LINKING ONSHORE AND OFFSHORE GEOLOGY IN GREENLAND
Characterisation and dating of faults and fractures in West Greenland

Jeroen van Gool and Knud Erik Klint (Department of Quaternary Geology), with Jonas Ekestubbe,Robert Wilson, Frederik Jensen (PhD and Master students).

Fault systems are fundamental in the development of sedimentary basins. Fault systems in the basins in the Davis Strait are expected to extend on land in West Greenland. In this project, the onshore fault systems in central west Greenland are studied in order to improve the understanding of the offshore basin development, which is important for the ongoing hydrocarbon exploration and promotion of the region towards the international petroleum industry.

Purpose of the study
- Distinguish, outline and characterise the different fault systems onshore
- Understand the kinematics and timing of the regional fault movements
- Correlate onshore fault systems with those offshore
- Improve the understanding of the fault control on basin development

Study area
In the summer of 2003 fieldwork was carried out in an area along the coast stretching from Nordre Strømfjord (Nassuttooq) in the north to Nordre Isortoq in the south. This area was selected for two reasons.
1. It is believed that the two ENE-striking Palaeoproterozoic shear zones that occur here, the Nordre Strømfjord shear zone and the Nordre Isortoq steep belt, were reactivated and their presence played an important role in the development of the Mesozoic to Tertiary sedimentary basins. The western along-strike projection of the Nordre Isortoq steep belt coincides with the southern fault boundary of the Sisimiut basin offshore.
2. Offshore basins occur very close to the coast in this area, and the offshore (extensional?) faults that drop the top of the basement down to 3 km below sea level, within 10 km west of the coast, are believed to correlate with fault escarpments on shore in this area.

Working method
During the fieldwork, fault and fracture systems were mapped and abundant structural data were collected for statistical/structural analysis. The work includes:
Characterisation of fault systems in terms of:
– orientation
– kinematics
– fault surface characteristics
– mineralisation
event stratigraphy – relative ages of deformation phases
age determinations of fault rocks, providing absolute ages
structural/statistical analyses to determine kinematic patterns

Dating of fault and fractures
We intend to estimate the timing of brittle deformation by dating of:
- pseudotachylite
- slickensides
- fracture fill (providing minimum age)
- hydrothermal alteration (providing minimum age)
- intrusive rocks
This will be done mainly by 40Ar/39Ar and Pb-Pb geochronology.

References
Chalmers, J. A. & Pulvertaft, T. C. R. (2001). Development of the continental margins of the Labrador Sea: a review. In Wilson, R. C. L., Whitmarsh, R. B., Taulor, B. &

Froitzheim, N., Non-volcanic Rifting of Continental Margins: A Comparison of Evidence from Land and Sea Geological Society (London) Special Publication, 187, p. 79-107.

Japsen, P., Bonow, J., Klint, K.E. and Jensen, F.K. 2002: Neogene uplift, erosion and resedimentation in West Greenland. Field report summer 2002. Geological Survey of Denmark and Greenland, rapport 2002/71.

van Gool, J.A.M., Connelly, J.N., Marker, M. and Mengel, F.C., 2002: The Nagssugtoqidian Orogen of West Greenland: tectonic evolution and regional correlations from a West Greenland perspective. Canadian Journal of Earth Sciences, 39, p. 665-686.

Figure captions
Structural map of the northern Labrador Sea, Davis Strait and southern Baffin Bay (modified from Chalmers & Pulvertaft, 2001) with the major onshore structural trends north of Sisimiut and south of Disko Bay shown in red. Note that the southern margin of the Sisimiut Basin appears to be the extension of the southern one of the two trends onshore. Faulting within the Sisimiut Basin can also be seen along the offshore extension of the northern trend.

Tectonic map of the Nagssugtoqidian orogen, showing the fieldwork area (summer 2003) and the location of the Nordre Strømfjord shear zone and Nordre Isortoq steep belt. From van Gool et al. 2002.

Fracture map of a key area near the mouth of Nordre Strømfjord.

Schematic representation of the preliminary interpretation of the main NNE- and ENE trending structures along the coast. Offset extensional faults down-drop the western block by about 1 km.