冀北金台子盆地早白垩世酸性火山岩地球化学、锆石年代学及其地质意义

华北克拉通在中生代以来遭受了显著破坏。前人的研究对克拉通破坏的机制和峰期取得了较大共识, 但是关于克拉通破坏的启动时间一直存在争议。本文通过对冀北金台子中生代盆地构造特征及其填充的火山岩地球化学和年代学进行分析, 为华北克拉通破坏启动时间提供新的约束。研究表明, 金台子盆地为一伸展断陷盆地。盆地呈北东-南西向展布, 东侧被正断层控制, 西侧为地层超覆边界。盆地内自下而上发育后城组、白旗组、啕北营组、九佛堂组火山-沉积组合。后城组是一套稳定的河流相红色砂砾岩沉积地层;白旗组和啕北营组主体为巨厚层流纹岩、流纹质凝灰熔岩, 局部夹安山岩和火山碎屑岩;九佛堂组是一套以砾岩、砂砾岩等为主体的碎屑岩。地球化学分析表明金台子盆地中发育的酸性火山岩源于地壳重熔。锆石U-Pb年代学研究显示, 金台子盆地内流纹岩自约145 Ma开始广泛喷发并形成巨厚层的酸性火山岩地层, 表明此时在华北北缘地区的岩石圈减薄和破坏可能就已非常剧烈, 据此华北克拉通在其北缘的破坏至少应早于145 Ma。

Geochemistry and geochronology of the Early Cretaceous acid volcanic rocks from the Jintaizi Basin,northern Hebei Province,China:Implications for the destruction of the North China Craton

The North China Craton (NCC) was severely destroyed during the Mesozoic. Although the main period of this destruction has been well established, the initial time of the destruction remains poorly understood. In this work, we analysed the tectonic setting of the Jintaizi Basin in northern Hebei Province of China, and determined the age and analysed chemical compositions of the volcanic rocks from the basin. The data was used to better constrain the time of the onset of the destruction of the NCC. Our structural analysis showed that the Jintaizi Basin was a NNE-striking half-graben controlled by normal faults on its eastern margin, whereas the fillings overlapped on to the basement on its western margin. The basin fills include detrital sediments and volcanic rocks, which constitute four formations. The lowest Houcheng Formation and the uppermost Jiufotang Formation are both composed mainly of detrital sediments. The Middle Baiqi Formation and the Taobeiying Formation comprise mainly thick rhyolite strata and rhyolitic tuff lava, locally interlayered with andesite and volcaniclastic rocks. Geochemical data indicated that the acid volcanic rocks were most likely derived from the crustal melting. U-Pb dating of zircon showed that the massive felsic volcanic magma began to erupt at about 145 Ma, which represented significant destruction and thinning of the lithosphere under the northern Hebei area during that time. We conclude, therefore, that the destruction of the northern margin of the NCC might have started by the turn of the Jurassic and the Cretaceous or earlier.