Tectonic Framework And Tectonic Evolution Of The Shandong Province

The position of Shandong province locate in east of China continente.Its geological structure is complicated.Its tectonic evolution can be divided into the early Precambrian stage,Meso- to Neoproterozoic stage,Paleozoic stage and Meso- to Cenozoic stage.There are three Early Pre-Cambrian micro-continental blocks consisting the basement of Shandong Province.they are Jiaoliao(Ludong),Bolu(Luxi),and Qianhuai(Dezhou).All of them have a complicated evolution history.In ca.2.8 Ga,Yishui Paleo-continental core of the Qianhuai and Tangjiazhuang Paleo-continental core of the Bolu formed,likely resulting from island-arc-like activation.During ca.2.8～2.7Ga,infantile oceanic crust appeared in Luxi area due to lithosphere extension,evidenced by occurrence of komatiite and pillow basalt.During ca.2.7～2.56Ga,the infantile ocean crust subducted under the continental core,giving rise to the Ludong and Luxi continental arcs respectively,which are indicated by the intrusion of the earlier stage TTG granite.By this process,the Luxi and Ludong infantile ensialic continental crust formed.The subsequent arc-continent collision at ca.2.56～2.4Ga has led to a large amount of collision-type plutons including later stage TTG granite and monzonitic granites.At this time, the Shandong crust evolved into semi-mature ones.The Paleoproterozoic anatectic magmatic activity completely matured the Shandong continental crust.During ca.2.4～2.1Ga,the matured Shandong continental crust experienced strongly extension,resulting in Sihaishan A-type grannite in the Luxi area and rift-related magma activity and sediments in the Ludong area.At ca.2.1～1.9Ga,the Ludong rift closed suggesting the completion of the cratonization in Shandong Province.Above mentioned cratonization resulted in two different cratons with different evolutional history: the Luxi belongs to the North China Craton and Ludong to the Dabie-Sulu orogenic belt at Mesoproterozoic and Neoproterozoic era.At Early Mesoproterozoic(1.84～1.72 Ma),crustal extension of the Luxi craton resulted in the Jining rift-type sedimentation and the first stage marie dike Swarm.Another crust extension occurred at Late Mesoproterozoic(1.2～1.05 Ma),the Haiyangsuo mantle-sourced magmatic rocks developed in the Ludong area,and the second stage mafic dyke swarm occurred in the Luxi area.During the early and middle period of Neoproterozoic(0.9～0.73 Ma),syncollision S-type and I-type granites and widespread compressional structures suggest a strong collision occurring in the Ludong area,resulting in the great Sulu collision orogenic belt.The Yishui basin as the foreland one,developed in the northwest of the Sulu orogenic belt.The collision might end at Late Neoproterozoic,being suggested by the emergence of Lanshantou A-type granite,and Penglai and Shiqiao basins which were superposed upon the orogenic belt.During the Paleozoic period,the Shandong Province might consisted of three tectonic units:the North China shallow marine basin(west Shandong),a passive continental margin basin(east Shandong) and the Dabie-Sulu rift basin(southeast Shandong).Whole-area scale outcropping of the early Paleozoic strata suggests a whole-area-scale subsidence synchronously in the Luxi area at the early Paleozoic.The most significant sedimentary facies includes platform,tidal flat,and lagoon facies,implying the earlier Paleozoic subsidence was quite slow.The absence of the Upper Ordovician to Devonian strata in the Luxi area suggests regional scale uplift during this period.Since the Late Carboniferous,a new continental basin developed overlapping the earlier Paleozoic strata,where deposited meta-platform,deltaic,tidal flat,and lagoon facies limestone,dark arenited mudstone,and coal bed.The development of the Late Paleozoic basin indicates a complete transformation of the paleogeography from the marine to terrestrial ones.The Palaeozoic sediments in the Ludong area were completely eroded during the Mesozoic uplifting;sparse information comes from provenance analyses on the strata of the Mesozoic basin. In the Mesozoic and Cenozoic period,Shandong Province totally belongs to the circum-Pacific foreland depression belt and the circum-Pacific magmatic province,which is consisted of sub-units as bellow:Bohaiwan basin,Luzhong Rise,Mengyin basin groups,Jining depression,Yishu rift,Jiaobei Rise, Jiaolai basin,Ludong exhumed UHP(ultrahigh pressure metamorphic) belt,and Subei exhumed HP belt (high pressure metamorphic belt).The Early Triassic collision between the south China and North China plates given raise the Sulu collision orogenic belt.During the Late Triassic,high potassium calc-alkaline granites intruded into the orogenic belt,which sourced from enriched lithosphere mantle,and indicated the beginning of post-orogen extensional collapse.In the Jurassic,Adakite-like high Sr granite developed in the Ludong area.Meanwhile,a series of extensional basins developed in the Luxi area,indicating locally crustal subsidence alternative with adjacent rising.The rising was accompanied by a suit of high Mg basic to andesitic intrusions.In the last stage of the Late Jurassic,the Yishu fault system began to sliding in sinistral manner.Intensive Cretaceous magmatic activity suggests the beginning of another thermo-tectonic event in the Shandong Province.The widespread Cretaceous igneous rock have the same geochemical features as those formed under back-arc spreading setting.The spreading-related magmatic activation ended in the appearing of the Laoshan A-type granite.From the Triassic to Cretaceous,the mantle of the Shandong province changed from the EMⅠ- to EMⅡ- type although it remained enriched.Also due to the westward subduction of the Pacific Ocean plate,significant sinistral movement occurred along the Tanlu fault system.Besides the sinistral displacement,large amount of plume-like,chess-board-like fault systems,and multi-level detachment developed within the two displaced fault-wall blocks.Meanwhile, several sag basins formed due to the detachments,resulting in ridge-basin structures.During the Cenozoic, the major tectonic grains of Shandong Province are basins that were controlled by boundary faults.Part of the boundary faults are re-active ones,while the other are newly formed.The formation of the Cenozoic basins is accompanied by basaltic volcano eruption.