Seismic Evidence for a Mantle Transition Zone Origin of the Wudalianchi and Halaha Volcanoes in Northeast China

Abstract

There exists much debate about origins of Cretaceous to present volcanism in northeast (NE) China. Here we present high‐resolution seismic images of the upper mantle beneath NE China obtained by inverting P wave traveltime data recorded by two dense linear arrays. The inclusion of the new data set has greatly improved sampling of the upper mantle beneath the study region, providing tight constraints on the seismic structure under the intraplate Wudalianchi and Halaha volcanoes. Local‐scale low P wave velocity (low‐Vp) anomalies are revealed in the shallow mantle beneath the two volcanoes, whereas a large‐scale high‐Vp zone is imaged in the mantle transition zone. These new results suggest that the two volcanoes, though located at different sites above the stagnant Pacific slab in the mantle transition zone, are likely related to the deep subduction and dehydration of the Pacific slab, possibly through hot and wet upwelling in the big mantle wedge beneath Wudalianchi and through deeper hydrous upwelling related to slab avalanche beneath Halaha. Our results also reveal other striking features, such as high‐Vp anomalies resting atop the 410‐km discontinuity beneath the Great Xing'an Range and the Songliao Basin, which are attributed to detached continental lithosphere. The delamination most likely occurred in the Cretaceous, which induced widespread magmatism in NE China.

Hot, volatile‐poor, and oxidized magmatism above the stagnant Pacific plate in Eastern China in the Cenozoic

“…Upwelling from the mantle transition zone and lower upper mantle or the deep mantle has also been proposed to have been active for >15 Ma, and thus for the entire younger Cenozoic (i.e., Quaternary and Neogene; Kimura et al, ; Kuritani et al, , ; Tang et al, ; Wang et al, ; Xu et al, ). The present‐day mantle above the stagnant plate, the so‐called big mantle wedge ‐ and also the upper mantle beyond it to the west and the lower mantle ‐ shows large‐scale dV S and dV P anomalies of mostly ≤ ±3% and ±2% (Figure b; Chen et al, ; Huang & Zhao, ; Kimura et al, ; Tang et al, ; Wei et al, ). The upper mantle seismic anomalies compare in intensity to those of, for example, the Yellowstone mantle plume ( dV S =−4 to +2%, dV P =−2 to +1%; Waite et al, 2006), but they are small compared to velocity variations in volcanic arc systems (with velocity anomalies of commonly up to ±10%; Widiyantoro et al, ).…”

“…Several of the low‐velocity anomalies beneath Eastern China unquestionably extend from the top of the mantle transition zone to the surface, while it remains debated if they also locally connect through slab gaps to the lower mantle (Chen et al, ; Tang et al, ; Wei et al, ), or if they connect to a deep mantle plume (i.e., the Datong mantle plume; Kimura et al, ). The large scale of the seismic anomalies in the upper mantle (Figure ) and vertical mantle flow velocities (≤4 cm/year; Cheng et al, ) highlight that the presently observed anomalies must have developed >10 Ma ago.…”

“…Seismic tomography as sketched in the profile shows the stagnant subducted slab of the Pacific plate with a possible slab break. The stagnant Pacific plate is characterized by high seismic velocities anomalies ( dV P ≥+1%), while the big mantle wedge above shows several low‐velocity seismic anomalies ( dV P ≤−1%; see also Fukao et al, ; Huang & Zhao, ; Wei et al, ). Note that the near‐surface low‐ V P anomalies image crustal lithologies.…”

“…Seismic tomography reveals that the Pacific plate, subducted along the Japan‐Izu‐Bonin‐Mariana arc, stagnates in the mantle transition zone below Eastern China, Russia, and the Koreas, currently extending for >1,500 km beyond the arc (Figure ; Fukao et al, ; Huang & Zhao, ; Zhao, ). Low S and P wave velocity anomalies extend from the top of the mantle transition zone, and possibly from the deep mantle, to several of the Cenozoic volcanic centers (e.g., at Changbaishan, Wudalianchi, Halaha; Figure a), suggesting a close relation between the mantle transition zone and the wide‐spread volcanism (Chen et al, ; Huang & Zhao, ; Kimura et al, ; Tang et al, ; Wei et al, ; Zhao, ). Many geochemical studies have further shown that enriched mantle components play an important role in the formation of the magmas, which are thought to derive from the stagnant Pacific slab and/or from ancient subducted slabs (Kimura et al, ; Kuritani et al, , ; Tang et al, ; Wang et al, ; Xu et al, ).…”

“…The low P and S wave velocity ( V P and V S ) anomalies that are linked to Eastern China's volcanism have been interpreted to delineate hydrous and hot mantle upwelling (Chen et al, ; Huang & Zhao, ; Wei et al, ; Zhao, ), as global electromagnetic induction studies indicate that the mantle transition zone is extremely wet with ~0.1–0.4 wt% H 2 O or more, with volatiles derived from the dehydration of the stagnant Pacific and ancient slabs (Kelbert et al, ). Interpreting the record of seismic wave velocity anomalies is, however, far from straightforward.…”