Study On The Geneses And Sources Of Pyroxene And Amphibole In The Offshore Sediments Around Hainan Island

The dissertation is supported by the Chinese Offshore Investigation and Assessment, the 908 Sub-project. In this project, the study area is around Hainan Island except Qiongzhou Strait and takes 190 surface sediments and 7 groups'sediments cores as researching samples.In this dissertation, inosilicate minerals: pyroxenes and hornblende which locate in 11 surface sediments samples have been chose for the research about its genesis and sediment source in the area. The microstructure and the compositional classification of the pyroxenes and hornblende in the chose samples have been examined by using optical microscope, scanning electronic microscope (SEM) and quantitative electron probe microanalysis (EPMA).Firstly, all the minerals in surface sediments have been analyzed and map which involved the minerals classification and the grain's percent, then the mineralogical mapping for the grain's percent about pyroxenes and hornblende has been used to figure out the tendency of spatial distribution of them. Under binocular stereoscope, the particle morphology of pyroxenes and hornblende has been observed and recorded and found that in the research area, both of them have suffered denudation during the sedimentation process. The chemical composition of the pyroxenes and hornblende in samples has been tested by EPMA. Combing the existed conclusions about the typomorphic chemical composition of minerals, the result of EPMA indicate that, in this area the most of pyroxenes are augite, coming from plutonic rock and hornblende are in the type of tremolite, actinolite and magnesio-hornblende, among them the tremolite, actinolite is from regional metamorphic rocks which is relate to hydrothermalism and accompanying metasomatism and the magnesio-hornblende is from acid magmatic rocks.The microstructure pyroxenes and hornblende has been observed from SEM, meanwhile combining the Energy Spectrum Analysis, it is found that following thedenudation process, the ions like Na⁺,K⁺,Ca²⁺,Mg²⁺ are corroded from pyroxenes and hornblende.In the end, given all the facts like the bottom geomorphology of offshore around Hainan Island, the ocean current and monsoon, and also the flood events in the Hainan Island on the sediment flux to the sea with its geology background, the sources of the sediments in this area has been deeply discussed and concluded. The conclusion is that the sediments in the offshore around Hainan Island especially the pyroxene and hornblende mostly come from the Hainan Island and the transportation includes sandy wind deposit, fluxing by river and coastline erosion.