École Normale Supérieure de Lyon
Laboratoire de Sciences de la Terre
The secular cooling of the Earth's mantle and the growth of the continental crust together imply changes in the isostatic balance between continents and oceans, in the oceanic bathymetry and in the area of emerged continental crust. The... more
The secular cooling of the Earth's mantle and the growth of the continental crust together imply changes in the isostatic balance between continents and oceans, in the oceanic bathymetry and in the area of emerged continental crust. The evolution of these variables is of fundamental importance to the geochemical coupling of mantle, continental crust, atmosphere and ocean. To explore this further, we developed a model that evaluates the area of emerged continental crust as a function of mantle temperature, continental area and hypsometry.
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.
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 secular cooling of the Earth's mantle and the growth of the continental crust together imply changes in the isostatic balance between continents and oceans, in the oceanic bathymetry and in the area of emerged continental crust. The... more
"The secular cooling of the Earth's mantle and the growth of the continental crust together imply changes in the isostatic balance between continents and oceans, in the oceanic bathymetry and in the area of emerged continental crust. The evolution of these variables is of fundamental importance to the geochemical coupling of mantle, continental crust, atmosphere and ocean. To explore this further, we developed a model that evaluates the area of emerged continental crust as a function of mantle temperature, continental area and hypsometry.
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 not, vert, similar 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."
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 not, vert, similar 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 secular cooling of the mantle and of the continental lithosphere trigger an increase in the area of emerged land. The corollary increase in weathering and erosion processes has major consequences for the evolution of Earth's external... more
"The secular cooling of the mantle and of the continental lithosphere trigger an increase in the area of emerged land. The corollary increase in weathering and erosion processes has major consequences for the evolution of Earth's external envelopes.
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 fi eld 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 eff ect 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."
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 fi eld 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 eff ect 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."
Le refroidissement seculaire du manteau terrestre et de la lithosphere continentale se traduit par l'augmentation de la surface de terres emergees. L'augmentation corollaire des processus d'alteration et d'erosion des silicates a des... more
Le refroidissement seculaire du manteau terrestre et de la lithosphere continentale se traduit par l'augmentation de la surface de terres emergees. L'augmentation corollaire des processus d'alteration et d'erosion des silicates a des consequences majeures pour les enveloppes externes.
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.
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.
Large basaltic provinces up to 15 km thick are common in Archean cratons. Many of these flood basalts erupted through continental crust but remained at sea level. While common in the Archean, subaqueous Continental Flood Basalts (CFBs)... more
Large basaltic provinces up to 15 km thick are common in Archean cratons. Many of these flood basalts erupted through continental crust but remained at sea level. While common in the Archean, subaqueous Continental Flood Basalts (CFBs) are rare to absent in the post-Archean. Here we show that gravity-driven lower crustal flow may have contributed to maintaining Archean CFBs close to sea level. Our numerical experiments reveal that the characteristic time to remove the thickness anomaly associated with a CFB decreases with increasing Moho temperature (TM) from 500 million years (Myr) for TM ≈ 320 °C to 1 Myr for TM ≈ 900 °C. This strong dependency offers the opportunity to assess, from the subsidence history of CFBs, whether continental geotherms were significantly hotter in the Archean. In particular, we show that the subsidence history of the ~2.7 billion-year-old upper Fortescue group in the East Pilbara Craton, Western Australia, requires Moho temperatures much greater than 700 °C. Applied to eight other unambiguous subaqueous Archean CFBs, our results indicate Moho temperatures well in excess of 650 °C at the time of eruption. We suggest that the decrease in the relative abundance of subaqueous CFBs over Earth’s history could reflect the secular cooling of the continental lithosphere due to the decrease in radiogenic heat production.
"Many continental growth models have been proposed over the years to explain geological and geochemical data. Amongst these data, the evolution of the 87Sr/86Sr of marine carbonates has been used as an argument in favour of delayed... more
"Many continental growth models have been proposed over the years to explain geological and geochemical data. Amongst these data, the evolution of the 87Sr/86Sr of marine carbonates has been used as an argument in favour of delayed continental growth models and of a Neoarchean pulse in continental
growth. This interpretation requires that continental freeboard and continental hypsometry have remained constant throughout Earth’s history. However, recent studies suggest that Archean sea levels were higher, and Archean relief lower, than present-day ones.
To assess the validity of the evolution of the 87Sr/86Sr of marine carbonates as a proxy for continental growth, we have developed a model that evaluates the co-evolution of mantle temperature, continental hypsometry, sea level, ridge depth, emerged area of continental crust and the 87Sr/86Sr of ocean water as a function of continental growth. We show that Archean sea levels were between ∼500 m and ∼1800 m higher than present-day ones, that Archean mid-oceanic ridges were between ∼700 m and ∼1900 m shallower than present-day ones, and that the Archean emerged land area was less than∼4% of Earth’s area. Importantly, the evolution of the area of emerged land, contrary to that of sea level and ridge depth, barely depends on continental growth models. This suggests that the evolution of surface geochemical proxies for felsic lithologies does not constrain continental growth. In particular, the evolution of the 87Sr/86Sr of ocean water predicted for an early continental growth model is in broad agreement with the 87Sr/86Sr data on marine carbonates when changes in continental freeboard and continental hypsometry are taken into account. We propose that the Neoarchean shift in the 87Sr/86Sr of marine carbonates recorded the emergence of the continents rather than a pulse in continental growth. Since the evolution
of other geochemical indicators for felsic crust used as proxies for continental growth is equally well explained by continental emergence, we suggest that there could be no need for delayed continental growth models."
growth. This interpretation requires that continental freeboard and continental hypsometry have remained constant throughout Earth’s history. However, recent studies suggest that Archean sea levels were higher, and Archean relief lower, than present-day ones.
To assess the validity of the evolution of the 87Sr/86Sr of marine carbonates as a proxy for continental growth, we have developed a model that evaluates the co-evolution of mantle temperature, continental hypsometry, sea level, ridge depth, emerged area of continental crust and the 87Sr/86Sr of ocean water as a function of continental growth. We show that Archean sea levels were between ∼500 m and ∼1800 m higher than present-day ones, that Archean mid-oceanic ridges were between ∼700 m and ∼1900 m shallower than present-day ones, and that the Archean emerged land area was less than∼4% of Earth’s area. Importantly, the evolution of the area of emerged land, contrary to that of sea level and ridge depth, barely depends on continental growth models. This suggests that the evolution of surface geochemical proxies for felsic lithologies does not constrain continental growth. In particular, the evolution of the 87Sr/86Sr of ocean water predicted for an early continental growth model is in broad agreement with the 87Sr/86Sr data on marine carbonates when changes in continental freeboard and continental hypsometry are taken into account. We propose that the Neoarchean shift in the 87Sr/86Sr of marine carbonates recorded the emergence of the continents rather than a pulse in continental growth. Since the evolution
of other geochemical indicators for felsic crust used as proxies for continental growth is equally well explained by continental emergence, we suggest that there could be no need for delayed continental growth models."
The 3.46 Ga Marble Bar Chert Member of the East Pilbara Craton, Western Australia, is one of the earliest and best preserved sedimentary successions on Earth. Here, we interpret the finely laminated thin-bedded cherts, mixed conglomeratic... more
The 3.46 Ga Marble Bar Chert Member of the East Pilbara
Craton, Western Australia, is one of the earliest and best preserved sedimentary successions on Earth. Here, we
interpret the finely laminated thin-bedded cherts, mixed
conglomeratic beds, chert breccia beds and chert folded
beds of the Marble Bar Chert Member as the product
of low-density turbidity currents, high-density turbidity
currents, mass transport complexes and slumps, respectively.
Integrated into a channel-levee depositional model, the
Marble Bar Chert Member constitutes the oldest documented
deep-sea fan on Earth, with thin-bedded cherts, breccia
beds and slumps composing the outer levee facies tracts,
and scours and conglomeratic beds representing the channel
systems.
Craton, Western Australia, is one of the earliest and best preserved sedimentary successions on Earth. Here, we
interpret the finely laminated thin-bedded cherts, mixed
conglomeratic beds, chert breccia beds and chert folded
beds of the Marble Bar Chert Member as the product
of low-density turbidity currents, high-density turbidity
currents, mass transport complexes and slumps, respectively.
Integrated into a channel-levee depositional model, the
Marble Bar Chert Member constitutes the oldest documented
deep-sea fan on Earth, with thin-bedded cherts, breccia
beds and slumps composing the outer levee facies tracts,
and scours and conglomeratic beds representing the channel
systems.
"The Eocene India-Eurasia collision is a first order tectonic event whose nature and chronology remains controversial. We test two end-member collision scenarios using coupled global plate motion-subduction models. The first, conventional... more
"The Eocene India-Eurasia collision is a first order tectonic event whose nature and chronology remains controversial. We test two end-member collision scenarios using coupled global plate motion-subduction models. The first, conventional model, invokes a continental collision soon after 60 Ma between a maximum extent Greater India and an Andean-style Eurasian margin. The alternative scenario involves a collision between a
minimum extent Greater India and a NeoTethyan back-arc at 60 Ma that is subsequently subducted along southern Lhasa at an Andean-style margin, culminating with continent-continent contact at 40 Ma. Our numerical models suggest the conventional scenario does not adequately reproduce mantle structure related to Tethyan convergence. The alternative scenario better reproduces the discrete slab volumes and their lateral and vertical distribution in the mantle, and is also supported by the distribution of ophiolites indicative of Tethyan intraoceanic subduction, magmatic gaps along southern Lhasa and a two-stage slowdown of India. Our models show a strong component of southward mantle return flow for the Tethyan region, suggesting that the common assumption of near-vertical slab sinking is an oversimplification with significant consequences for interpretations of seismic tomography in the context of subduction reference frames."
minimum extent Greater India and a NeoTethyan back-arc at 60 Ma that is subsequently subducted along southern Lhasa at an Andean-style margin, culminating with continent-continent contact at 40 Ma. Our numerical models suggest the conventional scenario does not adequately reproduce mantle structure related to Tethyan convergence. The alternative scenario better reproduces the discrete slab volumes and their lateral and vertical distribution in the mantle, and is also supported by the distribution of ophiolites indicative of Tethyan intraoceanic subduction, magmatic gaps along southern Lhasa and a two-stage slowdown of India. Our models show a strong component of southward mantle return flow for the Tethyan region, suggesting that the common assumption of near-vertical slab sinking is an oversimplification with significant consequences for interpretations of seismic tomography in the context of subduction reference frames."
Large basaltic provinces as much as 15 km thick are common in Archean cratons. Many of these flood basalts erupted through continental crust but remained at sea level. Although common in the Archean record, subaqueous continental flood... more
Large basaltic provinces as much as 15 km thick are common in Archean cratons. Many of these flood basalts erupted through continental crust but remained at sea level. Although common in the Archean record, subaqueous continental flood basalts (CFBs) are rare to absent in the post-Archean. Here we show that gravity-driven lower crustal fl ow may have contributed to maintaining Archean CFBs close to sea level. Our numerical experiments reveal that the characteristic time to remove the thickness anomaly associated with a CFB decreases with increasing Moho temperature (TM), from 500 m.y. for TM ≈ 320 °C to 1 m.y. for TM ≈ 900 °C. This strong dependency offers the opportunity to assess, from the subsidence history of CFBs, whether continental geotherms were significantly hotter in the Archean. In particular, we show that the subsidence history of the ca. 2.7 Ga upper Fortescue Group in the East Pilbara Craton, Western Australia, requires Moho temperatures >>700 °C. Applied to eight other unambiguous subaqueous Archean CFBs, our results indicate Moho temperatures >>650 °C at the time of eruption. We suggest that the decrease in the relative abundance of subaqueous CFBs over Earth’s history could reflect the secular cooling of the continental lithosphere due to the decrease in radiogenic heat production.
- by Patrice F Rey and +1
- •
- Tectonics, Geodynamics, Archean
The balance between the secular cooling of the Earth's mantle and the growth of the continental crust implies changes in the isostatic equilibrium between continents and oceans, in the oceanic bathymetry, and in the area of emerged... more
The balance between the secular cooling of the Earth's mantle and the growth of the continental crust implies changes in the isostatic equilibrium between continents and oceans, in the oceanic bathymetry, and in the area of emerged continental crust. The evolution of the latter is of fundamental importance to the geochemical coupling between the continental crust, the atmosphere and the oceans. The area of emerged land can be estimated from models that depend on mantle temperature, continental area and continental hypsometry. In the Archean, the mantle was probably 150-200°C hotter than present and the continental area could have increased from 20% of present at ~~3.5Ga to 80% of present by ~~2.5Ga. Using these values, and comparing different thermal evolution models for the Earth, we calculate that the area of emerged continental crust would be reduced to 1-12% of the Earth's area during the Archean (compared to 27.5% for present-day Earth). As for the continental hypsometry, a greater radiogenic crustal heat production and a greater mantle heat flow would have reduced the strength of the continental lithosphere in the Archean, thus limiting the crustal thickening due to mountain building processes and the maximum elevation in the Earth's topography [Rey and Coltice, Geology 36, 635-638 (2008)]. Taking this into account, we show that the continents were mostly flooded until the end of the Archean and that less than 3% of the Earth's area (which is roughly the superficy of South America) consisted of emerged continental crust by ~~2.5~Ga. These results are consistent with widespread Archean submarine continental flood basalts, and with the emergence of a sialic geochemical reservoir recorded from ~~2.5~Ga in (a) the composition of shales, (b) the isotopic ratio 87Sr/86Sr of marine carbonates and (c) the δ18O signature of igneous zircons. The progressive emergence of the continents as shown by our models from the late-Archean onward had major implications for the Earth's environment and for the evolution of early life. It contributed to the oxygenation of the atmosphere as it would result in (a) the reduction of the proportion of submarine LIPs, a major sink of oxygen [Kump and Barley, Nature 448 (2007)], (b) an increase in the weathering of emerged mafic material, a major sink of carbon dioxide, and (c) an increase of the release of nutrients such as iron and phosphorus into the oceans, increasing the activity of oxygen-producing cyanobacteria.
- by Nicolas Flament
- •
The secular cooling of the mantle and of the continental lithosphere trigger an increase in the area of emerged land. The corollary increase in weathering and erosion processes has major consequences for the evolution of Earth’s external... more
The secular cooling of the mantle and of the continental lithosphere trigger an increase in the area of emerged land. The corollary increase in weathering and erosion processes has major consequences for the evolution of Earth’s external envelopes.
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.
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.
- by Nicolas Flament
- •
In the long term, the total amount of emerged land at Earth’s surface and the depth of mid‐oceanic ridges are controlled by the growth of the continental crust and by the secular cooling of Earth’s mantle that implies changes in the... more
In the long term, the total amount of emerged land at Earth’s surface and the depth of mid‐oceanic ridges are controlled by the growth of the continental crust and by the secular cooling of Earth’s mantle that implies changes in the isostatic balance between continents and oceans. The evolution of the area of emerged land and of oceanic bathymetry are of fundamental importance to the geochemical coupling of mantle, continental crust, ocean and atmosphere.
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 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.
- by Nicolas Flament
- •
Potentially higher sea levels do not fully explain why subaqueous flood volcanism on top of continental crust was common throughout the Archean. One possible way of maintaining basaltic piles several kilometers thick below sea level is... more
Potentially higher sea levels do not fully explain why subaqueous flood volcanism on top of continental crust was common throughout the Archean. One possible way of maintaining basaltic piles several kilometers thick below sea level is via gravity-driven lower crustal flow of hot continental crust. In this paper, we run numerical experiments to determine the relaxation time of a topographic load emplaced on continental crust as a function of Moho temperature. We use a visco-plastic model in which the viscosity depends on temperature. We apply the results of these models to the Fortescue Group, in the Pilbara Craton. Data regarding the eruption time and stratigraphic thickness of the Maddina Formation basalts, together with sedimentary structures pointing to shallow initial and final depth of emplacement, constrain the relaxation time for this section of the Fortescue Group continental flood basalts to between < 3 Myr. According to our modeling results this translates to a Moho temperature > 700ºC for continental crust 40 km thick (> 660ºC for continental crust 30 km thick). This is significantly higher than the present-day Moho temperature range of 400 to 500ºC for Archean cratons, suggesting that the secular cooling of the studied continental lithosphere was > 150ºC over 2.72 Ga. The observation that many Archean continental flood basalts failed to emerge despite their thickness suggests that gravity-driven lower crustal flow of hot continental crust was an efficient process that maintained continents below sea level throughout the Archean.
- by Nicolas Flament
- •
Large basaltic provinces up to 15 km thick are common in Archean cratons. Despite significantly contributing to the thickening of the continental crust, many Archean flood basalts that show continental contamination remained below sea... more
Large basaltic provinces up to 15 km thick are common in Archean cratons. Despite significantly contributing to
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.
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.
- by Nicolas Flament
- •
The southwest Pacific is a frontier region for petroleum exploration. A complex series of subduction and back-arc basin forming episodes characterises the late Cretaceous to presentday evolution of the region. Controversial aspects of the... more
The southwest Pacific is a frontier region for petroleum exploration. A complex series of subduction and back-arc basin forming episodes characterises the late Cretaceous to presentday evolution of the region. Controversial aspects of the regional tectonic history include the presence or lack of subduction between 83 and 43 Ma, the polarity of subduction, the timing of back-arc basin formation, and whether or not Pacific plate motion can be tied to the motion of Australia via spreading in the Tasman Sea during the late Cretaceous-early Cenozoic. A combination of tectonic and geodynamic models has previously been used to propose that there was no subduction to the east of Australia between 83 and 43 Ma, with the Lord Howe Rise being part of the Pacific plate during this time period, contrary to alternative plate models that include a plate boundary to the east of the Lord Howe Rise. Determining which plate circuit to use for Pacific motion is critical for producing regional reconstructions for the southwest Pacific, and addressing specific problems on the chronology of tectonic and basin-forming events. To help resolve these long-standing disputes we test a recently published plate reconstruction in global mantle flow models with imposed plate motions. We use the 3D spherical mantle-convection code CitcomS coupled to the plate reconstruction software GPlates, with plate motions since 200 Ma and evolving plate boundaries imposed. We use seismic mantle tomography models to test the forward-modelled subduction history in the region. The reconstruction that we test incorporates east-dipping subduction from 85-45 Ma along the western margin of the Loyalty-Three Kings Ridge to close the South Loyalty Basin.
Flament, N., Gurnis, M. and Müller, R. D. The topography of Earth is primarily controlled by lateral differences in the density structure of the crust and lithosphere. In addition to this isostatic topography, flow in the mantle... more
Flament, N., Gurnis, M. and Müller, R. D.
The topography of Earth is primarily controlled by lateral differences in the density structure of the crust and lithosphere. In addition to this isostatic topography, flow in the mantle induces deformation of its surface leading to dynamic topography. This transient deformation evolves over tens of millions of years, occurs at long wavelength, and is relatively small (<2 km) in amplitude. Here, we review the observational constraints and modeling approaches used to understand the amplitude, spatial pattern, and time dependence of dynamic topography. The best constraint on the present-day dynamic topography induced by sublithospheric mantle flow is likely the residual bathymetry calculated by removing the isostatic effect of oceanic lithospheric structure from observed bathymetry. Increasing knowledge of the thermal and chemical structure of the lithosphere is important to better constrain present-day mantle flow and dynamic topography. Nevertheless, at long wavelengths (>5000 km), we show that there is good agreement between published residual topography fields, including the one described here, and present-day dynamic topography predicted from mantle flow models, including a new one. Residual and predicted fields show peak-to-peak amplitudes of roughly ±2 km and a dominant degree two pattern with high values for the Pacific Ocean, southern Africa, and the North Atlantic and low values for South America, western North America, and Eurasia. The flooding of continental interiors has long been known to require both larger amplitudes and to be temporally phase-shifted compared with inferred eustatic changes. Such long-wavelength inferred vertical motions have been attributed to dynamic topography. An important consequence of dynamic topography is that long-term global sea-level change cannot be estimated at a single passive margin. As a case study, we compare the results of three published models and of our model to the subsidence history of well COST-B2 offshore New Jersey. The <400 ± 45 m amount of anomalous subsidence of this well since 85 Ma is best explained by models that predict dynamic subsidence of the New Jersey margin during that period. Explicitly including the lithosphere in future global mantle flow models should not only facilitate such comparisons between model results and data, but also further constrain the nature of the coupling between the mantle and the lithosphere.
The topography of Earth is primarily controlled by lateral differences in the density structure of the crust and lithosphere. In addition to this isostatic topography, flow in the mantle induces deformation of its surface leading to dynamic topography. This transient deformation evolves over tens of millions of years, occurs at long wavelength, and is relatively small (<2 km) in amplitude. Here, we review the observational constraints and modeling approaches used to understand the amplitude, spatial pattern, and time dependence of dynamic topography. The best constraint on the present-day dynamic topography induced by sublithospheric mantle flow is likely the residual bathymetry calculated by removing the isostatic effect of oceanic lithospheric structure from observed bathymetry. Increasing knowledge of the thermal and chemical structure of the lithosphere is important to better constrain present-day mantle flow and dynamic topography. Nevertheless, at long wavelengths (>5000 km), we show that there is good agreement between published residual topography fields, including the one described here, and present-day dynamic topography predicted from mantle flow models, including a new one. Residual and predicted fields show peak-to-peak amplitudes of roughly ±2 km and a dominant degree two pattern with high values for the Pacific Ocean, southern Africa, and the North Atlantic and low values for South America, western North America, and Eurasia. The flooding of continental interiors has long been known to require both larger amplitudes and to be temporally phase-shifted compared with inferred eustatic changes. Such long-wavelength inferred vertical motions have been attributed to dynamic topography. An important consequence of dynamic topography is that long-term global sea-level change cannot be estimated at a single passive margin. As a case study, we compare the results of three published models and of our model to the subsidence history of well COST-B2 offshore New Jersey. The <400 ± 45 m amount of anomalous subsidence of this well since 85 Ma is best explained by models that predict dynamic subsidence of the New Jersey margin during that period. Explicitly including the lithosphere in future global mantle flow models should not only facilitate such comparisons between model results and data, but also further constrain the nature of the coupling between the mantle and the lithosphere.
The southwest Pacific is a frontier region for petroleum exploration. A complex series of subduction and back-arc basin forming episodes characterises the late Cretaceous to presentday evolution of the region. Controversial aspects of... more
The southwest Pacific is a frontier region for petroleum
exploration. A complex series of subduction and back-arc basin
forming episodes characterises the late Cretaceous to presentday
evolution of the region. Controversial aspects of the regional
tectonic history include the presence or lack of subduction
between 83 and 43 Ma, the polarity of subduction, the timing of
back-arc basin formation, and whether or not Pacific plate motion
can be tied to the motion of Australia via spreading in the Tasman
Sea during the late Cretaceous-early Cenozoic. A combination
of tectonic and geodynamic models has previously been used
to propose that there was no subduction to the east of Australia
between 83 and 43 Ma, with the Lord Howe Rise being part of
the Pacific plate during this time period, contrary to alternative
plate models that include a plate boundary to the east of the Lord
Howe Rise during this time period. Determining which plate
circuit to use for Pacific motion is critical for producing regional
reconstructions for the southwest Pacific, and addressing specific
problems on the chronology of tectonic and basin-forming events.
To help resolve these long-standing disputes we test a recently
published plate reconstruction in global mantle flow models with
imposed plate motions. We use the 3D spherical mantle-convection
code CitcomS coupled to the plate reconstruction software
GPlates, with plate motions since 200 Ma and evolving plate
boundaries imposed. We use seismic mantle tomography models
to test the forward-modelled subduction history in the region. The
reconstruction that we test incorporates east-dipping subduction
from 85-45 Ma along the western margin of the Loyalty-Three
Kings Ridge to close the South Loyalty Basin. Following collision
of the Loyalty Ridge with New Caledonia, west-dipping Tonga-
Kermadec subduction initiates along the eastern margin of the
Loyalty Ridge and opens the North Loyalty, South Fiji, Norfolk
and Lau basins. Contemporaneous with west-dipping Tonga-
Kermadec subduction, there is short-lived east-dipping subduction
between 36-18 Ma along the western margin of the Loyalty-Three
Kings ridge. We find that subduction to the east of Australia during
the period 85-45 Ma is necessary to account for the distribution of
lower mantle slab material that is imaged by seismic tomography
beneath New Zealand. Pacific plate motion therefore cannot be
directly tied to Australia via spreading in the Tasman Sea as a
convergent margin must have existed to the east of the Lord Howe
Rise at this time. We suggest that adopting a plate circuit that ties
Pacific plate motion directly to the Lord Howe Rise should be
avoided for this period. An unexpected result is that the regionallower mantle structure provides strong evidence for a long-lived
intra-oceanic subduction zone, located to the northeast of Australia
at about 10-25°S and 170°E-170°W, that was active during at least
the late Cretaceous. We propose that this subduction zone was
located outboard of the plate boundary that separated the palaeo-
Pacific ocean from the Tethys, and we speculate that arc remnants
may be preserved in southeast Asia.
exploration. A complex series of subduction and back-arc basin
forming episodes characterises the late Cretaceous to presentday
evolution of the region. Controversial aspects of the regional
tectonic history include the presence or lack of subduction
between 83 and 43 Ma, the polarity of subduction, the timing of
back-arc basin formation, and whether or not Pacific plate motion
can be tied to the motion of Australia via spreading in the Tasman
Sea during the late Cretaceous-early Cenozoic. A combination
of tectonic and geodynamic models has previously been used
to propose that there was no subduction to the east of Australia
between 83 and 43 Ma, with the Lord Howe Rise being part of
the Pacific plate during this time period, contrary to alternative
plate models that include a plate boundary to the east of the Lord
Howe Rise during this time period. Determining which plate
circuit to use for Pacific motion is critical for producing regional
reconstructions for the southwest Pacific, and addressing specific
problems on the chronology of tectonic and basin-forming events.
To help resolve these long-standing disputes we test a recently
published plate reconstruction in global mantle flow models with
imposed plate motions. We use the 3D spherical mantle-convection
code CitcomS coupled to the plate reconstruction software
GPlates, with plate motions since 200 Ma and evolving plate
boundaries imposed. We use seismic mantle tomography models
to test the forward-modelled subduction history in the region. The
reconstruction that we test incorporates east-dipping subduction
from 85-45 Ma along the western margin of the Loyalty-Three
Kings Ridge to close the South Loyalty Basin. Following collision
of the Loyalty Ridge with New Caledonia, west-dipping Tonga-
Kermadec subduction initiates along the eastern margin of the
Loyalty Ridge and opens the North Loyalty, South Fiji, Norfolk
and Lau basins. Contemporaneous with west-dipping Tonga-
Kermadec subduction, there is short-lived east-dipping subduction
between 36-18 Ma along the western margin of the Loyalty-Three
Kings ridge. We find that subduction to the east of Australia during
the period 85-45 Ma is necessary to account for the distribution of
lower mantle slab material that is imaged by seismic tomography
beneath New Zealand. Pacific plate motion therefore cannot be
directly tied to Australia via spreading in the Tasman Sea as a
convergent margin must have existed to the east of the Lord Howe
Rise at this time. We suggest that adopting a plate circuit that ties
Pacific plate motion directly to the Lord Howe Rise should be
avoided for this period. An unexpected result is that the regionallower mantle structure provides strong evidence for a long-lived
intra-oceanic subduction zone, located to the northeast of Australia
at about 10-25°S and 170°E-170°W, that was active during at least
the late Cretaceous. We propose that this subduction zone was
located outboard of the plate boundary that separated the palaeo-
Pacific ocean from the Tethys, and we speculate that arc remnants
may be preserved in southeast Asia.
- by Nicolas Flament and +1
- •
The easternmost Coral Sea region is an underexplored area at the northeasternmost corner of the Australian plate. Situated between the Mellish Rise, southern Solomon Islands, northern Vanuatu and New Caledonia, it represents one of the... more
The easternmost Coral Sea region is an underexplored area
at the northeasternmost corner of the Australian plate. Situated
between the Mellish Rise, southern Solomon Islands, northern
Vanuatu and New Caledonia, it represents one of the most
dynamic and tectonically complex submarine regions of the world.
Interactions between the Pacific and Australian plate boundaries
have resulted in an intricate assemblage of deep oceanic basins
and ridges, continental fragments and volcanic products; yet
there is currently no clear conceptual framework to describe
their formation. Due to the paucity of geological and geophysical
data from the area to constrain plate tectonic models, a novel
approach has been developed whereby the history of subduction
based on a plate kinematic model is mapped to present-day
seismic tomography models. A plate kinematic model, which
includes a self-consistent mosaic of evolving plate boundaries
through time is used to compute plate velocity fields and palaeooceanic
age grids for each plate in 1 million year intervals.
Forward geodynamic models, with imposed surface plate velocity
constraints are computed using the 3D spherical finite element
convection code CitcomS. A comparison between the present-day
mantle temperature field predicted by these geodynamic models
with seismic tomography suggests that the kinematic model for
the subduction history in the eastern Coral Sea works well for
the latest Cenozoic but fails to predict seismically fast material
in the lower mantle (indicative of cold, subducted material)
imaged in seismic tomography models. This implies that the
location and nature of the plate boundaries in the eastern Coral
Sea used in these models requires further refinement. A quantified
tectonic framework and subduction history of the region will
assist in assessing hydrocarbon and mineral resource potential of
northeastern Australia and Australia’s Pacific island neighbours,
the eastward extent of Australian continental lithosphere and will
help place further constrains on the subsidence and uplift history
of Australia’s eastern sedimentary basins and carbonate-capped
plateaus.
at the northeasternmost corner of the Australian plate. Situated
between the Mellish Rise, southern Solomon Islands, northern
Vanuatu and New Caledonia, it represents one of the most
dynamic and tectonically complex submarine regions of the world.
Interactions between the Pacific and Australian plate boundaries
have resulted in an intricate assemblage of deep oceanic basins
and ridges, continental fragments and volcanic products; yet
there is currently no clear conceptual framework to describe
their formation. Due to the paucity of geological and geophysical
data from the area to constrain plate tectonic models, a novel
approach has been developed whereby the history of subduction
based on a plate kinematic model is mapped to present-day
seismic tomography models. A plate kinematic model, which
includes a self-consistent mosaic of evolving plate boundaries
through time is used to compute plate velocity fields and palaeooceanic
age grids for each plate in 1 million year intervals.
Forward geodynamic models, with imposed surface plate velocity
constraints are computed using the 3D spherical finite element
convection code CitcomS. A comparison between the present-day
mantle temperature field predicted by these geodynamic models
with seismic tomography suggests that the kinematic model for
the subduction history in the eastern Coral Sea works well for
the latest Cenozoic but fails to predict seismically fast material
in the lower mantle (indicative of cold, subducted material)
imaged in seismic tomography models. This implies that the
location and nature of the plate boundaries in the eastern Coral
Sea used in these models requires further refinement. A quantified
tectonic framework and subduction history of the region will
assist in assessing hydrocarbon and mineral resource potential of
northeastern Australia and Australia’s Pacific island neighbours,
the eastward extent of Australian continental lithosphere and will
help place further constrains on the subsidence and uplift history
of Australia’s eastern sedimentary basins and carbonate-capped
plateaus.
- by Nicolas Flament
- •