GLOBAL GEOLOGICAL CORRELATION AND EARLY PRECAMBRIAN GEOLOGICAL EVOLUTION OF CHINA

The earth in its early time did not exhibit the model of modern plate tectonics, but its evolutionary trend was gradual with some interruptions and finally it approximates to this model. The author suggests that two end-me- mber models may be established: the early （lower） Archean model and the Phanerozoic model. During early Archean time, igneous activity was dominant. Though volcanic activity was also operative, the composition of the volcanics is close to basic and ultrabasic composition of the upper mantle, Meanwhile, a phenomenon that can not be neglected is the dominance of plutonism（which generated granite and mafic and ultramafic plutons）.In the late stage of the early Archean, such contemporaneous intrusions only occurred under special conditions in a few loci （such as ophiolite zones）. The formation of the belt-shaped folds in the modern model for the tectonic forms began with the formation of ovoid fold swarms, and the gelo- ogical units dominated by the early plutonic rocks were gradually divided into geosynclinal and platform facies, and the satulated irregular metamorphic zone became the non-satulated zone with multiple correlative types. This series of evolution was unidirectional; therefore the major model of the early earth has never recurred since the Phanerozoic. The study of the Phanerozoic geological history is based on the study of the formation of the geological units （which were dominated by deposition and last for a relatively long period of time） and then of the determination of the durations of geological intervals（with deposits as their sole expression）. On the other hand, the geological-structural movements are only considered to be operative in a short period and have been recorded in the forms of magmatic activity, deformation and metamorphism. But in the early time of the earth（A₁ and P. A）, the boundaries between these geological units and the products of the movements are not clear, nor are both distinguishable or can their time intervals be determined in any cases. Moreover, deposition was extremely lacking and plutonic intrusion pre- dominated. In this case, the plutons themselves are often the sole geologic bodies that may retain the record of this time.This is a problem that merits special attention. These phenamena also represent the gradation to the Phan- erozoic global tectonic model.