Constraints of rare detrital V-rich tourmaline and rutile on late Devonian palaeogeographic reconstruction in the Azarbaijan district, NW Iran

Abstract

• New geochemical data on detrital tourmaline and rutile from the Devonian sedimentary rocks in NW Iran. • Specific V-bearing tourmaline and rutile compositions indicate metaultramafic source rocks. • Evidence for far-distant transport of sediment from the Gondwanan-East African Belt to the distal margin of Gondwana . This paper presents the first geochemical data on detrital tourmaline and rutile from sedimentary rocks of the upper Devonian Ilanqareh Formation (Fm.) which is extended in the Azarbaijan area in NW Iran. The deposits have typically mature character with ultra-stable heavy minerals predominantly derived from the metamorphic rocks. The detrital tourmaline has mainly dravitic, uvitic and Mg-foititic composition, thus indicating metaultramafic source rocks and common metapelites and metapsammites. Detrital rutile geochemistry indicates the presence of lower-up-to-upper amphibolite facies metapelitic source rocks, and part of this rutile most likely underwent granulite facies metamorphism. Unique detrital V-bearing tourmaline with high V 2 O 3 content up to 8.93 wt% indicates its primary derivation from far-distant source rocks in the East African Belt and adjacent areas. This is confirmed by both the exceptional geochemistry and the shape and roundness of the tourmaline which indicate recycled detrital origin and multiple reworking. The less frequent V-bearing rutile also indicates the same sources. These results confirm the wide circulation of sediments distributed by the Gondwana super-fan system from the inner parts of this super-continent to the Gondwana and peri-Gondwanan terrain continental margins, and also their later re-distribution during the Devonian era. The results highlight the significant contribution from Gondwanan sources to the supply of upper Devonian siliciclastic formations in NW Iran compared to those from the Iranian plate.