school of geosciences - university of edinburghfigure 2. a) cosmogenic nuclide depth profiles can...
TRANSCRIPT
Cosmogenic nuclide concentrations are commonly used to determine ‘exposure ages’ and ‘erosion rates’. Some common examples include:
Exposure dating• Glacier erosion/deposition surfaces: striated bedrock, erratics, moraines• Fluvial and glaciofluvial terraces• Buried sediments: caves, glacial till• Rockfalls• Fault scarps• Lava flows• Flood deposits• Alluvial fans
Rates of landscape change• Rock surface erosion rates• Land surface degradation rates• Basin‐wide erosion rates• River incision rates• Modern erosion (meteoric 10Be)• Fault‐slip rates
1 INTRODUCTION 5 APPLICATIONS3 CAPABILITIES
2 FACILITY DESCRIPTION
Terrestrial cosmogenic nuclides form inrock minerals exposed in the upper ~2 mof Earth’s surface through interactionwith cosmic radiation (Fig. 1). Theconcentration of cosmogenic nuclides innear surface rocks will increase throughtime until their production is matched bytheir losses through physical erosion andradioactive decay. Thus, theconcentration of cosmogenic nuclides inrock or sediment is a balance betweenits exposure time and erosion rate. Thisknowledge can be applied in a range ofsettings to quantify dates and rates ofEarth surface processes.
This facility is designed to makepossible the measurement ofcosmogenic nuclides in rock andsediment. Here, we chemicallyextract cosmogenic isotopes fromrock and sediment and preparetargets ready for measurement byAccelerator Mass Spectrometry(AMS). We are able to supportpreparation work for all of the majorcosmogenic isotopes includingcosmogenic 10Be, 26Al, 36Cl, 21Ne, 3Heand 14C. The AMS or MS analysesare conducted at the ScottishUniversities Environment ResearchCentre or other collaborativeinstitutions.
Rock crushing and sieving‐Dedicated lab space‐Disk mill‐Sieves‐Frantz magnetic separator‐Sample splitter
Extraction of quartz from rock/sediment‐Dedicated lab space‐Shaker tables‐Ultrasonic baths‐Frantz magnetic separator‐HF‐rated fume cupboard with scrubber‐Scales‐Ovens
Preparation of 10Be, 26Al and 36Cl targets‐2xDedicated clean labs‐3xHF/Perchloric acid‐rated fume cupboards and scrubbers‐Laminar flow fume cupboard‐Ultrapure water system‐Scales‐Press‐Ovens
What can be analysed?Most nuclides are measured fromwithin quartz minerals. Therefore, anyquartz‐rich rock or sediment can beanalysed. However, chlorine can bemeasured in nearly any rock, and isparticularly useful for carbonate rockssuch as limestone.
We have a full‐time laboratory technician, post docs and PhD students associatedwith the lab. Charges are set for analyses to recover costs through a modelrecognised by UK Research Councils. We offer a reduced rate for PhD researchprojects. If you are considering a project that would involve cosmogenic nuclideanalysis, please speak to us!
Contact: Dr. Andrew Hein
6 FURTHER INFORMATION
‘Target’ nucleus16O
10Be
10Be ~98% production16O(n,4p3n)10Be28Si(n,6p3n)210Be
26Al ~98% production28Si(n,p2n)26Al
Fig. 1. Cosmogenic nuclide production occurs in nearsurface rocks, mainly through spallation reactions (leftdiagram): a fast incoming particle hits the nucleus of anatom. Nucleons (protons and neutrons) are sputteredoff leaving a lighter residual nucleus behind.Spallation reaction
SampleCrush
Mill and sieve Acid etch
10Be concentration!26Al concentration!36Cl concentration!
Crush
Chemical isolation and purification of 10Be, 26Al
AMS target
• isolate target mineral• remove meteoric variety
4 THE PROCESS
Figure 3. A) Cosmogenic 10Be dating of glacial erratics tocontrain the timing of thinning of the Antarctic Ice Sheet. B)Use of multiple cosmogenic nuclides (26Al, 10Be and 21Ne)can give insight on the exposure history; it is possible todetermine if a rock has been continuously exposed, or if ithas been buried for a significant period of time. C) We haveused this information to constrain the history of the WestAntarctic Ice Sheet (Hein et al., 2016a, 2016b).
C
B
A
Figure 3. Cosmogenic nuclides can be used to constrainbasin‐wide erosion rates. In this case, providing data thatcan be used to constrain land surface erosion models (Hurstet al., 2013).
A B
Figure 2. A) Cosmogenic nuclide depth profiles canadd valuable information on the age, erosion rateand inheritance. Here a 10Be depth profile is use toconstrain the age of a glacial outwash terrace. B)Modelling can then be used to optimise the best fitto the data (Hein et al., 2009).
School of GeoSciences