The magmatic activity mechanism of the fossil spreading center in the Southwest sub-basin, South China Sea

Petrogeochemical data indicate that after the end of seafloor spreading,residual magmatic activity still exists in the deep basin of the South China Sea.By using different viscous structure models beneath the fossil spreading center of the Southwest sub-basin we simulated the amount of melt produced,the length of the melting period,and the thermal evolution process in terms of geothermics and the buoyant decompression melting mechanism.We compared the results of our model with observed heat flow,seismic,and petrogeochemistry data.The results show that depletion buoyancy induced by buoyant decompression melting plays an important role in the melting process,while retention buoyancy,thermal buoyancy,and viscous shear force have only a weak influence on the melting process.From the length of the melting period,we determined that for the three viscous structures models the magmatic activity lasted about 5,12,and 15 Ma.Under the effect of buoyant depression melting,local high-temperature areas will develop under the basin,which can explain the low-velocity layer detected by seismic exploration in the middle and upper lithosphere of the Southwest sub-basin.We also simulated the possible lithology distribution beneath the fossil spreading center with the physical conditions of different viscous structure,different temperature structure,and different melting fraction,which provided a greater understanding of the rock petrogeochemical data of the deep sea basin in the South China Sea.

A new conception on the formation of the first bend of Yangtze River: its relations with Eocene magmatic activities

Based on field observations, the author proposes a new understanding on the formation of the first bend of the Yangtze River. The relationship between the formation of the first bend of the Yangtze River and Eocene magmatic activity is expounded, suggesting that the first bend of the Yangtze River is the result from choking of the strong magmatic activity in Eocene. As a result, the upstream became a natural reservoir, whose riverside between Mt. Yulong and Mt. Haba was burst, guiding Jinshajiang River running eastward. At the same time, the drastic uplift of the Qinghai-Tibet Plateau led to the deep dissection of the river cut down the channel, resulting in the formation of the Tiger Leaping Gorge. The magnitude of uplift in the study area (located in the eastern of the Tibetan Plateau) is calculated. Taking Mt. Yulong as a base, the magnitude of lift is 3,300 m from Eocene to Pliocene, adding 700 m since Pleistocene, totaling up to 4,000 m or so.

Genesis and Distribution of Ultra-alkaline Magmatism within the East Antarctic Associated with the Kerguelen Plume Activity

Alkaline magmatism is often associated with the initial or final stages of huge plume activity.The alkaline bodies are most often found within the boundary area of plume impact upon the continents.The initial stages of the

Mesozoic tectono-magmatic activities in South China:Retrospect and prospect

The South China Block was formed through the collisional orogeny between the Cathaysia Block and the Yangtze Block in the Early Neoproterozoic.The northern,western and southern sides of the South China Block were affected by disappearance of the Paleo-Tethyan Ocean during the Paleozoic.The southern and northern sides of the South China Block were respectively collided with the Indo-China Block and North China Block in the latest Paleozoic to form the basic framework of the Eastern China.The Eastern China has been affected by the westward subduction of the Pacific Plate since the Mesozoic.Therefore,the South China Block was influenced by the three major tectonic systems,leading to a superposed compound tectonics.The comparative study of the Mesozoic geology between the South China Block and its surrounding areas suggests that although the Mesozoic South China Block was adjacent to the subduction zone of the western Pacific,no juvenile arc-type crust has been found in the eastern margin.The main Mesozoic geology in South China is characterized by reworking of ancient continental margins to intracontinental tectonics,lacking oceanic arc basalts and continental arc andesites.Therefore,a key to understanding of the Mesozoic geology in South China is to determine the temporal-spatial distribution and tectonic evolution of Mesozoic magmatic rocks in this region.This paper presents a review on the tectonic evolution of the South China Block through summarizing the magmatic rock records from the compressional to extensional tectonic process with the transition at the three juncture zones and using the deformation and geophysic data from the deep part of the South China continental lithosphere.Our attempt is to promote the study of South China’s geology and to make it as a typical target for development of plate tectonic theory.