Fluids and noble gases of mantle-derived materials are important tracers for the mantle information. Compositions of primary fluids and noble gases in mantle-derived minerals from the Yishu area, Shandong Province, China, were tested by the methods of heat-bursting and heat-melting respectively. The fluids are mainly composed of CO2, CO and H2, which account for about 90% of the total, and are similar to the mantle-derived rocks from other areas of eastern China; ratios of 3He/4He in almost all samples range from 0.82 Ra to 2.74 Ra, whereas 40Ar/36Ar from 299.5 to 758.8. Both ranges are much lower than those of the typical ocean mantle-derived samples (such as MORB) and primarily reflect the influences of the atmospheric components and the radiogenic isotopes. Ratios of C/3He range from 27.6×109 to 1050×109, N2/Ar from 927 to 56612, and N2/3He from 2.5×109 to 27×109, similar to those in western United States and New Zealand which belong to the tectonic plate collision regions. The ratios fall in the intersect of mantle-crust-atmosphere in the comprehensive tracer-charts, reflecting the influences of the atmosphere and the crusts with organic components. Our results suggest that the composition of the primary fluids and the isotopic ratios of the noble gases may either reflect the evolution process of mantle-derived rocks connected with the rise and eruption of magma, or the influence of the ancient subduction-plate on the continental mantle of this region.
MA Jinlong1,2, TAO Mingxin2,3 & YE Xianren2 1. Resources and Environmental School, Lanzhou University, Lanzhou 730000, China
