Up until now I have written about very well understood geologic concepts. I think it is now time to push the boundaries a little bit and attempt to review and simplify ongoing research. The article I have chosen is hot off the press and I only learned about its existence through seeing a breakdown of the article on CBC and then hearing about it on Quirks and Quarks.
The article is entitled:
Neon identifies two billion year old fluid component in Kaapvaal Craton
Chemical Geology, In Press, Corrected Proof, Available online 6 February 2011
Johanna Lippmann-Pipke, Barbara Sherwood Lollar, Samuel Niedermann, Nicole A. Stroncik, Rudolf Naumann, Esta van Heerden, Tullis C. Onstott
Chemical Geology, In Press, Corrected Proof, Available online 6 February 2011
Johanna Lippmann-Pipke, Barbara Sherwood Lollar, Samuel Niedermann, Nicole A. Stroncik, Rudolf Naumann, Esta van Heerden, Tullis C. Onstott
Sounds pretty complicated eh? But it doesn't have to be...
First, lets describe the setting of this paper. The sample collection was performed at the bottom a large gold mine in the Witwatersrand Basin which is part of the Kaapvaal Craton located near Johannesburg, South Africa.
The Kaapvaal Craton was formed during the Archean period between about 3.07 and 2.71 billion years ago as a result of several large granite bodies emplacing themselves into the continental crust. The emplacement of the granite batholiths was then followed by several continental collisions by island arcs throughout the Archean. This led to mountain building and subsequent erosion of these mountains leading to the formation of thick sedimentary and volcanic sequences over the Kaapvaal Craton some of which now compose the Witwatersrand Basin. Many of these sedimentary were metamorphosed to a low degree over time giving rise to the hydrothermal gold deposits in the area.
In this study, water samples were collected from nine gold mines in the Witwatersrand basin in order to try to establish the age and origins of waters deep beneath the surface of the Earth and look for evidence of life in this hitherto unexplored potential ecosystem. The water samples came from fractures in the rock deep underground, fluid inclusions within the rock itself and fluid inclusions from quartz veins.
First, lets describe the setting of this paper. The sample collection was performed at the bottom a large gold mine in the Witwatersrand Basin which is part of the Kaapvaal Craton located near Johannesburg, South Africa.
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| Cratons of Southern Africa |
The Kaapvaal Craton was formed during the Archean period between about 3.07 and 2.71 billion years ago as a result of several large granite bodies emplacing themselves into the continental crust. The emplacement of the granite batholiths was then followed by several continental collisions by island arcs throughout the Archean. This led to mountain building and subsequent erosion of these mountains leading to the formation of thick sedimentary and volcanic sequences over the Kaapvaal Craton some of which now compose the Witwatersrand Basin. Many of these sedimentary were metamorphosed to a low degree over time giving rise to the hydrothermal gold deposits in the area.
In this study, water samples were collected from nine gold mines in the Witwatersrand basin in order to try to establish the age and origins of waters deep beneath the surface of the Earth and look for evidence of life in this hitherto unexplored potential ecosystem. The water samples came from fractures in the rock deep underground, fluid inclusions within the rock itself and fluid inclusions from quartz veins.
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| (J. Lippman-Pipke et al., 2011) |
These waters were analysed for their neon isotope ratios (turns out it can be used for more than just colourful signs after all). Neon (Ne) is one of the noble gases and is very nonreactive under normal environmental conditions. This inert nature of neon allows it to be used as a tracer. It can be used to trace fluids from their origins, fluid transport and the ages of the fluids that neon is dissolved in. I am calling the water in the fractures and fluid inclusions "fluids" because they are so saline that they don't fall under the same category as normal water. Neon has several natural isotopes that are produced in different ways and exist in constant ratios to one another. For example, the neon ratio of the atmosphere is different than that of the mantle as the neon in the atmosphere comes from different sources than neon in the mantle. Most of the ratios we find in water today are mixtures of many different neon sources making it difficult to distinguish one source. Much of the neon found in the subsurface comes from nucleogenic sources. What this means is that the neon we find in the subsurface is actually created there through the interaction of alpha radiation from uranium and thorium with oxygen and fluorine in the rocks. When the alpha radiation interacts with the the oxygen and fluorine it is changed into neon. This means that the amount of neon that is produced is proportional to the amount of uranium, thorium, oxygen and fluorine that is present. This process takes place in both the crust and the mantle, with each location having its own characteristic neon ratio, due to the differences in chemistry between the crust and the mantle.
In this study the neon isotope ratios were analyzed in the fracture water to see if there was any contribution of neon from the mantle and to date the water. The results of this paper show that there are some anomalous values for neon ratios present. Neon ratios traditionally plot along a straight line between the neon ratio found in air and that of crustal fluids and don't deviate from this line. This means that any neon ratio along this line is simply a mixture of these two end members. However, the neon ratios found in this study DO NOT fall on the neon mixing line and are unlike any neon ratios that have ever been reported!
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| (J. Lippmann-Pipke et al., 2011) |
These anomalous neon ratios are the highest ever recorded in groundwater or fluid inclusions. Now, given what we know about neon ratios this could be caused by any number of factors. For example, really high levels of uranium could produce a high neon ratio, or lots of oxygen and fluorine. However, this is not the case. To find the real answer for the anomalous values we have to examine the source of the water being analyzed.
The water that is being analyzed and contains the high neon ratios is not from a single source. It is, in fact, a combination of water from two isolated reservoirs. The reservoir that is the source of the high neon ratios is fluid inclusions. Fluid inclusions represent "time capsules" for geologists. They are like little bubbles of water that were trapped when the rock formed and have not been added to, subtracted from or changed in any way since the time of formation. This means that even if the water was trapped billions of years ago, as is the case in this setting, it has not changed since and represents the chemistry of water billions or millions of years ago.
The authors of this paper suggest that the water in the fluid inclusions contain a nucleogenic neon signature that is two billion years old and was produced by natural nuclear reactions and radioactive decay that took place in Earth's mantle!!! Pretty damn cool if you ask me.
So that is all for now. If you have any questions don't hesitate to ask. I'll do my best to answer. I leave for an international conference on Accelerator Mass Spectrometry in a few days so I'll post any cool things I see at the conference.
Matt
Quite interesting stuff. How they can date water based on composition is pretty amazing.
ReplyDeleteSo is this finding just really cool or are there more practical applications? Like does it much more insight into how life was like those billions of years ago?
Also what about the water's composition? Other than the neon ratios being a completely new thing, how much did other minerals differ from expected for that time, if at all?
Also I saw in the CBC article that it said that the microbes found were similar to deep see ones... do you ever think that geologists will find a vein of microbes buried deep beneath the earth surface, placed there by ancient dark gods, and when released result in the zombie apocalypse? Or will they be the helpful ones that will be able to be industrialized for good?
Thanks for your comment and questions.
ReplyDeleteAs far as the practicality of this research goes understanding the stability of environments like this can be used to evaluate these places for the storage of nuclear waste. Also, understanding ancient water chemistry can give us clues to how our planet and life may have begun and evolved.
Aside from the really, really high salinity and helium ratios as well I don't think much else was odd about this water.
I did skip out on mentioning the microbial side of the article, mainly for simplicity sake, but you are right, they are similar to the chemotrophic life found near deep sea vents. I just hope they don't start an apocalypse, haha.