ArticlePDF Available

The future of Earth's oceans: consequences of subduction initiation in the Atlantic and implications for supercontinent formation

January 2018
Geological Magazine 155(1)

DOI:10.1017/S0016756816000716

Authors:

Joao C. Duarte

University of Lisbon

Wouter P. Schellart

Vrije Universiteit Amsterdam (Netherlands)

Filipe Medeiros Rosas

University of Lisbon

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).

(Colour online) Conceptual model of the evolution of the disposition of the Earth's oceans and continents. In this scenario 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 propagation 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/).

…

Figures - uploaded by Joao C. Duarte

Content may be subject to copyright.

Content uploaded by Joao C. Duarte

Content may be subject to copyright.

Content uploaded by Joao C. Duarte

Content may be subject to copyright.

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

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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 ρ40 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,

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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.

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

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.

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

56 J. C. DUARTE, W. P. SCHELLART & F. M. ROSAS

References

AFONSO,J.C.,RANALLI,G.&FERNANDEZ, M. 2007. Dens-

ity structure and buoyancy of the oceanic lithosphere re-

visited. Geophysical Research Letters 34, L10302, doi:

10.1029/2007GL029515.

ALVA R E Z -MARRON,J.,RUBIO,E.&TORNE, M. 1997.

Subduction-related structures in the North Iberian mar-

gin. Journal of Geophysical Research 102, 22497–

511.

ANDERSON, D. L. 1982. Hotspots, polar wander, Mesozoic

convection and the geoid. Nature 297, 391–93.

BAES, M., GOVERS,R.&WORTEL, R. 2011. Switching

between alternative responses of the lithosphere to con-

tinental collision. Geophysical Journal International

187, 1151–74.

BARCKHAUSEN,U.,RANERO,C.R.,CANDE,S.C.,ENGELS,

M. & WEINREBE, W. 2008. Birth of an intraoceanic

spreading center. Geology 36, 767–70.

BARKER, P. F. 2001. Scotia Sea regional tectonic evolu-

tion: implications for mantle ﬂow and palaeocirculation.

Earth-Science Reviews 55, 1–39.

BRADLEY, D. C. 2008. Passive margins through Earth history.

Earth-Science Reviews 91, 1–26.

BRADLEY, D. C. 2011. Secular trends in the geologic record

and the supercontinent cycle. Earth and Planetary Sci-

ence Letters 108, 16–33.

BETTS,P.G.,GILES,D.,LISTER,G.&FRICK, L. R. 2002.

Evolution of the Australian lithosphere. Australian

Journal of Earth Sciences 49, 661–95.

BUROV,E.&CLOETINGH, S. 2010. Plume-like up-

per mantle instabilities drive subduction initiation.

Geophysical Research Letters 37, L03309, doi:

10.1029/2009GL041535.

CLOETINGH,S.,WORTEL,R.&VLAAR, N. J. 1989. On the

initiation of subduction zones. Pure and Applied Geo-

physics 129, 7–25.

CLOOS, M. 1993. Lithospheric buoyancy and collisional

orogenesis: subduction of oceanic plateaus, continental

margins, island arcs, spreading ridges, and seamounts.

Geological Society of America Bulletin 105, 715–

37.

COIRA,B.,DAV I D S O N ,J.,MPODOZIS,C.&RAMOS, V. 1982.

Tectonic and magmatic evolution of the Andes of north-

ern Argentina and Chile. Earth-Science Reviews 18,

303–32.

COLLINS, W. J. 2003. Slab pull, mantle convection, and

Pangaean assembly and dispersal. Earth and Planetary

Science Letters 205, 225–23.

COLTICE,N.,BERTRAND,H.,REY,P.,JOURDAN,F.,PHILLIPS,

B. R. & RICARD, Y. 2009. Global warming of the mantle

beneath continents back to the Archaean. Gondwana

Research 15, 254–66.

COLTICE,N.,ROLF,T.,TACKLEY,P.J.&LABROSSE, S. 2012.

Dynamic causes of the relation between area and age of

the ocean ﬂoor. Science 336, 335–8.

CONRAD,C.P.&LITHGOW-BERTELLONI, C. 2002. How

mantle slabs drive plate tectonics. Science 298, 207–9.

CONRAD,C.P.,STEINBERGER,B.&TORSVIK, T. H. 2013.

Stability of active mantle upwelling revealed by net char-

acteristics of plate tectonics. Nature 498, 479–82.

CROSBY,A.G.,MCKENZIE,D.&SCLATER, J.G. 2006. The re-

lationship between depth, age and gravity in the oceans.

Geophysical Journal International 166, 443–573.

CUNHA,T.,WATTS,A.B.,PINHEIRO,L.M.&MYKLEBUST,

R. 2010. Seismic and gravity anomaly evidence of

large-scale compressional deformation off SW Portugal.

Earth and Planetary Science Letters 293, 171–9.

DALZIEL,I.W.D.,LAW V E R ,L.A.,NORTON,I.A.&

GAHAGAN, L. M. 2013. The Scotia Arc: genesis, evolu-

tion, global signiﬁcance. Annual Reviews of Earth and

Planetary Sciences 41, 767–93.

DAVI E S ,G.F.&RICHARDS, M. A. 1992. Mantle convection.

Journal of Geology 100, 151–206.

DUART E,J.C.,ROSAS, F. M., TERRINHA,P.,GUTSCHER, M.-

A., MALAVIEILLE,J.,SILVA,S.&MAT I A S , L. 2011.

Thrust-wrench interference tectonics in the Gulf of

Cadiz (Africa-Iberia plate boundary in the North-East

Atlantic): insights from analog models. Marine Geology

289, 135–49.

DUART E,J.C.,ROSAS,F.M.,TERRINHA,P.,SCHELLART,W.P.,

BOUTELIER,D.,GUTSCHER,M.A.&RIBEIRO, A. 2013.

Are subduction zones invading the Atlantic? Evidence

from the SW Iberia margin. Geology 41, 839–42.

DUART E,J.C.,SCHELLART,W.P.&CRUDEN, A. R. 2013.

Three-dimensional dynamic laboratory models of sub-

duction with an overriding plate and variable interplate

rheology. Geophysical Journal International 195, 47–

66.

DUART E,J.C.,SCHELLART,W.P.&CRUDEN, A. R. 2015.

How weak is the subduction zone interface? Geophys-

ical Research Letters 41, 1–10.

DYMKOVA,D.&GERYA, T. 2013. Porous ﬂuid ﬂow enables

oceanic subduction initiation on Earth. Geophysical Re-

search Letters 40, 5671–76.

EAGLES,G.&JOKAT, W. 2014. Tectonic reconstructions for

paleobathymetry in Drake Passage. Tectonophysics 611,

28–50.

ELSASSER, W. M. 1971. Sea-ﬂoor spreading as thermal con-

vection. Journal of Geophysical Research 76, 1101.

FERNÁNDEZ-VIEJO,G.,PULGAR,J.A.,GALLASTEGUI,J.&

QUINTANA, L. 2012. The fossil accretionary wedge of

the Bay of Biscay: critical wedge analysis on depth-

migrated seismic sections and geodynamical implica-

tions. Journal of Geology 120, 315–31.

FORSYTH,D.W.&UYEDA, S. 1975. On the relative import-

ance of the driving forces of plate motion. Geophysical

Journal International 43, 163–200.

FUKAO, Y. 1973. Thrust faulting at a lithospheric plate bound-

ary, the Portugal earthquake of 1969. Earth and Planet-

ary Science Letters 18, 205–16.

GALINDO-ZALDIVAR,J.,BOHOYO,F.,MALDONADO,A.,

SCHREIDER,A.,SURIÑACH,E.&VÁZQUEZ, J. T. 2006.

Propagating rift during the opening of a small oceanic

basin: the Protector Basin (Scotia Arc, Antarctica).

Earth and Planetary Science Letters 241, 398–412.

GEISSLER,W.H.,MAT I A S ,L.,STICH,D.,CARRILHO,F.,

JOKAT,W.,MONNA,S.,IBENBRAHIM,A.,MANCILLA,

F., G UTSCHER, M.-A., SALLARÈS,V.&ZITELLINI,N.

2010. Focal mechanisms for sub-crustal earthquakes

in the Gulf of Cadiz from a dense OBS deploy-

ment. Geophysical Research Letters 37, L18309, doi:

10.1029/2010GL044289.

GERYA,T.V.,CONNOLLY,J.A.D.&YUEN, D. A. 2008. Why

is terrestrial subduction one-sided? Geology 36, 43–6.

GOREN,L.,AHARONOV,E.,MULUGETA,G.,KOY I ,H.A.

ART, Y. 2008. Ductile deformation of passive

margins: a new mechanism for subduction initiation.

Journal of Geophysical Research 113, B08411, doi:

10.1029/2005JB004179.

GUDMUNDSSON,O.&SAMBRIDGE, M. 1998. A regionalized

upper mantle (RUM) seismic model. Journal of Geo-

physical Research 103, 7121–36.

GURNIS, M. 1988. Large-scale mantle convection and the ag-

gregation and dispersal of supercontinents. Nature 332,

695–9.

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

The future of Earth’s oceans 57

GURNIS, M., HALL,C.&LAV I E R , L.2004. Evolving

force balance during incipient subduction. Geo-

chemistry, Geophysics, Geosystems 5, Q07001, doi:

10.1029/2003GC000681.

GUTSCHER,M.A.,DOMINGUEZ,S.,WESTBROOK,G.K.,

LEROY,P.,ROSAS,F.,DUA RTE,J.C.,TERRINHA,P.,

MIRANDA, J. M., GRAINDORGE,D.,GAILLER,A.&

SALLARES, V. 2012. The Gibraltar subduction: a dec-

ade of new geophysical data. Tectonophysics 574–575,

72–91.

GUTSCHER, M.-A., MALOD,J.,REHAULT,J.-P.,CONTRUCCI,

I., KLINGELHOEFER,F.,SPAKMAN,W.&MENDES-

VICTOR, L. 2002. Evidence for active subduction be-

neath Gibraltar. Geology 30, 1071–4.

HOFFMAN, P. F. 1997. In Earth Structure: An Introduction to

Structural Geology and Tectonics (eds B. van der Pluijm

& S. Marshak), pp. 459–64. New York: McGraw-Hill.

KRONER,A.&CORDANI, U. 2003. African, southern Indian

and South American cratons were not part of the Rodinia

supercontinent: evidence from ﬁeld relationships and

geochronology. Tectonophysics 375, 325–52.

LONERGAN,L.&WHITE, N. 1997. Origin of the Betic-Rif

mountain belt. Tectonics 16, 504–22.

LYNNER,C.&LONG, M. D. 2013. Sub-slab seismic aniso-

tropy and mantle ﬂow beneath the Caribbean and Sco-

tia subduction zones: effects of slab morphology and

kinematics. Earth and Planetary Science Letters 361,

367–78.

MAGNI,V.,FACCENNA,C.,VA N HUNEN,J.&FUNICIELLO,

F. 2014. How collision triggers backarc extension: in-

sight into Mediterranean style of extension from 3-D

numerical models. Geology 42, 511–4.

MARQUES,F.O.,NIKOLAEVA,K.,ASSUMPÇÃO, M., GERYA,

T. V., B EZERRA,F.H.R.,DO NASCIMENTO,A.F.&

FERREIRA, J. M. 2013. Testing the inﬂuence of far-ﬁeld

topographic forcing on subduction initiation at a passive

margin. Tectonophysics 608, 517–24.

MASSON,D.G.,CARTWRIGHT,J.A.,PINHEIRO, L. M.,

WHITMARSH,R.B.,BESLIER, M.-O. & ROESER,H.

A. 1994. Compressional deformation at the ocean-

continent transition in the NE Atlantic. Journal of the

Geological Society, London 151, 607–13.

MCKENZIE, D. P. 1977. The initiation of trenches: a ﬁnite

amplitude instability. In Island Arcs, Deep Sea Trenches

and Back-Arc Basins (eds M. Talwani & W. C. Pitman,

III), pp. 57–61. American Geophysical Union, Maurice

Ewing Series, Washington DC, USA.

MEERT, J. G. 2012. What’s in a name? The Columbia (Pa-

leopangaea/Nuna) supercontinent. Gondwana Research

21, 987–93.

MITCHELL,R.N.,KILIAN,T.M.&EVANS, D. A. D. 2012.

Supercontinent cycles and the calculation of absolute

palaeolongitude in deep time. Nature 482, 208–12.

MORESI,L.N.,BETTS,P.G.,MILLER,M.S.&CAYLEY,R.

A. 2014. The dynamics of continental accretion. Nature

508, 245–8.

MUELLER,S.&PHILLIPS, R. J. 1991. On the initiation of

subduction. Journal of Geophysical Research 96, 651–

65.

MÜLLER,R.D.,SDROLIAS, M., GAINA,C.&ROEST,W.

R. 2008. Age, spreading rates and spreading symmetry

of the world’s ocean crust, Geochemistry, Geophysics,

Geosystems 9, Q04006, doi: 10.1029/2007GC001743.

MURPHY,J.B.&NANCE, R. D. 2003. Do supercontinents in-

trovert or extrovert?: Sm–Nd isotopic evidence. Geology

31, 873–6.

MURPHY,J.B.&NANCE, R. D. 2008. The Pangea conundrum.

Geology 36, 703–6.

MURPHY,J.B.&NANCE, R. D. 2013. Speculations on the

mechanisms for the formation and breakup of supercon-

tinents. Geoscience Frontiers 4, 185–94.

NANCE,R.D.&MURPHY, J. B. 2013. Origins of the super-

continent cycle. Geoscience Frontiers 4, 439–48.

NANCE,R.D.,MURPHY,J.B.&SANTOSH, M. 2014. The

supercontinent cycle: a retrospective essay. Gondwana

Research 25, 4–29.

NANCE,R.D.,WORSLEY,T.R.&MOODY, J. B. 1986. Post-

Archean biogeochemical cycles and long-term episodi-

city in tectonic processes. Geology 14, 514–8.

NIELD, T. 2007. Supercontinent. London: Granta Books,

288 pp.

NIKOLAEVA,K.,GERYA,T.V.&MARQUES, F. O. 2010. Sub-

duction initiation at passive margins: numerical mod-

elling. Journal of Geophysical Research 115, B03406,

doi: 10.1029/2009JB006549.

NIKOLAEVA,K.,GERYA,T.&MARQUES, F. O. 2011. Nu-

merical analysis of subduction initiation risk along the

Atlantic American passive margins. Geology 39, 463–6.

NOCQUET, J.-M. & CALAIS, E. 2004. Geodetic measurements

of crustal deformation in the Western Mediterranean and

Europe. Pure Applied Geophysics 161, 661–81.

PALANO, M., GONZÁLEZ,P.J.&FERNÁNDEZ, J. 2015. The dif-

fuse plate boundary of Nubia and Iberia in the Western

Mediterranean: crustal deformation evidence for vis-

cous coupling and fragmented lithosphere. Earth and

Planetary Science Letters 430, 439–47.

PINDELL,J.L.&KENNAN, L. 2001. Kinematic evolution of

the Gulf of Mexico and Caribbean. In Petroleum Sys-

tems of Deep-Water Basins: Gulf Coast Section Society

of Economic Paleontologists and Mineralogists Found-

ation (GCSSEPM), 21st Annual Bob F. Perkins Research

Conference Transactions, Houston, Texas (eds R. Fillon,

N. Rosen, P. Weimer, A. Lowrie, H. Pettingill, R. Phair,

H. Roberts & B. van Hoorn), pp. 193–220.

PIPER, J. D. A. 1974. Proterozoic crustal distribution, mobile

belts and apparent polar movements. Nature 251, 381–4.

RIBEIRO,A.,CABRAL,J.,BAPTISTA,R.&MATIAS, L. 1996.

Stress pattern in Portugal mainland and the adjacent

Atlantic region, West Iberia. Tectonophysics 15, 641–

59.

ROGERS, J. J. W. 1996. A history of continents in the past

three billion years. Journal of Geology 104, 91–107.

ROLF,T.,COLTICE,N.&TACKLEY, P. 2012. Linking con-

tinental drift, plate tectonics and the thermal state of

the Earth’s mantle. Earth and Planetary Science Letters

351–352, 134–46.

ROLF,T.,COLTICE,N.&TACKLEY, P. J. 2014. Statistical cyc-

licity of the supercontinent cycle. Geophysical Research

Letters 41, 2351–8.

ROSAS, F. M., DUA RTE,J.C.,TERRINHA,P.,VALADARES,V.

ATIAS, L. 2009. Morphotectonic characterization

of major bathymetric lineaments in NW Gulf of Cadiz

(Africa-Iberia plate boundary): insights from analogue

modelling experiments. Marine Geology 261, 33–47.

ROSENBAUM,G.,LISTER,G.S.&DUBOZ, C. 2002. Recon-

struction of the tectonic evolution of the western Medi-

terranean since the Oligocene. Journal of the Virtual

Explorer 8, 107–30.

ROWLEY, D. B. 2008. Extrapolating oceanic age distributions:

lessons from the Paciﬁc region. Journal of Geology 116,

587–98.

ROYDEN, L. H. 1993. Evolution of retreating subduction

boundaries formed during continental collision. Tecton-

ics 12, 629–38.

SCHELLART, W. P. 2008. Kinematics and ﬂow patterns in deep

mantle and upper mantle subduction models: inﬂuence

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

58 The future of Earth’s oceans

of the mantle depth and slab to mantle viscosity ratio.

Geochemistry, Geophysics, Geosystems 9, Q03014, doi:

10.1029/2007GC001656.

SCHELLART,W.P.,FREEMAN,J.,STEGMAN,D.R.,MORESI,L.

AY, D. A. 2007. Evolution and diversity of subduc-

tion zones controlled by slab width. Nature 446, 308–11.

SCHELLART,W.P.,LISTER,G.&TOY, V. 2006. A Late Creta-

ceous and Cenozoic reconstruction of the Southwest Pa-

ciﬁc region: tectonics controlled by subduction and slab

rollback processes. Earth-Science Reviews 76, 191–233.

SCHELLART,W.P.,STEGMAN,D.,FARRINGTON,R.&MORESI,

L. 2011. Inﬂuence of lateral slab edge distance on plate

velocity, trench velocity, and subduction partitioning.

Journal of Geophysical Research 116, B10408, doi:

10.1029/2011JB008535.

SCOTESE, C. R. 2004. A continental drift ﬂipbook. Journal

of Geology 112, 729–41.

SCOTESE, C. R. 2007. PALEOMAP Project.http://www.

scotese.com/future2.htm.

SILVER,P.G.&BEHN, M. D. 2008. Intermittent plate tecton-

ics? Science 319, 85–8.

STEIN,C.&STEIN, S.1992. A model for the global variation

in oceanic depth and heat ﬂow with lithospheric age.

Nature 359, 123–8.

STEPHENSON,R.A.&CLOETINGH, S. A. P. L. 1991. Some

examples and mechanical aspects of continental litho-

spheric folding. Tectonophysics 188, 27–37.

STERN, R. J. 2004. Subduction initiation: spontaneous and

induced. Earth and Planetary Science Letters 226, 275–

92.

STERN,R.J.,REAGAN, M., ISHIZUKA,O.,OHARA,Y.&

WHATTAM, S. 2012. To understand subduction initiation,

study forearc crust; to understand forearc crust, study

ophiolites. Lithosphere 4, 469–83.

STICH,D.,MANCILLA,F.DE,L.,PONDRELLI,S.&MORALES,

J. 2007. Source analysis of the February 12th 2007, Mw

6.0 Horseshoe earthquake: implications for the 1755

Lisbon earthquake. Geophysical Research Letters 34,

12.

TERRINHA,P.,MAT I A S ,L.,VICENTE,J.,DUA RTE,J.,LUÍS,

J., PINHEIRO,L.,LOURENÇO,N.,DIEZ,S.,ROSAS,

F., M AGALHÃES,V.,VALADARES,V.,ZITELLINI,N.,

MENDES VÍCTOR, L. & MATESPRO Team. 2009.

Morphotectonics and strain partitioning at the Iberia-

Africa plate boundary from multibeam and seismic re-

ﬂection data. Marine Geology 267, 156–74.

TORSVIK,T.H.,GAINA,C.&REDFIELD, T. F. 2008. Antarc-

tica and global paleogeography: from Rodinia, through

Gondwanaland and Pangea, to the birth of the southern

ocean and the opening of gateways. In Antarctica: A

Keystone in a Changing World. Proceedings of the 10th

International Symposium on Antarctic Earth Sciences

(eds A. K. Cooper, P. J. Barrett, H. Stagg, B. Storey,

E. Stump, W. Wise & the 10th ISAES editorial team),

pp. 125–40. Washington, DC: The National Academies

Press.

TURCOTTE,D.L.&SCHUBERT, G. 2002. Geodynamics.Cam-

bridge: Cambridge University Press.

UEDA,K.,GERYA,T.&SOBOLEV, S. V. 2008. Subduction

initiation by thermal–chemical plumes. Physics of the

Earth and Planetary Interiors 171, 296–312.

VALENTINE,J.W.&MOORES, E. M. 1970. Plate-tectonic

regulation of faunal diversity and sea level: a model.

Nature 228, 657–9.

VEEVERS,J.,WALTER,M.&SCHEIBNER, E. 1997.

Neoproterozoic tectonics of Australia-Antarctica and

Laurentia and the 560 Ma birth of the Paciﬁc Ocean

reﬂect the 400 my Pangean supercycle. Journal of Geo-

logy 105, 225–42.

VÉRARD,C.,FLORES,K.&STAMPFLI, G. 2012. Geodynamic

reconstructions of the South America – Antarctica plate

system. Journal of Geodynamics 53, 43–60.

WALDRON,J.W.F.,SCHOFIELD,D.I.,MURPHY,J.B.&

THOMAS, C. W. 2014. How was the Iapetus Ocean in-

fected with subduction? Geology 42, 1095–8.

WEGENER, A. 1912. Die Entstehung der Kontinente. Geolo-

gische Rundschau 3(4), 276–92 (in German).

WEIL,A.B.,VAN DER VOO,R.,MAC NIOCAILL,C.&MEERT,

J. G. 1998. The Proterozoic supercontinent Rodinia:

paleomagnetically derived reconstructions for 1100 to

800 Ma. Earth and Planetary Science Letters 154, 13–

24.

WHATTAM,S.A.&STERN, R. J. 2011. The ‘subduction-

initiation rule’: a key for linking ophiolites, intra-

oceanic forearcs and subduction initiation. Contri-

butions to Mineralogy and Petrology 162, 1031–

45.

WHATTAM,S.A.&STERN, R. J. 2015. Late Cretaceous

plume-induced subduction initiation along the south-

ern margin of the Caribbean and NW South America:

the ﬁrst documented example with implications for the

onset of plate tectonics. Gondwana Research 27, 38–

63.

WHITMARSH,R.B.,PINHEIRO, L. M., MILES,P.R.,RECQ,M.

IBUET, J.-C. 1993. Thin crust at the western Iberia

ocean–continent transition and ophiolites. Tectonics 12,

1230–9.

WILSON, J. T. 1966. Did the Atlantic close and then reopen?

Nature 211, 676.

WORSLEY,T.R.,NANCE,R.D.&MOODY, J. B.1982. Plate

tectonic episodicity: a deterministic model for periodic

“Pangeas”. Eos, Transactions of the American Geophys-

ical Union 65, 1104.

WORSLEY,T.R.,NANCE,R.D.&MOODY, J. B. 1984. Global

tectonics and eustasy for the past 2 billion years. Marine

Geology 58, 373–400.

Yoshida. 2014. Effects of various lithospheric yield stresses

and different mantle-heating modes on the breakup of

the Pangea supercontinent. Geophysical Research Let-

ters 41, 3060–7.

YOSHIDA, M., IWA S E ,Y.&HONDA, S. 1999. Generation of

plumes under a localized high viscosity lid on 3-D spher-

ical shell convection. Geophysical Research Letters 26,

947–50.

YOSHIDA,M.&SANTOSH, M. 2011. Supercontinents, mantle

dynamics and plate tectonics: a perspective based on

conceptual vs. numerical models. Earth-Science Re-

views 105, 1–24.

ZHONG,S.,ZHANG,N.,LI,Z.X.&ROBERTS, J. H. 2007. Su-

percontinent cycles, true polar wander, and very long-

wavelength mantle convection. Earth and Planetary Sci-

ence Letters 261, 551–64.

https://doi.org/10.1017/S0016756816000716

Downloaded from https://www.cambridge.org/core. Monash University, on 08 Jan 2018 at 21:01:21, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.

Back to the future II: tidal evolution of four supercontinent scenarios

Article

Full-text available

Mar 2020
ESD

The Earth is currently 180 Myr into a supercontinent cycle that began with the break-up of Pangaea and which will end around 200–250 Myr (million years) in the future, as the next supercontinent forms. As the continents move around the planet they change the geometry of ocean basins, and thereby modify their resonant properties. In doing so, oceans move through tidal resonance, causing the global tides to be profoundly affected. Here, we use a dedicated and established global tidal model to simulate the evolution of tides during four future supercontinent scenarios. We show that the number of tidal resonances on Earth varies between one and five in a supercontinent cycle and that they last for no longer than 20 Myr. They occur in opening basins after about 140–180 Myr, an age equivalent to the present-day Atlantic Ocean, which is near resonance for the dominating semi-diurnal tide. They also occur when an ocean basin is closing, highlighting that within its lifetime, a large ocean basin – its history described by the Wilson cycle – may go through two resonances: one when opening and one when closing. The results further support the existence of a super-tidal cycle associated with the supercontinent cycle and gives a deep-time proxy for global tidal energetics.

Lateral propagation–induced subduction initiation at passive continental margins controlled by preexisting lithospheric weakness

Article

Full-text available

Mar 2020

Understanding the conditions for forming new subduction zones at passive continental margins is important for understanding plate tectonics and the Wilson cycle. Previous models of subduction initiation (SI) at passive margins generally ignore effects due to the lateral transition from oceanic to continental lithosphere. Here, we use three-dimensional numerical models to study the possibility of propagating convergent plate margins from preexisting intraoceanic subduction zones along passive margins [subduction propagation (SP)]. Three possible regimes are achieved: (i) subducting slab tearing along a STEP fault, (ii) lateral propagation–induced SI at passive margin, and (iii) aborted SI with slab break-off. Passive margin SP requires a significant preexisting lithospheric weakness and a strong slab pull from neighboring subduction zones. The Atlantic passive margin to the north of Lesser Antilles could experience SP if it has a notable lithospheric weakness. In contrast, the Scotia subduction zone in the Southern Atlantic will most likely not propagate laterally.

Plume‐Induced Sinking of Intracontinental Lithospheric Mantle: An Overlooked Mechanism of Subduction Initiation?

Article

Jan 2021
GEOCHEM GEOPHY GEOSY

Although many different mechanisms for subduction initiation have been proposed, only few of them are viable in terms of consistency with observations and reproducibility in numerical experiments. In particular, it has recently been demonstrated that intra‐oceanic subduction triggered by an upwelling mantle plume could greatly contribute to the onset and operation of plate tectonics in the early and, to a lesser degree, modern Earth. On the contrary, the initiation of intra‐continental subduction still remains underappreciated. Here we provide an overview of 1) observational evidence for upwelling of hot mantle material flanked by downgoing proto‐slabs of sinking continental mantle lithosphere, and 2) previously published and new numerical models of plume‐induced subduction initiation. Numerical modelling shows that under the condition of a sufficiently thick (>100 km) continental plate, incipient downthrusting at the level of the lowermost lithospheric mantle can be triggered by plume anomalies of moderate temperatures and without significant strain‐ and/or melt‐related weakening of overlying rocks. This finding is in contrast with the requirements for plume‐induced subduction initiation within oceanic or thinner continental lithosphere. As a result, plume‐lithosphere interactions within continental interiors of Paleozoic‐Proterozoic‐(Archean) platforms are the least demanding (and thus potentially very common) mechanism for initiation of subduction‐like foundering in the Phanerozoic Earth. Our findings are supported by a growing body of new geophysical data collected in various intra‐continental areas. Better understanding the role of intra‐continental mantle downthrusting and foundering in global plate tectonics and, particularly, in the initiation of “classic” ocean‐continent subduction will benefit from more detailed follow‐up investigations.

Историческая металлогения рудных месторождений лития

Chapter

Full-text available

Nov 2020

Andrey V. Tkachev

Проведенный анализ глобальной выборки месторождений, в которых заключены почти все промышленно значимые или потенциально экономически интересные запасы и ресурсы лития, показал, что они формировались в разные геологические эпохи в интервале от позднего мезоархея до миоцена. Размещение этих ресурсов на шкале геологического времени имеет ярко выраженный дискретный импульсный характер. Все импульсы тяготеют к периодам интенсификации орогенных процессов в глобальном масштабе, что характерно для тектонических фаз активного формирования суперконтинентов. Каждый из суперконтинентальных циклов, последовательно сменявших друг друга и определивших важнейшие черты геотектонического развития земной коры на протяжении последних трех миллиардов лет, имеет свои особенности в проявлениях металлогении лития. В кенорский, колумбийский и родинийский циклы формировались только пегматитовые месторождения лития. В пангейском цикле основные ресурсы также связаны с пегматитовым типом, но небольшая часть локализована в объектах гранитного и кальдерного типов. Пока незавершенный амазийский цикл столь же разнообразен в типах рудных месторождений лития, как и пангейский, но с лидирующей ролью кальдерного типа в количестве выявленных ресурсов. Среди рудных месторождений лития наиболее распространены объекты пегматитового типа, который является единственным сквозным в геологической истории. Максимальное количество месторождений данного типа, суммарных ресурсов в них и наиболее высокие средние содержания лития установлены для кенорского цикла. Это позволило предположить существование в архее особо благоприятных условий для возникновения продуктивных на литий пегматитов. Примечательно также, что пегматитовые месторождения именно кенорского цикла, в том числе и благодаря относительно высокому качеству руд, во многом обеспечили лавинообразный рост производства лития в мире в последние годы. Значение месторождений других типов (гранитного и кальдерного) в ресурсной базе лития пока намного превосходит их реальную роль в добыче этого вида сырья. Однако высокий интерес к выявлению и оценке таких объектов со стороны геологоразведочных и горнодобывающих организаций во многих странах мира, указывают на вероятное изменение этой ситуации в ближайшем будущем.

The core of Rodinia formed by the juxtaposition of opposed retreating and advancing accretionary orogens

Article

Oct 2020
EARTH-SCI REV

Long-lived (800 Ma) Paleo– to Mesoproterozoic accretionary orogens on the margins of Laurentia, Baltica, Amazonia, and Kalahari collided to form the core of the supercontinent, Rodinia. Accretionary orogens in Laurentia and Baltica record predominately radiogenic zircon εHf(t) and whole-rock Pb isotopic compositions, short crustal residence times (ca. 0.5 Ga), and the development of arc-backarc complexes. The accretionary orogenic record of Laurentia and Baltica is consistent with a retreating accretionary orogen and analogous to the Phanerozoic western Pacific orogenic system. In contrast, the Mesoproterozoic orogens of Amazon and Kalahari cratons record unradiogenic zircon εHf(t) values, ca. 0.8 Ga crustal residence times, and more ancient whole-rock Pb isotopic signatures. The accretionary orogenic record of Amazonia and Kalahari indicates the preferential incorporation of cratonic material in continental arcs of advancing accretionary orogens comparable to the Phanerozoic eastern Pacific orogenic system. Based on similarities in the geodynamic evolution of the Phanerozoic circum-Pacific orogens peripheral to Gondwana/Pangea, we suggest that the Mesoproterozoic accretionary orogens formed as peripheral subduction zones along the margin of the supercontinent Nuna (ca. 1.8–1.6 Ga). The eventual collapse of this peripheral subduction zone onto itself and closure of the external ocean around Nuna to form Rodinia is equivalent to the projected future collapse of the circum-Pacific subduction system and juxtaposition of Australia-Asia with South America. The juxtaposition of advancing and retreating accretionary orogens at the core of the supercontinent Rodinia demonstrates that supercontinent assembly can occur by the closure of external oceans and indicates that future closure of the Pacific Ocean is plausible.

The Climates of Earth’s Next Supercontinent: Effects of Tectonics, Rotation Rate, and Insolation

Article

Full-text available

Jul 2021
GEOCHEM GEOPHY GEOSY

We explore two possible Earth climate scenarios, 200 and 250 million years into the future, using projections of the evolution of plate tectonics, solar luminosity, and rotation rate. In one scenario, a supercontinent forms at low latitudes, whereas in the other it forms at high northern latitudes with an Antarctic subcontinent remaining at the south pole. The climates between these two end points are quite stark, with differences in mean surface temperatures approaching several degrees. The main factor in these differences is related to the topographic height of the high latitude supercontinents where higher elevations promote snowfall and subsequent higher planetary albedos. These results demonstrate the need to consider multiple boundary conditions when simulating Earth-like exoplanetary climates.

Subduction initiation at passive continental margins: A review based on numerical studies

Article

Jun 2021

The Wilson cycle predicted that the passive continental margin finally collapses and forms a new subduction zone, because the transition between oceanic and continental lithosphere provides as a natural boundary with great density and rheology contrasts. However, this process is hardly constrained, due to the lack of obvious Cenozoic examples in the natural Earth. The rather stable passive margin of Atlantic Ocean, without any clear sign for subduction initiation (SI), also challenges this hypothesis. In this study, we have reviewed the main ideas and models for the SI at passive margin, which are classified into two categories, i.e. driven by either local forces or external forces. The local forces, mainly due to the local gravitational instability, are generally insufficient to break the lithosphere and lead to SI on the present Earth, although they are possible driving mechanisms for the SI in early Earth with higher potential temperature of the mantle. The external forces may come from the push of mid-ocean ridge and/or mantle plume, the lateral drag of neighboring sinking slab, as well as the basal drag of large-scale mantle convection. They are feasible to drive SI for young oceanic basins with thin and weak lithosphere on the present Earth. But the old and stable Atlantic type margin with high rheological strength is difficult for SI, which requires pre-existing weakness and/or significant weakening mechanism. Previous numerical studies have generally focused on the geodynamic conditions of SI. However, the SI for either present or early Earth is still not well constrained, especially in the aspects of geological responses and possible petrological records, which thus requires further systematic comparative studies between numerical models and geological records.

A transdisciplinary and community-driven database to unravel subduction zone initiation

Article

Full-text available

Jul 2020

Subduction zones are pivotal for the recycling of Earth’s outer layer into its interior. However, the conditions under which new subduction zones initiate are enigmatic. Here, we constructed a transdisciplinary database featuring detailed analysis of more than a dozen documented subduction zone initiation events from the last hundred million years. Our initial findings reveal that horizontally forced subduction zone initiation is dominant over the last 100 Ma, and that most initiation events are proximal to pre-existing subduction zones. The SZI Database is expandable to facilitate access to the most current understanding of subduction zone initiation as research progresses, providing a community platform that establishes a common language to sharpen discussion across the Earth Science community. Despite numerous advances in our understanding of subduction since the theory of plate tectonics was established, the mechanisms of subduction zone initiation remain highly controversial. Here, the authors present a transdisciplinary and expandable community database of subduction zone initiation events in the last 100 Ma, which establishes a clear direction for future research.

O Geossinclinal nos finais do séc. XX em Portugal: revolução tardia ou evidências da natureza da Ciência?

Article

Full-text available

Jun 2020

Edite Bolacha

A teoria do geossinclinal (TG) no programa de Geologia do 12º ano, nos finais do séc. XX/início do séc. XXI, enquadrava a formação de cadeias de montanhas. O objetivo “…interpretar a teoria do geossinclinal à luz da Teoria da Tectónica de placas (TP) na explicação da formação de algumas cadeias de montanhas”, permite interpretá-la como História da Ciência, ou que a TP enquadrava algumas cadeias de montanhas. A análise de textos/imagens de manuais escolares evidenciou que a TG era aceite na época. No entanto, transparecem dúvidas e incertezas, quer na abordagem isolada quer quando acoplada à TP. Igual tipo de análise dos programas precedentes e de referências da época confirmam diferentes abordagens. Razões para as dúvidas persistentes podem residir; na complexidade da formação de montanhas, no fenómeno não ser central na primeira formulação da TP, ou na exigência de tempo para consolidar conhecimento científico no contexto da nova teoria.

Oceanic crust recycling controlled by weakening at slab edges

Article

Full-text available

Apr 2020

Retreating subduction zones such as the Lesser Antilles, Gibraltar and Scotia have been migrating towards the Atlantic Ocean by cutting their way through the oceanic crust. This spontaneously retreating subduction is enabled by the development of faults at the edges of the slab, but the physical mechanisms controlling fault propagation and direction remain unknown. Here, using 3D numerical subduction models we show that oceanic lithosphere recycling is mainly controlled by the intensity of strain-induced weakening of fractures forming at the edges of the slab. Intense strain-induced weakening causes predominantly brittle fault propagation and slab narrowing until detachment. Without weakening, preponderantly ductile slab edge propagation occurs, which causes slab widening. This rheological control is not affected by the proximity of non-weakened passive continental margins. Natural examples suggest that slab edges follow convergent paths that could be controlled by fractures weakening due to deep water penetration into the oceanic lithosphere.

Plate tectonic episodicity: a deterministic model for periodic Pangeas

Article

Full-text available

Jan 1982

How collision triggers backarc extension: Insight into Mediterranean style of extension from 3-D numerical models

Article

Full-text available

Jun 2014
GEOLOGY

The formation and evolution of a backarc basin are linked to the dynamics of the subduction system. The opening of the central Mediterranean basins is a well-documented example of backarc extension characterized by short-lived episodes of spreading. The underlying reasons for this episodicity are obscured by the complexity of this subduction system, in which multiple continental blocks enter the subduction zone. We present results from three-dimensional numerical models of laterally varying subduction to explain the mechanism of backarc basin opening and the episodic style of spreading. Our results show that efficient backarc extension can be obtained with an along-trench variation in slab buoyancy that produces localized deformation within the overriding plate. We observe peaks in the trench retreating velocity corresponding first to the opening of the backarc basin, and later to the formation of slab windows. We suggest that the observed episodic trench retreat behavior in the central Mediterranean is caused by the formation of slab windows.

Late Cretaceous Plume-induced Subduction Initiation along the southern margin of the Caribbean and NW South America: The first documented example with implications for the onset of Plate Tectonics

Article

Full-text available

Aug 2014
GONDWANA RES

Plate tectonics is the governing theory that unifies the Earth Sciences and is unique to Earth. The sinking of lithosphere in subduction zones drives plate tectonics but exactly how and why subduction begins (subduction initiation, SI) remains enigmatic. Most SI models require exploitation of existing lithospheric weaknesses but these are now produced by plate tectonics; so how did the first subduction zones form? One possibility is SI along a plume head-cold lithosphere interface, but no examples have been documented. On the basis of three key observations, we show here that the Late Cretaceous tectonic evolution of Central America, NW South America and the Leeward Antilles is consistent with plume-induced SI (PISI) which nucleated along the southern and western margins of the Caribbean Plate (Caribbean Large Igneous Province, CLIP) at similar to 100 Ma. (1) Trace element chemistry of most 100 Ma and younger units interpreted as CLIP that are exposed along the southern margin of the Caribbean Plate and NW South America, record subduction additions which increased with time beginning at 100 Ma. These 'plume- and arc-related' (PAR) units are distinguishable from: (a) global oceanic plateau basalts (OPB); (b) 140-110 Ma OPB along the western edge of the CLIP; and (c) post-100 Ma OPB in the northernmost CLIP. Whereas the older OPB are compositionally identical to global OPB, the younger northerly CLIP units are similar to oceanic island basalts and record lower degrees of partial melting than PAR units exposed along the southern and western peripheries of the CLIP. Both the older and the younger northerly CLIP units lack evidence of subduction modification. (2) There is no known hiatus between CLIP and younger arc units, suggesting continuous tectono-magmatic evolution from plume to arc. (3) Generation of the CLIP and earliest, overlying and crosscutting arc units overlaps in time, space, chemical and isotopic compositions; both units are consistent with derivation from Galapagos Plume-like mantle which became increasingly subduction-modified with time. These observations illustrate that formation of the CLIP and earliest arc volcanism reflects partial melting of the same hybrid plume-subduction-modified source in a single, rapidly evolving tectonic environment. The scale of Late Cretaceous PISI in the SW Caribbean realm is consistent with the expected large scale of lithospheric collapse as seen for other SI examples, extending some 1400 km from southern Costa Rica-Panama to western Colombia and 1700 km from Ecuador to the Leeward Antilles (Aruba and Curacao). This first documented example of PISI may be relevant to the start of plate tectonics which may have started when subduction began around Precambrian plume heads. Establishment of lava chemostratigraphy designed to establish the composition of early SI magmatic successions might provide keys for deciphering whether SI occurred along a collapsed transform (like the IBM arc; early MORB-like lavas) or around a mantle plume (like the Caribbean; early plateau-like lavas). Recognition of this first example of PISI further suggests that interaction of a sufficiently large plume head with sufficiently dense oceanic lithosphere in Precambrian time may have triggered the modern regime of plate tectonics.

Dynamics of continental accretion

Article

Full-text available

Mar 2014
Nature

Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon.

The Diffuse Plate boundary of Nubia and Iberia in the Western Mediterranean: Crustal deformation evidence for viscous coupling and fragmented lithosphere

Article

Aug 2015
EARTH PLANET SC LETT

A spatially dense GNSS-based crustal velocity field for the Iberian Peninsula and Northern Africa allow us to provide new insights into two main tectonic processes currently occurring in this area. In particular, we provide, for the first time, clear evidence for a large-scale clockwise rotation of the Iberian Peninsula with respect to stable Eurasia (Euler pole component: N42.612°, W1.833°, clockwise rotation rate of 0.07 deg/Myr). We favour the interpretation that this pattern reflects the quasi-continuous straining of the ductile lithosphere in some sectors of South and Western Iberia in response to viscous coupling of the NW Nubia and Iberian plate boundary in the Gulf of Cádiz. We furnish evidence for a fragmentation of the western Mediterranean basin into independent crustal tectonic blocks, which are delimited by inherited lithospheric shear structures. Among these blocks, an (oceanic-like western) Algerian one is currently transferring a significant fraction of the Nubia-Eurasia convergence rate into the Eastern Betics (SE Iberia) and likely causing the eastward motion of the Baleares Promontory. These processes can be mainly explained by spatially variable lithospheric plate forces imposed along the Nubia-Eurasia convergence boundary.

The initiation of trenches: A finite amplitude instability

Chapter

Jan 1977

D.P. McKenzie

How weak is the subduction interface?

Article

Mar 2015
GEOPHYS RES LETT

Several lines of evidence suggest that subduction zones are weak and that the unique availability of water on Earth is a critical factor in the weakening process. We have evaluated the strength of subduction zone interfaces using two approaches: i) from empirical relationships between shear stress at the interface and subduction velocity, deduced from laboratory experiments; and ii) from a parametric study of natural subduction zones that provides new insights on subduction zone interface strength. Our results suggest that subduction is only mechanically feasible when shear stresses along the plate interface are relatively low (less than ~35 MPa). To account for this requirement, we propose that there is a feedback mechanism between subduction velocity, water released from the subducting plate and weakening of the forearc mantle that may explain how relatively low shear stresses are maintained at subduction interfaces globally.

How was the Iapetus Ocean infected with subduction?

Article

Dec 2014
GEOLOGY

Because subduction in the Iapetus Ocean began only ~35 Myr after the end of rifting, spontaneous foundering of mature passive margins is an unlikely subduction-initiation mechanism. Subduction is more likely to have entered the Iapetus from the boundary with the external paleo-Pacific, similar to the incursion of the Scotia, Caribbean, and Gibraltar arcs into the modern Atlantic. The subduction zone probably became sinuous, entraining fragments of the Gondwanan margin along its complex sinistral southern boundary where oblique collision caused Monian/Penobscottian deformation. Following Taconian/Grampian collision of part of the subduction system with Laurentia, remaining parts of the Iapetus were progressively infected with subduction, leading to Silurian closure.

Effects of various lithospheric yield stresses and different mantle heating modes on the breakup of the Pangea supercontinent

Article

May 2014

Masaki Yoshida

Numerical simulations of three-dimensional spherical mantle convection were performed to investigate the effects of various lithospheric yield stresses and two different mantle heating modes (i.e., mixed heating from the bottom and interior and purely internal heating) on the breakup of the Pangea supercontinent and the subsequent continental drift for the past 200 Myr. Results show that the continental breakup and subsequent continental drift are accomplished in mantle convection models with two different heating modes. This implies that active upwelling plumes from the core-mantle boundary are not necessarily required for the breakup of Pangea. In addition, I found that the continental breakup is only realized when choosing a moderate value of the yield stress (~120 MPa). The bound on the yield stress derived in the present study will potentially enable the self-consistent reconstruction of continental breakup and drift as well as the accompanying pattern on mantle convection since 200 Ma.

Statistical cyclicity of the supercontinent cycle

Article

Apr 2014

Supercontinents like Pangea impose a first-order control on Earth's evolution as they modulate global heat loss, sea level, climate and biodiversity. In a traditional view, supercontinents form and break-up in a regular, perhaps periodic, manner in a cycle lasting several 100Myr as reflected in the assembly times of Earth's major continental aggregations: Columbia, Rodinia and Pangea. However, modern views of the supercontinent cycle propose a more irregular evolution on thebasis of an improved understanding of the Precambrian geologic record. Here, we use fully dynamic spherical mantle convection models featuring plate-like behavior and continental drift to investigate supercontinent formation and break-up. We further dismiss the concept of regularity, but suggest a statistical cyclicity in which the supercontinent cycle may have a characteristic period imposed by mantle and lithosphere properties, but this is hidden in immense fluctuations between different cycles that arise from the chaotic nature of mantle flow.

The future of Earth's oceans: consequences of subduction initiation in the Atlantic and implications for supercontinent formation

Abstract and Figures

Recommendations

FLOWS - Impact of fluid circulation in old oceanic lithosphere on the seismicity of transform-type plate boundaries: new solutions for early seismic monitoring of major European seismogenic zones

Subduction Initiation

The Supertidal Cycle

Transform faults and fracture zones

Weathering Rates and Major Transport Processes an Introduction

How deep can be a dyke?

A depth profile of uranium-236 in the Atlantic Ocean

Earth Evolution and Dynamics – A tribute to Kevin Burke