华北地块北缘中段早古生代-晚古生代初陆缘增生过程及机制

The northern margin of the North China Block (NCB or North China Paleoplate) south to the Solonker suture consists of two tectonic units including the Bainaimiao arc terrain and the northern margin of the North China Craton (NCC), which were seperated by the Bayan Obo-Chifeng-Kaiyuan fault (boundary fault of the northern margin of the NCC). The Bainaimiao arc terrain, which recorded the Early Paleozoic-earliest Late Paleozoic accretion history of the northern NCB, was probablly accreted to the northern margin of the NCC by arc-continental collision during Early Paleozoic to earliest Lare Paleozoic as revealed as recent researches. However, tectonic affinity of the Bainaimiao arc terrain is highly conversal, and the mechanism and processes of accretion of the Bainaimiao arc terrain to the northern magin of the NCC is still poorly understood. In this research, multiple methods including structural geology, igneous petrology, geochemistry and detrital zircon geochronology will be used to study the nature and deformation of the Bayan Obo-Chifeng fault, tectonic affinity of the Bainaimiao arc terrain and the mechanism and processes of attachment of the Bainaimiao arc terrain to the northern magin of the NCC during the Early Paleozoic to earliest Late Paleozoic in order to better understanding the mechanism and processes of continental accretion of the northern margin of the NCB. The results are of great significance for understangding the continental margin transition in the northern margin of the NCB from passive to active continental margins during the latest Early Paleozoic to Late Paleozoic as well as the accretion processes of the huge Central Asian Orogenic Belt.

华北地块（古板块）北缘包括了华北克拉通北缘及白乃庙岛弧岩带两个构造单元，二者之间被白云鄂博-赤峰-开原断裂（华北克拉通北缘断裂）所分开。白乃庙岛弧岩带记录了早古生代-晚古生代早期华北地块北缘的陆缘增生过程。已有的研究结果表明，华北地块北缘的早古生代-晚古生代初期的陆缘增生可能与白乃庙岛弧岩带与华北克拉通北缘的弧-陆碰撞有关。但目前关于白乃庙岛弧岩带的构造属性还有很大争议；关于白乃庙岛弧岩带向华北克拉通北缘的增生机制及过程还不清楚。本项目拟通过构造地质学、火成岩岩石学与地球化学及碎屑锆石分析等多学科方法，对华北地块北缘中段华北克拉通北缘断裂带的性质、白乃庙岛弧岩带的构造属性及其与华北克拉通北缘的拼贴过程及机制进行研究，确定古生代期间华北地块北缘陆缘的增生过程及机制。此研究成果对于认识华北地块北缘陆缘性质转换及中亚巨型增生型造山带的形成机制具有重要意义。

华北地块北缘包括了华北克拉通北缘及白乃庙岛弧岩带两个构造单元，二者之间被白云鄂博-赤峰-开原断裂所分开。白乃庙岛弧岩带记录了早古生代-晚古生代早期华北地块北缘的陆缘增生过程。已有的结果表明，华北地块北缘的早古生代-晚古生代初期的陆缘增生可能与白乃庙岛弧岩带与华北克拉通北缘的弧-陆碰撞有关。但目前关于白乃庙岛弧岩带的构造属性还有很大争议；关于白乃庙岛弧岩带向华北克拉通北缘的增生机制及过程还不清楚。项目组通过构造地质学、火成岩岩石学与地球化学及碎屑锆石分析等多学科方法，对华北地块北缘中段华北克拉通北缘断裂带的性质、白乃庙岛弧岩带的构造属性及其与华北克拉通北缘的拼贴过程及机制进行了研究。.项目组新获得的锆石U-Pb年代学及地球化学结果显示，白乃庙岛弧岩带的俯冲开始于中寒武世(520 Ma)，至晚志留世(420 Ma)结束，该岛弧岩带可能穿过松辽盆地向东延伸到吉林公主岭以东等地区。在白乃庙岛弧岩带内未见有早前寒武纪结晶基底岩系出露，但碎屑锆石及Sr-Nd-Hf同位素结果显示在该岛弧岩带深部可能存在有扬子(塔里木)型微陆块基底，其性质与中亚造山带内大多数微陆块性质相一致，而与华北克拉通演化历史明显不同。寒武纪-奥陶纪期间，在白乃庙岛弧岩带与华北克拉通之间，存在有一较为宽广的洋盆。志留纪末期，白乃庙岛弧岩带与华北克拉通北缘发生弧-陆碰撞而增生到华北克拉通北缘。类似的弧-陆碰撞可能是中亚巨型增生型造山带地壳侧向增生的最主要方式之一。泥盆纪期间，在华北北缘发育了大量的碱性岩及碱性花岗岩。项目组在乌兰哈达及三道沟碱性杂岩体中新发现了与碱性岩近同期形成的基性岩，并新发现了白菜沟泥盆纪碱性岩体。年代学结果显示，华北北缘泥盆纪侵入岩主要形成于中-晚泥盆世，并构成了沿华北北缘分布的长度近900km碱性岩带。岩石化学及Sr-Nd-Hf同位素地球化学结果显示，这些泥盆纪侵入岩主要起源于岩石圈地幔的局部熔融，并有少量地壳物质的混染。华北北缘泥盆纪碱性岩的形成与白乃庙岛弧岩带与华北克拉通北缘弧-陆碰撞后伸展有关，这种构造背景也与这些岩体弱变形或无变形的特征相吻合。泥盆纪碱性岩的Nd-Hf同位素组成显示华北克拉通北缘岩石圈地幔组成有明显不均一性。华北克拉通北缘发育有大量泥盆纪岩石圈地幔熔融所产生的碱性岩及碱性花岗岩的事实表明中-晚泥盆世期间华北克拉通北缘发生了强烈的陆壳垂向增生。