given superplume era, but the mean

age is outside the range defined for that superplume era. In that case, the inferred surface areas of those flood basaltsare included in the maximum area estimate but not the minimum area estimate of the superplume era. Minimum sur-face areas for events only defined by parenthesis are assumed to be 4.10E5 km2


Table 8Size ranking of superplume events and eras

Duration Number Minimumarea, km2

Maximumarea, km2

Ranking(min size)

Ranking(max size)

0–15* NI:0 8.00E+05 8.00E+05 25 3353–79 1 5.05E+06 5.05E+06 15 2282–99 2 3.78E+06 9.63E+06 17 13112–144 3 5.92E+06 8.11E+06 14 15

181–185 4 2.65E+06 2.65E+06 19 26197–206 5 7.00E+06 7.00E+06 12 17246–259 6 2.32E+06 2.32E+06 20 27

320–340* NI:6a 7.37E+05 7.37E+05 27 35361–379 7 7.28E+06 7.28E+06 11 16513–550* NI:7a 7.62E+05 7.62E+05 26 34

590–591 8 7.37E+05 7.37E+05 27 35657–707* NI:8a 7.37E+05 7.37E+05 27 35721–727 9 4.61E+06 5.35E+06 16 21

752–758* NI:9a 6.63E+06 6.63E+06 13 18778–780 10 1.08E+06 1.08E+06 24 31821–833* NI:10a 7.37E+05 7.37E+05 27 35981–1092* NI:10b 2.95E+06 2.95E+06 18 25

1044–1072* NI:10c 1.25E+06 1.25E+06 22 291098–1100 11 1.21E+06 1.21E+06 23 301103–1111 12 2.04E+07 2.04E+07 6 8

1139–1142 13 4.61E+06 5.18E+07 16 51195–1231* NI:13a 4.61E+06 4.61E+06 16 231235–1243* NI:13b 7.37E+05 7.37E+05 27 35

1265–1279 14 1.18E+07 5.13E+07 9 61477–1539* NI:14a 9.03E+06 9.03E+06 10 141480–1556* NI:14b 7.37E+07 7.37E+07 4 41519–1571* NI:14c 7.37E+07 7.37E+07 4 4

1528–1589* NI:14d 1.18E+07 1.18E+07 9 121570–1670* NI:14e 1.84E+07 1.84E+07 7 91610–1680* NI:14f 1.84E+07 1.84E+07 7 9

1640–1652* NI:14g 7.37E+07 7.37E+07 4 41640–1660* NI:14h 7.37E+05 7.37E+05 27 351659–1675* NI:14i 7.37E+07 7.37E+07 4 4

1637–1699* NI:14j 4.72E+05 4.72E+05 28 361680–1700* NI:14k 2.95E+06 2.95E+06 18 251715–1737* NI:14l 4.72E+05 4.72E+05 28 36

1758–1760 15 7.37E+07 7.37E+07 4 41788–1790 16 7.37E+07 7.37E+07 4 41844–1859 NI:(17) 4.10E+05 7.37E+05 29 351880–1886 18 1.06E+06 1.06E+06 24 32

1890–1891 19 2.95E+06 2.95E+06 18 251951–1999* NI:19a 4.26E+07 4.26E+07 5 72000–2020* NI:19b 7.37E+05 7.37E+05 27 35

2023–2030* NI:19c 7.37E+05 7.37E+05 27 352038–2041 20 7.37E+05 7.37E+05 27 35



The weighted superplume time series has many missing events. These represent superplumeevents that are only known from high Mg rocks and/or PGE /Cr rich layered intrusions. As wego back to earlier time periods, the total surface area of preserved continental crust decreasesgreatly. The overall degree of deformation also increases. Both of these effects decrease the like-lihood that large feeder dikes will be found and recognized. Thus, we are still uncertain as to theoverall magnitude of superplume activity prior to about 2.9 Ga.In order to compensate for superplume events with no record in dikes or flood basalts, we alsoconstruct a composite superplume time series. The composite time series (Fig. 5c) is a sum of theweighted superplume time series with an unweighted superplume time series derived from thehigh Mg rocks and layered intrusions (Fig. 5a). The composite superplume time series shows thatthere were superplume events after 1.1 Ga and prior to 2.9 Ga.

10. Discussion

In the preceding sections, we have shown how it is possible to derive a history of plume andsuperplume volcanism on the surface of the Earth by using plume-generated features that survivein the geological record. We have shown that both individual superplumes events and superplumeeras were much larger in the Precambrian than in the Phanerozoic. The chronology of super-plume events over Earth history shown in Fig. 5 allows us to compare the history of superplumemagmatism with the record of other types of events.

Table 8 (continued)

Duration Number Minimumarea, km2

Maximumarea, km2

Ranking(min size)

Ranking(max size)

2072–2081* NI:20a 7.37E+05 7.37E+05 27 352111–2116 21 1.47E+06 3.27E+06 21 242165–2168 22 4.61E+06 5.67E+06 16 20

2177–2190 NI:22a 1.10E+05 1.10E+05 31 382207–2211 23 7.37E+05 6.08E+06 27 192217–2220 24 4.07E+05 4.07E+05 30 372233–2238 25 1.25E+07 1.25E+07 8 11

2409–2413 26 7.42E+07 7.42E+07 3 32414–2425 NI:26a 4.72E+05 4.72E+05 28 362433–2451 27 1.47E+08 1.55E+08 1 1

2487–2494 28 6.63E+06 1.40E+07 13 102504–2506 NI:(29) 4.10E+05 7.37E+05 29 352582–2610* NI:29a 7.37E+07 7.37E+07 4 4

2696–2775 31 1.18E+08 1.18E+08 2 22784–2787 NI:(32) 4.10E+05 1.82E+06 29 282899–2903 NI:(33) 4.10E+05 7.37E+07 29 43460–3510 NI:35a 7.37E+05 7.37E+05 27 35

Durations for events and eras have two sources: Table 6 (Duration of major superplume eras) and the errors of indi-vidual radiometric ages for superplume events (*). Note that there are many superplumes tied for 4th, 27th and 16thplace.


The two most dominant superplume eras in the Proterozoic occurred circa 1.8 and 2.4 Ga ago.Interestingly, these two periods correspond with the periods when the bulk of the Fe in Pre-cambrian iron formations was deposited (Isley, 1995; Isley and Abbott, 1999). We suggest thatthe combination of massive amounts of tholeiitic volcanism, coupled with increases in the oxygencontent of the atmosphere (Kasting, 1987) produced a synergy of conditions that resulted in thedeposition of massive quantities of Fe on passive continental margins.

Fig. 5. Superplume time series. All time series are smoothed by setting the minimum error of well-dated ages to 5 my.

(A) time series constructed by adding gaussians derived from the ages and age errors of superplume type high Mg rocksand layered intrusions. (B) Weighted time series is constructed by adding gaussians whose initial size is determined bythe age and age error of superplume type flood basalts and dikes. Each individual gaussian is multiplied by the surface

area of the flood basalt inferred from the restored surface area of the flood basalt or our empirical relationship betweenmaximum width of feeder dikes and total surface area covered by flood basalts. (C) Sum of the time series in A and B.


One unexpected finding is the relatively small size of the peaks in the weighted plume time seriesat 2.7 and 1.9 Ga, which have both been identified as major periods of continental growth. Thereare several possible explanations. At 2.4 Ga, the addition of plume lavas to an extending passivemargin (along with Superior type iron formation) would not result in granitoid production untilthe next Wilson cycle. The ages of the resulting continental growth spurt, if defined by the ages ofgranites, would then be younger than the age of primary addition of the basaltic continentalcrust. At 2.7 Ga, we have a problem in the paucity of dike swarms of that age. Thus, we believethat it is likely that we have underestimated the size of the superplume events at 2.7 Ga.The maximum widths of the Avanavero dikes in South America largely define the size of thesuperplume era at 1.65 Ga. These dikes are very poorly dated, with ages ranging from 1650 topossibly as old as 1800 Ma (Ernst and Buchan, 2001). There are two sets of dikes with differingorientation, which makes it likely that they are of significantly different geological ages. Thus, weconsider the superplume era at 1.65 Ga to be somewhat uncertain.Two issues that remain are the sizes of the largest superplume events and of most events priorto 2.9 Ga. Because of the gravity surveys over it, we are confident that the feeders to the GreatDike of Zimbabwe and the Narakavaara dike were at least 1 km in width. This observationimplies that the largest Archean superplume events were at least 10 times larger than the largestPhanerozoic superplume events, covering about 73,000,000 km2. Taking the errors of ourempirical predictions into account, these events covered, at least, between 14 and 18% of theEarth’s surface. However, other large dikes, such as the Jimberlana dike in Australia have widthsof 1.5 km away from the wider dike sections that are layered intrusions (Hatton and Von Grue-newaldt, 1990). Nevertheless, without more geophysical constraints on feeder dike width, our bestestimate is that the largest Archean superplumes were at least 10 times larger than the largestPhanerozoic superplumes.Overall, there are six individual superplume events (Table 7) with conservative feeder dikewidths of at least 1 km and conservative lateral extents of at least 14–18% of the planet. Takentogether, these six events could have resurfaced the entire Earth with basalt. This conclusion isinteresting in view of the young age of the basaltic surface of Venus (Head, 1994; Herrick, 1994).Venus has been compared many times to the Archean Earth (Solomon, 1980; Head, 1989).Because of its larger size and higher radioactive element content, the thermal evolution of Venusis less advanced than that of the Earth (Taylor, 1991; Arkani Hamed et al., 1993). Thus, oursuperplume record may be recapitulating for the Archean Earth what we now see on the surfaceof Venus.

11. Conclusions

We defined four geological proxies for superplume activity: (1) High-Mg rocks (per Isley andAbbott, 2002); (2) Massive flood basalt provinces with an original surface area greater than410,000 km2; (3) Maximum feeder dike widths greater than 70 m; and (4) Layered intrusions withenrichments in Cr and/or PGEs. We have shown that by using these proxies for mantle super-plume magmatism in conjunction with their age dates, we are able to determine the duration andintensity of superplumes over Earth history. Our results show that overall superplume activity hasprogressively declined over the past 2.9 Ga. Our ranking of superplume events shows that the


strongest superplumes whose size we have been able to quantify occurred in Archean throughearly Proterozoic time (1.65–2.76Ga). Because of the limitations in geochronological, geophysi-cal, and geological data on surviving outcrops, our calculations probably underestimate theactual frequency and intensity of superplume activity over time. As additional research databecome available, it is highly likely that other distinct superplume events will be identified andthat our estimates of the intensities of some superplumes in the Archean and Early Proterozoicwill increase. We have demonstrated that it is possible to assess the relative size of Phanerozoicand Precambrian superplume events by using the maximum width of feeder dikes to predict theoverall surface area covered by superplume magmatic activity. This assessment suggests that thelargest Precambrian superplume events were at least ten times larger than the largest Phanerozoicsuperplume events. The largest Precambrian superplume events were essentially planetary inscale, involving at least 14–18% of the Earth’s surface area.We have also defined 36 major periods of continuous superplume activity (superplume eras),with durations ranging from 76 to 1 million years. Over two thirds of all superplume periods havea relatively brief duration of 8 million years or less. There is no significant difference in theduration of Archean and Phanerozoic superplume eras.

Acknowledgements

We thank Sarah Hoffman for editing. We thank Kent Condie, Ross Taylor and Richard Ernstfor helpful comments on the paper. LDEO Contribution # 6280.

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