High-resolution U–Pb(ID-TIMS,baddeleyite)ages are presented for mafic dykes from selected swarms in two important Amazonian regions:the Carajás Province in the east,and the Rio Apa block in the southwest–areas
At the end of the Cretaceous period,66 million years ago,the 7−19 km diameter Chicxulub asteroid hit the Yucatan Peninsula in Mexico,triggering global catastrophic environmental changes and mass extinction.The contrib...At the end of the Cretaceous period,66 million years ago,the 7−19 km diameter Chicxulub asteroid hit the Yucatan Peninsula in Mexico,triggering global catastrophic environmental changes and mass extinction.The contributions of this event towards changes in plate and plume geodynamics are not fully understood.Here we present a range of geological observations indicating that the impact marked a tectonic turning point in the behavior of mantle plume and plate motion in the Caribbean region and worldwide.At a regional scale,the impact coincides with the termination of seafloor spreading in the Caribbean Ridge.Shortly after the Cretaceous-Paleogene transition,magmatism associated with the Caribbean Large Igneous Province waned,and intensive Paleogene volcanism was initiated.These events happened synchronously with anomalously high mid-ocean ridge magmatism worldwide and an abrupt change in the relative motion of the South American and North American tectonic plates.The evidence for such abrupt changes in plate kinematics and plume behavior raises the possibility that the Chicxulub impact triggered a chain of effects that modified melt reservoirs,subducting plates,mantle flows,and lithospheric deformation.To explain how an asteroid impact could modify tectonic behavior,we discuss two end-member mechanisms:quasi-static and dynamic triggering mechanisms.We designed a numerical model to investigate the strain field and the relative plate motion before and after the impact.The model predicts an enhanced deformation associated with the impact,which surficially tapers off∼500 km from the crater.The impact modifies the subjacent mantle flow field,contributing to long-term mantle-driven dynamic changes.Additionally,deformation associated with seismic effects may have contributed to far-field effects and global changes.We conclude that large asteroid impacts,such as the Chicxulub collision,could trigger cascading effects sufficient to disrupt and significantly modify plate geodynamics.展开更多
The recent plethora of GPS observations compensates for the 20-year-old lack in vertical displacement data for the Guanzhong region. The 2001—2007 three-dimensional（3D） crustal deformation data suggest regional mov...The recent plethora of GPS observations compensates for the 20-year-old lack in vertical displacement data for the Guanzhong region. The 2001—2007 three-dimensional（3D） crustal deformation data suggest regional movement with a horizontal velocity of 3—7 mm/a,predominantly from SSE in the west to SE in the east, and vertical inherited movement with velocity of -7 mm/a to 4 mm/a. After the Wenchuan earthquake, the GPS data suggest that the effect of the earthquake on the regional deformation is greater in the west than the east.The horizontal displacement increased during 2007—2008; however, the reverse was observed in 2008—2009. The vertical displacement in the western part of the region increased in 2008 and has been gradually returning to normal since 2009; however, in the eastern part,the effect of the earthquake remains.展开更多
The long-term continuous gravity observations obtained by the superconducting gravimeters(SG)at seven globally-distributed stations are comprehensively analyzed.After removing the signals related to the Earth's ti...The long-term continuous gravity observations obtained by the superconducting gravimeters(SG)at seven globally-distributed stations are comprehensively analyzed.After removing the signals related to the Earth's tides and variations in the Earth's rotation,the gravity residuals are used to describe the seasonal fluctuations in gravity field.Meanwhile,the gravity changes due to the air pressure loading are theoretically modeled from the measurements of the local air pressure,and those due to land water and nontidal ocean loading are also calculated according to the corresponding numerical models.The numerical results show that the gravity changes due to both the air pressure and land water loading are as large as 100×10-9 m s-2 in magnitude,and about 10×10-9 m s-2 for those due to the nontidal ocean loading in the coastal area.On the other hand,the monthly-averaged gravity variations over the area surrounding the stations are derived from the spherical harmonic coefficients of the GRACE-recovered gravity fields,by using Gaussian smoothing technique in which the radius is set to be 600 km.Com-pared the land water induced gravity variations,the SG observations after removal of tides,polar mo-tion effects,air pressure and nontidal ocean loading effects and the GRACE-derived gravity variations with each other,it is inferred that both the ground-and space-based gravity observations can effec-tively detect the seasonal gravity variations with a magnitude of 100×10-9 m s-2 induced by the land water loading.This implies that high precision gravimetry is an effective technique to validate the re-liabilities of the hydrological models.展开更多
文摘High-resolution U–Pb(ID-TIMS,baddeleyite)ages are presented for mafic dykes from selected swarms in two important Amazonian regions:the Carajás Province in the east,and the Rio Apa block in the southwest–areas
文摘At the end of the Cretaceous period,66 million years ago,the 7−19 km diameter Chicxulub asteroid hit the Yucatan Peninsula in Mexico,triggering global catastrophic environmental changes and mass extinction.The contributions of this event towards changes in plate and plume geodynamics are not fully understood.Here we present a range of geological observations indicating that the impact marked a tectonic turning point in the behavior of mantle plume and plate motion in the Caribbean region and worldwide.At a regional scale,the impact coincides with the termination of seafloor spreading in the Caribbean Ridge.Shortly after the Cretaceous-Paleogene transition,magmatism associated with the Caribbean Large Igneous Province waned,and intensive Paleogene volcanism was initiated.These events happened synchronously with anomalously high mid-ocean ridge magmatism worldwide and an abrupt change in the relative motion of the South American and North American tectonic plates.The evidence for such abrupt changes in plate kinematics and plume behavior raises the possibility that the Chicxulub impact triggered a chain of effects that modified melt reservoirs,subducting plates,mantle flows,and lithospheric deformation.To explain how an asteroid impact could modify tectonic behavior,we discuss two end-member mechanisms:quasi-static and dynamic triggering mechanisms.We designed a numerical model to investigate the strain field and the relative plate motion before and after the impact.The model predicts an enhanced deformation associated with the impact,which surficially tapers off∼500 km from the crater.The impact modifies the subjacent mantle flow field,contributing to long-term mantle-driven dynamic changes.Additionally,deformation associated with seismic effects may have contributed to far-field effects and global changes.We conclude that large asteroid impacts,such as the Chicxulub collision,could trigger cascading effects sufficient to disrupt and significantly modify plate geodynamics.
基金supported by the Shanxi Science and Technology Research and Development program(2012SF2-17)National Nature Science Foundation of China(41174083)
文摘The recent plethora of GPS observations compensates for the 20-year-old lack in vertical displacement data for the Guanzhong region. The 2001—2007 three-dimensional（3D） crustal deformation data suggest regional movement with a horizontal velocity of 3—7 mm/a,predominantly from SSE in the west to SE in the east, and vertical inherited movement with velocity of -7 mm/a to 4 mm/a. After the Wenchuan earthquake, the GPS data suggest that the effect of the earthquake on the regional deformation is greater in the west than the east.The horizontal displacement increased during 2007—2008; however, the reverse was observed in 2008—2009. The vertical displacement in the western part of the region increased in 2008 and has been gradually returning to normal since 2009; however, in the eastern part,the effect of the earthquake remains.
基金Supported by Knowledge Innovation of Chinese Academy of Sciences(Grant No.KZCX2-YW-133)National Natural Science Foundation of China(Grant Nos.40730316 and 40574034)Frontier Domain Item of Chinese Academy of Sciences
文摘The long-term continuous gravity observations obtained by the superconducting gravimeters(SG)at seven globally-distributed stations are comprehensively analyzed.After removing the signals related to the Earth's tides and variations in the Earth's rotation,the gravity residuals are used to describe the seasonal fluctuations in gravity field.Meanwhile,the gravity changes due to the air pressure loading are theoretically modeled from the measurements of the local air pressure,and those due to land water and nontidal ocean loading are also calculated according to the corresponding numerical models.The numerical results show that the gravity changes due to both the air pressure and land water loading are as large as 100×10-9 m s-2 in magnitude,and about 10×10-9 m s-2 for those due to the nontidal ocean loading in the coastal area.On the other hand,the monthly-averaged gravity variations over the area surrounding the stations are derived from the spherical harmonic coefficients of the GRACE-recovered gravity fields,by using Gaussian smoothing technique in which the radius is set to be 600 km.Com-pared the land water induced gravity variations,the SG observations after removal of tides,polar mo-tion effects,air pressure and nontidal ocean loading effects and the GRACE-derived gravity variations with each other,it is inferred that both the ground-and space-based gravity observations can effec-tively detect the seasonal gravity variations with a magnitude of 100×10-9 m s-2 induced by the land water loading.This implies that high precision gravimetry is an effective technique to validate the re-liabilities of the hydrological models.
