摘要
文中报道了北京西山侏罗纪南大岭组玄武岩的锆石结晶年龄。115个已分析的南大岭组玄武岩中的锆石绝大部分是继承的。它们的年龄峰值集中在～190Ma，～310Ma，～430Ma和～520Ma。此外，还有～171Ma，～830Ma和1840Ma的年龄组，个别太古宙末和元古宙初期的继承锆石也可观察到。我们认为（174±8）Ma年龄组的锆石有可能是南大岭组玄武岩喷溢期结晶的锆石。古元古代和太古宙的继承锆石很可能来自中下地壳基底的岩石。～830Ma的锆石颗粒的来源有待今后资料进一步积累说明，不排除华北克拉通岩石圈也曾经历过此事件。190Ma的锆石组与区域早侏罗世陆内的构造-岩浆作用有关。～310Ma的锆石组形成于晚古生代古亚洲洋洋壳向华北克拉通的俯冲。而～430Ma和～520Ma的锆石组可能于古大陆拼合的全球事件引发的邻近陆块岩石圈深部的热扰动中生成。这些继承锆石的年龄表明：华北克拉通岩石圈至少在古生代就经历了幕式的改造。因此，其演化很可能是长期的、幕式的和渐进的。我们的观测不排斥早白垩世至早期新生代期间华北克拉通岩石圈可能经历的剧变，但是似乎不支持全球岩石圈在深部对超大陆裂解产生响应的观点。
This short note reports SHRIMP U-Pb ages of zircon grains from the Jurassic Nandaling basalt, the western Hills of Beijing. Most of 115 analyzed zircon individuals from the Nandaling basalt gives their crystallization ages and are obviously inherited. Their peak ages are clustered around 190M a, 310M a, 430Ma and 520Ma respectively. In addition, analyzed zircons with crystallization ages around 171Ma, 830Ma, 1840Ma as well as ca. 2500Ma can be observed. Interpretation of these crystallization ages is tentative because we have little knowledge of early Paleozoic magmatism of this region. We consider that a small zircon population aged at （174±8）Ma could form during eruption of the Nandaling basalt. The inherited zircons with early Precambrian ages come probably from basement rocks of North China Craton at deeper levels. Zircon grains with ages around 190Ma can be related to early Jurassic intracontinental tectono-magamtism of this region. Zircon individuals aged around 310Ma can be attributed to subduction of the oceanic crust of the Paleo-Asian Ocean beneath North China Craton southward in late Paleozoic. However we could not find any tectonothermal record in early Paleozoic in this region, but the zircon populations with ages at ca. 430Ma and ca. 520Ma are synchronous with the collision of North American Craton to East Europe Craton and the assembly of Gondwana respectively. That suggests that the global continental assemble may cause thermal disturbance at deeper levels of a lithosphere neighboring with the assembly. Those above demonstrate that the lithosphere of North China Craton underwent episodic modification from as early as early Paleozoic. Therefore the evolution of the lithosphere of North China Craton is probably gradual, episodic and secular.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2006年第2期184-190,共7页
Earth Science Frontiers
基金
国家自然科学基金项目(40132020)
国土资源大调查项目(200013000168)资助
