前寒武纪大陆地壳地质构造演化研究进展与问题

A Review on Precambrian Tectonic Evolution of Continental Crust

前寒武纪地质构造是地球系统科学研究的一个承前启后的重要组成部分,现存最古老的固体地球物质是38亿年前的大陆长英质岩石。以地质构造热事件为标志确认早中太古代已有30亿年年龄值的大陆克拉通化,而新太古代末大陆地壳已出现普遍的克拉通化。由深变质作用岩石测得的pt值推断当时地温梯度与现今大陆稳定区相似,大规模的陆壳区断块已具基本刚性特征,使板块构造运动模式基本适用于太古宙地壳演化。古元古代末陆壳普遍隆升和遭剥蚀,陆壳生长作用导致形成大陆区块上的裂谷型坳拉槽系。中元古代起,世界约于18亿年前近乎同时出现不变质的沉积盖层,使前寒武纪明显必需划分为早、晚前寒武纪两大阶段。华北克拉通区是世界大陆克拉通地壳的组成部分,与世界各大陆克拉通演化有很好的可对比性,在前寒武纪超级大陆重建中有一定位置。在现今阶段研究基础上,对华北克拉通区提出了几个前瞻性的基础研究课题,应予深入探索。

Precambrian tectonics represents one of the key research topics in the science of earth system. The preserved oldest continental crust is composed of felsic rocks with ages older than 3.8 Ga. As indicated by analysis of tectonothermal events, the continental blocks 3.0 Ga have been recognized, and Neoarchean cratonization is very common all over the world. It is suggested that the early geothermal gradient is comparable to that of present day by PT calculation on the basis of high-grade metamorphic rocks. Thus, the Archean continent crustal blocks were rigid enough to show kinematics, as described by present plate tectonics. Since the Mesoproterozoic (1.80 Ga), many cratons began to develop sedimentary covers synchronously, which are almost unmetamorphosed. So, it is suggested here that Precambrian geological evolution can be divided into two stages, the early stage and the late stage. The early crustal evolution of North China craton can be well correlated with other continents, and its tectonic position within the Precambrian Supercontinet should be reconstructed. Based on the current accumulation of research, several basic projects are proposed to focus on the frontier areas of Precambrian geology.