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| Titel |
Geochemical features of metabasic rocks from an Early to Middle Jurassic Accretionary Complex (Refahiye metamorphics, Eastern Pontides, NE Turkey): Implications for Late Jurassic-Early Cretaceous magmatic lull |
| VerfasserIn |
G. Göçmengil, G. Topuz, Ö. F. Çelik, İ. E. Altıntaş, M. Ozkan |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064261
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| Zusammenfassung |
| The Refahiye metamorphics (Eastern Pontides, NE Turkey) represent a metamorphosed
accretionary complex of Early to Middle Jurassic age and occur as an interleave between
coeval ophiolite. This Early to Middle Jurassic metamorphics and ophiolites are bound by a
Permo-Triassic accretionary complex in the north and a Late Cretaceous accretionary
complex in the south. The Refahiye metamorphics are made up of greenschist, marble,
serpentine, phyllite and subordinately amphibolite, micaschist, eclogite and metachert
knockers.
The Jurassic and Late Cretaceous accretionary complexes in Eastern Mediterranean are
related to the consumption of a Mesozoic ocean, the so-called Neo-Tethys. Regional geology
in the Eastern Pontides indicate that the Early to Middle Jurassic and Late Cretaceous times
correspond to volumious igneous activity, while Late Jurassic and Early Cretaceous time
to an igneous lull. Here we present whole-rock geochemical data on metabasic
rocks from the Refahiye accretionary complex, and discuss these data in terms
of accreted material and its implications for the Jurassic evolution of the Eastern
Pontides.
All the metabasic rocks are well recrystallized, free of any relict texture and are variably
hydrated (LOI ~ 1.3-5.1 wt%). Some samples are characterized by the unusually high-Al2O3
contents (up to 20.8 wt%) suggestive of derivation from high-Al basalts. Geochemically
three distinct metabasic group are distinguished, on the basis of fluid immobile
HFSEs and REEs. Group I is characterized by moderately to strongly fractionated
REE patterns [(La/Yb)cn ~8-18], absence of any Nb-Ta anomaly in multi element
variation diagrams and high Ti and low Zr/Nb ratios (3.68-5.72), corresponding to
unorogenic alkaline basalts (ocean island basalt). Group II characterized by moderately
fractionated REE ratios [(La/Yb)cn ~0.6-2.6], absence of any Nb-Ta anomaly, resembling
unorogenic tholeiitic basalts (E and N-MORB). Group III on the other hand, displays
unfractionated, nearly flat REE patterns [(La/Yb)cn ~0.6-1.1], negative Nb-Ta anomaly
and enormously high Zr/Nb values (38-62), corresponding to orogenic tholeeitic
basalts.
These data indicate accretion of unorogenic alkaline and tholeiitic basalts similar to those
in seamounts, MORB and IAB during the Early to Middle Jurassic subduction. This together
with widespread Early to Middle Jurassic magmatism in Eastern Pontides and Crimea and
absence in the southern Menderes-Taurus continental block, conclusively indicate for a
northvergent subduction. On the basis of the general absence of a Middle to Upper Jurassic
unconformity, we tentatively ascribe the Late Jurassic-Early Cretaceous magmatic
lull to the accretion of large submarine topographic highs to the subduction zone. |
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