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DEPARTMENT OF PETROLOGY AND ECONOMIC GEOLOGY

Geological Survey of Denmark and Greenland (GEUS) 		GEUS logo - link to main page

GEOCHRONOLOGY AND APPLIED MINERALOGY
Contact
Nynke Keulen
Nynke Keulen
CCSEM, rubies and provenance
 
E-mail: ntk@geus.dk
Telephone: 3814 2251

Thomas Find Kokfelt
Thomas Find Kokfelt
Geochronology and ICP-MS on trace elements
 
E-mail: tfk@geus.dk
Telephone: 3814 2273

Kristine Thrane
Kristine Thrane
Geochronology and provenance

E-mail: kt@geus.dk
Telephone: 3814 2256


The Scanning Electron Microscopy (SEM) and Laser-Ablation ICP-MS laboratories at GEUS are used for geochronology, and applied mineralogy. Both methods can be used to determine the source region (provenance) of sediments. Geochronology
Laser-Ablation Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS) analyses are applied to determine the age of rock samples and geological processes. Analyses are routinely performed on zircon grains, a mineral that occurs in trace amounts in a broad variety of crystalline and sedimentary rocks. The age determination is based on the principles of radioactive decay of uranium (238U and 235U) to lead (206Pb and 207Pb), as zircon typically contains abundant uranium. The standard applied method involves in situ measurement of mounted and polished grains and analysis by mass spectrometry. Apart from zircon, the lab has experience with dating of baddeleyite and perovskite, minerals that often occur in rock types that are barren of zircon, and we are looking to develop new dating techniques utilizing, for example, rutile, monazite and apatite.

Applied Mineralogy
The Scanning Electron Microscope (SEM) can be applied to characterize sand, ores, and non-geological materials like building materials, concrete or dust. Both the chemical properties (major and minor elements) and material properties (grain size, grain shape) are analysed by a combination technique of Energy Dispersive X-ray spectrometry (EDX) measurements and image analysis. The measurements are performed semi-automatically by so-called Computer-controlled Scanning Electron Microscopy (CCSEM). We perform routine analyses on sand, crushed sandstones, soil samples and certain kinds of ores, and we have experience with a range of other materials.

The LA-ICP-MS can be used to determine accurate trace element concentrations in various geological materials such as minerals (e.g. ruby corundum), sands, sandstones and ores, as well as in materials such as mollusk shells and fish shales. The fingerprinting of chemical characteristics in such materials can be used to determine the likely origin (provenance) of a specific sample.

Provenance analysis
The source region (provenance) of a sediment sample can be determined by combining one or several of the tools mentioned above. It is aimed to reconstruct the parent rock of sand and, if possible, the climate conditions during the formation of the sediments. The source rock can be 'reconstructed' from a comparison of zircon age distributions (or of other minerals suitable for dating like rutile or monazite) with age patterns of potential source rocks; this is done by matching the mineral suite in the sediment to that of the source rock.

Zircon mineral with a baddeleyite core
Zircon mineral (ZrSiO4) with a baddeleyite
(ZrO2) core.

Sapphirine mineral with inclusions of rutile (dark red) and biotite (brown)
Sapphirine mineral (Al2O3) with inclusions
of rutile (dark red) and biotite (brown).
Differences in colour of the sapphirine
result from different fractions of the trace
elements Titanium, Chromium and Iron.

Geological map of part of East-Greenland with a sedimentary basin in brown

Geological map of part of East-Greenland
with a sedimentary basin in brown. Different
mineral suites in the sediment are indicated
by pie diagrams. Red arrows indicate where
the parent rock of the sediment might be
located. ( See large figure)

[Top]   Last modified: September 15, 2011 © Geological Survey of Denmark and Greenland - GEUS
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