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| Titel |
The Archaean-Paleoproterozoic transition: First results of detrital zircon U-Pb-geochronology and provenance from the FAR DEEP drill cores |
| VerfasserIn |
C. Gärtner, H. Bahlburg, V. A. Melezhik, A. Lepland, J. Berndt, E. Kooijman, The FAR DEEP Scientists |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043781
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| Zusammenfassung |
| The Archaean-Paleoproterozoic transition is marked by several events that were important for
the evolution of the Earth system. We applied U-Pb-geochronology on detrital zircons by
LA-ICP-MS to improve age constraints on the duration of three of these events: 1) the
Huronian Glaciation, which is the first known worldwide glaciation, 2) the Lomagundi-Jatuli
event, characterized by a large excursion of δ13C in carbonate sediments and 3) the
Shunga event, the first deposition of very Corg-rich sediments, so-called “shungites”.
During the Fennoscandian Arctic Russia - Drilling Early Earth Project (FAR DEEP),
which is part of the International Continental Scientific Drilling Program (ICDP),
volcano-sedimentary successions of early Paleoproterozoic age were drilled in the Pechenga
and Imandra-Varzuga Greenstone belts, as well as in the Onega basin in Russian
Fennoscandia.
The first results of detrital zircon dating provided an age range from 1.85 up
to 3.5 Ga having one prominent age-group of 2.5-2.9 Ga for each sample. The
youngest ages in individual samples vary due to their stratigraphic position. The
youngest zircons from the Seidorechka Sedimentary Formation below Huronian glacial
deposits in the Imandra-Varzuga Greenstone Belt yielded ages around 2.42 Ga, which
are interpreted as the age close to the onset of the Huronian Glaciation. Zircon
ages from the Polisarka Sedimentary Formation above Huronian diamictites in the
Imandra-Varzuga Greenstone Belt indicate that the glaciation had ended at 2.22 Ga. The
youngest zircon ages from the sequence containing isotopically heavy carbonates of the
Kuetsjärvi Sedimentary Formation in the Pechenga Greenstone Belt suggest that the
Lomagundi-Jatuli event started around 2.32 Ga and that its end is younger than 2.06
Ga. Age constraints of ca. 2.0-1.9 Ga for the beginning of the Shunga Event were
obtained by dating zircons from the Kolasjoki Sedimentary Formation in the Pechenga
Greenstone Belt. Considering the error, these zircon ages confine the transition
from the Lomagundi-Jatuli event to the Shunga event at 2.06-2.0 Ga. These first
results provide independent evidence in support of previous age indications for these
events.
Another aim of the study is to investigate provenance and source areas of the
analysed detrital zircons. The largest age group around 2.9-2.5 Ga points to orogenic
processes during the formation of the Fennoscandian Shield. Collisional and accretional
processes during the Saamian (3.1-2.9 Ga) and Lopian orogeny (2.9-2.6 Ga) recycled
detritus from surrounding Archaean granitoid sources into the study area. Ages
around 2.4 Ga indicate maximum depositional ages for the Seidorechka Sedimentary
Formation. At this time, earliest Paleoproterozoic magmatism occurred which might have
produced source rocks for stratigraphically younger sedimentary successions like
the Polisarka, Neverskrukk and Kuetsjärvi Formations. In combination, zircon
ages of 2.6-2.1 Ga from these formations may be linked to active plate-margin
complexes, accreted to Fennoscandia, which also includes mafic plateau volcanicsm,
intracratonic sedimentation and continental rift systems. Furthermore, break-up of the
shield followed by drifting was underway at 2.2-1.95 Ga. Zircon grains having
ages of 2.1-1.9 Ga derived from sources connected to the Svecofennian orogeny. |
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