Lithospheric composition and thermal structure of the Arabian Shield in Jordan

Abstract

In this paper, a unique set of samples from the uppermost crust down to the lithospheric mantle of Jordan is analyzed for composition and petrophysical properties (density, thermal conductivity, radiogenic heat production). These data, covering a vertical section of almost 65 km, are used in conjunction with surface heat flow to generate a detailed and comprehensive lithospheric thermal model that reflects the conditions of the Arabian Shield (AS) prior to the post-Oligocene onset of lithosphere thinning and voluminous basaltic volcanism. The pre-Miocene model geotherms, based on conductive surface heat flows of 55 and 60 mW m − 2, (a) meet the range of lithosphere–asthenosphere boundary depths of 110–160 km known from seismology, (b) conform to results of thermomechanical models on the origin of the Dead Sea basin that started in Miocene time, and (c) are consistent with typical xenolith-derived geotherms for terranes of similar age and lithospheric thickness. Moho temperatures (at depths between 35 and 40 km) of the AS in pre-Miocene times were most likely in the order of 530–650 °C, with mantle heat flows averaging between 24 and 29 mW m − 2. Results contradict former views of the late Proterozoic/early Cambrian-stabilized AS being an anomalously cold terrane. A “cold” thermal structure inferred from previously measured low surface heat flows (generally ≤ 45 mW m −2) is inconsistent with the thickness, composition, and petrophysical properties of the stable lithosphere of the shield.