Petrogenesis And Tectonic Significance Of Zibo Jinling And Linqu Tiezhai Gabbro Diorite In Western Shandong

During the Mesozoic era,the North China Craton underwent large-scale destruction and thinning,and induced large-scale magmatism.Luxi area is located in the east of the North China Craton.There was large-scale medium basic intrusive rock activity in the early Cretaceous and showed the temporal and spatial heterogeneity of EM1 and EM2 mantle source areas.It is a natural laboratory to study the destruction of the North China Craton.Dabie Sulu orogenic belt and Tanlu fault zone are important lithospheric weak zones in the North China plate.They have an important impact on the destruction and magmatism of the North China Craton.Zibo Jinling and Linqu Tiezhai gabbro diorites,western Shandong are located in the southeast margin of the North China Craton,close to the Tan Lu fault zone,and formed at about 128 Ma and 132 Ma.The two rock bodies have high contents of Mg O,Fe₂O₃ and Cao and low contents of Si O₂,Ti O₂ and Na₂O.Most of them belong to high potassium calc alkaline series.There is an obvious positive correlation between Mg O and Cao,Fe₂O₃ and Ti O₂,and there is also a good linear relationship between Cr and Ni and V,indicating that there is the separation crystallization of olivine and pyroxene in the formation of the two rock bodies;In terms of trace element composition,the two rock bodies are rich in large ion lithophile elements and light rare earth elements,deficient in high field strength elements,and have obvious Nb-Ta-Ti negative anomalies,and there is no obvious correlation between Zr/Hf,Th/U and Nb/Ta,indicating that there is no obvious crustal contamination in the two rock bodies;The two rock masses have relatively high initial ⁸⁷Sr/⁸⁶Sr ratios(0.7045?0.7068,0.7040?0.7062)?_Nd(t)(t=130Ma)value(-3.0?-9.1,-3.5?-7.7),and higher zircon?_Hf(t)values(-5.1?-2.4,-2.4?+3.2)may indicate the addition of asthenosphere mantle material in its mantle source area.The analysis of geochemical characteristics of Jinling and Tiezhai gabbro diorites in Zibo and Linqu shows that they have no obvious crustal contamination,and there is the fractional crystallization of olivine and pyroxene.Their mantle source area is an ancient enriched lithospheric mantle,belonging to EM1 type mantle source area.There is the addition of ancient North China lower crust material and possibly asthenosphere mantle material in the mantle source area.As a weak zone of lithospheric mantle structure,the Tanlu fault zone provides a channel for the upwelling of asthenospheric mantle material in the mantle source areas of Jinling and Tiezhai gabbro diorite in Zibo and Linqu,and is an important factor affecting the destruction of the North China Craton.