摘要
大兴安岭中段明水地区头道河岩体主要由花岗闪长岩、二长花岗岩组成。锆石LA-ICP-MS U-Pb同位素测年结果显示,头道河岩体形成于243~240 Ma的中三叠世。岩石地球化学资料显示头道河岩体具有高硅(Si O2=61.32%~78.19%),富铝(Al2O3=11.85%~16.87%),贫铁(TFe2O3=0.56%~5.93%)、镁(Mg O=0.16%~3.30%)、钙(Ca O=0.26%~2.94%)的特征,为一套高钾钙碱性的I型花岗岩;稀土元素总量偏低(ΣREE=75.5×10-6~149.49×10-6),稀土元素分馏明显,(La/Yb)N介于8.71~17.61之间,无明显铕异常;微量元素以富集Rb、Pb、Th、U等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素为特征。锆石原位Hf同位素分析表明,该岩体花岗质岩石的176Hf/177Hf值为0.282 811~0.283 227,εHf(t)为较高的正值(+6.55^+12.19),Hf二阶段模式年龄(tDM2)介于595~1 107 Ma之间。上述地球化学特征指示,头道河岩体源区物质为中元古代显生宙期间从亏损地幔增生的年轻火成岩地壳物质。结合区域地质资料及同期火成岩物质的时空展布规律,认为中三叠世头道河岩体形成于古亚洲洋闭合后的造山后伸展构造环境。
The Toudaohe pluton, located in Mingshui area of middle Da Hinggan Mountains, is mainly composed of granodiorite and monzogranite. LA-ICP-MS zircon U-Pb data indicate that the Toudaohe pluton formed during the Middle Triassic with the ages of 243 - 240 Ma. Geochemically, the granitic rocks are high in Si O2（ 61. 32% -78. 19%）, and Al2O3（ 11. 85% - 16. 87%）, but low in total Fe2O3（ 0. 56% - 5. 93%）, Mg O（ 0. 16% - 3. 30%）,and Ca O（ 0. 26% - 2. 94%）, suggesting that they are high-K calc-alkaline I-type granites. These granitoids have low total REE content（ ΣREE = 75. 5 × 10^- 6- 149. 49 × 10^- 6） with fractionated REE [（ La / Yb）N= 8. 71 - 17. 61], and no remarkable Eu anomalies. Moreover, they are enriched in large ion lithophile elements（ e. g., Rb, Pb, Th, U）,and depleted in high field strength elements（ e. g., Nb, Ta, Ti）. Zircon Hf isotope analyses show that these granitoids have high initial ^176 Hf /^177 Hf ratios（ 0. 282 811 - 0. 283 227）, positive εHf（ t） values（ 6. 55 - 21. 28）, and young Hf two-stage model ages of 595 - 1 107 Ma. These geochemical characteristics indicate that the source materi als of Toudaohe pluton were juvenile igneous crust rocks which originated from depleted mantle during the Mesoproterozoic to Phanerozoic period. Based on regional geological investigations and spatial and temporal distribution of the coeval igneous materials, the authors hold that the Middle Triassic Toudaohe pluton was emplaced in a post-orogenic extensional environment linked with the final closure of the Paleo-Asian Ocean.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2015年第2期143-158,共16页
Acta Petrologica et Mineralogica
基金
国家自然科学基金资助项目(41272076)
