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| Titel |
Geochemical and detrital zircon studies of meta-sedimentary rocks from the Teletsk and Ulagan blocks, Russian Altai: Implications on their tectonic affinity and geodynamic evolution |
| VerfasserIn |
Ming Chen, Min Sun |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108397
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| Publikation (Nr.) |
 EGU/EGU2015-8150.pdf |
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| Zusammenfassung |
| Abstract: A combined whole-rock geochemical and detrital zircon geochronological and
Hf-isotope study was conducted on meta-sedimentary sequences of the Teletsk and Ulagan
blocks in order to trace their provenance, depositional setting and tectonic affinity.
Samples from the Teletsk and Ulagan blocks underwent epidote-amphibole- and
greenschist-facies metamorphism, respectively, but all of them show comparable
geochemical characteristics. They are characterized by high Al2O3/SiO2 ratios
and ICV (Index of Chemical Variability) values, while (Gd/Yb)N ratios and REEs
compositions are comparable to those of the upper continental crust, indicating that
their protoliths were immature and probably deposited proximal to the source areas
without significant sedimentary sorting. The low CIA (Chemical Index of Alteration)
values for these samples (47.3-74.5 and 52.5-74.5, respectively) further suggest
that the source rocks underwent mild to moderate chemical weathering. All the
samples show major elements (e.g., Al2O3/TiO2, TiO2/Fe2O3T, Fe2O3T/Al2O3),
REEs concentrations, HFSEs and transition elements compositions between the
typical andesites and granites, but deviate from those of basaltic rocks, implying that
intermediate-felsic rocks served dominant sources during the sedimentation. These
geochemical characteristics are consistent with the continental island arc setting, which is
discriminated by the TiO2, Al2O3 and Fe2O3T + MgO concentrations higher than those
of passive marginal depositions, but La/Sc, Ti/Zr, La/Th, La/Sc and Zr/Th ratios
comparable to those of depositions in continental island arc settings. Two samples
from the Teletsk and Ulagan blocks yield similar detrital zircon age spectra, with
the most prominent population of ca. 620-470 Ma old and a subordinate one of
ca. 943-743 Ma old. Comparison with surrounding tectonic units shows that the
Tuva-Mongolian terrane and surrounding island arcs in western Mongolia probably provided
substantial sources to the protoliths. The similarities in geochemical compositions and
detrital zircon patterns with those for the Altai-Mongolian terrane suggest that the
Teletsk and Ulagan blocks possibly represented the northern margin of this terrane
with different crustal levels. Our study places further constraints that the whole
Altai-Mongolian terrane possibly represented a large subduction-accretion complex
built upon the active margin in the western Mongolia during the early Paleozoic. |
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