Mineral records of the pyroxenites formed within harzburgites (Ulaş, Sivas, Turkey):  implications on petrogenesis and tectonic setting

Hasan KOLAYLI,Özgür BİLİCİ

doi:10.3906/yer-1802-13

Abstract

In this article, the petrological processes of the clinopyroxenite dykes and host peridotites occurring in Ulas District (Sivas, mid-Anatolia, Turkey) are discussed. The new geochemical data from major minerals in the clinopyroxenite dykes and host harzburgites revealed differences to the supra-subduction zone (SSZ)-type pyroxenites and peridotites. In particular, the NiO content of olivines in the host harzburgites showed the signature of the mantle, whereas rare olivines of the clinopyroxenites had a NiO content and Fo number that were inferior to those of mantle peridotites. The high Mg-number of clinopyroxenes in the clinopyroxenites was likely associated with the partial remelting of the host harzburgites. Additionally, the rare earth element pattern of clinopyroxenes from the studied clinopyroxenites exhibited a similar pattern to those of the other SSZ or fore-arc clinopyroxenes. Additionally, the low Mgnumber and relatively high Cr-number of spinels in the clinopyroxenites showed similarity to the subduction-related origin. Based on textural and geochemical evidence, the harzburgites were interpreted as depleted mantle rock, which was modified by melt-peridotite interactions. Consequently, the pyroxenites likely occurred as a crystallizing or cumulative zone of the SSZ-type melt and the minerals were gained from partial melting of the harzburgites through the interaction with such magma.

Highlights

Pyroxenites generally occur as veins or dykes in peridotites related to ophiolites and represent up to 5% of all ultramafic bodies (Pearson and Nowell, 2004; Downes, 2007; Van Acken et al, 2010)
Field observations and petrography The pyroxenites generally occur as dykes with varying sizes having relatively sharp contacts with the host harzburgitic peridotites (Figures 3a–3d)
Field observations and petrographic properties show that clinopyroxenite dykes occur within the harzburgite from Ulaş District, as part of the Divriği ophiolite

Summary

Introduction

Pyroxenites generally occur as veins or dykes in peridotites related to ophiolites and represent up to 5% of all ultramafic bodies (Pearson and Nowell, 2004; Downes, 2007; Van Acken et al, 2010). Despite the fact that the pyroxenites represent a very small portion of the upper mantle, essential information is provided within on the petrological and dynamic processes of the Earth This includes crustal recycling and melt-rock interaction in order to interpret the different tectonic environments (Downes, 2007; Gonzaga et al, 2010; France et al, 2015). Numerous studies examined the pyroxenite developments in the mantle, including the collaboration between peridotite and penetrating melt or the response amongst the peridotite and liquefied subducted lithosphere (Yaxley and Green, 1998; Garrido and Bodinier, 1999; Santos et al, 2002; Bodinier and Godard, 2003; Brooker et al, 2004; Berly et al, 2006; Downes, 2007; Van Acken et al, 2010; France et al, 2015)

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Conclusion