What is it about?
We have studied by SHRIMP-II the U-Pb system and REE composition of titanite from the Western Keivy and Ponoy massifs of alkaline granitoids.
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Why is it important?
The Baltic Shield is one of the world's largest (ca 2500 km2) provinces of alkaline granites which are confined to the Keivy segment of the Kola fold system and are represented by three series of mantle-source rocks of different origin, but close in time of formation linked to the Late Archaean mantle plume. The temperature of the U-Pb system closing is comparable to the crystallization temperature of granite melts (600-800°C), which makes it possible to correspondence the U-Pb age of titanite with the primary crystallization of alkaline granite massifs at 2710 Ma, but the latest titanite formed at about 1750 Ma reflects the influence of the tectonometamorphic paleoproterozoic event widespread on the Kola Peninsula. These estimations are well supported by single local age determinations on zircon inclusions in titanite.
Perspectives
The obtained data support the concept that the titanite can remain a closed system to Pb diffusion at temperatures of peralkaline granite melt as long as the crystals escape magmatic or metamorphic recrystallization. The more stable zircon retains a memory of the major episodes of granite evolution, but the coexisting titanite provide additional information on crystallization, subsequent growth, cooling, and alteration of the plutonic complexes. That's can be tested on other massifs.
Boris V Belyatsky
Karpinsky Geological Institute (VSEGEI)
Read the Original
This page is a summary of: Evolution of the Neoarchaean Kola alkaline granites, northeastern Fennoscandian Shield: insights from SHRIMP-II titanite and zircon U-Pb isotope and rare earth elements data, Geological Society London Special Publications, March 2023, Geological Society,
DOI: 10.1144/sp537-2022-233.
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