Episodic kinematics in continental rifts modulated by changes in mantle melt fraction

Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor ‘spreading centres’ found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres1, b...

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Main Authors: Moore, James Daniel Paul, Smith, Euan, Stern, Tim, Lamb, Simon
Other Authors: Earth Observatory of Singapore
Format: Article
Language:English
Published: 2017
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Online Access:https://hdl.handle.net/10356/86884
http://hdl.handle.net/10220/44212
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spelling sg-ntu-dr.10356-868842020-09-26T21:28:41Z Episodic kinematics in continental rifts modulated by changes in mantle melt fraction Moore, James Daniel Paul Smith, Euan Stern, Tim Lamb, Simon Earth Observatory of Singapore Geodynamics Geophysics Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor ‘spreading centres’ found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres1, but direct observation of this process is difficult beneath the oceans. Continental rifts, however—which are also associated with mantle melt production—are amenable to detailed measurements of their short-term kinematics using geodetic techniques. Here we show that such data can provide evidence for an upwelling mantle flow, as well as information on the dimensions and timescale of mantle melting. For North Island, New Zealand, around ten years of campaign and continuous GPS measurements in the continental rift system known as the Taupo volcanic zone reveal that it is extending at a rate of 6–15 millimetres per year. However, a roughly 70-kilometre-long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence, and is flanked by regions of extension and uplift. These features fit a simple model that involves flexure of an elastic upper crust, which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15 kilometres. We propose that flexure is caused by melt-induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis, triggering a transient lower-crustal flow. A drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence, whereas melt accumulation reduces viscosity and allows uplift—processes that are also likely to occur in oceanic spreading centres. NRF (Natl Research Foundation, S’pore) Accepted version 2017-12-28T05:01:17Z 2019-12-06T16:30:54Z 2017-12-28T05:01:17Z 2019-12-06T16:30:54Z 2017 Journal Article Lamb, S., Moore, J. D. P., Smith, E., & Stern, T. (2017). Episodic kinematics in continental rifts modulated by changes in mantle melt fraction. Nature, 547, 84-88. 0028-0836 https://hdl.handle.net/10356/86884 http://hdl.handle.net/10220/44212 10.1038/nature22962 en Nature © 2017 Macmillan Publishers Limited, part of Springer Nature. This is the author created version of a work that has been peer reviewed and accepted for publication by Nature, Macmillan Publishers Limited, part of Springer Nature. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [http://dx.doi.org/10.1038/nature22962]. 36 p. application/pdf
institution Nanyang Technological University
building NTU Library
country Singapore
collection DR-NTU
language English
topic Geodynamics
Geophysics
spellingShingle Geodynamics
Geophysics
Moore, James Daniel Paul
Smith, Euan
Stern, Tim
Lamb, Simon
Episodic kinematics in continental rifts modulated by changes in mantle melt fraction
description Oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor ‘spreading centres’ found between diverging tectonic plates. Modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres1, but direct observation of this process is difficult beneath the oceans. Continental rifts, however—which are also associated with mantle melt production—are amenable to detailed measurements of their short-term kinematics using geodetic techniques. Here we show that such data can provide evidence for an upwelling mantle flow, as well as information on the dimensions and timescale of mantle melting. For North Island, New Zealand, around ten years of campaign and continuous GPS measurements in the continental rift system known as the Taupo volcanic zone reveal that it is extending at a rate of 6–15 millimetres per year. However, a roughly 70-kilometre-long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence, and is flanked by regions of extension and uplift. These features fit a simple model that involves flexure of an elastic upper crust, which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15 kilometres. We propose that flexure is caused by melt-induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis, triggering a transient lower-crustal flow. A drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence, whereas melt accumulation reduces viscosity and allows uplift—processes that are also likely to occur in oceanic spreading centres.
author2 Earth Observatory of Singapore
author_facet Earth Observatory of Singapore
Moore, James Daniel Paul
Smith, Euan
Stern, Tim
Lamb, Simon
format Article
author Moore, James Daniel Paul
Smith, Euan
Stern, Tim
Lamb, Simon
author_sort Moore, James Daniel Paul
title Episodic kinematics in continental rifts modulated by changes in mantle melt fraction
title_short Episodic kinematics in continental rifts modulated by changes in mantle melt fraction
title_full Episodic kinematics in continental rifts modulated by changes in mantle melt fraction
title_fullStr Episodic kinematics in continental rifts modulated by changes in mantle melt fraction
title_full_unstemmed Episodic kinematics in continental rifts modulated by changes in mantle melt fraction
title_sort episodic kinematics in continental rifts modulated by changes in mantle melt fraction
publishDate 2017
url https://hdl.handle.net/10356/86884
http://hdl.handle.net/10220/44212
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