3-D numerical constraints for the Triassic mafic igneous system of Antalya (SW Turkey): Magma generation associated with southern Neotethyan slow seafloor spreading

Abstract

A ~ 400 m thick Middle-Late Triassic volcano-sedimentary succession crops out in a relatively narrow corridor ~75 km long and ~ 25 km wide close to Antalya Gulf, SW Turkey. The volcanic and subvolcanic rocks represent the majority of the succession and are associated with epiclastic breccia, turbiditic sediments as well as chert and limestone layers. The igneous rocks are alkali basalts, with incompatible element content matching the classical HiMU-OIB types. These are considered as the precursors of a rift system that would have later evolved into a mature Neotethyan oceanic system, with emplacement of massive tholeiitic basalt sequences, not recorded in the investigated area.Clinopyroxene-melt thermobarometric constraints indicate the presence of two main magma chambers, one equilibrated at ~7–10 km depth and ~ 1070 °C and the other at ~15–21 km depth and ~ 1300 °C. Based on these estimates, a 3-D finite element modelling has been applied, simulating the presence of ellipsoidal magma chambers at different depths and with variable sizes, applying different boundary loading conditions. The scenario that best fits the distribution of the volcanic rocks assumes the contemporaneous presence of two magma reservoirs. One is shallow, with a size of ~17 × 1.5 × 1.5 km, and the second is deeper, with a size of ~37 × 3 × 3 km. Numerical simulations show maximum 6 m opening and dilation through horizontal plane at the surface during the Permian/Triassic intracontinental rift phases. Morphological constraints of this rift zone, with the presence of massive lava eruptions also as pillow facies, have been simulated with the existence of a slowly opening rift system. In order to produce the voluminous magma batches in the Antalya region, pure extensional tectonic regimes seem insufficient, and the presence of a transtensional regime must have accompanied the tectonic forces during the Triassic intracontinental rifting stage.