University of Leicester
2021EneVPhD.pdf (22.78 MB)

Crustal recycling in the magmatic evolution of post-subduction provinces: The South Apuseni Mountains, Romania

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posted on 2021-11-11, 14:14 authored by Vlad-Victor Ene
Adakitic magmas usually form in subduction environments due to the melting of hot, young, eclogitized oceanic crust. However, a number of different mechanisms such as fractionation of amphibole and/or garnet, suppression of plagioclase, and melting of clinopyroxene- and amphibole-rich lower crustal lithologies have been shown to produce similar signatures. Adakite-like rocks can be found in the Neogene and Quaternary rocks of the South Apuseni Mountains, a NW–SE trending magmatic corridor formed in extensional settings generated by the rotation of the underlying Tisza–Dacia crustal block. By reconstructing the igneous evolution of the province, this thesis tests a number of different hypotheses regarding arc-like and adakite-like magmatism in a post-subduction setting and constrains the source of arc-like and adakite-like magmas in the South Apuseni Mountains.
Regional geochronology shows that the area was active between 13.63 and 7.24 Ma with a small trachyandesite intrusion at Uroi at 1.45 Ma. However, antecrystic zircon present in a number of samples indicate that magmatism predates 14 Ma. The majority of volcanic centres were active for ~700 kyrs with two samples exhibiting continuous populations for ~2 Myrs. Adakitic signatures are time-dependent, representing the younger products in centres exhibiting both populations.
Whole-rock geochemistry indicates that almost all samples fractionated a gabbro-type assemblage. Plagioclase suppression did not occur and amphibole fractionation cannot explain the adakitic signatures in high MgO samples. My geochemical modelling has shown that magmas with arc-like and adakite-like signatures can be obtained by melting gabbroic cumulates forming a clinopyroxene-rich restite. Melting of a lower crust fluxed by asthenospheric melt would cause an increase in the adakitic signatures. Isotopically, all samples plot between the isotopic signatures of coterminous Jurassic and Cretaceous arc rocks. Mixing with asthenospheric melts can also be observed, and the more positive εHf(t) values of the Deva zircons can be explained by mixing a Jurassic component with ~10% asthenospheric melts. Thus, I propose that asthenospheric upwelling led to lithospheric mantle melting and underplating causing melting in the lower crust. In specific areas, asthenospheric melts interacted with the lower crust, modifying its chemistry and isotopic signatures and generating magmas with strong adakitic signatures and positive Nd and Hf signatures.



Daniel Smith; Simon Tapster; Jon Naden; Marian Munteanu

Date of award


Author affiliation

School of Geography, Geology and the Environment

Awarding institution

University of Leicester

Qualification level

  • Doctoral

Qualification name

  • PhD



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