Thursday, 5 September 2013

Drilling an ancient orogen by Nick Roberts

Me [Nick Roberts] on top of Åreskutan, Sweden
The UK has recently become a member of the International Continental Scientific Drilling Program (ICDP); Mel Leng recently blogged about the UK’s involvement and her trip to Japan for the ICDP Executive Committee’s meeting, where new potential projects were discussed. Sweden became a member of ICDP in 2008, and has one ICDP project that is currently underway in Scandinavia: COSC – Collisional Orogeny in the Scandinavian Caledonides. Last month I returned from a field-based workshop on this drilling project, where I discussed the potential involvement and collaboration between the BGS, particularly the NERC Isotope Geosciences Laboratory, and scientists from the Nordic countries involved in this project.

The COSC Project: 

The objectives of the COSC project are to 1) improve our understanding of collisional orogenesis, 2) investigate the geothermal gradient and its response to palaeoclimatic influences, along with the nature of the hydrogeological-hydrochemical state of the crust and deep biosphere, 3) calibrate the surface geophysics and geology. These have direct relevance for society by improving our understanding of mountain building processes, hydrological-hydrochemical regimes in mountain areas and Precambrian shields, deep subsurface conditions for underground engineering, ore genesis and assessment of geothermal potential. 

Prof. David Gee on Areskuten mountain,
close to the proposed drilling sites, explaining
the origin and transportation of this 'hot nappe'


The Scandinavian Caledonides provide a well exposed example of an ancient continental collision, where Baltica (Scandinavia) was underthrust beneath Laurentia (Greenland), leading to thickening of the continental crust to at least 100 km. Slices of Laurentia and Baltica were buried, then exhumed, then transported large distances (>300km) over the Baltic continent. Such processes are seen in the Himalayan orogen today. The COSC drilling project will drill two holes through one of these slices, with one penetrating all the way into the underlying basement crust. 

The workshop:

The aim of this workshop was to bring together scientists ranging from Masters’ students to Professors, with expertise on both the Caledonides and on orogens further afield, such as the Himalaya. The workshop was led by experts on the geology of the Caledonides, Professors David Gee (Uppsala), Alan Krill (Trondheim) and Peter Robinson (NGU); who between them have nearly a hundred years of experience working on this mountain belt! Following in the footsteps of pioneering geologists, such as Goldschmidt and Törnebohm, we traversed the Caledonian mountains from central Sweden to western Norway, observing key localities where the history of the Caledonian orogen has been studied. 

Prof. Allan Krill explaining how a 1200 million year old
granite has been involved and deformed in the Silurian
Caledonian orogeny
Along the way we discussed in the field and in evening lectures, how we could investigate this orogen further, and how we might go about answering some of the unresolved questions; many of these questions boil down to one important factor – timing. As a geochronologist, I offered my advice on what dating techniques and which minerals could be used to look at specific objectives, for example the timing of individual nappe movements. The NERC Isotope Geosciences Laboratory is highly experienced in using geochronology to understand orogens, having been involved in many projects in the Himalaya-Tibet orogen amongst others over the years. Now we have the opportunity of pushing the limit of these techniques in a much older orogen, and one that has been described as an ancient example of a Himalayan-type collision. 

Prof. Peter Robinson explaining rare exposures of micro-diamond
bearing rocks that have undergone ultra high pressure through
their burial to depths greater than 150km
Drilling will start in early 2014. It will take several months for the first borehole to be drilled, and then drilling will commence in the second location at a later date. The extracted core will provide excellent samples for study, which will no doubt be used for ongoing research for many years after drilling. Watch this space for future news on NIGL’s involvement in the COSC drilling project. 

By Nick Roberts

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