Journal of Geophysical Research: Solid Earth RESEARCH ARTICLE Craton Destruction 2: Evolution of Cratonic Lithosphere After a 10.1029/2017JB015374 Rapid Keel Delamination Event Special Section: Liang Liu1,2,3 , Jason P. Morgan2,4, Yigang Xu1 , and Martin Menzies1,2 Magnetism in the Geosciences - Advances and Perspectives 1Department of Earth Sciences, Royal Holloway University of London, Egham, UK, 2State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China, 3College of Earth 4 This article is a companion to Liu et al. Sciences, University of Chinese Academy of Sciences, Beijing, China, Department of Earth and Planetary Sciences, Harvard (2018), https://doi.org/10.1029/ University, Cambridge, MA, USA 2017JB015372. Abstract Cratonic lithosphere beneath the eastern North China Craton has undergone extensive Key Points: • Keel delamination followed by destruction since early Jurassic times (approximately 190 Ma). This is recorded in its episodic tectonic and convective erosion and lithospheric magmatic history. In this time, its lithosphere changed thickness from approximately 200 km to <60 km. This extension can explain the change was associated with a peak time (approximately 120 Ma) of lithospheric thinning and magmatism destruction of the eastern North fl China Craton that was linked with high surface heat ow recorded in rift basins. We believe that these records are best • Reactivation of an enriched mantle explained by a two-stage evolutionary process. First, approximately 100 km of cratonic “keel” underlying a layer is critical in leading to weak midlithospheric discontinuity layer (approximately 80–100 km) was rapidly removed in <10–20 Ma. delamination of cratonic bottom and – early postdelamination magmatism This keel delamination stage was followed by a protracted (approximately 50 100 Ma) period of convective • The heterogeneous lithosphere erosion and/or lithospheric extension that thinned the remaining lithosphere and continuously reworked the beneath North China can be former cratonic lithospheric mantle. This study focuses on numerical exploration of the well-recorded second produced by postdelamination ’ fi convective erosion and lithospheric stage of the eastern North China Craton s lithospheric evolution. We nd that (1) lithospheric mantle extension capped by thick crust can be locally replaced by deeper mantle material in 100 Ma due to small-scale convective erosion; (2) asthenospheric upwelling and related extension can replace lithospheric mantle over – “ ” Supporting Information: horizontal length scales of ~50 150 km, and account for observed mushroom-shaped low-velocity • Supporting Information S1 structures; (3) modeling shows conditions that could lead to the multiple eastern North China Craton • Figure S1 magmatic pulses between 190 and 115 Ma that are associated with temporal and spatial changes in magma • Movie S1 “ ” • Movie S2 source petrology and a magmatic hiatus; and (4) a wet midlithospheric discontinuity layer provides a • Movie S3 potential source material for on-craton magmatism. • Movie S4 • Movie S5 • Movie S6 • Movie S7 1. Introduction • Movie S8 • Movie S9 Cratons are generally observed to retain tectonic and magmatic quiescence for billions of years. However, some cratonic regions do record extensive crustal deformation and on-cratonic magmatism that reflect cra- Correspondence to: fi L. Liu, J. P. Morgan, and Y. Xu, ton destruction processes (Grif n et al., 1998; Menzies & Zhang, 1993). The eastern part of the North China [email protected]; Craton (ENCC) is the best-known Archaean craton to have experienced a recent destruction process [email protected]; (Griffin et al., 1998; Menzies et al., 2007; Menzies & Zhang, 1993; Xu, 2001; Xu et al., 2009; Zhu et al., 2012). [email protected] Here cratonic lithosphere (approximately 180–220 km; Griffin et al., 1998; Menzies & Zhang, 1993) was thinned to ~60–80 km between early Jurassic and early Cretaceous times (approximately ~190–115 Ma; Citation: Xu et al., 2009; Zhu, Jiang, et al., 2012). The process of the ENCC thinning was mainly reflected in the Liu, L., Morgan, J. P., Xu, Y., & Menzies, M. – “ ” – “ ” (2018). Craton destruction 2: Evolution approximately 190 155-Ma cold and 135 115-Ma hot on-cratonic magmas (Figure 1; Wu et al., 2005; of cratonic lithosphere after a rapid Zhang et al., 2014). Peak ENCC thinning occurred at approximately 120 Ma, and is apparent as widespread keel delamination event. Journal of crustal melting and formation of metamorphic core complexes (Xu et al., 2009; Zhu et al., 2012; Zhu, Jiang, Geophysical Research: Solid Earth, 123, fl 10,069–10,090. https://doi.org/10.1029/ et al., 2012; Figure 1b), rapid syn-rift surface subsidence, and high heat ow recorded in syn-rift basins 2017JB015374 (Jiang et al., 2016; Qiu et al., 2016). The modern ENCC lithospheric mantle is a reworked product after craton destruction, and is mainly composed of young asthenosphere-derived lithospheric mantle (Menzies et al., Received 21 DEC 2017 2007; Xu, 2001; Xu et al., 2009), that still contains preexisting Archean “cratonic” relics (Zhang et al., 2008; Accepted 17 JUL 2018 Accepted article online 29 JUL 2018 Zheng et al., 2001). Published online 8 NOV 2018 We think that this craton’s thinning and reworking is best understood as a two-stage evolutionary process. First, approximately 100 km of cratonic keel underlying a weak midlithospheric discontinuity layer – < – fi “ ” ©2018. American Geophysical Union. (approximately 80 100 km) was rapidly removed in 10 20 Ma. This rst stage of keel delamination is the All Rights Reserved. focus of a companion paper: Craton Destruction Part 1: Cratonic Keel Delamination; Liu et al., 2018; which we LIU ET AL. 10,069 Journal of Geophysical Research: Solid Earth 10.1029/2017JB015374 Figure 1. Geological map of the eastern North China craton (ENCC). (a) Distribution of Jurassic magmatism (approximately 190–160 Ma). (b) Distribution of Cretaceous magmatism (approximately 150–100 Ma) and major faults. See details for Cretaceous magma distribution in Figure 11. TNCO = Trans-North China Orogen, WNCC = Western North China Craton. will hereafter refer to as Part 1. A schematic cartoon of the proposed keel delamination process is shown in Figures 2a and 2b, and a video of a numerical experiment illustrating this delamination stage is shown in Supplementary Video 9. The keel delamination stage was followed by a protracted (approximately 50–100 Ma) period of small-scale convective erosion and/or lithospheric extension that thinned the remaining lithosphere and continuously reworked the former cratonic lithospheric mantle beneath the Moho. The goal of the current study is to better understand this second stage of postkeel-delamination Figure 2. Two-stage craton destruction model. (a and b) Intramantle keel delamination model. (a) An ~10-km weak, partly discontinuous layer (e.g., the metasome midlithosphere discontinuity layer (MLDL)) exists between ~80- and 100-km depths in the craton lithosphere. Because the lower keel is denser than its adjacent asthenosphere and materials adjacent to the edge of metasome are soft enough, the denser lower keel starts to delaminate along the metasome. (The conditions for and evolution of this delamination process are the focus of Part 1; Liu et al., 2018.) (b) Delamination stops where the metasome MLDL disappears. After the dela- mination of the lower keel, pockets of metasome material locally survive at the base of the lithosphere. The overlying lithosphere initially retains its cool cratonic temperature and does not melt, leading to a magmatic hiatus after initial melting of the metasome warmed by contact with asthenosphere. (c and d) Postdelamination lithospheric evolution. (c) Cold remaining lithosphere can be locally denser than underlying hot asthenosphere. Therefore, dense lithosphere will tend to sag during convective erosion, leading to local thinning of lithosphere and intrusion of asthenosphere and metasome material into the relic cratonic lithosphere. During this process, the remaining lithosphere is slowly heated, and the lower crust can sometimes locally melt. (d) Later lithospheric extension (approximately <140 Ma) can lead to focused magmatism and lithospheric replacement in regions close to preexisting translithospheric weak zone (e.g., the Tan-Lu fault zone). LIU ET AL. 10,070 Journal of Geophysical Research: Solid Earth 10.1029/2017JB015374 evolution of relic ENCC crust and uppermost lithospheric mantle. Our pri- mary tool to do this will be to explore and compare the implications of a suite of numerical experiments with observed patterns of post-Jurassic magmatism and deformation in the ENCC. Before diving into the numeri- cal experiments and their ability to match the ENCC’s well-documented postdelamination history, we first summarize the petrological, geochem- ical, geological, and geophysical observations that have been used to con- strain the ENCC’s recent evolution. 2. Tectonic and Magmatic Evolution During ENCC Destruction The ENCC destruction process is reflected in its episodic tectonic and mag- matic (felsic-magma-dominated) record. Due to its location adjacent to active subduction-collision zones, a primarily compressional state of the ENCC appeared no later than approximately 320 Ma (Meng, 2003; Xu et al., 2009). During this time, the crust along its margins is proposed to be locally thickened to approximately 50 km (cf. Meng, 2003). (Alternatively, it is also possible that