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As a result of its long tectonic and magmatic history,
complex topography and distinct geological provinces,
West Antarctica defies simple classification as a conver-
gent margin, magmatic arc or rifted continental mar-
gin1,2. This region, which is ~4,700 km long and up to
1,600 km wide (FIG.1a), consists of crustal blocks of dis-
parate tectonic origins, all of which have been affected
by complex convergent margin processes3,4. Compared
with East Antarctica, West Antarctica is younger, less
tectonically stable and has a lower average elevation.
The majority of West Antarctic crust developed between
~500 and 90 million years ago (Ma) along the active
ocean–continent convergence zone that borders the
ancient Pacific margin of Gondwana, which has left a
lasting impact on the geology of the region.
Due to the complex tectonic setting, sparse rock
exposure (FIG.1b) and lack of detailed exploration, the
fundamental structures and evolution of West Antarctica
are actively debated. However, the integration of geolog-
ical and geophysical techniques (BOX1), together with
tectonic frameworks from well-studied once-conjugate
continents, has advanced our understanding of the
region in recent decades5–8. In return, improved knowl-
edge of the geology of West Antarctica has provided key
geological evidence of the processes that lead to conti-
nental growth9–11, as well as insight into the evolution
of the overlying West Antarctic ice sheet12–15. These
advances motivate continued study of West Antarctica
and highlight the importance of understanding its
geological evolution.
In this Review, we give an overview of the West
Antarctic region. We divide West Antarctica into three
broad physiographic provinces (FIG.1) with differing, but
often overlapping, geological histories: the Weddell Sea
sector, which includes the elevated Ellsworth–Whitmore
Mountains, Haag Nunataks and the low-lying Weddell
Sea rift system; the low-lying Ross Embayment and West
Antarctic rift system (WARS), and the elevated Marie
Byrd Land (MBL) dome; and the arcuate, elevated spine
of the Antarctic Peninsula and adjacent Thurston Island
crustal block. For each of these provinces, we describe
regional-scale physical characteristics, geological his-
tory and the current understanding of the area’s tec-
tonic evolution. Finally, we consider what makes West
Antarctica a unique and important system.
The Weddell Sea sector
The Weddell Sea sector, which includes the shallow
marine Weddell Sea rift system and onshore high-
lands of the Haag Nunataks and Ellsworth–Whitmore
Mountains block (FIG.1a), is the oldest and most enig-
matic part of West Antarctica. It is bounded to thenorth
by the Jurassic and younger oceanic crust of the southern
Weddell Sea and to the south by the abrupt topographic
step between the Ellsworth–Whitmore Mountains
and the low-lying WARS. The Weddell Sea sector is
flankedby the generally younger Antarctic Peninsula to
the west and by the ancient cratonic East Antarctic con-
tinent and overlying Jurassic Ferrar magmatic province
to the east.
Nunataks
An isolated rock outcrop
standing proud of the
surrounding ice sheet,
often used as a descriptive
Antarctic place name.
The geological history and evolution
of West Antarctica
TomA.Jordan
1*, TealR.Riley1 and ChristineS.Siddoway
2
Abstract | West Antarctica has formed the tectonically active margin between East Antarctica
and the Pacific Ocean for almost half a billion years, where it has recorded a dynamic history of
magmatism, continental growth and fragmentation. Despite the scale and importance of West
Antarctica, there has not been an integrated view of the geology and tectonic evolution of the
region as a whole. In this Review , we identify three broad physiographic provinces and present
their overlapping and interconnected tectonic, magmatic and sedimentary history. The Weddell
Sea region, which lays furthest from the subducting margin, was most impacted by the Jurassic
initiation of Gondwana break-up. Marie Byrd Land and the West Antarctic rift system developed
as a broad Cretaceous to Cenozoic continental rift system, reworking a former convergent margin.
Finally , the Antarctic Peninsula and Thurston Island preserve an almost complete magmatic arc
system. We conclude by briefly summarizing the geologic history of the West Antarctic system as
a whole, how it provides insight into continental margin evolution and what key topics must be
addressed by future research.
1British Antarctic Survey,
Cambridge, UK.
2Geology Department,
Colorado College, Colorado
Springs, CO, USA.
*e-mail: tomj@bas.ac.uk
https://doi.org/10.1038/
s43017-019-0013-6
REVIEWS
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Earth & EnvironmEnt
Precambrian evolution. The oldest rocks exposed in West
Antarctica form a ~2-km2 outcrop at Haag Nunataks,
providing a unique window into the basement geology of
the region (FIG.1b). The rocks at Haag Nunataks formed in
a magmatic arc during the Mesoproterozoic at ~1,170 Ma
and were subsequently deformed at ~1,060 Ma (REF.16),
making them more than twice as old as any otherrocks
identified in West Antarctica (FIG.2). Theexposed rocksare
juvenile, that is, they formed through the direct melting
of the mantle, rather than through remelting of existing
crustal rocks17. Although the rock outcrop is small, aero-
magnetic data (BOX2) indicate that this basement prov-
ince extends beneath a region of at least 120,000 km2, as
marked by high-amplitude magnetic anomalies matching
those at Haag Nunataks18,19.
The age and petrology of the Haag Nunataks block is
distinct from the adjacent, younger Antarctic Peninsula
but similar to the age and petrology of the Natal
Embayment of Southern Africa20 and the basement of
East Antarctica. Therefore, the Haag Nunataks juvenile
arc terrane might have developed on the accretionary
margin of the proto-Kalahari Craton at ~1,200 Ma
(REF.21) during the wider Grenvillian amalgamation of
the Neoproterozoic supercontinent of Rodinia22. The
absence of subsequent deformation events in the rocks
of Haag Nunataks16 suggests that these rocks acted as an
undeforming microcontinental block from Grenvillian
time onwards23.
Paleozoic development. Adjacent to the Haag Nunataks
province are the Ellsworth Mountains (FIG.1b), a
~350-km-long mountain range that includes Mount
Vinson (4,892 m), the highest peak in Antarctica.
A succession over 13 km thick of conformable Cambrian
to Permian sedimentary rocks are exposed along
these mountains and likely extend across the wider
Ellsworth–Whitmore Mountains region5,24, as indicated
by exposures in sparse nunataks. The basement geology
of this region is not exposed; however, Hf (Hafnium)
isotopic signatures from detrital zircons25, along with
mantle extraction ages (estimated to be 1,370 to 1,600 Ma)
from Jurassic granites17, indicate that Proterozoic-age
basement is present across the region, meaning that the
Ellsworth–Whitmore Mountains basement is similar in
age to the exposed Haag Nunataks. Although of similar age,
aeromagnetic data show that the weakly magnetized
Ellsworth–Whitmore Mountains basement is distinct
from the highly magnetic Haag Nunataks basement2,18
(BOX2). It is proposed that the Ellsworth–Whitmore
Mountains were thrust over the margin of the Haag
Nunataks block in the Permo-Triassic (~250 Ma)26, indi-
cating that the boundary between these two regions has
been a long-standing geological discontinuity.
The oldest exposed rocks in the Ellsworth Mountains
are the Cambrian Heritage Group (FIG.2), which includes
~7.5 km of clastic, basaltic volcaniclastic and fossili-
ferous carbonate sediments27 formed between ~532
and ~505 Ma (REF.28). Unlike the Paleo-Pacific conti-
nental margin magmatic arc along the Transantarc-
tic Mountains in East Antarctica at this time29, the
Ellsworth–Whitmore Mountains region was dominated
by a rapidly subsiding continental rift basin associated
with extension either in a back-arc or embayment set-
ting5. The precise location of the Ellsworth–Whitmore
Mountains at this time is under debate (FIG.3). Provenance
data based on Heritage Group zircon ages suggest an
East Antarctic or Australian source for these sediments30,
but a combined Laurentian and South African sediment
source has also been proposed28. Other geochemical
proxies (such as Hf isotopes) suggest that the sediments
were from Southern Africa or locally derived basement25.
Paleomagnetic data from the Cambrian Heritage Group
Key points
•WestAntarcticaisageologicallycomplexregionthatdevelopedalongthemarginof
GondwanabetweenthesubductingPaleo-PacificoceanicplateandthecratonicEast
Antarcticcontinent.
•WestAntarcticacanbebrokenintothreebroadgeologicalandphysiographic
provinces:theWeddellSeasector;theWestAntarcticriftsystemandMarieByrd
Land;andtheAntarcticPeninsulaandThurstonIsland.
•TheWeddellSeasectorincludestheoldestrocksinWestAntarctica,wasleast
affectedbythemarginalsubductionsystemanditsmovementtoitscurrentposition
duringtheJurassicinitiationofGondwanabreak-upwasassociatedwithback-arc
extensionintheWeddellSeariftsystem.
•TheWestAntarcticriftsystemandMarieByrdLandregionfollowedasanactive
subductingmarginandmagmaticarcoutboardfromtheEastAntarcticRossorogen.
SubductionceasedduringtheCretaceous,associatedwithextremecrustalextension
andresultinginabroadriftbasinand,ultimately,NewZealandriftingaway.
•TheAntarcticPeninsulaandThurstonIslandexemplifyacontinentalmargin
magmaticarc,preservingarecordoftheflare-upsinmagmatism.Arcmagmatism
ceasedfromsouthtonorthbetween90and20millionyearsagoasthePhoenix
oceanicspreadingcentrereachedthecontinentalmargintrench.
Fig. 1 | West Antarctic setting. a | Complex West
Antarctic subglacial topography from Bedmap2, derived
from airborne ice-penetrating radar157, with bathymetry
beneath the Ross Ice Shelf derived from gravity data77.
The thick red lines demarcate the three main geotectonic
provinces and the dashed black lines mark sub-provinces.
The main provinces include the Weddell Sea sector, which
includes the shallow marine Weddell Sea rift system and
onshore highlands of the Haag Nunataks and Ellsworth–
Whitmore Mountains (EWM) block; Marie Byrd Land (MBL)
and the West Antarctic rift system (WARS), which are
underlain by highly extended crust; and the Antarctic
Peninsula and Thurston Island (TI), which expose a well-
preserved continental marginal arc. Note the broad
variety of distinct topographic provinces, which reflect
the complex and contrasting geology that developed
along the convergent margin. The camera symbols locate
photographs in BOX1. b | Outcrop geological age from
SCAR GeoMAP and GNS Science 2019 (REF.162). Sparse
outcrop data means that much of the sub-ice geology is
interpolated from these outcrops based on geophysical
data. The oldest province is the Weddell Sea sector, with
rocks in places over a billion years old. The MBL and WARS
region is dominated by rocks between 500 and 66 Ma,
while the Antarctic Peninsula is dominated by younger
rocks formed from 251 Ma to present day. Also shown
are the locations of known Cenozoic volcanoes68.
AT,Adare Trough; BSB, Byrd Subglacial Basin; BST, Bentley
Subglacial Trench; CeH, Central High; CoH, Coulman
High; FRD, Ford Ranges; H, Haag Nunataks sub-province;
M, Mount Murphy ; NVL , northern Victoria Land;
PCM,Pensacola Mountains.
Grenvillian
The mountain-building event
~1,000 million years ago, seen
in continents around the world,
which led to the assembly of
the supercontinent of Rodinia.
Hf
(Hafnium). A geologically useful
isotope, as its value is strongly
controlled by its magmatic
source, which is linked to
tectonic setting.
Zircons
Highly resistant silicate
minerals formed by igneous
and metamorphic processes;
the isotopes they contain and/
or exclude make them ideal
for radiometric dating and
geochemical analysis.
Mantle extraction ages
Isotopically determined ages
when the minerals making up a
crustal rock were first extracted
from the underlying mantle.
Laurentian
Referring to a large continental
craton, which, today, forms the
core of North America, but
which was likely positioned
close to Antarctica within the
supercontinent of Rodinia.
Paleomagnetic data
The preserved orientation of
magnetic minerals in rocks,
which can be used to
reconstruct where the rock
was formed.
▶
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indicate a location towards the Natal Embayment during
this time, andthatthe region was rotated by 90° after
deposition of the sediments during the Cambrian6,31.
Despite the controversy over sediment sources, there
is general consensus that the Ellsworth–Whitmore
Mountains lay to the north of their current location in
Cambrian times, and were receiving sediments from the
interior of the Gondwana supercontinent.
Between the Late Cambrian and Devonian, a period
of relative tectonic quiescence was marked by the depo-
sition of ~3 km of shallow marine sandstone in the
Ellsworth–Whitmore Mountains, forming the exten-
sive Crashsite Group32. This formation is overlain by the
Whiteout Conglomerate, ~1 km of unsorted sediment
deposited during the Upper Carboniferous–Permian
Gondwanan glaciation33. Ice streams flowing out-
wardfrom East Antarctica transported glacial sediments
from the Transantarctic Mountains to the Ellsworth
Mountains area, as suggested by ice-flow markers and
limestone clasts with distinctive Cambrian fossils33,34.
Similar Permo-Carboniferous glacial tills in the Pensacola
Mountains (FIG.1a) have been used to constrain the
position of the Ellsworth–Whitmore Mountains at this
time to a region north of the present-day Pensacola
Mountains33,35. The Whiteout Conglomerate glacial
unit is overlain by the Permian Polarstar Formation,
bb
e
ef
f
d
dc
c
a
b
Amundsen
Sea
Ross Embayment
–150°
180
°
150
°
180
°
Formation age (Ma)
0.25–66
150
°
–120°–90°
–150° –120°
120° 90° 60° 30° 0°
120° 90° 60° 30° 0°
–90°
–60°
–30°
–60°
–30°
Weddell
Sea
Ross
Sea
CeH
CoH
Ross Ice
Shelf
?
?
?
Antarctic
Peninsula
East
Antarctica
South
Shetland
Islands
Photographic locations
South
Orkney
Islands
Alexander
Island
James Ross
Island
Haag
Nunataks
Ellsworth
Mountains
Neoproterozoic
rifted margin
Bransfield
Strait
Transantarctic Mountains
Weddell Sea
rift system
Graham Land
Palmer Land
Amundsen
province
Ross
province
Cratonic margin
province
MBL
WARS EWM
PCM
TI
H
M
BSB
FRD
BST
AT
NVL
66–251 251–541 >541 Cenozoic volcanoes Ice sheet Ice shelf
500 5000
(km)
500 5000
(km) <–3,000 –2,000 –1,000 1,000 2,000 3,0000
(m)
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a ~1-km-thick unit dominated by shallow marine sand-
stones, with increasing amounts of siltstone and coals
in the upper levels, marking a transition from marine
delta to onshore coastal plain36. Detrital zircons and
stratigraphic analysis both suggest that the youngest
sediments in the Ellsworth Mountains were deposited in
a basin with sediments sourced from the Transantarctic
Mountains37, rather than from Southern Africa. Volcanic
tuff units interbedded in the Polarstar formation are
dominated by mid-Permian to late-Permian prismatic zir-
cons, indicating a link between the tuffs and a major mag-
matic flare-up event along the Paleo-Pacific margin28,37
(BOX3; FIG.2).
The entire Paleozoic sedimentary succession was
deformed into a series of closed-to-tight folds by a major
dextral transpressive Permo-Triassic orogenic event38.
This event is inferred to be part of the wider Andean-style
Gondwanide orogeny, extending from South America
through the Cape Fold Belt of South Africa and the
Falkland Islands to the Pensacola Mountains on the edge
of East Antarctica39 (FIG.1a). The assumption that this
orogen was originally a linear structure is consistent
with the hypothesis that the Ellsworth–Whitmore
Mountains rotated through 90° in post-Permian times,
as, today, the Ellsworth Mountains’ structural trends
are orthogonal to many other parts of the orogen40,41.
However, as other parts of this orogen are not straight42,
the paleomagnetically observed rotation might have
occurred during Gondwanide deformation43. An isolated
Triassic granite (~208 Ma) intruded into the Ellsworth–
Whitmore Mountains44 indicates that subduction along
the Paleo-Pacific margin continued after the Gondwanide
orogen, although the location of the subduction zone is
not clear.
Jurassic magmatism and microcontinental movement.
The Early Jurassic is marked by a major pulse of large
igneous province (LIP) magmatism that includes
emplacement of both the Karoo and Ferrar mafic igne-
ous provinces around 183–182 Ma in South Africa and
East Antarctica45,46 (FIG.3a). The formation of these
LIPs is considered a precursor of Jurassic continental
break-up and magmatism in the Weddell Sea region47,
but the origin of the Ferrar magmas is debated. It has
been proposed that melting and magmatism was driven
by an upwelling mantle plume48,49, which triggered
the break-up of the Gondwana supercontinent in the
Weddell Sea region47,49. However, geochemical analysis of
the isotopic signatures indicates that the more extensive
Ferrar magmas are distinct from typical plume-derived
magmas50,51. This evidence favours the conclusion that
the Ferrar LIP resulted from extension and decompres-
sional melting in response to changes in subduction
along the Paleo-Pacific margin50,51.
Though magmatic rocks directly attributed to the
Ferrar or Karoo LIPs are not seen anywhere in West
Antarctica, the Ellsworth–Whitmore Mountains do
contain at least four granites from the Middle Jurassic
Box 1 | Key techniques for exploring West Antarctica
Geophysicaltechniquesimageorsensetherocksbeneaththeicysurfaceandincludebothairborneandground-basedsurveys.Airbornesurveysoften
includeice-penetratingradartorevealthemountainsandvalleysburiedbeneathupto5kmofice157(FIG.1).Aeromagneticsensors,suchaswing-tippods
thathousemagnetometers(seethefigure,parta),areusedtomapthepatternofsub-surfacefaults,intrusionsandgeologicalprovincesbased
onthevaryingmagneticpropertiesofthedifferentrocksinvolved19.Aerogravitydatacanbeusedtomapsub-surfacedensityvariationsthat,when
combinedwithtopographyandmagneticdata,reveallargeintrusions,thicksedimentarybasinsandregional-scalevariationsincrustalthickness.
SeismicdatausesoundwavestravellingthroughtheEarth’scrusttomapsub-surfacestructures.Reflectionseismicdatausingaman-madesource
typicallyimageshallowerstructures,suchasstacksofsediments.Refractionseismicorpassiveseismicobservationsusingman-madeornatural
sources,respectively,imagethestructureoftheentirecrustandmantlebeneath54(BOX2).
OtheraspectsofgeologicalexplorationinWestAntarcticaincludeground-basedfieldwork(seeanexampleofafieldcampinthefigure,partb).
Fieldworkcaninclude,forexample,samplingbasementmaterial,silicicignimbrites,carboniferousgranitesandarccolumnarjointedrhyolitictuff
(seethefigure,partsc,d,eandf,respectively).
a
b
c
d
e
f
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(177–174 Ma)44,52. These granites are geochemically
defined as being syn-collisional to within-plate (back-arc
and/or continental rift), and, hence, distinct from typi-
cal volcanic arc granites44. The Middle Jurassic granites
are thought to be derived from a combination of crustal
melting due to upwelling of hot mantle and direct frac-
tionation of the mantle-derived Ferrar magmas2,44. If the
latter contribution was dominant, a relatively long crustal
residence is required, as the granites post-date the Ferrar
magmatism by at least 5 Ma (REFS44,46,52). Aeromagnetic
data show that, in contrast to the three approximately cir-
cular Middle-Jurassic granites, the 174.6 ± 0.2 Ma Pagano
Nunatak granite at the western edge of the Ellsworth–
Whitmore Mountains province is highly elongated53. It is
suggested that this granite was emplaced within a major
shear zone that facilitated left lateral movement of the
Ellsworth–Whitmore Mountains block along the margin
of East Antarctica43 (FIG.3a).
Offshore, the thin continental crust of the southern
Weddell Sea rift system54 (BOX2) is thought to have devel-
oped as a broad back-arc55 in response to south-westerly
movement of the Ellsworth–Whitmore Mountains and
Haag Nunataks block43,56 (FIG.3a). However, the extent
of Jurassic movement of the Ellsworth–Whitmore
Mountains and Haag Nunataks block is controversial
(FIG.3a). Movement from a position in the Natal Embay-
ment is suggested based on geological, stratigraphic and
paleomagnetic data5,6,40,57,58. However, geophysical analysis
and resulting interpretation of the Weddell Sea rift sys-
tem as a region of stretched continental crust challenges
the concept of microcontinental movement from further
north43,59–62. Most significantly, seismic refraction data
crossing the Weddell Sea rift system along the ice shelf
front (FIG.1b) reveal ~12-km-thick sediments with low
modelled seismic velocities, which overlay lower crust
with unusually fast modelled seismic velocities60,63,64. The
high-seismic-velocity layer was originally interpreted as
stretched continental crust63, but interpretations based
on reprocessing of the seismic data suggest the pres-
ence of unusually thick oceanic (~20 km) or transitional
continental margin crust in this region60.
In light of the proposed origin of this crust as a transi-
tional continental margin, the magnetic anomalies in
the northern Weddell Sea rift system (BOX2) may reflect
continental fragmentation between Southern Africa and
East Antarctica43,60,63,65 (FIG.3b). In contrast, magnetic
anomalies in the southern Weddell Sea rift system reflect
the more limited movement of the Ellsworth–Whitmore
Mountains prior to Gondwana break-up (BOX2; FIG.3a).
The oldest oceanic magnetic anomalies offshore from
the Weddell Sea sector are 145–160 Ma (REF.60), suggest-
ing that all major tectonic movements were complete
by this time.
MBL, WARS and the Ross Embayment
MBL comprises a Paleozoic–Mesozoic-age archipelago
of islands and submerged continental crust (FIG.1). Rock
exposures forming the Ford Ranges in western MBL
(BOX1) exemplify the geological framework of the region.
The oldest rocks here are immature sediments depos-
ited in slope or trench settings that host subsequent
mid-Paleozoic continental margin arc and late Mesozoic
back-arc plutons. In contrast, central and eastern MBL
host sparse coastal exposures that reflect mid-Paleozoic
and Permo-Triassic convergent margin arcs3,66,67. The
youngest rocks in MBL are basaltic scoria and lava flows
exposed on the slopes of quiescent alkaline volcanoes
(up to 4,285 m elevation), which are distributed along
the crest and north flank of an elongate elevated region
of disputed origin known as the MBL dome68 (FIG.1a).
The WARS is a ~600-km-wide region of thinned,
subsided continental crust that borders the prominent
Transantarctic Mountains (FIG.1a). The rift topography
here narrows and deepens southward from the shallow
marine Ross Embayment, which spans the Ross Sea
and Ross Ice Shelf, into the rugged, lineated subglacial
troughs surrounding the Bentley Subglacial Trench
(−2,555 m) and Byrd Subglacial Basin (−2,870 m). The
narrow troughs and ridges imply fault-control and young
or active tectonism upon new or inherited structures
beneath the West Antarctic ice sheet.
Metamorphic basement and a concealed Precambrian
element. The oldest known rocks of MBL form the gneis-
sic crystalline basement beneath a late Miocene stratovol-
cano, Mount Murphy. A crystallization age of 505 ± 5 Ma
for granodiorite66 (based on U-Pb dating in zircons) implies
that this basement originated in close proximity to the
Transantarctic Mountains’ Ross orogen69. Isotopic signa-
tures from mantle xenoliths and later-emplaced granites
indicate that Precambrian litho sphere underpins MBL66,70.
Together with bedrock ages and geophysical contrasts,
Nd isotopic data delineate two tectonic sub-provinces: an
older, inboard Ross province and a younger, outboard
Amundsen province66 (FIG.1b). Ultramafic xenoliths
sampling the lithospheric mantle were erupted from
Miocene volcanoes in this region. These xenoliths show
diverse mineralogy, geochemical properties and equili-
bration temperatures70,71, substantiating the presence of
heterogeneous Precambrian lithosphere beneath MBL.
Paleozoic development of a convergent margin. The
extensive Cambrian–Ordovician turbidites and flysch72,
which form the Swanson Formation in western MBL
(FIG.2), are part of a voluminous, immature sedimen-
tary sequence deposited in a series of slope aprons and
submarine fans along the Gondwanide margin (FIG.3a).
The oldest sediments in this formation are derived from
the final stages of the Ross–Delamerian orogen, which
formed along the Australian–East Antarctic continental
margin of Gondwana between 514 and 490 Ma (REF.73)
during the Neoproterozoic and Cambrian. Subsequently,
in West Antarctica, these sediments were deformed
into strongly cleaved, km-scale upright folds by coeval
and subsequent contractional tectonics74.
Pulses of granitoid magmatism and metamorphism
occurred in MBL during the Ordovician–Silurian,
Devonian–Carboniferous and Permo-Triassic3,66,74
(FIGS2,4a). Permian volcanic ash falls deposited in the
adjacent Transantarctic Mountains are interpreted to have
come from volcanoes along that convergent margin75.
These ash falls and the formation of leucogranites by
crustal melting of immature sediments reflect arc mag-
matism due to plate convergence and the incremental
U-Pb dating
Use of the relative abundances
of isotopes of uranium (U) and
lead (Pb) to determine the age
that crystals formed within a
magma or metamorphic rock.
Nd isotopic data
The use of samarium–
neodymium (Sm–Nd) isotope
decay system to determine the
age of formation and evolution
of the continental crust.
Leucogranites
Granites with a high
proportion of light-coloured
minerals compared with
darker-coloured minerals;
they are typically formed in
continental collision settings.
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Convergent
margin
Convergent
margin
Passive
margin
Passive
margin
margin
Renewed
WARS
extension
WARS
formation
Gondwana
breakup
Core
complexes
Fore-arc/
accretionary
prism
sedimentation
Continental
slope and
rise
sedimentation
Localized
sediments
in narrow
grabens
Unnamed
sediments
basins
Glaciomarine
sedimentation
Weddell Sea
sediments?
Polarstar
Formation
1,000 m
Alexandra
Complex
(protolith)
Youngest
zircon
ages
Swanson
Formation
Antarctic Peninsula and Thurston Island Weddell Sea sector
Magmatism Magmatism Magmatism
Sedimentary
basins
Sedimentary
basins
Sedimentary
basins
Fore-
arc
Back-
arc
Tectonic
events
Tectonic
events
Tectonic
events
Setting SettingSetting
alkaline
magmatism Alkaline
magmatism
Alkaline
magmatism
Alkalic
magmatic
province
(MBL dome)
Subduction
ceased
(~20 Ma)
Arc
volcanism
Arc
volcanism
Permian
flare-up
Arc
volcanism
Arc
volcanism
Arc magmatism
Arc magmatism
Arc
volcanism
Arc
volcanism
Back-arc
extension
Back-arc
extension
Dyer
Arc
CENOZOICCRETACEOUSJURASSIC
Latady and Larsen basins
Trinity Peninsula Group Fossil Bluff Group
LeMay Group
TRIASSICPERMIANCARBONIFEROUSDEVONIAN
SILU-
RIAN
ORDOVICIANCAMBRIAN
100
Ma
200
300
400
500
Palmer Land
event 2
(103 Ma)
Gondwana
breakup
Gondwanide
deformation
Gondwanide
deformation
Palmer Land
event 1
(107 Ma)
JRI
Drake
Passage
opening
(34 Ma)
Byers
Whiteout
Conglomerate
1,000 m
Continental
Orogeny
Juvenile
arc
Subduction-
related
granite
Intraplate
granites
Gondwanide
glaciation
Gondwanide
deformation
Youngest
zircon ages
Crashsite
Group
3,000 m
Heritage
Group
7,000 m
MESO-
PROTEROZOIC
1,000
1,300 1,100
1,200
Haag Nunataks
magmatism
First oceanic
crust
Weddell Sea
Subsiding
passive
margin
Mid-
Cretaceous
flare-up
Chon Aike
flare-up
Permian
flare-up
Chon Aike
flare-up
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formation of new continental crust76. Over time, plutonism
shifted outboard from the western Ross province of
MBL to the eastern and central Amundsen province
and Zealandia. Geochemical evidence suggests that the
MBL and Zealandia subduction zone was retreating
through Carboniferous to Permian times, which would
favour crustal thinning and maximize the proportion
of juvenile crustal material generated in this region9.
Geochronological evidence suggests that successor basins
containing Permo-Triassic sediments were deposited and
subsequently metamorphosed. On the basis of coastal
exposures and the geophysical characteristics of the con-
cealed crust (BOX2), this geological pattern is inferred to
continue beneath the eastern half of the Ross Ice Shelf
and Ross Sea77.
In total, the ~400 million years of ocean–continent
convergence described in this section resulted in an
approximately threefold increase in the thickness of the
continental crust in the MBL and WARS region. This
increase might have resulted in lithospheric thickening
and the development of a linear belt of elevated topog-
raphy or an orogenic plateau78 that was subsequently
extended and thinned.
Cretaceous magmatism and intracontinental extension.
The WARS and MBL contain no geological record of
notable Jurassic or Early Cretaceous events. However,
during this time, the thickened crust may have led to
incipient partial melting of the lower crust that was
important in subsequent events (FIG.4b). Renewed sub-
duction of oceanic crust and calc-alkaline plutonism
occurred from 124 to 110 Ma, overlapping with the
granulite-facies metamorphism and alkaline granite plus
mafic plutonism that occurred between 115 to 96 Ma
(FIG.4b). Over the wide back-arc region, bimodal mag-
matism was accompanied by normal to oblique-normal
slip upon low-angle to high-angle faults, resulting in
crustal thinning and broad extension across the WARS
(FIGS3c,4b). In <20 million years (between ~105 and
85 Ma), central West Antarctica underwent ~600 km of
extension and >1,000 km of stretching occurred across
the Ross Sea through western MBL79–81.
The large-scale extension and crustal thinning led
to exhumation of mid-crustal migmatite gneiss–granite
complexes along detachment faults82, in both MBL and
once-contiguous southern Zealandia. Isotopic and geo-
chemical ties exist between these granites (which were
formed by melting of the middle crust) and the upper
crustal plutons83. The resulting crust beneath MBL
and the Ross Embayment varies in thickness from
14 km beneath the basins up to 21–24 km beneath the
Coulman and Central Highs54,84 (BOX2). The thinned
crust attributed to West Antarctic extension and rifting
continues to the foot of the Transantarctic Mountains54.
However, recent airborne geophysical surveys indicate
that the short-wavelength, high-amplitude magnetic
anomalies that are characteristic of MBL and much of
the WARS do not extend beneath the Ross Ice Shelf
tothe Transantarctic Mountain front77 (BOX 2; FIG.1b).
Magnetically, the signatures of the ‘cratonic margin
province’ of the WARS resemble the adjacent area of the
Neoproterozoic (~670 Ma) passive margin and subse-
quent sequences of orogen-derived sediments exposed
in the Transantarctic Mountains85 and the turbidite-
dominated Robertson Bay terrane of northern Victoria
Land86,87. The cratonic margin province is, therefore,
likely underlain by faulted Neoproterozoic crust of the
pre-Ross rifted margin that is blanketed by sedimen-
tary molasse eroded from the Ross orogen and younger
strata77, with limited Cretaceous or younger magmatic
reworking (FIG.4b). This province boundary intersects
the Transantarctic Mountains at the junction of two East
Antarctic basement provinces88, but lack of aeromag-
netic data coverage means continuation of this province
boundary across the Transantarctic Mountains into East
Antarctica is speculative (FIG.1).
The Cretaceous events from 115 to 90 Ma reflect a
dramatic change in the continental tectonic regime in
MBL, Zealandia and the Antarctic Peninsula and the
oceanic Phoenix and Pacific plates89. The regional impor-
tance of this change is demonstrated by the synchronicity
of the pulses of magmatism seen along the Paleo-Pacific
margin at this time (BOX3). In MBL and the WARS, the
subduction-related magmatism and wrench component
of deformation was driven by the oblique subduction of
young, hydrated oceanic lithosphere of the Phoenix
plate90,91 (FIG.3c). As subduction waned, potentially due
to the approach of the Phoenix spreading centre and
Hikurangi Plateau to the continental margin trench
~100 Ma, extreme transtensional back-arc extension was
distributed across MBL and the WARS82,92.
Continental margin break-up and tectonic quiescence.
The final stage of break-up in East Gondwana — leading
to the eventual isolation of Antarctica over the South Pole
— was driven by the rapid oblique sub duction of young,
hydrated oceanic lithosphere of the Phoenix plate90,91,
oceanic ridge–trench interaction93,94 and encroachment
of the Hikurangi LIP and oceanic plateau upon the
trench95 (FIG.3c). The initial regional high-temperature
metamorphism and extensive mid-crustal melting
~100 Ma weakened the crust of MBL, which was already
scored by high-angle transcurrent faults due to oblique
convergence. Plate separation between West Antarctica
and Zealandia occurred along a narrow zone orthogonal
to the rift basins of the Ross Sea96 (FIG.3c,d), suggesting
that a pre-existing high-angle strike–slip fault system97
was exploited for continental separation. The subsequent
demise of the convergent boundary progressed from west
to east. As the plate boundary shifted from convergentto
divergent, seafloor spreading commenced between
Zealandia and both West Antarctica and Australia by
83 Ma (REFS7,98,99) (FIG.3d). Tectonic restoration of the
Plutonism
The formation of intrusive
magmatic rocks beneath
the Earth’s surface, in contrast
to volcanism, where magmas
are erupted onto the Earth’s
surface.
Calc-alkaline
Magmas that are typically
hydrous and oxidized, and
are generally found in arcs
above subduction zones.
Migmatite
A metamorphic rock where
significant partial melting
has begun.
Molasse
Poorly sorted terrestrial and
shallow marine deposits
associated with erosion from
a nearby active orogenic belt.
Fig. 2 | Timeline of key West Antarctic tectonic and magmatic events. Tectonic and
magmatic events evolved differently across the three provinces of West Antarctica (the
Antarctic Peninsula and Thurston Island, Marie Byrd Land (MBL) and the West Antarctic
rift system (WARS), and the Weddell Sea sector), as depicted in this timeline. The red and
blue bands in the ‘Magmatism’ column show the relative magnitude of arc-related
andrift-related magmatism, respectively. The arrows in the ‘Tectonic events’ columns
indicate relative compression (inward-facing arrows) or extension (outward-facing
arrows). Exposed (in grey text boxes with solid outlines) and inferred (in grey text boxes
with dashed outlines) sedimentary successions are also shown in the ‘Sedimentary
basins’ columns. The yellow squares are detrital zircon ages reflecting the minimum
depositional ages. JRI, James Ross Island.
◀
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Box 2 | Geophysical features of West Antarctica
GeophysicaldataplayakeyroleindefiningWestAntarctica.Seismicdatarevealthethicknessofthecontinentalcrust,
whichreflectsthickeningbycompressionandadditionofmagmaandthinningbyextensionandrifting.Aeromagnetic
datacanbeusedtodeterminewhichareashaverockswithsimilaramountsofmagneticmineralsandhowtheyhave
beensubsequentlyjuxtaposedanddeformed.Here,crustalthicknessderivedfrompassiveseismicobservations54clearly
separatethe35–45-km-thickcratoniccrustinEastAntarcticaandtheWestAntarcticcrustwithameanthicknessofjust
25km.Together,crustalthickness54andaeromagneticpatterns19,77(seethefigure,partsaandb,respectively)helpto
furtherrefineunderstandingofWestAntarcticprovincesandtheprocessesthatformedthem.Thequestionmarks
indicatespeculativeextensionsofprovinceboundaries.
Weddell Sea
TheWeddellSeaprovincerevealsgenerallylong-wavelengthmagneticfeatures.Offshore,theNorthernWeddellMagnetic
Province(NWMP)andSouthernWeddellMagneticProvince(SWMP)43,crust~30kmthick53,62,reflecttheJurassicriftfabric43
andthicksedimentarycover158duetosubsequentsubsidenceandsedimentation.
Antarctic Peninsula
TheAntarcticPeninsulaismarkedbythe~2,600-km-longmagneticPacificMarginAnomaly(PMA),attributedtoa
well-preservedmagmaticarc159.Thickercrustandthedetailedstructuresofthemagneticanomaliesreflectperiods
ofcompressionandtectonicthickeningofthecrust11,149.
WARS
TheWestAntarcticriftsystem(WARS)ischaracterizedbybroadareasofcrust20–25kmthickattributedtoCretaceous
toCenozoicextension.Thedisorderedhigh-amplitudemagneticpatternsareattributedtowide-spreadmagmatism,
includingbothintrusionsandvolcanoes77,160.
AT,AdareTrough;CD,CentralDomain;ED,EasternDomainsintheAntarcticPeninsula;EWM,Ellsworth–WhitmoreMountains;
FRD,FordRanges;H,HaagNunataks;M,MountMurphy;MBL,MarieByrdLand;NVL,northernVictoriaLand;TI,ThurstonIsland.
a
b
180
°
150
°
180
°
150
°
–150°–120° –90°
–150°–120°
120° 90°60° 30°0°
120° 90°60° 30°0°
–90°
–45 –35 –25 –20 –10 –9 –8 –7–40
–225 –50 –25 02550 100175
nT
km
–75–125
–60°
–30°
–60°
–30°
Amundsen
Sea
Weddell
Sea
Ross
Sea
?
?
?
?
?
?
?
?
Antarctic
Peninsula
East
Antarctica
Transantarctic Mountains
Weddell Sea
rift system
MBL
MBL
WARS
TI
H
M
FRD
AT
500 5000
(km)
EWM
NVL
NVL
AT
PMA
CD ED
SWMP
NWMP
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CP
Phoenix
Plate
Phoenix
Plate
Phoenix
Plate
Phoenix
Plate
Passive
margin
Passive
margin
Passive
margin
Passive margin
Pacific Plate
Waning convergence
Hikurangi Plateau
Line of~83 Ma
breakup
NNZ
SNZ
CP
CP
CP
MBL EWM
EWM
EWM FI
FI
M
M
Patagonia
Patagonia
TI
TI
AP
AP
AT
LHR
LHR
LHR
Australia
East Antarctica
East Antarctica
LIPsOceanic crust Oceanic plateau
Cambro-Ordovician marginal turbidites Triassic fore-arc accretionary rocks Incipient continental riftingSubduction zone
West Antarctic blocks Other known continental crust Inferred continental crust
Fault lines Ocean spreading centresMargins
Silicic LIP volcanism
Alternative location and movement of EWM Movement relative to East Antarctica
Southern Africa
Ferrar
~182.7 Ma
Karoo
~183.2 Ma
a~175 Ma
b~165 Ma c~100 Ma
d~83 Ma
e~46 Ma
Fig. 3 | Plate tectonic reconstruction from 175 to 45 Ma. Plate tectonic
reconstruction maps that show motion in an East Antarctica fixed reference
frame. West Antarctic blocks40, including Marie Byrd Land (MBL), Thurston
Island (TI), the Antarctic Peninsula (AP) and the Ellsworth–Whitmore
Mountains (EWM), are depicted as pale pink regions and modern coastlines
are shown for reference. Other known present-day continental regions are
shown in dark grey. Inferred intervening areas of continental crust are shown
in light grey ; such regions have been deformed and distorted to such an
extent that they cannot be meaningfully be traced through time. a | Middle
Jurassic initiation of Gondwana break-up is shown37,43; the hashed regions
mark Jurassic mafic large igneous provinces (LIPs)48 and the dark-pink
regions mark silicic LIP volcanism134. Cambro-Ordovician marginal turbidites
(blue stars) were widespread, whereas Triassic fore-arc accretionary rocks
(orange stars) were rare. The dashed outline marks alternative location and
rotation of the EWM. b | Separation of Southern Africa163. c | Initiation of
MBL , Ross Sea and West Antarctic rift system extension97. d | Separation
of Zealandia7,8,97,98,164. e | Final stages of West Antarctic rift development
linked to extension in the Adare Trough (AT)100,102,156. CP, Campbell Plateau;
FI, Falkland Island Plateau; LHR , Lord Howe Rise; M, Maurice Ewing Bank;
NNZ, North Island New Zealand; SNZ, South Island New Zealand.
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abrupt, steep, rifted margins of Zealandia and West
Antarctica produces a tight fit of the already-extended
crust, providing clear evidence that major extension
across West Antarctica and Campbell Plateau occurred
prior to break-up of this part of Gondwana96 (FIG.3c).
Neogene volcanism and landscape rejuvenation. The
post-East Gondwana break-up period of quiescence
was broken at ~45 Ma by renewed extension and basin
sedimentation100,101, spurred by a short-lived episode of
spreading in Adare Trough102 (FIG.3e). Fault-controlled
mafic dyking likely occurred during the ~45-Ma exten-
sional phase. At ~34 Ma, mafic alkaline magmatism com-
menced in central MBL103, although the construction
of prominent large volcanoes and small monogenetic
cones occurred from 13 Ma (REFS104,105). The presence of
high-amplitude, short-wavelength magnetic anoma lies
(BOX2) and peaks in subglacial topography (FIG.1) sug-
gests that such volcanic centres are spread over a vast
region of MBL and the eastern Ross Embayment106–108.
Cenozoic magmatism in MBL may have been driven by
a mantle plume105,109 or by the large quantities of hydrous
sediments and oceanic lithosphere that were subducted
into the mantle beneath MBL during the preceding
~400 million years91. In the latter explanation, sub-
duction, in effect, fertilized the mantle with water and
easily fusible minerals, leading to the development of a
hydrous mantle wedge. Once subduction ceased, the hot,
low-density material rose up from the lower mantle and
supplied MBL magmatism90,91,110.
The upwelling low-density mantle associated with
Cenozoic volcanism likely provides dynamic support
for the currently elevated MBL dome. This is suggested
by the seismically imaged thin crust underlying the ele-
vated MBL topography54 (BOX2), which would otherwise
require a thick underlying crustal root. It has been pro-
posed that the timing of uplift is constrained by a dis-
sected low-relief planation surface overlain by Neogene
volcanic rocks extending across MBL103,111–113. This pla-
nation surface is interpreted as a regional Cretaceous
sea-level erosion surface formed after ~ 83-Ma break-up
between West Antarctica and Zealandia113. Subsequent
uplift to current elevations, peaking at ~2,700 m in the
centre of MBL, were likely driven by buoyant mantle
effects since ~34 Ma (REF.113). Although central MBL has
been the site of uplift, coastal fjords in MBL where gla-
ciers were once grounded but are now over 2 km below
sea level and the presence of drowned wave-cut plat-
forms in WARS are consistent with marked Neogene
subsidence114 in the regions flanking the MBL dome. The
origin of this subsidence and the competing hypotheses
of uplift driven by plume14,108,115 versus hydrous mantle
wedge91 remain to be tested.
Antarctic Peninsula and Thurston Island
The Antarctic Peninsula is an arcuate mountainous belt
that reaches heights of 3,200 m and preserves a complex
geological and tectonic history from the Ordovician to
the present day as a long-lived accretionary continen-
tal margin. This geological record has been shaped by
Box 3 | Magmatic flare-ups in West Antarctica
Magmatic‘flare-up’eventscharacterizethegeologicalhistoryofthePaleo-Pacificmargin(seethefigure)andcontributed
substantiallytothecrustalgrowthalongtheaccretionarycontinentalmargin.Thesolidredlineshowsthefrequency
curveformagmaticeventsontheAntarcticPeninsula119,134,143,161.Thesolidbluelineshowsthefrequencycurvefor
mid-CretaceousgranitoidsfromMarieByrdLand(MBL)143andthedashedbluelineshowstheagefrequencyforvolcanic
zirconsintheTransantarcticMountains(TM)thoughttobesourcedfromMBL75.Highmagmaadditionratesduringthe
CretaceousandPermianareevidentalongtheentireproto-PacificmarginofWestGondwana.HighratesofAntarctic
PeninsulaJurassicmagmatismcorrespondtoaflare-upalsoseeninSouthAmerica.Magmaticepisodicitytypicallyincludes
enhancedactivityfor~4millionyearsandlullsof~10millionyears,withactivityoftenenhancedby~100–1,000times
comparedwithperiodsofquiescence.
Thesynchronicityofepisodicflare-upmagmatismalongthePaleo-Pacificmargindemonstratesthatthisprocessis
controlledbycomplextectono-magmaticrelationshipsthatareoftenexternaltothelocalarc,forexample,plate
reorganizationormantle-plumeactivity.
Normalized frequency
Millions of years ago
MBL (granitoids)
MBL (TM volcanic zircons)
Antarctic Peninsula
29027025023021019017015013011090
0
0.5
1
104
116
125
133
267
107–103
118–115
130–126
171–168
185–182
267–262
155 252 280
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subduction along the proto-Pacific margin and rifting
in the Weddell Sea sector, with contrasting tectonic
models proposed to explain the composite nature of
the Antarctic Peninsula. Early models suggest that the
Antarctic Peninsula is an amalgamation of relatively
far-travelled terranes that accreted to the Gondwana
margin, akin to the tectonic model for the formation
of New Zealand116. However, a recent model proposes
that, similar to the formation of Patagonia, the compo-
nent provinces of the Antarctic Peninsula are not far
travelled11. Today, the Antarctic Peninsula preserves
a geological record through a continental margin
arc, including well-preserved fore-arc, back-arc and
magmatic successions.
Thurston Island exhibits close geological links to the
Antarctic Peninsula117,118, including the presence of a
Devonian–Carboniferous basement, Mesozoic magma-
tism associated with the accretionary margin and a pulse
of Early to mid-Cretaceous granitic magmatism. Many
of these Mesozoic events correlate with those in MBL,
highlighting the extent to which tectonic processes were
coupled along the Paleo-Pacific margin.
Basement rocks. The oldest identified basement on
the Antarctic Peninsula is early Ordovician (~485 Ma)
diorite gneisses from the eastern Antarctic Peninsula119,
representing early arc magmatism (FIG.2). Ordovician
arc magmatism is recognized elsewhere along the
proto-Pacific margin of Gondwana, particularly from
the Famatinian complex in northwest Argentina andthe
North Patagonian Massif, and Silurian arc magmatism
(~430 Ma) has been identified from western Palmer
Land120. The Devonian–Carboniferous Target Hill
metamorphic complex121 is marked by magmatism at
~399 Ma and a metamorphic event at ~330 Ma (REF.120).
Granodiorite basement gneiss dated at 349 ± 4 Ma
outcrop on Thurston Island117 and rare outcrops in
South America have been dated to 346 ± 4 Ma (REF.122).
Arc magmatism
Ongoing deformation
Turbidite deposition
Fore-arc sediments
Jurassic silicic LIP
Water
Amundsen
province
Passive
margin Arc magmatism
Basement and sediments Magmatic rocks
Jurassic–Cenozoic sediments Cretaceous arc volcanism
Jurassic LIP volcanism
Back-arc magmatism
Migmatitic melts
Migmatitic magmatism
Metamorphism and
deformation
Cambrian–Triassic sediments
Metamorphic basement
Normal faulting
Oceanic crust
500 Ma–1 Ga passive margin
East Antarctic craton >1 Ga
Strike–slip deformation
Ross province Cratonic margin
province
Upper crustal
granites
Exhumed
lower crust
East
Antarctic
craton
Crustal
thinning
Weddell Sea
back-arc
extension
Neoproterozoic rifted
margin and Ross orogen
Campbell Plateau/
south New Zealand
Hikurangi
Plateau
~120 Ma Incipient
partial
melting
Spreading
centre
MBL
MBL
WARS
WARS
Early Jurassic to
Early Cretaceous
Late Cretaceous
to Early Paleogene
Interior
sedimentation
aPermian–Triassic
bcAntarctic PeninsulaMBL and WARS
Fig. 4 | Cross sections of the evolution of West Antarctica. a | In Permo-Triassic times, an arc was present along the
margin of West Antarctica. b | In the Jurassic, Marie Byrd Land (MBL), the West Antarctic rift system (WARS) and the
Antarctic Peninsula had developed different tectonic settings. There was limited magmatism in MBL and the WARS,
where thickened crust might have given rise to an elevated plateau and incipient melting of the lower crust. In the Late
Cretaceous, MBL was characterized by broad extension exhuming lower crustal rocks, triggering melting and
emplacement of upper crustal granites. c | Subduction and magmatism are ongoing in the Antarctic Peninsula in the
Jurassic. In contrast to MBL and the WARS, the Antarctic Peninsula was marked by ongoing magmatism but limited
extension. LIP, large igneous province. Cross sections based on information in REFS11,77. Parts a and c were adapted from
REF.11 CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/). Part b was adapted from REF.77, Springer Nature Limited.
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However,despite their lithological similarities to else-
where on the Antarctic Peninsula, Devonian magmatism
and Carboniferous metamorphism are now thought to
be restricted events119. Together, these rocks form a long
but discontinuous record of ongoing magmatism along
the Antarctic Peninsula throughout the Paleozoic.
Carboniferous to Permian arc development. The
>5-km-thick metasedimentary Trinity Peninsula
Group (TPG) marks the onset of sedimentation on the
Antarctic Peninsula (FIG.2), beginning during the Late
Carboniferous and continuing during the Permian123.
The TPG was deposited in a supra-subduction setting
during the early stages of subduction development and
might result from debris flows and slides at the conti-
nental margin123. A potential correlative of the TPG is
the Scotia metamorphic complex of the South Shetland
Islands124, which would indicate that subduction was
ongoing along the Antarctic Peninsula at this time.
The Devonian FitzGerald Bluffs quartzite beds in
southern Palmer Land are a stable margin sequence
and, hence, distinct from the active continental mar-
gin sedimentary units elsewhere on the Antarctic
Peninsula125. It has been suggested that, along with the
younger (Permian) Erewhon Beds, these rocks are more
com parable to the Ellsworth–Whitmore Mountains
sequences and formed on a far-travelled block that
originated inboard from the margin125.
During the Permian, distinct episodes of granitoid
magmatism and metamorphism at ~270 and ~255 Ma
occurred across large parts of the Antarctic Peninsula119.
A similar age distribution is also recorded from the North
Patagonian Massif (280–250 Ma)122, where Permian
granitoid magmatism is extensive. Investigations of the
detrital zircon population from the TPG of northern
and eastern Graham Land show that it is dominated
by Permian ages, with three prominent peaks between
285 and 260 Ma (REFS75,126) (BOX3). The upper Permian
Erewhon Beds of southern Palmer Land are thought to be
derived from silicic volcanic rocks127 and also to include
peaks in zircon ages of 263 and 275 Ma, indicating that
Permian arc volcanism (the Choiyoi province in Patagonia
and the Antarctic Peninsula) extended into the south-
ern Antarctic Peninsula and likely into MBL125. Analysis
of detrital zircons from the Duque de York Complex of
Patagonia128 with a similar age profile to the TPG, and
of Permian rocks in New Zealand with abundant ~250-Ma
zircons129, highlight the extensive nature of this magmatic
event along the Gondwanide margin. However, although
a Permian flare-up in magmatism is seen along the
margin, geo chemical analyses suggests that, in contrast to
NewZealand and MBL, the South American and Antarctic
Peninsula subduction zone was advancing in Permian
times and led to magmatism dominated by continental
crustal recycling9.
Triassic magmatism is essentially absent in northern
Graham Land but is prevalent in southern Graham Land119,
Palmer Land120,130 and continues into theThurston
Island crustal block117, with magmatism in the interval
240–220 Ma. The primary Triassic magmatic lithologies
are granodiorite-tonalite gneisses and migmatites that
have been attributed to emplacement in a convergent
continental margin arc setting. Coincident with Triassic
magmatism, the LeMay Group of Alexander Island was
deposited in a deep-water fan setting as part of the out-
board accretionary complex123,131, similar to the Triassic
Torlesse rocks in New Zealand132 (FIG.3a).
Jurassic to Cretaceous peak of arc magmatism. The
Jurassic to Cretaceous period shaped the geological
setting of the Antarctic Peninsula and reflects an epi-
sode of notable tectonic, magmatic and depositional
evolution. Early Jurassic magmatism across the Antarctic
Peninsula is represented by two contemporaneous but
distinct magmatic events that developed in different
tectonic settings. First, the felsic volcanism of the Chon
Aike silicic LIP present across Patagonia and the eastern
Antarctic Peninsula133 (FIG.3a). This LIP is characte rized
by three distinct volcanic episodes, or ‘flare-ups’ (BOX3),
at ~185, ~170 and ~155 Ma, and is associated with nota-
ble crustal melting134. The earliest episode of this silicic
magmatism is coeval with the mafic Karoo–Ferrar LIP
and is thought to result from intra-arc extension and
heating by peripheral plume activity during the initial
stages of West Gondwana break-up135. The later epi-
sodes of Jurassic silicic volcanism are linked to extension
within a more typical destructive plate margin setting134.
The second key magmatic event was coeval granitic
magmatism recognized from multiple sites along the
Antarctic Peninsula and Patagonia dated in the interval
188–180 Ma (REFS136,137). This magmatic event is repre-
sented along the Antarctic Peninsula by moderate to
strongly foliated granitoids136. In contrast to the vol-
canic sequences, geochemical data from Patagonia
suggest that the granitoid rocks were derived from
subduction-related melting, confirming that subduction
was ongoing at the time of extension-related silicic LIP
volcanism117,136,137.
The Early Jurassic saw the development of two dis-
tinct sedimentary depocentres to the east and west ofthe
Antarctic Peninsula. East of the Antarctic Peninsula,
theLarsen and Latady Basins developed as a result of
continental rifting and back-arc extension during the
early stages of Gondwana break-up and record sed-
imentation from Jurassic to Cretaceous times138,139.
The more northerly Larsen Basin records a largely
terrestrial syn-rift megasequence, correlated with the
Magallanes Basin of southern South America and a
marine-dominated post-rift megasequence. The Latady
Basin to the south preserves a sedimentary succession
several kilometres in thickness, recording sediment
deposition from ~185 to ~150 Ma and a shift from a ter-
restrial to a shallow marine setting139,140. Broadly coeval
with the early development of the Latady Basin is the
emplacement of a ~1-km succession of 180–177-Ma
basaltic lavas close to the east coast of the Antarctic
Peninsula55,141. Geochemical signatures indicate that
these basalts were emplaced in a back-arc setting likely
associated with the development of the adjacent Weddell
Sea rift system43,141. An extensional regime associated
with ongoing subduction was, therefore, present during
the Early Jurassic.
West of the Antarctic Peninsula, the Fossil Bluff Group
preserves an Early Jurassic through to mid-Cretaceous
Supra-subduction
Being in a position overlying
the subducting slab in a
subduction zone system.
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volcanic-sedimentary sequence >8 km thick142. The
sequence unconformably overlies the Triassic LeMay
Group accretionary complex and is one of the most
complete fore-arc successions in the world. Correlative
volcaniclastic successions on Adelaide Island dated to
150–120 Ma (REF.119) indicate that the fore-arc continues
north of Alexander Island. The volcaniclastic sediments
and conglomerates of the upper parts of the Fossil Bluff
Group eroded from the main volcanic arc, indicating
coeval volcanic activity. This sedimentary source implies
that Alexander Island was not far from the magmatic
arc at this time116, and a model of far-travelled terrane
accretion for the Mesozoic Antarctic Peninsula may not
be applicable here11.
The Cretaceous represents the main phase of con-
tinental margin arc magmatism across the Antarctic
Peninsula and Thurston Island (FIG.4c). Mid-Cretaceous
magmatism is widespread along the entire proto-Pacific
margin of Gondwana at a time of global plate reorgan-
ization (BOX3). The Lassiter Coast intrusive province
along the eastern margin of Palmer Land shows volu-
minous intrusive magmatism demonstrated to have
developed with three distinct flare-ups at ~125, ~115
and ~105 Ma (REF.143). A major magmatic episode in
the Andean Cordillera, further along the margin from
West Antarctica, also comprises three flare-up events
in the interval 130–105 Ma (REF.144). Cretaceous mag-
matism on Thurston Island117,145 and in MBL82,83 also
occurred around 110–95 Ma, but Cretaceous magma-
tism on Thurston Island is not as extensive as on the
Antarctic Peninsula143. The arc volcanic record during
the Cretaceous is less well documented than the plutonic
record, but mid-Cretaceous volcanism is recorded from
central and western Palmer Land146,147.
One of the main tectonic events to affect the geology of
the Antarctic Peninsula was the two-phase mid-Cretaceous
Palmer Land event116,148. Phase 1 at ~107 Ma was a sinistral
transpressional event that is well developed in southern
Palmer Land, whereas phase 2 at ~103 Ma was a dextral
transpressional event. Aeromagnetic data confirm that
distinct central and eastern domains are present in Palmer
Land149 (BOX2b). While geological evidence of deform ation
suggest that these domains collided116, these provinces
were likely not far travelled11.
The Cretaceous sequences also include records of
magmatism and sedimentation in the northern Antarctic
Peninsula, particularly the South Shetland Islands and
James Ross Island (FIG.1b). The South Shetland Islands’
Lower Cretaceous is dominated by the 2.7-km-thick
intra-arc succession of the Byers Group150, which consists
of basaltic to silicic volcanic and volcaniclastic rocks. The
Upper Cretaceous successions of James Ross Island, col-
lectively referred to as the Gustav Group, form a >2-km
succession of coarse-grained, marine siliciclastic sedi-
ments and volcanic rocks reflecting deposition on slope
aprons and deep-water fans.
Decline of Cenozoic arc magmatism. From the Late
Cretaceous to the Neogene, the collision of spreading
ridge segments at the continental ocean boundary trig-
gered the progressive shutdown of subduction along
the Antarctic Peninsula margin from south to north151.
Arcmagmatism finally ceased on the Antarctic
Peninsula at ~20 Ma on the South Shetland Islands,
even though subduction still continues today. This ongo-
ing subduction has led to rifting along the Bransfield
Strait at ~10 Ma, which split the Pacific margin mag-
netic anomaly (BOX2) and is associated with ongoing
alkaline magmatism on the South Shetland Islands152.
Contemporaneous with Cenozoic magmatism,
extension between South America and the Antarctic
Peninsula, coupled with back-arc extension of the Scotia
subduction zone, led to the opening of the Drake Passage
at ~34 Ma (REF.153), which permitted the development of
the Antarctic Circumpolar Current.
Neogene magmatism on James Ross Island and
neighbouring islands is characterized by lava-fed deltas,
basaltic lavas, tuffs, and hyaloclastite breccias emplaced
in a primarily subglacial setting154. The James Ross
Island volcanic group, which forms the largest Neogene
volcanic field on the Antarctic Peninsula and extends
over 7,000 km2, comprises a major shield volcano on
James Ross Island and multiple satellite volcanoes.
This late-stage volcanism has been associated with
a deep thermal anomaly attributed to a slab window
generated by the cessation of subduction155. Although
post-subduction magmatism occurred, the extent of tec-
tonic reactivation is limited, especially in comparison
with the hyper-extended MBL and WARS region. This
means that the Antarctic Peninsula remains as one of the
best-preserved magmatic arcs on the planet.
Conclusions
This Review highlights the diverse nature of the West
Antarctic region. Its different provinces reflect theimpact
of distinct tectonic processes, but all relate to the ongo-
ing evolution of the Paleo-Pacific margin. The thin crust
and extensive magmatism attest to the repeated tectonic
reworking that has created, moved and overprinted
every part of the system over the last ~500million
years. Today, most of the region is blanketed by ice,
but, together, geological analysis of the exposed rocks
and geophysical observations are revealing the complex
history of the region.
West Antarctic tectonic evolution summary. In sum-
marizing the evolution of West Antarctica, we con-
sider it as an evolving tectonically active margin from
~500 Ma. The earliest rocks in West Antarctica are
sedimentary sequences laid down ~500 Ma along an
active margin facing the Pacific Ocean72. Subduction
along the entire margin of West Antarctica had com-
menced by the Ordovician (488–444 Ma) and continued
to the Permo-Triassic (~250 Ma)3,66,74,119 (FIG.4a). From
Ordovician times, the Antarctic Peninsula was closest
to the trench and marked by almost continuous mag-
matism119,120. MBL and the proto-WARS lay inboard of
New Zealand and the Campbell Plateau; hence, arc mag-
matism appears to have been less prevalent than onthe
Antarctic Peninsula. A retreating subduction zone in
theMBL sector, rather than an advancing subduction sys-
tem as in the Antarctic Peninsula, may have favoured the
development of more juvenile magmatism in MBL9 rela-
tive to the Antarctic Peninsula. TheEllsworth–Whitmore
Transpressional
Having undergone
simultaneous strike–slip and
compressive deformation.
Hyaloclastite
Volcaniclastic breccia
emplaced in a submarine
or subglacial setting.
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Mountains province (the most inboard province) only
received notable magmatic input of ash-fall sediments
in the Permian, during a major flare-up in magmatism
along the margin125. The Permian to Triassic also saw
deformation of the Ellsworth–Whitmore Mountains
province, which was potentially driven by changes in
the outboard subduction system5.
The Jurassic marks the point where the tectonic
setting of different provinces began to clearly diverge
(FIG.4b,c). Extensive magmatism in the Antarctic
Peninsula has a variety of drivers, including ongo-
ing subduction, potential interaction with a mantle
plume and back-arc extension in the Weddell Sea rift
system55,134. In the Ellsworth–Whitmore Mountains44,
intra-plate granites, some of which are localized along
the boundary with East Antarctica53, show that this block
was being translated along the edge of the East Antarctic
Craton, which facilitated back-arc extension in the
Weddell Sea rift system43. Although MBL is associated
with limited magmatism at this time, a major flare-up
in magmatism occurred82,83,143 by the mid-Cretaceous.
Initially, the Cretaceous magmatic events appear syn-
chronous along the margin and are attributed to arc
magmatism along a common and extensive subduction
system. However, cessation of subduction outboard of
MBL from ~100 Ma, potentially due to jamming of the
subduction zone by a spreading ridge or the Hikurangi
Plateau, dramatically changed the tectonic regime in
this part of West Antarctica7,94. Extensive magmatism
occurred and was associated with 600 to 1,000 km of
extension across MBL and the WARS, leading to crustal
thinning and exhumation of lower crustal rocks79,80,97.
From the Late Cretaceous, MBL and the WARS
evolved as a passive margin, reactivated by renewed
continental rifting 43–26 Ma (REF.156) and by upwelling
hot mantle that triggered sparse but widespread mafic
volcanism91,105. In contrast, arc magmatism progressively
ceased beginning ~90 Ma from south to north along
the Antarctic Peninsula due to collision of the Phoenix
spreading centre with the trench151. The main phase
of Phoenix plate subduction ceased by ~20 Ma, with
localized subduction and limited back-arc spreading
confined to the tip of the Antarctic Peninsula today152.
Unlike MBL and the WARS, post-subduction magma-
tism on the Antarctic Peninsula was limited to a few
volcanic centres, and post-subduction extension also
appears to have been limited155.
Broader implications. The tectonic and geological evolu-
tion of West Antarctica illustrates the complexity of con-
vergent continental margins, with the hyper-extended
MBL and WARS region standing in contrast to the
well-preserved magmatic arc along the Antarctic
Peninsula. The long-lived nature of subduction in the
West Antarctic region resulted in multiple magmatic and
tectonic events that provide rich insights into the meta-
morphic and tectonic processes that contribute to the
geological evolution of marginal systems. For example,
West Antarctica reveals the episodic nature of magmatic
events in these convergent systems and demonstrates
that these events appear to be synchronous along large
parts of the entire margin. These observations highlight
the fact that processes acting on a global-plate-tectonic
scale can have a direct local influence.
Future challenges in West Antarctica. West Antarctica
preserves a diverse record of the ~500-million-year
evolution of a tectonically active continental margin
and could, thus, provide key insights into how tectonic
processes operate along this type of margin, in the geo-
logical record and today. Despite substantial advances in
our understanding of how the West Antarctic evolved,
large gaps in knowledge remain. The most fundamen-
tal gap is whether West Antarctica is best conceived as
an accreted collection of rigid microcontinental blocks
(as commonly depicted)40 or as a plastically deforming
and constantly growing melange of continental frag-
ments and juvenile magmatic regions. This is essential
to how we understand and describe the tectonic evolu-
tion of young continental lithosphere. New modelling
techniques, such as finite-element modelling, have the
potential to better describe the evolution of this system.
For these models to be robust, more detailed geophysical
and geological studies are required. Geophysical data can
provide new constraints on the extent of magmatism and
the areal extent and geometry of the underlying prov-
inces, and geological observations and dating provide
information about how and when the different compo-
nents of the system were active. Going forward, defining
the underlying geological template of West Antarctica
and constraining its linkages to the dynamics of the
overlying ice sheet, which is vulnerable to change due to
human activity, are more important than ever.
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Acknowledgements
This paper was supported by the British Antarctic Survey
Geology and Geophysics team (T.A.J. and T.R.R.), NSF
Antarctic Integrated System Science award 1443497 and the
Geology Department of Colorado College (C.S.S.).
Author Contributions
The Weddell Sea province section was led by T.A.J., the Marie
Byrd Land and West Antarctic rift system section was led by
C.S.S. and the Antarctic Peninsula and Thurston Island section
was led by T.R.R.
Competing interests
The authors declare no competing interests.
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional
claims in published maps and institutional affiliations.
Reviewer information
Nature Reviews Earth & Environment thanks John Bradshaw,
Sergio Rocchi and Simon Harley for their contribution to the
peer review of this work.
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