Distribution Summary And Topgraphic Response Of Cenozoic Basalts In Central And Eastern China

Cenozoic basalts exposed in land of Central and Eastern China is representative of the continental interior mantle-derived magmatism. In order to explore the mantle-derived magmatism related mantle depth process how to transform Chinese landscape, we use image processing technology to recount the Cenozoic basalt in the area of space and time distribution, quantitative geomorphic types of basalt, and attempt to explore the basalt in geomorphology, gravity anomaly area and the surrounding area on the spatial relationships.Utilizing digital image processing, we extracted Cenozoic basalts from the geological map of Central and Eastern China and exported them onto the high-precision geomorphologic map. Based on this, we estimate the total area and sub-regional area of Cenozoic basalts exposed in Central and Eastern China. The result showed that:(1) The total area of Cenozoic basalts in Central and Eastern China is80600±3300km2.(2) The area of Cenozoic basalts in Central China is35487±1451km2, while that in Eastern China is45094±1844km2, with a ratio of44:56.(3) The area of Cenozoic basalts increased along with younger era, and the ratio of which from Paleogene, through Neogene, to Quaternary is0.4:21.1:78.5.(4) Cenozoic basalts of Central China are mainly distributed in areas north of the Huaihe River, with three outcrops exposing from the north to south:Great Xing’an Range, Xilin Gol region and Northern edge of North China, and the size of them is7334±300km2,13843±566km2,14310±238km2respectively.(5)It shows that Cenozoic basalts of Eastern China show boarder scope than that of Central China, which dispersedly distributed from Heilongjiang province to Hainan Island. They can divide into three regions from the north to south:Northeast China east to the Songliao basin (35380±1447km2), Eastern China including Shandong, Zhejiang, Jiangsu and Fujian provinces (1707±70km2) and Leiqiong region including Hainan Island and Leizhou Peninsula (8006±327km2).(6) Overall, Cenozoic basalts of Central and Eastern China are mainly distributed in areas north to the Shandong Province. Area of Cenozoic basalts in the northern part is71247km2and that in the southern part is9334km2, with a ratio of88:12.Cenozoic basalts in Central and Eastern China mainly distributed in low altitude landforms, partly in intermediate altitude, and area in high altitude is very few. The landform of Cenozoic basalt outcrop is composed of low hill, plain and high hill in either case. A small part of them distritubed in low relief and intermediate mountain.Cenozoic basalt is seldom distributed in intermediate relif and intermediate mountain, but some basalt in Changbai Mountain is distributed in intermediate relif and intermediate mountain in North Korea. Some Cenozoic basalt’s landforms in Central and Eastern China are consisting with the surrounding area. However, some are different. In Central China, basalts exposed in Great Xing’an Range and Xilin Gol region raised with surrounding area. However the landform of Northern edge of North China differs with surrounding area.In Eastern China, Landforms of basalts erupted in Jingpo Lake,Nanjing and Hainan Island and Leizhou Peninsula differs with surrounding area,but the landform of the rest basalts in Eastern China have no difference with surrounding area.Cenozoic basalts in Central and Eastern China are located in land which Bouguer gravity anomaly>0.The relationship of distribution of Cenozoic basalts and Bouguer gravity anomaly can be classified into four types:The first one is coincidence.The most characteristic case is the shape of Abaga-Dariganga basalts fits the isograms of Bouguer gravity anomaly in Xilin Gol region. The second type is partly coincidece.They are less significant that the eruption out lines overlap with most of the body of Bouguer gravity anomaly>0including Chifeng basalts, Daxinganling basalts except Nuomin River basalts, Wudalianchi-Yichun basalts and Changaishan basalts. In addition, their landform types are abundant. The first and second types distributed in North China.They have larger scale and younger volcanoes than other types. The third type is characteristic by shape of basalts located along the boundary of isograms with Bouguer gravity anomaly>0, such as Jixi basalt, Shandong basalt, Nanjing basalt and Zhejiang basalt.They have smaller scale and elder age, scattered distributed. The fourth type is characteristic by shape of basalt located in the saddle of isograms with Bouguer gravity anomaly>0, such as Jingpo Lake basalt, Nuomin River basalts,Jining-Zhangjiakou basalt and Hainan Island and Leizhou Peninsula basalt. The key feature of type4is their landforms differ from the surrouding area. They behaved as:Underlying area of Jining-Zhangjiakou, Leiqiong, Jingpo Lake basalt,Nuomin River basalt corresponding to the saddle Bouguer gravity anomaly>0is Fenwei rift valley system, Qiongzhou strait,’sanwich’ between Zhangguangcai-Laoye mountain and Changbai mountain,Nuomin river valley, respectively. Landforms of Leiqiong and Jingpo Lake basalt decouple from Bouguer gravity anomaly, which means high laltitude get low Bouguer gravity anomaly. The landforms of the fourth type are low hill and plain with minor high hill. Deep fractures are common in the fourth type.Response of asthenosphere upwelling in Central and Eastern China can conclude into four situations by area of basalts, relationships with isograms with Bouguer gravity anomaly and landforms.Basalts of type1were erupted under the background of landforms reclaimed by massive asthenosphere upwelling. Regional uplift happened when the top surface of asthenosphere arrived.Intermediate altitude plain reflects transformed in CenozoicXilin-Gol basalts is model of type1.The second type basalts erupted along rifts when the top surface of asthenosphere arriving thick crust.Basalts layer overlaid on the earth’s surface. At the same time, mountains formed. In Cenozoic, YanShan Mountain and Daxinganling Range uplift rapidly. Vertical contour of Bouguer gravity anomaly is in accord with landforms evolution trend. It shows that upwelling of asthenosphere lead to density increases.The third case is the top surface of asthenosphere arriving thick crust without rifts evelopt.Rigional uplifted happened. Upwelling of asthenosphere leads to regional uplift first, fractures produced by uplift turned to the channels of basaltic magma like Shandong basalt.The fourth basalts erupted under the background of upwelling of asthenosphere at low-density crust. When fractures eveloped in the surface; they erupted along fractures and the landform usually appears as valley such as Jining area. When asthenosphere’surface met surface without fractures eveloped, Upwelling will lead to regional uplift first, fractures produced by uplift turned to the channels of basaltic magma like Leiqiong basalt.Overall, the relationship of basalts location and Bouguer gravity anomaly reflects that ground uplift and basalts are two respondings to asthenosphere upwelling. Location of basalts depends on where the fractures are.