The Characteristics Of Petrology And Geochemical Of Taershan And Erfengshan Alkaline, Subalkaline Complex

The intrusive activities of alkaline,subalkaline complex happened in Mesozoic Period in Taershan and Erfengshan districts. Three units (the units of syenite-diorite,aegirine-syenite,and quartz-monzonite) which make up the main rock types of the alkaline complex.The author attempts to treat the complex as a deep probe,based on the study of petrology,mineralogy,major and trace element,Sr-Nd-Pb isotope geochemistry to further explore the rock series of the complex,the source of magma material and other issues,and acquired the following conclusion:The alkaline,subalkaline complex located in the central turning place of Fenwei rift system in North China block. The complex is characterized by complex lithology,multiple period of magmatism,lasting a long time. Through field survey and investigation, the author identified that various types of rock′s intruded stratum is Ermaying group of Triassic period,and show that the invasion time is between 90～140Ma,equivalent with late jurassic to early cretaceous period,belong to the products of motion of Yanshan period. According to the complex interspersed,cutting,wrapping relations among all the complex, we can determine their order of formation which is syenodiorite to aegirine-syenite to quartz-monzonite to granite-porphyry to syenite porphyry. The rock mineral composition is characterized by all of the syenodiorite,aegirine-syenite,quartz-monzonite,granite-porphyry,syenite porphyry are contained with orthoclase, plagioclase, quartz as main minerals,but rhe content is various in different rocks, aegirine-augite only appeared in aegirine-syenite,the content is up to 15%, mineral composition difference show that the magma source material components may be different during the different periods. Syenodiorite of Taershan and Ludingshan,quartz-monzonite of Laoshan and Erfengshan,syenite porphyry of Taershan and Laoshan mineral composition and content is completed same,and indicated that they were the product of the same period of intrusion, and magma derived from the same source material.The alkaline complex has the petrochemistry characteristics of alkali,K,Na,Al-rich, Ca-medium, Fe-poor. The complex evolution series is potassic magmatic evolution series. From the early intrusion syenodiorite to the latest invasion quartz-monzonite,the variation characteristics of major elements of alkaline complex are as follows: the content of SiO2,alkali (ALK), alkalinity rate are gradually increased, w(Al2O3) did not change significantly and the content of T(Fe2O3),MgO,CaO,TiO2 are gradually decreased,but w(SiO2) is obviously increased and w(Al2O3) is obviously decreased in the latest intrusion of granite-porphyry.REE patterns of syenodiorite,aegirine-syenite,quartz-monzonite are characterized by very similar right-hand curve patterns and no significant negative Eu,Ce anomalies;From the mantle-normalized spider diagram,it is known that the complex is enrich with large ion lithophile elements (LILE) such as Ba,Sr, and lost in Ni,Co(TE);From the discrimination diagram of Ti-Zr-Y,Zr/Y-Zr,Nb-Zr-Y,Th-Hf-Ta,All the parameters point focus on the WPB and WPA range;Sr-Nd-Pb isotopes diagram showed that all the parameters point focus on the EMI. We can confirm that the complex of syenodiorite,aegirine-syenite,quartz-monzonite originated from same magma source of enrichment mantle I(EMI),the magmatism of partial melting is leading role ,no crystallization differentiation. Granite-porphyry and syenite-porphyry magma derived from crustal source.Based on the studies of petrology,mineralogy,geochemistry of elements and Sr-Nd–Pb isotopes of Taershan and Erfengshan alkaline,subalkaline complex,it can provide lots of important information about magmatic rocks with regard to the destruction in central region of North China Craton.