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| Titel |
Compositional change of granitoids from Eastern Pontides Orogenic Belt (NE Turkey) at ca. 84 Ma: Response to slab rollback of the Black Sea |
| VerfasserIn |
Ze Liu, Di-Cheng Zhu, Yener Eyuboglu, Fu-Yuan Wu, Tamer Rızaoğlu, Zhi-Dan Zhao, Li-Juan Xu |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130374
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| Publikation (Nr.) |
 EGU/EGU2016-10623.pdf |
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| Zusammenfassung |
| Magma generation and evolution is a natural consequence of mantle dynamics and
crust-mantle interaction. As a result, changes of magma compositions in time and space can
be used, in turn, to infer these deep processes. In this paper we report new zircon U-Pb age
and Hf isotope, whole-rock major and trace element, and Nd isotope data for the granitoids
from Kürtün in Eastern Pontides. These data, together with the data in the literature, reveal
the occurrence of magma compositional variations at ca. 84 Ma in the region, providing new
insights into the mantle dynamics responsible for the generation of the extensive
Late Cretaceous felsic magmatism in Eastern Pontides Orogenic Belt (NE Turkey)
(Eyuboglu et al., 2015). Group I samples (SiO2 = 77-62 wt.%) were concentrated in
91-86 Ma and are characterized by their low CaO (1.6-1.5 wt.%) and Th (8.2-3.0
ppm) contents and low K2O/Na2O (0.7-0.1) and Th/La (0.4-0.2) ratios. Group II
samples (SiO2 = 71-63 wt.%) were concentrated in 82-72 Ma and include high
concentrations of CaO (5.2-3.0 wt.%) and Th (29.6-14.3), high K2O/Na2O (1.5-1.1) and
varying Th/La (1.0-0.5) ratios. Group I samples have positive zircon eHf(t) (+9.6
to +7.6) and whole-rock eNd(t) (+3.5 to +2.5), significantly differing from those
of Group II samples with eHf(t) of +1.9 to -1.5 and whole-rock eNd(t) of -3.6 to
-3.8. Modeling results indicate that the Nd-Hf isotopic compositions of Group I
and II samples can be interpreted as having derived from partial melting of the
low-K amphibolite within the juvenile lower crust beneath the Eastern Pontides
Orogenic Belt that incorporated into 15-20% and 70-75% enriched components
from the basement rocks represented by the Carboniferous granites exposed in the
region, respectively. In combination with the geological observations that indicate the
occurrence of regional thermal subsidence (Bektaş et al., 1999) and extensional structure
(Bektaş et al., 1999, 2001) during the Campanian (83.6-72.1 Ma), the coeval intense
magmatism represented by Group II samples along the Eastern Pontides Orogenic
Belt was linked with the enhanced melting of the juvenile lower crust due to the
upwelling of hot asthenosphere material in an extensional regime. In such a case, the
enhanced incorporation of basement-derived melts induced by the extensive melting of
the juvenile lower crust would result in the changes of magmatic compositions
from Group I to Group II. Considering the southward decrease in zircon eHf(t)
documented by the Cretaceous granitoids from the northern part of the Eastern
Pontides Orogenic Belt, we tentatively suggest that the Group I and II samples may be
associated with the southward subduction and subsequent slab rollback of the Black
Sea seafloor, respectively. However, we address that such slab rollback hypothesis
remains to be verified by future work using the information from the spatial and
temporal migration of the Cretaceous magmatism and the origin of coeval mafic
rocks.
References
Bektaş, O., Şen, C., Atici, Y., Köprübaşi, N., 1999. Migration of the Upper Cretaceous
subduction-related volcanism towards the back-arc basin of the eastern Pontide magmatic arc
(NE Turkey). Geological Journal 34, 95-106.
Bektaş, O., Capkinoglu, S., Akdag, K., 2001. Successive extensional tectonic regimes
during the Mesozoic as evidenced by neptunian dikes in the Pontide Magmatic Arc,
Northeast Turkey. International Geology Review 43, 840-849.
Eyuboglu, Y., Dudas, F.O., Santosh, M., Xiao, Y., Yi, K., Chatterjee, N., Wu, F.Y.,
Bektaş, O., 2015. Where are the remnants of a Jurassic ocean in the eastern Mediterranean
region? Gondwana Research in press, doi:http://dx.doi.org/10.1016/j.gr.2015.08.017. |
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