Continental Crust Chemical Structure, Geochemical Subdivision And Mapping Of Qinling-Dabie Orogen

Map is important media to express information. By comparition with the intimate cooperation of geology and geophysics studies in GGT program and their relatively mature regional mapping citrtion, systemic regional geochemistry research and mapping is still in exploring. Qinling-Dabie Orogen,the mainly part of central orogenic belt of China,is chosen as the subjiect region. This disseration probes to the orogenic geochemical mapping and makes a study of the continental crust chemical structure and geochemical subdivision. The detail as follows:1. Disscusion of orogenic geochemical mapping in theory.Present map can be divided into two types: one is the division of map elements as the assumpsit model,and the other is the onefold field temporal-spatial strength determined by special pattern, geological map and geophysical map as the sample respectively.Until now, to make geechemical map as the field pattern is difficult.The author thinks that geochemical map should express the lithosphere mantle character, regional crust growth, geotectonic ascription and chronlogy dates et. al.,. We chose Ln(Co*Cr*Ni), Nb/Ta, plumbum isotopes composition, neodymium isotope two stage model age of depleted mantle (T2DM) andεNd(t) indexs to express the information and give the introduction of theory in the relevant chapters.2. Continental crust chemical structure of Qinling-Dabie Orogen. This disseration brings forward the continental crust chemical structure concept after comparing with geological and geophysical concepts concerning the different aspects of crust's samdwich structure. Elements abundence of continental crust different layers provided by Geochemical Earth Reference Model (GERM) are used to give the way to standard the continent crust. This way's key point is the comparability of different elements which shows the continent crust chemical differenation. Research of continental crust chemical structure shows: crustal differation of Qinling-Dabie orogen is weak; Taihua group and Kongling group, the basements of the adjacent zones, can only represent the upper lower crust; the Dabie group ,basement of the South Qining block, may have experienced complex structural maturation process; the middle crust of South Qinling Block and western part of Yangtze carton north margin may be dominanted by upplanting and consequently the crust differation is unobvious. Ln(Co*Ni*Cr),Nb/Ta and KN/A about granites indexs are used to make in the ichnography to express continental crust chemical stucture. Mapping results shows that Ln(Co*Ni*Cr)can indicate the maturality character of different curst layers; KN/A on regional granites can disclose the basement maturality character;but Nb/Ta can't indicate the source of sediment cover well.3. Isotopic geochemistry subdivision. On the statistical rusults of 784 collected samples'lead isotopic composition dates, different blocks' character are described and blocks' geotectonic ascription are disscused. South margin of North China carton has lower 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values as a whole. North Qinling-Noth Huaiyang belt has bigger 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values. South Qinling block is depleted in U plumbum isotopes by comparison with North Qinling belt, but they have almost the same 208Pb/204Pb limits, and this indicates they both have the enrichment of Th. North Dabie block' 206Pb/204Pb is alike to that of North China carton, but its 208Pb/204Pb is similar to that of South Qinling Block, bigger than North China carton's 208Pb/204Pb. The ultra-high perssure metamorphism unit, mainly part of South Dabie block, has almost the same lead isotopes composition as South Qinling block. This indicates that the Dabie block may be the eastern externed part of Souther Qinling Block. Statistic of about 630 Sm-Nd isotopic dates from Qinling-Dabie Orogen shows: 1. mass in this area is complex, Sm-Nd isotopic system has the tendency of changing from depleted mantle to upper continental crust. This is consistent with the intense crust-mantle interaction...