New insight to paleogeography and structural evolution

Category Tectonic & Seismotectonic
Group GSI.IR
Location The 25 Symposium of Geosciences
Author Nazari H-Ritz J-F
Holding Date 01 July 2007



Alborz is an elongated block in active tectonic zone of Iran which has been affected by most of distinguished geological events in both mega continents of Eurasia۱:place> and Gondwana.

Although, it has been referred to existence of Ordovician and Silurain volcanic series in northern Alborz as evidenvces of opening of Paleotethys as a result of transtentional system between Turan and Alborz but our recent data from field investigations and interpretation of our balanced cross sections suggest an older basin.  We refer to this as Orthotethys which its evidences has been seen in ophiolithic and metamorphic rocks of Precambrian- Lower Paleozoic and nonconformity between Permian and lower Paleozoic rocks in western part of central Alborz. This may be related to Hercynian orogeny.

The North Alborz۱:place> fault as a fundamental structure has some characteristic features (flower structure) in internal part of central Alborz. Detachment folding systems with uplifted Paleozoic rocks along its hanging wall are apparent features. More folding and dislocated unites in western part comparing to eastern part of North Alborz۱:place> fault are other characteristic feature of this structure.

North Alborz, Mosha and Taleghan faults mention as principal inner faults of Central Alborz that the North Tehran۱:place> and Khazar faults are in fact two propagated branches of these major faults to the south and north.  These two take up most of present-day shortening in central Alborz.

Two sub-parallel balanced cross sections (Karadj-Chalus and Damavand-Amol sections with ~۸۰ km distance) were made across Central Alborz۱:place>. (Figure)

  Our data derived from these sections lead us to determine total horizontal shortening of ۳۸% ± ۲% (about ۳۸ km in ۱۰۰ km long of Karadj-Chalus line) in this part of the range.  A reconstruction of Karadj-Chalus section for Eocene basin show only ۱۲% ± ۲% shortening suggesting that ~%۷۵ of shortening are related to post Eocene time. Both crust and sediments in Alborz show gradual increase in thickness, with almost constant gradient toward the Caspian basin.  


Keywords: Tethys – Orthotethys- paleotethys –Gondwana-Eurasia- Balanced section-Alborz-۱:city> Iran۱:country-region>۱:place>.


tags: QAZVIN