The Study Of Genetic Mineralogical Of Inherited Zircons In Early Cretaceous Intrusive Rocks In Han-Xing Area,Southern Hebei Province

The Han-Xing area is located in the central part of the North China Craton and the southern section of the Mesozoic Taihang intraplate orogenic belt.Due to its unique tectonic location,the Han-Xing area has unique advantages in discussing the time limit and destruction mechanism of the North China Craton.It is generally believed that the western subduction of the Mesozoic Paleo-Pacific plate was the main driving force for the destruction of the North China Craton.However,the mechanism,duration and process of the destruction of the craton are still controversial.These controversies focus on the stability of the North China Craton and its deep geological processes during the Late Paleozoic and Early Mesozoic.Due to the high sealing temperature,wide distribution and stable properties of zircons,they can“survive”in various geological processes and record complex information about magma evolution and ages.In this study,a large number of 2.5 Ga inherited zircons of old metamorphic basement and some 200-400 Ma inherited zircons were found in the Early Cretaceous intrusive rocks in the Han-Xing area.The restoration of the protolitic properties and tectonic setting of these inherited zircons opens a new way for us to study the stability and deep processes of the North China Craton before the Early Cretaceous.The cause of these inherited zircons were researched in details in this paper.Genetic mineralogy is the main research method.Through the morphological,compositional typomorphic characteristics of inherited zircons and detailed analysis of the chronology,Lu–Hf isotope,the inversion of the original rock information were made,and explore the tectono-magmatic activity features of the central North China Craton during Late Paleozoic and Early Mesozoic and its relationship with the North China Craton destructio.The mechanism and process of the destruction of the North China Craton were further examined and discussed.The crystallization ages of zircons from the early Cretaceous intrusive rocks in Han-Xing area are reported 96 data are inherited Zircons.The morphological and compositional typomorphic studies of these inherited zircons show that they are short columnar,elliptic and long columnar,with an length-width ratio of 1-2.5 and an obvious oscillating ring texture,and the Th/U ratio is much higher than 0.1,indicating obvious magmatic origin.According to the classification regression tree,the protolitic rock types of inherited zircons are mainly diorite and granite（Si O₂<65%and70-75%Si O₂）,a few samples belong to syenite,syenite pegmatite and carbonate.The results show that the Si O₂content of the 200-550 Ma zircon equilibrium melt（protolite）ranges from 53.60 to 88.91 wt.%,with an average of 63.41 wt.%.The Si O₂content of the 700-2700 Ma zircon equilibrium melt（protite）ranges from 49.74 to95.52 wt.%,with an average of 64.15 wt.%.The calculated results of physico-chemical conditions show that the temperature range is mainly 700-800℃,and the oxygen fugacity ranges from-5 to-25.The inherited zircons with U-Pb age of200-400 Ma have higher temperature and lower oxygen fugacity than the older zircons with U-Pb age of 1800-2500 Ma.The peak ages of the measured zircons are～230 Ma,～1.85 Ga,～2.5Ga.In addition,there are～255 Ma,～285Ma,～320 Ma,～426 Ma and 520 Ma age groups.Some Neoproterozoic and Mesoproterozoic inherited zircons can also be observed.We conclude that the inherited zircons of the～230 Ma age group may have formed during the magmatism after the collision of the South China and North China plates.The formation of inherited zircons of～255 Ma,～285Ma and～320 Ma age groups may be related to the Late Paleozoic magmatism of the Andean continental margin in the northern margin of the North China Craton.Two groups of inherited zircons,～426Ma and 520 Ma,may have crystallized during thermal disturbances deep in the lithosphere of adjacent landmasses triggered by the global event of the merging of ancient continents.Inherited zircons of～2.5 Ga age group indicate the existence of2.5 Ga Precambrian basement,TTG granitic gneiss,in the depth of the Han-Xing area.The inherited zircons of～1.85 Ga age group recorded the main event of collision and merging of the eastern and western landmasses of the North China Craton.The ages of these inherited zircons suggest that the lithosphere of the North China Craton underwent episodic transformation at least during the Paleozoic.Thus,its evolution is likely to be long-term,episodic,and gradual.According to the discriminant map of zircon trace element tectonic background,all the measured inherited zircons belong to continental zircons and originated in continental arc background.Crustal thickness calculation results show that the crust thickness of Han-Xing area during the early Paleozoic is about 80 km,lithosphere,which is thinning to about 40 km from Permian to Triassi,,suggests that the North China Craton began to lose its stable tectonic properties during the Late Paleozoic to Early Mesozoic.