Opening of the Algerian Basin: Petrological, geochemical and geochronological constraints from the Yaddene Complex (Lesser Kabylia, Northeastern Algeria)

The Yaddene complex, located in Lesser Kabylia (northeastern Algeria), is composed of Tertiary mafic and ultramafic rocks that outcrop within syn-rift sedimentary rocks of the Algerian marginal basin, in the Maghrebide belt of North Africa. Petrographic observations show that the Yaddene complex is composed mainly of two distinct lithologies: (1) a layered quartz-bearing gabbro at the bottom, which consists mainly of plagioclase (An(93)), clinopyroxene (altered to actinolite) and rare interstitial quartz; and (2) layered plagioclase-bearing lherzolites composed of olivine (Fo(86-88)) orthopyroxene (En(86-87)), clinopyroxene (diopside and augite), rare plagioclase (anorthite) and amphibole of pargasitic composition. The trace element concentrations in pyroxenes and olivine of the Yadenne complex show a depletion in light rare earth elements (LREE) similar to basalts of the Mid-Ocean Ridge (N-MORB), which reflects the depletion of the mantle source. In addition, high #Cr in spinel reflects a high degree of partial melting of the mantle source. On the other hand, slight enrichment in Large Ion Lithophile Elements (Cs, Rb, Ba), weak but significant negative Nb, Ta, Zr, Hf and Ti anomalies, and positive Pb spikes are observed in both whole-rocks and minerals. These patterns are best explained by interaction between parental mantle and fluids and/or siliceous melts derived from a subducting oceanic slab. The tectonic discrimination diagrams of minerals and whole rocks indicate that the most likely geodynamic setting for emplacement of the Yaddene Complex is a back arc basin environment. In situ U-Pb dating of euhedral zircons and titanite from a quartz-bearing gabbro yields an age of 18.97 +/- 0.12 Ma (20, which is interpreted as the crystallization age of magmatic zircons and the gabbroic magma. Zircons from a plagioclase-bearing lherzolite gave a consistent age of 19.05 +/- 0.39 Ma (2 sigma), which is attributed to zircon growth during metamorphic/metasomatic processes coeval to gabbmic magma emplacement. The mafic/ultra-mafic rocks of the Yaddene complex are intercalated within fine-grained sediments of the syn-rift Oligo-Miocene Kabyle and the obtained early Burdigalian ages are interpreted as the early stages of an extensional regime that ultimately led to the opening of the oceanic Algerian Basin.

Automated summary

The Yaddene complex in northeastern Algeria is composed of mafic and ultramafic rocks. Petrographic observations indicate depletion of rare earth elements and high Cr content, suggesting depletion and partial melting of the mantle source. The presence of element anomalies suggests interaction between fluids or siliceous melts from subducting oceanic slab. Dating analysis shows that the complex formed around 18.97 Ma and 19.05 Ma.