Geochemical Characteristics of Granitoids in the Eastern Sector of the Northern Tianshan Mountains in Xinjiang

The granitioids in question are located in the geosynclinal fold belt of the Northern Tianshan Mountains.The magmas are intruded into a Carboniferous marine volcanic-sedimentary rock series. forming a contempo-raneous. intermediate-basic to acid. composite intrusion. With a whole-rock Rb-Sr isochron age of 315.7 Ma. itis considered to be of middle Heicynian age. The granitoids have a SiO_2 content of 48-78%, a calc-alkali indexof 60 and silica-alkali indices ρ=2.2-2.4 and σ=1.5-2. From basic to acid compositions, the total REE con-tent increases from 38 to 143 ppm. δEu ranges from 0.47 to 0.86 and the Eu anomalies are negative. Thenormalized curves of REE of various rock types are very similar. These coupled with the characteristics of traceelement geochemistry show that the intrusion is an island arc-continental margin, calc-alkaline one. Theδ^(18)O values range from 5.8 to 8.9‰ and the ^(87)Sr/^(86)Sr initial ratio is 0.705. The materials of the intrusion arecomposed of a mixture of the magmas at the top of the upper mantle and in the lower crust, This indicates thatthe rocks might be consanguineous. differentiated and evolved products and possess the characteristics of Ⅰtype granites.

The pH value and electrical conductivity of atmospheric environment from ice cores in the Tianshan Mountains

Electrical Conductivity Measurement （ECM） from ice core is a representative index for atmospheric environmental change. The pH value and ECM from three shallow ice cores （each 3.85 m, 231 ice samples total） on Glacier No.1 at the headwater of Urumqi River, Glacier No.48 in Kuitun area, and Miaoergou Glacier in Hami area in the eastern Tianshan Mountains, western China, were measured and analyzed for atmospheric environment records research. Ice core record shows that the changing trend of pH and ECM in three sites in recent years is different： ECM in Kuitun increases with the ice depth change, but ECM in Hami and Urumqi Glacier No.1 ice cores show a decreasing trend. Average ECM value in Hami is much larger than other two sites, just as the dust concentration and ions concentration are also very high in this site. ECM records in all three sites are mainly affected by aerosol mineral dust of Central Asia, and correlative coefficients of ECM and mineral ions such as Ca^2＋, Mg^2＋, Na^2＋ are all significantly high. The pH value and ECM are also significantly high correlative coefficients in the eastern Tianshan Mountains. Comparison between the eastern Tianshan Mountains and other sites in western China, and Polar Regions, shows that the difference of ECM can very well reflect the spatial difference of worldwide atmospheric environment.