【摘要】 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。更多还原

【Abstract】 The alkali-rich intrusive rocks in Alxa Fault Block are characterized by （1） supersaturation of silica, （with appearance of quartz and concentrations of SiO₂ reaching 62.01%⁶7.28%）, （2） meta-aluminum（（wt% Al₂O₃=）12.20%¹6.83%）, （3） alkali-rich （wt% K₂O+Na₂O=11.14%¹4.18% and the Rittmann Index （σ） varing from 6.40 to 8.65）, （4） potassium-rich （K₂O/Na₂O=1.01¹.79） and （5） low concentrations of Fe and Mg. The total rare earth element concentrations （∑REE） of the rocks are relatively high, with the REE patterns being sub parallel and with strong LREE enrichment. Multi-element spidergrams exhibit strong LILE and LREE enrichments and Nb, Ta, Ti, P depletion . The （above） together with low Nd （ε（Nd,t）=-7.3^-9.4） and high Sr （ε（Sr,t） =（+53.9⁺99.9）） indicate that these rocks originated from an enriched upper mantle but were contaminated by crustally derived materials. Nd, Sr and Pb plots show that the alkali-rich intrusive rocks in Alxa have common features with Indosinian alkali-rich intrusives in Yanliao-Yinshan area. However, they are different from alkali-rich intrusive rocks from the north margin of the Tarim Block.The spatial and temporal distribution data, the isotopic characteristics and the geodynamic settings support the conclusion that the Alxa alkaline-rich intrusive rocks are the westward extension of the Indosinian alkaline-rich intrusion belt of the northern margin in North China Block. The Alxa Fault Block and the North China Block at least since the Late Paleozoic to Indosinian period.更多还原