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| Titel |
Adakitic- and lamproitic- like (?) source signatures in the Tertiary alkaline volcanics of Trabzon (NE Turkey) area: implications for petrogenesis and mantle source characteristics |
| VerfasserIn |
Mehmet Arslan, Cem Yücel, İrfan Temizel, Emel Abdioğlu |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047133
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| Zusammenfassung |
| The Eastern Pontide Tertiary Volcanic Province (EPTVP) in NE Turkey is divided into two
sub-provinces as a northern alkaline and a southern calcalkaline one on the basis of
lithological and petrochemical differences. The Tertiary alkaline volcanics along the Black
Sea coast in the Trabzon area are represented by (1) pyroclastics composing of breccias and
tuffs; (2) basaltic dikes and sills, trachytic dikes, andesitic dikes and domes; (3) lavas
composing of foid bearing brecciated lavas, pillow lavas and basaltic lavas (Yücel et al.,
2009). Petrochemically, the volcanics have low to mildly alkaline affinities, and medium to
high-K contents. Basaltic dikes and sills, basaltic lavas, pillow lavas, basaltic breccias are
classified as basalt, trachy-basalt and basaltic trachy-andesite (BTB) suite; andesitic dikes and
domes, trachytic dikes are described as trachyte and trachy-andesite (TT) suite; foid
bearing brecciated lavas and foid bearing breccias are named as basanite-tephrite (BT)
suite.
All these suites show subduction signature (fluids±melts) and some suites (especially BT
suite) also exhibit enrichment in some incompatible elements, reflecting adakitic like source
signature. The BT suite rocks differing from the BTB and TT suite rocks have high Sr/Y and
La/Y ratios close to adakitic volcanics of Defant et al. (2002). Varying Sr/Y ratios and
similar Y contents in all suite rocks may suggest different mantle source region but
adakitic-like signature in the BT suite rocks may be related to (1) contribution of
subduction melts and/or (2) lower crust assimilation-fractional crystallization (AFC).
Adakitic indexes (Sr/Y, La/Yb, Na2O, Sr, Al2O3) and Nb/Ta ratio versus SiO2
fractionation index show varying degrees of correlations between the BT suite and other
suites, revealing source signatures as well as AFC processes. Comparatively, high
incompatible element (La, Ce, Sr, Ba, Th, Pb etc.) enrichment in the BT suite may
be explained by a two staged enrichment in parental source; the first stage covers
pre-collisional enriched mantle source component, and the second stage involves
contribution of crustal melts/fluids to this enriched mantle source. The volcanics have
common clinopyroxene and less phlogopite phenocrysts in modal mineralogy, and
show generally potassic and locally low SiO2 contents in composition; all of these
features may correlate to those of collisional-post collisional orogenic lamproitic-
potassic volcanics and/or –like source magmas. Al2O3, TiO2, Nb, Zr, Th contents and
K2O/Na2O ratio of the volcanics may reveal mainly subduction induced potassic
volcanism. SiO2 vs. CaO and K2O/Al2O3, and Al2O3 vs. CaO lamproitic-potassic index
corelations of the volcanics are similar to Group III Roman Province type of Foley et
al. (1987). Furthermore, low K2O/Al2O3 ratio ( |
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