North China Craton mainly metamorphic core complex Late Mesozoic granites, genetic type and significance of contrast

Title: North China Craton mainly metamorphic core complex Late Mesozoic granites, genetic type and significance of contrastAuthor: Ouyang Zhi XiaDegree awarded: Chinese Academy of Geological SciencesKeywords: zircon U-Pb geochronology;; geochemistry;; granite;; late Mesozoic;; metamorphic core complex;; North China CratonSummary:Since the Mesozoic, East Asia, especially North China Craton occurred in large-scale crustal extension, metamorphic core complex this issue is typical of Neodymium Magnets the role of crustal extension. Extensional and magmatic activity close relationship between the space-time the vast majority of the characteristics of metamorphic core complexes, almost all of the metamorphic core complex of the nuclear department have different periods of granitic intrusive rocks. Currently, these granite geochronological framework, a combination of rock types, causes the evolution of a lack of systematic research and comprehensive analysis and comparison, especially with the relationship between metamorphic core complex is not very clear, stretching and magmatic events of the entire relationship between the lack of overall understanding. Carry out these research and study can be no doubt that a comprehensive understanding of the development of metamorphic core complex formation time, and provide new information and valuable reference.This paper selected the North China craton Yunmengshan, trouble shops, Yiwulvshan and southern Liaoning four major metamorphic core complex in Mesozoic granites of the study, based on the previous work by the deformation characteristics of these granites, zircon U-Pb zircon geochronology, major, trace element geochemistry of the comprehensive analysis and comparative studies, with some success.1) obtain a new zircon U-Pb ages: the use of LA-MC-ICPMS zircon U-Pb method to obtain Yunmengshan metamorphic core complex north of Feng Jiayu rock age of 126.6 ± 1.8Ma, west valley lotus ring age of the inner ring-shaped rock 122.5 ± 1.8Ma, cypress fork rock age of 127.4 ± 1.2Ma, which cut off the rock rock foliation and lineation of regional and rock itself is not deformed, their age may representatives Yunmengshan metamorphic core complex activities limit. Using SHRIMP zircon U-Pb method to obtain trouble shops metamorphic core complex core of settled camp rock age of the child 124.8 ± 2.4Ma, Ma On Shan rock age of 155.9 ± 1.6Ma, further confirmation of these two rocks formed in the late Mesozoic; using LA-MC-ICPMS zircon U-Pb method to obtain trouble shop area of ​​the original 1:50000 regional geological survey in the late Mesozoic age rocks between the 204-232Ma, indicating that these rocks formed in the Early Mesozoic , not the original that the late Mesozoic. Using SHRIMP zircon U-Pb method to obtain metamorphic core complex in southern Liaoning Jinzhou detachment fault in the mylonitic granite veins at the age of 129 ± 2Ma, limits the metamorphic core complex in southern Liaoning lower activity.2) According to previous data collected and measured the age, the initial establishment of the various core complex evolution of the geochronological framework of granite, metamorphic core complex in Mesozoic granites mainly developed in the 175-113Ma, which can be divided into three: 175-141Ma ,135-120Ma and 113Ma, of which ,165-150Ma ,130-120Ma for the two distinct peak.Through the main, trace geochemical study and compare the system to determine the metamorphic core complex in Mesozoic granitic rocks are similar, rocks are mainly K-feldspar granite - monzogranite, generally shows metaluminous - weakly peraluminous quality, high-K calc-alkaline, high-Sr granite features; rare earth elements are relatively enriched in light rare earth elements display overall, weight loss is relatively rare and do not have significant negative Eu anomaly; trace elements showed relative enrichment LREE, LILE elements and loss of HFSE, with Ta-Nb-Ti negative anomalies. Among the early (175-141Ma) granites late stage (135-123Ma) high-silica, alkali-rich (K2O + Na2O), aluminum index (A / CNK or ASI) is high; early granite appears as iron, compared with late magnesium; late granite REE and trace elements than the total rare earth element fractionation and the early high is more obvious.Core complex in Mesozoic granites are mainly I-type granite, IA transition-type granites, as well as a small amount of S-type granites. SI type granite granite display of early transition characteristics of late granite shows the characteristics of the transition type IA. Reflect the nature of the source area Nb / La, Nd / Th, Ti / Y values, Ti / Zr, Nb / Ta and Zr / Hf values ​​mostly in the mantle-derived rocks and continental crust values ​​between the values ​​in a large range of . Combined with previous data to determine a preliminary study of the Late Mesozoic granites is not a single source, the source region of mantle-derived components should have the participation of crustal components. http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets These characteristics of metamorphic core complex extrusion thickening - relaxation - Melt - extensional collapse of the genetic mechanism and provide support.3) Preliminary studies and summarizes the deformation characteristics of these granites by strongly deformed rock and not chronological study of rock deformation, generally limited to the different core complex extension of time limit: Yunmengshan metamorphic core complex should limit activities between 144-123Ma; trouble shops metamorphic core complex activities, time should be between 150-124Ma; Yiwulvshan metamorphic core complex of activities between the time in the 163-123Ma; metamorphic core complex in southern Liaoning activity time in the 129 - 113Ma between. The study developed a comprehensive understanding of the history of extensional tectonics, crustal extension time limit as well as the precise limits of lithosphere and crustal thinning and craton destruction provided the time to construct new evidence.4) The above study, further confirmed the previous understanding that the 165-150Ma granite magmatism may occur in the context of the thickened crust, deep crustal thinning may begin at 150Ma, 130Ma-110Ma reach the peak, to metamorphic core complex area of ​​rapid uplift and emergence of A-type granites characterized. The study area are between 165-120Ma granite high Sr and low Y magmatic activity, pre-165-150Ma, may squeeze caused by thrusting the thick crust, thick crust so that the temperature gradient increases, warming the lower crust partial melting, magma mixing to the granite part of the early transition-type granites with SI characteristics; 150-120Ma, although the deep crustal thinning process has started strong, you can still produce from deeper crustal level granitic magma, part of the areas due to the heterogeneity of crustal thickness, resulting in A-type granite; 125Ma so, with the cooling metamorphic core complex uplift and erosion, may start with a deep mantle-derived magma underplating, A-type granites in large numbers.Degree Year: 2010