内蒙古苏尼特右旗白乃庙地区徐尼乌苏组的形成时代及其地质意义

发布时间：2018-07-01 14:30

本文选题：徐尼乌苏组 + 早志留世　；参考：《岩石学报》2017年10期

【摘要】：本文对白乃庙地区徐尼乌苏组沉积特征、原岩建造、变质火山岩及变质碎屑岩的年代学和地球化学进行了研究,探讨了白乃庙地区早古生代构造演化。本次研究采集了徐尼乌苏组中具有代表性的变质含砾粗粒杂砂岩、变质英安质晶屑凝灰岩和变质长石石英细砂岩样品,进行了锆石LA-ICP-MS U-Pb年代学和岩石地球化学分析。结果显示,2个变质英安质晶屑凝灰岩锆石的加权平均年龄分别为440.9±1.8Ma(MSWD=0.10)和440.9±1.7Ma(MSWD=0.15),锆石Th/U比值为0.46~1.59,自形程度较好,发育有典型的岩浆锆石振荡环带结构,显示为岩浆成因锆石的特点,表明徐尼乌苏组的形成时代为早志留世。变质含砾粗粒杂砂岩的碎屑锆石年龄在452.0±1.3Ma~535.0±1.0Ma之间,最高峰值年龄为490Ma左右;变质长石石英细砂岩碎屑锆石年龄则在440.1±5.7Ma~3268.9±57.7Ma之间,最小谐和年龄为440.1±5.7Ma,峰值年龄为490Ma左右,另有1.0Ga、1.6Ga、1.8Ga和2.5Ga四个明显的峰值年龄。根据研究区徐尼乌苏组岩性组合与结构构造,可将该组划分为3个不同的沉积旋回。结合白乃庙地区徐尼乌苏组测年结果、岩石地球化学特征、原岩建造及区域岩浆岩资料,白乃庙弧后盆地沉积可划分为三个演化阶段:早期快速堆积阶段(452.3~440.9Ma),形成了一套成熟度较低的粗碎屑岩建造,物源主要来源于白乃庙岩浆弧中的岩浆岩;中期火山喷发阶段(440.9~440.1Ma),以火山沉积作用为主,为火山碎屑岩建造夹有碳酸盐建造和少量碎屑岩建造,碎屑物质主要来源于该时期的火山活动;晚期稳定沉积阶段(440.1Ma),形成一套细碎屑岩建造和碳酸盐建造,为浅海相稳定沉积,此时物源广泛,分别来源于华北克拉通基底、兴蒙造山带和白乃庙早古生代火山弧。根据徐尼乌苏组的沉积建造和火山建造特征,结合白乃庙火山弧岩浆活动特征,认为徐尼乌苏组形成于早古生代弧后盆地中,此时华北板块北缘属于安第斯型活动大陆边缘。
[Abstract]:In this paper, the geochronology and geochemistry of Xunisu formation, protolith formation, metamorphic volcanic rock and metamorphic clastic rock are studied, and the early Paleozoic tectonic evolution in Bainaimiao area is discussed. The typical samples of metamorphic gravel-grained complex sandstone, metamorphic amphitic tuff and metamorphic feldspar quartz fine sandstone in Xunisu formation were collected in this study. The zircon LA-ICP-MS U-Pb geochronology and petrogeochemical analysis were carried out. The results show that the weighted mean zircon ages of the two metamorphic amphitic tuff rocks are 440.9 卤1.8 Ma (MSWD0. 10) and 440.9 卤1.7 Ma (MSWD0. 15), respectively. The ratio of zircon to zircon Th/ U is 0. 46- 1. 59. The zircon has a good automorphic degree. There is a typical magmatic zircon oscillatory ring structure, which shows the characteristics of magmatic zircon. It shows that the formation age of Xuniwusu formation is early Silurian. The zircon age of metamorphic coarse grained sandstone is between 452.0 卤1.3 Ma and 535.0 卤1.0 Ma, and the highest peak age is about 490 Ma, while that of metamorphic feldspar quartz fine sandstone is between 440.1 卤5.7 Ma and 3268.9 卤57.7 Ma, the minimum harmonic age is 440.1 卤5.7 Ma, and the peak age is about 490 Ma. There are also four distinct peak ages of 1.0Ga1.Ga1.8Ga and 2.5Ga. According to the lithologic assemblage and structural structure of Xunisu formation in the study area, the formation can be divided into three different sedimentary cycles. Combined with the dating results of Xuniwusu formation, petrogeochemical characteristics, original rock formation and regional magmatic rock data in the Bainaimiao area, The sediments of the back arc basin of Bainaimiao can be divided into three stages: the early rapid accumulation stage (452.3N 440.9 Ma), which formed a set of low-maturity coarse clastic rocks, mainly derived from the magmatic rocks in the bainaimiao magmatic arc; The middle stage of volcanic eruption (440.9 ~ 440.1 Ma) is dominated by volcanic sedimentation, which is composed of carbonate formation and a small amount of clastic rock formation in the volcanic clastic rock formation. The clastic material is mainly derived from volcanic activity in this period. In the late stable sedimentary stage (440.1 Ma), a set of fine clastic rock formation and carbonate formation were formed, which are shallow marine facies stable deposits. At this time, their provenances are extensive and are derived from the North China craton basement, the Xingmeng orogenic belt and the early Paleozoic volcanic arc of the Bainaimiao, respectively. According to the sedimentary formation and volcanic formation characteristics of Xunisu formation, combined with the characteristics of bainaimiao volcanic arc magmatic activity, it is considered that the Xuniwusu formation was formed in the early Paleozoic back-arc basin, and the northern margin of the North China plate belongs to the active continental margin of the Andes type.
【作者单位】：吉林大学地球科学学院;东北师范大学地理科学学院;吉林省地震局;
【基金】：国家自然科学基金项目(41272223) 中国地质调查局项目(1212011120709、1212011220459、1212011085252)联合资助
【分类号】：P534.4;P542

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