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Geol. Mag. 155 (1), 2018, pp. 45–58. c
Cambridge University Press 2016 45
doi:10.1017/S0016756816000716
The future of Earth’s oceans: consequences of subduction initiation
in the Atlantic and implications for supercontinent formation
JOÃO C. DUARTE∗‡§†, WOUTER P. SCHELLART§¶& FILIPE M. ROSAS∗‡
∗Instituto Dom Luiz, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
‡Departamento de Geologia, Universidade de Lisboa, Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
§School of Earth, Atmosphere & Environment, Monash University, Melbourne, VIC 3800, Australia
¶Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
(Received 25 March 2016; accepted 23 June 2016; first published online 3 October 2016)
Abstract – Subduction initiation is a cornerstone in the edifice of plate tectonics. It marks the turning
point of the Earth’s Wilson cycles and ultimately the supercycles as well. In this paper, we explore the
consequences of subduction zone invasion in the Atlantic Ocean, following recent discoveries at the
SW Iberia margin. We discuss a buoyancy argument based on the premise that old oceanic lithosphere
is unstable for supporting large basins, implying that it must be removed in subduction zones. As a
consequence, we propose a new conceptual model in which both the Pacific and the Atlantic oceans
close simultaneously, leading to the termination of the present Earth’s supercycle and to the formation
of a new supercontinent, which we name Aurica. Our new conceptual model also provides insights
into supercontinent formation and destruction (supercycles) proposed for past geological times (e.g.
Pangaea, Rodinia, Columbia, Kenorland).
Keywords: subduction invasion, Atlantic Ocean, Wilson cycle, supercycle, supercontinent, Aurica.
1. Wilson cycles and supercontinents
Alfred Wegener was the first to convincingly propose
the existence of a past supercontinent gathering all the
Earth’s continental masses (e.g. Wegener, 1912). Five
decades later, while seeding the theory of plate tec-
tonics, Tuzo Wilson provided evidence that the ‘At-
lantic’ had closed and re-opened more or less in the
same place (Wilson, 1966). These conspicuous obser-
vations suggested a pattern of cyclicity in the creation
and destruction of large oceanic basins. Later on in the
1970s evidence for the existence of a number of other
past supercontinents started to emerge (e.g. Valentine
& Moores, 1970; Piper, 1974) and the idea of a cycli-
city in the dispersion and assembly of continents over
the Earth’s history was established. At the largest time
scale a supercycle (also referred to as a supercontin-
ental cycle), encompasses the recurring dispersion and
assembly of almost all continental masses in supercon-
tinents such as Pangaea (Worsley, Nance & Moody,
1982,1984). At an immediately lower time scale order
is the Wilson cycle (named in honour of Tuzo Wilson),
which describes the history of a particular ocean from
its birth to its death, in three phases: (1) opening and
spreading; (2) foundering of its passive margins and de-
velopment of new subduction zones; and (3) consump-
tion and closure. Even though not all Wilson cycles (i.e.
the closure of a given ocean) lead to the formation of a
supercontinent, the concepts are tightly related because
the formation of a supercontinent is always preceded by
†Author for correspondence: jdduarte@fc.ul.pt; joao.duarte@
monash.edu
the closure of one or more oceans (Yoshida & Santosh,
2011). A supercycle can thus be seen as a sort of a super-
position of different Wilson cycles acting at the same
time, but potentially shifted in phase (and orientation).
So, to understand how supercontinents form we first
have to understand how Wilson cycles operate. Most
of the Wilson cycle stages can be seen somewhere in
the world today (e.g. the newly formed continental rift
in Africa, the subduction zones surrounding the Pacific
Ocean and the Himalayan collision) and are relatively
well understood. However, its key phase of subduction
initiation remains largely unknown: how do subduction
zones initiate in pristine Atlantic-type oceans? Is there
a common mechanism governing the formation of new
subduction zones?
2. Ending Atlantic-type oceans
As oceanic lithosphere spreads and cools, it becomes
gravitationally unstable. Oceanic lithosphere older than
10 Ma has an average density that is higher than the as-
thenosphere, promoting collapse and sinking into the
asthenosphere and formation of new subduction zones
(Cloos, 1993). The pull at the subduction zones will
eventually drive the continents back together. How-
ever, for subduction to initiate at passive margins the
oceanic lithosphere has to break where it is generally
very strong. This is because oceanic plates also become
stronger with age making the process of spontaneous
subduction very difficult or even unlikely (Cloetingh,
Wortel & Vlaar, 1989). Hence, in passive margins there
are generally no tectonic forces with the magnitude
46 J. C. DUARTE, W. P. SCHELLART & F. M. ROSAS
Figure 1. Location of the Atlantic subduction zone arcs invading the Atlantic: Scotia, Lesser Antilles and Gibraltar. White arrows
show the direction of present-day movement of the plates (from Schellart et al. 2007).
required to spontaneously initiate subduction (Mueller
& Phillips, 1991). Even though there is a potential
energy gradient across passive margins, calculations
show that the potential energy difference between con-
tinental and oceanic lithosphere is insufficient to ini-
tiate subduction (Lonergan & White, 1997). An addi-
tional force or pre-existing convergence is thus required
(McKenzie, 1977), and the only source to provide a
force conceivably capable of inducing subduction ini-
tiation along a pristine passive margin is another sub-
duction system or an associated collision belt (Mueller
& Phillips, 1991; Duarte et al. 2013). Alternatively,
weakening processes such as the hydration of a hyper-
extended oceanic lithosphere (by serpentinization) or
thermal erosion through mantle upwelling (e.g. plume)
have been suggested as mechanisms that can aid sub-
duction initiation (Masson et al. 1994; Ueda, Gerya
& Sobolev, 2008; Burov & Cloetingh, 2010; Whattam
& Stern, 2015). However, this does not seem to be a
widespread and sufficient mechanism, otherwise sub-
duction zones should be starting all over the Atlantic
margins (in particular when considering weakening by
hydration). Or maybe pervasive weakening processes
are limited to specific tectonic environments, such as
transform plate boundaries (e.g. the Azores–Gibraltar
fracture zone), or only have an effect over long time
scales (>200 Ma).
An alternative to the spontaneous subduction ini-
tiation model considers that subduction zones are
triggered by stress transmission from a nearby colli-
sion belt or converging region such as the Scotia and
Lesser Antilles subduction zones, which were transmit-
ted from the Pacific into the Atlantic (note that in those
two cases the subduction polarity was reversed; Figs 1,
2; Mueller & Phillips, 1991; see also Stern, 2004; Baes,
Govers & Wortel, 2011), or simply propagate from one
ocean to another (Royden, 1993). We will use from
now on the term ‘subduction invasion’ to signify a
general process of subduction initiation in an Atlantic-
type ocean in which the formation of the subduction
zone is or was induced by an external (to the pristine
basin) mechanism or force (see Duarte et al. 2013). In
this context, the concept of invasion is similar to the
infection mechanism proposed by Mueller & Phillips
The future of Earth’s oceans 47
Figure 2. Evolution of the three arcs invading the Atlantic. Panels on the left-hand side are reconstructions based on previous works,
with the Gibraltar Arc reconstruction (top left) from Rosenbaum, Lister & Duboz (2002) and Duarte et al.(2011,2013); the Lesser
Antilles (middle left) from Pindell & Kennan (2001); the Scotia Arc (bottom left) from Eagles & Jokat (2014); and the tectonic map
from Galindo-Zaldívar et al. (2006). Speculative scenarios for the future in 20 Ma are also shown, illustrating lateral subduction
zone propagation into previously inactive passive margin locations. Grey areas outline the underwater continental promontories.
(1991). Oceans such as the Atlantic are not completely
isolated and if a connection (or narrow land bridge)
to an ocean with active subduction zones exists they
are likely to be ‘invaded’ by subduction zones (Mueller
& Phillips, 1991; Royden, 1993; Duarte et al. 2013;
Murphy & Nance, 2013; Waldron et al. 2014). That
is because far-field stresses from nearby convergent
regions can be transferred to adjacent passive margins
(this could have been the case for the Scotia Arc). Also,
if a passage exists, trenches can directly migrate from
one ocean to another (as may have been the case for the
Lesser Antilles). This is because trenches are highly
movable and once they form they tend to migrate into
places where negatively buoyant oceanic lithosphere
is available (Moresi et al. 2014), especially in the fi-
nal stages of consumption that precede full continental
collision when the incoming plate starts to diachron-
ically collide and decelerates (Royden, 1993; Loner-
gan & White, 1997; Rosenbaum et al. 2002; Magni
et al. 2014). Because of this slow down the plate can-
not maintain the mass influx into the subduction zone,
which causes the rapid trench retreat (Royden, 1993).
Even though passive margins are very stable features
and ageing by itself alone does not constitute a suffi-
cient condition to its foundering, it is conceivably very
difficult, for whatever reason, to maintain a pristine
Atlantic-type ocean for long periods (>200 Ma). This
inference is supported by the almost absence of oceanic
lithosphere older than this age in the presently existing
oceans and in the geological record and by the fact that
the average age of the oceanic lithosphere on Earth
today is 60 Ma (Turcotte & Schubert, 2002; Müller
et al. 2008). Also, in a seminal paper, Bradley (2008)
showed that the present-day passive margins have a
mean age of 104 Ma, with a maximum age of 180 Ma.
Moreover, he concluded that the 76 analysed passive
margins that existed since Archaean time had a mean
life span of 178 Ma and a range of life spans from 25 to
48 J. C. DUARTE, W. P. SCHELLART & F. M. ROSAS
590 Ma. But only five of those passive margins, all of
them of Mesoproterozoic age, had life spans exceeding
350 Ma.
Oceanic lithosphere near passive margins is negat-
ively buoyant and its natural tendency is to sink. But
despite the fact that its negative buoyancy increases
with age, causing it to subside, this increase seems to
asymptotically approach a maximum value of negat-
ive buoyancy after 80–100 Ma (Cloos, 1993; see also
Stein & Stein, 1992; Crosby, McKenzie & Sclater,
2006). Note that this is in agreement with the fact that
with ageing the seafloor seems to approach a maximum
depth. This is why deep abyssal plains form. However,
there is a trade off between negative buoyancy of old
lithosphere and its higher resistance to breaking, and
therefore the negative buoyancy only becomes domin-
ant in the process of subduction and subduction zone
propagation if the lithosphere has already been broken
(for whatever reason) elsewhere nearby. Negative buoy-
ancy of old lithosphere alone cannot provide the force
necessary to break a pristine passive margin, unless a
strong weakening mechanism comes into play, or an ex-
ternal force is applied (otherwise subduction would be
starting spontaneously anywhere on present-day Earth
where old lithosphere exists). The dynamic explanation
for this is that a finite amount of energy is required to
break the lithosphere at these locations and thus it re-
mains in a meta-stable equilibrium. An external force is
needed to overcome such an energy barrier (McKenzie,
1977; Mueller & Phillips, 1991). But once this barrier
is overcome the ocean may enter a point of no return
and the propensity is for subduction zones to propagate.
We observe an analogous phenomenon in most labor-
atory models of subduction, in which the surface ten-
sion of the ambient fluid (representing sub-lithospheric
mantle) keeps the negatively buoyant plates at the sur-
face rather than letting them collapse at once (Schellart,
2008; Duarte, Schellart & Cruden, 2013). Only with a
small subduction perturbation does the subduction of
the oceanic plate progress in a realistic manner. But
once it starts and a significant portion of the plate is
subducted (180 km according to McKenzie, 1977) the
process becomes irreversible (see also Gurnis, Hall &
Lavier, 2004). In this example the fluid surface tension
can be seen as an analogue of the lithospheric strength.
That is because in nature the negatively buoyant por-
tions of the plates are maintained at the surface because
they are attached to buoyant ridges and continents. But
once a negatively buoyant portion of the plate breaks
and is forced down into the mantle (subduction initi-
ation) the subduction will likely propagate as long as
negatively buoyant lithosphere is available. There will
be a point where the resisting forces no longer have the
magnitude required to oppose the slab pull and the pro-
cess becomes irreversible and self-sustained (McKen-
zie, 1977; Gurnis, Hall & Lavier, 2004). For further use,
we will call this the buoyancy argument. In short, the
buoyancy argument states that once a subduction sys-
tem has invaded an old ocean (with negatively buoyant
lithosphere) the system will likely propagate and the
ocean may enter its closing phase. Note that it would
only be possible to maintain an ocean with an active
continental-scale subduction system if the spreading
rate at the corresponding ridge system was higher (or
precisely the same) than the consumption rate at the
bounding subduction zones. However, such a scenario
is unlikely since most of the spreading centres on Earth
are passive as plate tectonics is driven, essentially, by
the slab pull at subduction zones (Forsyth & Uyeda,
1975; Davies & Richards, 1992; Conrad & Lithgow-
Bertelloni, 2002). For these reason, ridges can migrate
towards the subduction systems and shut down (as is
observed in the Pacific Ocean). Only in a perfectly sym-
metric steady-state system would the ridges remain at
the centre of the ocean. Moreover, because subduct-
ing slabs have a slab-normal component of sinking, the
trenches generally migrate either towards the margins
or towards the ridges. The only way to keep an ocean
with active subduction zones open is if there is a con-
stant regeneration of marginal seas. However, because
trenches migrate and drag portions of the plates and
the sinking slabs pull their trailing plates, the contin-
ents will eventually start to approach. This seems to
be the case for the Pacific Ocean, where the ridges are
presently being subducted. In addition, the subduction
zone trenches in the Western Pacific and Eastern Pa-
cific are migrating towards each other, as already noted
by Elsasser (1971). Therefore, the Pacific Ocean ap-
pears destined to close. Note that it is possible to start
new spreading ridges in the interior of oceanic plates,
and there is at least one documented case (Barckhausen
et al. 2008), but because the oceanic lithosphere is very
strong, such phenomenon seems to be rare. The Pacific
may have persisted for such a long period because it
simply grew very big around Pangaea and even though
subduction zones started more than 200 Ma ago the
ocean did not have the time to close yet. Presently, the
observations show that the western margin and the east-
ern margin are approaching each other. The oceans do
not necessarily have to close after 200–400 Ma of
their formation, as testified in the case of the Pacific.
But there is evidence that subduction zones have to start
after 200 Ma and migrate to the passive margins (to
explain their limited life span) and that once subduc-
tion zones form the ocean may be destined to close,
even though that can potentially take a long time (up to
600 Ma).
One could also conceive, by applying the buoyancy
argument, that older oceanic plates (>100 Ma) are
more likely to start being consumed in the mantle. This
is because older plates are more negatively buoyant.
Oceanic plates younger than 10 Ma are positively
buoyant, at 10 Ma they become neutrally buoyant
and older than that they are negatively buoyant (with a
density contrast of ρ40 kg/m3). Therefore, there
is more potential energy available to trigger subduction
(Cloos, 1993; Afonso, Ranalli & Fernandez, 2007).
However, because oceanic plates become stronger dur-
ing their first 100 Ma of cooling (e.g. Stephen-
son & Cloetingh, 1991; Afonso, Ranalli & Fernandez,
The future of Earth’s oceans 49
2007) the energetic threshold that needs to be over-
come to trigger foundering of an old passive margin
(>100 Ma) is at a high level. This is why old passive
margins are very stable features. Thereby, for a subduc-
tion zone to be initiated, the following ingredients may
be required: the action of an external force (Mueller
& Phillips, 1991; Marques et al. 2013; Duarte et al.
2013), the existence of pre-existing fractures / trans-
form faults (Mueller & Phillips, 1991; Waldron et al.
2014) and/or a weakening mechanism, e.g. serpentiniz-
ation, thermal erosion by the action of a plume (McK-
enzie, 1977; Whitmarsh et al. 1993; Stern, 2004; Baes,
Govers & Wortel, 2011; Whattam & Stern, 2015). But
because the strength of the lithosphere increases with
age, subduction zones may actually be more likely to
nucleate in juvenile to middle aged lithosphere (20
to <100 Ma) rather than in locations with very old
oceanic lithosphere (100 to 200 Ma) (Cloetingh, Wortel
& Vlaar, 1989; Mueller & Phillips, 1991; Cloos, 1993).
In fact, the models of spontaneous subduction initiation
of Nikolaeva, Gerya & Marques (2010,2011) sugges-
ted that age (and strength) of the oceanic lithosphere
on its own has a secondary influence on the initiation
of trenches, and that the main controlling parameters
are the thermal structure and chemical buoyancy of the
continental lithosphere. The potential likelihood for in-
duced subduction to initiate in young to middle aged
lithosphere can also explain why subduction initiated
in the Scotia and Lesser Antilles arcs (and potentially
in SW Iberia, that shows some signs of passive mar-
gin reactivation that may have already started during,
or even before, Miocene time), while the older Moroc-
can and Eastern North American margins (180 Ma)
show no clear signs of subduction initiation (see Figs 1,
2). Nevertheless, it is likely that the subduction zones
will propagate laterally into these regions of very old
lithosphere (see Fig. 2 and discussion below).
3. Are subduction zones invading the Atlantic?
The Atlantic margins are generally described as the typ-
ical case of passive margins. However, there are at least
two regions where Atlantic oceanic crust is already be-
ing consumed in subduction zones: in the Scotia and in
the Lesser Antilles arcs (Figs 1,2). These subduction
zones seem to have been transmitted (by direct migra-
tion or by stress propagation from a nearby convergent
region along a transform structure that could have acted
as a stress guide) from the Eastern Pacific Ocean to the
Atlantic (see Fig. 2;Barker,2001; Dalziel et al. 2013;
Eagles & Jokat, 2014). The exact physical mechanism
by which this happened is still being investigated and
is a matter of debate, but Goren et al. (2008) proposed
that the Atlantic passive margins were weakened by
fluids emanated from the East Pacific subduction sys-
tem, while Vérard, Flores & Stampfli (2012) suggested
that subduction in the Scotia Arc was initiated by the
differential motion of Antarctica and South America.
Plate congestion and stress transmission from nearby
subduction zones have been proposed as one of the
most plausible mechanisms for subduction initiation
in those regions (Mueller & Phillips, 1991). Recently,
Whattam & Stern (2015) suggested that subduction
initiation in the Caribbean might have been driven by
a plume. Notwithstanding, it is well known that the
Lesser and Greater Antilles arcs formed in Early Creta-
ceous time and propagated radially into the Atlantic
until the trench eventually collided with the Yucatan
and the Bahamas continental promontories (see grey
area in Fig. 2), in the north, and with South America
in the south, restraining the arc to its present geometry
(Pindell & Kennan, 2001). Similar constraints were im-
posed on the Scotia Arc after its formation by the Falk-
land (continental) promontory and the Georgia Rise
(to the north; see grey area in Fig. 2) and the South
America – Antarctica spreading centre in the Weddell
Sea (to the south; see Fig. 2; Eagles & Jokat, 2014).
It is thus expected, and geodynamically plausible, that
the arcs will propagate laterally northwards once they
surpass these obstacles (Moresi et al. 2014). This is
likely to happen because as the trench approaches the
Mid-Atlantic Ridge the lithosphere becomes less neg-
atively buoyant in relation to its adjacent segments, and
therefore it is more likely that the subduction will first
propagate northwards (parallel to the East American
passive margins) where negatively buoyant lithosphere
is available. Note that this was what happened when
the Greater Antilles arc formed and spread over the
Atlantic until it collided with the Bahamas promontory
(Pindell & Kennan, 2001). Evidence for this present-
day lateral northwards propagation can be observed
in the northern (Puerto Rico) segment of the Lesser
Antilles subduction zone where a short S-dipping slab
segment already has a northward-retreating component
(Schellart et al. 2011). Also in the Scotia Arc there is
already a S-dipping segment of the slab that will likely
migrate northwards (see Fig. 2; Gudmundsson & Sam-
bridge, 1998; Lynner & Long, 2013). A propagation
scenario is schematically illustrated in Figure 2, which
is inspired by the recent numerical models presented
by Moresi et al. (2014) that showed that subduction
systems tend to engulf and move beyond these kinds of
continental obstacles.
The Gibraltar Arc is a third place on Earth that has
been described as a potential locus for subduction to
propagate or induce the nucleation of a new subduction
zone in the Atlantic (Figs 1,2; Duarte et al. 2013; see
also McKenzie, 1977; Mueller & Phillips, 1991;Roy-
den, 1993; Ribeiro et al. 1996; Gutscher et al. 2002,
2012). But in this case there is no polarity reversal of
the subduction zone (i.e. change in the dip direction;
also know as ‘subduction flip’). Instead, the Gibraltar
subduction zone is already synthetic (i.e. dipping to the
east) with the thrust fault structures at the West Iberia
margin and it will likely either retreat to the Atlantic
and/or force (together with the overall Africa–Iberia
convergence) the initiation of a new subduction zone
along the Iberia margin (see Fig. 2). Note that, contrary
to the Scotia and Lesser Antilles, in the Gibraltar re-
gion a thrust system is already propagating along the
50 J. C. DUARTE, W. P. SCHELLART & F. M. ROSAS
adjacent West Iberia passive margin (Terrinha et al.
2009; Cunha et al. 2010; Duarte et al. 2013). Such
induced passive margin reactivation is assisted by the
ongoing terminal stages of collision between Africa and
Eurasia (a consequence of the closing of the Tethys) that
produces compressive stresses at this location; while in
the Scotia and Antilles arcs the adjacent continents
are not fully colliding yet. This arc-orthogonal conver-
gence is accommodated by a NE–SW thrust system
that extends for 300 km along the West Iberia ‘pass-
ive’ margin (Terrinha et al. 2009; Duarte et al. 2013).
The thrust-related morphologies have prominent es-
carpments reaching up to 5 km in height in the case of
the Gorringe Bank and the thrusts root deep into the
mantle. Even though the Gorringe thrust has been act-
ive since at least Palaeogene time, younger thrust faults
are nucleating further north away from the Azores–
Gibraltar plate boundary and along the west Portuguese
passive margin (e.g. the Tagus Abyssal Plain Fault; Ter-
rinha et al. 2009; Duarte et al. 2013). This deforma-
tion peaked in Miocene time upon the arrival of the
Gibraltar Arc and the Alboran microplate, whose west-
ward movement is still continuing (as observed with
GPS data; e.g. Palano, González & Fernández, 2015).
The seismicity is concentrated at depths of 40–60 km
(Geissler et al. 2010) with very high magnitude (thrust-
ing) seismic events (Ms 8–9) such as the 1969 Horse-
shoe earthquake and possibly the 1755 Great Lisbon
Earthquake (Fukao, 1973; Stich et al. 2007; Terrinha
et al. 2009). Together, these structures are the expres-
sion of a compressive deformation front forming to the
west of the Gibraltar Arc and along the SW Iberia mar-
gin, and appear to correspond to the onset of the margin
tectonic inversion and nucleation of a new subduction
zone (Terrinha et al. 2009; Rosas et al. 2009; Duarte
et al. 2013).
It is worth mentioning that the Asturian margin,
North Iberia (Bay of Biscay), also underwent some
shortening during middle Eocene to late Oligocene
times with the formation of a small accretionary
wedge (subduction initiation). However, the system
became inactive during Burdigalian time (probably
because the portion of the oceanic plate subducted was
not long enough for the subduction to become self-
sustained) and is now sealed by younger sediments
(Alvarez-Marron, Rubio & Torne, 1994; Fernández-
Viejo et al. 2012). This wedge formed during a period
of convergence between Iberia and Europe, which res-
ulted in the formation of the Pyrenees, but since then
Iberia remained attached to Europe. The present-day
convergence is now accommodated mainly between
Africa and Iberia with an oblique WNW–ESE direc-
tion, orthogonal to the West Iberian margin (Nocquet
& Calais, 2004; Duarte et al. 2011). Therefore, SW
Iberia is the only case of an active stage of this pro-
cess of passive margin inversion (subduction invasion)
in the Atlantic, thereby providing crucial insights on
how this process may unfold. Together, the three arcs
(Scotia, Lesser Antilles and Gibraltar) are likely the
precursor of a large-scale Atlantic subduction system
that may ultimately lead to its closing (end of a Wilson
cycle) and to the formation of a new supercontinent
(new supercycle). This hypothesis will be discussed in
the following sections.
4. Supercycles
When the concept of supercycles was first proposed
they were believed to have a periodicity of about
400–600 Ma (Worsley, Nance & Moody, 1982,1984;
Veevers, Walter & Scheibner, 1997). But it has been
recently recognized that the cycles are probably less
periodic than it was originally envisaged (Meert, 2012;
Nance & Murphy, 2013; Nance, Murphy & Santosh,
2014). The timescales of supercycles are difficult to
estimate and are not well defined. Neither break-up
nor collision happens instantaneously, but rather dur-
ing time ranges that might even comprise some degree
of overlap. Owing to the scarcity of data and the limited
number of cycles that Earth underwent, supercyclicity
can only be tested using numerical models. Such invest-
igations started several decades ago (e.g. Gurnis, 1988)
but only recently codes reached the sophistication re-
quired to solve many of the long-standing problems, in-
cluding the potential cyclicity in continental drift (see
e.g. Yoshida & Santosh, 2011). As an example it is
worth mentioning the work of Rolf, Coltice & Tackley
(2014) that, using 2D and 3D dynamic numerical mod-
els, dismissed the existence of regularity in the disper-
sion and aggregation of supercontinents, suggesting in-
stead a statistical cyclicity with a characteristic period
imposed by mantle and lithosphere properties (see also
Section 8, Autocyclicity). According to these authors,
such a characteristic period is hidden in the immense
fluctuations between different cycles that arise from
the chaotic nature of mantle convection. For example,
in one of their runs with moderate plate strength, six
completed cycles occurred during a period of 4 Ga,
with an average duration of 640±105 Ma. The same
models showed that stronger or weaker plates promote
longer supercycles: stronger plates by hampering su-
percontinent break-up and thus giving origin to longer
periods of aggregation, and weaker plates by sustaining
longer periods of dispersion. Rolf, Coltice & Tackley
(2014) also showed statistically that a dispersed con-
figuration can be maintained for up to 2 Ga and argued
that this could be a consequence of the higher degrees
of freedom in a dispersed configuration, as suggested
by Gurnis (1988). However, such long cycles appear
to be at odds with natural observations, suggesting the
importance of other factors that might not have been
tested in these models.
Over the last years some discussion has also revolved
around the precise definition of supercontinent (see e.g.
Bradley, 2011) and their pre-Pangaea existence is still a
matter of debate (e.g. Kroner & Cordani, 2003). Never-
theless, it is commonly agreed that Pangaea (250 Ma)
and Rodinia (1.1 Ga) were supercontinents, gather-
ing ‘almost’ all the continental masses (e.g. Nance,
Worsley & Moody, 1986; Rogers, 1996; Weil et al.
The future of Earth’s oceans 51
1998; Scotese, 2004; Torsvik, Gaina & Redfield, 2008;
Murphy & Nance, 2008). Therefore, a supercycle can
be defined as the period of time that spans from Rodinia
break-up to Pangaea assembly. However, some authors
also consider Gondwana (600 Ma) a supercontinent
(see e.g. Nance, Murphy & Santosh, 2014 and ref-
erences therein), even though it did not gather all (or
almost all) the Earth’s continental masses. Indeed, ma-
jor continental masses such as Laurentia, Siberia and
Baltica were separated from Gondwana. An alternative
has been to consider Gondwana as a megacontinent.
From this perspective two supercycles can be envis-
aged in the time span between Rodinia and Pangaea.
This ambiguity lies in the existence of some confusion
between the classical definition of the Wilson cycle (to
describe the evolution of a single ocean) and the more
recent concept of supercycle (to describe the cyclical
gathering of all or almost all continental masses). Note
that the two concepts are indistinguishable when only
two oceans and two continental masses are considered
(as it is often the case in discussions of whether the
Pacific or the Atlantic will close). With more than two
continental masses being dispersed and diachronically
colliding it becomes clear that the Wilson cycle is of
lower order than the supercycle (several oceans close
to form a new supercontinent; Murphy & Nance, 2003;
Yoshida & Santosh, 2011). This problem is also dir-
ectly related with the modes of supercontinent forma-
tion: introversion (Atlantic-type closure) versus extro-
version (Pacific-type closure), and potential combina-
tions of both (Murphy & Nance, 2003; Silver & Behn,
2008). In introversion a supercontinent such as Pangaea
breaks up to form an internal Atlantic-type ocean. After
about ten million years onwards the margins become
negatively buoyant and new subduction zones may in-
vade the ocean, bringing the continents back together.
The almost non-existence of oceanic lithosphere older
than 200 Ma argues in favour of this mode of closure
(we could invoke the buoyancy argument here). In ex-
troversion, the continental masses diverge right after
the break-up, laterally drifting over the Earth’s surface
eventually to meet and collide at another given position.
In the present-day Earth this mode would correspond to
the closure of the Pacific. But, the Pacific also has very
old and negatively buoyant oceanic lithosphere and thus
we could also apply the buoyancy argument here to con-
clude that the Pacific is also destined to close. A third
possible mode of closure – named orthoversion – was
proposed by Mitchell, Kilian & Evans (2012) whereby
the succeeding supercontinent forms 90 degrees away,
within the great circle of subduction encircling its rel-
ict predecessor. In this case both oceans are conserved
while a third (orthogonal) closes. The question now
arises if there are any other alternatives that are not just
complex variations of these three hypotheses.
5. The closure of the Atlantic, the Pacific or both?
The Auri ca hypothesis
Most authors agree that the Pacific is going to be the
next major oceanic basin to close (e.g. Silver & Behn,
2008 and references therein). But it is also known that
the Atlantic has been opening for 200 Ma, and at
the present rate at which the Americas in the east are
approaching East Asia and Australia in the west (3–
4cmyr
−1) the Pacific may close roughly in 300 Ma.
Accordingly with the extroversion mode of evolution,
if subduction zones do not propagate along the Atlantic
margins this ocean would thus continue to open for an-
other 300 Ma leaving very old (500 Ma) oceanic
lithosphere behind. It is, however, difficult to con-
ceive 500 Ma old oceanic lithosphere, having in mind
that the present-day average age of the seafloor is
60 Ma. Considering that negative buoyancy does not
constitute a sufficient condition for the lithosphere to
founder, this fact alone seems to suggest that there
may be some kind of lithospheric weakening mechan-
isms operating at these time scales (e.g. the hydration
of the lithosphere, serpentinization, hydrothermal cir-
culation; all recognized as presently ongoing in the
West Iberia margin, see Duarte et al. 2013 and refer-
ences therein). Furthermore, the present state of know-
ledge suggests that the Atlantic oceanic lithosphere is
already broken (and gravitationally unstable) and new
subduction zones are propagating (Duarte et al. 2013).
Therefore, an alternative scenario can also be envis-
aged, in which both the Atlantic and the Pacific will
close.
Within this context several specific scenarios have
been proposed for the evolution of the Earth’s oceans
and continents. One is the closure of the Pacific at
the expense of the opening of the Atlantic leading
to the formation of a new supercontinent by extro-
version. This supercontinent was named Novopangaea
by Roy Livermore in a BBC documentary (http://www.
thefutureiswild.com/; see also Nield, 2007). Another
scenario, opposite to this one, is the closure of the
Atlantic, preserving the Pacific. In such case the result-
ant continent is formed by introversion and was named
Pangaea Proxima (Scotese, 2007). A third hypothesis –
orthoversion – was proposed in which the North Amer-
ica and Eurasia plates migrate northwards and gather
near the North Pole (Mitchell, Kilian & Evans, 2012).
The resulting continent was named Amasia (following a
previous proposal by Hoffman, 1997).All these models
require that the Pacific, the Atlantic or both continue to
grow for another 100–400 Ma, leaving very old oceanic
lithosphere behind (up to 600 Ma old). As mentioned
earlier, this appears to be unlikely.
Even though the prediction of plate movement bey-
ond 10 Ma is speculative (Rowley, 2008), it is, never-
theless, possible to envisage a fourth alternative class
of scenarios in which both the Atlantic and the Pacific
will close: the Atlantic by introversion and the Pacific
by extroversion (Fig. 3). Such a scenario has the advant-
age of allowing the removal of very old and negatively
buoyant lithosphere that presently covers some areas of
the seafloor and at the same time allowing the Atlantic
passive margins to disappear. One could even argue that
this is not only a possibility but a necessary condition
imposed by the buoyancy argument (coupled with the
52 J. C. DUARTE, W. P. SCHELLART & F. M. ROSAS
Figure 3. (Colour online) Conceptual model of the evolution of
the disposition of the Earth’s oceans and continents. In this scen-
ario both the Atlantic and the Pacific will close at the expense of
the formation of a new superocean (Indian +Southern oceans)
and eventually lead to the formation of a new supercontinent:
Aurica, with Australia and the Americas in the core of the new
supercontinent. The position of the future plate boundaries does
not pretend to be precise but, instead, to illustrate the propaga-
tion of the main subduction systems. The construction of Aurica
was done by manipulating the present-day continents on a sphere
using the software GPlates (http://www.gplates.org/).
action of weakening mechanisms over long time scales)
and the subduction invasion mechanism.
A scenario in which both the Atlantic and the Pa-
cific will close is possible if we consider the expansion
of a third or more oceanic basins. For example, the
Indian (or a future intra-African ocean, as the Indian
Ocean is also relatively old and may be recycled as
well) and Southern oceans where more recent ridges
are spreading and younger buoyant oceanic lithosphere
exists (even though the northward movement of Ant-
arctica may remove part of the Southern Ocean). This
scenario requires that a new rift propagate from the
Indian Ocean northwards across Eurasia. Such a rift
can hypothetically nucleate as a consequence of the
gravitational collapse of the Himalayan plateau, as it
is recognized that rifts often form near terminal col-
lision belts (where an excess of potential energy ex-
ists, especially after the delamination of the root of
the belt) and propagate along previous suture zones.
This was the case for the Atlantic that formed near
the Variscan suture zone, as noted by Tuzo Wilson
many years ago (Wilson, 1966). Such a hypothetical rift
could propagate along the western margin of the East
Asian (active) deformation zone through the Baikal
rift, connecting with the spreading centre in the Arctic
Ocean.
According to this scenario, the Pacific Ocean may
continue to close. But because subduction zones seem
to be terminating in the western margin of North Amer-
ica, if new subduction zones do not re-form here, the
North American continent may stay relatively station-
ary or rotate slightly clockwise. Alternatively, it may
move eastwards if a new subduction system indeed
propagates along the western Atlantic margin. In such
case, in 20 Ma, South America will separate from
North America, and together with Australia, will rotate
and move further north. Simultaneously the subduc-
tion zones in the Atlantic may propagate from the arcs
along the western passive margins. This will induce
an asymmetry in the closure of the Atlantic pulling
westwards the then-formed megacontinent Eurafrica
(Europe +Africa). At the same time, subduction zones
may propagate along the eastern Atlantic margins. A
subduction system may also propagate from the South
Shetland Islands along the Antarctica margin, forcing
it to rotate and move northwards, and eventually collide
with the westerns margin of South America.
In about 150 Ma, Australia docks with continental
East Asia, while South America rotates further west
and Antarctica moves further north. From the great Pa-
cific Ocean only a small internal sea will then remain.
At this stage, Eurafrica will be completely detached
from East Asia and the Atlantic will also become nar-
rower. The Indian and Southern oceans will expand
and will become a new superocean. Notwithstanding,
the present-day subduction zones are also starting to
propagate into the Indian Ocean (e.g. the Sunda trench)
and a new one may even initiate offshore south India
(e.g. Mueller & Phillips, 1991). This system may de-
velop in what will be a peripheral subduction system
that will circumvent a hypothetical new supercontinent.
Having taken into account the present-day average
plate velocities a new supercontinent may be fully
formed in approximately 300 Ma. Most of the con-
tinental masses will move and collide at a point centred
slightly north of the equator and Australia and the
Americas will gather at its interior and form the core
The future of Earth’s oceans 53
of the supercontinent. For this reason, we have named
the future supercontinent Aurica (Fig. 3).
6. Thoughts on past cycles
As we have discussed, the process of subduction inva-
sion and propagation at Atlantic-type oceans can have
a crucial role in the turning point of Wilson cycles
and supercycles. In this paper we have shown that by
applying the dynamic buoyancy argument assisted by
oceanic lithosphere weakening, coupled with the sub-
duction invasion mechanism, to our reasoning it is con-
ceivable (if not mandatory) that in the long term both
the Pacific and the Atlantic oceans will close. This reas-
oning can also help us to gain insights into what might
have happened in the past. For example, it becomes
evident that plate reconstructions should incorporate
dynamic constrictions, such as the ones imposed by the
buoyancy argument and the action of weakening mech-
anisms (e.g. hypothetical upper limits for oceanic plate
ages). So far, owing to technical limitations a large
number of reconstructions are purely kinematical. But
we hope to have shown that they should also account for
(and be dynamically consistent with) the history, evol-
ution and geometry of the oceans, oceanic lithosphere
ages, spatial distribution of subduction zones, timing
and position of subduction initiation, the mechanisms
by which subduction zones propagate, and how they
can close oceans. Such approach was recently applied
by Waldron et al. (2014) to the Iapetus Ocean. The
authors proposed that an analogue ‘infection’ mechan-
ism to the one observed in the Gibraltar, Scotia and
Lesser Antilles was responsible for the introduction of
subduction zones in the relatively young Iapetus and
eventually its closing.
Because the geological record is scarce and incom-
plete it is a scientific challenge to constrain the evol-
ution of ancient oceans, in particular it is difficult to
reconstruct when, where and how subduction zones
started. Notwithstanding, there are particular geolo-
gical features that can provide crucial evidence on past
subduction zone initiation. Fossilized passive margins
and reactivated passive margins, ophiolites and suture
zones can give information on the age and position
of ancient oceanic basins. Also, well-preserved fore-
arc ophiolites usually keep a high-fidelity magmatic
and stratigraphic record of subduction initiation (e.g.
fore-arc basalts covered by boninites and andesites;
Stern et al. 2012). Therefore, by mapping and dating
such rocks it should be, in principle, possible to dia-
gnose where and when a certain subduction system
nucleated and how it propagated. Such studies would
require a good understanding of the present-day fore-
arc stratigraphy, mineralogy and geochemistry. These
studies are still scarce but are starting to emerge (see
e.g. Whattam & Stern, 2011; Murphy & Nance, 2013).
Furthermore, for a given supercycle (or a Wilson cycle,
if only two megacontinents are considered) the chrono-
logical relationship (age difference) between the em-
placed ophiolites during closure and the break-up of
the previous supercontinent can be used to distinguish
between the two modes of closure: introversion versus
extroversion (Murphy & Nance, 2003). If the ophiolite
rocks are younger than the age of break-up of the previ-
ous supercontinent then the new supercontinent formed
by introversion. If the ophiolites are older than the age
of break-up of the preceding supercontinent then the
new supercontinent formed by extroversion. Such rela-
tionships can be obtained from the geological record.
For example these types of studies revealed that the
supercontinent Pangaea and the megacontinent Gond-
wana formed by introversion and extroversion, respect-
ively. And thus, strictly, Pangaea preserved elements of
both types of closure, because Gondwana was part of
Pangaea (Murphy & Nance, 2003).
It is worth mentioning here that terms such as Wilson
cycle, supercycle, supercontinent and megacontinent
are qualitative and not always well defined. This fact
was outlined by Bradley (2011), who advised that these
terms should be used with caution to ‘avoid the artifi-
cial pitfall of an all-or-nothing definition’. The author
also proposed the usage of the semi-quantitative term
‘supercontinentality – area of the largest continent and
number of continents’, but noted that there are still
some difficulties in proceeding as such: ‘Precambrian
plate reconstructions are not nearly as robust as Phan-
erozoic ones, so quantitative measures of “supercon-
tinentality” ( ...)arefraught with uncertainty. Proxies
are needed.’
7. Simplifications, limitations of our approach
The ideas presented in this contribution incorporate
a significant number of simplifications and as a con-
sequence may have some inherent limitations. For ex-
ample, we preferentially consider subduction invasion
as the main mechanism for subduction initiation at
Atlantic-type oceans. This assumption is founded on
two main reasons, one dynamic and another observa-
tional: (1) analytic calculations show that under typical
plate tectonic condition the only source of force that
can trigger subduction initiation is another subduction
system or a collision belt (Mueller & Phillips, 1991),
at least for short timescales (<200 Ma). But, it should
be noted that other (different or auxiliary) mechanisms
may play (or may have played) a role in the initiation of
subduction zones, e.g. the impact of voluminous mantle
plumes or meteorites, anomalous hydration of the litho-
sphere, among others; (2) adding to this, there is an
observational reason to favour the process of subduc-
tion invasion as the dominant mechanism of subduction
initiation: in the present day the only two (or three, if
Gibraltar is considered) cases of subduction initiation
in the Atlantic were invasion cases. Moreover, all the
other Cenozoic subduction systems seem to have been
induced by other convergent systems (Mueller & Phil-
lips, 1991; Stern, 2004). In this paper we favour the
invasion mechanism for the formation of new subduc-
tion zones in an Atlantic-type ocean that is not con-
verging. However, it is possible for subduction zones
54 J. C. DUARTE, W. P. SCHELLART & F. M. ROSAS
to start intra-oceanically in oceans where convergence
is already occurring (e.g. Indian and Pacific; McKen-
zie, 1977; Mueller & Phillips, 1991). A present-day
example may be the Capricorn plate. Even though this
is a different mechanism from direct invasion it can be
included in the class of induced subduction initiation
(Stern, 2004). The consideration of other subduction
initiation mechanisms may promote variations within
our general model.
We are also considering that the present-day tec-
tonic drivers will not change significantly in the next
100–200 Ma. This is because subduction zones cor-
respond to major mantle downwellings that delimit
major mantle convective cells (Conrad, Steinberger &
Torsvik, 2013). These cells are expected to be relat-
ively stable over geological time scales of the order of
100 Ma (Collins, 2003). Our assumption is reasonable
when considering, for example, the South American
subduction zone, which has been active continuously
since Jurassic time (Coira et al. 1982), and the eastern
boundary of the Australian plate, which has been a zone
of subduction for most of Phanerozoic time (e.g. Betts
et al. 2002; Schellart, Lister & Toy, 2006). However, we
need to be aware that locally (at smaller scales) things
can change dramatically (Rowley, 2008).
The evolutionary model shown in Figure 3 is a sim-
plified sketch that does not pretend to reproduce all
possible details of what a more realistic reconstruction
would look like. Instead, it should be seen as a class
of scenarios in which both the Atlantic and the Pacific
close, but an infinite number of variations of this spe-
cific scenario are possible. For example, the movement
of the continents past 20 Ma is highly speculative and
simplified and the proposed time of formation for Aur-
ica is a rough estimation. For a matter of clarity and
consistency the models have a minimum amount of
complexity. For instance, we do not take into account
the creation and evolution of small internal oceans
(Wilson cycles). There are two main reasons for this
choice. Firstly, the present-day configuration corres-
ponds to a stage of high dispersion with three mature
oceans (the Atlantic, Pacific and the Indian) and a fourth
terminal one (Tethys) and therefore it is difficult to en-
visage how a new major ocean would form if not by
the propagation of a pre-existent one along a suture or
active deformations zone (such as the Indian Ocean).
Secondly, even if small ocean basins do form (such as
by the propagation of the East African Rift) their evol-
ution will be largely controlled by the dynamics of the
major tectonic plates. Notwithstanding, it is worth rein-
forcing here that the opening of an intra-African ocean
along the East African Rift and eastwards migration of
the Somalian continental block would allow the Indian
Ocean to be recycled.
Complex resurfacing due to the retreat of intra-
oceanic arcs is also lacking in our models. This is be-
cause, contrary to the large continents and continental
subduction zones, isolated trenches are highly movable
and their kinematics is difficult to predict. Also, we
do not account for the formation of new intra-oceanic
rift systems, such as by the propagation of back-arc
basins. Notwithstanding, it should be noted that the
complete resurfacing of an ocean due to the migration
of intra-oceanic trenches or by the formation of new
rifts is possible, which could, in principle, preserve a
mature ocean for longer than would be expected from
the application of the buoyancy argument alone (e.g.
the Pacific).
8. Autocyclicity
It should be noted that our conceptual view implies that
plate tectonics and mantle convection behave in some
sort of autocyclic manner and that Wilson cycles and
supercycles are the manifestation of a quasi-periodic
variation in states of convergentness and divergentness.
Rolf, Coltice & Tackley (2014) using global dynamic
numerical models showed that a statistical cyclicity
should exist in an Earth-like system with mantle con-
vection, plate tectonics and continental drift. Several
previous works suggested cycles with lifetimes of 500
to 1 Ga, or longer, depending on parameters such as the
strength of the lithosphere, viscosity and temperature
of the mantle, and number of continents, among several
others factors. As discussed in Section 4, these authors
showed that the strength of the plates is a key factor
in controlling the lifetime of a cycle. Cycles of the
order of 500–700 Ma are compatible with plates with
moderate strength, while stronger and weaker plates
promote longer periods of aggregation and dispersion,
respectively, and consequently longer supercycles.
We further suggest that this cyclicity is inherent to
the metastability of old oceanic plate material and that
its destruction is somehow preordained. This is because
as oceanic lithosphere ages it becomes more negatively
buoyant and/or weaker, and therefore oceanic basins
must grow and shrink (and therefore continents must
disperse and then assemble) in some sort of cyclic man-
ner with combinations of introversion and extroversion.
In this work, we have favoured the invasion mechanisms
for the introduction of new subduction zones in pristine
basins because it is presently occurring in the Atlantic.
However, it should be noted that a scenario could be
envisaged in which the oceanic lithosphere simply be-
comes very weak after a certain age (>> 200 Ma) and
therefore if subduction zones do not invade an ocean
within this period, new subduction zones may spontan-
eously initiate (intra-oceanically or at passive margins;
Nikolaeva, Gerya & Marques, 2010,2011;Dymkova&
Gerya, 2013). However, we do not have any present-day
example of oceanic lithosphere of this age to test this
hypothesis. Further knowledge on oceanic plate weak-
ening mechanisms (such as serpentinization or thermal
erosion) and testing of complying conjectures through
numerical modelling may bring new insight into this
matter.
A new interesting insight was provided by Rolf,
Coltice & Tackley (2012) who showed that there is
a feedback between the size of the oceanic plates and
continents and the temperature of the sub-lithospheric
The future of Earth’s oceans 55
mantle. It was already known that the presence of a
supercontinent in the Earth’s surface would have the
effect of thermal blanketing (i.e. the temperature in-
crease of the sub-lithospheric mantle due to the low
heat conduction of the lithosphere; Anderson, 1982;
Gurnis, 1988; Yoshida, Iwase & Honda, 1999; Coltice
et al. 2009), which could be the main cause of su-
percontinental break-up and consequent dispersal. In-
terestingly, Rolf, Coltice & Tackley (2012) showed
that large oceanic plates also cause thermal blanket-
ing, increasing the temperature of the sub-lithospheric
mantle. This is because oceanic plates become thicker
and denser with age, isolating the mantle underneath.
We can thus envisage a trade off between the num-
ber and size of plates, continental dispersion and sub-
lithospheric mantle temperatures. When a supercon-
tinent forms the mantle temperatures start to increase
and mantle flow reorganizes, eventually leading to the
generation of partial melts and supercontinent break-
up (see also Yoshida & Santosh, 2011). The continents
then start to disperse at the expense of the creation
of new oceanic lithosphere. Maximum dispersion with
many different plates and continental blocks allows
temperatures to drop. However, if the newly formed
oceanic plates grow too big they will start to increase
again the temperatures of the sub-lithospheric mantle,
which will eventually cause thermal erosion and pro-
mote the weakening and failure of the oceanic plates.
Note that the plates will be thicker near the passive mar-
gins and therefore this is where the temperatures are
expected to be higher. This feedback between oceanic
plate thickness and sub-lithospheric mantle temperat-
ures may also have a fundamental role in the process of
subduction initiation at Atlantic-type passive margins,
especially for time scales of the order of >> 200 Ma.
It is also possible to envisage a purely geometric
explanation for this (apparently observed) cyclicity, re-
lated with the ratio between the surface area of the
planet and the area of randomly moving continents.
One can imagine an Earth-like sphere with a surface
area of 5 ×108km2with one-third of continental litho-
sphere, in which several dozens of plates composing
the outer shell of this sphere constantly move relative
to each other such that, at any one time, areas of con-
tinental lithosphere become increasingly aggregated or
dispersed. Therefore, even though the movement of
the continents seems random (chaotic?) at relatively
short planetary time scales (<100 Ma) it may cre-
ate patterns (order) at larger time scales (>> 200 Ma)
(see also the statistical approach of Rolf, Coltice &
Tackley, 2014). More interestingly, one can think that
there might exist a feedback between these kinematic
constraints and the dynamic ones (such as the mag-
nitude of the slab pull force and the viscosity of the
mantle), in particular, because the movement of plates
and mantle convection cells should work in tandem
(see e.g. Gurnis, 1988; Yoshida & Santosh, 2011 and
references therein). Still, Yoshida & Santosh (2011)re-
cognized and adverted that one of the major challenges
in Earth sciences is to resolve the thermal and mech-
anical feedback between mantle convection and con-
tinental/supercontinental drift. We would add that this
cannot be done without better understanding the dy-
namics of oceanic plates and their complex rheological
evolution. In particular, the impact of some present-day
characteristics of the planet is still not clear, particularly
since these may have been different in the past, as for
instance the inherent asymmetry of subduction zones
(always one-sided; Gerya, Connolly & Yuen, 2008)or
the presence of vast quantities of water pervasively cir-
culating within the oceanic lithosphere (e.g. Duarte,
Schellart & Cruden, 2015 and references therein). Fu-
ture geodynamic modelling work will certainly allow
testing some of these ideas, conjectures and hypotheses.
9. Conclusions
An almost classic discussion in plate tectonics is which
of the main oceans on Earth will be the next to close:
the Pacific or the Atlantic? These two closure scenarios
have been often presented as exclusive. In this paper we
argued that it is probable (if not necessary) to envisage
a class of future scenarios in which both the Pacific and
the Atlantic close simultaneously. This model has the
advantage of complying with the buoyancy argument
at the same time that it strongly fits the observations
of the present-day age of the seafloor, the existence of
small subduction zones in the Atlantic and the concepts
of subduction zone invasion, migration and expansion.
The ideas presented here are expected to be testable
by the next generation of dynamic numerical models.
Such endeavour has already started (e.g. Zhong et al.
2007; Yoshida & Santosh, 2011; Coltice et al. 2012;
Rolf, Coltice & Tackley, 2012,2014; Yoshida, 2014).
Encouraging results and new ideas are emerging in this
field and could provide additional constraints on our
conceptual model for the formation of the supercontin-
ent Aurica and the closure of both the Pacific and the
Atlantic oceans.
Acknowledgements. Pedro Terrinha, with whom J. Duarte
started discussions on tectonic arcs many years ago, is
warmly thanked for great discussions over the years. Nic-
olas Riel, António Ribeiro, David Boutelier and Rui Dias
are thanked for enthusiastic discussions on most of the
subjects discussed here. We would also like to thank Di-
etmar Muller and Kara Matthews from the GPlates com-
munity (http://www.gplates.org/) for encouraging us using
GPlates and giving us some hints. Publication supported
by FCT through project UID/GEO/50019/2013 – Instituto
Dom Luiz. The authors also acknowledge financial sup-
port from Discovery Grant DP110103387 from the Aus-
tralian Research Council awarded to WPS. JD acknowledges
the financial support from the Australian Research Coun-
cil through DECRA (Discovery Early Career Researcher
Award) Grant DE150100326. WPS acknowledges financial
support from the Australian Research Council through Fu-
ture Fellowship FT110100560. FMR thanks the project Pest-
OE/CTE/LA0019/2011-12. Finally, we would like to thank
the editor Mark Allen for handling the paper and for the
encouraging comments, as well as Taras Gerya and an an-
onymous reviewer for their constructive reviews.
56 J. C. DUARTE, W. P. SCHELLART & F. M. ROSAS
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