Eruptions

Continuing my series where I try to define words of volcanic interest, the new Eruptions Word of the Day is a favorite of mine, mostly because my undergraduate thesis on Vinalhaven Island in Maine ended up dealing with a lot of these types of deposits … so, without further ado, the word is peperite!

Now, what exactly is a “peperite”?

Well, a picture is worth 1,000 words, right (so that will save me some time):

i-3c662c403c572586398089d692f808d8-Peperite-thumb-400x267-53930.jpg
Peperite in the Vinalhaven Diabase, Vinalhaven Island, Maine. Image by Erik Klemetti. Click on the image to see a larger version.

Let’s make some observations:

  1. The rock is full of red-to-black clasts of various sizes and shapes.
  2. The clasts are almost all basaltic andesite in composition.
  3. Some of the clasts look like they have a “chilled” margin, where hot molten material came into contact with colder material.
  4. Some of the clasts look like you could piece them back together – as if they were shattered.
  5. The material between them (the matrix) is mostly light grey/tan, looks to be fine grained.
  6. On closer inspection, the matrix looks like mud or sand.
  7. In some spots, the matrix looks “baked”, like it was exposed to high temperatures.
  8. In other spots, the matrix looks like it was squeezed into cracks and open spaces in the basaltic andesite clasts.

So, what does this suggest?
First off, it looks like sediment (the muddy matrix) is mixed with magma (basaltic andesite clasts). The chilled margins on the clasts and the baked areas of the sediment suggest that the magma was still hot and the sediment was cool (relatively speaking). This is supported by shattered clasts of basaltic andesite in the deposit (thermal shock). The sediment looks to have squeezed its way into spaces between clasts, so the sediment was likely not solid – unconsolidated sediment – and like wet, as mud should be. First order conclusion: It appears that hot basaltic andesite magma interacted with wet, unconsolidated muddy sediment.

And there you have it: peperite – magma interacting, sometimes explosively, with wet, unconsolidated sediment, producing a mixed rock with magmatic clasts and a sediment matrix.

The image above is from Vinalhaven Island in Maine, where the Siluro-DevonianVinalhaven Diabase, a thick basaltic andesite sill intruded the Seal Cove Formation (a sedimentary unit). Along the contact in places you find these peperites where the sill intruded into this wet sediment. This likely means that the sill was being intruded fairly shallowly in the crust as sediment begins to compact and loose pore water quickly as it is buried. Peperites have been recognized in locales all over the world and has been interpreted as one of the steps towards explosive hydrovolcanism – and experiments have been tried to recreate a peperite in the lab. There is some evidence that even lava flows on the surface can form peperite deposits as well. However, the thing to remember is that when you find peperites in the rock record, what you are seeing is evidence of shallow emplacement of magma in the crust where it can interact with wet, soft sediment – a current analog might be if magma intruded underneath Mono Lake in California or in the shallow seas along an oceanic arc like the Marianas or Tonga (think about the Hunga Tonga-Hunga Ha`apai eruption).


Another example of a peperite, courtesy of Highly Allochthonous.

And from where is the name “peperite” derived? It comes from the type locality of peperites, Peper Limagne d’Au- vergne region of central France, where the rocks reminded George Scropes in 1827 of ground pepper.

Comments

  1. #1 Greg
    August 2, 2010
  2. #2 Jack
    August 2, 2010

    Looks nice. I’d like to have one in my aquarium.

  3. #3 birdeyeUSA
    August 2, 2010

    Ah, one of the ‘good rocks’ of Home! : )

  4. #4 Lurking
    August 2, 2010

    I’ve heard mention of the Sun-EQuake connection before, but it was only from the … “excitable” community.

    This should make for a good read later. Thanks.

    Ref the word of the day, this one caught my attention. It’s always a good thing when you learn something new and unique.

    Is there a relationship between clast size and violence of the interaction?

  5. #5 Diane N CA
    August 2, 2010

    @Paaerby from last thread: thanks for the references. I will have to get to them eventually. As for the wobble issue, I am not sure I was referring to it having anything to do with quakes or eruptions. I think it is an interesting feature that happens, but I don’t know of any relationship to quakes or eruptions. It may or may not and I don’t think we even have an idea what the wobble (or wobbles)do to the magnetic field or the earth itself. I can see why there would be some angst about it if it stopped. That is probably just because we don’t have a full understandin of it. I would suppose it has done that before when no one was able to notice.

    I find this stuff interesting rather than scary or having some kind of import about what is going to happen.

  6. #6 Diane N CA
    August 2, 2010

    OOPS! That is supposed to be “Passerby” above! I think my computer is playing games with me. :-}

  7. #7 mike don
    August 2, 2010

    Seems like peperites (fairly mafic magma intruding wet sediments at shallow depth) ought to have some connection to maar formation (often fairly mafic magma interacting with wet sediments at shallow depth) Are there cases where the presence of peperites could be used to infer the likely former presence of a maar at the surface, a volcanic landform which can sometimes be rapidly destroyed by other geological processes?

  8. #8 Birger Johansson
    August 2, 2010

    (OT) Regarding mixing of magma… “Eruptive characteristics of Oregon’s Mount Hood analyzed” http://www.physorg.com/news199976527.html

  9. #9 Erik Klemetti
    August 2, 2010

    @8 – I’ll have more to say about Hood in the nearish future (especially considering I helped collect some of the samples used in that study!)

  10. #10 VMJC
    August 2, 2010

    Where is Peper in France?

    Google maps seems to have never heard of it! If anyone can help out here I would appreciate it.

  11. #11 Erik Klemetti
    August 2, 2010

    VMJC – Thanks for catching that mistake, I misinterpreted the origin. It is now fixed!

  12. #12 Kultsi, Askola, FI
    August 2, 2010

    Wikipedia explains the name to be because of the look of the stone (black pepper) and the original region to be Limagne region of France.

  13. #13 Passerby
    August 2, 2010

    Lacustrine means ‘lake environment’. In this case, it refers to limestones that formed in

    Perpite originates from the Gergovie Volcanic Complex.
    The Gergovie plateau is a plateau of the Massif Central Auvergne.

    A quickie look at Wikipedia for peperite affords a reference to the LeMagne Trench.

    Further lookup on Wiki gives us the LiMagne Plain in the Massif Central (Central France).

    en.wikipedia.org/wiki/File:MC_Limagnes.jpg

    Volcanism accompanied the rifting and continued into the Pleistocene. The sediments deposited in the basin are affected by numerous intrusions. The area was the first where peperites were described, from a basaltic intrusion into lacustrine limestone.

    The reference can be read through Google Books.

    The LiMagne Plain lies in the département of Puy de Dôme (region).

    gitelink.com/auvergne/departments.htm

    ‘The “Puy de Dome” in the middle – largely mountainous, but with a large fertile agricultural plain, the Limagne, in the middle, to the east of Clermont Ferrand. ‘

    http://en.wikipedia.org/wiki/Gergovie_plateau

    Type locality would be the plain or town of Gergovie, located in the commune (county) of La_Roche-Blanche
    en.wikipedia.org/wiki/La_Roche-Blanche_%28Puy-de-D%C3%B4me%29.

  14. #14 Passerby
    August 2, 2010

    Sedimentation episodes that formed the limestones mentioned above, but truncated to point to general locale first.

    Clarification of the LiMagne Plain and Gergovie volcanic complex:

    Morphostructural evolution of the Gergovie Lower Miocene volcano-sedimentary system : geodynamical implications on the late-tectonic Limagne rift (Massif central, France).
    Canadian J. Earth Sci. (2008). 45(6):641-650.

    Abstract: The Gergovie plateau is a Lower Miocene topographically inverted volcano-sedimentary system located in the monogenetic volcanic field of the Limagne rift Tertiary basin. It is composed of three east-west aligned maars partly covered by a basaltic lava flow. The eruption of the central maar (maar 1) occurred at the Oligocene-Miocene transition, during the first volcanic phase.

    This phreatomagmatic structure was almost totally cut through by the opening of a second maar (maar 2) during the next eruptive phase. The basaltic lava flow at the summit and the eastern maar (maar 3) were placed during a third and last eruptive phase during the Middle or Upper Burdigalian (similar to 19-16 Ma).

    Between these periods of volcanism, three fluvial to fluviolacustrine sedimentation episodes, separated by two erosive stages, followed one another. A bedrock thickness of 100-300 m was eroded from maar 2 during the upper Aquitanian and (or) the lower Burdigalian (similar to 22-19 Ma). This erosion is partly due to a volcano-tectonic uplift in the southern Limagne.

    The complex morphostructural evolution of the Gergovie plateau demonstrates the north-south geodynamic differentiation of the Limagne rift during the Lower Miocene, since the northern part of the basin corresponded to a relatively calm lacustrine sedimentation area. More generally, the Miocene volcanic field in the South of the Limagne gives an opportunity to study interactions between volcanism, tectonics, and erosion during the late passive rifting activity phase.

  15. #15 Passerby
    August 2, 2010

    Above post also made to answer Mike Don’s question.

  16. #16 Henrik, Swe
    August 3, 2010

    Is “Peperite” an internationally recognised term? The International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks* refers to “Peperite” as a “local term” but does not give the locality, nor a recognised scientific name other than “a tuff or breccia” (formed by the intrusion of magma into wet sediments). Obviously, there is a need for a specific name for this type of rock as “Vinalhaven Island peperite” is far more succinct than “the tuff (or breccia) formed by the intrusion of magma into wet sediments found at Vinalhaven Island, Maine”. However, the name is not officially recognised by the International Union of Geological Sciences?

    * Le Maître, R. W. et al. (Eds.). Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks p.126, Cambridge University Press, Cambridge 2002

  17. #17 leon
    August 3, 2010

    space.com northern lights show sun waking up http://www.space.com/scienceastronamy/sun-eruption-aurora-activity-100802.html
    and found this also shift an pole reversal http://survive2012.com/index.php/geryl-pole-shift.html

  18. #18 Lurking
    August 3, 2010

    @leon [16]

    Dunno how wakey wakey the sun is…

    http://i37.tinypic.com/f5gqu.png

    A CME does not make a highly active sun. They happen all the time. We just happen to have been in the bore sight of this one.

    And now that some sources are starting to use the Solar Dynamics Observatory with it’s much greater resolving power, you have to wonder just how skewed the reported and official sunspot numbers are going to be. This was not available for most of the observations (1749 to 2010.) How do reconcile the Sunspot Number with new equipment with old data? In fact, there are some people who take exception to some of the “sun specks” that have been reported as full on “spots.”

    http://www.landscheidt.info

    Either way, the plot that I made uses the SIDC count, which is accepted as the internationally recognized “official” count. And with that, you can see that cycle 24 is a bit behind the power curve.

    BTW, the first of 2 CME’s hit at 1730 UT today. Iceland’s earthquake count responded with indifference. So far, it looks like that idea presented in the paper http://www.mdpi.com/1424-8220/8/12/7736/pdf is worth a good airplane or two.

    (The author didn’t really present anything to support his argument other than cherry picking a quake here or there… and you know how plentiful they are)

  19. #19 leon
    August 4, 2010

    @17 lurking, thanks for that yeah looking at one of your links above i came across ‘A massive winter heading for the Northern hemisphere?/planetary theory moves’ which is linked to solar activity being low and your graphs shows this, so does the PDO. were we going in to a La’nina and a continued one, according to this site-Joe Bastardi from accuweather.com is an avid follower of this site is also predicting the same cooling trend.he also adds the possible cooling effects that could result from impending volcanic eruptions,and to expect conditions similar to the little ice age[1250-1850] http://www.landscheidt.info/?q=node/189 and looking at my weather world temp map [weatheronline he right you clearly see the drop happening except the Atlantic which will do in the near month or so when the hurricanes carry all that heat and spread that all out.so much media on global warming when in fact we just coming or have already come out of a strong El nino moving to La nina phrase. ‘global warming v global cooling’ we have to see who right

  20. #20 Lurking
    August 4, 2010

    Not really a strong El Nino either. The press tends to like to toss “strong” “above normal” “greater than expected” and other such modifiers to various things.

    Recently, a phenomena known as El Niño “Modoki” or Central-Pacific El Niño has been discovered. And, as regular as clockwork “the new El Niño leads to more hurricanes more frequently making landfall in the Atlantic.” And yet 2010 is another year with a very late “first named storm.” On average, from 1995 to 2008, the First Named Storm occurred by 16 Jun. In 2009, it formed 11 August. In 2010, 25 June saw the formation of Alex which immediately headed for the speed bump known as the Yucatan. The season so far seems a bit anemic to me. It doesn’t mean that it wont become worse later in the year, but the predictions of a highly active season seem to be as wrong as it is every year.

    So, when you see a headline like

    El Nino Modoki a Climatic Hybrid for 2009-2010
    Winter Weather Forecast Predicts Hurricanes, Rain, and Flooding

    You have to sit back and think to yourself “Okay…”

  21. #21 leon
    August 4, 2010

    but 1998 was record El Nino and 2007 2nd strongest El Nino i need more time on this i get to this later very complex stuff

  22. #22 Lurking
    August 4, 2010

    Tough things about records. They only apply for the period that the data was being collected.

    That’s right back to that tree in the forest thing.

    With ENSO (also referred to as the El Nino / El Nina thing or any variety of Multidecadal Oscillations), some weather guessers/analysts/prognosticators have noted what appears to be a step pattern to the heat flow as it progresses further and further north.

    I dug around trying to find the link, but was unsuccessful. I ran across it while reading some of Bob Tisdale and Anthony Watts’ post at Watts Up with That.

    bobtisdale.blogspot.com/2009/04/misunderstandings-about-pdo-revised.html

    wattsupwiththat.com/2009/04/28/misunderstandings-about-the-pacific-decadal-oscillation/

    Alternatively, Passerby posted a fascinating link that references El Nino/El Nina as it relates to Earth’s rotational momentum:

    http://www.examiner.com/x-17371-Raleigh-Climate-Examiner~y2009m8d30-Atmospheric-Angular-Momentum-AAM-oversimplified

  23. #23 mike don
    August 5, 2010

    Passerby: Thanks for that info. Only just got back to checking this topic, hence delay in reply, sorry.

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