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Continental-scale geographic change across Zealandia during Paleogene subduction initiation

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Data from International Ocean Discovery Program (IODP) Expedition 371 reveal vertical movements of 1–3 km in northern Zealandia during early Cenozoic subduction initiation in the western Pacific Ocean. Lord Howe Rise rose from deep (~1 km) water to sea level and subsided back, with peak uplift at 50 Ma in the north and between 41 and 32 Ma in the south. The New Caledonia Trough subsided 2–3 km between 55 and 45 Ma. We suggest these elevation changes resulted from crust delamination and mantle flow that led to slab formation. We propose a “subduction resurrection” model in which (1) a subduction rupture event activated lithospheric-scale faults across a broad region during less than ~5 m.y., and (2) tectonic forces evolved over a further 4–8 m.y. as subducted slabs grew in size and drove plate-motion change. Such a subduction rupture event may have involved nucleation and lateral propagation of slip-weakening rupture along an interconnected set of preexisting weaknesses adjacent to density anomalies.
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Manuscript received 15 September 2019
Revised manuscript received 17 December 2019
Manuscript accepted 26 December 2019
https://doi.org/10.1130/G47008.1
© 2020 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license.
CITATION: Sutherland, R., et al., 2020, Continental-scale geographic change across Zealandia during Paleogene subduction initiation: Geology, v. 48, p. XXX–XXX,
https://doi.org/10.1130/G47008.1
Continental-scale geographic change across Zealandia during
Paleogene subduction initiation
R. Sutherland1, G.R. Dickens2, P. Blum3, C. Agnini4, L. Alegret5, G. Asatryan6, J. Bhattacharya2, A. Bordenave7, L. Chang8,
J. Collot7, M.J. Cramwinckel9, E. Dallanave10, M.K. Drake11, S.J.G. Etienne7, M. Giorgioni12, M. Gurnis13, D.T. Harper11,
H.-H.M. Huang14, A.L. Keller15, A.R. Lam16, H. Li17, H. Matsui18, H.E.G. Morgans19, C. Newsam20, Y.-H. Park21,
K.M. Pascher19 , S.F. Pekar22, D.E. Penman23, S. Saito24, W.R. Stratford19, T. Westerhold25 and X. Zhou26
1 SGEES, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand
2 Earth, Environmental and Planetary Sciences, Rice University, Houston, Texas 77005, USA
3 International Ocean Discovery Program, Texas A&M University, College Station, Texas 77845-9547, USA
4 Dipartimento di Geoscienze, Università di Padova, 35131 Padova, Italy
5 Departamento de Ciencias de la Tierra & IUCA, Universidad de Zaragoza, 50009 Zaragoza, Spain
6 Museum für Naturkunde, Leibniz-Institut für Evolutions und Biodiversitätsforschung, 10115 Berlin, Germany
7 Geological Survey of New Caledonia, Noumea BP 465, New Caledonia
8 School of Earth and Space Sciences, Peking University, Beijing, China
9 Department of Earth Sciences, Utrecht University, 3584 CB Utrecht, The Netherlands
10 Faculty of Geosciences, Universität Bremen, 28359 Bremen, Germany
11 Ocean Sciences Department, University of California, Santa Cruz, California 95064, USA
12 Instituto de Geociência, Universidade de Brasília, Brasília, Brazil
13 Seismological Laboratory, California Institute of Technology, Pasadena, California 91125, USA
14 Atmosphere and Ocean Research Institute, University of Tokyo, Tokyo 113-8654, Japan
15 Department of Earth Sciences, University of California, Riverside, California 92521, USA
16 Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003-9297, USA
17 Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
18 Department of Earth Science, Tohoku University, Sendai 980-8572, Japan
19 GNS Science, P.O. Box 30368, Lower Hutt 5040, New Zealand
20 Department of Earth Sciences, University College London, London WC1E 6BT, UK
21 Department of Oceanography, Pusan National University, Busan 46421, Republic of Korea
22 School of Earth and Environmental Sciences, Queens College (CUNY), Flushing, New York 11451, USA
23 Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06511, USA
24 Research and Development Center for Ocean Drilling Science, Japan Agency for Marine-Earth Science and Technology
(JAMSTEC), Yokohama, 236-0001, Japan
25 Center for Marine Environmental Sciences (MARUM), University of Bremen, 28359 Bremen, Germany
26 Institute of Marine and Coastal Sciences, Rutgers University, Rutgers, New Jersey 08854, USA
ABSTRACT
Data from International Ocean Discovery Program (IODP) Expedition 371 reveal verti-
cal movements of 1–3 km in northern Zealandia during early Cenozoic subduction initia-
tion in the western Pacic Ocean. Lord Howe Rise rose from deep (1 km) water to sea level
and subsided back, with peak uplift at 50 Ma in the north and between 41 and 32 Ma in
the south. The New Caledonia Trough subsided 2–3 km between 55 and 45 Ma. We suggest
these elevation changes resulted from crust delamination and mantle ow that led to slab
formation. We propose a “subduction resurrection” model in which (1) a subduction rup
-
ture event activated lithospheric-scale faults across a broad region during less than 5 m.y.,
and (2) tectonic forces evolved over a further 4–8 m.y. as subducted slabs grew in size and
drove plate-motion change. Such a subduction rupture event may have involved nucleation
and lateral propagation of slip-weakening rupture along an interconnected set of preexisting
weaknesses adjacent to density anomalies.
INTRODUCTION
Major global plate-motion change occurred
between 52 and 43 Ma, as manifested by the
Emperor-Hawaii bend (Steinberger etal., 2004;
O’Connor etal., 2013), reorientation of mid-
ocean ridges (Muller etal., 2000; Steinberger
etal., 2004; Cande etal., 2010), and rifting of
Antarctica (Cande etal., 2000). This coincided
with subduction initiation (Fig.1) in the Izu-
Bonin-Mariana (IBM) system (Arculus etal.,
2015; Reagan etal., 2017), and nascent colli-
sion of the Indian and Asian plates (Aitchison
etal., 2007). Development of western Pacic
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slab pull explains the sense of plate-motion
changes (Gurnis etal., 2004).
Zealandia, a distinct but mostly submerged
continent (Mortimer etal., 2017), has a low
median elevation (Fig.1), which is primarily
an isostatic response to its relatively thin crust
(18 km on average). Between 83 Ma and
79 Ma, Zealandia separated from Gondwana
(Gaina etal., 1998; Sutherland, 1999), and much
of the continent has been below sea level since,
as documented by now-uplifted marine strati-
graphic records in New Zealand and New Cale-
donia (Paris, 1981; Laird and Bradshaw, 2004)
and submarine sections recovered by the Deep
Sea Drilling Program (DSDP; Fig.2; Burns and
Andrews, 1973).
However, the topographic history of Zea-
landia is not straightforward. Seismic reection
surveys and geological mapping reveal wide-
spread Eocene deformation in northern Zea-
landia (Bache etal., 2012; Browne etal., 2016).
This has been coined the “Tectonic Event of the
Cenozoic in the Tasman Area” (TECTA; Suther-
land etal., 2017), and it appears to have begun
about the same time as cessation of spreading
in the Tasman Sea (Gaina etal., 1998) and sub-
duction initiation near or east of Norfolk Ridge
(Fig.2; Gurnis etal., 2004; Cluzel etal., 2006;
Sutherland etal., 2010; Bache etal., 2012; Mat
-
thews etal., 2015).
International Ocean Discovery Program
(IODP) Expedition 371 (Sutherland etal., 2019)
was designed to determine the Cenozoic paleo-
geography of northern Zealandia, and how and
why this large region (3 × 106 km2) evolved
over time. We discuss the evidence collected and
reasons for topographic change, and we propose
a new framework for understanding subduction
initiation.
Zealandia
Australia
Eurasia
Africa
Antarctica
North
America
South
America
IBM
Hawaii
Pacific Ocean
B
C
A
India
Japan
PNG
Emperor
020406080100
Area (%) lower than elevation
−4000
−3000
−2000
−1000
0
1000
2000
3000
4000
Elevation (m)
Eurasia (73.6)
North America (37.2)
Africa (34.7)
South America (22.8)
Antarctica (19.5)
Australia (14.0)
Zealandia (5.2)
Ice included
Marine
continental
slopes
Mountains
01020304050607
080
Crustal thickness (km)
−4000
−3000
−2000
−1000
0
1000
2000
3000
4000
Elevation (m)
Figure 1. (A) Global continents on a shaded elevation model (ETOPO1, https://www.ngdc.noaa.gov/mgg/global/), Izu-Bonin-Mariana margin
(IBM), Papua New Guinea (PNG), and “Pacic Ring of Fire” (red dots). Arrows show plate movement during formation of Emperor-Hawaii sea-
mounts. (B) Hypsometric proles of continents (area in legend, ×106 km2). Ice (dashed) and rock (solid) surfaces are shown for Antarctica and
North America (includes Greenland). (C) Crustal thickness (CRUST1.0, https://igppweb.ucsd.edu/gabi/crust1.html) versus surface elevation.
Ellipses show one standard deviation for each continent (same legend as in B).
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DRILLING RESULTS
Before IODP Expedition 371, only three
boreholes, DSDP Sites 206–208, each with lim-
ited core recovery, penetrated strata in northern
Zealandia beneath the TECTA unconformity.
We drilled six sites in the context of seismic
reection surveys (Fig.2; Figs. DR1 and DR2
in the GSA Data Repository
1
). We classied pa-
leodepth (meters below modern sea level [mbsl])
into the following categories (Van Morkhoven
etal., 1986): neritic (<200 mbsl), upper bathy-
al (200–600 mbsl), middle bathyal (600–1000
mbsl), lower bathyal (1000–2000 mbsl), and
abyssal (>2000 mbsl). We discovered Paleogene
fossils indicative of nearby neritic conditions at
sites now far below sea level (Fig. DR3).
Parts of northern Zealandia were transiently
uplifted and then subsided. IODP Site U1506
on northern Lord Howe Rise rose close to sea
level with a shallow carbonate platform at ca.
50 Ma, and subsided to a bathyal environment
(600 mbsl) by 45 Ma. Neritic fossils of Eo
-
cene (ca. 50 Ma) age at Site U1506 are now
1770 mbsl. At DSDP Site 208 (Fig.2), middle
Eocene (45–43 Ma) cores contain benthic fora-
minifers indicative of middle bathyal conditions,
but planktic-benthic ratios in Paleocene (65–
56 Ma) cores indicate shallower conditions, and
unconformities separate Paleocene from older
and younger strata (Burns etal., 1973).
Southern Lord Howe Rise experienced lat-
er transient uplift. Beneath an unconformity at
IODP Site U1510 (1238 mbsl), upper Eocene
(41–37 Ma) siliceous chalk was deposited at
middle bathyal depths, and neritic fossils indicate
downslope transport. Site U1510 is 80 km from
DSDP Site 592 (1088 mbsl), where an unconfor-
mity separates lower Miocene (23–19 Ma) chalk
from lower Oligocene (33–32 Ma) ooze (Kennett
etal., 1986). Fossils indicate a lower or middle
bathyal environment since the late Eocene at Site
592, but lower Oligocene strata contain layers
of coarse (1–4 cm) mollusk (Ostrea) fragments
(Kennett etal., 1986), consistent with nearby
shallow water. DSDP Site 207 (Fig.2) subsided
from upper bathyal to middle bathyal depths dur-
ing the Paleocene to middle Eocene, but an un-
conformity separates Eocene (43–38 Ma) from
middle Miocene (15–13 Ma) strata, and inclusion
of slumped upper Eocene (38–36 Ma) material
along the unconformity is consistent with peak
regional uplift in the latest Eocene and early Oli-
gocene (36–32 Ma). The crest of southern Lord
Howe Rise has a current depth of 900–1000 mbsl.
Bioclastic limestone dredged from 1750
mbsl in southwest Reinga Basin (Fig.2) con-
tains neritic benthic foraminifers with ages of
36–30 Ma, and reworked Eocene (43–38 Ma)
planktic species (Browne etal., 2016; Suther-
land etal., 2017). At IODP Site U1508 (1609
mbsl), in the eastern Reinga Basin, onlap indi-
cates deformation started at ca. 39 Ma (Figs.
DR1, DR2, and DR4), and Oligocene (26–
23 Ma) chalk contains a middle to lower bathyal
fauna mixed with shallow-water ostracods and
benthic foraminifers, along with palynoora
indicating downslope transport from land. Re-
inga Basin and Lord Howe Rise sample loca-
tions have erosional unconformities identied
on seismic reection proles (Fig. DR4).
At IODP Site U1509 (2911 mbsl), in the
southern New Caledonia Trough, we drilled
into Cretaceous Fairway–Aotea Basin strata
(Fig.2; Collot etal., 2009). Pleistocene to Oli-
gocene ooze and chalk contain lower bathyal
to abyssal benthic foraminifers. Eocene assem
-
blages indicate lower bathyal paleodepths. Pa
-
leocene and Cretaceous assemblages indicate
a paleo–water depth of 1000 m. Cretaceous
claystones contain plant fragments and fern
spores that indicate coastal proximity. Com-
bined data suggest 2000 m of Cenozoic sub-
sidence, with most accomplished after 59 Ma
and before 45 Ma.
1
GSA Data Repository item 2020110, geologi-
cal and geophysical data; New Caledonia geology;
paleontological evidence used to infer paleogeogra-
phy; and Figures DR1–DR4, is available online at
http://www.geosociety.org/datarepository/2020/, or
on request from editing@geosociety.org.
Figure 2. (A) Zea-
landia bathymetry (m),
new (stars) and exist-
ing (circles) drill sites,
New Caledonia Trough
(NCT), Norfolk Ridge
(NR), D’Entrecasteaux
Ridge (DER), Reinga
Basin (RB), and outline
of Zealandia (dotted).
B.—Basin. (B) Timing of
events inferred from inte-
grated analysis (see the
Data Repository [see foot-
note 1]). Plio.—Pliocene;
Pleist.—Pleistocene;
DSDP—Deep Sea Drilling
Project.
150°E
30°
20°S
160° 170° 180°
Water depth (m)
206
207
208
592
1122
Australia
New Caledonia
New
Zealand
U1506
U1507
U1508
U1509
U1510
U1511
Zealandia
continent
Fiji
Vanuatu
Tonga
Tonga-Kermadec T rench
Lord
Howe
Rise
NCT
NCT
RB
NR
Challenger
Plateau
4000 2000 0
Fairway B.
Taranaki
Kenn
Plateau
DER
Tasman Sea
abyssal plain
South Fiji Basin
A
B
New Caledonia flysch deposition
Age (Ma) 50 45 40 35 30 25 20 15 10 5
U1511 folding
U1510 folding
U1508 folding
U1509 Slope failure
U1508, Northland arc
Lord Howe Rise intraplate
U1507
D'Entrecasteaux arc
U1506 neritic fossils
Southwest Reinga Basin neritic fossils
U1510 & DSDP 592 near shallow water
U1508 near shallow water
U1507 New Caledonia Trough formation
U1509 New Caledonia Trough subsidence
Cooling
Seafloor spreading in the Tasman Sea
New Caledonia blueschist metamorphism
Rapid seafloor spreading south of New Zealand & Australia
Prograde
Tonga forearc
Volcanism UpliftDeformation
0
Age (Ma) 50 45 40 35 30 25 20 15 10
50
Pleist.
Plio.
MioceneOligoceneEocene
Northland allochthon
40°
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At IODP Site U1507 (3568 mbsl), we
drilled sediments of the northern New Caledo-
nia Trough for the rst time. Fossils from the
oldest drilled sediments (864 m below seaoor
[mbsf]) indicate lower bathyal depths at 41 Ma
(Sutherland etal., 2019). Sedimentation rates
increase downhole from 10 m/m.y. to 40 m/m.y.
(Fig. DR2), and extrapolation to the base of the
unit, determined from seismic reection data
to be 1300 mbsf, indicates a Paleogene age
for the basin.
GEOGRAPHIC CHANGE
Cretaceous rifting from Gondwana likely
thinned the crust of Zealandia, but large elevation
changes (1–3 km) across a wide region (Fig.3)
occurred during the Paleogene. Lord Howe Rise
uplifted by at least 1 km, with a southeast mi-
gration in this motion from 50 to 35 Ma. New
Caledonia Trough subsided 1–3 km, starting at
ca. 55–45 Ma, with no resolvable difference in
timing between north and south. The East Re-
inga Basin records deformation at ca. 39 Ma
with peak uplift at ca. 26–23 Ma (Fig.2; details
of fossil evidence are given in the “Paleogeogra-
phy” section of the Data Repository).
Flexure would not produce the magnitude,
wavelength, nor timing of observed elevation
changes, so we suggest crustal delamination and
slab formation by reactivation of a west-dipping
Cretaceous subduction zone (Fig.4; Sutherland
etal., 2010) to explain the observed features.
Thermal isostatic and dynamic forces (upwell-
ing) are inferred to have driven uplift of Lord
Howe Rise, while delamination of basaltic lower
crust, minor local extension, and dynamic forces
(downwelling) caused New Caledonia Trough
to subside.
SUBDUCTION INITIATION
Subduction initiation can be spontaneous
if gravitational instability and a weakness are
juxtaposed (Stern, 2004), or it can be induced
if gravitational instability grows during con-
vergence across a fault (Gurnis etal., 2004).
We propose an additional case: A stable gravi-
tational anomaly may exist but will founder to
produce a slab if failure occurs. Time scales,
ABC
DE
50 Ma ?
?
?
40°S
50°S
500 km0
45 Ma
40°S
50°S
500 km0
35 Ma
40°S
50°S
500 km0
25 Ma
40°S
50°S
Taranaki
Reinga
Lord Howe Rise
New Caledonia Trough
Norfolk R.
Northland
Kenn
Plat.
Fairway
Challenger
Plat.
New Caledonia
500 km0
IODP/DSDP Site
Tectonic extension
Tectonic compression
Tectonic uplift
Tectonic subsidence
Active arc volcanism
Extinct arc volcanism
Active subduction trench
Propagating trace of trench
Possible island
Land
Water depth <200 m (neritic)
Water depth 200-2000 m (bathyal)
Water depth >2000 m (abyssal)
Present day coastline (reference)
KEY
55 Ma
?
?
40°S
50°S
1506
208 1507
206
1509
1508
1510 592
207
Mesozoic
arc rocks
Poya ridge
Coral Sea
triple junction
?
Louisiade rift
Fig. 4
?
?
500 km0
Figure 3. Paleogeographic reconstructions at 55, 50, 45, 35, and 25 Ma. Dark blue is >2000 m water depth, cyan is 20 00–200 m, pink is 200–0 m,
and white is land. Stars are new drill sites. Present coastline (gray) is shown for reference. Filled arrows show uplift (up) or subsidence (down).
Open arrows show active convergent or divergent crustal deformation. Triangles show active (red) or extinct (gray) arc volcanic activity. Black
line with teeth is a suggestion for trench location, but alternate hypotheses exist. Plat.—Plateau; R.—Ridge; IODP—International Ocean Dis-
covery Program; DSDP—Deep Sea Drilling Project.
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length scales, and processes may differ, but the
idea has similarities to velocity-weakening be-
havior on a fault during an earthquake. We pro-
pose the term subduction rupture event (SRE)
to describe the nucleation and lateral propaga-
tion of the onset of fault slip and slip-weakening
on lithospheric faults during subduction initia-
tion. Induced subduction initiation requires re-
gional forcing, whereas an SRE requires only
local forcing (nucleation of initial failure) and
slip-weakening processes that facilitate lateral
propagation.
Extension and volcanic activity associated
with IBM subduction started at 53–52 Ma (Ar-
culus etal., 2015), and the onset of metamor-
phism in New Caledonia was at 55–50 Ma (Pi-
rard and Spandler, 2017; Vitale-Brovarone etal.,
2018; Fig.2; see the Data Repository). In the
Tonga forearc, the oldest plagiogranites have
ages ca. 51–50 Ma, and arc activity is evident
after ca. 48 Ma (Meffre etal., 2012). Seaoor
spreading in the Tasman Sea also ended at ca.
52 Ma (Gaina etal., 1998). The Emperor-Ha-
waii bend records onset of Pacic plate-motion
change at ca. 50 Ma, with a time of maximum
curvature at ca. 48–47 Ma (O’Connor et al.,
2013), and magnetic anomalies record rapid sea-
oor spreading south of Australia and New Zea-
land after 45–43 Ma (Sutherland, 1995; Cande
and Stock, 2004). These major tectonic changes
in the western Pacic were broadly synchronous
with subsidence of the New Caledonia Trough
and transient uplift of the northern Lord Howe
Rise, and we interpret them to have been caused
by initial slab formation.
Geological evidence from New Zealand,
New Caledonia, and magnetic data show that a
fossil Mesozoic arc lies beneath the New Cale-
donia Trough, and the Norfolk Ridge contains
forearc accretionary complexes (Paris, 1981;
Sutherland, 1999; Mortimer, 2004). Collision
of a young large igneous province caused Cre-
taceous at-slab subduction death and hence un-
derplating of a thick basaltic lower crust (Davy
etal., 2008). We propose that metamorphism of
delaminated lower crust to eclogite provided a
density anomaly that led to slab formation dur-
ing the Eocene (Fig.4).
Suitable conditions for reactivation might
exist in an extinct subduction zone, including
weakness of the subduction fault zone, and
gravitational instability of buoyant arc rocks and
serpentinized mantle set against dense eclogite
of the slab and/or root of the arc, in addition
to thermal contrasts (Leng and Gurnis, 2015).
Subducted sediment or continent slivers may
also play some role. Subduction zones have high
continuity, so resurrection could propagate over
a large distance.
Subduction initiated along 10,000 km of
the western Pacic between 55 and 50 Ma and
seemingly preceded major plate-motion change.
In our SRE hypothesis, subduction was induced
as slip laterally propagated to resurrect extinct
subduction zones. The rate of lateral propagation
(>1 m/yr) was about two orders of magnitude
faster than typical plate-motion rates.
After the SRE, forces, topography, and vol-
canism evolved in response to local conditions.
The ca. 48 Ma change in Pacic plate direction
and speed toward the western Pacic occurred
earlier than the ca. 44 Ma acceleration in Aus-
tralia toward Indonesia. The 4–8 m.y. delay
before plate motions changed reects progres-
sive growth of slabs and reductions in fault resis-
tance. The North Pacic evolved fastest, but the
SRE may have nucleated elsewhere. The oldest
evidence for SRE activity that we are aware of
is in Papua New Guinea, where ophiolites were
emplaced at ca. 58 Ma (Lus etal., 2004).
There has been one major kinematic change
during Earth history for which we know plate
motions through magnetic anomalies, hotspots,
and now regional topographic changes: the Eo-
cene event of the western Pacic. We suggest
that subduction initiation involves: (1) an SRE,
and (2) development of forces as slabs grow
and faults weaken. Fossil subduction margins
provide the right ingredients for this to happen:
lateral continuity, weakness, and density con-
trasts. The Pacic “subduction resurrection”
context contrasts with the Mediterranean, where
subduction initiation was induced by Oligocene
continental collision (Handy etal., 2010), but
prolonged (>30 m.y.) slab foundering had lim-
ited impact on global plate motions, perhaps
due to limitations of suitability and continuity
of inherited geology.
Subduction initiation beneath northern Zea-
landia altered geography, crustal thickness, and
likely also crustal composition. It may be that
other continents were shaped at a similar time
(e.g., thin continental parts of Indonesia and
South China Sea). As there has been only one
major plate-motion change event since 83 Ma,
the frequency-magnitude relationship for SRE
events over geological time is hard to determine.
It is plausible, though, that between 40 and 100
such events have occurred since the onset of
plate tectonics. The unstable dynamical behav-
ior we infer challenges the principle of unifor-
mitarianism for plate tectonics because there
is likely no modern analogue for the SRE pro-
cesses that occurred at ca. 55–50 Ma. However,
the geographical, geological, and geochemical
evolution of continents and mantle probably was
affected by these infrequent events. The records
in Zealandia provide unique insight for recog-
nizing and understanding them, and may even
be a basis for prediction of favorable geological
conditions: subduction resurrection.
ACKNOWLEDGMENTS
We thank the International Ocean Discovery Program
(IODP); the personnel of R/V JOIDES Resolution on
Expedition 371; proponents unable to sail on Expe-
dition 371; and everyone on surveys TAN1312,
TAN1409, and TECTA. This work was funded by the
Figure 4. Cartoon cross
sections illustrating the
transition from Paleo-
cene rifted margin to
Eocene subduction. Line
is between northern Lord
Howe Rise and southern
New Caledonia (Fig.3A).
Pink—continental crust;
red—arc plutons; green—
Cretaceous subducted
slab (dark blue where
it is eclogite); purple—
ocean crust, gray—mantle
lithosphere, and yellow—
asthenosphere.
Lord Howe Rise New Caledonia uplift, collapse
New Caledonia Trough
Fairway Basin
60 Ma passive margin
Eclogite
mass anomaly
Fossil arc
Flat basalt slab
Zealandia continent Fossil forearc
Poya
seafloor
spreading
incipient mantle instability
Slab founders
Invasion of mantle
Asthenosphere
upwelling
Lithospheric
window closed
Volcanism, uplift Crust delamination, subsidence Convergence
50 Ma convergence
C
B
A
40 Ma subduction roll-back
ophiolite
collision
Melt generation
Melt generation
Subsidence
Blueschist
Asthenosphere
upwelling
Rifted margin
Conversion
to eclogite
Sea level
Lithosphere
Asthenosphere
Southwest Northeast
Buoyant rising
of blueschist
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6 www.gsapubs.org
|
Volume XX
|
Number XX
|
GEOLOGY
|
Geological Society of America
U.S. National Science Foundation; IODP participating
countries; New Zealand, France, and New Caledonia
(site surveys); the Spanish Ministry of Economy and
Competitiveness and Fondo Europeo de Desarrollo
Regional (FEDER) funds project CGL2017–84693-R
and a Leonardo Grant, BBVA Foundation (Alegret);
Korean IODP (K-IODP) (Park); China grant NSFC
41473029, 91958110 (He Li); and Brazil grant
183/2017-CII/CGPE/DPB/CAPES (Giorgioni).
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We present a suite of 15 palaeogeographic maps illustrating the geological evolution of the entirety of Zealandia, from mid-Cretaceous to present, highlighting major tectonic phases, from initial Gondwana rifting through to development of the Neogene plate boundary. They illustrate palaeobathymetric and palaeofacies interpretations along with supporting geological datasets and a synthesis of regional tectonics. The maps are underpinned by a geologically-constrained and structurally-based rigid retro-deformation block model. This model, tied to the global plate circuit, is relatively simple for the main regions of Northern and Southern Zealandia, but breaks central Zealandia into numerous fault-bounded blocks, reflecting complex Neogene deformation associated with the modern plate boundary. Production of maps using GPlates and GIS allows for simple alteration or refinement of the block model and reconstruction of any geological dataset at any time. Reconstructions are within a palaeomagnetic reference frame, allowing assessment of palaeo-latitude, critical for palaeo-climatic and palaeo-biogeographic studies.
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Recent progress in plate tectonic reconstructions has seen models move beyond the classical idea of continental drift by attempting to reconstruct the full evolving configuration of tectonic plates and plate boundaries. A particular problem for the Neoproterozoic and Cambrian is that many existing interpretations of geological and palaeomagnetic data have remained disconnected from younger, better-constrained periods in Earth history. An important test of deep time reconstructions is therefore to demonstrate the continuous kinematic viability of tectonic motions across multiple supercontinent cycles. We present, for the first time, a continuous full-plate model spanning 1 Ga to the present-day, that includes a revised and improved model for the Neoproterozoic–Cambrian (1000–520 Ma) that connects with models of the Phanerozoic, thereby opening up pre-Gondwana times for quantitative analysis and further regional refinements. In this contribution, we first summarise methodological approaches to full-plate modelling and review the existing full-plate models in order to select appropriate models that produce a single continuous model. Our model is presented in a palaeomagnetic reference frame, with a newly-derived apparent polar wander path for Gondwana from 540 to 320 Ma, and a global apparent polar wander path from 320 to 0 Ma. We stress, though while we have used palaeomagnetic data when available, the model is also geologically constrained, based on preserved data from past-plate boundaries. This study is intended as a first step in the direction of a detailed and self-consistent tectonic reconstruction for the last billion years of Earth history, and our model files are released to facilitate community development.
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The absolute position during the Cenozoic of northern Zealandia, a continent that lies more than 90% submerged in the southwest Pacific Ocean, is inferred from global plate motion models, because local paleomagnetic constraints are virtually absent. We present new paleolatitude constraints using paleomagnetic data from International Ocean Discovery Program Site U1507 on northern Zealandia and Site U1511 drilled in the adjacent Tasman Sea Basin. After correcting for inclination shallowing, five paleolatitude estimates provide a trajectory of northern Zealandia past position from the middle Eocene to the early Miocene, spanning geomagnetic polarity chrons C21n to C5Er (∼48–18 Ma). The paleolatitude estimates support previous works on global absolute plate motion where northern Zealandia migrated 6° northward between the early Oligocene and early Miocene, but with lower absolute paleolatitudes, particularly in the Bartonian and Priabonian (C18n–C13r). True polar wander (solid Earth rotation with respect to the spin axis), which only can be resolved using paleomagnetic data, may explain the discrepancy. This new paleomagnetic information anchors past latitudes of Zealandia to Earth's spin axis, with implications not only for global geodynamics, but also for addressing paleoceanographic and paleoclimate problems, which generally require precise paleolatitude placement of proxy data.
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A deep-marine sedimentary succession of Whaingaroan to Altonian age (Early Oligocene–Early Miocene), cropping out near Weber, southern Hawke’s Bay, records abrupt changes in depositional paleoenvironments and sedimentary lithofacies. Highly calcareous early Waitakian (latest Oligocene) Weber Formation (Mangatu Group/Waka Supergroup) is unconformably overlain by terrigenous-dominated late Waitakian–Otaian (Early Miocene) Coast Road or Whakataki formations (Tolaga Group/Māui Supergroup). Most notably, in some localities, lowermost parts of the Coast Road Formation (Mangapuku Mudstone Member) contain prominent matrix-supported extra-formational olistoliths of centimetre to decametre scale derived from the underlying Weber Formation. Deposition of these blocks is attributed to deep-water collapse of parts of rapidly growing, over-steepened, reverse-fault-controlled thrust ridge(s). The onset of Coast Road and Whakataki formation deposition and associated abrupt changes in sedimentary lithofacies correlate to prominent Early Miocene lithological, mineralogical, and paleoenvironmental changes elsewhere along the Hikurangi Margin. We attribute these bio- and lithostratigraphic changes as evidence for significant shortening and upper-plate reverse faulting marking the onset of subduction beneath eastern North Island during the mid-Waitakian (c. 23 Ma). Proposed lithostratigraphic revisions presented herein help clarify depositional events and correlative sedimentary packages within the Miocene Hikurangi margin.
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International Ocean Discovery Program (IODP) Expedition 352 recovered a high-fidelity record of volcanism related to subduction initiation in the Bonin fore-arc. Two sites (U1440 and U1441) located in deep water nearer to the trench recovered basalts and related rocks; two sites (U1439 and U1442) located in shallower water further from the trench recovered boninites and related rocks. Drilling in both areas ended in dolerites inferred to be sheeted intrusive rocks. The basalts apparently erupted immediately after subduction initiation and have compositions similar to those of the most depleted basalts generated by rapid sea-floor spreading at mid-ocean ridges, with little or no slab input. Subsequent melting to generate boninites involved more depleted mantle and hotter and deeper subducted components as subduction progressed and volcanism migrated away from the trench. This volcanic sequence is akin to that recorded by many ophiolites, supporting a direct link between subduction initiation, fore-arc spreading, and ophiolite genesis.
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We report the U-Pb age, and trace element and hafnium isotope composition of zircons recovered from clastic metasedimentary rocks that span a range of metamorphic grades (prehnite-pumpellyite to eclogite facies) across the high-pressure metamorphic belt of Northern New Caledonia. We use these data to evaluate the sedimentary source and environment of formation of these rocks, as well as their respective metamorphic evolution.
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A 4.9 Mkm2 region of the southwest Pacific Ocean is made up of continental crust. The region has elevated bathymetry relative to surrounding oceanic crust, diverse and silica-rich rocks, and relatively thick and low-velocity crustal structure. Its isolation from Australia and large area support its definition as a continent- Zealandia. Zealandia was formerly part of Gondwana. Today it is 94% submerged, mainly as a result of widespread Late Cretaceous crustal thinning preceding supercontinent breakup and consequent isostatic balance. The identification of Zealandia as a geological continent, rather than a collection of continental islands, fragments, and slices, more correctly represents the geology of this part of Earth. Zealandia provides a fresh context in which to investigate processes of continental rifting, thinning, and breakup.
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Eocene onset of subduction in the western Pacific was accompanied by a global reorganization of tectonic plates and a change in Pacific plate motion relative to hotspots during the period 52–43 Ma. We present seismic-reflection and rock sample data from the Tasman Sea that demonstrate that there was a period of widespread Eocene continental and oceanic compressional plate failure after 53–48 Ma that lasted until at least 37–34 Ma. We call this the Tectonic Event of the Cenozoic in the Tasman Area (TECTA). Its compressional nature is different from coeval tensile stresses and back-arc opening after 50 Ma in the Izu-Bonin-Mariana region. Our observations imply that spatial and temporal patterns of stress evolution during western Pacific Eocene subduction initiation were more varied than previously recognized. The evolving Eocene geometry of plates and boundaries played an important role in determining regional differences in stress state.
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Sandstone, mudstone and limestone samples dredged in the Reinga and Aotea basins, NW New Zealand during voyage TAN1312 provide age and lithological constraints on the Cretaceous–Neogene succession. A total of 46 micropaleontology and 7 macropaleontology samples were examined along with 84 thin-sectioned petrographical samples. Some were examined by X-ray diffraction and porosity-permeability analyses. Late Cretaceous sandstones are dominated by feldspathic and lithofeldspathic compositions, with mixed granitic plutoniclastic and volcaniclastic provenance; a comparison with Pakawau Group of Taranaki Basin is appropriate. Late Cretaceous–Paleogene mudstones are widespread and display close petrographical and age similarities to the Whangai Formation facies of other parts of New Zealand and fine-grained carbonate facies of the Weber and Amuri formations of eastern North and South Islands, respectively. Cretaceous limestone and Paleogene sandstone were not recovered. Carbonates and mudstones dominate the Neogene succession of Reinga and Aotea basins; rare Neogene sandstones have feldspatholithic compositions and resemble Waitemata Group sandstones of the northern North Island. In terms of petroleum prospectivity, Cretaceous sandstones represent a potential reservoir facies but are lithic with low permeability.
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Although plate tectonics is well established, how a new subduction zone initiates remains controversial. Based on plate reconstruction and recent ocean drilling within the Izu-Bonin-Mariana, we advance a new geodynamic model of subduction initiation (SI). We argue that the close juxtaposition of the nascent plate boundary with relic oceanic arcs is a key factor localizing initiation of this new subduction zone. The combination of thermal and compositional density contrasts between the overriding relic arc and the adjacent old Pacific oceanic plate promoted spontaneous SI. We suggest that thermal rejuvenation of the overriding plate just before 50 Ma causes a reduction in overriding plate strength and an increase in the age contrast (hence buoyancy) between the two plates, leading to SI. The computational models map out a framework in which rejuvenated relic arcs are a favorable tectonic environment for promoting subduction initiation, while transform faults and passive margins are not.