Seminar

Plate subduction is of critical importance for the plate tectonic and transportation of materials from the surface to the mantle of the Earth. In nascent intra-oceanic subduction zone, the basal mantle of the future ophiolite is located just above the subduction interface. Ophiolites thus provide the best examples of shallow incipient mantle wedges. The Cyprus ophiolite is the classic ophiolite in the world with complete ophiolitic sequence from the mantle peridotites at the bottom to the lavas at the top. The ultrabasic lavas in the Margi area contain large olivine phenocrysts; the compositions of the olivine and the spinel inclusions indicate that the parental magmas have compositions similar to the boninitic rocks. Detailed EPMA mapping suggests the olivines are not in equilibrium with the groundmass; further analysis on glass or the trapped melts in the groundmass also confirms that the parental magma of the groundmass is much different to the olivines. Therefore, ultrabasic rocks in the Margi area record at least two stages of magmatism. However, lavas that have compositions affinitive to the groundmass have not been found above the boninitic rocks; this may imply restricted mantle flow and short-lived initiation magmatism. In addition, detailed observation of the mantle sequence also indicates later melt infiltration process, the REE compositions of the clinopyroxene favor an origin of boninitic lavas. In summary, both the mantle and crustal sequences well record magmatism related to subduction initiation; further studies will bring new insights into the element recycling in the subduction zone.