I agree with Ernie Rutter and, to avoid "young scientist confusion",
here is a definition from the Passchier and Truow book:
One of the most common patterns of heterogeneous
deformation is the concentration of deformation in planar
zones that accommodate movement of relatively rigid
wall-rock blocks. Deformation in such high-strain zones
usually contains a rotation component, reflecting lateral displacement
of wall rock segments with respect to each other;
this type of high-strain zone is known as a shear zone. Deformation
in a shear zone causes development of characteristic
fabrics and mineral assemblages that reflect
P-T conditions, flow type, movement sense and deformation
history in the shear zone. As such, shear zones are an
important source of geological information.
Shear zones can be subdivided into brittle zones or faults,
and ductile zones (Chap. 3). Ductile shear zones are usually
active at higher metamorphic conditions than brittle shear
zones (Figs. 3.44, 5.2).
Cheers
Francesca Meneghini
On 28 July 2010 12:04, Ernest Rutter <[log in to unmask]> wrote:
> Hello All,
> The term 'shear zone' should not be restricted to faults in which there is so-called 'ductile' (meaning intracrystalline plastic) deformation. Look at the magnificent cataclastic shear zones (wide zones of localized cataclastic deformation but a meter or more width) at Durdle Door (S coast of England), for example. Shear zone is (like mylonite) a field term and no mechanism should be implied - it is easy to deduce mechanism wrongly. John is quite correct in his usage.
> Ernie Rutter
>
> -----Original Message-----
> From: Tectonics & structural geology discussion list [mailto:[log in to unmask]] On Behalf Of Uwe Altenberger
> Sent: 28 July 2010 10:25
> To: [log in to unmask]
> Subject: Re: Anchi-metamorphic shear zones
>
> Dear John, dear Graham
> are these really shear zones? The classical and modern textbooks
> define shear zones as ductile fault zones. The anchimetamorphic zones
> are probable brittle faults? I know, it is only a semantic problem.
> However, younger scientists get be confused.
>
> best wishes
>
> uwe
>
>>Dear John
>>Have a look at what Bernard and I did with the Orlock Bridge Fault...it's all
>>anchizone........sorry I don't have a pdf
>>
>>Anderson, T B. & Oliver, G J H (1986). The Orlock Bridge Fault: a major Late
>>Caledonian sinistral fault in the Southern Uplands Terrane, British Isles.
>>Trans. R. Soc. Edin: Earth Sci. 77, 203-222.
>>
>>Cheers
>>Grahame (Still at the National University of Singapore and loving it)
>>
>>Quoting "John F. Dewey" <[log in to unmask]>:
>>
>>> Dear Colleagues,
>>>
>>> For some years, I have been working on the anchi-metamorphic shear
>>> zones of the North Cornwall/Devon coast between Crackington Haven and
>>> Hartland Quay. Rob Strachan got me going by, generously, giving me a
>>> sliced pebble through one of the finest shear zones of my experience
>>> from the beach at Hartland Quay. I have, now, analysed many large
>>> thin sections across these shear zones, which combine sigmoidal
>>> tension gashes with solution cleavages. Most are transtensional plane
>>> strain zones of volume increase. I would be most grateful to hear
>>> from anyone who has studied such shear zones.
>>>
>>> Best wishes,
>>> John Dewey
>>> --
>>>
>>> -----------------------------------
>>> Please update your address book to use [log in to unmask] as my
>>> e-mail address.
>>>
>>> Prof. John F. Dewey FRS, Hon. M.R.I.A., Mem. Acad. Eur., For. Mem.
>>> US Nat. Acad. Sci, Distinguished Emeritus Professor University of
>>>California,
>>> Emeritus Professor University College Oxford.
>>>
>>> Sherwood Lodge,
>>> 93 Bagley Wood Road,
>>> Kennington,
>>> Oxford OX1 5NA,
>>> England, UK
>>>
>>> University College,
>>> High Street,
>>> Oxford OX1 4BH
>>>
>>> Telephone Nos:
>>> 011 44 (0)1865 735525 (home Oxford)
>>> 011 44 (0)1865 276792 (University College Oxford)
>>> email: [log in to unmask]
>>>
>>
>>
>>
>>
>>------------------------------------------------------------------
>>University of St Andrews Webmail: https://webmail.st-andrews.ac.uk
>
>
> --
> Uwe Altenberger
> Institute of Earth and Environmental Sciences
> University of Potsdam
> Karl-Liebknecht-Str. 24
> D-14476 Potsdam-Golm
> Tel. +49 331 977 5806
> Fax +49 331 977 5700
> [log in to unmask]
>
--
Un vero viaggio di scoperta non è cercare nuove terre, ma avere nuovi
occhi - M. Proust
><><><><><><><
Francesca Meneghini, PhD
Dept. of Earth Sciences,
Stellenbosch University,
Private Bag X1, Matieland 7602,
Stellenbosch, South Africa.
e-mail: [log in to unmask]
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