Mesozoic basin inversion in Central Alborz, evidence from the evolution of Taleqan-Gajereh-Lar paleograben

Abstract

This paper presents evidence on Mesozoic inversion of basin bounding faults within the Taleqan-Gajereh-Lar Paleograben (TGLP) in Central Alborz Range. For this purpose, well documented stratigraphy data across the TGLP together with the new acquired structural data on the geometry and kinematics of the paleograben basin bounding faults are utilized. The TGLP has evolved through the Early and Middle Cimmerian and the Late Cretaceous tectonic events. The Early Cimmerian north verging folds of Paleozoic rocks with development of axial foliation is proposed to be related to inversion of the basin bounding Mosha and Hasanakdar faults. During the Middle Cimmerian (Bajocian), synchronous to opening of the Caspian basin, the TGLP was extended through the growth of the Gajereh half-graben on the hanging wall of the Mosha Fault. This half-graben that accommodated the thickest portion of the Jurassic rocks in the south Central Alborz is considered as the depocenter of Jurassic basin in this region. The Late Cretaceous-Early Paleocene event associated with folding, and thrust faulting of Jurassic and Cretaceous rocks, causes inversion of the TGLP along its north bounding Taleqan Fault. Development of an angular unconformity between the Eocene Karaj Formation and Mesozoic deposits is the result of this inversion. This event that made the TGLP as upland causes deposition of a thick succession of Paleocene Fajan conglomerate outside the TGLP. The presented interpretation of the Mesozoic evolution of the TGLP in the Central Alborz Range is a key finding, applicable to similar paleograbens along the range and the neighboring Caucasus region.