All,
There thousands beautiful "sand dikes" all along the north shore
of Lake Huron as one gets within 100 km to Sudbury. They are cutting
biotite to staurolite zone metamorphic rocks, but features of the host
rocks (climbing ripples, strong but nonpenetrative deformation,
extensive zones of brecciation in now lithified clastic sediments (not
limestone or Ca sulfate sediments) suggest soft sedimentary processes
too. I think the sand dikes occurred early after deposition in the
Huronian and that soft sedimentary features in the host rock formed at
the same time as the "sand dikes", both driven by a major impact, not
later when the host rocks had became crystalline. That suggests the
dikes were metamorphosed to the same grades as the host. The same
sedimentary rocks are metamorphosed forming cordierite schists on a
regional scale. The metamorphism has been interpreted to be post-
impact and post-shatter cone. There are also "breccia dikes" in the
impact zone in and immediately around Sudbury. I think the "sand
dikes" were driven by the major impact rather than indicating
endogenic processes in this case.
The question of "sand dikes" in crystalline rocks is the source
of soft sand in a crystalline terrane. I suppose one could have
thrusts of crystalline rock over unconsolidated sediment just before
the earthquakes indicated by the "diking" event. We have looked at
many exposures of the main frontal thrust in the S. Appalachians where
metamorphic rocks to the east were thrust over unmetamorphosed and
often poorly consolidated clastic sediment in basins to the west with
westward transport on the order of many hundreds of km. without seeing
these features. The crystalline rocks are biotite to garnet zone
phyllites along current exposures on this fault. I would describe them
as weakly crystalline.
cheers,
Eric
On Nov 26, 2009, at 8:39 AM, Christine Siddoway wrote:
> Greetings, Carl and others,
> AMS on sandstone intrusions: Mike Petronis and I have an
> investigation
> underway of sandstone dikes within crystalline rock in the Front
> Range of
> Colorado. Our recent abstract with initial results is at:
> http://aapg09.mapyourshow.com/2_1/sessions/session.cfm?ScheduledSessionID=15
> 32. The scale of the intrusions, incidentally, is 5 cm to >7
> meters, with
> many exceeding 2 m in width.
>
> I'd like to now ask, can any list members tell me of other examples of
> clastic dikes within a crystalline host? My web searches yield
> little!
>
> Regards,
> Christine Siddoway
>
>
> On 11/26/09 4:24 AM, "Carl Stevenson" <[log in to unmask]>
> wrote:
>
>> Hi all,
>>
>> Sedimentary intrusions - does anyone know of any AMS (anisotropy of
>> magnetic
>> susceptibility) work on these?
>>
>> Desperately resisting getting drawn in to a semantic debate, I
>> think 'igneous
>> intrusion' is fine. I guess it is as opposed to igneous extrusion -
>> lavas and
>> ash etc. Sometimes in when subvolcanic roots are exposed it is
>> actually
>> equivocal. There are instances when ash can fall back into a vent.
>>
>> An example I am aware of is:
>> ALMOND, D. C. 1977. Sabaloka Igneous Complex, Sudan. Philosophical
>> Transactions of the Royal Society of London Series a - Mathematical
>> Physical
>> and Engineering Sciences, 287, 595-633.
>>
>> Cheers
>> Carl
>>
>> -----Original Message-----
>> From: Tectonics & structural geology discussion list
>> [mailto:[log in to unmask]] On Behalf Of Stu Clarke
>> Sent: 26 November 2009 10:23
>> To: [log in to unmask]
>> Subject: Re: Anderson Stress Meeting: September 2010 reminder
>>
>> Don't you hate it when someone gets that email in just before
>> you......
>>
>> I too have no particular stand on terminology, but I too was
>> surprised by
>> the stated scale of sedimentary intrusions. I have examined large
>> scale
>> sedimentary intrusions in deltaic settings and currently work with
>> colleagues using oil-industry datasets on the same thing. I don't
>> think
>> sedimentary intrusions have to be small scale......
>>
>> Stu
>>
>>
>> -----Original Message-----
>> From: Tectonics & structural geology discussion list
>> [mailto:[log in to unmask]] On Behalf Of Macdonald,
>> Professor
>> David I. M.
>> Sent: 26 November 2009 10:11
>> To: [log in to unmask]
>> Subject: Re: Anderson Stress Meeting: September 2010 reminder
>>
>> Dear Eric
>> I have no particular stand on the terminology for igneous rocks,
>> but you are
>> incorrect in your assertions on the scale of sedimentary
>> intrusions. Salt
>> is a sedimentary rock which can be injected through kilometers of
>> strata in
>> bodies hundreds of metres to kilometers across. Anyone who has
>> ever worked
>> on deltas can point to mud diapirism on a similar scale. Even the
>> humble
>> sand injection feature is much larger than you make out; your
>> description
>> seems to be of sand filling pre-existing cracks, whereas most sand
>> injections are of a fluid slurry under pressure. These intrusions
>> can be
>> huge. In the Mesozoic forearc basin of the Antarctic Peninsula,
>> sandstone
>> dykes have been mapped with MINIMUM dimensions: 6 km long, cutting
>> 350 m of
>> strata, and 1 m wide. For more examples, see, among other papers:
>>
>> Hurst A. & Cartwright J. A. Eds. 2007. Sand Injectites:
>> Implications for
>> hydrocarbon exploration and production. Memoir 87 American
>> Association of
>> Petroleum Geologists
>>
>> Hurst A., Cartwright J. & Duranti D. 2003. Fluidization
>> structures in
>> produced by upward injection of sand through a sealing lithology.
>> In:
>> Subsurface sediment mobilization (eds. Van Rensbergen P.,Hillis
>> R.,Maltman
>> A. J. & Morley,C.K.), Geological Society Of London, London, 123-127
>>
>> Jonk R., Hurst A., Duranti D., Mazzini A., Fallick A. E. & Parnell
>> J.
>> 2005.The origin and timing of sand injection, petroleum migration and
>> diagenesis: the Tertiary petroleum system of the South Viking
>> Graben, North
>> Sea. AAPG Bulletin, 89, 329-357
>>
>> Hurst A. & Duranti D. 2004. Fluidisation and injection in the deep-
>> water
>> sandstones of the Eocene Alba Formation (UK North Sea).
>> Sedimentology, 51,
>> 3, 503-529
>>
>> Hope this helps
>> David Macdonald
>>
>> -----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..
>>>
>>>
>>
>>
>> The University of Aberdeen is a charity registered in Scotland, No
>> SC013683.
>
>
