长江河源区的河水主要元素与Sr同位素来源

Origin of major elements and Sr isotope for river water in Yangtze River source area

长江源区河水化学成分来自雨雪、蒸发盐岩、碳酸盐岩和硅酸盐岩。主要支流楚玛尔河、北麓河的主要阳离子为Na+、Ca2+和Mg2+,占阳离子总量的97%以上.Ca Na,Mg Na,K Na的比值较低,87Sr 86Sr为0 709180±20～0 710280±11,河水成分以蒸发岩类溶解为主。发源于唐古拉山北坡的长江源头,及其支流主要阳离子为Ca2+,Mg2+,Na+占阳离子总量的97%以上,Ca Na,Mg Na,K Na的比值较楚玛尔河等河流高,87Sr 86Sr为0 708954±20～0 710455±18,表现为以碳酸盐岩和硅酸盐岩的溶解为主。计算表明,长江河源区河水中主要化学成分来自蒸发岩中Na+和Cl-,在河流水化学成分中占比例最大,长江河水中Cl-含量从河源区向下游明显逐渐减小,反应出河源区高寒干旱环境下河流蒸发岩的化学侵蚀作用较强的特征。

By analyzing the data, it's know that Na\++ and Cl\+- are highest concentration in Yangtze River source area. Further more, Cl\+- content of river water drops off markedly from upstream to downstream, which just is the showing of feature that chemical erosion on evaporate is strong relatively in river source area under high sea level\|frigid and arid area. Material equilibrium equations are established by analyzing rations of Ca/Na, Mg/Na, Cl/Na and Sr/Na. Dissolved load of river water primarily come from weathering rocks of silicate, carbonate and evaporate as well as atmosphere rainfall. Of which, Na\++ is mostly from silicate and salt, slightly from carbonate rocks dissolution and atmosphere. Ca\+\{2+\}, Mg\+\{2+\}, K\++ and Sr\+\{2+\} are concerned with all three rocks dissolutions. Cl\+- is mainly supplied from atmosphere rainfall and salt rock dissolution. Basing on the condition, balance equation can be worked out:Cl\-riv=Cl\-\{rw\}+Cl\-\{eva\};\ Z\-\{riv\}=Z\-\{rw\}+Z\-\{sil\}+Z\-\{car\}+Z\-\{eva\};\ Z:Na\++, Ca\+\{2+\},Mg\+\{2+\} or Sr\+\{2+\}Corresponding stand balance equation:Cl/Na)\-\{riv\}=X(Na)\-\{rw\}(Cl/Na)\-\{rw\}+(1-X)(Na)\-\{eva\}(Cl/Na)\-\{eva\};(Z/Na)\-\{riv\}=X(Na)\-\{rw\}(Z/Na)\-\{rw\}+X(Na)\-\{sil\}(Z/Na)\-\{sil\}+X(Na)\-\{sil\}(Z/Na)\-\{car\}(Z/Na)\-\{car\}+X(Na)\-\{eva\}(Z/Na)\-\{eva\};The hydrochemistry compouent and isotope fractionation and inversion theory is applied to analyze the characteristic for sediment sand, supended and dissolved load. End\|member element valuse of silicate and carbonate are confirmed by analyzing the relation between Sr isotope ratio and major element ratio, the element content proportion of different river water in carbonate and silicate can be rough estimate.\;The elementary compositions of river water in Yangtze River source area, that is derived from rain, snow, evaporate, carbonate and silicate. Major cation, in main tributaries of Tongtian River named Chumar River and Tuotuo River, are Na+, Ca2+ and Mg2+, that is 97% or more in total cation. Ratios of Ca/Na, Mg/Na and K/Na are low relatively, and specific value of 87Sr/86Sr ranges from 0708954±20 to 0711860±11, which shows that elementary compositions of rivers next to Yangtze River source area mainly come from evaporate rocks. Major cations of Tuotuo River source area originated from north slope of Tanggula Mountain, Ca2+, Mg2+ and Na+ account for 97% which are more than Chumar River. But the ratios of Ca/Na, Mg/Na and K/Na is relatively high, and 87Sr/86Sr were changes from 0705534±16 to 0722856±14, which includes that elementary compositions of rivers are mostly from carbonate and silicate.