Font Size: a A A

The Tectonic Implication Of Changchun-Yanji Suture Zone:Constraints Of The Mesozoic Accectionary Complex

Posted on:2021-03-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:J L CaoFull Text:PDF
GTID:1360330611471944Subject:Structural geology
Abstract/Summary:PDF Full Text Request
The northeast China located among the North China Craton,the Siberia Craton and the Pacific plate.As this region was not only influenced by the collision of Paleo-Asian Ocean during the Paleozoic,but also influenced by the subduction of Pacific plate along the eastern margin of Asian Continent.Changchun-Yanji Suture Zone,or the Changchun-Yanji Accretionary Complex Belt,is a subduction-accretion complex and formed at the collisional belt between the Jiamusi-Khanka Block and the North China Craton.This is an ideal area for geologists to study the evolution and transformation of Paleo-Asian Ocean and Paleo-Pacific tectonic implication.Yantongshan Complex is one of the important part of Changchun-Yanji suture zone,we focus on the provenance characteristics and U-Pb ages of the piemontite-bearing chert,combined with the metamorphic p-t condition and Paleontology data to discuss the final collision of the Jiamusi-Khanka Block and the North China Craton.Through the field geological survey,the intense deformation of the rocks and resulting destruction of the original sedimentary sequence indicate that most of the Paleozoic strata in theis region might be tectonic mélange without any significance for the traditional stratigraphic division and correlation.The typical metamorphic mineral assemblages: Quartz + Muscovite + Piedmontite + Garnet + Feldspar.Which muscovite can indicate the rock pressure environment,the electron microprobe analyzes show that the muscovite is Phengite,it should be the product of high-pressure metamorphism.The white mica can indicate the rock pressure environment,electron probe analysis shows that the white mica Si?3.305(based on the oxygen = 11),which white mica as silica white mica,as a product of high pressure metamorphism,to prove that the experience of high pressure reaction.The piedmontite schist LA-ICP-MS U-Pb datas result shows that the minimum age is for the 237 Ma,according to the protolith age is formed on indosinian epoch;The ~498Ma ages indicate the North China Khondalite Blet and the maximum age is for the 1808 Ma,the existence of the ancient basement of information for the northeast region.Combining with the weighted average of the felsic vein age is 217±5 Ma(MSWD=0.37),the final closure timing of the Changchun-Yanji suture zone should be at he Middle Triassic,and not Late Paleozoic or more early as previously considered.The Seluohe group is not a complete rock-stratigraphic unit,but a set of tectonic mélange.The main lithology of the formation of the Seluohe group includes: complex sandstone,chlorite schist,mica schist,mica quartz schist and metamorphic andesite.The formation time of the Seluohe group was not in the middle Neoproterozoic as previously thought,but in the late Permian,with a time of 253.0±3.3 Ma.The tectonic melanges of the seluohe group were formed in a mature island arc environment,indicating that the area where the Seluohe group is located was subjected to plate subduction at the end of the late Permian,and the ancient Asian ocean was not completely closed before that.The Dajianggang Formation is located in the Changchun-Yanji suture zone of central Jilin Province and unconformably overlies the Changchun-Yanji Accretionary Complex,which is a mélange resulting from subduction of the Jiamusi-Khanka Block beneath the North China Craton.The samples were collected from the bottom part of the standard section-?the Xiaoshipeng-Paodingzi section?.As shown by cathodoluminescence(CL)images,the detrital zircons are mostly the stubby to elongate in shape with magmatogenic oscillatory zonings.Their chondrite-normalized patterns mostly share similar characteristics,with enriched LREE and flat HREE and the Th/U ratios ranging from 0.15~2.50,indicating the magmatic origin as well.LA-MC-ICP-MS U-Pb dating of detrital zircon from four samples of the formation yields ages of 2516 to 216 Ma.Zircons with U-Pb ages at 2516-2501 Ma and 1897-1832 Ma indicate a provenance from Precambrian basement rocks of the NCC.The 525-482 Ma ages indicate a provenance from metamorphic rocks of Late Pan-African age in the JKB that have a tectonic affinity to the Central Asian Orogenic Belt(CAOB).Zircon grains with ages of 383-314 Ma and 275-250 Ma were likely derived from the underlying Changchun-Yanji suture zone.The youngest population has a peak age of ca.225 Ma,which together with Late Triassic fossils,suggests that deposition of the Dajianggang Formation was Late Triassic or younger.This result supports the view that the final collision of the Jiamusi-Khanka Block and North China Craton along the Changchun-Yanji suture zone took place before the Late Triassic,indicating the final closure timing is before the deposition of the Late Triassic Dajianggang Formation.According the regional tectonic analyses,the Changchun-Yanji suture zone is not eastern segment of the Tianshan-Beishan-Xra-Moron-Changchun suture zone,but the southern segment of the Jilin-Heilongjiang High-pressure Metamorphic Belt(Ji-Hei HP Belt).The Ji-Hei HP Belt did not result from subduction between the Siberia and North China cratons within the Paleo-Asian Ocean,but instead was due to subduction of the Pacific Ocean from the east.The Triassic is thus the time when major north-south subduction in the Central Asian Orogenic Belt had ceased and westward-directed Pacific Ocean plate subduction commenced in NE China.We propose a tectonic model for Paleo-Pacific Plate subduction–accretion along the Changchun–Yanji suture zone as follows.1)subduction-accretion(240-220Ma),the Jiamusi-Khanka Block driffed westward due to he subduction of the Pacific Plate,and occured along the Changchun-Yanji suture zone;2)orogenesis-denudation(220-180Ma),scissors collage occurred between the Jiamusi-Khanka Block and Songliao Block,causing the orogenesis-denudation in the Changchun-Yanji suture zone and molasse deposition.
Keywords/Search Tags:Mesozoic Accretionary Complex, Changchun-Yanji suture zone, Paleo-Pacific plate, Central Asian Orogenic Belt, Eastern Margin of the Eurasia
PDF Full Text Request
Related items