Cretaceous magmatic evolution in the Deylaman igneous complex, Alborz zone, Iran: change from extensional to compressional regime

Abstract

As so ci ate ed i tor: Tomasz Bajda The Deylaman ig ne ous com plex, as a part of the Late Cre ta ceous rock unit that lies be hind the Paleogene Alborz mag matic arc, in the north ern Alborz zone, is com posed of ba saltic sheet lavas al ter nat ing with the pe lagic cal car e ous sed i ments, basaltic pil low lavas, fel sic lavas and gabbroic-monzodioritic in tru sions. The pe lagic cal car e ous de pos its con tain microfossils rep re sent ing the Santonian-Maastrichtian ages. Fur ther more, petrographic tex tures such as the hyalomicrolitic tex ture and swal low-tail plagioclase crys tals in the pil low lavas, and also seg re ga tion ves i cles in the ba saltic sheet lavas, im ply high exter nal (hy dro static) pres sures as the magma was ex truded in a deep-wa ter en vi ron ment. The rock sam ples show both compositional bimodality and char ac ter is tic trends in the vari a tion di a grams. Also, some geo chem i cal char ac ter is tics im ply that the ba saltic lavas orig i nated from the par tial melt ing of an undepleted deep man tle source con tain ing spinel lherzolite: the en rich ment pat terns of LREE/HREE ra tios of the sam ples [(La/Yb)n = 3.93-4.16 for ba saltic lavas and 10.92 for fel sic lavas] ly ing be tween those char ac ter is tic of OIBs [(La/Yb)n = 12.92] and EMORBs [(La/Yb)n = 1.91]; sim i lar i ties be tween the pat terns of multi-el e ment spi der-di a grams; LILE bulges in the ba saltic sam ples com pared with those of OIBs. More over, the sam ples show in flu ence from two geotectonic en vi ron ments: su pra-subduction zone (SSZ) set tings and plume-type within-plate mag mas. There fore, be cause of the deep sub ma rine en vi ron ment in ferred for the ef fu sive vol ca nic erup tions in Santonian-Maastrichtian time, it seems that the Deylaman ig ne ous com plex evolved through two stages: first, a ten sional re gime in a su pra-subduction zone (far ther from the Me so zoic mag matic arc) and for ma tion of an em bry onic rift-re lated oceanic ba sin in the Late Ju ras sic-Early Cre ta ceous; sec ondly, a com pres sive re gime in the Late Cre ta ceous-Early Paleocene and in land mi gra tion of the mag matic arc. Con se quently, the Cre ta ceous magmatism can be in ter preted as a pre lude to the Eocene mag matic flare-up in the mag matic arcs of Iran.