Study On The Distribution And Origin Of The Seafloor Detrital Minerals In The Offshore Water Of Hainan Island

The unique geographic position of shelf and marginal sea causes the material supply of seafloor sediments plenteous and the material sources of them diverse. As terrigenous materials being input into the sea continually and a great deal of authigenous minerals coming into being, the sediments can be used to study the change of sea level and the meterail and energy exchange between the sea and the land. According the demand of the national"908"special project, the distribution of the detrital minerals and the characteristics of genetic mineralogy of the surficial sea-floor sediments offshore Hainan islands(CJ19 subzone) were studied by means of lens stereoscope, micropolariscope, SEM, EMPA and LA-ICPMS. The conclusions were drawn as follow: (1) There are 40 kinds of detrital minerals in the 190 surficial sea-floor deposit samples in this sea area, including 13 kinds of light minerals and 26 kinds of heavy minerals, and the chlorite(2.6-3.3g/cm3) can be found in both light minerals and heavy minerals. The content of the heavy minerals is very low and they are 0.81% of the weight of all detrital minerals. According to different methods of classification, both the light minerals and the heavy minerals can be also classified to different sub-kinds whose distributing characteristics are different in the studying sea area. (2)The studies on the appearance typomorphism, physical typomorphism, inner structure typomorphism and chemical typomorphism of the zircon and garnet, and the result of U-Pb isotopic age dating of zircon indicate that the zircons are meta-morphogenic genesis but two or three of them are magmatic genesis and most meta-morphogenic zircons have a basic magmatic zircon core which was generated in Stage of Yanshand and Indo-Chinese epoch. The genesis and origin of the garnet is very complicated. The garnets are main almandine with high Fe and Mg content and were proposed their souce rocks are mostly regional mid-degree-metamorphic rocks. (3) In this sea area, the main origin of the detrital minerals is Hainan island, and the characteristics of genetic mineralogy of the zicon and garnet indicate that the detrital minerals mainly come from regional mid-degree-metamorphic area.