Aim of the project

There is a continuous geological cycle on the planet Earth which emphasizes the transition between the three major rock groups; sedimentary, metamorphic and igneous rocks. At any stage in this cycle the different rock types can be uplifted and eroded to produce sediments, which lithify to form sedimentary rocks. Sedimentary rocks are metamorphosed to form metamorphic rocks, and at the highest levels of metamorphism are melted to form igneous rocks. Migmatites are a special group of rocks which are generated at the highest levels of metamorphism. They consist of rocks which start to melt and often leave an unmelted metamorphic rock surrounded to a greater or lesser extent by a granitoid melt (photo 1). This cycle is intimately connected with plate tectonics. At convergent plate margins rocks are subducted to great depths and therefore to higher pressures and temperatures. Due to the high pressure and temperature environment new minerals are created or mineral structures change, adapting to the increased temperature and pressure. Hence the rock is metamorphosed. When plates collide, rocks are not only subducted but also pressed upwards, thickening the crust. This thickening produces mountain chains. When rocks are uplifted, topographic relief increases, erosion increases, bedrock is eroded and in time more sedimentary rocks are produced. This entire cycle is exposed in north-western Spitsbergen.

This expedition is a continuation of last year’s work along the NW coast of Spitsbergen (Pease, 2003). The primary aim of this research is to unravel the origin of northwest Spitsbergen’s exotic terranes, and ultimately to understand the tectonic development of the Arctic. The question to answer is: where did Spitsbergen’s northwestern terranes originate, north or east Greenland? Last summer migmatites and granites were sampled. The zircon ages from the collected samples will be compared with the zircon ages preserved in the Signehamna Formation (photo 2), which consists mainly of schists and quartzites (Ohta, 2002). This correlation will show whether the migmatites and granites are coeval and a result of extreme metamorphism (migmatite genesis) of the Signehamna Formation. If the Signehamna Formation is ”parent” to the granitic rocks, the inherited zircons in the granites will have the same ages as the zircons in the Signehamna Formation. Other granites from the NW terrane yield mainly late Caledonian ages between 420-430 Ma (Ohta et al., 2002; Balasov et al., 1996).

Field season 2004

The expedition arrived via helicopter on 28 July at base camp 1, east of Krossfjorden. We worked for two weeks in the area around Krossfjorden with the aid of a Zodiac boat. Thereafter our Russian colleagues moved further south and transported the Swedish-Norwegian group to base camp 2, located at the northern side of Kongsfjorden. The fieldwork continued with Zodiac transport to selected parts of Kongsfjorden. After one week at base camp 2, the Swedish participant left the camp as a passenger with the tourist boat MS Nordstjernan back to Longyearbyn.

Luckily polar bears were absent this field season. Instead we had more friendly visitors like beluga whales and very curious seals. Also, a reindeer happened to set off our tripwires. Probably he was a bit upset with us since we collected same delicate mushrooms growing close to base camp 1 (photo 3), which he quite likely wanted to have for himself.

Preliminary results

The primary focus of this field season was the schists of the Signehamna Formation and the migmatites and granites to the east, which occur in a north-south swath all the way up to the north coast. The samples were collected along north-south and west-east profiles. It is not only their ages which are of interest; their chemical characteristics may reveal if the schist and granitic rocks are related. The schists were also sampled for pressure and temperature studies, to deduce how deep they were before being exposed at the surface. The majority of the granites give late Caledonian ages, however the timing of migmatization is not known. Ohta et al. (2002) reported Grenville and older ages for zircons collected from a granitic part of the migmatite, therefore they suggested that a significant tectonothermal event occurred during Grenvillian time (approximately 1 050 Ma) with a less extensive tectonothermal event in the Caledonian.

Working on the genesis of the migmatites will consequently also determine which tectonothermal event produced the majority of the migmatites. A recent study (Johansson et al., in press) dated migmatites in the Eastern terrane to 410-430 Ma. Are they related to the migmatites in the NW terrane? Work during the coming year will address that question by comparing the data from Johansson et al., (in press) with the determined ages and chemistry from the sampled migmatites.

Signehamna Formation also contains marble units, which reflects a different depositional environment relative to the dominant siliciclastic facies. The migmatites do occasionally contain large marble blocks. To what extent did the marbles in the migmatites take part in the melting and do they have the same geochemistry as the marble units in the Signehamna Formation? Hence, if their isotopic signatures are similar, they will give further support to the hypothesis that the Signehamna Formation is the parental rock to the migmatites. In Blomsterhalvøya, the Precambrian Generalfjella Formation is in tectonic contact with Silurian-Devonian (approximately 420-400 million years ago) sedimentary rocks. Their appearance is very similar to the Silurian-Devonian sedimentary rocks found in Raudfjord. Do their external similarities indicate the same source area, from which the sediments were derived? This kind of problem will be addressed with the help of zircons. Zircon is very useful for deducing the provenance of sedimentary rocks. Due to its resistance to weathering and erosion, zircon ages are preserved. Therefore if these sediments have zircon grains with comparable ages it is likely that they have a common bedrock source. More importantly, this information indicates the ages of rocks that were eroding at the time the sedimentary rocks were being formed. So where can we find them today?

There are several questions to be answered, but the major question is how these different rocks are related to Greenland. That question will hopefully be answered when the ages, geological history and chemical characteristics of these samples are compared with those of north and east Greenland.