An interconnected network of core-forming melts produced by shear deformation

Bruhn, David; Groebner, N. J.; Kohlstedt, D. L.

doi:10.1038/35002558

Cited by 105 publications

(53 citation statements)

References 22 publications

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“…If the deformation becomes isovolumetric, the stable continuation of localized flow demands that the material inside the fault zone be weaker than that outside. It is clear, however, that even high-temperature shearing can be accompanied by some dilatancy, which may be crucial to explain the FAULT ZONE WEAKENING 3 ability of deep shear zones to transport fluids, both aqueous and melts (Bruhn et al 2000). Even at the very high pressures in the deeper parts of subduction zones (400-600km depth), localized deformation is indicated by the occurrence of earthquakes whose first-motion patterns indicate shear faulting.…”

Section: Regime Jmentioning

confidence: 99%

The nature and tectonic significance of fault-zone weakening: an introduction

Rutter

Holdsworth

Knipe

2001

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Fault zones control the location, architecture and evolution of a broad range of geological features, act as conduits for the focused migration of economically important fluids and, as most seismicity is associated with active faults, they also constitute one of the most important global geological hazards. In general, the repeated localization of displacements along faults and shear zones, often over very long time scales, strongly suggests that they are weak relative to their surrounding wall rocks. Geophysical observations from plate boundary faults such as the San Andreas fault additionally suggest that this fault zone is weak in an absolute sense, although this remains a controversial issue. Our understanding of fault-zone structure and mechanical behaviour derive from three main sources of information: (1) studies of natural fault zones and their deformation products (fault rocks); (2) seismological and neotectonic studies of currently active natural fault systems; (3) laboratory-based deformation experiments using rocks or rock-analogue materials. These provide us with a basic understanding of brittle faulting in the upper crust of the Earth where the stress state is limited by the frictional strength of networks of faults under the prevailing fluid-pressure conditions. Under the long-term loading conditions typical of geological fault zones, poorly understood phenomena such as subcritical crack growth in fracture process zones are likely to be of major importance in controlling both fault growth and strength. Grain-size reduction in highly strained fault rocks produced in the plastic-viscous and deeper parts of frictional regime can lead to changes in deformation mechanisms and relative weakening that can account for the localization of deformation and repeated reactivation of crustal faults. Our understanding the interactions between deformation mechanisms, metamorphic processes and the flow of chemically active fluids is a key area for future study. An improved understanding of how fault-or shear-zone linkages, strength and microstructure evolve over large changes in finite strain will ultimately lead to the development of geologically more realistic numerical models of lithosphere deformation that incorporate displacements concentrated into narrow, weaker fault zones.In continental and oceanic regions, the deformation of the Earth's crust (and lithosphere) is characteristically heterogeneous, with most displacements being localized into linked systems of faults and shear zones. In both intraplate and plate margin settings, these approximately planar or tabular deformation zones influence strongly the location, architecture and evolution of a broad range of geological features, including rift basins, orogenic belts and transcurrent fault systems. Many fault zones are known to act as conduits for the focused migration of fluids and clearly play a central role in determining the location, modes of transport and emplacement of economically important hydrocarbon reservoirs, hydrothermal mineral d...

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Section: Regime Jmentioning

confidence: 99%

The nature and tectonic significance of fault-zone weakening: an introduction

Rutter

Holdsworth

Knipe

2001

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“…Above the percolation threshold, believed to be roughly 6% by volume for dihedral angles of 100° 6,14,15 , an interconnected melt yields high permeability, below this threshold isolated melt pockets (non-wetting) or tubules, interconnected along threegrain edges (wetting), result in negligible permeability at low melt volume fractions.…”

Section: Ia Scientific Basis For the Projectmentioning

confidence: 99%

Constraints on the Nature of Terrestrial Core-Forming Melts: Ultra-High Pressure Transport Property Measurements and X-Ray Computed Tomography Final Report

Roberts¹,

Kinney²,

Ryerson³

2006

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“…While stresses associated with the changes could connect otherwise isolated pockets of fluid (Mibe et al, 2003, Bruhn et al, 2000 and the valley like topography formed by the changes in dip could channel fluids over a short horizontal profile, the presence of fluids would not be required. Likewise, this interpretation would not explain differences in the Z corridor seaward of the change in dip.…”

Section: Implications For Regional Tectonicsmentioning

confidence: 99%

The CAFE Experiment : a joint seismic and MT investigation of the Cascadia Subduction System

McGary¹

2013

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In this thesis we present results from inversion of data using dense arrays of collocated seismic and magnetotelluric stations located in the Cascadia subduction zone region of central Washington. In the migrated seismic section, we clearly image the top of the slab and oceanic Moho, as well as a velocity increase corresponding to the eclogitization of the hydrated upper crust. A deeper velocity increase is interpreted as the eclogitization of metastable gabbros, assisted by fluids released from the dehydration of upper mantle chlorite. A low velocity feature interpreted as a fluid/melt phase is present above this transition. The serpentinized wedge and continental Moho are also imaged. The magnetotelluric image further constrains the fluid/melt features, showing a rising conductive feature that forms a column up to a conductor indicative of a magma chamber feeding Mt. Rainier. This feature also explains the disruption of the continental Moho found in the migrated image. Exploration of the assumption of smoothness implicit in the standard MT inversion provides tools that enable us to generate a more accurate MT model. This final MT model clearly demonstrates the link between slab derived fluids/melting and the Mt. Rainier magma chamber.

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An interconnected network of core-forming melts produced by shear deformation

Cited by 105 publications

References 22 publications

The nature and tectonic significance of fault-zone weakening: an introduction

The nature and tectonic significance of fault-zone weakening: an introduction

Constraints on the Nature of Terrestrial Core-Forming Melts: Ultra-High Pressure Transport Property Measurements and X-Ray Computed Tomography Final Report

The CAFE Experiment : a joint seismic and MT investigation of the Cascadia Subduction System

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