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| Titel |
A segment of oceanic crust, in Macedonian (FYROM) ophiolites, seen through sheeted dyke diabases, keratophyres and adakite-like volcanics |
| VerfasserIn |
Milica Bozovic, Dejan Prelevic, Rolf L. Romer, Matthias Barth, Blažo Boev, Paul Van den Bogaard |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038617
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| Zusammenfassung |
| Macedonian Eastern Vardar Ophiolitic unit represents a part of the Neotethys that was
obducted onto the European Margin (Serbian Macedonian Massif). It comprises of well
exposed sheeted dykes complex, with pillow lavas as a top unit, which is intruded by
intermediate to acid dykes and sills of different geochemistry. We present new geochemical
data for both of the units as well as an Ar-Ar age for acid rocks.
Investigated samples can be clearly distinguished into the two groups based on
geochemical features:
i) Samples collected from the sheeted dykes and pillows, show SiO2ranging from
47-56%, relatively high TiO21.5-2.8%, and Al2O3 ranging from 12-15 %. In terms
of trace element geochemistry, they show flat trace element patterns ((La/Yb)n
= 0.5-2.4, (La/Sm)n =0.5-1.3 and (Sm/Yb)n = 0.8-1.2) consistent with MORB
compositions;
ii) Intermediate to felsic intrusions (keratophyres and adakite-like volcanic) show large
range of SiO2and Al2O3 contents (45-73% and 16-13.5%, respectively), and are markedly
depleted in TiO2, Nb and Ta, as well as enriched in LILE, like U, Th; they also show enriched
REE patterns ((La/Yb)n = 3.56-14.79, (La/Sm)n =2.30-3.70 and (Sm/Yb)n =1.20-4.04)
characteristic for arc volcanic rocks generated in a subduction zone environment. The most
mafic members of this group demonstrate many features typical for adakites, like high Al2O3,
extreme depletion in HREE with large extent of REE fractionation, high Sr concentrations
and high Sr/Y, Sr/Yb, Dy/Yb ratios. Their adakitic features are also seen in trace
element compositions of clinopyroxene (cpx) phenocrysts, having high Sr and Dy/Yb
for high Mg#, comparable to cpx from Aleutians which is adakitic type locality
..........(Yogodzinski and Kelemen, 1998). On the other hand, the most evolved rocks
from this group geochemically resemble upper Jurassic granitic rocks from the
area: Fanos (Greece), Furka and Stip granites (FYRO-Macedonia) ..(...)..(Saric et
al., 2009). Our Ar-Ar potassium feldspar dating gave 164 ± 0.15 Ma which is in
agreement with K-Ar ages available for Macedonian granitic rocks (around 160
Ma).
In our view, the rocks which occur within volcanic sequence of Macedonian (FYROM)
ophiolites, represent two genetically different magmatic suites. The first one represents a
volcanic member of oceanic crust of MORB composition, probably erupted in a
fast-spreading environment. The second suite is younger and we interpret it as being
produced by simple mixing or AFC, of the adakite-like primary melts and a felsic
end-member similar to the melts which crystallized Jurassic granitic rocks from the area. The
extent of granite involvement goes up to 45% for the most felsic samples from our
intermediate suite. In our contribution, we will combine our geochemical data with available
geological data, in order to review possible geodynamic scenarios which enable formation of
Macedonian ophiolites.
.Saric, K., Cvetkovic, V., Romer, R.L., Christofides, G. and Koroneos, A., 2009.
Granitoids associated with East Vardar ophiolites (Serbia, F.Y.R. of Macedonia and northern
Greece): Origin, evolution and geodynamic significance inferred from major and trace
element data and Sr-Nd-Pb isotopes. Lithos, 108(1-4): 131-150.
Yogodzinski, G.M. and Kelemen, P.B., 1998. Slab melting in the Aleutians: implications
of an ion probe study of clinopyroxene in primitive adakite and basalt. Earth and Planetary
Science Letters, 158(1-2): 53-65. |
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