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| Titel |
Petrological and geochemical constraints on the origin of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc, NE Turkey |
| VerfasserIn |
Faruk Aydin, Simge Oğuz, Rasim Baser, İbrahim Uysal, Cüneyt Şen, Orhan Karsli, Raif Kandemir |
| 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 |
250113673
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| Publikation (Nr.) |
 EGU/EGU2015-14323.pdf |
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| Zusammenfassung |
| Geological, petrographical and geochemical data of mafic dykes intruding the composite
Kaçkar Pluton from the eastern Blacksea magmatic arc (EBMA), NE Turkey, provide new
insights into the nature of the metasomatizing agents in subcontinental lithospheric mantle
beneath the region during the late Mesozoic-early Tertiary. Mafic dykes from the Çaykara and
Hayrat (Trabzon), and also Ikizdere (Rize) areas from the northern margin of the
EBMA consist of basalts, dolerites, lamprophyres (basic member) and lesser basaltic
andesites and trachyandesites (evolved member). All dykes have no deformation and
metamorphism. The outcrops of these dykes vary, with thickness from 0.2 to 10
m. and visible length from 3 to 20 m. In general, the mafic dykes dip steeply and
cut directly across the Kaçkar Pluton, and show NW- and NE-trending, roughly
parallel to the orientations of the EBMA main faults. Most of the dyke samples
display subaphyric to porphyritic texture with phenocrysts of plagioclase (up to 10%),
clinopyroxene (5-20%), amphibole (5-15%), and some contain variable amount
of biotite (5-20%), lesser quartz (1-2%), and minor euhedral zircon, apatite and
Fe-Ti oxides. The basic members of the mafic dykes have SiO2 of 44.1-51.9%,
MgO of 4.5-12.1%, and TiO2 >mostly 0.8% (up to 2.3%) with K2O+Na2O of
1.3-6.6% with mostly subalkaline character. They are relatively high in mg-number
(0.45-0.73) and transition metals (V=171-376 ppm, Co=22-45 ppm, Ni=3-148 ppm, and
Sc=21-49 ppm). The evolved members of the dykes exhibit relatively higher SiO2
(57.1–60.2%) and K2O+Na2O (5.6-9.0%), and lower MgO (2.2-5.9%) and TiO2
(0.5-0.8%) contents than those from the basic dykes. Also, these samples have slightly
low mg-number (0.41-0.65) and transition metals (V=99-172 ppm, Co=9-22 ppm,
Ni=1-43 ppm, and Sc=9-20 ppm). In the Harker diagrams, all samples of the mafic
dykes form a continuous array, and exhibit similar geochemical characteristics.
In general, SiO2 inversely correlates with MgO, Fe2O3t, TiO2, CaO and P2O5.
Transition metals (Ni, Co, Sc) drastically decrease with decreasing SiO2. Such
characteristics support fractionation of Ol+Cpx+Amp+Fe-Ti oxides+Apatite from parental
magmas. On the chondrite-normalized REE patterns, the all samples are enriched in
LREEs, and show variable LREE/HREE fractionation ((La/Yb)N=0.8–22.2) with
slightly negative Eu anomalies (Eu/Eu*=0.7–1.3). On the N-MORB normalized
diagrams, the samples from both dyke members are generally enriched in LILEs
and depleted in HFSEs. They are also characterized by subparallel patterns with
pronounced depletion of Nb and Ti. Slightly negative Eu anomaly and negative Sr
anomaly in the spider diagram for some samples may be attributed to fractionation of
plagioclase. Depletion in Nb and Ti, and negative correlation between P2O5, TiO2 and
SiO2 are likely related to amphibole, Fe–Ti oxides and apatite fractionation. The
LILE and LREE enrichment and HFSE depletion suggest that the mantle source of
the mafic dyke samples has compositional similarity with metasomatized mantle
wedge. High La/Nb (2-8), Ba/Nb (20-850) and Zr/Nb ratios (5-41) in the mafic dyke
samples are clearly distinctive to the features for most intraplate volcanic rocks
(La/Nb=0.5–2.5, Ba/Nb=1–20 and Zr/Nb |
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