Nicolas Flament
I am currently working on a project "The geodynamics of past sea level change" funded by the Australian Research Council
Phone: +61 2 4221 5455
Address: Room 167, Building 41
University of Wollongong
Northfields Avenue, Wollongong, New South Wales 2522, Australia
Phone: +61 2 4221 5455
Address: Room 167, Building 41
University of Wollongong
Northfields Avenue, Wollongong, New South Wales 2522, Australia
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We developed a physical model to evaluate the area of emerged land as a function of mantle temperature, continental area, and of the distribution of continental elevations. Our numerical results show that less than 15% of Earth's surface consisted of emerged land by the end of the Archaean. This is consistent with many geological and geochemical observations.
To estimate the secular cooling of the continental lithosphere, we combined thermo-mechanical models with field observations. Our results, constrained by geological data, suggest that the Moho temperature has decreased by ~ 200ºC over 2.7 Ga in the Pilbara Craton.
To evaluate the effect of continental growth on the evolution of the area of emerged land, we developed a model based on published thermal evolution models. Our results suggest that the area of emerged land was less than 5% of Earth's surface in the Archaean, and that it does not depend on crustal growth. This allows to reconcile the evolution of oceanic 87Sr/86Sr with early
crustal growth models.
Continents are enriched in phosphorus, which is essential to the biosphere. The emergence of the continents would thus have triggered an increase in the production of oxygen by photosynthetic micro-organisms, possibly contributing to the oxidation of the atmosphere 2.4 Ga ago."
Nous avons developpe un modele physique qui permet d'evaluer la surface de terres emergees en fonction de la temperature du manteau, de la surface totale de continents, et de la distribution des altitudes continentales. Nos resultats numeriques montrent qu'a la fin de l'Archeen, moinsde 15% de la surface terrestre etaient emergee, en accord avec nombre d'observations geologiques et geochimiques.
Pour estimer le refroidissement seculaire de la lithosphere continentale, nous avons combine des modeles thermo-mecaniques avec des observations de terrain. Nos resultats, contraints par des donnees geologiques, suggerent que la temperature au Moho a diminue de ~ 200ºC en 2,7 Ga dans le craton des Pilbaras.
Pour evaluer l'effet de la croissance continentale sur l'evolution de la surface de terres emergees, nous avons developpe un modele base sur un modele d'evolution thermique publie. Nos resultats suggerent que la surface emergee, de moins de 5% de la surface terrestre a l'Archeen, depend peu de la croissance continentale. Ceci permet de reconcilier l'evolution du 87Sr/86Sr oceanique avec une croissance continentale precoce.
Les continents sont enrichis en phosphate, element essentiel a la biosphere. Leur emergence aurait donc engendre une augmentation de la production d'oxygene par des micro-organismes photosynthetiques, contribuant ainsi a l'oxydation de l'atmosphere il y a 2,4 Ga.
The global plate motion model presented in this study captures the time-dependent evolution of plates and their tectonic boundaries since 160 Ma, which are assimilated as surface boundary conditions for numerical experiments of mantle convection. We evaluate subducted slab locations and geometries predicted by forward mantle flow models against P- and S-wave seismic tomography models. This approach harnesses modern plate reconstruction techniques, mantle convection models with imposed one-sided subduction, and constraints from the surface geology to address a number of unresolved Tethyan geodynamic controversies. Our synthesis reveals that north-dipping subduction beneath Eurasia in the latest Jurassic consumed the Meso-Tethys, and suggests that northward slab pull opened the younger Neo-Tethyan ocean basin from ~ 155 Ma. We model the rifting of ‘Argoland’, representing the East Java and West Sulawesi continental fragments, as a northward transfer of continental terranes in the latest Jurassic from the northwest Australian shelf – likely colliding first with parts of the Woyla intra-oceanic arc in the mid-Cretaceous, and accreting to the Borneo (Sundaland) core by ~ 80 Ma. The Neo-Tethyan ridge was likely consumed along an intra-oceanic subduction zone south of Eurasia from ~ 105 Ma, leading to a major change in the motion of the Indian Plate by ~ 100 Ma, as observed in the Wharton Basin fracture zone bends.
We investigate the geodynamic consequences of long-lived intra-oceanic subduction within the Neo-Tethys, requiring a two-stage India-Eurasia collision involving first contact between Greater India and the Kohistan-Ladakh Arc sometime between ~ 60 and 50 Ma, followed by continent-continent collision from ~ 47 Ma. Our models suggest that the Sunda slab kink beneath northwest Sumatra in the mantle transition zone results from the rotation and extrusion of Indochina from ~ 30 Ma. Our results are also the first to reproduce the enigmatic Proto South China Sea slab beneath northern Borneo, as well as the Tethyan/Woyla slab that is predicted at mid-mantle depths south of Sumatra. Further east, our revised reconstructions of the New Guinea margin, notably the evolution of the Sepik composite terrane and the Maramuni subduction zone, produce a better match with seismic tomography than previous reconstructions, and account for a slab at ~ 30°S beneath Lake Eyre that has been overridden by the northward advancing Australian continent. Our plate reconstructions provide a framework to study changing patterns of oceanic circulation, long-term sea level driven by changes in ocean basin volume, as well as major biogeographic dispersal pathways that have resulted from Gondwana fragmentation and accretion of Tethyan terranes to south- and southeast-Eurasia.
In this paper, we investigate the continental freeboard predicted using different models for the cooling of the Earth. We show that constancy of the continental freeboard (± 200 m) is possible throughout the history of the planet as long as the potential temperature of the upper mantle was never more than 110–210 °C hotter than present. Such numbers imply either a very limited cooling of the planet or, most likely, a change in continental freeboard since the Archaean. During the Archaean a greater radiogenic crustal heat production and a greater mantle heat flow would have reduced the strength of the continental lithosphere, thus limiting crustal thickening due to mountain building processes and the maximum elevation in the Earth's topography [Rey, P. F., Coltice, N., Neoarchean strengthening of the lithosphere and the coupling of the Earth's geochemical reservoirs, Geology 36, 635–638 (2008)]. Taking this into account, we show that the continents were mostly flooded until the end of the Archaean and that only 2–3% of the Earth's area consisted of emerged continental crust by around 2.5 Ga. These results are consistent with widespread Archaean submarine continental flood basalts, and with the appearance and strengthening of the geochemical fingerprint of felsic sources in the sedimentary record from 2.5 Ga. The progressive emergence of the continents as shown by our models from the late-Archaean onward had major implications for the Earth's environment, particularly by contributing to the rise of atmospheric oxygen and to the geochemical coupling between the Earth's deep and surface reservoirs.
We developed a physical model to evaluate the area of emerged land as a function of mantle temperature, continental area, and of the distribution of continental elevations. Our numerical results show that less than 15% of Earth's surface consisted of emerged land by the end of the Archaean. This is consistent with many geological and geochemical observations.
To estimate the secular cooling of the continental lithosphere, we combined thermo-mechanical models with field observations. Our results, constrained by geological data, suggest that the Moho temperature has decreased by ~ 200ºC over 2.7 Ga in the Pilbara Craton.
To evaluate the effect of continental growth on the evolution of the area of emerged land, we developed a model based on published thermal evolution models. Our results suggest that the area of emerged land was less than 5% of Earth's surface in the Archaean, and that it does not depend on crustal growth. This allows to reconcile the evolution of oceanic 87Sr/86Sr with early
crustal growth models.
Continents are enriched in phosphorus, which is essential to the biosphere. The emergence of the continents would thus have triggered an increase in the production of oxygen by photosynthetic micro-organisms, possibly contributing to the oxidation of the atmosphere 2.4 Ga ago."
Nous avons developpe un modele physique qui permet d'evaluer la surface de terres emergees en fonction de la temperature du manteau, de la surface totale de continents, et de la distribution des altitudes continentales. Nos resultats numeriques montrent qu'a la fin de l'Archeen, moinsde 15% de la surface terrestre etaient emergee, en accord avec nombre d'observations geologiques et geochimiques.
Pour estimer le refroidissement seculaire de la lithosphere continentale, nous avons combine des modeles thermo-mecaniques avec des observations de terrain. Nos resultats, contraints par des donnees geologiques, suggerent que la temperature au Moho a diminue de ~ 200ºC en 2,7 Ga dans le craton des Pilbaras.
Pour evaluer l'effet de la croissance continentale sur l'evolution de la surface de terres emergees, nous avons developpe un modele base sur un modele d'evolution thermique publie. Nos resultats suggerent que la surface emergee, de moins de 5% de la surface terrestre a l'Archeen, depend peu de la croissance continentale. Ceci permet de reconcilier l'evolution du 87Sr/86Sr oceanique avec une croissance continentale precoce.
Les continents sont enrichis en phosphate, element essentiel a la biosphere. Leur emergence aurait donc engendre une augmentation de la production d'oxygene par des micro-organismes photosynthetiques, contribuant ainsi a l'oxydation de l'atmosphere il y a 2,4 Ga.
The global plate motion model presented in this study captures the time-dependent evolution of plates and their tectonic boundaries since 160 Ma, which are assimilated as surface boundary conditions for numerical experiments of mantle convection. We evaluate subducted slab locations and geometries predicted by forward mantle flow models against P- and S-wave seismic tomography models. This approach harnesses modern plate reconstruction techniques, mantle convection models with imposed one-sided subduction, and constraints from the surface geology to address a number of unresolved Tethyan geodynamic controversies. Our synthesis reveals that north-dipping subduction beneath Eurasia in the latest Jurassic consumed the Meso-Tethys, and suggests that northward slab pull opened the younger Neo-Tethyan ocean basin from ~ 155 Ma. We model the rifting of ‘Argoland’, representing the East Java and West Sulawesi continental fragments, as a northward transfer of continental terranes in the latest Jurassic from the northwest Australian shelf – likely colliding first with parts of the Woyla intra-oceanic arc in the mid-Cretaceous, and accreting to the Borneo (Sundaland) core by ~ 80 Ma. The Neo-Tethyan ridge was likely consumed along an intra-oceanic subduction zone south of Eurasia from ~ 105 Ma, leading to a major change in the motion of the Indian Plate by ~ 100 Ma, as observed in the Wharton Basin fracture zone bends.
We investigate the geodynamic consequences of long-lived intra-oceanic subduction within the Neo-Tethys, requiring a two-stage India-Eurasia collision involving first contact between Greater India and the Kohistan-Ladakh Arc sometime between ~ 60 and 50 Ma, followed by continent-continent collision from ~ 47 Ma. Our models suggest that the Sunda slab kink beneath northwest Sumatra in the mantle transition zone results from the rotation and extrusion of Indochina from ~ 30 Ma. Our results are also the first to reproduce the enigmatic Proto South China Sea slab beneath northern Borneo, as well as the Tethyan/Woyla slab that is predicted at mid-mantle depths south of Sumatra. Further east, our revised reconstructions of the New Guinea margin, notably the evolution of the Sepik composite terrane and the Maramuni subduction zone, produce a better match with seismic tomography than previous reconstructions, and account for a slab at ~ 30°S beneath Lake Eyre that has been overridden by the northward advancing Australian continent. Our plate reconstructions provide a framework to study changing patterns of oceanic circulation, long-term sea level driven by changes in ocean basin volume, as well as major biogeographic dispersal pathways that have resulted from Gondwana fragmentation and accretion of Tethyan terranes to south- and southeast-Eurasia.
In this paper, we investigate the continental freeboard predicted using different models for the cooling of the Earth. We show that constancy of the continental freeboard (± 200 m) is possible throughout the history of the planet as long as the potential temperature of the upper mantle was never more than 110–210 °C hotter than present. Such numbers imply either a very limited cooling of the planet or, most likely, a change in continental freeboard since the Archaean. During the Archaean a greater radiogenic crustal heat production and a greater mantle heat flow would have reduced the strength of the continental lithosphere, thus limiting crustal thickening due to mountain building processes and the maximum elevation in the Earth's topography [Rey, P. F., Coltice, N., Neoarchean strengthening of the lithosphere and the coupling of the Earth's geochemical reservoirs, Geology 36, 635–638 (2008)]. Taking this into account, we show that the continents were mostly flooded until the end of the Archaean and that only 2–3% of the Earth's area consisted of emerged continental crust by around 2.5 Ga. These results are consistent with widespread Archaean submarine continental flood basalts, and with the appearance and strengthening of the geochemical fingerprint of felsic sources in the sedimentary record from 2.5 Ga. The progressive emergence of the continents as shown by our models from the late-Archaean onward had major implications for the Earth's environment, particularly by contributing to the rise of atmospheric oxygen and to the geochemical coupling between the Earth's deep and surface reservoirs.
the thickening of the continental crust, many Archean flood basalts that show continental contamination remained
below sea level during their eruption. In this contribution, we suggest that one possible way of maintaining basaltic
piles several kilometers thick below sea level is via gravity-driven lower crustal flow of hot continental crust.
Using numerical experiments, we show that the characteristic time to remove the anomaly in crustal thickness
associated with a continental flood basalt (CFB) decreases exponentially with Moho temperature (TM) from 2.5
Gyr for TM 300 C to 5 Myr for TM 1050 C. Therefore, the removal of the thickness anomaly associated
with CFBs erupted on cold continents occurs by a combination of brittle deformation and erosion, two processes
of time scale of a few tens of million years. This is consistent with observations for Phanerozoic CFBs that are
subject to important erosion and would not be preserved in the geological record over billions of years, contrary to
subaqueous Archean CFBs. We show, based on sedimentary and structural observations, that the subsidence of the
1.4-km-thick basalts of the Kylena Formation and lower 600-m-thick basalts of the Maddina Formation in the
Meentheena Centrocline (Pilbara Craton, Western Australia) occurred without any significant tectonic extension
in 15 Myr and 11 Myr, respectively. We interpret our observations as the surface expression of the removal
of thickness anomaly by the flow of lower continental crust. From our modeling results, the subsidence of these
basalts over such time scales requires Moho temperatures 900 ºC. The example of the Fortescue Group illustrates
that thick subaqueous Archean CFBs are the result of the accumulation of several basaltic packages, each erupted
over 30 Myr. Moho temperatures 800 C are required to maintain such basaltic packages below sea level
by lower crustal flow. Thus, the prevalence of subaqueous CFBs in the Archean record suggests that they were
dominantly emplaced on hot, weak continental crust and that Archean continental geotherms were significantly
warmer than their modern counterparts.
We developed a model to evaluate the area of emerged continental crust as a function of mantle temperature, continental area and hypsometry. For constant continental hypsometry and for three different thermal evolution models, we find that a constant continental freeboard (± 200 m) throughout Earth’s history is possible as long as the potential temperature of the upper mantle never exceeded its present value by more than 110–210°C. This implies either a very limited cooling of the planet or, most likely, a change in continental freeboard since the Archaean. As for the area of emerged land, our calculations suggest that less than ~ 12% of Earth’s surface were emerged in the Archaean, compared to ~ 28% at present.
Of importance to the evolution of the area of emerged land is the shape of the continents. During the Archaean, a greater radiogenic crustal heat production and a possibly greater mantle heat flow would have reduced the strength of the continental lithosphere, thus limiting crustal thickening due to
mountain building processes and the maximum elevation in Earth’s topography (Rey and Coltice, 2008). Taking this effect into account, we show that the continents were mostly flooded until the end of the Archaean, with 2‐3% of Earth’s area emerged by 2.5 Ga. These results are consistent with the widespread occurrence of submarine continental flood basalts in the Archaean, and with the appearance and strengthening of the geochemical fingerprint of felsic sources in the sedimentary record from 2.5 Ga.
In order to investigate the influence of crustal growth models on the area of emerged land and on the evolution of oceanic 87Sr/86Sr, we developed an integrated model based on the thermal evolution model of Labrosse and Jaupart (2007). Modelling results suggest that the area of emerged land does
not closely depend on crustal growth models, and that less than 5% of Earth’s area was emerged in the Archaean. Furthermore, our models reconcile early crustal growth models with the evolution of oceanic 87Sr/86Sr as recorded by marine carbonates when a reduced emerged area and lower continental elevations are accounted for. Thus, a delayed crustal growth model is not needed to account for the observed trend in oceanic 87Sr/86Sr.
References
Labrosse, S., Jaupart, C., 2007. Thermal evolution of the Earth: Secular changes and fluctuations of plate characteristics. Earth Planet. Sc. Lett. 260, 465–481.
Rey, P. F., Coltice, N., 2008. Neoarchean strengthening of the lithosphere and the coupling of the Earth’s geochemical reservoirs. Geology 36, 635–638.
We developed a physical model to evaluate the area of emerged land as a function of mantle temperature, continental area, and of the distribution of continental elevations. Our numerical results show that less than 15% of Earth’s surface consisted of emerged land by the end of the Archaean. This is consistent with many geological and geochemical observations.
To estimate the secular cooling of the continental lithosphere, we combined thermo-mechanical models with field observations. Our results, constrained by geological data, suggest that the Moho temperature has decreased by ~ 200◦C over 2.7 Ga in the Pilbara Craton.
To evaluate the effect of continental growth on the evolution of the area of emerged land, we developed a model based on published thermal evolution models. Our results suggest that the area of emerged land was less than 5% of Earth’s surface in the Archaean, and that it does not depend on crustal growth. This allows to reconcile the evolution of oceanic 87Sr/86Sr with early crustal growth models.
Continents are enriched in phosphorus, which is essential to the biosphere. The emergence of the continents would thus have triggered an increase in the production of oxygen by photosynthetic microorganisms, possibly contributing to the oxidation of the atmosphere 2.4 Ga ago.
geodynamical phenomena, such as volcanic island chains showing an age pro-
gression. Numerical studies suggest that mantle plumes could originate deep
within the Earth, possibly at the core-mantle boundary, as a result of thermal
instabilities. Thermal buoyancy causes such plumes to rise through the man-
tle and reach the base of the lithosphere. Numerical models of mantle plumes
are routinely used to study their inception and subsequent ascent through the
mantle. Numerous 2D studies have been performed - however, the combined
effects of temperature dependent viscosity, thermal and chemical boundary
layers on plume generation and their subsequent ascent velocities are still
relatively poorly understood. Significant advances in computational capac-
ity now allow for systematic 3D studies to be undertaken at resolutions fine
enough to resolve highly convective plume features.
We first design simple 3D isoviscous regional plume models under the
Boussinesq approximation in CitcomS as a starting point, comparing results
against analytical solutions. We impose a hot sphere of radius 200 km with
an excess temperature of ~200 K - at the base of the lower mantle - to
initiate our plume models. We study the effects of mesh resolution on re-
solving fine structures of ascending plumes, along with associated return flow
as they reach the base of the lithosphere, and on that of the rate of conver-
gence to analytical solutions. Building onto these results we then investigate
the effects of thermal and chemical boundary layers, heat content and heat
distribution of the initial temperature anomaly and temperature-dependent
viscosity on the ascent velocity of plumes. In addition, we investigate the
predicted evolution of dynamic topography and surface heat flux. We will
use the results of our regional tests to devise appropriate parametrizations
to implement active upwellings in forward global mantle flow models with
compositionally distinct thermal boundary layers.