甘肃北山古生代造山带地壳演化的同位素和稀土元素地球化学特征

在甘肃北山地区，自前加里东至印支６个不同构造阶段的１２个火成岩侵入体采集了岩石样品，系统地做了Ｏ、Ｓｒ，Ｎｄ和Ｐｂ同位素分析，并测定了包括这１２个岩体在内的４０个火成岩样品的稀土元素含量。从不同构造阶段各种同位素的变异可以看出：随着地壳从不成熟到成熟，从成熟度低到成熟度高的变化，同位素的变异也是有规律的。如果把地壳成熟度增高过程同位素的变异视为“正向”演化，则地壳成熟度降低同位素变异呈“逆向”演化。在拉张型过渡壳的特定时期地壳成熟度降低，同位素变异明显“逆向”变化。高度成熟的地壳由于多期次多来源导致同位素变异表观上的“无定向”。甘肃北山南北两带分属塔里木板块和哈萨克斯坦板块，在同位素地球化学上也显示出租应的差异。稀土元素地球化学也给出了相似的佐证。

Isotope and REE Geochemical Characteristics of CrustEvolntion in the Paleozoic Orogenic Belt ofBeishan Region, Gansn Province

O, Sr, Nd and Pb isotope composition and ratio of the rocks collected from 12intrusive massesof Beishan region in Gansu province have been determined. Their agesare from Pro-Caledonian to indoChina period. In addition, REE content of 40 igneousrocks including above 12 intrusive masses were analyzed. The isotopic variability issystematic resulted from each isotope variation of different tectonic period with lessmature getting more and more mature as well as with from lower mature to highermature of crust. If we thought that it was normal evolution of isotope with getting upof crust maturity, then it would appear reverse isotope evolution while the crust matu-rity was getting down, and 'random' or 'diverse' isotope evolution would occur whilethe superlative maturity of crust was coming also. The two tectonics units, belong tothe Tarim plate and to Kazakhstan Plate, respectively, have different characteristics ofisotope variation. They have similar different characteristics of REE distribution also.