Age of Rifting of the South Caspian Basin: Inference from its Margins in Azerbaijan and Iran

By

 Marie-Françoise Brunet¹

(1) UMR 7072 Tectonique CNRS-UPMC, 75252 Paris cedex O5, France

 The age of the first deposits in the deep (20 km) central part of the South Caspian basin (SCB) is not known. Moreover, the basin being probably underlain by an oceanic crust, the first steps of the basin’s evolution, before opening (i.e. the rifting phase) are not present and not possible to analyse in the central basin. Therefore, in order to characterize the rifting phases and to infer the timing of oceanic opening, the study is focused on some tectonic units surrounding the SCB (in Azerbaijan and especially North Iran) which were formerly margins or prolongations of the SCB. Subsidence analysis is combined with tectonic and geodynamic reconstructions.

A calendar is deduced of the SCB evolution from the analysis of tectonic subsidence on its margins. The data on the Alborz show that the rifting phase on the southern margin of SCB took place in Early? to Middle Jurassic at the same time as the opening of the Great Caucasus Trough which occurred since Sinemurian (?). Its north margin was prolongated into the SCB northern margin, towards the Great Balkhan. The Callovian-Late Jurassic phase of subsidence mainly seen in the basinal area and in the lateral extensions of the SCB seems to indicate the beginning of oceanic opening. This opening worked in the frame of an important back-arc extension of a very long basin behind an arc, supported by the presence of an important Middle Jurassic volcanism going from Pontides to Alborz through the Lesser Caucasus.