May 6th – 8pm In person and online
The Gjerdingen Ekerite, Oslo Rift Valley, Norway
The Oslo Rift Valley covers an area of approximately 100,000 km2 and is made up of a wide variety of both volcanic and plutonic rocks. It is most famous for the Larvik Plutonic Complex, which consists of 10 plutons or “rings” from which 260 mineral species, including 35 type mineral species, have been described, and quarrying for larvikite is the main industry. The Oslo Rift Valley has been the subject of geological and mineralogical research since the 1800’s, with W.C. Brøgger writing the quintessential monograph on the Larvik area entitled “Die Mineralien der Syentipegmatitgänge der südnorwegischen Augit-und Nephelinsyenite” in 1891. The Gjerdingen ekerite, or alkali granite, is a small (2 x 4 km) intrusion located ~ 30 km north of Oslo, Norway. It is one of the latest phases of magmatism in the Oslo Rift Valley sequence, formed after the Larvik Plutonic Complex. The Gjerdingen ekerite is dominated by quartz, anorthoclase perthite feldspar, Na-amphibole, aegirine and the rare mineral elpidite. It is rich in miarolitic cavities which contain a wide array of rare mineral species including a suite of rare fluoride minerals. To date, 60 mineral species have been found at the locality, including 3 type minerals – janhaugite, gjerdingenite-(Fe) and gjerdingenite-(Mn). Early work by Gunnar Raade from the Natural History Museum in Oslo, now retired, lead to detailed articles on the mineralogy of the cavities and the discovery of three new species. Further work on the ekerite and the neighbouring nordmarkites (syenite) at the Delebekken locality is being conducted in collaboration with the Natural History Museum in Oslo with the goal of shedding light on the paragenesis of these unique and famous mineral collecting sites. This talk will focus on the history of the Oslo Rift Valley and a summary of recent fieldwork in the Gjerdingen area.
Dr. Paula Piilonen is a research scientist in the Mineralogy Section at the Canadian Museum of Nature in Ottawa where she has worked for the last 24 years. She completed a B.Sc. in geology at Laurentian University (1997), a Ph.D. in Earth Sciences at the University of Ottawa (2001), and a post-doctoral fellowship at Université de Marne-la-Vallée (France, 2002) before starting with the Museum in April 2002. Her work is focused on the mineralogy, crystal chemistry and behavior of rare elements in alkaline systems, in particular the minerals that are formed during late-stage, autometasomatic or hydrothermal processes. Her fieldwork has brought her to Norway, Cambodia, Thailand, the USA and across Canada including Baffin Island, Mont Saint-Hilaire, Quebec, and the Rocky Mountains in British Columbia. She lives in rural Dunrobin on the Ottawa River with her husband, Reni, and their very entitled cat Fergus. She is an avid squash player, a certified Muay Thai instructor, enjoys mountain biking, kayaking and fishing on the Ottawa River but more likely can be found relaxing on the deck with a beverage watching the sunsets.