Geological Records Of The Late Silurian-Devonian Arc-continent Collision In The Northern Margin Of The North China Block And Craton-orogen Boundary

The northern margin of the North China Block(NCB)consists of the Bainaimiao arc belt in the north and northern margin of the North China Craton(NCC)in the south,and the Bayan Obo-Duolun-Chifeng-Kaiyuan fault was considered as the boundary between these two east-west trending tectonic units.The Bainaimiao arc belt was regarded as a continental arc in an active continental margin of the NCC or Japan-style island arc.However,recent researches suggest that it was an early Paleozoic island arc characterized by distinct tectonic history and basement compositions with the northern NCC and was accreted to the northern NCC in the late Silurian-early Devonian by arc-continent collision.The origin and evolution of the Bainaimiao arc belt are well constrained in present,but the tectonic process of arc-continent is still not clear.Moreover,the Bayan Obo-Duolun-Chifeng-Kaiyuan fault was considered as the northern boundary of the NCC and separated the Bainaimiao arc belt from the northern NCC.However,the location of this boundary from Duolun to Chifeng have not been well constrained due to poor occurrence of outcrops,especially in some study areas located at the junction of the craton and orogen.To resolve the above scientific problems,two main contents are carried out in this thesis basis on the existing researches:(1)the sedimentation,magmatism,metamorphism and tectonic deformation in syn-collisional stage,as well as alkaline magmatic belt and bimodal volcanic rocks developed in post-collisional stage related to arc-continent collision are systematically summarized and studied;(2)some key study areas located at the boundary of the craton and orogen are selected,and the boundary position of the two tectonic units is precisely defined by rock assemblages and Nd-Hf isotopic composition of the magmatic rocks.The main advancements obtained from this thesis are as follows:1.The early Paleozoic arc-island intrusive and volcanic-sedimentary rocks were widely unconformably overlain by the Xibiehe Formation in the north Bayan Obo-Damaoqi area.U-Pb geochronology of detrital zircons indicate that the Xibiehe Formation formed during the late Silurian-early Devonian period,and this unconformable relationship is considered as the sedimentation evidence of the arc-continent collision.2.The metamorphism connected with the arc-continent collision was firstly identified from metamorphic sedimentary rocks that formed the early Paleozoic period in the north Bayan Obo-Damaoqi area,and the time of arc-continent is constrained at ?420 Ma based on the monazite LA-ICP-MS U-Pb dating.3.New zircon U-Pb dating identified bimodal volcanic rocks formed the early-middle Devonian period from the metamorphic volcanic-sedimentary rocks that were previously considered as the early Palaeozoic in age in Jiefangyingzi area.The occurrences of Devonian bimodal volcanic rocks,combined with the Devonian alkaline magmatic belt,suggesting that the northern margin of the NCB was a post-collisional extension environment during the early-middle Devonian period.4.The occurrences of Neoarchean basement rocks,combined with previous Nd-Hf isotopic data of the late Paleozoic magmatic rocks,suggesting that the Jiefangyingzi area has a tectonic affinity with the Eastern Block of the NCC rather than the Bainaimiao arc belt.5.Analyzing and comparing the Nd-Hf isotopic compositions of the Permian-early Triassic felsic magmatic rocks that widely distributed from the north Chifeng and adjacent region in the middle part of the northern margin of the NCB,which provide new constraints on the boundary of the craton-orogen in these areas.