Looking For Detachment

One author of the abstract I quoted in an earlier post - the talk about The Serpentosphere given at last month's GSN meeting in Reno, NV - contacted me via comment on this blog. Martin Hovland pointed out his website, which has numerous references to the interconnections between mud volcanoes, salt diapirism, hydrothermal activity, and deep sources of hydrocarbons and some interesting links. He also referenced his EOS 2005 paper on the Chapopote asphalt volcano. At least one petroleum company is using ideas discussed at the March GSN to find oil. Andrew on Nonmagmatic volcanism:

There are less well-known types of volcanism that don't involve magma: mud volcanism is one. Mud volcanoes come in two types. On land, hundreds of them occur in areas where hydrocarbons are abundant, like Trinidad or Azerbaijan (see this one in the Image Gallery). Under the sea, thousands of them occur near subduction trenches, where serpentinite mud is abundant (about serpentinization). 

Another newly discovered form of volcanism involves asphalt. Asphalt flows were first documented on the floor of the Gulf of Mexico in 2003. No one knows how many of these tar volcanoes there are.

A few more references: Supercritical water and Hydrothermal Chimneys 

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.