THE YANGTZE PLATFORM AND THE NORTH CHINA PLATFORM AS OF THE SAME LITHOSPHERIC PLATE

By using the theories of regional control and irreversihility in mineralization, the authors suggest that the Yangtze and North China platforms have been of one and the same lithospherie plate. This conclusion is supported by a comparison between the two platforms in six aspects, i.e. metallogenic formations of iron and gold,geochronology,magmatism and magmatie rocks,formation age of khondalite and geophysical fields of their basement. The first breakup in the Qinling area took place in the middle Early Proterozoic（Ca.2250 Ma ago）, resulting in the formation of the North China and Yangtze platforms and the paleo-Qinling oceanic taphrogenic trough between them. Based on their basement depths and cutting depths of their boundary, the plates within China can be divided into three categories,i, e. the lithospheric plate （with a cutting depth of over 100 km）, the Mohorovicic plate （with a cutting depth of 45-100kg） and the crustal plate （with a cutting depth less than 45km）. In most stages of the evolution of the North China platform and the Yangtze plaform, they were of mohorovicic type, and in few stages, they were of crustal one. This paper expounds that the Qinling tectonic belt is a complex polyeyclic and stacked breakup-collision orogenic belt. Its evolution underwent 5 stages and 9 phases, including 6 breakups and 6 collisions or compressions. There is enough evidence to show that the breakup depths of the Qinling belt are small,generally a few tens of kilometers, although it had been separated several times. The magmatic activity seems to be frepuent, but ultramafic rocks, especially dunities, rarely occur, and sheeted dykes are not developed either; therefore the ophiolite suite in this area is not typical. The authors call it the ophiolite-like suite, representing a transitional oceanic crust. In other words, the whole Qinling orogenic belt evolved in one single lithospheric plate, no true oceanic crust being involved. This view can be borne out from the history of mineralization in the area, which is integrated with the history of the geological evolution. The mineralizations are mainly of silver, gold and nonferrous metal（Pb, Zn, Mo, Cu）types, indicating the tranisitional feature of the crust. The gold mineralization is considered to have continued through the whole geological history, and gold deposits of major economic importance were formed in various geological stages under favourable geological and physiochemical conditions. The authors hold that the Shanyang-Lixian fault is not only a syngenetic fault belt that controls the Qinling Pb,Zn,Hg and Sb metallogenic belt but also an amalgamation belt between the Yangtze and North China platforms which collided in the Early-Middle TriassiC. Both the platforms as a whole began to drift northward from near the equator in the late Paleozoic. In the course of drifting, the Yangtz platform was nearing and collided with the North China platform and eventually they were fully amalgamated in the Middle Triassic. Because the platforms have belonged to the same lithospheric plate all the time, they did not belong to Gondwana in the south, nor belong to Laurasia in the north, but belonged to a third paleocontinent between the two supercontinents （e.g. possibly＂paleo-Pacific Land＂）.