Saturday, March 15, 2008

At it Again

Well, Stan Keith is at it again, at least in making up new words that can be applied to either plate tectonics or mineral deposit formation. Unfortunately for all, the new word "Serpentosphere" can only be investigated, as far as I can find, by attending an upcoming meeting of the Geological Society of Nevada on Friday, March 21st in Reno, NV. Free beer is at 6:00 pm, dinner at 7:00, and the talk at 8:00. (Contact Kelly Parsons for reservations or more info, 775/323-3500, gsn@gsnv.org.) The talk is being authored also by Monte M. Swan, Martin Hovland, Hakon Rueslatten, and Hans Konrad Johnsen. Because the abstract has been published in a newsletter by the Geological Society of Nevada (GSN), I'll quote it below:

The Serpentosphere consists of an earth-wide nearly continuous layer (or spherical shell) of rock dominated by serpentine group minerals (serpentinite). The Serpentosphere is typically about two kilometers thick beneath ocean basins where it is mainly composed of lizardite. Beneath continents, the Serpentosphere is mainly composed of antigorite (alpine peridotite/serpentinite) and may be several kilometers thick. The base of the Serpentosphere coincides with the gravity and high-velocity seismically defined transition beneath both continents and ocean basins commonly referred to as the Moho. Beneath ocean basins and adjacent to spreading centers, oceanic Serpentosphere is continuously generated by the interactions of deep circulating marine composition water – partly in super-critical state –with harzburgitic peridotite in a process referred to as serpentinization. Conversion of the harzburgite to lizarditic serpentine under supercritical condition is texturally preservative and probably induces about 40% volume expansion. The volume expansion provides an excellent mechanism to expel and propel fluid products – including hydrocarbons – from the area of serpentinization to seep sites at the crust hydrosphere/atmosphere interface. A downward diffusing, super-critical serpentinization front is present beneath every ocean basin and is more active where it originally formed near oceanic ridge thermal anomalies. When ocean Serpentosphere is subducted beneath continental or oceanic crust areas, it converts to antigorite-dominated serpentinite rock (generally coincident with greenschist facies metamorphism). During flat subduction, the relatively lowdensity antigorite ‘floats’ and is underplated to the base of the continental crust at the Moho geophysical interface.

In effect, both oceanic and continental Serpentospheres reflect a deep ‘weathering’ process that consists of the interaction of deep crustal and oceanic, water-dominated fluids with the upper portion of a mainly harzburgitic peridotite at the top of the earth’s lithospheric mantle. The process is analogous to the formation of the pedosphere through interactions of the earth’s hydrosphere-atmosphere layer with the top of the earth’s lithospheric crustal layer. In this context, the Serpentosphere may be viewed as a thin membrane that separates water-absent, life-free abiogenetic processes in the mantle from water-present, life-related processes above the Serpentosphere in the oceanic crust.

The Serpentosphere has enormous and novel implications for four major geologic problems that are of current interest to the geologic and social community: the driving mechanism for plate tectonics, the origin of life, the origin of hydrocarbons, and contributions to global climate. A close relationship between trace elements in crude oils and serpentinite has been found. Migration of the serpentine-associated hydrocarbons to seep sites on the ocean floor and in subaqueous continental environments is essentially the base of the food chain for the biosphere and provides a nutrient and energy source for life in these environments. Heat, methane and carbon dioxide generated during the serpentinization reaction provide a major thermal and greenhouse effect to the earth’s hydrosphere-atmosphere system that is overlooked and underappreciated by the current global climate science. The ductility of the serpentine group minerals provides the tectonic “grease” that allows crustal plates to be able to slide and glide around on the earth’s crust at the Serpentosphere/Moho interface. Because Serpentosphere has been continuously generated since the beginning of geologic time it must be considered as one of the fundamental entities of our water-surfaced planet – the only water-planet we know of ...

Online references to this idea are scant, consisting of these two, and this interesting cartoon:

I won't analyze this Serpentosphere concept, and will just say that I find it interesting because it is related to flat subduction and the concept of hydrothermal hydrocarbons, evidence for which has been seen in the mercury deposits of the California Coast Ranges. Also, he is trying to promote a new model for oil exploration, which can't be knocked these days (unless it doesn't pan out). I won't be at the meeting, so will not be able to hear about this first hand.

7 comments:

The Lost Geologist said...

It does sound like it is well thought through. Could be very interesting when some good prove comes out. And I really like the cartoon!

Fault Rocks said...

this strikes me as patently false! known direct samples of the mantle at or near the moho are at slow spreading ridges (where both serpentinite and unhydrous mantle rocks are found) and by xenolith (to my knowledge, no serpentinite xenolith has ever been described). I think hydrothermal hydrocarbons describes a mechanism for thermally maturing organic material but not a source. Wish i could have seen the talk to see what new evidence is suggested! Alas, too far to travel.

Silver Fox said...

Yes, I would have liked to have seen this one. One thing that S.K. does, or has in the past admitted to doing, is to stir up controversy in order to spark ideas. Many ideas lead nowhere, but some do.

By hydrothermal hydrocarbons, I personally meant hydrocarbons deposited by hydrothermal springs or waters, which is not to mean that would be their source.

It might have been in some comments elsewhere, or maybe in something I haven't posted yet: the occurrence of hydrocarbons in vugs in silicified, Hg-bearing, Au-anomalous serpentinite near the McLaughlin gold mine - that was what I was referring to. The hot water sources are thought to be deep, the hydrocarbons could be from Great Valley sediments (?) or some other source.

I think there is another major reference, Professional Paper or Bulletin, but maybe it's 1382-A.

1973 Bulletin 1382-A
Chemical composition of naturally occurring fluids in relation to mercury deposits in part of north-central California
Barnes, Ivan; Hinkle, M. E.; Rapp, J. B.; Heropoulos, Chris; Vaughn, W. W.

Also:
Characterization of Northern California
Petroleum by stable carbon isotopes
[paper edition]
by Paul G. Lillis1, Leslie B. Magoon, Richard G. Stanley, Robert J.
McLaughlin, and Augusta Warden
Open-File Report 99-164

martin said...

The serpentosphere's oily fingerprints shows up in the least expected locations all over the globe. For example at Chapopote, one of the Kampeche exposed salt stocks, exposed at 3000 m in the GoM. Check out my website at www.martinhovland.com, and also the paper in EOS, of 2005 where we describe how supercritical water (actually originating from serpentinization) not only brings salt to the surface, but also molten asphalt.

Silver Fox said...

Hello, Martin - good to hear from you. Thanks for the link to your web page and EOS paper. I had tried to find some information online related to the Serpentosphere, but had only found the two items. Stan Keith is an old colleague of mine, although he wouldn't recognize the pseudonym I'm using here. I'm sorry I missed the talk at GSN - when working, it seems like I only get to those maybe 3 - 4 times per year.

Chuck said...

I'm pretty sure this is crap, as seismic data doesn't allow for a world-wide a low velocity serpentinite zone in or near the moho. But it has been a decade since I was involved in seismic constraints on the lower crust or upper mantle.

Under thick continental crust, there is the additional problem that the temperature will be too high (>600) for serpentine to be stable.

Some constraints:
This abstract suggests that *If serpentine is present* it is generally less than 15% http://cat.inist.fr/?aModele=afficheN&cpsidt=14892708

This abstract seems to show that in the atlantic, serpentine is present, but not abundant.

Silver Fox said...

Chuck, amazingly this is one of my most popular pages! Thanks for the info and abstract. If you'd like, I (or you!) could contact the authors via email and send them this new info! (See update post.)