Petrological and geochemical studies help to unravel the geological history of regions, rock formations, and mineral deposits. Together with geological mapping they form the basis for evaluation of economic potentials.
We use microscopy of rocks and mineral textures, rock geochemistry, mineral geochemistry, isotope chemistry, fluid inclusion studies, age dating, and modelling in the studies.
Greenland is dominated by metamorphic rocks formed during plate tectonic cycles of rifting, collision, mountain building, denudation, and metamorphism. Petrological, geochemical and age studies are used for understanding:
• Regional metamorphic regimes during assemblage of continents
• Regional and local geochemical regimes related to mineralisation events
• The history and age of the continental areas
Igneous rocks are related to continental break-up, continental rifting, and collision of land masses. The petrology and geochemistry of igneous rocks reflect the dynamic environment and give indications for the economic potential of individual occurrences as well as larger igneous provinces both onshore and offshore. The studies include:
• Volcanics of the Tertairy North Atlantic Igneous Province: description of geological history, environments, mantle melting processes, and melt fractionation processes
• Fundamental principles of magma evolution and crystallisation in magma chambers
• Description and evaluation of ore deposits in igneous complexes
• Origin of continental carbonate-rich magmatism in central complexes and kimberlitic provinces
• Regional lithological, textural and geochemical environments of mineralisation events
• Critical parameters for the development of mineral deposits
• Parageneses of mineralisation for evaluation of potentials and processing
Geochronology and applied mineralogy
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.
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 mass spectrometry. Apart from zircon, the lab has experience with dating of baddeleyite, perovskite and rutile minerals that often occur in rock types that are barren of zircon, and we are looking to develop new dating techniques utilizing, for example, monazite and apatite.
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 fingerprint of chemical characteristics in such materials can be used to determine the likely origin (provenance) of a specific sample.
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 bodies 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 or by matching the mineral suite in the sediment to that of the source rock.