Pyroxenite as a Product of Mafic-Carbonate Melt Interaction (Tazheran Massif, West Baikal Area, Russia)

Eugene V Sklyarov,Anastasia E Starikova,Anna G Doroshkevich,Sergei V Kanakin,Andrey V Lavrenchuk

doi:10.3390/min11060654

Eugene V Sklyarov, Anastasia E Starikova + Show 3 more

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https://doi.org/10.3390/min11060654

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Journal: Minerals	Publication Date: Jun 20, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: Siberian Branch of the Russian Academy of Sciences

Abstract

Pyroxenite and nepheline-pyroxene rocks coexist with dolomite-bearing calcite marbles in Tazheran Massif in the area of Lake Baikal, Siberia, Russia. Pyroxenites occur in a continuous elongate zone between marbles and beerbachites (metamorphosed gabbro dolerites) and in 5 cm to 20 m fragments among the marbles. Pyroxene in pyroxenite is rich in calcium and alumina (5–12 wt% Al2O3) and has a fassaite composition. The Tazheran pyroxenite may originate from a mafic subvolcanic source indicated by the presence of remnant dolerite found in one pyroxenite body. This origin can be explained in terms of interaction between mafic and crust-derived carbonatitic melts, judging by the mineralogy of pyroxenite bodies and their geological relations with marbles. According to this model, the intrusion of mantle mafic melts into thick lower crust saturated with fluids caused partial melting of silicate-carbonate material and produced carbonate and carbonate-silicate melts. The fassaite-bearing pyroxenite crystallized from a silicate-carbonate melt mixture which was produced by roughly synchronous injections of mafic, pyroxenitic, and carbonate melt batches. The ascending hydrous carbonate melts entrained fragments of pyroxenite that crystallized previously at a temperature exceeding the crystallization point of carbonates. Subsequently, while the whole magmatic system was cooling down, pyroxenite became metasomatized by circulating fluids, which led to the formation of assemblages with garnet, melilite, and scapolite.

Highlights

Interaction of silicate and carbonate magmas is a common process responsible for the compositional diversity of the crust
Major elements were determined by X-ray fluorescence spectrometry (XRF) at the Center for Geodynamics and Geochronology of the Institute of the Earth’s Crust (Irkutsk, Russia)
The pyroxenite and nepheline-pyroxene rocks of the Tazheran complex occur in a long continTuhoeupsyzroonxeenbeittewaenedn bneeeprhbealcinheit-epsy(rporxoednuecerodcbkys tohfetrhmeaTl amzehtearmanorcpohmispmlexofotchcouleriiintica dloonlegritceosn)tainnudoduoslozmoniete-bbeetawreinegn cbaelecirtbeamchaitrebsle(sp, roordauscemdmbytotnh·e1r0mmal fmraegtmamenotrsphamismongof tholeiitic dolerites) and dolomite-bearing calcite marbles, or as mm to n∙10 m fragments the marbles

Summary

Introduction

Interaction of silicate and carbonate magmas is a common process responsible for the compositional diversity of the crust. Intruding melts and related fluids either cause isochemical thermal and metasomatic alteration to carbonate country rocks, with skarn and other metasomatic effects ([1,2,3] and references therein), or become assimilated by silicate magma, changing its composition [4,5,6,7,8], etc. These processes produce unusual mineral assemblages, which often include Ca-Al-rich pyroxene almost free from alkalis, called fassaite. Fassaite sometimes occurs in xenoliths of metasomatized carbonates among mafic or alkaline mafic rocks [6,10,11,12], etc.) but is most often found in metamorphic limestone near

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