Résumé
Trace-element composition of clinopyroxenes from the mantle peridotites of Kizildag Ophiolite (Hatay, S. Turkey) were determined by laser ablation ICP-MS to better understand the geochemical processes and the formation of the ophiolite. The peridotite sequence is composed of tectonized harzburgite and ultramafic cumulate rocks representing refractory mantle source and Moho Transition Zone (MTZ), respectively. Harzburgites contain spinel with Cr# 47-70 and Mg# 37-66, indicating that they are residue of high degrees of partial melting. Ultramafic cumulates are mainly dunite and wehrlites. Tectonized harzburgites show two different types of compositions. First type of harzburgites are refractory and have primary pyroxene crystals with ductile deformation signs. Second type of harzburgites are more fertile and have interstitial clinopyroxenes showing similar characteristics with rocks from MTZ. Chondrite-normalized rare earth element (REE) patterns of clinopyroxenes from Kizildag Ophiolite are clearly depleted in light REE (LREE) ([Lu/La] (sub N) >100), and have slightly similar patterns with clinopyroxenes of abyssal peridotites from normal mid-ocean ridges (MOR). Interstitial clinopyroxenes in MTZ dunites have flatter patterns ([Lu/La] (sub N) approximately 10) comparable with those from other dunites of all the Tethyan ophiolites (e.g. Oman, Troodos). Clinopyroxenes in tectonized harzburgites having extremely downward REE patterns, characterized by a strong depletion from heavy REE (HREE) to middle REE (MREE), suggest that they are residue of first stage fractional melting in the garnet stability field in a MOR setting. Interstitial clinopyroxene from impregnated harzburgites have more enriched REE patterns than those of depleted harzburgites, indicating spinel field melting in a SSZ setting where melts can percolate within upwelling mantle.