INTRUSIVE LHERZOLITES WITHIN THE BASALTS OF KüRE OPHIOLITE (TURKEY): AN OCCURRENCE IN THE TETHYAN SUPRASUBDUCTION MARGINAL BASIN

Abstract

The Küre ophiolite is interpreted as the remnants of the suprasubduction marginal basin formed on the northwardly subducted Tethyan oceanic lithosphere. The Küre Basin was opened during late Late Triassic and closed during late Middle Jurassic. Intrusive lherzolites cut the lower part of the basalts forming the volcanic upper unit of the Küre ophiolite. Lherzolites occur in tabular form with hectometric dimensions and have a massive character. High temperature metamorphic effects were developed in the wallrock along a zone a few metres thick. The lherzolite is relatively fresh and displays poikilitic texture where subhedral and anhedral olivines are included in large pyroxenes. The primary mineral paragenesis of the lherzolite is represented by olivine and chromite as early cumulus phases. Diopside, bronzite and plagioclase are the late igneous minerals. Hornblende and titanite formed during the late stage of crystallization at the expense of clinopyroxene. Serpentine minerals, phlogopite and hydrogrossular are the secondary minerals formed at the expense of olivine, bronzite and diopside. Tremolite, actinolite, chlorite and sericite are the late alteration products of the lherzolite. High temperature and low pressure conditions are indicated based on the mineral compositions. The crystallization temperature of the olivine and chromite is estimated to be 1015-1070°C, and that of the pyroxenes, the last crystallized primary minerals, around 900-950°C. The solidification of the magma was completed in the lower part of the basalts, at a depth of c. 2.7 km. The Küre lherzolite has a very high oxygen fugacity indicating an oxidized arc magma origin. The magma rose as a crystal mush and intruded the basalts. The generation of the parental magma may be explained by extensive melting of the upper mantle, facilitated by the presence of hydrous fluids released from the subducted Tethyan oceanic lithosphere. Copyright © 2006 John Wiley & Sons, Ltd.