Thermal, rheological and kinematic conditions for channelized lower crustal flow in a threshold example

A. R.A. Aitken, R. Quentin de Gromard, A. Joly, H. M. Howard, R. H. Smithies

Research output: Contribution to journalArticle

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Abstract

Lower crustal flow zones occur in large and hot orogens and rifts, where they occur in association with large areas possessing high gravitational potential energy (GPE) and low lower crust viscosity. Lower crustal flow zones are also known from regions where neither the rheological nor GPE conditions are sufficiently well developed for widespread flow to occur. For these examples, the conditions required to form crustal flow zones are less well defined. One such case occurs within the ca. 600–530 Ma Petermann Orogeny in central Australia. This work investigates the conditions under which this flow zone developed, considering differences with the adjacent regions where flow is not observed. A transect of crustal structure in the central Petermann Orogen is developed that takes into account geological and geophysical data, including time-constrained pressure and temperature estimates for the Petermann Orogeny. The deformation of this region is reconstructed, showing that lower crustal flow was driven by high amplitude crustal-scale folding. The folding extruded the lower crust towards the foreland, causing crustal thickening and buoyant uplift of the orogenic core. Channelized lower crustal flow is not known from either the eastern or western parts of the orogen, and a comparison with these regions suggests three main conditions are required: Firstly, the lower crust must be sufficiently hot and volatile-rich to allow melt-weakening. Secondly, crustal rheology must allow ductile deformation of the mid to lower crust without high-strength layers. Finally, a high degree of lateral confinement is required to form pressure-gradients capable of driving flow. These three conditions were met only in the central Petermann Orogen, and not in the east or the west. This example of a lower crustal flow zone illustrates the combined influence of thermal, rheological and kinematic threshold conditions on the initiation and development of channelized lower crustal flow in orogens.

Original languageEnglish
Pages (from-to)63-78
Number of pages16
JournalTectonophysics
Volume753
DOIs
Publication statusPublished - 20 Feb 2019

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kinematics
thresholds
lower crust
crusts
potential energy
orogeny
folding
gravitational fields
ductile deformation
crustal thickening
crustal structure
high strength
rheology
pressure gradients
pressure gradient
viscosity
transect
uplift
melt
estimates

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Aitken, A. R.A. ; Quentin de Gromard, R. ; Joly, A. ; Howard, H. M. ; Smithies, R. H. / Thermal, rheological and kinematic conditions for channelized lower crustal flow in a threshold example. In: Tectonophysics. 2019 ; Vol. 753. pp. 63-78.
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Thermal, rheological and kinematic conditions for channelized lower crustal flow in a threshold example. / Aitken, A. R.A.; Quentin de Gromard, R.; Joly, A.; Howard, H. M.; Smithies, R. H.

In: Tectonophysics, Vol. 753, 20.02.2019, p. 63-78.

Research output: Contribution to journalArticle

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AU - Joly, A.

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AU - Smithies, R. H.

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