A heterogeneous subcontinental mantle under the African\u2013Arabian Plate boundary revealed by boron and radiogenic isotopes

Samuele Agostini,Piero Manetti,Carlo Doglioni,Paolo Di Giuseppe,Sandro Conticelli

doi:10.1038/s41598-021-90275-7

Abstract

The northern and northwestern margins of the Arabian Plate are a locus of a diffuse and long-lasting (early Miocene to Pleistocene) Na-alkali basaltic volcanism, sourced in the asthenosphere mantle. The upwelling asthenosphere at the Africa–Arabia margin produces very limited magma volumes in the axial zone. Therefore, portions of hot, fertile mantle continue their eastward migration and are stored at shallower depths under the 100-km thick Arabian lithosphere, which is much thinner than the African one (≈175 km): this causes the occurrence and 20-Ma persistence of magma supply under the study area. Erupted basalts sampled a continuous variation of the mantle source, with a striking correlation among temperature, pressure and isotopic composition shifting between two end members: a 100 km-deep, more depleted source, and a 60 km-deep, more enriched one. In particular, we observed an unusual variation in boron isotopes, which in the oceanic domain does not vary between more depleted and more enriched mantle sources. This study shows that, at least in the considered region, subcontinental mantle is more heterogeneous than the suboceanic one, and able to record for very long times recycling of shallow material.

Highlights

The geochemical and isotopic signature of basaltic magmas can provide unique insights into the characteristics of the upper mantle and of its dynamics, with fundamental implications for the tectonic framework
While in the north this convergence induced the Neotethys Ocean to subduct along the Eurasian margin, farther south the counter-clockwise rotation of the Arabian Plate at the beginning of the late Oligocene to early Miocene led to the initial opening of the Gulf of Aden, followed by the development of the Red Sea and Gulf of Suez Rift Systems, so that the African Plate and the Arabian Plate began to s eparate[12]
Volcanic activity in the region started in the early Miocene (21 Ma) with the emplacement of abundant Na-alkaline products and subordinate silica-oversaturated basaltic and andesitic rocks in the north sector of the Arabian foreland, within the Gaziantep Basin

Summary

Introduction

The geochemical and isotopic signature of basaltic magmas can provide unique insights into the characteristics of the upper mantle and of its dynamics, with fundamental implications for the tectonic framework. Unlike magmas generated in ocean islands and continental rifts, mantle-derived partial melts erupted in a within-plate continental tectonic setting, as well as those along continental strike-slip areas, may interact with the lithospheric mantle and/or the crust during their ascent to the surface. For this reason, the primary character of intraplate-type basaltic magmas ascending through the continental lithosphere may be significantly modified by fractional crystallisation, eventually matched by crustal assimilation. Extensive intraplate-like volcanism occurred in South-East Anatolia and the north foreland of the Arabian Plate (Fig. 1)

Methods

Results

Conclusion