A Study Of The Silurian-Triassic Paleo Latitude Migration In The Central Uplift Of The South Yellow Sea

The drift,fragmentation and convergence of the Yangtze block from Luo Di ya to the United continent are hot topics and difficult points in geosciences.The rapid development of paleomagnetism has provided important evidence for the drift,cracking and aggregation of plates.It is a very important and essential way to study the drift of block bodies by using paleomagnetic method.Scholars at home and abroad have carried out a large number of geological and geophysical research work in the Yangtze area,and accumulated a large amount of geological and geophysical data,including paleomagnetic data.On the basis of previous work,this study has collected and collate the paleomagnetic data of the lower Yangtze block,and carried out a large number of sampling work on the basis of the continental shelf Scientific Drilling Project in the South Yellow Sea.Under the demagnetization and rock magnetic experiment,the paleomagnetic data in the Silurian Triassic period of the lower Yangtze block were reanalyzed and explained in accordance with the criteria for the reliability of paleomagnetic data.Based on the quantitative constraints of palaeomagnetic data and the qualitative constraints of palaeontological data,the following understanding is made for the migration of palaeo latitudes in the lower Yangtze block.(1)during the Silurian late Devonian period,the Silurian paleoglatitudes of the lower Yangtze block were around 10 S,the late Devonian paleo latitude was about5°S and the drift rate was 0.085-0.152°/Ma,and the Yangtze block was highly likely to be the pro Gondwana block.(2)in the late Devonian Early Carboniferous period,the Yangtze block wascollided with the Southern China block in the Caledonian movement.The Yangtze block was about 5°S in the middle of the Devonian period,the Early Carboniferous palaeoglatitudes were at 9 N,the minimum drift rate was 0.209°/Ma,the Yangtze block quickly cracked and moved northward fast and close to the equator.(3)the Early Carboniferous and Late Carboniferous period,the Late Carboniferous paleo latitudes of the lower Yangtze block were about 18°N,the drift amount reached 9°,the minimum drift rate was 0.15°/Ma,and the stability continued to move northward.(4)during the Late Carboniferous Early Permian,the Hercynian movement gradually entered its final stage.In this experiment,the paleo latitude of the Permian lower Yangtze block is about 18°N,and the trend of the lower Yangtze block to the north is slowed down,and the drift of the lower Yangtze block is less than that of 1 °.(5)in the early Permian Triassic period,the Early Triassic lower Yangtze block was around 12°N,and the drift of the lower Yangtze block reached 5° and the minimum drift rate was 0.185° /Ma.(6)the tendency of the lower Yangtze block in the period of the Silurian to Permian period is to drift northward,gradually moving from 10°S to 20°N,and clockwise from the end of the Permian to the Early Triassic,causing the sampling location to drift southward to 12°N.In the middle and Late Permian,the southward drift can be considered as the clockwise rotation of the lower Yangtze block during the collision of the lower Yangtze block with the North China block.As can be seen from the above,there is a certain difference between some data and the collected data.This is due to the previous data in which each data source is obtained under different reference positions;and this sample is derived from the lower Yangtze block,which,to a certain extent,makes a partial difference with other data;there is one of them.The strata have undergone thrusting and magmatic activities,which will bring visual errors and practical errors to data measurement.With the inspection and correction,after eliminating the data that did not conform to the experimental standard,it can be seen that the lower Yangtze block has a tendency to move northward from the overall latitude.