Upper mantle conditions in the North Atlantic Ocean and their implications for continental break-up
File(s)
Author(s)
Zalai, Zsófia
Type
Thesis
Abstract
Mantle conditions during the opening of the North Atlantic Ocean and specifically the presence or otherwise of a deep mantle plume have been much debated. Current models fall into
two groups: plume impingement and plate-driven models. The Plume model associates
the arrival of the Icelandic plume with continental break-up of the North Atlantic and
the observed excess magmatism is associated with passive upwelling and elevated mantle
potential temperatures. However, the Plate model associates this excess magmatism with
increased mantle fertility due to inherited lithospheric structure, small-scale convection
induced by sub-lithospheric topography and/or extensive warming of the mantle beneath
a supercontinent. I examine the spatial and temporal variation of upper mantle conditions
at the time of continental break-up using an inventory of 42 published seismic refraction
velocity-depth profiles acquired between the Charlie Gibbs and the East Greenland Fracture
Zones. I make use of the Hc-Vp method to estimate mantle potential temperature and
the ratio of active to passive upwelling by extracting igneous crustal thickness, Hc, and its
mean p-wave velocity, Vp. Finally, I compare the spatial and temporal patterns obtained
to those predicted by previously proposed models of mantle conditions around the time
of break-up. My results show more than 300°C variation in mantle potential temperature
across the study area. The hottest areas are the Northeast Greenland margin and the
Greenland-Iceland-Faroes Ridge, while the coldest are located near the extinct spreading
centre, Aegir Ridge and offshore the Hatton Bank. Mantle potential temperatures
are generally high shortly after break-up or at the time of break-up and they decrease
with time, reaching steady-state ~10 Ma after break-up with temperatures around normal
mantle temperatures of 1300°C. A few places are characterised by active upwelling
including the Greenland-Iceland-Faroes Ridge and the Voring Spur. Elsewhere passive
upwelling dominates. I model the observed temperature anomaly with an axisymmetric
synthetic thermal anomaly to determine whether the observed pattern can be reproduced
by a circular mantle plume. Parameters of the thermal anomaly, a varying peak temperature
amplitude between 1350 and 1600C, wavelength (σ = 400 km), were chosen to best
match observations. I apply a grid search method to locate the centre of the anomaly for
every 5 million years from the plate reconstructed positions of mantle potential temperature
observations. These locations reveal that the Iceland plume traversed Greenland
in 15 million years, being located beneath West Greenland at 55 Ma and arriving at the
Northeast Greenland margin by 40 Ma. The
fluctuation in plume centre temperature
based on the inversion results indicates the effect of continental insulation, but that alone
is unable to account for the more than 250°C excess mantle potential temperature. Hence
both a mantle plume and continental insulation could have played a role in the break-up
of the North Atlantic Ocean.
two groups: plume impingement and plate-driven models. The Plume model associates
the arrival of the Icelandic plume with continental break-up of the North Atlantic and
the observed excess magmatism is associated with passive upwelling and elevated mantle
potential temperatures. However, the Plate model associates this excess magmatism with
increased mantle fertility due to inherited lithospheric structure, small-scale convection
induced by sub-lithospheric topography and/or extensive warming of the mantle beneath
a supercontinent. I examine the spatial and temporal variation of upper mantle conditions
at the time of continental break-up using an inventory of 42 published seismic refraction
velocity-depth profiles acquired between the Charlie Gibbs and the East Greenland Fracture
Zones. I make use of the Hc-Vp method to estimate mantle potential temperature and
the ratio of active to passive upwelling by extracting igneous crustal thickness, Hc, and its
mean p-wave velocity, Vp. Finally, I compare the spatial and temporal patterns obtained
to those predicted by previously proposed models of mantle conditions around the time
of break-up. My results show more than 300°C variation in mantle potential temperature
across the study area. The hottest areas are the Northeast Greenland margin and the
Greenland-Iceland-Faroes Ridge, while the coldest are located near the extinct spreading
centre, Aegir Ridge and offshore the Hatton Bank. Mantle potential temperatures
are generally high shortly after break-up or at the time of break-up and they decrease
with time, reaching steady-state ~10 Ma after break-up with temperatures around normal
mantle temperatures of 1300°C. A few places are characterised by active upwelling
including the Greenland-Iceland-Faroes Ridge and the Voring Spur. Elsewhere passive
upwelling dominates. I model the observed temperature anomaly with an axisymmetric
synthetic thermal anomaly to determine whether the observed pattern can be reproduced
by a circular mantle plume. Parameters of the thermal anomaly, a varying peak temperature
amplitude between 1350 and 1600C, wavelength (σ = 400 km), were chosen to best
match observations. I apply a grid search method to locate the centre of the anomaly for
every 5 million years from the plate reconstructed positions of mantle potential temperature
observations. These locations reveal that the Iceland plume traversed Greenland
in 15 million years, being located beneath West Greenland at 55 Ma and arriving at the
Northeast Greenland margin by 40 Ma. The
fluctuation in plume centre temperature
based on the inversion results indicates the effect of continental insulation, but that alone
is unable to account for the more than 250°C excess mantle potential temperature. Hence
both a mantle plume and continental insulation could have played a role in the break-up
of the North Atlantic Ocean.
Version
Open Access
Date Issued
2021-07
Date Awarded
2021-12
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Collier, Jennifer
Roberts, Gareth
Lonergan, Lidia
Publisher Department
Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Masters
Qualification Name
Master of Philosophy (MPhil)