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Department of Earth Sciences

Orogenic Plateau Magmatism

 

Mark Allen, together with Jon Davidson, Jeroen van Hunen, Dr Iain Neill, and partners at the Geological Survey of Iran and the National Academy of Sciences of Armenia are funded for three years in a multi-disciplinary project to study the origin of recent mantle-derived magmatism on the Turkish-Iranian plateau, and in continental collision zones generally.

Background

 

The Turkish-Iranian orogenic plateau is one of the best modern examples, alongside Tibet, of a high plateau in a continental collision zone. Plateaux represent first-order topographic features of the continents and are strongly associated with their climactic effects, seismic hazard and volcanism. One of the surprising aspects of these regions is that the least-evolved volcanism is mafic and derived from melting of the mantle beneath the plateaux. There is no clear consensus on what is melting, and why, and it is clear that plateau magmas have a very diverse range of geochemical compositions. Models involving slab break-off and lithospheric delamination, allowing upwelling and decompression of hot asthenosphere to trigger partial melting, are popular in the literature for places such as Eastern Anatolia and Tibet, but they require rigorous testing by a variety of geochemical, geophysical and geodynamic modelling methods. We also wish to establish if there are repeated patterns in the record of collision zone magmatism in orogens young and ancient.

What we are doing

 

We have been exploring a variety of different models for the generation of mantle-derived magmatism during continental collision using:

- Field investigations in Iran (with Dr Monireh Kheirkhah, Geological Survey of Iran) and Armenia (with Dr Khachatur Meliksetian, National Academy of Sciences of the Republic of Armenia).

- Elemental and isotopic laboratory analyses of Late Miocene to recent lavas from these countries at NCEIT, Durham.

- Geodynamic modelling involving PhD student Lars Kaislaniemi, also funded by the TOPOMOD project.

Mark and Iain have travelled to Iran and Armenia on several occasions to collect samples of Miocene to recent lavas which are representative of the magmatism, and we also receive samples from fieldwork undertaken independently by the Geological Survey of Iran. The geochemical work at Durham involves major and trace element and Nd and Sr radiogenic isotope analyses to add to the significant volume of material that has already been published from across the plateau. This is a broad-brush approach for finding general geochemical patterns and comparing large datasets utilising commonly analysed elemental and isotopic tracers. Models that we have explored using geochemical data include: lithospheric delamination, melting of the mantle above the subducted Arabian passive margin, and melting of the hydrated lithospheric mantle during ongoing collision-related thickening.

In a completely different approach to the problem of the source of the magmatism, geodynamic modelling involves building a dynamic thermo-chemical model of continental collision zones using the numerical finite element software, Citcom. For this, we have been working extensively with Lars Kaislaniemi who is constructing a model demonstrating the viability of small-scale sub-lithospheric convection in generating small to moderate volumes of partial melt in the upper asthenosphere and at the base of the lithosphere. His models demonstrate startling spatial and temporal similarities to the magmatism observed in the Turkish-Iranian plateau in the last 10 Myr.


Papers directly associated with this project so far:

 

Kheirkhah, M., Neill, I., Allen, M.B., Agjari, K. (in press) Small-volume melts of lithospheric mantle during continental collision: late Cenozoic lavas of Mahabad, NW Iran. Journal of Asian Earth Sciences.

Neill, I., Meliksetian, Kh., Allen, M.B., Navasardyan, G., Karapetyan, S. in press. Pliocene-Quaternary volcanic rocks of NW Armenia: magmatism and lithospheric dynamics in an active orogenic plateau. Lithos.

Allen, M.B., Saville, C., Blanc, E.J-P., Talebian, M., Nissen, E. (2013) Orogenic plateau growth: Expansion of the Turkish-Iranian Plateau across the Zagros fold-and-thrust belt. Tectonics 32, 171-190

Allen, M.B., Kheirkhah, M., Neill, I., Emami, M.H., Mcleod, C.L. 2013. Generation of arc and within-plate chemical signatures in collision zone magmatism: Quaternary lavas from Kurdistan Province, Iran. Journal of Petrology 45, 887-911.

Bottrill, A.D., van Hunen, J., Allen, M.B. 2012. Insight into collision zone dynamics from topography: numerical modelling results and observations. Solid Earth 3, 387-399.

 

Conference abstracts (June 2013):

 

Kaislaniemi, L., van Hunen, J., Allen, M.B., Neill, I.; 2013. Sub-lithospheric small scale convection - a process for continental collision magmatism. Geophysical Research Abstracts 15, EGU2013-8040.

Allen, M.B., Neill, I., Kheirkhah, M., van Hunen, J., Davidson, J.P., Meliksetian, Kh., Emami, M.H. 2012. Orogenic plateau magmatism of the Arabia-Eurasia collision zone. Geophysical Research Abstracts 14, EGU2012-7812.

Kheirkhah, M., Allen, M.B., Neill, I., Emami, M., McLeod, C. 2012. Mantle amphibole control on arc and within-plate chemical signatures: Quaternary lavas from Kurdistan Province, Iran. Geophysical Research Abstracts 14, EGU2012-190.

Meliksetian, Kh., Neill, I., Allen, M.B., Navasardyan, G., Karapetian, S. 2012. Pliocene-Quaternary syn-collision volcanism of the Javakheti Ridge, NW Armenia: impact on models of magma generation in the Arabia-Eurasia collision zone. Geophysical Research Abstracts 14, EGU2012-7894.

Neill, I., Meliksetian, Kh., Allen, M.B., Navasardyan, G. 2012. Petrogenesis of syn-collision Plio-Quaternary lavas in NW Armenia: magma generation in the Turkish-Armenian-Iranian plateau. AGU Fall Meeting Abstracts. T21E-2619.

van Hunen, J., Allen, M.B., Bottrill, A., Magni, V., Kaislaneimi, L., Neill, I.; 2012. Continental collision and slab break-off: modelling results and implications for topography, trench migration and magmatism. AGU Fall Meeting Abstracts. T34-C02.

Mark and Iain have also contributed talks and discussion to a 2-day workshop at Leeds University on Volcanism and Tectonics, focussed on Armenia, in October 2011.