Mineralogy and trace elements variation of subsurface cretaceous basalts in the Eastern Tunisian margin and the Pelagic Sea: New data and geodynamic implication

Abstract

Abstract- Eastern Margin of Tunisia and the Pelagic Sea were affected by four magmatic events during the Cretaceous. During these events, the products are mainly interbedded basalts, numerous mafic sills and dykes, volcanic breccias and pyroclastic products. Petrography, mineralogy and geochemistry studies prove two lineages of basalts: basalts with tholeiitic affinity and alkali basalts. Electronic microprobe studies of clinopyroxene prove an anorogenic context of this magmatism. We used variable distribution of incompatible trace element ratios, such as Th/Ta, Th/Tb, or Th/Hf. These elements are characterized by distinct mantle composition source and different partial melting trends. These data suggest that the magma of tholeiitic affinity basalt is originated within the enriched mantle (EM1), moderate impoverishment in light rare-earth elements (LREE). The mantle source of alkali basalt is compositionally transitional between the high-U/Pb mantle (HIMU) and enriched mantle (EM2). The tectonic history of the area combined to the new mineralogical and geochemical investigations of subsurface cretaceous basalts will contribute significantly to place this magmatism in its Mediterranean context. Tectonic models are proposed to explain the geodynamic and the tecto-magmatic history of the studied area during Cretaceous.