Литосфера (Aug 2016)
Geochemistry of rare, rare earth elements and platinum group elements in rocks of Shaman ultramafic massif (Eastern Transbaikalia)
Abstract
The research on petrochemistry and geochemistry of rare, rare earth and platinum group elements in the rocks Shaman massif - the largest ultramafic protrusion body in eastern branch of the Baikal-Muya ophiolite belt, performed using a different of analytical techniques (X-ray fluorescence analysis, mass spectrometry analysis with inductively coupled plasma and laser ablation; synchrotron radiation method). Harzburgites and subordinate dunites, composing massif, depleted TiO2, Na2O, K2O and CaO, and rare earth elements (REE). The total content of the latter in harzburgites somewhat higher (0.29-3.01 ppm) than in dunites (0.12-1.54 ppm). The patterns of chondrite-normalized REE contents in ultramafic rocks are arched downward configuration, due to their abnormal enrichment nonstructural admixture of light elements, centered as it is assumed in the intergranular and within granular microcracks. Massif is characterized by higher contents of Zr and Hf, the hub of which is supposed to be an accessory zircon. The total content of platinum group elements (PGE) in the harzburgite and dunite are from 12.50 to 24.35 ppb, while the predominant element is Ru. There was an inverse relationship between its content and the content of heavy rare earth elements (Er, Tm, Yb, Lu), and between the total content of PGE and REE, which are supposed to be due to divers directional fractionation of these groups of elements with contrasting properties in the process of partial melting of upper mantle protolithe. Prevalence of Ru in the rocks suggested that PGE concentrated mainly in the such minerals as rutenosmirid and laurite.
