New Geology Articles Published Online Ahead of Print in August
Boulder, Colo., USA: Article topics and locations include galactic spiral
arms and crust production on early Earth; the role of metamorphic mica;
seawater during Snowball Earth; a novel hybrid pyroclastic lithofacies
found on Tenerife (Canary Islands) and Pantelleria (Italy); and the 2001
Kokoxili earthquake in Tibet. These Geology articles are online at
https://geology.geoscienceworld.org/content/early/recent
.
Trench retreat recorded by a subduction zone metamorphic history
Jie Dong; Marty Grove; Chunjing Wei; Bao-Fu Han; An Yin ...
Abstract:
Upper amphibolite-facies metamorphism in subduction zone rocks may occur
under exceptional tectonic settings. Differentiating competing mechanisms
for its occurrence requires carefully integrated, high-resolution
thermobarometric and geochronologic studies of mélange rocks with
well-defined field relationships. We present new pressure, temperature, and
age data from the classic Cretaceous Catalina Schist in southern California
(USA) that allow us to establish a plausible model for its high-temperature
metamorphic history. Our results indicate that garnet-amphibolite blocks in
the structurally highest amphibolite-facies mélange preserve evidence of
three stages of tectonic evolution: (1) prograde lawsonite eclogite-facies
metamorphism that peaked at 2.4–2.7 GPa with temperatures >580 °C during
fixed-trench subduction (120–115 Ma); (2) post-peak epidote eclogite-facies
metamorphism followed by amphibolite-facies metamorphism at 1.4–1.3 GPa
with temperatures of 740–790 °C during trench retreat (115–105 Ma); and (3)
isothermal decompression (1.3 GPa to <1.0 GPa at temperatures of ~780
°C) and cooling during trench advance and slab-flattening subduction (ca.
105–100 Ma). Our model implies the presence of a continuous Cordilleran
subduction system in the Cretaceous, which had varying tectonic regimes
through episodes of trench retreat/advance and slab shallowing/steepening
that, in turn, dictated the development of the Cordilleran arc system.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50385.1/616541/Trench-retreat-recorded-by-a-subduction-zone
Transient fault creep on the Xidatan (Tibet) fault driven by
viscoelastic relaxation following the 2001 Kokoxili earthquake
Dezheng Zhao; Chunyan Qu; Xinjian Shan; Roland Bürgmann; Han Chen ...
Abstract:
Recent geodetic observations of shallow fault creep have illuminated
increasingly complex, time-dependent slip behaviors, including quasi-steady
creep and temporary accelerations, termed slow-slip events. We documented
two decades of deformation on the Xidatan fault on the Tibetan Plateau
measured by radar interferometry during 2003–2010 and 2015–2020 CE, to
probe the temporal evolution of shallow creep and illuminate the underlying
mechanisms. The geodetic observations reveal an ~80-km-long fault section
with temporally decaying creep along the Xidatan fault, one of the current
seismic gaps along the Kunlun fault. The transient creep is likely driven
by postseismic deformation processes, dominated by viscoelastic relaxation
after the 2001 Kokoxili earthquake, rather than triggered by the coseismic
rupture. The transient creep behavior, indicating rate-strengthening
frictional properties of the fault, contradicts the inference of locking
along the Xidatan fault, based on geodetic imaging before the Kokoxili
earthquake and on historical ruptures. We propose that, during the
interseismic period, the frictionally unlocked shallow portions of the
fault are located in the stress shadow cast by the deeper locked
asperities, but they creep at resolvable rates when exposed to transient
stress and stressing rate increases. We argue that stress interactions in
the triple junction of the Kusai Hu, Xidatan, and Kunlun Pass faults
promote complex slip behaviors throughout the earthquake cycle.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50380.1/616542/Transient-fault-creep-on-the-Xidatan-Tibet-fault
Time constraints on hydrocarbon migration and caprock formation
recorded by calcite spar in a Carboniferous–Permian carbonate-evaporite
succession, Finnmark Platform, Barents Sea
Malcolm S.W. Hodgskiss; Nivedita Thiagarajan; Yue Wang; Niels Rameil;
Harald Brunstad ...
Abstract:
A late Carboniferous to early Permian carbonate and evaporite succession
from the Finnmark Platform (southern Barents Sea) contains nodules of
anhydrite partially to fully replaced by calcite spar and native sulfur
genetically linked to hydrocarbon migration and/or oxidation, analogous to
processes observed in salt diapir caprocks in the Gulf of Mexico. In situ U-Pb dating of this calcite spar therefore has the
potential to directly date hydrocarbon migration and provide further
insight into the geochemical and temperature conditions during this event
when coupled with traditional stable and clumped isotope ratios (δ 13C, δ18O, and Δ47). Results indicate
calcite formed ca. 50–15 Ma, postdating host-rock deposition by 250–285
m.y. Strongly negative δ13C values in the calcite spar (mean =
–15‰) are consistent with a major contribution of carbon from hydrocarbons,
and Δ47 paleothermometry indicates a mean precipitation
temperature of 46 ± 11 °C. These geochemical results are consistent with
the local burial history and suggest protracted hydrocarbon migration
and/or oxidation and caprock formation spanning ~35 m.y.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50244.1/616543/Time-constraints-on-hydrocarbon-migration-and
Onset of long-lived silicic and alkaline magmatism in eastern North
America preceded Central Atlantic Magmatic Province emplacement
Sean T. Kinney; Scott A. MacLennan; Dawid Szymanowski; C. Brenhin Keller;
Jill A. VanTongeren ...
Abstract:
The White Mountain magma series is the largest Mesozoic felsic igneous
province on the eastern North American margin. Previous geochronology
suggests that magmatism occurred over 50 m.y., with ages for the oldest
units apparently coeval with the ca. 201 Ma Central Atlantic Magmatic
Province, the flood basalt province associated with the end-Triassic mass
extinction and the opening of the Atlantic Ocean. We use zircon U-Pb
geochronology to show that emplacement of White Mountain magma series
plutons was already underway at 207.5 Ma. The largest volcanic-plutonic
complex, the White Mountain batholith, was emplaced episodically from ca.
198.5 Ma to ca. 180 Ma and is ~25 m.y. older than published ages suggest,
and all samples we dated from the Moat Volcanics are between ca. 185 Ma and
180 Ma. The Moat Volcanics and the White Mountain batholith are broadly
comagmatic, which constrains the age of a key Jurassic paleomagnetic pole.
Our data indicate that a regional mantle thermal anomaly in eastern North
America developed at least 5 m.y. prior to the main stage of Central
Atlantic Magmatic Province flood basalt volcanism and suggest a geodynamic
link between the White Mountain magma series and the Central Atlantic
Magmatic Province.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50181.1/616544/Onset-of-long-lived-silicic-and-alkaline-magmatism
Small impact cratering processes produce distinctive charcoal
assemblages
A. Losiak; C.M. Belcher; J. Plado; A. Jõeleht; C.D.K. Herd ...
Abstract:
The frequency of crater-producing asteroid impacts on Earth is not known.
Of the predicted Holocene asteroid impact craters of <200 m diameter,
only ~30% have been located. Until now there has been no way to distinguish
them from “normal” terrestrial structures unless pieces of iron meteorites
were found nearby. We show that the reflective properties of charcoal found
in the proximal ejecta of small impact craters are distinct from those
produced by wildfires. Impact-produced charcoals and wildfire charcoals
must derive from different heating regimes. We suggest that charcoal with
specific reflective properties may help to recognize the meteoritic origin
of small craters.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50056.1/616545/Small-impact-cratering-processes-produce
Orogenic belt resulting from ocean-continent collision
Jun-Hong Zhao; Ting Yang; Wei Wang
Abstract:
Orogenic belts have been thought to form through plate convergence,
involving subduction of oceanic lithosphere at continental margins
(accretionary orogens), which may ultimately lead to ocean closure and
continent-continent collision (collisional orogens). Intraplate orogens
away from plate margins have been known, but the mechanisms controlling
their evolution are poorly understood. The South China craton, including
the Yangtze and Cathaysia blocks, underwent a Paleozoic orogenesis that
formed a >500-km-wide orogenic belt with widespread granitoids that are
unconformably overlain by Devonian cover sequences. The pre-Devonian
basement rocks were subjected to strong deformation and greenschist- to
amphibolite-facies metamorphism at 460–400 Ma. Paleozoic magmatism was
characterized by voluminous crustally derived Silurian granitoids
associated with incorporation of ancient crustal materials at 450–440 Ma
and addition of juvenile mantle-derived melts at 420–410 Ma. Based on the
absence of arc-like magmatism and the existence of ophiolites in the West
Cathaysia terrane, geochemical evidence that oceanic crust existed beneath
the East Cathaysia terrane, and geophysical evidence of contrasting
lithospheres on both sides and two discrete slabs beneath their fault
boundary, we propose that this Paleozoic orogenic belt was formed by
collision between the two terranes that was driven by far-field forces
during the assembly of Gondwana, and the East Cathaysia terrane represents
oceanic lithosphere that was overthrusted by the continental crustal
materials of the West Cathaysia terrane. Numerical modeling shows that this
type of collision can explain the dynamics of the Paleozoic orogenesis in
the South China craton and may be a mechanism for some orogens in which
subduction-related igneous and metamorphic rocks are lacking.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50337.1/616546/Orogenic-belt-resulting-from-ocean-continent
Sublithospheric melt input in cratonic lamproites
Soumendu Sarkar; Andrea Giuliani; David Phillips; Geoffrey H. Howarth;
Sujoy Ghosh ...
Abstract:
Cratonic lamproites are diamondiferous ultrapotassic rocks that are
emplaced through thick continental lithosphere and thought to derive from
melting of metasomatized (i.e., geochemically enriched) regions of the
subcontinental lithospheric mantle (SCLM). We explored the alternative
hypothesis that melts sourced from sublithospheric (i.e., convective
mantle) sources dominate the genesis of cratonic lamproites. Supporting
evidence includes a robust linear correlation between the Mg/Fe ratios of
xenocrystic and magmatic olivine in lamproites worldwide, overlapping the
trend observed for kimberlite olivine. This indicates that, similar to
kimberlites, primary lamproite melts originate from broadly similar
sublithospheric mantle sources before assimilating SCLM material of
variable composition. The lamproites are also characterized by a direct
correlation between olivine Mg/Fe ratio and bulk-lamproite K2
O/Al2O3, an index of potassium enrichment in the melt
that is independent of mantle-xenocryst entrainment and magmatic
differentiation. Quantitative modeling indicates that this correlation
results from the interaction between carbonate-bearing sublithospheric melt
and phlogopite-rich wall rocks in the SCLM. Our data show that cratonic
lamproites and kimberlites have similar mantle sources in the convective
mantle, with lamproites acquiring their peculiar enrichment in K by
interaction with metasomatized SCLM en route to the surface. Modification
of sublithospheric melts during transit through the continental lithosphere
might represent a common process for the genesis of alkaline
mafic/ultramafic magmas.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50384.1/616547/Sublithospheric-melt-input-in-cratonic-lamproites
The northern Hikurangi margin three-dimensional plate interface in New
Zealand remains rough 100 km from the trench
Harold Leah; Åke Fagereng; Ian Bastow; Rebecca Bell; Victoria Lane ...
Abstract:
At the northern Hikurangi margin (North Island, New Zealand), shallow slow
slip events (SSEs) frequently accommodate subduction-interface plate motion
from landward of the trench to <20 km depth. SSEs may be spatially
related to geometrical interface heterogeneity, though kilometer-scale
plate-interface roughness imaged by active-source seismic methods is only
constrained offshore at <12 km depth. Onshore constraints are
comparatively lacking, but we mapped the Hikurangi margin plate interface
using receiver functions from data collected by a dense 22 × 10 km array of
49 broadband seismometers. The plate interface manifests as a
positive-amplitude conversion (velocity increase with depth) dipping west
from 10 to 17 km depth. This interface corroborates relocated earthquake
hypocenters, seismic velocity models, and downdip extrapolation of
depth-converted two-dimensional active-source lines. Our mapped plate
interface has kilometer-amplitude roughness we interpret as oceanic
volcanics or seamounts, and is 1–4 km shallower than the regional-scale
plate-interface model used in geodetic inversions. Slip during SSEs may
thus have different magnitudes and/or distributions than previously
thought. We show interface roughness also leads to shear-strength
variability, where slip may nucleate in locally weak areas and propagate
across areas of low shear-strength gradient. Heterogeneous shear strength
throughout the depth range of the northern Hikurangi margin may govern the
nature of plate deformation, including the localization of both slow slip
and hazardous earthquakes.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50272.1/616548/The-northern-Hikurangi-margin-three-dimensional
Extensional mountain building along convergent plate boundary: Insights
from the active Taiwan mountain belt
Chih-Tung Chen; Ching-Hua Lo; Pei-Ling Wang; Li-Hung Lin
Abstract:
Late brittle extension is a common feature in orogenic belts, and its role
in mountain building processes is still the subject of debate. Its timing
relationship with crustal thickening, the building of topography, basin
infill, and rock exhumation are of key importance in determining whether it
is a major factor in orogenic development or merely causes near-surface
secondary effects. We examined this question in relation to the active
arc-continent collision of Taiwan, studying its structural evolution by
integrating new and critical geochronological results for tensile vein
filling of hinterland metamorphic terrane with syn-collision deposition
records. Acceleration of rock exhumation and molasse deposition was found
to be coeval with the initiation of brittle tensile structures at ca. 1.6
Ma, which was long overdue as continental subduction started well before
6.5 Ma in central to northern Taiwan. The topographic mountain of Taiwan
was thus constructed when the upper crust of the thickened orogenic prism
turned extensional, as orographic elevation and relief are prerequisites
for molasses production. Syn-collisional brittle extension is therefore
proposed as a possible facilitator of both augmented extrusive exhumation
and the formation of orography.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50311.1/616374/Extensional-mountain-building-along-convergent
Critical metal enrichment in crustal melts: The role of metamorphic
mica
Barbara E. Kunz; Clare J. Warren; Frances E. Jenner; Nigel B.W. Harris; Tom
W. Argles
Abstract:
Metals such as Li, Be, V, Co, Nb, In, Cs, Sn, Ta, and W are considered
resources that are critical for modern economies. They can be significantly
enriched in granites and pegmatites, but the mechanisms of enrichment
remain poorly understood. Many metal-enriched granitic magmas form through
mica dehydration reactions during high-grade metamorphism. The preferential
incorporation of these metals into micas provides a mechanism for
concentration and mobilization during crustal melting. Comprehensive data
sets of these elements and their partitioning in metamorphic micas across
different metamorphic grades are currently lacking. We present the first
extensive in situ laser ablation–inductively coupled plasma–mass
spectrometry element data set collected from metasediment-hosted muscovite
and biotite from three different metamorphic cross sections traversing
sub-greenschist- (~400 °C) to granulite-facies conditions (>900 °C).
Within the same sample, Li, V, Co, Cs, and Ta concentrations are higher in
biotite, whereas Be, In, Sn, and W concentrations are higher in muscovite.
Subsolidus micas record only nonsystematic compositional variations between
samples. Suprasolidus biotites show systematic depletion in Li, Be, Sn, and
Cs and enrichment in V and Co with increasing temperature in the
highest-grade (muscovite-absent) samples. Indium and W reach peak
concentrations in biotite at 750 °C and 850 °C, respectively. Muscovites
record systematic enrichment in In and W and depletion in Be, Sn, and Cs
with increasing metamorphic grade. These distinctive trends appear to be
independent of tectonic setting (i.e., continental collision and crustal
thinning). Our data set highlights the importance of higher-temperature
melting (>750 °C), in particular, biotite breakdown reactions, for the
release of Li, Be, Sn, Cs, and W into crustal melts.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50284.1/616375/Critical-metal-enrichment-in-crustal-melts-The
Mode of continental breakup of marginal seas
G. Mohn; J.C. Ringenbach; M. Nirrengarten; C. Lei; A. McCarthy ...
Abstract:
We investigated the continent-ocean transition (COT) structure of three
main marginal seas in the western Pacific Ocean (South China Sea, Coral
Sea, and Woodlark Basin) to determine the tectono-magmatic processes acting
during continental breakup. The COT formed from the activity of a low-angle
normal fault system localizing deformation during final rifting. Extension
was contemporaneous with magmatic activity, including volcanic edifices,
dikes, and sills in the distalmost parts of these basins. The COT shows a
sharp juxtaposition in space and time of continental crust against igneous
oceanic crust, and its overall structure differs from that of magma-poor or
magma-rich passive-margin archetypes. We propose that this mode of breakup
is characteristic of marginal seas due to the high extension rates imposed
by kinematic forces of nearby subduction zones. Revealed in the context of
marginal seas, this mode of breakup and the resulting COT structures
highlight the underestimated diversity of continental breakup mechanisms.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50204.1/616376/Mode-of-continental-breakup-of-marginal-seas
Did transit through the galactic spiral arms seed crust production on
the early Earth?
C.L. Kirkland; P.J. Sutton; T. Erickson; T.E. Johnson; M.I.H. Hartnady ...
Abstract:
Although there is evidence for periodic geological perturbations driven by
regular or semi-regular extra-terrestrial bombardment, the production of
Earth’s continental crust is generally regarded as a function of planetary
differentiation driven by internal processes. We report time series
analysis of the Hf isotopic composition of zircon grains from the North
Atlantic and Pilbara cratons, the archetypes of Archean plate tectonic and
non-plate tectonic settings, respectively. An ~170–200 m.y. frequency is
recognized in both cratons that matches the transit of the solar system
through the galactic spiral arms, where the density of stars is high. An
increase in stellar density is consistent with an enhanced rate of Earth
bombardment by comets, the larger of which would have initiated crustal
nuclei production via impact-driven decompression melting of the mantle.
Hence, the production and preservation of continental crust on the early
Earth may have been fundamentally influenced by exogenous processes. A test
of this model using oxygen isotopes in zircon from the Pilbara craton
reveals correlations between crust with anomalously light isotopic
signatures and exit from the Perseus spiral arm and entry into the Norma
spiral arm, the latter of which matches the known age of terrestrial
spherule beds. Our data support bolide impact, which promoted the growth of
crustal nuclei, on solar system transit into and out of the galactic spiral
arms.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50513.1/616377/Did-transit-through-the-galactic-spiral-arms-seed
Paleoclimates inform on a weakening and amplitude-reduced East Asian
winter monsoon in the warming future
Shugang Kang; Xulong Wang; Jinhua Du; Yougui Song
Abstract:
The East Asian winter monsoon (EAWM) has significant impacts on the weather
and climate, and subsequently on the economy and society, in East Asia
during boreal winters, and its projection into the future is scientifically
and practically significant. However, projections relying on geological
EAWM reconstructions, which can compensate for instrumental record
limitations, are still lacking and urgently needed. It is more promising to
conduct prediction under the background of not only instrumental but also
geological changes in the EAWM. We used grain-size records from four
high-resolution, chronologically well-defined loess sections on the Chinese
Loess Plateau to represent past EAWM intensity and its amplitudes. Our
results show that the EAWM is weaker and has lower amplitudes during warm
periods than during cold stages at various time scales. Moreover,
instrumental records reveal that the EAWM shows a weak level and reduced
interannual amplitudes after the mid-1980s under the context of global
warming. We propose that the EAWM will experience long-term weakening and
reduced (e.g., interannual) amplitudes under 21st century
global-warming scenarios.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50246.1/616378/Paleoclimates-inform-on-a-weakening-and-amplitude
Secular variation in seawater redox state during the Marinoan Snowball
Earth event and implications for eukaryotic evolution
Weibing Shen; Xiangkun Zhu; Bin Yan; Jin Li; Pengju Liu ...
Abstract:
The ocean is hypothesized to have been anoxic throughout the Marinoan
“Snowball Earth” event, from ca. 649 to 635 Ma, with potentially
catastrophic implications for the survival of eukaryotic life. However, the
precise nature of ocean redox chemistry across this critical interval, and
hence the factors that governed the persistence of eukaryotes, remains
unknown. We report records of pyrite iron and sulfur isotopes, combined
with Fe speciation, for glaciogenic diamictites from the Nantuo Formation
of South China. These data provide constraints on seawater redox state
across the Marinoan glaciation, and they reveal that the redox state of the
ocean fluctuated in concert with waxing and waning extents of glaciation,
to include intervals of expanded oxygenation. The input of
meltwater-derived oxygen provides a potential explanation for the
persistence of eukaryotes through the Cryogenian “Snowball Earth” events,
which ultimately paved the way for subsequent intervals of rapid biological
innovation.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50147.1/616379/Secular-variation-in-seawater-redox-state-during
Magma pressurization sustains ongoing eruptive episode at dome-building
Soufrière Hills volcano, Montserrat
J. Hickey; K. Pascal; M. Head; J. Gottsmann; N. Fournier ...
Abstract:
Dome-building volcanoes, where long-term eruptive episodes can be
interspersed with periods of intra-eruptive repose, are particularly
challenging for volcanic hazard assessment. Defining the end of eruptive
episodes is vitally important for the socioeconomic recovery of affected
communities but highly problematic due to the potential for rapid
transition from prolonged, seemingly low-risk repose to dangerous effusive
or explosive activity. It is currently unclear what constitutes the end of
repose and an eruptive episode. We show that analysis of surface
deformation can characterize repose and help define an eruptive episode. At
Soufrière Hills volcano, Montserrat, the long-term post–2010 deformation at
12 continuous GPS stations requires the pressure in the magma system to
have increased with time; time-dependent stress relaxation or crustal creep
cannot explain the deformation trends alone. Continued pressurization
within the magmatic system during repose could initiate a renewed eruption,
qualifying as sustained unrest and therefore continuation of the eruptive
episode. For Soufrière Hills volcano, persistent magma pressurization
highlights the need for sustained vigilance in the monitoring and
management of the volcano and its surroundings, despite the last eruptive
activity ending in 2010. Our results show promise for application to other
dome-building volcanoes.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50239.1/616380/Magma-pressurization-sustains-ongoing-eruptive
Simultaneous fall and flow during pyroclastic eruptions: A novel
proximal hybrid facies
Natasha Dowey; Rebecca Williams
Abstract:
The deposits of Plinian and subplinian eruptions provide critical insights
into past volcanic events and inform numerical models that aim to mitigate
against future hazards. However, pyroclastic deposits are often considered
from either a fallout or pyroclastic density current (PDC) perspective,
with little attention given to facies exhibiting characteristics of both
processes. Such hybrid units may be created where fallout and PDCs act
simultaneously, where a transitional phase between the two occurs, and/or
due to reworking. This study presents analysis of a novel hybrid
pyroclastic lithofacies found on Tenerife (Canary Islands) and Pantelleria
(Italy). The coarse pumice block facies has an openwork texture and
correlates with distal Plinian units, but it is cross-stratified and
relatively poorly sorted with an erosional base. The facies is proposed to
record the simultaneous interaction of very proximal fallout and turbulent
PDCs, and it reveals a fuller spectrum of hybrid deposition than previously
reported. This work highlights the importance of recognizing hybrid
deposition both in the rock record and in hazard modeling.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G50169.1/615943/Simultaneous-fall-and-flow-during-pyroclastic
Preserved intercratonic lithosphere reveals Proterozoic assembly of
Australia
Yongjun Lu; Michael T.D. Wingate; Robert H. Smithies; Klaus Gessner; Simon
P. Johnson ...
Abstract:
The Proterozoic assembly of Australia, the understanding of which is
critical for reconstructing Proterozoic supercontinents, involved
amalgamation of the West Australian (WAC), North Australian (NAC), and
South Australian cratons (SAC). However, the basement between these Archean
to early Proterozoic lithospheric blocks is mostly buried beneath younger
basins; hence, its composition and age and the timing of Proterozoic
assembly remain uncertain. In situ zircon U-Pb-O-Hf analyses of
igneous rocks from drillholes that intersected basement beneath the
northwestern Canning Basin reveal the presence of a substantial domain of
juvenile Proterozoic lithosphere, the Percival Lakes province, between the
WAC and NAC. Although isotopically distinct from the neighboring WAC and
NAC, the Percival Lakes province is strikingly similar to other juvenile
Proterozoic tectonic elements between the WAC, NAC, and SAC. Combining
isotope and seismic data, we interpret the Percival Lakes province as part
of an ~1700 × 400 km Proterozoic lithospheric domain that lacks evidence of
Archean provenance but consists mainly of reworked remnants of
Mesoproterozoic oceanic crust that survived WAC-NAC-SAC convergence. The
apparent absence of Archean lithosphere between the cratons implies they
never directly collided or that complete collision was prevented by
impingement of three-dimensional promontories in the converging
lithospheric blocks. Instead, the Percival Lakes province and other
Proterozoic elements between the WAC, NAC, and SAC consist of oceanic
lithosphere extracted from Earth’s mantle in the Proterozoic. Our results
imply that WAC-NAC convergence was younger than Columbia amalgamation at
ca. 1.8 Ga and that Proterozoic Australia formed during the earliest phases
of Rodinia assembly at ca. 1.3 Ga.
View article:
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G50256.1/615944/Preserved-intercratonic-lithosphere-reveals
GEOLOGY articles are online at
https://geology.geoscienceworld.org/content/early/recent
. Representatives of the media may obtain complimentary articles by
contacting Kea Giles at the e-mail address above. Please discuss articles
of interest with the authors before publishing stories on their work, and
please make reference to GEOLOGY in articles published. Non-media requests
for articles may be directed to GSA Sales and Service,
gsaservice@geosociety.org.
https://www.geosociety.org
# # #