Hello,
There is always the risk of sliding into pedantry; the terms "igneous
intrusion", "sedimentary dyke" are well understood and I don't think really
confuse or annoy anyone.
What should be of common interest is how the space problem is resolved with
respect to the stress conditions during intrusion of whatever the intruding
material is (hot, cold, hot liquid, slurry etc.) and what the state of the
country rock is (soft, hard, hot, cold etc.) at the time of intrusion. Those
of us who have worked in both hard and soft rock areas have been struck by
the similarities of intrusion style rather than by their undoubted
differences.
I hope that the conference can open up some discussion and debate on this
and what it tells us about the natural system and avoid worrying too much
about whether we think the other guy is using needless adjectives or sloppy
terms like those in brackets above.
alan
-----Original Message-----
From: Tectonics & structural geology discussion list
[mailto:[log in to unmask]] On Behalf Of Eric Essene
Sent: 26 November 2009 07:39
To: [log in to unmask]
Subject: Re: Anderson Stress Meeting: September 2010 reminder
Rob,
The term igneous intrusions is functionally a terrible term, a
distinction without a difference. More than 99.9% (or more?) of the time it
means igneous rocks where the term is redundant. If one talks about
sedimentary intrusions it is on a meter scale feature, commonly even less--I
have seen some down to cm scale. When they formed and well afterward they
did not look like dikes, just fractures filled with loose sediment. I
discount the poor term "sandstone dikes" as needing yet another confusing
term.
On the other hand salt domes are metamorphic (recrystallized) but not
molten rock, well a little brine. They were not in the sedimentary group
during formation. Yes, we have diapirs of metamorphic rock, although a lot
of those gneiss domes probably have a little melt. I would agree about
metamorphic diapirs but simply would not call them metamorphic intrusions to
avoid confusion on a transitional rock. Gneiss domes are a nice description
for them.
It must be exceedingly rare for igneous petrologists/geochemists
to be presenting data on "sand dikes". Salt domes are much larger
but are as they form. Do you know of any igneous petrologist/ geochemist who
would report on them in your symposium? So "sandstone dikes" are fractures
filled with loose clastic material and water, salt diapirs are all
metamorphic and may have brine, gneiss domes are often partial melts then at
least partly igneous, and the term "igneous intrusion" is clearly redundant
to the average passerby. Is this really a useful terminology?
cheers,
eric
On Nov 26, 2009, at 12:17 AM, Butler, Robert wrote:
> Eric
> Actually - there are lots of non-igenous intrusions in basins -
> sandstone dykes through 100s metres of strata. Not to mention mud
> diapirs, salt etc etc.... gas chimneys....
> go google!
> Cheers
> Rob
>
> ________________________________________
> From: Tectonics & structural geology discussion list
> [[log in to unmask] ] On Behalf Of Eric Essene
> [[log in to unmask]]
> Sent: 26 November 2009 05:09
> To: [log in to unmask]
> Subject: Re: Anderson Stress Meeting: September 2010 reminder
>
> Rob, Zoe, and all,
> Igneous intrusions as opposed to all those sedimentary plutons?
> The phrase is nearly always meaningless and should not be used.
> Sounds like a great trip.
> cheers,
> eric
>
>
> On Nov 25, 2009, at 11:28 PM, Butler, Robert wrote:
>
>> Dear all
>> As we get our diaries together for 2010 we thought it timely to
>> remind you of the conference next year:
>>
>> Stress controls on faulting, fracturing and igneous intrusion in the
>> Earth's crust
>>
>> A meeting to commemorate the work of Ernest Masson Anderson on the
>> 50th anniversary of his death.
>>
>> 6-8 September 2010 at the University of Glasgow, UK
>>
>> Organisers: Zoe Shipton, Rick Sibson, Dave Healy, Rob Butler
>>
>> We will send out details of the meeting ("First Circular") in January
>> - Abstract deadline will be end April with a preliminary programme
>> drawn up through May.
>> We are also planning a fieldtrip to the Hebrides and NW Scotland to
>> examine a variety of faults and the Tertiary igneous complexes.
>> Again - further information will be included in the first circular.
>>
>> Hope to see a bunch of you in Scotland next September!
>> Zoe, Rick, Dave and Rob.
>>
>>
>> The University of Aberdeen is a charity registered in Scotland, No
>> SC013683..
>>
>>
>
>
> The University of Aberdeen is a charity registered in Scotland, No
> SC013683..
>
>
