地中海东部地幔演化过程:来自希腊Lesvos岛中新世钾质岩浆作用的启示

希腊Lesvos岛广泛出露的中新世钾质岩浆岩为深入探讨地中海东部地区新生代构造演化和深部过程提供了宝贵机会.本文对Lesvos岛碰撞后钾质岩石开展了系统的矿物电子探针分析、锆石U-Pb定年和Hf同位素分析及全岩地球化学分析.研究结果表明:Lesvos岛出露的碰撞后火山岩主要由玄武粗安岩、玄武安山岩和粗面岩组成,锆石U-...

Mantle evolution of the eastern Mediterranean Sea: Implications from the Miocene potassic rocks in Lesvos Island, Greece

The widespread Miocene potassic rocks in the Lesvos Island, Greee, offer a prime opportunity to probe into the Cenozoic tectonic evolution and deep processes of the eastern Mediterranean Sea. Here we carried out a combined study of mineral electron probe anlaysis, in situ zircon U-Pb dating and Hf isotopic compositions, and whole-rock geochemistry analyses on the postcollisional potassic rocks in the Lesvos Island. It can be found that these postcollisional volcanic rocks are mainly composed of basaltic trachyandesite, basaltic andesite, and trachyte, with a zircon U-Pb age of 17.2Ma. These three kinds of potassic rocks are characterized by relative enrichments of large ion lithophile elements and depletions in high field strength elements. Basaltic trachyandesite and basaltic andesite have simialr and enriched Sr-Nd-Pb isotpic compositions. The relatively low Dy/Yb and variably high Ba/La and Zr/Hf indicate that these basaltic rocks were derived from low-degree partial melting of spinel-facies lithospheric mantle that had been metasomatized by fluids/melts orignating from subducted terrigeneous sediments. In contrast, the coeval trachyte samples exhibit more depleted Sr-Nd isotopes, and their homogeneous Hf isotopic compositions in co-magmatic zircon preclude the occurrence of significant crustal assimilation and magma mixing during magmatic evolution. The relatively high Y and Yb concentrations and low Sr/Y and (La/Yb)_N ratios in these felsic rocks suggest that they were derived from partial melting of upper-middle crust. With respect to the seismic profiling studies and the initiation of continental collision between Pelagonia block and Apulian block, the postcollisional potassic volcanism in the Lesvos Island may result from the break-off of the subduced Pindos oceanic lithosphere in the Miocene.