Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Multiple source downwellings beneath eastern North China revealed by 3-D CCP migration of receiver function data Jiahui Zuo a , Liwei Wang a , Fenglin Niu a,b, ⁎ a State Key Laboratory of Petroleum Resources and Prospecting, and Unconventional Petroleum Research Institute, China University of Petroleum Beijing, Beijing 102249, China b Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, USA ARTICLE INFO Keywords: Mantle discontinuities Phase transition Receiver function North China Delamination and Subduction ABSTRACT We collected and processed a total of 97,700 teleseismic receiver functions recorded by 580 broadband seismic stations from 686 earthquakes to study the mantle transition zone beneath eastern North China. We employed a recently developed 3-D P- and S-wave velocity model (the East Asia Radially Anisotropic Model, EARA2014) to compute Pds moveouts to migrate receiver function data. Amplitudes of the stacked P660s and P410s using the 3- D Pds moveout table are approximately 30% higher than those calculated from the 1-D iasp91 model. The 3-D volume of CCP (common-conversion-point) stacked images that covers the area of 110–125°E and 36–43°N revealed two remarkable mantle transition zone anomalies with significant depression of the 660-km dis- continuity. Together with other seismic observations, we speculated that these two anomalies are resulted from two different dynamic processes beneath eastern North China. 1. Introduction The North China Craton (NCC) formed in the Archean is one of the oldest continental cratons in the world. It is bound with the Xing-Meng Block to the north by the Central Asian Orogenic Belt, and with the Yangtze Block to the south by the Qinling-Dabie Belt (Fig. 1a). Tecto- nically, the craton consists of an active eastern block (ENCC) and an inactive western block (WNCC), which are separated by the Central Orogenic Belt (Fig. 1a). Global tomography studies (e.g., Megnin and Romanowicz, 2000; Grand, 2002) showed that the ENCC and the Yangtze craton to the south are the only large ancient cratons on Earth that do not have high shear velocity roots beneath them. Meanwhile, geochemical studies of xenoliths in ENCC found that the kimberlite pipes and basalts, which brought the xenoliths to the surface, erupted during two distinct time periods, first during the Ordovician and then later from the Mesozoic through the Tertiary (Menzies et al., 1993; Griffin et al., 1998; Gao et al., 2002). The Ordovician garnet peridotite xenoliths indicated that the craton had a typical depleted, cool Archean root to a depth near 200 km at ~400 Ma (Griffin et al., 1998). In contrast, abundant spinel lherzolite xenoliths brought up in Tertiary to Quaternary basalts showed a hot and relatively undepleted mantle across the ENCC (O’Reilly et al., 2001). These observations have led to the hypothesis that the mantle cratonic root has been removed beneath at least the ENCC (Menzies et al., 1993; Griffin et al., 1998; Gao et al., 2002), which is consistent with the global tomographic images. The xenolith sites are, however, spatially restricted; they could be special places where the cratonic lithosphere was displaced. The lateral and depth resolutions of the global tomographic models are also greatly limited; therefore it is unclear on the lateral extent of the removal of the cratonic lithosphere beneath ENCC. Since the Mesozoic, the craton has undergone massive extension, which is likely caused by its interaction with subduction to the east – a situation similar to what has occurred in the western United States during the Cenozoic. The subduction is also attributed to have caused the removal of the cratonic keel beneath ENCC (Windley et al., 2010; Wang et al., 2016), although details on the subduction-induced removal are still debated (Zhu et al., 2012a), partly because there is a lack of knowledge about the slab geometry beneath ENCC. Early studies of P- wave traveltime tomography (Fukao et al., 1992, 2001; Huang and Zhao, 2006) revealed a large-scale high-velocity anomaly in the mantle transition zone beneath a large portion of the ENCC. This high-velocity anomaly was interpreted as the stagnated Pacific slab that lies hor- izontally after it enters into the transition zone. Recent finite-frequency traveltime and waveform tomography studies (e.g., Obayashi et al., 2013; Tang et al., 2014; Chen et al., 2015; Tao et al., 2018), however, found that the geometry of the high-velocity anomalies inside the https://doi.org/10.1016/j.jseaes.2020.104266 Received 10 October 2019; Received in revised form 31 January 2020; Accepted 1 February 2020 ⁎ Corresponding author at: State Key Laboratory of Petroleum Resources and Prospecting, and Unconventional Petroleum Research Institute, China University of Petroleum Beijing, Beijing 102249, China. E-mail address: niu@rice.edu (F. Niu). Journal of Asian Earth Sciences 192 (2020) 104266 Available online 03 February 2020 1367-9120/ © 2020 Elsevier Ltd. All rights reserved. T