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RESEARCH PRODUCT

Orogenic vs anorogenic lamproites in a single volcanicprovince: Mediterranean-type lamproites from Turkey

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Lamproites are mantle-derived ultrapotassic volcanic rocks, derived from phlogopite-bearing harzburgitic source. The origin of the metasomatism which enriched their mantle source is either an old event with a metasomatic component derived from the convecting mantle, or is a more recent introduction of an already aged metasomatic component. Together with different trace element signatures, this view serves for a general distinction between anorogenic and orogenic lamproites worldwide. In Turkey, lamproitic volcanism resulted from interplay of subduction/collisional and postcollisional/extensional regime since Miocene until Pliocene, in the Western Anatolia-Aegean and Kirka-Afyon-Isparta region. We present new set of Ar-Ar age data together with geochemical data, including Sr, Nd and Pb isotopes, of all Turkish lamproites. Our study revealed the most intriguing geochemical data: although the majority of lamproites have an orogenic affinity, with radiogenic 87Sr/86Sr, 207Pb/204Pb, and unradiogenic 143Nd/144Nd and 206Pb/204Pb, and high LILE/HFSE ratios, the lamproites from the most southern localities (Bucak area) exhibit geochemical features characteristic for anorogenic lamproites, with unradiogenic 87Sr/86Sr, 207Pb/204Pb, and radiogenic 143Nd/144Nd and 206Pb/204Pb, coupled with rather smooth incompatible trace element pattern with low LILE/HFSE ratios and high concentrations of Nb and Ti. The common and coeval occurrence of anorogenic and orogenic lamproites in a single volcanic province suggests that geodynamic distinction of lamproites based only on geochemistry may be questioned.