Mantle dynamics of the reactivating North China Craton: Constraints from the topographies of the 410-km and 660-km discontinuities

Abstract

The topographies of the 410-km and 660-km discontinuities have important implications for mantle dynamics. Here we present high-resolution seismic imaging of the 410-km and 660-km discontinuities beneath the North China Craton (NCC) employing the receiver function method. Depth anomalies (deeper or shallower than the global average depths) at both discontinuities were detected by introducing a three-dimensional regional velocity model. The depressions of the 410-km discontinuity are mostly located in the eastern NCC. A local elevation of the 660-km discontinuity appeared in the northwest of the NCC and a significant depression of the 660-km discontinuity is located in the southeast of the NCC. Two dynamic mantle regimes are speculated to explain the formation of the anomalous depth zones in the NCC. One possibility is a complex mantle upwelling linked to edge-derived convection between the stagnant slab and the thick cratonic root. The other potential dynamic regime is slab stagnating, sinking, and induced upwelling at the neighboring slab front. These regimes hint that the mantle flow was possibly dominated by dynamic interactions among the subducting slab, cratonic root, and ambient mantle beneath the NCC. 410-km discontinuity, 660-km discontinuity, receiver function imaging, dynamic mantle regime, North China Craton Citation:Xu W W, Zheng T Y, Zhao L. Mantle dynamics of the reactivating North China Craton: Constraints from the topographies of the 410-km and 660-km discontinuities.The mantle transition zone (MTZ) is a hallmark structure of the mantle with important implications for geodynamics. The top and bottom discontinuities of the MTZ have been demonstrated by laboratory experiments to represent pressure-induced mineral phase transitions of olivine to wadsleyite at ~410 km and of ringwoodite to perovskite and magnesiowustite at ~660 km, respectively [1-4]. Changes in temperature or composition shift the pressure of the mineral phase transition, creating the topography of the velocity discontinuity [5,6], which can be used as an indicator of mantle dynamics. The thickened MTZ underlain by a depressed 660-km discontinuity has been generally found to occur near subduction zones and attributed to the stagnancy of the subducted slab or remnants of detached oceanic lithosphere [7][8][9][10][11][12]. The slightly thinned MTZ beneath ridges and hotspots has been attributed to the influence of thermal plumes [13,14]. Seismic-related observations of the 410-km discontinuity (hereafter referred to as 410-) have been used to interpret lateral variations in temperature and water content in the MTZ [14][15][16][17]. The "transition zone water filter" hypothesis predicts that a spatially localized layer of melt, resulting from the difference in water solubility between the MTZ and the overlying upper mantle, may pool atop the 410- [15]. The observed low-velocity layer above the 410-suggests an association between the velocity decrement and

The bending mechanism of Anping ground fissure in the Hebei Plain, North China

“…Since Pliocene or earlier, the inherited regional tectonic stress characteristics led to the formation of an NW-SE stretching stress environment (Zhang et al 2003;Zhu et al 2013). The deep substances migrated eastward owing to the control of the long-range effect of the Indian Plate, while the upper-mantle substances upwelled owing to the blocking effect (subduction) of the Pacific-Philippine Plate (Xu et al 2011). The North China basin depression as well as the normal fractures of its major faults was formed under this background (Jia et al 2014).…”

Timing, scale and mechanism of the destruction of the North China Craton

“…It has long been realized that the structure of major discontinuities in the Earth's deep interior is of key importance in the context of plate tectonics and mantle dynamics, and therefore is pivotal to unraveling the deep processes and mechanisms of cratonic destruction. Based on the dense seismic array data, the discontinuity structure of the mantle transition zone beneath the NCC has been carefully investigated and imaged [42][43][44][45]. The imaging results show that the thickness of the mantle transition zone varies sharply at around the boundary between the eastern and central NCC, which coincides with an obvious variation in the structural features of the lower boundary of the mantle transition zone (the 660-km discontinuity) (Figure 3(a)).…”

“…The newly constructed seismic images reveal a close correspondence between the geographic scope of lithospheric modification and destruction and the surface geological structures as well as the morphology of the stagnant Pacific slab in the mantle transition zone beneath the NCC (Figures 2 and 3). The striking structural features suggest that the subduction process of the Pacific Plate has strongly affected the entire upper mantle and the overlying lithosphere system of the eastern NCC in a coupled manner [45]. The Pacific subduction may have caused unsteady mantle flow, which resulted in a highly heterogeneous discontinuity structure of the mantle transition zone; the continuous subduction probably also led to partial penetration of the stagnant slab into the lower mantle, decompression melting and upward migration of hot mantle materials.…”

Crustal thickness and vP/vS ratio in Shanxi Graben, China

“…Many studies have shown that there are regional variations of rock compositions and velocity structure in the crust and the upper mantle in the North China Craton (Gao et al 2010;Xu et al 2011). At present, there are two controversial hypotheses about what leads to the destruction in the NCC: one is plate edge effect caused by plate movement (Gao et al 2002;Wu et al 2005), and the other is driven primarily by plate basal force associated with smallscale mantle convection (Xu 2001).…”