Pyrochlore chemistry and the transition from Ca-carbonatites and phoscorites to Mg-Fe carbonatites at Sokli (Finland)
✍ Scribed by M.J. Lee; D. Garcia; J. Moutte; F. Wall; C.T. Williams; A.R. Woolley
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 232 KB
- Volume
- 32
- Category
- Article
- ISSN
- 1464-343X
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✦ Synopsis
A large body of coarse-grained calcite carbonatite is located in the northern marginal zone of the Kovdor Massif (Mt Mogo-Vid). The form of this body resembles a huge geode 5 x 2 m in size. The host rocks are ijolites alternating with relics of melilitic rock. Big phlogopite crystals (up to 40-50 cm) grow from the contact of the carbonatite toward the centre, as determined by their zoning patterns and primary dislocation structures. Cubic or cubic-octahedral perovskite crystals (up to 5-6 mm) are associated with fine-grained apatite and coarsegrained Ti-andradite (Table 1 below). The following scheme of carbonatite formation is suggested: some carbonatite magma penetrated a cavity formed inside the alkaline and melilitic rocks, where it slowly cooled. The crystallisation and recrystallisation of phlogopite, garnet and partly of diopside, in this relatively preserved chamber, proceeds like in a geode, from the margin to the centre. This process resulted in the formation of this strange pegmatite-like carbonatite.