GEUS Bulletin (Geological Survey of Denmark and Greenland)
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Analysis of Palaeogene strike-slip tectonics along the southern East Greenland margin (Sødalen area)
No full textThis paper describes structural data collected during field work in southern East Greenland, a region characterised by a complex tectonic history. Here, 3D photogeology based on aerial and oblique photographs using high-resolution photogrammetry of a 150 km2 area in Sødalen in southern East Greenland shows ESE–WNW-trending faults cross-cutting Paleocene rift structures and flexure-related normal faults. The kinematic analysis highlights oblique and left-lateral strike-slip movements along faults oriented 120°. Strike-slip and dip-slip kinematic indicators on the walls of the chilled contacts between alkaline E–W-oriented dykes and the volcanic host rocks suggest that the faults and dykes formed at the same time, or maybe the faults were re-activated at a later stage. Palaeostress analysis, performed by inversion of fault-slip data, shows the presence of three different tectonic events. Coupling the 3D photogeological tool with structural analysis at key localities is a fundamental way to understand better the tectonic history of such a large area
The East Greenland rifted volcanic margin
No full textThe Palaeogene North Atlantic Igneous Province is among the largest igneous provinces in the world and this review of the East Greenland sector includes large amounts of information amassed since previous reviews around 1990.
The main area of igneous rocks extends from Kangerlussuaq (c. 67°N) to Scoresby Sund (c. 70°N), where basalts extend over c. 65 000 km2 , with a second area from Hold with Hope (c. 73°N) to Shannon (c. 75°N). In addition, the Ocean Drilling Project penetrated basalt at five sites off South-East Greenland. Up to 7 km thickness of basaltic lavas have been stratigraphically and chemically described and their ages determined. A wide spectrum of intrusions are clustered around Kangerlussuaq, Kialeeq (c. 66°N) and Mesters Vig (c. 72°N). Layered gabbros are numerous (e.g. the Skaergaard and Kap Edvard Holm intrusions), as are under- and oversaturated syenites, besides small amounts of nephelinite-derived products, such as the Gardiner complex (c. 69°N) with carbonatites and silicate rocks rich in melilite, perovskite etc. Felsic extrusive rocks are sparse. A single, sanidine-bearing tuff found over an extensive area of the North Atlantic is thought to be sourced from the Gardiner complex.
The province is famous for its coast-parallel dyke swarm, analogous to the sheeted dyke swarm of ophiolites, its associated coastal flexure, and many other dyke swarms, commonly related to central intrusive complexes as in Iceland. The dyke swarms provide time markers, tracers of magmatic evolution and evidence of extensional events. A set of dykes with harzburgite nodules gives unique insight into the Archaean subcontinental lithosphere.
Radiometric dating indicates extrusion of huge volumes of basalt over a short time interval, but the overall life of the province was prolonged, beginning with basaltic magmas at c. 60 Ma and continuing to the quartz porphyry stock at Malmbjerg (c. 72°N) at c. 26 Ma. Indeed, activity was renewed in the Miocene with the emplacement of small volumes of basalts of the Vindtoppen Formation to the south of Scoresby Sund.
Although the basalts were extruded close to sea level, this part of East Greenland is a plateau raised to c. 2 km, but the timing of uplift is controversial. Superimposed on the plateau is a major dome at Kangerlussuaq.
East Greenland presents a rich interplay between magmatic and tectonic events reflecting the birth of the North Atlantic Ocean. It was active over a much longer period (36 Ma) than other parts of the province (5 Ma in the Hebrides, Northern Ireland and the Faroe Islands) and contains a wider range of products, including carbonatites, and felsic rocks tend to be granitic rather than syenitic. As expected, there are many similarities with Iceland, the present-day expression of activity in the province. Differences are readily explained by higher production rates and the thicker lithospheric lid during the early stages of development in East Greenland. The igneous and related activity clearly results from plate-tectonic factors, but the relationship is not understood in detail. In particular, the nature of the underlying mantle processes, primarily the presence or absence of a plume, is still not resolved
Geological characterisation of potential disposal areas for radioactive waste from Risø, Denmark
No full textLow- and intermediate-level radioactive waste from the Danish nuclear research facility, Risø, includes construction materials from the reactors, different types of contaminated material from the research projects and radioactive waste from hospitals, industry and research institutes. This material must be stored in a permanent disposal site in Denmark for at least 300 years (Indenrigs- og Sundhedsministeriet 2007). The Ministry of Health and Prevention presented the background and a decision plan for the Danish Parliament in January 2009 (Ministry of Health and Prevention 2009) and all political parties agreed to the plan. In the beginning of 2011 three studies were presented to the parliament (http://www.im.dk/Aktuelt/Nyheder/ Forebyggelse/2011/Maj/Slutdepot.aspx): (1) A pre-feasibility study for the final disposal of radioactive waste, (2) a study on radiation doses from the transport of radioactive waste to a future repository and (3) a study on identifying potential disposal areas. The latter study was conducted by the Geological Survey of Denmark and Greenland (GEUS) and the aim was to locate a sediment or rock body with low permeability down to 100–300 m below the ground surface. The ultimate goal is long-term protection of people and environment by isolating the radioactive waste in a final depository. This goal can be reached by identifying a significant volume of sediments or rocks characterised by a low flow regime and high absorption potential. GEUS was given the task to locate approximately 20 potential disposal areas
Quality control of airborne geophysical data from the EU Mining Sector Support Programme, Ghana
No full textOn 2 December 2002, EU Commissioner Poul Nielson on behalf of the European Development Fund signed a €40 million grant to the Ghana Government. The purpose of this grant was to finance a Mining Sector Support Programme (MSSP) that covered a broad spectrum of geoscientific projects and other projects aimed at an overall strengthening and modernisation of Ghana’s mining sector. One of the major components was collection and interpretation of airborne geophysical data contracted to the two commercial geophysical companies Fugro Airborne Surveys and Geotech Airborne Ltd. The Geological Survey of Denmark and Greenland (GEUS) was contracted to perform the quality control (QC) of the airborne geophysical data collection and processing in a separate MSSP project (No 8 ACP GH 027/37). The initial Provision of quality-control services to the Airborne Geophysical Survey required GEUS to be on site in Ghana for 22 man-months; an expansion of the programme and various circumstances (see below) resulted in a total of 37.25 man-months before the project was completed in January 2010. The Danish National Space Center was subcontracted by GEUS to perform part of the QC of gravity data acquisition and processing. The QC project was reported by Thorning et al. (2010)
Differentiation of Palaeogene sand by glauconitic and geochemical fingerprinting, Siri Canyon, Danish North Sea
No full textThe submarine Siri Canyon is NE–SW-oriented and located in the Danish North Sea (Fig. 1). It contains a number of oil reservoirs with glauconite-rich sand. The reservoirs of interest in the Nini oil field are the Late Paleocene Tyr Member of the Lista Formation and the Kolga Member of the Sele Formation (Schiøler et al. 2007), presumably of Early Eocene age. These members have previously been known as the Ty and Hermod members (Hamberg et al. 2005; Poulsen et al. 2007). The sand shows signs of injection, both in cores and in seismic data. The aim of this work is to chemically characterise and fingerprint the sand in order to reveal the origin of the sand found in three horizontal wells, which could have been injected from one or both of the Tyr and Kolga members. Core samples were collected from two vertical wells of known stratigraphy to make a basis of comparison, whereas samples of the cuttings were collected from the three horizontal wells with ages primarily corresponding to the Kolga Member. The purpose was moreover to evaluate whether cuttings samples can be used for fingerprinting as an alternative to core samples
Free, online Danish shallow geological data
No full textGeological data at the Geological Survey of Denmark and Greenland (GEUS) have been available on the internet for more than 10 years. The first step in making geological data available online was the launch of web access to data from water supply wells (Tulstrup 2004). The database is called Jupiter, and currently data from more than 260 000 shallow wells are available to the public. Figure 1 shows an example of a map from the Jupiter database available in a web-browser. The first web access was via a text-based search form which supplied data lists and graphical well reports. In recent years, the interface has been extended with more data, map interfaces and extra functionality. This paper describes this development and illustrates the increasing value of the digital data at GEUS
Comprehensive Nuclear-Test-Ban Treaty – a peace-keeping initiative with scientific impact
No full textAny major shaking of the Earth can be recorded on a seismograph regardless of the nature of the source. Earthquakes and large explosions generate waves with similar frequency content. This fact has been used for decades to construct systems to monitor detonations of underground nuclear explosions. The quality of the monitoring system has increased significantly in recent years, and we demonstrate here that the data are useful in Danish earthquake research
Remnants of Mesoarchaean oceanic crust in the Tartoq Group, South-West Greenland
No full textThe Tartoq Group is located in the Sermiligaarsuk fjord region in South-West Greenland in an area of approximately 20 × 50 km (Fig. 1). The Tartoq Group consists of several discrete, fault-bound blocks of metavolcanic rocks, surrounded by Archaean tonalite-trondhjemite-granodioritetype (TTG) gneisses. A zircon age of 2996.3 ± 5.9 Ma of a TTG intrusion provides a minimum age for the formation of the Tartoq Group (Fig. 2). The metavolcanic rocks probably show the lowest degree of metamorphism found anywhere in the Archaean craton of Greenland. Here we present a new model for the origin of the metavolcanic rocks of the Tartoq Group based on geochemical, metamorphic and structural data. The samples used for this study were collected by the Geological Survey of Denmark and Greenland (GEUS) in 2009 and 2010. The study is part of a joint project between the Greenland Bureau of Minerals and Petroleum and GEUS on the mineral potential of south-western Greenland
Identifying potential geothermal reservoirs in Denmark
No full textConcerns about climate change have led to increased interest in geothermal energy as one way of reducing the consumption of fossil fuels and thus limit CO2 emissions. Use of geothermal energy is based on well-established technologies, a high degree of security of supply, and little visual or noise inconvenience. More than one hundred plants have been established in Europe. There is a large potential for using geothermal energy from the Danish subsurface, as first pointed out by Balling (1976). Geothermal energy is highly suitable for district heating systems and is expected to cover a large part of the demand for district heating in the future. Two Danish geothermal plants, the Thisted plant in northern Jylland and the Margretheholm demonstration plant near Copenhagen (Fig. 1), have shown that it is possible to produce large amounts of warm water for district heating. Only 5–10% of the total energy output from the plant is used to extract the heat from the subsurface by pumping warm formation water to the surface and returning it to the subsurface in a closed system. The plants use absorption warmth pumps, which need steam and hence give rise to consumption of (fossil) fuel. Both Danish plants have two wells, a production well and an injection well in which the cooled formation water is returned to the geological reservoir at about 1 km away from the production point, in order to avoid mixing of warm and cold water (Fig. 2). Geothermal energy can also be used for electricity production, but Danish subsurface tem-peratures are currently not believed to be sufficiently high to produce electricity directly
Vietnamese sedimentary basins: geological evolution and petroleum potential
No full textA number of sedimentary basins of various ages are located onand offshore Vietnam (Fig. 1). Some of them have significant petroleum resources and have thus attracted interest from industry and academia (Rangin et al. 1995; Matthews et al. 1997; Lee & Watkins 1998; Lee et al. 2001). Moreover, Vietnam is located in a position central to the understanding of the geological development of South-East Asia (Hall & Morley 2004). The structural style and the stratigraphy of the Vietnamese basins thus provide a valuable record about the development of South-East Asia throughout the Phanerozoic and the subsequent Eocene as well as younger deformation associated with the collision and indentation of India into Eurasia and the opening of the South China Sea (Fyhn et al. 2009a, 2010a)