祁连北麓黑河河漫滩沉积物碎屑锆石U-Pb年龄、Hf同位素组成及其地质意义

发布时间：2018-06-30 06:40

本文选题：黑河 + 河漫滩碎屑锆石　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：本文通过碎屑锆石的U-Pb年龄来研究北祁连地区岩浆事件的发生时间;通过Hf同位素分析岩浆事件中新生地壳和被改造古老地壳的信息,并用来估算新生地壳的产生时间;结合主微量元素,获得源区区域地壳的基本特征、形成演化历史及其地球化学意义。得出如下认识:(1)黑河河漫滩沉积物中的碎屑锆石U-Pb年龄主要分为232~551Ma(54.9%),982~1163Ma(1.5%),1500~2202Ma(34.7%)和2350~2681Ma(8.9%)四个年龄段。(2)前寒武纪年龄主要分布在元古代,黑河河漫滩沉积物碎屑锆石900~1200Ma的年龄可与同时期全球的Rodinia超大陆裂解事件做对比,另外根据1800Ma左右的峰值年龄信息推断物源区存在该时期明显的岩浆作用事件。(3)新元古代末-古生代年龄信息里面,晚震旦纪到早奥陶纪形成祁连洋盆,且北祁连洋盆于奥陶纪开始俯冲消减,并且贯穿整个奥陶纪;于早志留纪已经发生碰撞造山作用,且持续到泥盆纪时期;而黑河河漫滩碎屑锆石测年工作获得了海西期的年代学信息,印证了前人关于北祁连西段存在海西期岩浆活动的报告,且北祁连地区加里东中期和晚期的侵入花岗岩体都有经历海西期的岩浆热事件的改造。(4)黑河河漫滩沉积物样品13HH-1与HH1-1和HH2相比缺少980~1160Ma的年龄数据,主要是由于碎屑锆石随着水迁移距离的增加,粒度逐渐变小,甚至滞留在上游,不易被检测。(5)黑河河漫滩沉积物中明显亏损Nb、Ta等高场强元素,轻度富集Cs、Rb、Nd、La等大离子亲石元素。(6)祁连地块提供了黑河河漫滩碎屑沉积物的几乎全部物源贡献。(7)黑河河漫滩沉积物物源区平均大陆地壳各时期均有新生地壳的产生和古老地壳的重熔。具体来说2350-2681Ma期间以新生地壳为主,兼有部分古老地壳的重熔;1500-2202Ma期间以古老地壳的重熔为主;显生宙以来主要以古老基底岩石的重熔再造为主。
[Abstract]:In this paper, the occurrence time of magmatic events in North Qilian area is studied by U-Pb age of clastic zircon, the information of new crust and reformed old crust in magmatic event is analyzed by HF isotope, and the generation time of new crust is estimated. Combined with main trace elements, the basic characteristics, evolution history and geochemical significance of the regional crust in the source area are obtained. The main results are as follows: (1) the zircon U-Pb ages in the sediments of the Heihe River floodplain are mainly divided into four age groups: 232A551 Ma (54.9%), Precambrian ages (1.5%), 1500220Ma (34.7%), and 2350,2681Ma (8.9%). (2) the Precambrian ages are mainly distributed in Proterozoic. The age of 900 ~ (200 Ma) zircon from sediments of Heihe River floodplain can be compared with the Rodinia supercontinental pyrolysis event of the same period. In addition, it is inferred from the peak age information of about 1800 Ma that magmatism events occurred in the source area of this period. (3) in the information of Neoproterozoic and Paleozoic ages, the Qilian ocean basin was formed from late Sinian to early Ordovician. The North Qilian ocean basin began to subduction in Ordovician and ran through Ordovician, and collisional orogeny occurred in early Silurian and lasted until Devonian. The dating of detrital zircon in the Heihe River floodplain obtained the chronological information of the Hercynian period, which confirmed the previous reports on the existence of the Hercynian magmatic activity in the western part of North Qilian. Moreover, the intrusive granite bodies in the middle and late Caledonian periods in North Qilian area have undergone the transformation of the Hercynian magmatic thermal events. (4) the age data of 13HH-1 in the sediment samples of Heihe River floodplain are less than those of HH1-1 and HH2 at 980,1160Ma. The main reason is that the grain size of the detrital zircon becomes smaller with the increase of water migration distance, and even stays upstream, which is not easy to detect. (5) the high field strength elements, such as NB, Ta and so on, are obviously depleted in the sediments of Heihe River floodplain. (6) the Qilian massif provides almost all the contribution of the detrital sediments of the Heihe River floodplain. (7) the average continental crust of Heihe River floodplain sediment source area has the occurrence of new crust in every period. And the remelting of the ancient crust. Specifically, during 2350-2681 Ma, the new crust dominated, and part of the ancient crust was remelted during 1500-220Ma, and since the Phanerozoic, the remelting of the ancient basement rocks was the main one.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P597.3;P588.21

【参考文献】