1. Mesoproterozoic orangeite of Karelia (Kostomuksha-Lentiira): evidence for composition of mantle lithosphere
Alexey Kargin, Anna Nosova, Yulia Larionova, Victoria Kononova, Sergey Borisovskiy, Elena Kovalchuk, and Irina Griboedova
Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry Russian Academy of Sciences (IGEM RAS)

2. Geological setting
Orangeite of Kostomuksha and Lentiira were emplaced in the Archean Karelian Terrane (north part of East European Craton) and have Mesoproterozoic ages: 1.23 Ga (Belyatsky et al., 1997) and 1.20 Ga (O’Brien et al., 2007).
after Samsonov et al., 2012
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

3. Geological setting
after map by R.I. Borisova et al., 2002
More than 80 orangeite and lamproite bodies found in the Kostomuksha structure are grouped in four clusters.
The orangeite, usually form thin (0.1–15 m) dikes with 15 to 400 m long that are traced to a depth of 850 m. They have a magmatic texture with hardened zone.
Intrusion was frequently accompanied by the formation of metasomatic glimmerite aureoles in host rocks.
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

4. Mineralogical composition
The orangeite were divided into three types: Cpx–Phl–Ol, Phl–Ol, and Phl–Carb
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

5. Olivine
Fresh olivine was found in the Lentiira orangeite. There are three olivine generations by morphology and composition.
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

6. Olivine
Large rounded, usually zoned crystals with Fo92 core, 0.33–0.37 wt. % NiO, and 0.03–0.04 wt. % CaO; this olivine is interpreted as xenocrysts from depleted peridotite; Anhedral rounded zoned olivine of inter-mediate size with Fo82–83 cores, 0.03–0.05 wt. % CaO, 0.12–0.17 wt. % NiO, and up to 0.40 wt. % MnO. These crystals could were derived from metasomatized lithospheric peridotite; Small fine euhedral crystals and rims of olivine firsts groups that has Fo88–89 composition with 0.10–0.42 wt. % CaO, 0.14–0.35 wt. % NiO, and up to 0.07–0.21 wt. % MnO; their origin was presumably related to the crystallization from orangeite melt. I II
III
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

7. Phlogopite
In the Al2O3–FeO and Al2O3–TiO2 diagrams, the phlogopite defines trends that are consistent with fractional crystallization of phlogopite from orangeites (Mitchell, 1995): decrease content of Al2O3 is accompanied by decrease content of FeO at persistent content of TiO2, in spite of their total enrichment in FeO and TiO2.
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

8. Mineralogical composition
Clinopyroxene, spinel group, apatite and perovskite have magmatic origin from orangeitic or lamproitic melts. Some of these minerals in Cpx-Phl-Ol orangeite show xenogeneic origin from lithospheric mantle.
clinopyroxene
spinel group
apatite
perovskite
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

9. Geochemical composition
Major and trace elements data of orangeite widely vary in the variation diagrams and show transitional position between orangeite, aillikite and lamproite.
From Cpx–Phl–Ol and Phl–Ol to Phl–Carb varieties, the rocks show a decrease in MgO and SiO2 and increase in Fe2O3, TiO2, and P2O5, and to lesser extent, Al2O3. These petrochemical variations demonstrate an increasing role of phosphate, titanate, and carbonate.
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

10. Geochemical composition
Orangeite is strongly enriched in LILE and less in HFSE to comparative with primitive mantle.
In general, Karelia orangeite are comparable with orangeite of South Africa by their geochemical composition.
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

11. Rb-Sr and Sm-Nd isotopic characteristics
The orangeite have low- to moderate radiogenic initial (87Sr/86Sr)1220 ratio varying from to and low radiogenic 143Nd/144Nd ratio: εNd varies from –6.9 to –12.
Orangeite are divided into 2 groups: first group has low-radiogenic Sr composition and less radiogenic Nd isotope composition (εNd from –9 to –12) than second group. Sr systematic in second group has positive correlation with CO2 in whole rock. This suggests that Sr systematic of orangeite group 2, probably, had been broken while post magmatic metamorphic processes took place.
The source of orangeite had geochemically enriched ancient material.
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

12. Sm-Nd isotopic system
To determine what of geochemically enriched material had been in source, we considered available Nd isotope data on the Paleoproterozoic lamprophyre and carbonatite of Karelia with age 2.0 Ga and 1.8 Ga (Antonov et al., 2009; Tichomirowa et al., 2006; Andersson et al.,2006; Kononova et al., 2006), which may represent derivatives of ancient enriched source in the lithospheric mantle underlying the Karelian Craton.
The Nd isotope compositions of Karelia orangeite overlap the evolution field of mantle sources of 2.0 Ga and 1.8 Ga lamprophyre.
lamprophyre 2.0 Ga (Antonov et al., 2008); lamprophyre 1.8 Ga (Andersson et al., 2006; Kononova et al., 2000; Woodard, 2010); data for source of lamprophyre 1.8 Ga from (Becker et al., 1999).
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

13. Rb–Sr isotopic system
The Rb–Sr systematic of orangeite precludes origination of carbonate component in their source by input from asthenosphere mantle;
The most primitive orangeite fall in the field of Sr isotope evolution of the Rb–Sr compositions of the 1.8 Ga old lamprophyre from the Svecofennian domain;
Thus, our Rb–Sr data are consistent with the proposed model of additional enrichment of orangeite source by ~2.0 Ga old subduction component.
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

14. The sequence of the formation of orangeite
Metasomatic reworking of previously depleted lithospheric source in base of Karelian terrane could be at the during Paleoproterozoic orogenic events (2.1–1.9 Ga) before assemblage of Columbia supercontinent:
~2100–1960 Ma - metasomatic reworking during subduction at the initial stages of the formation of the Lapland–Kola orogen (Daly et al., 2001; Samsonov et al., 2012); emplacement Tikshozero carbonatite, Kimozero kimberlite;
~1910–1800 Ma - metasomatic reworking during subduction at the initial stages of the formation of the Svecofennian orogen; emplacement of lamprophyre (Korja et al., 2006; Andersson et al., 2006; Woodard, 2010).
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

15. The sequence of the formation of orangeite
Generation of orangeite melts of Karelia 1.23–1.20 Ga ago initialed by back-arc extension during orogenic events of preceding pre-Sveconorwegian orogeny (1.34–1.14 Ga, Bingen and Nordgulen, 2008; Brabder et al., 2011; Soderlund et al., 2005, 2006) prior to the assembly of the Rodinia supercontinent and led to the formation of dolerites in the PR domain (Soderlund et al., 2006).
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

16. The sequence of the formation of mantle orangeite source
Similar processes took place at the paleo-continent Laurentia, where the intrusions of Ga lamproite of Sisimiut Greenland and Napoleon Bay, Baffin Island are comparable by time with a generation of an extension-related magmatism in the age range Ga in Labrador and South Greenland.
According to reconstructions of supercontinents at 1.25 Ga the orangeite and lamproite formed linear zone on the Laurentia and the Baltica continents; This zone took place in the rear end of orogenic belt in Archean terrane with thick lithospheric mantle after zone of basic rocks with back-arc extensions origin.
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

17. Conclusions
The study of Sm–Nd and Rb–Sr isotope systems provided evidence for contribution from an ancient enriched source to the orangeite magmas. The lithospheric mantle under Archean Karelian terrane had metasomatic vein systems that were formed during subduction processes in Paleoproterozoic. This metasomatic source was activation in Mesoproterozoic during processes of extension of Proterozoic lithospheric mantle in central part of Svecofennian shield. Evolution of mantle source of orangeite involved two stages: (a) metasomatic reworking of previously depleted lithospheric source at the Karelian Craton base during 2.1–2.0 Ga Paleoproterozoic orogenic events; (b) extension related generation of orangeite melts 1.23–1.20 Ga ago. 1 2 3 1
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)

18. Thank you for your attention!
Kargin et al: Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira)