The Rock Geochemistry Characteristics And Tectonic Implications Of Mafic Dyke Swarms And Syenite Porphyry Veins In Zhenba Eastern Area, The South Of Shaanxi Province

Appears massive NW-SE distributed Mafic Dyke Swarms in Zhenba eastern area,in north Dabashan structure belt ,the south of Qinling, meanwhile appears has the few Syenite Porphyry Veins to assume the approximate direction mop. Decides the year after the isotope and the open country research indicated, This magmatic activity occurs in the eopaleozoic later period late Ordovician world - early silurian period world, Belongs to east Gary the mid and late stage structure magmatic activity event record. In which basic crag by splendor long diabase primarily, has the few diabase arteries partially, They together constitute a set of typical alkalinity split-blip type magmatic rock characteristic rock combination with this area Syenite Porphyry Veins, Had indicated this area had a continental crust extension in the eopaleozoic later period to pull opens the event. Two big crag class homogeneous phases to concentrate the light rare-earth element, The light and weight rare-earth element fractionation is intense, the overall has demonstrated the more consistent right deviation spectrum, And the trace element primitive mantle standardization spider web chart demonstrated various rocks sample concentrates LILE relatively, and concentrates not accommodating element Ba, Nb, Ta obviously and so on, with OIB characteristic match case. The dike Mg^# value is low, is lower than the proto magma Mg^# value obviously, Explained in the area the dike should be the proto magma experience high degree evolves after the product. Eu demonstrates in the basite for exceptionally, but in the orthophyre the demonstration is the negative anomaly, It had instructed before forms in the basic crag, the rock magma occurs by no means take the plagioclase feldspar as the main crystallization phase fractional crystallization, In the process which evolved to the syenite has only then had the plagioclase feldspar fractional crystallization in the basic crag, In this process, the synchronize take rich Ti and P apatite and contained the titanomagnetite as the main crystal showing off crystallization differentiation function, Finally forms poor P, Ti and loses Sr obviously the orthophyre. Unifies these characteristics, again pulls the spot basalt according to the research area obviously flaw mainland only to appear the alkalinity basic crag the characteristic inference, the home court dike should form in the mainland rift valley early time evolution stage. In addition, research area all basite all high Ti (TiO₂ average 4.55%), has demonstrated the high titanium basalt characteristic (TiO₂>4%), and the Ti/Y ratio is extremely high (between 423.1～2771.5, average 1235.35), This is similar with the Mt. Emei high Ti(TiO₂>4%, Ti/Y>500) basalt characteristic which forms with the mantle plume magmatic activity. Two kind of rock Ta/Hf values between 0.27～0.90, Th/Ta value between 0.68～1.59, with mantle plume origin basalt series characteristic (Ta/Hf>0.3, Th/Ta<1.6) match case, It had indicated that their formation is controlled by the mantle plume magmatic.Through the present paper research, promulgated the eopaleozoic later period, south the reason of the Qinling area in north the Yangzi tectonic plate has had a time important mantle plum magmatic activity, Also is precisely because this depth portion mantle plume magmatic activity existence only then initiated this area wide range to pull opens the decomposition. This mantle plume magmatic activity should be the main depth portion driving influence origin which the eopaleozoic period entire south Qinling area structure evolves, and possibly made an effort for the Mianlue ocean basin in the late Paleozoic Era time to open slightly is having the important influence.