Geochemistry and Petrogenesis of Shoshonitic Dyke Swarm in the Northeast of Meshkinshahr, NW Iran

Mohammad Fadaeian,Wenjiao Xiao,Songjian Ao,Amin Allah Kamali,Ahmad Jahangiri

doi:10.3390/min12030309

Abstract

The study area is located in Ardabil province in the northeast of Meshkinshahr city. More than 200 small and large Eocene-age dykes form outcrops in this area. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U–Pb zircon analyses yield a consistent age of 44.3 ± 1.8 Ma for the dyke swarms. These dykes include tephritic, andesitic and basaltic compositions, and show enrichment in LREEs (relative to HREEs) and are characterized by enrichment in LILEs and depletion in HFSEs. Petrological observations, along with major, rare earth and trace elements geochemistry, suggest that the dykes have a shoshonitic signature. All the rocks are highly enriched in incompatible trace elements and have variable Sr–Nd isotopes. Enrichment in incompatible elements and other geochemical features for the dyke swarm rocks suggest that a metasomatized subcontinental lithospheric mantle is the magma source. The negative Nb–Ta–Ti anomalies in the rocks are comparable with the features of subduction-related magmatism and contamination with ancient crustal components. The radiogenic 87Sr/86Sr isotopic values of the rocks imply the involvement of slab terrigenous sediments and/or a continental lithosphere. Isotopically, the volcanic rocks exhibit a binary trend, representing 1–5% mixing between the primary mantle and sediment melts. Our melting models suggest that there are residual garnet + spinel in the source, which are incompatible with the partial melting of amphibole- and/or phlogopite-bearing lherzolites. The geochronological, geochemical and isotopic data for the northeast Meshkinshahr dyke swarms suggest that these Late Eocene magmas were derived from a small degree of partial melting of a subduction-metasomatized lithospheric mantle source in a post-collisional setting.

Highlights

Introduction published maps and institutional affilOur understanding of dyke emplacement mechanisms is important, as dykes are feeders of volcanic eruption in which magmatic evolution take place
It is widely accepted that the Late Cenozoic magmatism in the Mediterranean–Iran regions occurred in a post-collisional setting and resulted from the partial melting of a subduction-related metasomatized sub-continental lithospheric mantle [37,72–80]
The dyke swarms of northeast of Meshkinshahr are enriched in lithophile elements (LILEs) and LREEs relative to the primary mantle and indicate quite a flat HREE pattern (Figure 9)

Summary

Introduction

Our understanding of dyke emplacement mechanisms is important, as dykes are feeders of volcanic eruption in which magmatic evolution take place. Crust–mantle interaction plays a significant role in the delineation of crustal provinces, as well as in deciphering crustal evolution events [1–3]. Shoshonitic rocks generally show SiO2 at less than 70 wt. On the other hand, [5] suggested that shoshonites should include more silicic rocks, such as dacite and rhyolite. The authors only regarded volcanic rock types with SiO2 < 63 wt. Shoshonites can be subdivided into basic (SiO2 < 53 wt.%), intermediate (SiO2 = 53–63 wt.%) and silicic (SiO2 > 63 wt.%) types [7]

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Discussion

Conclusion