Monday, January 17, 2011

Chasing volcanic intruders on Greenland

As a follow-up to the Arctic adventure from the last blog post, I will show some of the geological gems of West Greenland. Along Vaigat north of Ilulissat, volcanic rocks belonging to the North Atlantic igneous province crop out. The volcanism took place in a near-shore environment about 55-56 million years ago. At the same time, the Earth experienced a 200.000 year period of global warming (the so called Paleocene-Eocene thermal maximum; PETM). I went there the summer of 2006 to sample sills, dikes, and metamorphic sediments, as I work with an hypothesis linking the volcanism to the climate change.

The pictures of the week show 1) igneous dikes cross-cutting Cretaceous sandstone and coal beds, and 2) a sill intrusion outcropping like a big massive whale. Spectacular outcrops, indeed. 

The whale:

An interesting feature of volcanic intrusions is that they heat the surrounding sediments. This may sometimes lead to mobilization of the sediments. The picture below shows a sandstone intrusion into coal beds, possibly mobilized as a consequence of volcanic activity – although high pressures in the sand layer (for instance due to high water content and rapid burial) could have played a role as well. 

Saturday, January 8, 2011

The wonders of winter geology

One of the great things about being a geologist is the possibility to go to warm places when it’s winter and cold in Norway. I can’t imagine anything better than leaving Oslo in, lets say April, and heading for late summer in South Africa. The warm weather feels inspiring and even rewarding for the field work. And of course, when coming back to Oslo again, the spring miracle has arrived. 

In April 2010 I did the opposite. Instead of seeking the exciting geology of South Africa, with all the sill intrusions and metamorphic sediments, I headed north. To Svalbard. As far as I’m concerned, this is ultima Thule. 78 degrees north. And very cold indeed.

But the geology is fantastic (and actually fairly similar to what we find in South Africa). The picture of this week shows a landscape where the topography is dominated by black hills. Site: Diabasodden. These black hills represents volcanic sill intrusions and the primary target for the fieldwork.

The sills are part of a Large igneous province that formed in the Cretaceous, with remnants scattered across the Arctic. The precise ages of the intrusions are actually not known, and together with colleagues the plan was to find out when the rocks formed – once and for all. So we needed to find zircons. Easier said than done… Zircon is commonly absent from basaltic rocks.

Rumors from the lab: the zircons are there!

We collected nice pieces of blackish rocks, and headed back to Longyearbyen with the snow scooters. They are truly remarkable pieces of machinery, and after some practice I did 100 km/h on the snow and ice.

I’m sure you wonder why we went to Svalbard to do geology during winter. Well, the 10 degrees below zero made the snow scooter trips easy, and we could reach far out from Longyearbyen without having to hike forever or rely on helicopter – as you normally will have to if you go there in the summer. The sills form vertical escarpments commonly without snow cover.  

One of the best fieldtrips ever!