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阿拉善断块富碱侵入岩具有硅过饱和(出现石英,w(SiO2)=62.01%~67.28%)、准铝(w(Al2O3)=12.20%~16.83%)、富碱(w(Na2O) +w(K2O) = 11. 14% ~ 14. 18%,里特曼指数σ= 6. 40 ~ 8. 65)、富钾(w(K2O)/w(Na2O)=1.01~1.79)和低铁、镁的特征。总稀土较高,稀土配分曲线呈陡右倾模式。微量元素强烈富集LILE和LREE,相对亏损Nb、Ta、Ti 和P。上述特征以及低钕(ε(Nd,t) = - 7. 3 ~ - 9. 4)高锶(ε(Sr,t)=+53.9~+99.9)的同位素特征反映物质来源主要与富集型上地幔有关,但受到不同程度壳源物质的混染作用。Nd、Sr、Pb联合示踪表明阿拉善断块富碱侵入岩与华北断块北缘印支期富碱侵入岩带具有相似性,但不同于塔里木北缘富碱侵入岩。结合时空分布、同位素组成以及所处的构造动力学体系等因素将阿拉善断块富碱侵入岩和燕辽—阴山印支期富碱性侵入岩带划归为同一印支期富碱性侵入岩带。指出至少到晚古生代—印支期时阿拉善断块已经与华北断块构成了一个整体。
The alkali-rich intrusions in the Alxa fault block have the characteristics of over-saturation of silicon (quartz, w (SiO2) = 62.01% -67.28%), quasi-aluminum w203-12.20% ~ 16.83% + K (K2O) = 11. 14% ~ 14. 18%, Rittman’s index σ = 6. 40 ~ 8. 65), potassium (K2O) / w (Na2O) = 1.01 ~ 1.79) Iron, magnesium features. The total rare earth is higher, rare earth distribution curve is steep right tilt mode. Trace elements strongly enrich LILE and LREE, relative loss of Nb, Ta, Ti and P. The above characteristics and isotopic characteristics of low neodymium (Nd, t) = - 7.3 ~ -9.4 high strontium (ε (Sr, t) = +53.9 ~ + 99.9) Upper mantle, but by varying degrees of contamination of the shell material. The combined tracing of Nd, Sr and Pb shows that the alkali-rich intrusive rocks in the Alxa faulted block are similar to the Indosinian alkali-rich intrusive rocks in the northern margin of the North China block, but different from the alkali-rich intrusive rocks in the northern margin of the Tarim Basin. According to the space-time distribution, isotopic compositions and the tectonic dynamics system, the Alxa faulted-in alkali-rich intrusive rocks and Yanliao-Yinshan Indosinian alkaline-rich intrusive rock belts are classified into the same Indosinian alkaline-rich intrusive Rock band. It is pointed out that the Alxa block has formed a whole with the North China block at least until the Late Paleozoic-Indosinian period.