Geochemistry and tectonics of Cenozoic volcanism in the Lesser Caucasus (Azerbaijan) and the peri-Arabian region: collision-induced mantle dynamics and its magmatic fingerprint


Dilek Y., IMAMVERDIYEV N., Altunkaynak Ş.

INTERNATIONAL GEOLOGY REVIEW, cilt.52, ss.536-578, 2010 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 52
  • Basım Tarihi: 2010
  • Doi Numarası: 10.1080/00206810903360422
  • Dergi Adı: INTERNATIONAL GEOLOGY REVIEW
  • Sayfa Sayıları: ss.536-578

Özet

The Lesser Caucasus occurs in the hinterland of the Arabia-Eurasia collision zone in the broad Alpine-Himalayan orogenic belt and includes Cenozoic plutonic and volcanic sequences that provide important clues for collision-driven continental magmatism and mantle dynamics. Two main magmatic episodes (Eocene and late Miocene-Quaternary) formed the volcanic landscape and the igneous assemblages in the Lesser Caucasus of Azerbaijan. (1) The Eocene sequence consists of trachybasalt and basaltic trachyandesite with subordinate tephrite-basanite, basaltic andesite, and trachyandesite, showing shoshonitic and mildly alkaline compositions. The Miocene-Quaternary magmatic episode is represented by (2a) an early phase of upper Miocene-lower Pliocene andesite, trachyandesite, trachydacite, dacite and rhyolite lavas, and by (2b) a late phase of upper Pliocene-Quaternary trachybasalt, basaltic trachyandesite, basaltic andesite, trachyandesite, trachyte, and rhyolite flows. The rocks of the early phase have high-K calc-alkaline compositions, whereas those of the late phase show high-K shoshonitic compositions, defining an alkaline trend and a K2O-enriched melt source. All three volcanic associations show variant troughs in Nb, Ta, Hf, and Zr, strong enrichment in Rb, Ba, Th, La, and depletion in Ti, Yb, Y relative to mid-ocean ridge basalt N-(MORB) in their multi-element patterns. The enrichment of incompatible elements and K suggests derivation from a metasomatized mantle source, whereas the troughs in Nb and Ta indicate a subduction influence in the mantle melt sources. Mantle-derived magmas were modified by AFC/FC processes for all three volcanic sequences. These geochemical features are similar to those of coeval volcanic associations in the peri-Arabian region, and indicate the existence of subduction-metasomatized lithospheric mantle beneath the Lesser Caucasus during the Cenozoic. Partial melting of this subduction-modified subcontinental lithospheric mantle in the peri-Arabian region was triggered initially by slab breakoff following discrete continental collision events in the early Eocene. The heat source for the later Miocene-Quaternary volcanism in the entire peri-Arabian region was provided by asthenospheric upwelling, which itself was caused by delamination of the mantle lithosphere following the final Arabia-Eurasia collision at 13Ma. Increased alkalinity of successively younger units in the Plio-Quaternary volcanic associations resulted from the input of enriched asthenospheric melt during the last stages of post-collisional magmatism. Active, crustal-scale and orogen-parallel, transtensional fault systems in the peri-Arabian region facilitated the formation of fissure eruptions and stratovolcanoes in the latest Cenozoic.