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Nicolas Thebaud - One of the best experts on this subject based on the ideXlab platform.
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contribution of mantle plumes crustal thickening and greenstone blanketing to the 2 75 2 65ga global crisis
Precambrian Research, 2003Co-Authors: Pascal Philippot, Nicolas ThebaudAbstract:Abstract Assuming that the period 2.75–2.65 Ga corresponds to a single, but global, geodynamic event, we investigate—through numerical experiments—the mechanisms that could have led to the profound continental reworking that occurred at that time. Although the extent of the crisis at the Earth’s surface pledges in favour of the involvement of mantle plumes, our numerical experiments suggest that the Thermal impact of mantle plumes is unlikely to explain both the amplitude and timing of the Thermal Anomaly, as observed in the Superior Province (Canada) and the Yilgarn Craton (Australia). Similarly, moderate crustal thickening can not lead to significant reworking of the continental crust within the observed time constraint. Crustal thickening with a factor ≥1.5 is also unlikely because it is not consistent with the moderate metamorphic grade observed at the surface of many Archaean cratons. Burial of a radiogenic crust under a 10 km thick greenstone cover also falls short of explaining, not so much the amplitude and the extent, but the timing of the Thermal Anomaly. In contrast, the combination of the Thermal Anomaly related to the greenstone blanketing effect with the heat transfer from a plume head spreading at the top of the Thermal boundary layer can adequately explain the amplitude, the timing, and the extent of the 2.75–2.65 Ga crisis. Our favoured model involves a global rearrangement of convection cells in the deep mantle and formation of multiple mantle plumes. The greenstones emplaced at the surface and the plumes that spread in the Thermal boundary layer contributed to heat the crust from both above and below. This produced massive crustal partial melting that reached its climax ca. 40 Myr after the emplacement of the plumes and associated greenstone cover rocks. This led to gravitational instabilities in the crust, as dense greenstone cover rocks began to sink into the Thermally softened crust and granite domes rose in response. The extraction of heat-producing elements toward the upper part of the crust has contributed to the cooling and stabilisation of the cratons. This succession of events, which is not incompatible with plate-tectonic processes, may have profoundly changed the nature of the crust exposed at the surface and could explain the contrasting geochemical signatures of Archaean and post-Archaean shales.
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contribution of mantle plumes crustal thickening and greenstone blanketing to the 2 75 2 65ga global crisis
Precambrian Research, 2003Co-Authors: Pascal Philippot, Nicolas ThebaudAbstract:Abstract Assuming that the period 2.75–2.65 Ga corresponds to a single, but global, geodynamic event, we investigate—through numerical experiments—the mechanisms that could have led to the profound continental reworking that occurred at that time. Although the extent of the crisis at the Earth’s surface pledges in favour of the involvement of mantle plumes, our numerical experiments suggest that the Thermal impact of mantle plumes is unlikely to explain both the amplitude and timing of the Thermal Anomaly, as observed in the Superior Province (Canada) and the Yilgarn Craton (Australia). Similarly, moderate crustal thickening can not lead to significant reworking of the continental crust within the observed time constraint. Crustal thickening with a factor ≥1.5 is also unlikely because it is not consistent with the moderate metamorphic grade observed at the surface of many Archaean cratons. Burial of a radiogenic crust under a 10 km thick greenstone cover also falls short of explaining, not so much the amplitude and the extent, but the timing of the Thermal Anomaly. In contrast, the combination of the Thermal Anomaly related to the greenstone blanketing effect with the heat transfer from a plume head spreading at the top of the Thermal boundary layer can adequately explain the amplitude, the timing, and the extent of the 2.75–2.65 Ga crisis. Our favoured model involves a global rearrangement of convection cells in the deep mantle and formation of multiple mantle plumes. The greenstones emplaced at the surface and the plumes that spread in the Thermal boundary layer contributed to heat the crust from both above and below. This produced massive crustal partial melting that reached its climax ca. 40 Myr after the emplacement of the plumes and associated greenstone cover rocks. This led to gravitational instabilities in the crust, as dense greenstone cover rocks began to sink into the Thermally softened crust and granite domes rose in response. The extraction of heat-producing elements toward the upper part of the crust has contributed to the cooling and stabilisation of the cratons. This succession of events, which is not incompatible with plate-tectonic processes, may have profoundly changed the nature of the crust exposed at the surface and could explain the contrasting geochemical signatures of Archaean and post-Archaean shales.
Daniel T I Bayley - One of the best experts on this subject based on the ideXlab platform.
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coral bleaching impacts from back to back 2015 2016 Thermal anomalies in the remote central indian ocean
Coral Reefs, 2019Co-Authors: Catherine E I Head, Daniel T I Bayley, Gwilym Rowlands, Ronan Roche, David Tickler, Alex Rogers, Heather J KoldeweyAbstract:Studying scleractinian coral bleaching and recovery dynamics in remote, isolated reef systems offers an opportunity to examine impacts of global reef stressors in the absence of local human threats. Reefs in the Chagos Archipelago, central Indian Ocean, suffered severe bleaching and mortality in 2015 following a 7.5 maximum degree heating weeks (DHWs) Thermal Anomaly, causing a 60% coral cover decrease from 30% cover in 2012 to 12% in April 2016. Mortality was taxon specific, with Porites becoming the dominant coral genus post-bleaching because of an 86% decline in Acropora from 14 to 2% cover. Spatial heterogeneity in Acropora mortality across the Archipelago was significantly negatively correlated with variation in DHWs and with chlorophyll-a concentrations. In 2016, a 17.6 maximum DHWs Thermal Anomaly caused further damage, with 68% of remaining corals bleaching in May 2016, and coral cover further declining by 29% at Peros Banhos Atoll (northern Chagos Archipelago) from 14% in March 2016 to 10% in April 2017. We therefore document back-to-back coral bleaching and mortality events for two successive years in the remote central Indian Ocean. Our results indicate lower coral mortality in 2016 than 2015 despite a more severe Thermal Anomaly event in 2016. This could be caused by increased Thermal resistance and resilience within corals surviving the 2015 Thermal Anomaly; however, high bleaching prevalence in 2016 suggests there remained a high sensitivity to bleaching. Similar coral mortality and community change were seen in the Chagos Archipelago following the 1998 global bleaching event, from which recovery took 10 yr. This relatively rapid recovery suggests high reef resiliency and indicates that the Archipelago’s lack of local disturbances will increase the probability that the reefs will again recover over time. However, as the return time between Thermal Anomaly events becomes shorter, this ability to recover will become increasingly compromised.
Catherine E I Head - One of the best experts on this subject based on the ideXlab platform.
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coral bleaching impacts from back to back 2015 2016 Thermal anomalies in the remote central indian ocean
Coral Reefs, 2019Co-Authors: Catherine E I Head, Daniel T I Bayley, Gwilym Rowlands, Ronan Roche, David Tickler, Alex Rogers, Heather J KoldeweyAbstract:Studying scleractinian coral bleaching and recovery dynamics in remote, isolated reef systems offers an opportunity to examine impacts of global reef stressors in the absence of local human threats. Reefs in the Chagos Archipelago, central Indian Ocean, suffered severe bleaching and mortality in 2015 following a 7.5 maximum degree heating weeks (DHWs) Thermal Anomaly, causing a 60% coral cover decrease from 30% cover in 2012 to 12% in April 2016. Mortality was taxon specific, with Porites becoming the dominant coral genus post-bleaching because of an 86% decline in Acropora from 14 to 2% cover. Spatial heterogeneity in Acropora mortality across the Archipelago was significantly negatively correlated with variation in DHWs and with chlorophyll-a concentrations. In 2016, a 17.6 maximum DHWs Thermal Anomaly caused further damage, with 68% of remaining corals bleaching in May 2016, and coral cover further declining by 29% at Peros Banhos Atoll (northern Chagos Archipelago) from 14% in March 2016 to 10% in April 2017. We therefore document back-to-back coral bleaching and mortality events for two successive years in the remote central Indian Ocean. Our results indicate lower coral mortality in 2016 than 2015 despite a more severe Thermal Anomaly event in 2016. This could be caused by increased Thermal resistance and resilience within corals surviving the 2015 Thermal Anomaly; however, high bleaching prevalence in 2016 suggests there remained a high sensitivity to bleaching. Similar coral mortality and community change were seen in the Chagos Archipelago following the 1998 global bleaching event, from which recovery took 10 yr. This relatively rapid recovery suggests high reef resiliency and indicates that the Archipelago’s lack of local disturbances will increase the probability that the reefs will again recover over time. However, as the return time between Thermal Anomaly events becomes shorter, this ability to recover will become increasingly compromised.
Quan Shi - One of the best experts on this subject based on the ideXlab platform.
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low temperature heat capacity and standard molar enthalpy of formation of crystalline 2 pyridinealdoxime c6h6n2o
The Journal of Chemical Thermodynamics, 2007Co-Authors: Quan Shi, Zhicheng Tan, Bo Tong, Zhiheng Zhang, Julan ZengAbstract:Abstract The thermodynamic properties of 2-pyridinealdoxime were investigated through the thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Low-temperature heat capacity Cp,m of 2-pyridinealdoxime (C6H6N2O; CAS 873-69-8) was measured in the temperature range from (80 to 373) K with a high precision automated adiabatic calorimeter. No phase transition or Thermal Anomaly was observed in this range. The thermodynamic functions [HT − H298.15] and [ST − S298.15] were calculated in the range from (80 to 375) K. The constant-volume energy and standard molar enthalpy of combustion have been determined, Δ c U ( C 6 H 6 N 2 O,cr ) = Δ c H m ∘ (C6H6N2O, cr) = − (3297.11 ± 1.53) kJ · mol−1 (based on Δn being zero in reaction of the combustion), by means of a precision oxygen-bomb combustion calorimeter at T = (298.15 ± 0.001) K. The standard molar enthalpy of formation has been derived, Δ f H m ∘ (C6H6N2O, cr) = (78.56 ± 2.43) kJ · mol−1, from the standard molar enthalpy of combustion in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.
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heat capacity and standard molar enthalpy of formation of crystalline 2 6 dicarboxypyridine c7h5no4
The Journal of Chemical Thermodynamics, 2006Co-Authors: Quan Shi, Zhicheng Tan, Bo Tong, Lixian Sun, Zhiheng Zhang, Tao ZhangAbstract:Abstract Low-temperature heat capacity Cp,m of 2,6-dicarboxypyridine (C7H5NO4; CAS 499-83-2) was precisely measured in the temperature range from (80 to 378) K with a high precision automated adiabatic calorimeter. No phase transition or Thermal Anomaly was observed in this range. The thermodynamic functions [HT − H298.15] and [ST − S298.15] were calculated in the range from (80 to 378) K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined, Δ c H m ∘ ( C 7 H 5 NO 4 , cr ) = - ( 2741.41 ± 0.49 ) kJ · mol - 1 and Δ f H m ∘ ( C 7 H 5 NO 4 , cr ) = - ( 727.74 ± 1.50 ) kJ · mol - 1 , by means of a precision oxygen-bomb combustion calorimeter at T = 298.15 K. The thermodynamic properties of the compound were further investigated through differential scanning calorimeter (DSC) and the thermogravimetric (TG) analysis.
Pascal Philippot - One of the best experts on this subject based on the ideXlab platform.
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contribution of mantle plumes crustal thickening and greenstone blanketing to the 2 75 2 65ga global crisis
Precambrian Research, 2003Co-Authors: Pascal Philippot, Nicolas ThebaudAbstract:Abstract Assuming that the period 2.75–2.65 Ga corresponds to a single, but global, geodynamic event, we investigate—through numerical experiments—the mechanisms that could have led to the profound continental reworking that occurred at that time. Although the extent of the crisis at the Earth’s surface pledges in favour of the involvement of mantle plumes, our numerical experiments suggest that the Thermal impact of mantle plumes is unlikely to explain both the amplitude and timing of the Thermal Anomaly, as observed in the Superior Province (Canada) and the Yilgarn Craton (Australia). Similarly, moderate crustal thickening can not lead to significant reworking of the continental crust within the observed time constraint. Crustal thickening with a factor ≥1.5 is also unlikely because it is not consistent with the moderate metamorphic grade observed at the surface of many Archaean cratons. Burial of a radiogenic crust under a 10 km thick greenstone cover also falls short of explaining, not so much the amplitude and the extent, but the timing of the Thermal Anomaly. In contrast, the combination of the Thermal Anomaly related to the greenstone blanketing effect with the heat transfer from a plume head spreading at the top of the Thermal boundary layer can adequately explain the amplitude, the timing, and the extent of the 2.75–2.65 Ga crisis. Our favoured model involves a global rearrangement of convection cells in the deep mantle and formation of multiple mantle plumes. The greenstones emplaced at the surface and the plumes that spread in the Thermal boundary layer contributed to heat the crust from both above and below. This produced massive crustal partial melting that reached its climax ca. 40 Myr after the emplacement of the plumes and associated greenstone cover rocks. This led to gravitational instabilities in the crust, as dense greenstone cover rocks began to sink into the Thermally softened crust and granite domes rose in response. The extraction of heat-producing elements toward the upper part of the crust has contributed to the cooling and stabilisation of the cratons. This succession of events, which is not incompatible with plate-tectonic processes, may have profoundly changed the nature of the crust exposed at the surface and could explain the contrasting geochemical signatures of Archaean and post-Archaean shales.
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contribution of mantle plumes crustal thickening and greenstone blanketing to the 2 75 2 65ga global crisis
Precambrian Research, 2003Co-Authors: Pascal Philippot, Nicolas ThebaudAbstract:Abstract Assuming that the period 2.75–2.65 Ga corresponds to a single, but global, geodynamic event, we investigate—through numerical experiments—the mechanisms that could have led to the profound continental reworking that occurred at that time. Although the extent of the crisis at the Earth’s surface pledges in favour of the involvement of mantle plumes, our numerical experiments suggest that the Thermal impact of mantle plumes is unlikely to explain both the amplitude and timing of the Thermal Anomaly, as observed in the Superior Province (Canada) and the Yilgarn Craton (Australia). Similarly, moderate crustal thickening can not lead to significant reworking of the continental crust within the observed time constraint. Crustal thickening with a factor ≥1.5 is also unlikely because it is not consistent with the moderate metamorphic grade observed at the surface of many Archaean cratons. Burial of a radiogenic crust under a 10 km thick greenstone cover also falls short of explaining, not so much the amplitude and the extent, but the timing of the Thermal Anomaly. In contrast, the combination of the Thermal Anomaly related to the greenstone blanketing effect with the heat transfer from a plume head spreading at the top of the Thermal boundary layer can adequately explain the amplitude, the timing, and the extent of the 2.75–2.65 Ga crisis. Our favoured model involves a global rearrangement of convection cells in the deep mantle and formation of multiple mantle plumes. The greenstones emplaced at the surface and the plumes that spread in the Thermal boundary layer contributed to heat the crust from both above and below. This produced massive crustal partial melting that reached its climax ca. 40 Myr after the emplacement of the plumes and associated greenstone cover rocks. This led to gravitational instabilities in the crust, as dense greenstone cover rocks began to sink into the Thermally softened crust and granite domes rose in response. The extraction of heat-producing elements toward the upper part of the crust has contributed to the cooling and stabilisation of the cratons. This succession of events, which is not incompatible with plate-tectonic processes, may have profoundly changed the nature of the crust exposed at the surface and could explain the contrasting geochemical signatures of Archaean and post-Archaean shales.
