HR: 08:35h
AN: T31E-03    [Abstracts]
TI: The Late Paleozoic- Early Mesozoic tectonomagmatic activities in the Yanshan belt: implications for the Mesozoic intraplate deformation
AU: * Zhang, S
EM: tozhangshuanhong@163.com
AF: Institute of Geomechanics, Chinese Academy of Geological Sciences, No.11 Minzudaxue Nan Road, Haidian District, Beijing, 100081 China
AU: Zhao, Y
AF: Institute of Geomechanics, Chinese Academy of Geological Sciences, No.11 Minzudaxue Nan Road, Haidian District, Beijing, 100081 China
AU: Song, B
AF: Beijing SHRIMP center and Institute of Geology, Chinese Academy of Geological Sciences, No.26 Baiwanzhuang Road, Xicheng District, Beijing, 100037 China
AU: Hu, J
AF: Institute of Geomechanics, Chinese Academy of Geological Sciences, No.11 Minzudaxue Nan Road, Haidian District, Beijing, 100081 China
AU: Xu, G
AF: Institute of Geomechanics, Chinese Academy of Geological Sciences, No.11 Minzudaxue Nan Road, Haidian District, Beijing, 100081 China
AU: Wu, H
AF: Geological Information Center, Ministry of Land and Resource, Yanjiao, Hebei Province, Sanhe, 065201 China
AU: Liu, J
AF: Institute of Geomechanics, Chinese Academy of Geological Sciences, No.11 Minzudaxue Nan Road, Haidian District, Beijing, 100081 China
AU: Pei, J
AF: Institute of Geomechanics, Chinese Academy of Geological Sciences, No.11 Minzudaxue Nan Road, Haidian District, Beijing, 100081 China
AB: Reactivation of pre-existing structures or thermal weakening zones associated with magmatism is very important for the localization of intraplate deformations (e. g., Holdsworth et al, 1997; D­_Lemos et al, 1997). The Yanshan tectonic belt, which is located at the northern margin of the North China block (NCB), is a typical intraplate fold-and-thrust belt in Mesozoic (Davis et al, 1998; 2001). Although much work has been done during last a few decades, the Late Paleozoic-Early Mesozoic magmatic and deformation history of the Yanshan tectonic belt is still poorly understood. Recently, several variably deformed Late Paleozoic-Early Mesozoic granitoid plutons such as Longhua quartz diorite (311 ­A2 Ma), Daguangding quartz diorite (327 ­A7 Ma), Boluonuo quartz diorite (303 ­A4 Ma), Guanglingshan granite (253 ­A4 Ma) etc. in the Yanshan belt were determined from the so-called Archean-Paleoproterozoic ­øcrystalline basement­ñ by our SHRIMP U-Pb zircon dating, which indicate that the strong magmatisms accompany with deformation occurred during Late Paleozoic to Early Mesozoic. Preliminary geochemical analysis results show that the formation of these plutons is a result of the southward subduction of the Paleo-Asian oceanic plate beneath the NCB and the collision between the Paleo-Mongolian composite terrane and the NCB. Structural analyses of the Late Paleozoic plutons and the country rocks revealed several E-W trending mylonite zones formed during Late Paleozoic-Early Mesozoic, and the inherences between the former mylonite zones and the Mesozoic regional fault zones such as the Damiao fault, the Shangyi-Chicheng fault, and the Fengning-Longhua fault, are very obvious. Because some of the mylonite zones and deformed plutons are unconformably overlain by Jurassic volcanic or sedimentary rocks, and the eldest strata overlain upon the unconformity are Lower Jurassic Nadaling Formation and Xiahuayuan Formation, they had been deformed and exhumed to surface before Early Jurassic. 40Ar-39Ar dating and deformation environment analysis results of the mylonites indicate a multistage process of deformation from Late Paleozoic to Early Mesozoic (Cui et al, 2000; Hu, et al, 2003; Zhang, 2004). These multistage deformation zones, with strong Late Paleozoic-Early Mesozoic magmatic activities, formed many pre-Mesozoic crustal heterogeneities and thermally weakened zones, which played a very important role on the initiation of the intraplate deformation in Yanshan area from Early Mesozoic (pre-180 Ma?, Davis et al, 2001). Therefore the Mesozoic Yanshan intraplate fold-and-thrust belt is developed from a Late Paleozoic plate boundary tectonic belt.
UR: http://www.agu.org/yanshan
DE: 9320 Asia
DE: 8035 Pluton emplacement
DE: 8100 TECTONOPHYSICS
DE: 8160 Rheology--general
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting