Deep-sea drilling project financed Liberian carnage

Despite the common knowledge of rapidly deteriorating conditions for civilians in Liberia for the last 10 years or so, the Joint Oceanographic Institutions’ drilling vessel Resolution and its predecessors continues to this day to be registered under a Liberian flag of convenience.  Shipping registrations form a major part of Liberia’s foreign earnings, and have been used for purchase of arms that have been used on its population, and quite possibly on that of Sierra Leone.  Flags of convenience allow ship owners to avoid taxation and internationally agreed regulations for the safety and working conditions of its crew.  So, the International Ocean Drilling Program and NSF which funds it are in an awkward position.  The whole venture is privatised, NSF funding JOI, which in turn co-owns the famous vessel with Transocean, the world’s largest offshore drilling company.  ODP, which directs operations claims to have been too busy with that to consider the implications of ship registry….

Source:  Dalton, R. 2003.  Ship row flags up funding of war in Africa.  Nature, v.  426, p. 485.

Wildfires and uplift chronology

The “next big thing” in geomorphological studies has been said to be precisely dating crustal exhumation during erosion and uplift.  Fission tracks produced in some minerals by particles emitted by radioactive isotopes within them are preserved only when temperature is below that at which annealing can take place.  That temperature varies from mineral to mineral.  By counting the tracks it is possible to estimate the time since the containing mineral cooled below its annealing temperature during its rise to the surface.  Analysing surface samples from different topographic elevations in an area can therefore build up a history of uplift, those lowest in the section being the last to pass through the temperature, and vice versa.  Similarly, radiogenic gases only accumulate in a mineral once it cools below a temperature at which the molecular structure blocks diffusion of the gas from the mineral.  One example is radiogenic argon produced by decay of 40K.  Ages of potassium minerals, such as micas and feldspars, determined by the Ar-Ar technique relate to the time when the containing samples rose through the blocking temperature.  There are numerous problems with fission track dating, although most users assume that the ages that they get are real.  For Ar-Ar “thermochronology” the blocking temperatures are above 150ºC, which is also problematic, because for a normal continental geothermal gradient of 30ºC km-1 a sample would have to rise 5 km to reach the surface before yielding an age relevant to uplift and erosion history.  Unless a study area has much higher geothermal heat flow, or has undergone enormous rapid uplift, most ages obtained by such studies are much older than the event of interest.  In the case of helium, the blocking temperatures are lower, about 70ºC in the case of apatite.  So dating the accumulation of helium produced by decay of uranium and thorium in apatite offers a tool that seems near-ideal for studying rapid exhumation of the order of a couple of kilometres, and that seems likely for many mountain belts and continental margins.  It is the apatite U-Th/He dating method that has spurred a flurry of new studies, now that mass spectrometry is capable of precisely measuring the tiny amounts of helium in single apatite grains.  But that has its drawbacks too.  On that is pretty obvious is the effect of heating of the surface in recent times.  Sara Mitchell and Peter Reiners of the universities of Washington and Yale studied the effects of biomass burning on the method (Mitchell, S.G & Reiners, P.W. 2003.  Influence of wildfires on apatite and zircon (U-Th)/He ages.  Geology, v. 31, p. 1025-1028) because modelling suggests that fires can reset apatite ages.  They found that resetting and scrambling of ages does indeed occur, down to depths of 3 cm in surface samples.  That casts doubt on this dating not only on detrital apatites found in soils and sediment, but also in rocks, unless the exposed surfaces are ground away before separating mineral grains.  Fires are not the only means of heating rock surfaces, and high temperatures are experienced daily by many rocks due simply to solar heating at low latitudes.  This affects depths down to as much as 30 cm, especially in rocks with a dark surface.  It is possible to fry eggs on exposed rock in some parts of the world, though they are not very appetizing.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s