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| Titel |
Geochemistry and Geochronology of the Early Paleoproterozoic Volcanism of the Karelian Craton: Petrogenetic and Geodynamic Implications |
| VerfasserIn |
M. M. Bogina, V. L. Zlobin |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250019472
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| Zusammenfassung |
| The Early Paleoproterozoic time is characterized worldwide by large-scale magmatic,
especially volcanic activity, which was related to the onset of global rifting at the
Archean-Proterozoic boundary. At the Karelian craton, its volcanic products compose giant
nearly submeridional belts several hundreds kilometer long. The Early Paleoproterozoic
volcanosedimentary sequences (2-3 km thick) from the bottom upward are made up of
coarse-grade mature sediments, predominant pillow-textured and massive lavas, tuffs, and
tuffobreccia of basaltic andesites and andesites, which through felsic tuffs grade into quartz
porphyries. Two types of basaltic andesites are distinguished. The Type I show MORB-like
flat to slightly LREE-depleted or insignificantly LREE-enriched patterns with (La/Sm)N =
0.7-1.5, and (La/Yb)N = 0.35-1.3, and minor negative or absent Eu, Nb, and Ti anomalies.
The type II rocks show LREE enrichment relative to HREE, (La/Sm)N = 1.5-3.84 and
(La/Yb)N=6.5-11.67, with minor negative to non-existent Eu anomalies (Eu/Eu) = 0.99-1.15,
prominent negative Nb and Sr anomalies, and subtle Ti anomaly. Trace element patterns show
that the rocks are enriched in LILE relative to HFSE and in LREE relative to HREE.
Negative Nb and Ti anomalies could be inherited from a previous subduction event
or result from crustal contamination. Nb-Ta-Th systematics can serve in support
of the former interpretation, indicating that the rocks exibit “island arc” affinity
with low to moderate (Nb/La)N ratio and extremely low (Nb/Th)N ratio. HREE
patterns are weakly fractionated, and show no significant depletion, indicating that
garnet was absent from the source rocks during generation of the primary magma.
The relatively low Ni and Cr contents suggest that the rocks undergone significant
fractional crystallization from mantle-derived melts. The upper age limit of the mafic
rocks is constrained by the U-Pb SHIRMP zircon age of cross-cutting felsic dike
at 2416 |
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