Welcome

1 Kimberlites in Finland

Guides:
Hugh O’Brien (GTK)
Petri Peltonen (GTK)
Marja Lehtonen (GTK)

Pre-conference fieldtrip: 7.8.-9.8.2008

Departure/Arrival: Helsinki / Helsinki

Approximated costs: 620 €

Min. participants: 20
Max. participants: 40


Abstract

The field trip will make a three-day visit to

  1. the Archean (~2600 Ma) Siilinjärvi carbonatite complex;
  2. the Neoproterozoic (~600 Ma) Kaavi-Kuopio Group I kimberlites and Proterozoic (~1230 Ma) Kuhmo olivine lamproites/Group II kimberlites in eastern Finland; and
  3. the Paleoproterozoic Jormua Ophiolite complex, specifically, alkaline dikes crosscutting upper mantle tectonites (Archean subcontinental lithospheric mantle)

We will make a ~800-km-traverse across southern and central Finland, from Helsinki on the south coast to Jormua in east-central Finland near the Russian border.

The Siilinjärvi carbonatite complex is located in eastern Finland near the city of Kuopio. It consists of a steeply dipping lenticular body roughly 16 km long with a maximum width of 1.5 km. The calcite- and dolomite-bearing phlogopite rocks form a central tabular body 600-700 m wide that is surrounded by fenite. White-green medium-grained pure carbonate rocks are not abundant at Siilinjärvi and in general true carbonatite (>50 modal % carbonates) is a relatively minor rock type. The vast majority of the central body is formed of phlogopite-rich rocks ranging from almost pure glimmerite (biotitite) via carbonate glimmerite to silicocarbonatites and finally to carbonatites. Apatite occurs throughout the central body, but is concentrated in the more carbonate-rich rocks. A concordant zircon U-Pb age of 2609 ± 6 Ma (Lukkarinen et al., 2003) shows that Siilinjärvi is one of the oldest carbonatites in the world.

As a result of active exploration during the last 20 years, twenty Group I kimberlite intrusive bodies, dominated by diatremes but also forming hypabyssal dikes, have been found in eastern Finland. They have been dated at ~600 Ma and occur near the edge of the Archean Karelian craton in two clusters, one near Kaavi and one near Kuopio. Most of these are diamondiferous. Further into the Karelian craton, in the region of Kuhmo, a series of 1200 Ma rocks intermediate to olivine lamproite and Group II kimberlite occur, predominantly as dikes and in places containing significant mantle material.

The Jormua Ophiolite Complex is a truly unique mafic-ultramafic rock complex that consists of two distinct components: (1) subcontinental (>2.8 Ga) lithospheric mantle that became exposed at seafloor due to detachment faulting, and (2) a suite of convective mantle -derived alkaline and tholeiitic igneous rocks that intruded the SCLM before and during the continental rifting between 2.1–1.95 Ga. The mantle exposed in Jormua thus mainly represents the uppermost sub-crustal lithosphere of the Archean Karelian Craton. Intriguingly, mantle xenoliths representing deeper parts of this same continental mantle have been recently recovered from 600 Ma kimberlite pipes that intrude the craton margin 100 km SSE of Jormua. In Jormua, we will particularly examine residual mantle tectonites and alkaline ultramafic lamprophyre (ankaramites) dike rocks – and their pyroxenitic and hornblenditic mantle cumulates –that intruded the mantle tectonites during initial stages of rifting of the Karelian Craton at c. 2 Ga.

 

 

 



Day-to-day

Thursday 7.8.
08.00   Bus departs from Helsinki central railway station to the Helsinki-Vantaa airport
08.30 Depart from the Cumulus Airport hotel
10.00 Arrival at Loppi drill core repository Introduction to drill core material of Finnish kimberlites, olivine lamproites and carbonatites BBQ lunch on the lawn sponsored by GTK
14.00 Depart to Siilinjärvi
19.00 Arrival to Kunnon Paikka Hotel, Siilinjärvi, sauna+swimming
20.00 Dinner

Friday 8.8.                                       
08.00 Leave to the Archean Siilinjärvi carbonatite complex
08.30 Arrive Siilinjärvi Mine and tour the open pit
11.30 Lunch at the mine
12.30 Depart to Kaavi
13.15 Kimberlite exposures of Pipes 1 & 2, and kimberlite boulders
15.15 Leave to Kuhmo
18.00 Arrival to Hotel Kalevala, Kuhmo
18.30 Sauna
19.45 Dinner

Saturday 9.8.
08.00 Leave for Seitaperä
09.00 Stop at Seitaperä Group II kimberlite-Olivine Lamproite intrusion
10.30 Leave to Jormua complex
12.00 Arrive Proterozoic Jormua ophiolite complex, upper mantle lithologies, field lunch
16.00 Drive from Jormua to Kajaani Airport
16.45 Arrival at Kajaani airport for 17.55 evening flight to Helsinki.