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中亚造山带早古生代的构造演化一直存在不同的认识,特别是其俯冲转为碰撞的时限.内蒙古朱日和南部的额尔登陶勒盖地区出露的早古生代岩浆岩,对于限定白乃庙岛弧的延伸方向、岛弧演化和拼贴时间具有重要意义.对额尔登地区出露的火山岩和侵入岩进行了精确的锆石SHRIMP和LA-ICP-MS U-Pb定年、锆石Lu-Hf同位素和地球化学分析以确定其时代和成因.研究获得4个岩浆岩年龄,1件英安岩年龄为434.0±4.4Ma,2件花岗岩年龄分别为432.8±2.6Ma和428.1±1.8Ma,此3件样品形成于早中志留世;另有1件流纹岩年龄为411.8±1.0Ma,形成于早泥盆世.早中志留世侵入岩为低钾、过铝质钙碱性中酸性岩石,富集Rb、Th,弱富集Zr、Hf,明显亏损Nb、Ta、P、Ti.在稀土配分曲线上,侵入岩均不存在Eu的负异常.其中2件花岗岩样品的锆石基本为正εHf(t)值(-1.19~11.51,3.32~10.28),TDM2为684~1 493Ma及759~1 202Ma,主要来自新生地壳;早中志留世火山岩具有中-低钾、偏铝质-过铝质、钙碱性酸性岩石特征,富集Rb、Th,弱富集Zr、Hf,明显亏损Nb、Ta、P、Ti.在稀土配分曲线上,多数火山岩不存在Eu负异常.英安岩中的锆石具有正εHf(t)值(3.70~7.94),TDM2为912~1 183Ma,主要来自新生地壳;而早泥盆世流纹岩(411 Ma)存在明显的Eu负异常,其锆石具有负εHf(t)值(-14.95~-7.07),TDM2为1.8~2.3Ga,应为古老地壳再循环的产物,与早中志留世岩浆岩源区明显不同,可能代表构造环境的转变.综合区域地质和前人研究资料表明,早志留世英安岩和花岗岩形成于俯冲岛弧环境,白乃庙岛弧向东可延伸至本区,而早泥盆世流纹岩可能形成于后碰撞环境.
The Early Paleozoic tectonic evolution of the Central Asian orogenic belt has had different understanding, especially the time limit of its subduction to collision. The Early Paleozoic magmatic rocks exposed in the Ertung Tolgoi area in Zhuri and southern Inner Mongolia, The extension of the island arc, the island arc evolution and the collage time are of great significance.Exact zircon SHRIMP and LA-ICP-MS U-Pb dating of volcanic rocks and intrusive rocks exposed in the Erdeng area are carried out, Lu-Hf isotopic and geochemical analyzes to determine the age and genesis of the magmatic rocks.A total of four magmatic rocks were obtained, including 1 member of the age of 434 ± 4.4 Ma and 2 members of the age of 432.8 ± 2.6 Ma and 428.1 ± 1.8 Ma , The three samples were formed in the Early Middle Chiocene, and the other one rhyolite was 411.8 ± 1.0Ma, formed in the Early Devonian.The Early Middle Zhoushi intrusive rocks are low potassium, perchlorate Acidic and moderately acidic rocks, enrichment of Rb and Th, weak enrichment of Zr and Hf, obvious loss of Nb, Ta, P and Ti.No negative anomalies of Eu are present in intrusive rocks on the RE patterns.Of the two granite samples The zircons are basically positive εHf (t) values (-1.19 ~ 11.51, 3.32 ~ 10.28), TDM2 is 684 ~ 1 493Ma and 759 ~ 1 202Ma, mainly from the new Early Cretaceous volcanic rocks have the characteristics of medium-low potassium, partial-aluminum-perlalite and calc-alkaline acidic rocks, enrichment of Rb, Th, weak enrichment of Zr, Hf, significant loss of Nb, Ta, P , Ti.No negative anomalies of Eu exist in most volcanic rocks on the REE distribution curve.The zircons in the dacite have positive εHf (t) values (3.70 ~ 7.94) and TDM2 ranges from 912 ~ 1 183Ma, mainly from the nascent crust. However, The Early Devonian rhyolite (411 Ma) has obvious Eu anomaly with negative εHf (t) values (-14.95 ~ -7.07) and TDM2 of 1.8 ~ 2.3Ga, which should be the result of the reclamation of ancient crust The product is obviously different from that of the Early Mesozoic magmatic source rock area, which may represent the change of tectonic environment. According to the comprehensive regional geology and previous research data, the Early Silurian diorite and granite formed in the subduction island arc environment, Arc to the east can extend to this area, while the Early Devonian rhyolite may be formed in the post-impact environment.