HR: 13:45h
AN: T13E-01 INVITED     [Abstracts]
TI: The making and remaking of the North China Block
AU: * Li, Z X
EM: zli@tsrc.uwa.edu.au
AF: Tectonics Special Research Centre, The University of Western Australia, Crawley, WA 6009 Australia
AB: The North China Block (NCB) consists of two major Archaean crustal nuclei that collided together by ca. 1800 Ma (e.g., Zhao, 2001), although some argue that they came together as early as ca. 2500 Ma (e.g., Zhai and Liu, 2003; Kusky and Li, 2004). No orogenic event is known within the NCB from ca. 1800 Ma until Permian. The shape and lithospheric architecture of this seemingly stable continental block were significantly reworked by Mesozoic-Cenozoic events. Continental collision between the NCB and South China Block (SCB) started from their eastern ends as early as Permian, leading to the initial continental subduction and subsequent exhumation of 240-235 Ma UHP metamorphic rocks (e.g., Hacker et al., 2000; Ayers et al., 2002) to the crustal level by ca. 220 Ma (Hacker et al., 2000). This was followed by the development of flake tectonics in the region east of the Tanlu Fault between Late Triassic and mid-Jurassic (Li, 1994, 1998), where the lower crust and lithospheric mantle of the SCB continued to subduct beneath the NCB, whereas the upper crust of the SCB, along with the UHP rocks at the upper crustal level along the former plate margin, were obducted over the lower crust of the NCB for up to 500 km. We thus have a composite crust in the Sulu-Yellow Sea-central Korea region. Extensive thin- to thick-skinned thrusting also developed in both the Jiao-Liao region east of the Tanlu Fault and the Xu-Huai and Luxi regions west of the Tanlu Fault during this process, all within the upper crust of the NCB. This complex crustal architecture may still influence distribution of epicentres in the region. Late Jurassic-Cretaceous thin-skinned thrusts were well developed along northern NCB (e.g., Davis et al., 1998) possibly due to the closure of the Mongolo-Okhotsk sea to the north. For reasons still being debated, eastern NCB underwent dramatic lithospheric thinning (locally total erosion of lithospheric mantle?) during the Cretaceous and early Tertiary (e.g., O'Reilly et al., 2001). Although new (still very thin) mantle lithosphere was subsequently regenerated in this region, lithospheric thinning continues today in central NCB (Xu et al., 2004). This significantly thinned (80-60 km) lithosphere may be partly responsible for the abnormally high intra-plate seismicity in the region.
DE: 8102 Continental contractional orogenic belts
DE: 8110 Continental tectonics--general (0905)
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting