内蒙古朱日和地区早古生代岩浆岩年代学、地球化学特征及其构造意义

发布时间：2018-05-07 16:28

本文选题：内蒙古 + 额尔登陶勒盖　；参考：《地球科学》2017年09期

【摘要】：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.
[Abstract]:The tectonic evolution of the Central Asian orogenic belt in the early Paleozoic has been well understood, especially the time limit for its subduction to collision. The early Paleozoic magmatic rocks in the Erden Tolgoi area of Zhu and the south of Inner Mongolia play an important role in limiting the extension direction of the bainaimiao island arc, the evolution of the island arc and the collage time. Zircon SHRIMP and LA-ICP-MS U-Pb dating, zircon Lu-Hf isotopic and geochemical analysis were carried out to determine the age and origin of the volcanic rocks and intrusive rocks exposed in Erdeng area. Four magmatic ages and one dolomite age of 434.0 卤4.4 Ma were obtained. The age of two granite samples were 432.8 卤2.6Ma and 428.1 卤1.8 Ma.The three samples were formed in early and Middle Silurian, and the other one was formed in early Devonian with an age of 411.8 卤1.0 Ma. The early and middle Silurian intrusive rocks are low potassium, peraluminous calc-alkaline, intermediate-acid rocks, rich in RbPh, weak in Zr-Hf. On the REE partition curve, there is no negative EU anomaly in the intrusive rocks. The zircon values of 2 granite samples are basically positive 蔚 Hftt) -1.19 ~ 11.51C ~ 3.32 ~ (10. 28) TDM2 = 684 ~ 1 493Ma and 759 ~ (1) 20Ma. the volcanic rocks of early Middle Silurian are characterized by middle-low potassium, meialuminite and peraluminous, calc-alkaline acid rocks, which are mainly derived from the Cenozoic crust, and the volcanic rocks of the early Middle Silurian are characterized by moderate to low potassium, meialuminite and peraluminous, calc-alkaline acid rocks. The enrichment of Rbn Thand and the weak enrichment of Zr-Hf are obviously depleted of NbTa-Ta-Pa-Ti. On the REE distribution curve, there is no negative EU anomaly in most volcanic rocks. The zircon in the dolomite has a positive 蔚 Hftt) value of 3.70 ~ 7.94 / TDM2, which is mainly derived from the new crust, while the early Devonian rhyolite (411 Maa) has obvious negative EU anomalies, and its zircon has a negative 蔚 Hft2 value of -14.95- 7.07TDM2, which is a product of the ancient crustal recirculation, and the zircon has a negative 蔚 Hft2 value of -14.95- 7.07TDM2, which is the product of the ancient crustal recirculation. It is different from the early and Middle Silurian magmatic source area and may represent the change of tectonic environment. The comprehensive regional geology and previous research data show that the early Silurian dolomite and granite were formed in subduction island arc environment, the bainaimiao island arc extended eastward to this area, and the early Devonian rhyolite may be formed in the post-collision environment.
【作者单位】：北京大学造山带与地壳演化教育部重点实验室;北京大学地球与空间科学学院;
【基金】：国家重点基础研究发展计划项目(No.2013CB429801) 中国地质调查局地质大调查项目(No.1212010050503)
【分类号】：P588.1;P597.3

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