Bill,
Sure, I just mentioned that same field area an hour ago. It is a
wonderful area.
I had to look up Neptunian dikes in the Glossary of Geology. They
are clastic injectites (OK, OK, sandstone dikes). I have never seen
them in the Adirondacks despite working with John Valley, Steve Bohlen
and Meg Streepey, who did Michigan PhDs there. There are real
postmetamorphic dikes of basalt in the Adirondack Lowlands. I also
have seen cave-like structures in Grenville marbles filled with
sedimentary debrii and blocks of marble. They look like sedimentary
collapse breccias but not sandstone dikes. The main sedimentary
lithology capping the Grenville is Ordovician black shale, but SW of
the Adirondacks there are Cambrian and perhaps older clastic
sequences. At Oka one sees dikes of Cretaceous carbonatites cutting
Grenville marble and Paleozoic limestones,
cheers,
eric
cheers,
eric
On Nov 26, 2009, at 10:46 AM, WRChurch wrote:
> Another relatively rare form of non-igneous intrusion is
> represented by the 'Sudbury breccias' associated with the Sudbury
> meteorite impact structure here in Ontario. The 'breccias' - should
> they be called 'impactite injectites? - form sheets, dikes, diapirs,
> and irregular masses of fluidized Paleoproterozoic (Huronian)
> sedimentary material, and can be found at least 100 km out from the
> supposed impact centre. The Huronian is also the home of the well
> known Espanola clastic dike exhibiting a 'Bernoulli' concentration
> of clasts in the centre of the dike. These silt/mud intrusions
> (injectites) transect kilometre-size recumbent fold structures in
> sandstone units below the Gowganda glacial unit - a nice example of
> large-scale non-tectonic folding and non-igneous injection
> material! The sand filled cracks referred to by Eric used to be
> known in my days in the Trias-Lias of Glamorgan as Neptunian dykes,
> and, I would tend to believe, are distinct from sedimentary
> 'injectites' .
> Re- Christine's query, I have a recollection that there are
> Neptunian dikes in Adirondack gniesses below their contact with the
> Potsadam sandstone in northern New York State, but I would have to
> confirm that, or have someone confirm it for me!
>
> Rgds to all , Bill Church
>
> ----- Original Message -----
> From: "Macdonald, Professor David I. M." <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, November 26, 2009 5:11 AM
> 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.
