Removal of continental lithosphere beneath the Canary archipelago revealed from a U[sbnd]Pb Age and Hf/O isotope study of modern sand detrital zircons

Abstract

We present new geochemical, UPb age, HfO isotope compositions for more than 400 detrital zircons collected from modern sands located throughout western Fuerteventura, Canary Islands as a proxy for the timing and origin of its plutonic history. This approach provides a new perspective and more complete time-integrated record of the islands geologic evolution. Fuerteventura UPb detrital zircon age spectra document that magmatism was initiated at ~35 Ma, was most prolific during the main shield-building stage (30–15 Ma), youngs southward, corroborates the existence of a low magma fluxing period (15–6 Ma), and provides new evidence for the existence that Pliocene and younger (at least as young as 0.24 ± 0.02 Ma) plutons with a variety of magma compositions accompanied post-shield volcanism until recent times. Most Fuerteventura detrital zircons have sub-mantle SIMS oxygen isotope compositions (δ18O < 5.0‰), and overlap compositions reported previously for gabbro/basalt xenoliths entrained in nearby Gran Canaria lavas, interpreted to be fragments of high-temperature seawater-altered Layer 3 oceanic crust.The detrital zircon Hf isotope compositions (εHfi: +15.0 to −0.2) display a much larger variation than recorded in previous studies of volcanic rocks from the Canary or Cape Verde islands. This extreme isotopic variation demonstrates that Fuerteventura detrital zircons provide a more sensitive record of the involvement of multiple sources in magma genesis. The high-εHf (>+12) zircons document the involvement of a depleted reservoir that is isotopically most similar to Middle Atlas SCLM. The low-εHf zircons, specifically those <+1, document the involvement of a reservoir that is more enriched than HIMU and overlaps the composition of NW African lower crust. These extreme εHf compositions indicate the presence of NW African lithosphere beneath Fuerteventura during the shield-building stage of island growth. The absence of a highly depleted Hf isotopic signature in young detrital zircons is interpreted to document the removal of SCLM during a magmatic shutdown initiated at ~15 Ma. Lithosphere erosion could be linked to a pulsed edge-driven convection cell responsible for SCLM delamination along a NE-trending corridor in NW Africa. The detrital zircon Hf and O isotope compositions indicate that both oceanic and continental lithosphere have existed beneath the island. This lithosphere is heterogeneous, consisting of high-T seawater altered oceanic crust, continental lower crust, and subcontinental mantle lithosphere; consistent with formation above a complex lithospheric transition zone created during Triassic-Jurassic rifting and opening of the Central Atlantic Ocean. Importantly, this detrital zircon study demonstrates that a more complete time-integrated record of a long-lived ocean island's geological history is preserved in modern sand samples, in part because a significant portion of Fuerteventura has been removed by erosion.