Geochemical and PGE compositional characteristics of the serpentinite in the Laowangzhai gold deposit of the Western Yunnan:Implications for the Paleo-Tethyan Ocean evolution
The Laowangzhai gold deposit in the western Yunnan is located in the northern part of the Ailaoshan tectonic belt.The early Carboniferous ophiolite mélanges,mainly composed of serpentinized ultramafic rocks,are exposed in the Laowangzhai gold deposit.Due to the unclear understanding of the petrogenesis,tectonic setting,and geodynamic background of the ophiolite mélanges,the understanding of the Paleo-Tethys tectonic evolution is limited.In this paper,based on the systematic field geological survey and observation,and sampling of the fresh serpentinite,we have carried out petrological study and the analysis of whole rock chemical compositions and platinum group element compositions of these rocks,and then have comprehensively discussed the original source and genesis of the serpentinite.The serpentinite is mianly composed of fine isogranular serpentine,with minor brucite and mgnetite.The serpentinite rocks are featureed with high contents of MgO,Ni,Cr,and Mg# values(96.6-97.8),but low Al2O3 contents(1.60％-2.30％).The primitive mantle-normalized trace element spidergrams show that the serpentinite rocks are depleted in some high field strength elements(such as Nb,and Ti).They have flat REE distribution patterns with no obvious Eu anomalies.They also have high contents of Ir group of PGE(IPGE:Ir=0.78×10-9-2.9×10-9,Os=2.40×10-9-6.50×10-9,Ru=1.10×10-9-4.00×10-9),and high IPGE/PPGE ratos(1.8-2.2),indicating that they were originated from the residual mantle rock rather than the ultramafic melt cumulate.The geochemical features of the Laowangzhai serpentinites are similar to those of the Early Carboniferous harzburgites in the Shuanggou region,indicating that they are both residual mantle rocks which had undergone a certain degree of melt extraction and they represent remnants of the lithospheric mantle of the Paleo-Tethyan Ocean.
Serpentinitegeochemistryplatinum group elementsmantle rockPaleo-Tethyan OceanLaowangzhai gold depositAilaoshan tectonic belt
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维普
