摘要
早前寒武纪花岗质岩年龄统计结果显示,华北克拉通经历了3.8,3.3,2.9,2.5和1.8～1.9Ga等多个旋回才从陆核成长为陆台,与之对应沉积岩也由少变多,大约以500Ma为一周期。由于沉积作用出现在成陆间歇期,所以二者在时间上相间互补,其状如同显生宙超大陆裂解和拼合的周期交替。这一现象不但是地壳演化的普遍规律,而且也可反过来用沉积岩反映陆壳的演化。然而,早前寒武纪尤其是太古宙的沉积岩毕竟太少,无法用来恢复当时古陆块的面貌,但古元古代的特别是陆缘沉积的孔兹岩,尽管已进入下地壳并成为克拉通基底的组成,则以保存甚多、分布延续,使其重塑克拉通的拼合成为可能。已有的华北克拉通的构造划分方案多种多样,但以陆缘沉积的古元古代孔兹岩作为地块的边界,理当最能反映当时古陆块的面貌。因此,以孔兹岩为主要依据,并综合考虑岩石组合、构造环境、变质p-T轨迹、同位素年龄、以及不变质的沉积盖层等地质特征,将华北克拉通主体从西往东划分为:鄂尔多斯地块/晋蒙弧形拼合带/冀鲁豫地块/(郯庐断裂)/胶辽地块群等构造单元,所得到的不同于以往的构造轮廓,显示华北陆台并非一统的太古宙克拉通,而是吕梁运动拼合成的古元古代大陆。
The basement of the North China craton, like many other old cratons in the world, consists mainly of tonalitetrondhjemite-granodiorite gneisses （TTG）, greenstone belts and a small amount of Precambrian meta-sedimentary rocks. Although the meta-sedimentary rocks are less distributed, their evolution regularities can be reflected by TTG, because a sedimentation in Precambrian always followed a cycle of granitoid continental crust. According to incomplete statistics of the Precambrian granitoid ages from the North China craton, it is showed that the craton experienced multiple phases of evolution from a nucleus to a mature continent through the cycle events at 3.8 Ga, 3.3 Ga, 2.9 Ga, 2.5 Ga and 1.8-1.9 Ga, which are exhibited by peaks on the histograms of granitoid ages and by ca. 500 Ma as a period. Correspondingly, the amount of sedimentary rocks increased along with evolution of granitic crust, but the deposition was temporally different from the granitoid events, i.e. deposition took place between two cycles of granitoids crust with a period of ca. 500 Ma. This period is similar to the interval in a Phanerozoic supercontinental cycle from breakup to assembly, indicating similar continent evolution regularities in both Precambrian and Phanerozoic. Therefore, it is possible for using meta-sedimentary rocks to interprete the craton evolution. However, the Precambrian （especially the Archean） sedimentary rocks are so minor that they cannot reveal the shape of the old blocks. Meanwhile, the Paleoproterozoic khondalite series was deposited in a continent-marginal setting and is better conserved and distributed, it can be used to model the assembly of craton. Generally speaking the tectonic division based on khondalite should be the best among many other tectonic models for the North China craton, because the marginal sedimentary rock was the boundary of block. Thus, based on khondalite and combined with magmatism, sedimentology, metamorphism, structural deformation, and geochronology in a variety of Archean terranes, a new tectonic subdivision model for North China craton is presented in the paper. The tectonic units are succesively： from west to east, Ordos block / Central （Jin- Meng） assembly belt / Ji-Lu-Yu block / （Tan-Lu fault） / Seashore （Jiao-Liao） block group.Because the protolith ages of the khondalite are Paleaoproterozoic, the final assembly occurred at -1.8-1.85 Ga, i.e. the famous Lüliang Movement in China.
出处
《高校地质学报》
CAS
CSCD
北大核心
2007年第3期442-457,共16页
Geological Journal of China Universities
基金
国家自然科学基金(49972065)
关键词
华北克拉通
变质沉积岩
孔兹岩
早前寒武纪
大地构造划分
North China Craton
meta-sedimentary rock
khondalite
Early Precambrian
tectonic division
