Elsevier

Lithos

Volumes 256–257, July 2016, Pages 88-108
Lithos

Magmatic evolution of the Early Pliocene Etrüsk stratovolcano, Eastern Anatolian Collision Zone, Turkey

https://doi.org/10.1016/j.lithos.2016.03.017Get rights and content

Highlights

  • We constructed a composite chemo-stratigraphic section of the Etrüsk volcano.

  • Our study presents new geochemical, isotopic and K–Ar radiometric dating.

  • We constructed petrologic models to interpret the mantle source characteristics.

  • AFC and periodic replenishment were operational during evaluation of the Etrüsk.

  • Magma chamber was possibly located around 10–12 km depth beneath the Etrüsk.

Abstract

The Pliocene Etrüsk stratovolcano, located in the northeast of Lake Van (Eastern Anatolia; Turkey), is one of the important volcanic centres in the Eastern Anatolian collision zone. Mt. Etrüsk overlies a widespread volcanic plateau, consisting of basaltic and hawaiitic lavas formed by fissure eruptions between 4.9–4.5 Ma. These basic lavas contain a phenocryst phase consisting of olivine, plagioclase and clinopyroxene. Trace element ratio diagrams imply that these basic magmas were generated from a mantle that contained a clear subduction component that is related to the subducted sediments rather than fluids or altered oceanic crust. Results of the melting models on the basaltic plateau lavas indicate that there was a marked variation both in the mantle source mineralogy (i.e. the ratio of garnet peridotite to spinel peridotite in the source varies between 60/40% and 40/60%) and the degree of melting (i.e. F between 0.8–4%). This can be explained by a model in which magmas were generated by partial melting of both metasomatised lithospheric and deeper asthenospheric mantle sources in an extensional setting in response to the partial delamination of the lithospheric mantle of Eastern Anatolia and then mixed with each other during Pliocene times.

Central eruptions that formed the Etrüsk volcano lasted ~ 600 kyr between 4.3–3.7 Ma during Zanclean times. The estimated depth of the Etrüsk magma chamber is ~ 9–12 km. The volcano erupted lavas with a rather narrow compositional range from latite to rhyolite, which are either transitional or mildly alkaline in character. The Etrüsk lavas contain plagioclase, clino- and orthopyroxene, biotite, K-feldspar and rarely, minor amounts of olivine and amphibole in the phenocryst phase. A composite chemo-stratigraphic section of the volcano and petrological models indicate that the evolved lavas of the Etrüsk volcano differentiated from a parental magma composition, which is similar to that of the most primitive plateau basalt lavas underlying the volcano, via the AFC process, and experienced at least two major magma replenishment episodes at 4.1 Ma and 3.8 Ma during the magma chamber evolution.

Introduction

Collision-related Neogene volcanism in the Eastern Anatolia region began after the continent–continent collision between the Arabian and Eurasian plates and covered wide areas extending from the Arabian foreland in the south to the Erzurum-Kars plateau in the north (Fig. 1). Results of seismic tomography studies in E Anatolia (Al-Lazki et al., 2003, Sandvol et al., 2003a) revealed that the lithospheric mantle was either very thin (Angus et al., 2006) or completely absent (Şengör et al., 2008) beneath a 38–40 km-thick crust (Zor et al., 2003) which was represented by an accretionary complex (i.e. Eastern Anatolian Accretionary Complex: EAAC; Şengör et al., 2008), and hence the asthenosphere has been very close to the surface.

The Etrüsk volcano is located almost on the southern edge of the collision-related volcanic province of Eastern Anatolia within the Northern Lake Van neovolcanic area, as described by Milanovskii and Koronovskii (1973). It is also situated on the culmination of the Lake Van regional dome structure of Şengör et al. (2008). At present, the Etrüsk volcano has a horse-shoe (or amphitheatre)-shaped circular crater with a diameter of ~ 4.5 km at the top (almost twice as large as that of Mt. St. Helens in NW USA) with a depth of ~ 700 m, open to the south towards the Lake Van. It has a footprint area of ~ 380 km2, an average diameter of ~ 22 km and an approximated eruptive volume of 150 km3. The maximum present-day altitude of the Etrüsk volcano is 3100 m at the western part of the crater rim. Apart from a couple of geochemical analyses (Pearce et al., 1990) and one isotope (K–Ar) dating (Innocenti et al., 1982b), there is virtually no information available in the literature about this volcano.

The aims of this paper are (1) to present new geochronological, petrological, geochemical and isotopic data and a detailed volcano- and chemical stratigraphy of this volcano, (2) to present our results concerning the mantle source characteristics and the degree of partial melting, (3) to present our interpretations about the temporal variations in magma chemistry with special reference to a number of important parameters related to the magma chamber processes such as fractional crystallisation, magma mixing/replenishment and assimilation we obtained from our petrological models, and finally (4) to discuss the importance of all these findings in the magmatic history of the Etrüsk volcano and in the framework of the tectono-magmatic evolution of the Eastern Anatolia region.

Section snippets

Analytical techniques

Major oxide, trace and rare earth element concentrations of the samples were analysed by ICP-ES and ICP-MS at the ACME Laboratories of Vancouver, Canada. The analytical accuracy is better than ± 3%. A 1 g sample split is ignited for 2 hours at 1000 °C, cooled in a desiccator, then weighed with the difference expressed as percentage Loss on Ignition (% LOI). A set of USGS standards (i.e. W-2, AGV-1, G-2, GSP-2, BCR-2) and an in-house standard (Reference Material STD SO-18) were analysed together

Volcano-stratigraphy and geochronology

The basement of all the Neogene volcanic units in the northeast of Lake Van is composed of an ophiolitic mélange named as the EAAC. It contains large sporadic blocks of metamorphic units (i.e. mostly marbles, meta-sandstones, gneisses and schists of presumably Palaeozoic age) in various sizes. Milanovskii and Koronovskii (1973) considered the outcrops of metamorphic rocks north of Lake Van as the Aladağ crystalline massif, and interpreted them as being a part of a micro-continent. However,

Nature of the mantle source region

OIB and MORB generally exhibit positive HFSE (Nb and Ta) anomalies in N-MORB or Primitive Mantle-normalised multi-element diagrams (e.g. Hofmann, 1986. Conversely, BPS lavas display strong negative Nb-Ta anomalies with respect to LIL elements and REE, implying that they were not derived from typical mid-oceanic ridge basalt (MORB) and (or) ocean island basalt (OIB) source mantle. Petrochemical studies (Hawkesworth et al., 1997, Pearce, 1983, Pearce et al., 2005) show that magmatic rocks related

Conclusions

The primitive magmas that fed the Etrüsk volcano were generated from a mantle that contained a clear subduction component. This component may be linked to the subduction of the Neotethys Ocean beneath the EAAC and Pontides and the chemical signature of its subducted sediments, rather than fluids or altered oceanic crust. The results of our melting models indicate that there was a marked variation both in the source mineralogy (i.e. garnet peridotite vs. spinel peridotite sources) and the degree

Acknowledgements

Our first deployment in the southern portion of the Eastern Anatolian collision zone in 2007 was financially supported by the Istanbul University Research Fund (Project #ACIP-1282). We continued collaborative efforts in 2008 through two PhD projects (2008-Fbe-D137 and 2008-Fbe-D138) supported by the Research Fund of the Van Yüzüncü Yıl University. Our research reached a climax between 2009 and 2011 with the generous support of a major Turkish-Russian project financed and supported by TUBITAK

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