Lyell Collection
Geological Society, London, Special Publications
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Handy, M. R.
Right arrow Articles by Rosenberg, C. L.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Geological Society, London, Special Publications; 2001; v. 186; p. 305-332;
DOI: 10.1144/GSL.SP.2001.186.01.18
© 2001 Geological Society of London

Insights from Lithosphere- to Crustal-scale Fault Zones

The role of fault zones and melts as agents of weakening, hardening and differentiation of the continental crust: a synthesis

M. R. Handy1, A. Mulch1,2, M. Rosenau1,3 & C. L. Rosenberg1

1 Freie Universität Berlin, Geowissenschaften, Malteserstrasse 74-100, Haus B, Geologie, D-12249 Berlin, Germany mhandy{at}zedat.fu-berlin.de
2 Université de Lausanne, Institut de Minéralogie et Pétrographie, BFSH 2, CH-1015 Lausanne, Switzerland
3 Geoforschungszentrum Potsdam, Haus C, D-14473 Potsdam, Germany

The rheology of crustal fault zones containing melts is governed primarily by two strain-dependent mechanical discontinuities: (1) a strength minimum parallel to mylonitic foliation just below the active brittle-viscous (b-v) transition; (2) the anatectic front, which marks the upper depth limit of anatectic flow. The mode of syntectonic melt segregation in fault zones is determined by the scale of strain localization and melt-space connectivity, to an extent dependent on strain, strain rate and melt fraction in the rock. Melt drains from the mylonitic wall rock into dilatant shear surfaces, which propagate sporadically as veins. Anatectic flow at natural strain rates therefore involves melt-assisted creep punctuated by melt-induced veining. On the crustal scale, dilatant shear surfaces and vein networks serve as conduits for the rapid, buoyancy-driven ascent of transiently overpressured melt from melt-source rocks at or just below the anatectic front to sinks higher in the crust. Strength estimates for natural rocks that experienced anatectic flow indicate that melts weaken the continental crust, particularly in depth intervals where they spread laterally beneath low-permeability layers or along active shear zones with a pronounced mylonitic foliation. However, acute weakening associated wit h strength drops of more than an order of magnitude occurs only during short periods (103–105 a) of crustal-scale veining. Cooling and crystallization at the end of these veining episodes is fast and hardens the crust to strengths at least as great as, and in some cases greater than, its pre-melting strength. Repeated melt-induced weakening then hardening of fault zones may be linked to other orogenic processes that occur episodically (shifting centres of clastic sedimentation and volcanism) and has implications for stress transmission across orogenic wedges and magmatic arcs.





This article has been cited by other articles:


Home page
 Geological Society, London, Special PublicationsHome page
M. Brown
Synergistic effects of melting and deformation: an example from the Variscan belt, western France
Geological Society, London, Special Publications, 2005; 243: 205 - 226.
[Abstract] [PDF]

Home page
 Geological Society, London, Special PublicationsHome page
J. Carreras, E. Druguet, A. Griera, and J. Soldevila
Strain and deformation history in a syntectonic pluton. The case of the Roses granodiorite (Cap de Creus, Eastern Pyrenees)
Geological Society, London, Special Publications, 2004; 224: 307 - 319.
[Abstract] [PDF]

Home page
 Geological Society, London, Special PublicationsHome page
K. J. W. McCaffrey, J. Grocott, A. A. Garde, and M. A. Hamilton
Attachment formation during partitioning of oblique convergence in the Ketilidian orogen, south Greenland
Geological Society, London, Special Publications, 2004; 227: 231 - 248.
[Abstract] [PDF]