2011

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Epochs of long duration Kola alkaline province of Fennoscandian Shield

Mitrofanov F.P., Bayanova T.B.

Geological Institute of Kola Science Centre RAS, Apatity, Russia

felix@geoksc.apatity.ru

New U-Pb on zircon and baddeleyite data from alkaline and carbonatites of Neoarhean, Paleoproterozoic and Paleozoic rocks of Fennoscandian Shield is introduced.

In Kola alkaline province are wide known its complete spectrum of different alkaline rocks of Paleozoic age, but in recent time there are established alkaline rocks of Neoarhean and Paleoproterozoic ages.

For the first time in Murmansk domene zircon from albite syenite of Paneavrsky massif yielded U-Pb age with 2653±9 Ma (Petrovsky et.all, 2009). New U-Pb ages 2668±7Ma on zircon gave for eugerin-auvgite granosyenite Mt.Sylngyraz (collection of Chshashin V.).

In Keivy terrane Neoarhean alkaline granite and sienite are widespread with massifs Belaya Tundra (U-Pb age on zircon 2654±5Ma), Zapadno-Keivsky (2674±6 Ma), Saharjok, Ponoisky et.set. For zircon from Saharjok massif with zircon deposit has been yielded 2613±35 Ma for late phase of nepheline syenite. The U-Pb age on zircon from yearly phase of the massif is 2682±10 Ma. For the first time baddeleyite have been separated from carbonatites of Siilinjarvy (Finland) and U-Pb age gave 2613±18 Ma which are coeval on U-Pb age on big zircon crystal with 2611±10 Ma (Bayanova, 2006).

Kanozersky massif of alkaline granite lies in Central –Kola Arhean domene and zircon yielded U-Pb age 2667±16 Ma. Therefore take into account all U-Pb isotope data on zircon and baddeleyite duration of Neoarhean alkaline magmatism are more than 60 Ma from interval 2.61 to 2.67 Ga.

Isotope U-Pb data on zircon from sanukitoids granites of Karelia region (massifs Nukozersky, Xaytavaarsky, Elliysky et set.) and eastern Finland (massifs Kiiittila, Silvevaara, Tasanvaara et set.) and connected with sanukitoids lamprophyres dykes have yielded Neoarhean age interval origin from 2.74- to 2.70 Ga (Chekulaev et all., 2004, Lobach-Zhuchenko et all., 2005, Geoscience…2011). Sanukitoids in genesis are result of enriched mantle reservoir (Lobach-Zhuchenko et all., 2005). All isotope data for alkaline granites-syenites of Kola Neoarhean structures and carbonatites of Siilinjarvy which based on εNd, ISr, REE and He³/He⁴ data belong to enriched mantle EM-2 reservoir according to (Zozulya et all., 2005, 2007). This epoch formation from 2.74 to 2.61 Ga of alkaline and subalkaline magmatism is corresponded time of origin Kenorland supercontinent according to investigation (Lubnina, 2009).

Age of Paleoproterozoic alkaline granites were dated by U-Pb method on zircon from Gremaysha-Virmes complex with 1980±10 Ma. For the first time single baddeleyite grains from carbonatites of Tiksheozero massif (Karelia region) gave U-Pb age 1999±5 Ma which are the same on SHRIMP data with 1999±2 (Rodionov et all., 2009). In Pechenga Cu-Ni ore deposit zircon from lamprophyres rocks has U-Pb age 1710±12 Ma (Skufiun et all., 1999). Therefore all Paleoproterozoic alkaline magmatism has long interval origin in epoch of forming Columbia supercontinent (Lubnina, 2009).

Paleozoic alkaline magmatism of Fennoscandian Shield is characterized by variety of composition from kimberlites and carbonatites to agpaitil nepheline syenites. According to (Corfu et all., 2006) riftogenic intracratonic Paleozoic alkaline magmatism of the Shield were connected with spreading of Yapetus ocean and break up of supercontinent of Lavrentia-Baltika.

In Norway it prosess are dated by 438-427 Ma (Corfu et all., 2006). In Precambrian structures of Fennocsandian Shield have dated mesoproterozoic kimberlate-like rocks with age 1.3-1.1.Ga and diamond pipe with age 600 Ma and 460 Ma (Geoscience…2011, Bayanova, 2004), but the main epoch of alkaline magmatism are dated with interval from 382-347 Ma (Kramm, 1993, Kogarko et all., 1981, Bayanova, 2006, Arzamaszev et all., 2007).

Thus Kola province of Fennocsandian Shield based on all geology-geochronology investigations has development from end of Neoachean to Paleozoic time and is characterized by alkaline trend of magmatism from granitic in early Precambrian time up to ultra-basic and alkaline in late Precambrian and Paleozoic.

It can suggested that first Neoarhean alkaline processes and second Paleozoic magmatism belongs to ultraplate plume geodynamics

All investigations are supported by RFBR grants 10-05-00058 and 11-05-00570 and Department of Earth Division RAS, programs 2, 4 and 6.

References

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