Future supercontinent assembled in the northern hemisphere

Masaki Yoshida1 and M. Santosh2

1Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15

Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan; 2Division of Interdisciplinary Science, Faculty of Science, Kochi University,

Akebono-cho 2-5-1, Kochi 780-8520, Japan

Introduction

The convergence of multiple continen-tal fragments carrying ancient cratonstogether with accreted terranes havecreated large landmasses on our planettermed as supercontinents (Worsleyet al., 1984, 1986; Nance et al., 1988).Whereas various models have beenproposed for the formation anddisruption of supercontinents (Condie,2004; Santosh et al., 2009), stochasticand numerical models predict thatmantle convection has significante!ects on the amalgamation of super-continents (Zhang et al., 2009).Several configurations of superconti-nents which shaped the globe duringvarious periods in Earth history havebeen proposed, including Vaalbara(3.2 Ga), Ur (3.0 Ga), Kenorland(2.7–2.5 Ga), Columbia (1.8–1.9 Ga),Rodinia (1.1 Ga), Gondwana(0.54 Ga) and Pangea (0.25 Ga) (Rog-ers and Santosh, 2004). The termNuna was applied by Ho!man (1989)to describe the Palaeoproterozoicsupercontinent, although its recon-struction is based on di!erent criteria,mostly focusing on the amalgam ofNorth American terranes. It should benoted that not all the continental

assemblies through Earth!s historymentioned above qualify to be definedas supercontinents in terms of theirsize and well-defined configurations(e.g. Pangea vs. Ur), although relativeto the amount of continental litho-sphere on the planet in the Archaean,even the early landmasses (e.g. Vaal-bara) can be considered as superconti-nents. The debates surrounding thedefinition of supercontinents, includ-ing their dynamics and periodicity havebeen dealtwith elsewhere (Yoshida andSantosh, 2011).The history of supercontinental

cycles through time has received con-siderable attention in the recent years,specifically in relation to the processof crustal growth of the continents,the history of life and major surfaceenvironmental changes (Nance et al.,1988; Santosh, 2010). Whereas hypo-thetical models supported by geolog-ical correlations have attempted theconfigurations of past superconti-nents, the question of when and wherethe future supercontinent will form iscontroversial. A popular concept isthat as the Pacific Ocean is shrinkingand the Atlantic Ocean is widening,Asia is moving towards America withthe western Pacific region defining thefrontier of the future supercontinent,dubbed "Amasia! (Ho!man, 1992,1999; Maruyama et al., 2007), postu-lated to be assembled after 250 Mafrom present. However, if the rapidnorthward migration of Australia istaken into consideration, this conti-nent could be wedged between Asiaand North America within next

70 Ma (Scotese, 2001). The model ofthe hypothetical supercontinent "Am-asia! faces another more critical prob-lem that the South Pacific large-scaleupwelling plume lies central to thepath of migration of the Asian conti-nental mass to join America and formthe future supercontinent. An alter-nate concept is that if modern sub-duction in the Caribbean and Scotiaarcs spreads along the Atlantic sea-board, then convergence and destruc-tion of the Atlantic Ocean wouldresult in a supercontinent, termed"Pangea Ultima! (Scotese, 2000). Thishypothesis, however, faces the chal-lenge that if the subduction within theAtlantic realm spreads laterally, theassembly of Pangea Ultima cannot beachieved as postulated, although thismodel needs to be tested further.Trubitsyn et al. (2008) formulated a

three-dimensional (3-D) numericalmodel to realize the continental driftfrom present to 100 Ma into thefuture to predict a configuration ofthe future supercontinent. The modelcontinents were assumed to be thin"rigid! (non-deformable) caps that canbe drifted by an Euler!s solid bodyequation and arranged in a real dis-tribution of continents on the presentday globe. The initial temperaturecondition of mantle was given by thepresent mantle flow pattern estimatedfrom a seismic tomography model.Their simulation reveals that after100 Ma, all the continents wouldmove to the southern hemisphere,with Africa, Eurasia, Australia, Ant-arctica and South America assembling

ABSTRACT

Continental masses were amalgamated, broken apart andreassembled within supercontinents during different times inEarth history. Here, we attempt to predict the configuration of apotential future supercontinent based on a numerical simula-tion model of mantle convection. The mantle convection in ourmodel is driven by a density anomaly compiled from a globalseismic tomography model. The temporal evolution of a highlyviscous continent with an initial present-day configuration issimulated for over 250 Ma. The result reveals that Australia,Eurasia, North America and Africa would gather in the northern

hemisphere to form the future supercontinent. On the otherhand, Antarctica and South America remain in the present-dayposition even after 250 Ma from present, and do not join thefuture supercontinent amalgam. The configuration of the futuresupercontinent numerically simulated herein is broadly consis-tent with the hypothetical model of the future supercontinentAmasia speculated from geological correlations.

Terra Nova, 23, 333–338, 2011

Correspondence: Masaki Yoshida, Insti-tute for Research on Earth Evolution(IFREE), Japan Agency for Marine-EarthScience and Technology (JAMSTEC), 2-15Natsushima-cho, Yokosuka, Kanagawa237-0061, Japan. Tel.: +81 46 867 9814;fax: +81 46 867 9315; e-mail: myoshida@jamstec.go.jp

! 2011 Blackwell Publishing Ltd 333

doi: 10.1111/j.1365-3121.2011.01018.x

to form a supercontinent around Ant-arctica. This model also relies on thesubduction zones in the westernPacific to e!ectively "pull together!the continental fragments.However, including the study by

Trubitsyn et al. (2008), most of thenumerical attempts so far have as-sumed the continent ⁄ supercontinentto be rigid or non-deformable bodiesmainly because of the limitations inthe numerical simulations, as well asthe simplification of models (seereview by Yoshida and Santosh,2011). In this study, we use a pre-liminary, but more robust numericalmodel which enables us to treat theevolution of deformable, mobile con-tinental lithosphere both in space andtime (Yoshida, 2010), and attempt toanswer the question of when andwhere the future supercontinent mightform.

Model description

The details of model description formantle convection and continent aredescribed in Supporting Information.The temperature (T)-, phase (G)-,

composition (C)-dependent rheologyis considered in the mantle. Thedimensionless viscosity form used isgiven by;

g ! Dg"C#Dgcont C" #

Æ2E

T $ Ttop % DT$ 2E

0:5% DT

! ";

"1#

where Ttop is the temperature at thetop surface (=0.1092), DT is the tem-perature di!erence across the mantle(=1), E is the dimensionless activationenergy that controls the viscosity con-trast across the mantle and set to beln(103) = 6.91 so as to set the viscos-ities at the top and bottom surfaces tobe 102 and 10)1, respectively. Theviscosity contrast between the conti-nent and surrounding mantleDgcont(C) is fixed at 102 or 103 in thecontinent if C = 1 and 1 in the mantleif C = 0. The value of Dg(G) is fixed at1 in the olivine-spinel phase and 30 inthe post-spinel phase.The initial temperature field, Tinit(r,

h, /), is obtained from a composition-ally homogeneous convection modelwith no continental material ("freeconvection!) that reaches well-devel-oped, statistically steady state (Fig. 1)

and mainly from a seismic tomogra-phy model. The initial state of tem-perature field is given by

Tinit"r; h;u# ! Tconv"r# % dTseis"h;u#;"2#

where Tconv(r) is the laterally averagedtemperature of free convection (Fig. 1c)and dTseis(h, /) is the lateral tem-perature anomaly determined by seis-mic tomography models, named"smean! and "pmean! models (Beckerand Boschi, 2002) (see SupportingInformation) and the regionalizedupper mantle seismic model based onseismicity in the upper mantle, named"RUM! model (Gudmundsson andSambridge, 1998).Following Karato (2008), the seis-

mic velocity anomaly dVS,P is con-verted into the temperature anomalydTseis applying the following relation-ship (see Supporting Information):

dTseis ! A$1VS;PT dVS;P; "3#

where AVS;PT is the temperature deriv-ative of seismic wave velocity asa function of radius; AVS;PT &@ ln VS;P=@T , which is determined bymineral physics (Karato, 2008). Thedepth profile of AVS;PT used in ourmodel is shown in Fig. 2a (see Sup-porting Information). The calculateddTseis for smean and pmean models areillustrated in Fig. 2b and c, respec-tively. The smean and pmean modelsare adapted in the regions under350 km depth. The RUM model,which represents the configuration ofsubducting slabs, is adapted in theregions above 660 km depth. Thelateral temperature anomaly of sub-ducting slabs in the upper mantle isherein fixed at )500 K.The present-day continental distri-

bution used in this study is compiled

A B C D A

(a)

(b)

1000 1500 2000Temperature (K)

A

B

C

D

4000

5000

6000

Rad

ius

(km

)

1000 2000Temperature (K)

(c)

Fig. 1 Snapshot of the initial temperature field from a compositionally homogeneousconvection model with no continental material ("free convection!) that reaches well-developed, statistically steady state. (a) The temperature at the mid-mantle (1433 km)depth. (b) A cross-section of mantle along the path A–B–C–D–A shown in (a). (c)Depth profile of the laterally averaged temperature in the mantle.

Future supercontinent in northern hemisphere • M. Yoshida and M. Santosh Terra Nova, Vol 23, No. 5, 333–338.............................................................................................................................................................

334 ! 2011 Blackwell Publishing Ltd

from the ETOPO1 model (Amanteand Eakins, 2009). The continentsinitially cover '35% of the total

surface and have a uniform thicknessof 250 km (see Supporting Informa-tion). Following the previous work

(Yoshida, 2010), the time integrationof the advection of compositio-nally di!erent continental materials(C-field) with zero chemical di!usionis performed by a tracer particlemethod (see Supporting Information).The continent is instantaneously seton the mantle convection model withthe initial temperature field, Tinit(r, h,/). To give plate-scale flow around thesurface boundary, the present-dayplate motion (Argus and Gordon,1991) is imposed for the first stage ofthe simulation (for 5 Ma) as thevelocity boundary condition (Fig. 2d)instead of the free-slip condition. Therun continues for over 250 Ma.

Result

In the present study, we test fourpotential scenarios with di!erenttomography models (i.e. smean andpmean) and di!erent viscosity of conti-nents, that is, Dgcont(C) (Table 1). Thepattern and magnitude of temperatureanomaly between smean and pmeanmodels is quite di!erent (Fig. 2b,c),which allows us to study the modelsensitivity to the obtained result.Furthermore, the previous studyshowed that the viscosity of continentssignificantly depends on the behaviourof the continental movement (Zhanget al., 2009; Yoshida, 2010). This alsoallows us to study the model sensitiv-ity to the obtained result.We first show the result for Model

S2 with the smean-based initial con-dition and Dgcont(C) of 10

2. Figure 3illustrates the temporal evolution ofcontinental distribution (left panel)and the temperature anomaly of themantle (right panel). The four selectedtime stages at 33, 90, 139 and 250 Maare shown. The continents start tomove on the start of the simulation at0 Ma. The most interesting resultobtained in our study is that Australiamoves northwards at a high speed; anoutcome of extrapolating the currentrapid northward movement. Ulti-mately, Australia, Eurasia, NorthAmerica and Africa gather in thenorthern hemisphere to form a futuresupercontinent. Conversely, Antarc-tica and South America remain intheir present-day position even after250 Ma and are not assembled in thefuture supercontinent, primarily be-cause of the two large-scale upwellingplumes beneath the present-day South

2713 km

2024 km474 km

990 km

Temperature anomaly (K)

–500 –250 0 250 500

4000

5000

6000

Rad

ius

(km

)

0 105 15 20–AVST, –AVPT (10–5 K–1)

–AVST

–AVPT

474 km 2024 km

990 km 2713 km

(a) (d)

(b)

(c)

Fig. 2 (a) Depth profile of the temperature derivatives of seismic wave velocity, AVS;PT ,compiled from the data given by Karato (2008). (b, c) The temperature anomaly ateach depth compiled from the (b) "smean! and (c) "pmean! seismic tomography models(Becker and Boschi, 2002), which is adapted in the regions under 350 km depth. TheRUM model (Gudmundsson and Sambridge, 1998), which represents the configu-ration of subducting slabs, is adapted in the regions above 660 km depth. The lateraltemperature anomaly of subducting slabs in the upper mantle is herein fixed at)500 K. (d) The present-day continental configuration imposed in the simulationmodel. White arrows show the plate motions imposed for the first stage (£5 Ma) ofsimulation.

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Pacific and South Africa that lie alongthe path between these continents andthe future supercontinent. These twolarge-scale upwellings almost remainstable for 250 Ma (see white arrows inright panel).We next show the result for Model

P2 with pmean-based initial conditionand Dgcont(C) of 102 in Fig. 4. Thefour selected time stages at 31, 88, 129and 248 Ma are shown. It is clear thatthe overall movement of the conti-nents in Model P2 does not show anysignificant change from that in ModelS2. Thus, Australia, Eurasia, NorthAmerica and Africa gather in thenorthern hemisphere to form a futuresupercontinent, and the two large-scale upwelling plumes beneath thepresent-day South Pacific and Africaremain almost stable for 250 Ma. Thisresult implies that the future conti-nental movements numerically pre-dicted herein do not depend on theinitial condition of the temperaturefield based on the tomography model,even though the magnitude and pat-tern of temperature anomaly in themantle interior is quite di!erent be-tween smean and pmean models(Fig. 2b,c).

Discussion and conclusions

Our study suggests that the Africanand South Pacific large-scale upwell-ing plumes will remain stable for thenext few hundred million years, asthey seem to have done over the last500 Ma (Torsvik et al., 2010). Torsviket al. (2010) suggested that the mar-gins of large low-shear-wave-velocityprovinces, stable for at least 200 Maand possibly for 540 Ma, seem to havecontrolled the eruption of most Pha-nerozioc kimberlites. On the otherhand, Zhong et al. (2007) argued thatPangea was assembled above a majordownwelling, and following its assem-bly, a sub-Pangea upwelling associ-ated with the African large-scale

upwelling plume developed relativelyfast (c. 50 Ma) as mantle return flowin response to circum-Pangea subduc-tion. If this numerical model is cor-rect, the African large-scale upwellingplumes would not have existed priorto Pangea, and this would mean that

the Earth alternates between degree 1and degree 2 convections. Zhang et al.(2010) recently suggested that themantle in the African hemispherebefore the assembly of Pangea wascharacterized by a cold downwellingstructure resulting from plate conver-

Table 1 Model studied.

Modelname

Tomographymodel Dgcont(C) Figure

Model S2 smean 102 3Model P2 pmean 102 4Model S3 smean 103 S1 (Supporting

Information)Model P3 pmean 103 S2 (Supporting

Information)

33 Ma

90 Ma

139 Ma

250 Ma

AN

AU

EU

AFNA

6.2 cm a–1

(a)

(b)

(c)

(d)

Fig. 3 Temporal evolution of deformable continents at (a) 33 Ma, (b) 90 Ma, (c)139 Ma and (d) 250 Ma for Model S2 with the smean-based initial condition and theviscosity contrast between the continent and surrounding mantle [Dgcont(C)] of 10

2.Left panel: White arrows show the flow field at the surface of mantle. Australia,Eurasia, North America and Africa gather in the northern hemisphere to form thefuture supercontinent. On the other hand, Antarctica and South America remain intheir present-day position even after 250 Ma and are not assembled in the futuresupercontinent. Right panel: 3-D views of the temperature anomaly and the positionof the continents. Blue and yellow isosurfaces indicate temperature anomalies (i.e.temperature deviations from the lateral mean at each radius) of )200 and +300 K,respectively. Brown colour indicates the position of the continent (AU, Australia;EU, Eurasia; AF, Africa; NA, North America; AN, Antarctica). The white arrowsshow the positions of the two large-scale upwelling plumes beneath the present-dayAfrica and South Pacific. The isosurfaces of the temperature field at depths of<660 km are omitted for clarity. The white spherical surface shows the bottom of themodel mantle.

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gence between Gondwana and Lau-russia, and therefore it is unlikely thatthe bulk of the African "superplume!structure formed before c. 230 Ma.They concluded that the plate motionduring last 120 Ma played an impor-tant role in generating the Africansuperplume.There are several other suggestions

for the long-term stability of the twosuperplumes. The Pacific superplumewas suggested to have formedc. 700 Ma ago during the breakup ofRodinia supercontinent and hasremained largely unchanged sincethen (Maruyama, 1994; Maruyamaet al., 1997, 2007; Condie, 2003), asinferred from evidence for long-livedsubduction zones along the

continental margins surrounding thePalaeo-Pacific (Li and Powell, 2001;Scotese, 2001; Collins, 2003). On theother hand, the African superplumemight have been located beneath thesupercontinent Pangea that existedbetween 330 and 180 Ma. It has beenproposed that the African superplumeformed during Pangea time as a resultof thermal insulating e!ects fromPangea and that, the superplumemay eventually have caused the break-up of Pangea (Anderson, 1982). Rec-ognizing that most of the largeigneous provinces generated in thepast 300 Ma erupted near the edgesof the Africa and Pacific superplumes,Torsvik et al. (2006, 2008) suggestedthat the African and Pacific superp-

lumes and the degree 2 mantle struc-ture probably existed for the last300 Ma [see review by Zhang et al.(2010) for details].The mechanisms of assembly and

dispersal of supercontinents on theEarth have drawn considerableattention in the recent years withvarious configurations of the pastcontinental amalgams derived fromgeological jigsaw puzzles. Althoughsome attempts have been made toconfigure the future supercontinent,these studies were largely speculativeor were pivoted on simplified param-eters and models. Our study pro-vides the first attempt based on apreliminary, although robust numer-ical simulation model involvingdeformable, mobile continental lith-osphere and their time-dependentevolution.Tectonic models that emphasize the

role of double-sided (as in the westernPacific region, see Maruyama et al.,2007) or multiple subduction aspotential zones to pull together dis-persed continental fragments are sig-nificant and o!er clues to theamalgamation of supercontinents.Although the configuration of a futuresupercontinent numerically simulatedherein is broadly consistent with ahypothetical future supercontinentAmasia predicted from geological cor-relations, the speculated configurationof Amasia is not fully realized in ournumerical simulations, inhibited bylarge-scale upwellings along the pathof migration of some of the conti-nents. Thus, according to our model,the next supercontinent to be assem-bled at around 250 Ma into the futurewould comprise an amalgam of Aus-tralia, Eurasia, North America andAfrica lying in the northern hemi-sphere of our planet.

Acknowledgements

We thank J. Brendan Murphy, an anony-mous referee, and the associate editor fortheir thoughtful comments, which helpedto improve the manuscript. Some of thefigures were produced using the GenericMapping Tools (GMT) of Wessel andSmith (1998). The calculations presentedwere performed on the supercomputerfacilities (SGI Altix 4700) at JAMSTEC.M.Y. was supported by a Grant-in-Aid (Nos. 20740260, 23340132) from theMinistry of Education, Culture, Sports,Science and Technology, Japan.

31 Ma

88 Ma

129 Ma

248 Ma6.2 cm a–1

(a)

(b)

(c)

(d)

Fig. 4 Temporal evolution of deformable continents at (a) 31 Ma, (b) 88 Ma, (c)129 Ma and (d) 248 Ma for Model P2 with the pmean-based initial condition andDgcont(C) of 10

2. See Fig. 3 for details.

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Received 4 November 2010; revised versionaccepted 19 July 2011

Supporting Information

Additional Supporting Informationmay be found in the online versionof this article:Table S1. Model parameters used.Figure S1. Temporal evolution of

deformable continents at (a) 32 Ma,(b) 84 Ma, (c) 140 Ma, and (d) 243 Mafor Model S3 with the smean-basedinitial condition and Dgcont (C) of 10

3.See Fig. 3 for details.Figure S2. Temporal evolution of

deformable continents at (a) 31 Ma,(b) 76 Ma, (c) 130 Ma, and (d) 244 Mafor Model P3 with the pmean-basedinitial condition and Dgcont (C) of 10

3.See Fig. 3 for details.Please note: Wiley–Blackwell are

not responsible for the content orfunctionality of any supporting mate-rials supplied by the authors. Anyqueries (other than missing material)should be directed to the correspond-ing author of the article).

Future supercontinent in northern hemisphere • M. Yoshida and M. Santosh Terra Nova, Vol 23, No. 5, 333–338.............................................................................................................................................................

338 ! 2011 Blackwell Publishing Ltd