太行山南段早元古代基性脉岩的~(40)Ar-~(39)Ar年代学及其构造意义

针对华北克拉通中部地区(即Zhaoetal.(2001)称之的中部带)内元古代未变形变质基性岩墙群重要组成部分的太行山南段基性岩脉开展了较为系统的40Ar-39Ar年代学研究,研究结果表明:区内三条NWW或NNE走向的基性岩脉(99JX-16、99JX-65、99JX-71)在>80%的39Ar累积量基础上分别给出了1765.3±1.1Ma,1774.7±0.7Ma,1780.7±0.5Ma的坪谱年龄。1781～1765Ma的年龄限定了区内基性岩脉的侵位年龄,该年龄也一致于恒山NWW向未变形基性岩脉1769.1±2.5Ma的单颗粒锆石U-Pb年龄。上述资料较好地约束了华北陆块早元古代基性岩脉的形成年龄。这为深入理解华北陆块1800Ma左右的热构造事件和华北早前寒武纪构造演化提供新的年代学资料。

40Ar-39Ar GEOCHRONOLOGY OF PALEOPROTEROZOIC MAFIC DYKES FROM SOUTHERN TAIHANG MOUNTAINS AND ITS GEOLOGICAL SIGNIFICANCE

In this paper, 40Ar 39Ar geochronological data of three mafic dykes, devoid of deformation and metamorphism from southern Taihang Mountains that are the cells of the Proterozoic dyke swarm of the trans North China Orogen, have been presented in order to better understand the tectonic setting of the ca. 1800 Ma event. Three representative samples from WNW or NEN trending mafic dykes (99JX 16? 99JX 65? 99JX 71) yielded the plateau ages of 1765.3± 1.1 Ma, 1774.7± 0.7 Ma, and 1780.7± 0.5 Ma respectively. These plateau ages are defined by the 80% 83% of total 39Ar released with invariability for seven successive intermediate and high temperature steps at 1σ level of uncertainty. The plateau is somewhat consistent with a single grained zircon U Pb age of 1769.1± 2.5 Ma given by an unmetamorphosed NWW striking diabase dyke from the Hengshan area. This age of 1781 1765 Ma is considered as the best estimate of their emplaced age of these mafic dykes in southern Taihang Mountains, probably also that of the mafic dyke swarm in the central North China Craton. These data provide new information to better understand the thermotectonic event of ca. 1800 Ma and the Precambrian crustal evolution of the North China Craton.