元古代基性岩墙群的成因机制、构造背景及其古板块再造意义

GENETIC MECHANISM AND TECTONIC SETTING OF PROTEROZOIC MAFIC DYKE SWARM:ITS IMPLICATION FOR PALEOPLATE RECONSTRUCTION

大陆克拉通广泛发育元古代镁铁质岩墙群，其形成时限短，侵位机制复杂，可以侵位于不同的地壳层次。岩墙群的岩浆可能有多种来源，但主要来自陆下软流圈或地幔岩石圈，很少经历结晶分异与地壳混染。岩墙群的总体化学成分是富集型的，从古元古代到新元古代，其碱性组分逐渐增多，反映地幔演化特征。板块构造理论可应用于晚太古代－古元古代的构造研究，元古代以超级大陆的聚合及裂解为特征。岩墙群的形成普遍与伸展体制相联系，是超级大陆开始裂解或地幔柱活动的重要标志。华北克拉通区广泛发育中元古代镁铁质岩墙群，对其进行多学科的研究，将为确定华北克拉通在中元古代超级大陆中的构造位置及其古板块再造提供重要依据。

Proterozoic mafic dyke swarms occur in nearly every Archean continental craton, and recorded significant geological events of continental evolution .It is generally recognized that the generation and emplacement time of dyke swarm is relatively short,while its genetic mechanism is complex. At different conditions, dyke swarms have different propagation mechanism. Commonly, each dyke fracture initially fills vertically, then propagates laterally and not always intrudes perpendicularly to the lowest normal stress axis. Dykes can intrude in different crustal levels, but distinct with each other. Although there are different magma sources, the major source of dyke swarm is continental asthenosphere or lithospheric mantle. The evidence of crystallization differentiation or crustal contamination is rarely documented. Dykes' bulk geochemical feature is enriched and shows some small changes which could be used to detect the evolution of mantle process. Because extension can occur in different tectonic settings, where dykes actually generated still needs careful study. The plate tectonics had been operating at least from Neoarchean to Paleoproterozoic, and in the Proterozoic, the earth lithosphere was characterized by assembly and breakup of continental cratonic blocks. The occurrence of mafic dyke swarms marked the initial breakup of the supercontinents.A wide range of Proterozoic mafic dyke swarm,occurred in North China Craton,which will provide important constraints on reconstructing North China Craton and its position in the Mid Proterozoic supercontinent.