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Growth of the Archean sialic crust as revealed by zircon in the TTGs in eastern Finland
Author(s) -
Pentti Hölttä,
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Irmeli Mänttäri,
Hannu Huhma,
Matti Kurhila,
Tapio Ruotoistenmäki,
Asko Kontinen,
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AUTHOR_ID,
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Publication year - 2021
Publication title -
bulletin of the geological society of finland
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.4
H-Index - 24
eISSN - 1799-4632
pISSN - 0367-5211
DOI - 10.17741/bgsf/93.2.001
Subject(s) - zircon , archean , geology , crust , geochemistry , mantle (geology) , population , petrology , sociology , demography
U–Pb age determinations on zircon from granitoids in the Archean of eastern Finland were conducted using the SIMS, LA-ICP-MS and TIMS techniques, with an emphasis on low-HREE granitoids. The oldest rocks in the Fennoscandian Shield are 3.4–3.5 Ga. Several samples were collected close to these rocks, but none of the samples were as old, indicating that the oldest rocks are only small, possibly allochthonous fragments in the Neoarchean bedrock. Some tonalite–trondhjemite–granodiorite (TTG) samples yielded homogeneous 2.72–2.73 Ga zircon populations, and in these samples, the initial εNd was also close to the depleted mantle (DM) values. However, several granitoid samples with a main zircon population of 2.7–2.8 Ga had 2.9–3.2 Ga grains or inherited cores, and in some samples, all grains were of 2.9–3.0 Ga. In these samples, the εNd value was also close to zero or slightly negative. These features suggest that apart from the juvenile Neoarchean magmas, the abundance of reworked 2.9 Ga material is considerable in the Archean crust, which developed during successive juvenile magmatic inputs that melted and assimilated the older sialic crust. The low- HREE geochemical character of granitoids has no correlation with their age, with the low-HREE granitoids yielding an age span of 2.72–2.98 Ga.

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