https://doi.org/10.1130/G48483.1 Manuscript received 7 October 2020 Revised manuscript received 27 December 2020 Manuscript accepted 12 January 2021 © 2021 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 22 March 2021 North China craton: The conjugate margin for northwestern Laurentia in Rodinia Jikai Ding1,2, Shihong Zhang1,3*, David A.D. Evans2, Tianshui Yang1, Haiyan Li1, Huaichun Wu1 and Jianping Chen3 1 State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China 2 Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut 06520, USA 3 School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China ABSTRACT ern NCC and northwestern Laurentia (present In the Rodinia supercontinent, Laurentia is placed at the center because it was flanked coordinates) was proposed (Fu et al., 2015; by late Neoproterozoic rifted margins; however, the conjugate margin for western Laurentia Zhao et al., 2020) but required rigorous testing is still enigmatic. In this study, new paleomagnetic results have been obtained from 15 ca. by coeval pairs of high-quality poles with pre- 775 Ma mafic dikes in eastern Hebei Province, North China craton (NCC). Stepwise thermal cise age constraints. In this study, we report a demagnetization revealed a high-temperature component, directed northeast or southwest new high-quality paleomagnetic pole obtained with shallow inclinations, with unblocking temperatures of as high as 580 °C. Rock magne- from ca. 775 Ma mafic dikes in the eastern He- tism suggests the component is carried by single-domain and pseudo-single-domain magnetite bei Province, NCC. This pole, combined with grains. Its primary origin is supported by a positive reversal test and regional remanence the late Mesoproterozoic to early Neoproterozo- direction correlation test, and the paleomagnetic pole (29.0°S, 64.7°E, A95 = 5.4°) is not simi- ic (ca. 1110–775 Ma) paleomagnetic database lar to any published younger poles of the NCC. Matching the late Mesoproterozoic to early of the NCC and Laurentia, supports an endur- Neoproterozoic (ca. 1110–775 Ma) apparent polar wander paths of the NCC and Laurentia ing NCC–northwestern Laurentia connection suggests that the NCC could have been the conjugate margin for northwestern Laurentia in in Rodinia. Rodinia, rather than sitting off the northeast coast of the main Rodinian landmass. Geological data indicate that breakup of the NCC and Laurentia occurred between ca. 775 and 720 Ma. REGIONAL GEOLOGY AND SAMPLING INTRODUCTION ences therein). Alternatively, the South China Two generations of unmetamorphosed Pre- Laurentia is placed at the center of the Ro- block was placed between eastern Australia and cambrian mafic dikes exist in the Lulong re- dinia supercontinent because it is flanked by western Laurentia, known as the “missing link” gion, eastern Hebei Province, the northeastern Neoproterozoic passive margins (Hoffman, model (Li et al., 2008), but more recent paleo- NCC (Fig. 1). Both sets of dikes vertically or 1991; Li et al., 2008, and references therein). magnetic studies suggested the South China subvertically intruded into Archean–Paleopro- The present eastern and southern margins of block and Laurentia were separated by a large terozoic gneisses (Figs. 1B and 1C; Fig. S1 Laurentia could connect with Baltica, Amazo- latitudinal gap ca. 800 Ma (Jing et al., 2020; in the Supplemental Material1; Wang et al., nia, and Kalahari (Li et al., 2008; Merdith et al., Xian et al., 2020). Recently, Wen et al. (2017, 2016; Ding et al., 2020). Dikes of the older 2017, and references therein), and its northern 2018) suggested that the Tarim craton could group are 10–30 m wide and were dated at margin could connect with Siberia (Evans et al., have occupied a similar missing-link position 1236.4 ± 7.3 Ma (baddeleyite, Pb-Pb second- 2016, and references therein); however, the based on new paleomagnetic data, although the ary ion mass spectrometry [SIMS] method; dike continent(s) once adjacent to its present west- Tarim craton is too small to match the entire LL02, Fig. 1B; Wang et al., 2016). They are ern margin are still enigmatic (Eyster et al., length of Laurentia’s western margin. Alterna- north-trending alkaline gabbro dikes (Wang 2020). In earlier published papers for Rodinia tive reconstruction models were also proposed et al., 2016) and carry paleomagnetic direc- reconstructions (Dalziel, 1991; Hoffman, 1991; to link other continents to the western margin tions pointing east and downward with moder- Moores, 1991), Australia-Antarctica was linked of Laurentia, such as Siberia (Sears and Price, ate inclinations (Ding et al., 2020). Dikes of the to the western margin of Laurentia, named the 2003), Congo–São Francisco (Maloof et al., younger group are 5–15-m-wide, ENE-trending “SWEAT” (southwestern United States and 2006), or West Africa (Evans, 2009), but these porphyritic diabase dikes, tholeiitic in compo- East Antarctica) model, but subsequent paleo- models are not supported by available paleo- sition with oceanic island basalt (OIB)–type magnetic data excluded a tight configuration of magnetic data. Owing to a series of high-quality geochemical features (Wang et al., 2016), and Australia against the western Laurentia margin late Mesoproterozoic to early Neoproterozoic were dated at 775 ± 5 Ma (zircon, U-Pb SIMS (Li et al., 2008; Eyster et al., 2020, and refer- paleomagnetic and geochronological data re- method; Wang et al., 2016). Paleomagnetic ported from the North China craton (NCC), a results from two dikes of the younger group *E-mail: [email protected] ca. 1100–920 Ma connection of the northeast- were reported previously, the remanence being 1Supplemental Material. Laboratory methods, paleomagnetic data table, selected paleomagnetic poles, Euler rotation parameters, and supplemental references. Please visit https://doi.org/10.1130/GEOL.S.14120423 to access the supplemental material, and contact [email protected] with any questions. CITATION: Ding, J., et al., 2021, North China craton: The conjugate margin for northwestern Laurentia in Rodinia: Geology, v. 49, p. 773–778, https://doi.org/10.1130/ G48483.1 Geological Society of America | GEOLOGY | Volume 49 | Number 7 | www.gsapubs.org 773 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/49/7/773/5335994/g48483.1.pdf by guest on 30 September 2021 r( r( r( r( A B LL08 N LL01 LL07 LL09 Fig. C r1 LL06 LL04 Beijing 775 ± 5 Ma Fig. B r1 Wang et al. (2016) Lulong r1 LL05 Exposed basement LL02 1236 ± 7 Ma 2 km Mafic dikes Wang et al. (2016) 200 km LL03 Major fault r( r( C N 40.5°N Heshangfangzi Mutoudeng LL12 LL11 LL10 40.4°N LL14 LL13 40.3°N LL15 40.2°N Guanchang LL16 LL17 LL18 40.1°N Wanjia NP Duzhuang Bohai Sea 92r( 93r( 94r( 95r( 96r( 97r( 98r( 99r( Archean– Paleo–Mesoproterozoic Phanerozoic Paleozoic– ca. 1220 Ma Paleoproterozoic Cretaceous granitoids mafic dikes ca. 780 Ma Phanerozoic dikes Reservoir Reported by This study mafic dikes Ding et al. (2020) Figure 1. (A) Schematic map showing the distribution of basement rocks, unmetamorphosed Precambrian mafic dikes, and locations of the study regions (blue rectangles) in the North China craton. (B,C) Simplified geological maps of the studied regions and distribution of studied dikes. obviously different to that of the ca. 1236 Ma PALEOMAGNETIC RESULTS mostly below 400 °C (Fig. 2). Directions of the dikes (Ding et al., 2020). In this study, we col- The natural remanent magnetization in- LC distribute around the present geomagnetic lected 214 paleomagnetic core samples from 13 tensities of the samples from the ca. 775 Ma field (PGF) direction in the region and are thus additional ca. 775 Ma dikes. In order to conduct mafic dikes range from 0.01 to 1.2 A/m. For interpreted to be a viscous remanent magneti- baked-contact tests, 24 samples from the baked most samples, after stepwise thermal demagne- zation. The high-temperature component (HC) and unbaked gneisses in the proximity of two tization, two components can be isolated. The is generally defined in higher-temperature dikes were also collected. low-temperature component (LC) is identified steps up to ∼580 °C. This is consistent with 774 www.gsapubs.org | Volume 49 | Number 7 | GEOLOGY | Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/49/7/773/5335994/g48483.1.pdf by guest on 30 September 2021 N Up 17LL11U2 N Up 18LL01E2 N ABN NRM NRM 570ć ć 580 450ć 230ć 580ć E 150ć E 530ć 515ć NRM Down NRM Down 580ć 570ć Up Up 580ć W E W E S S Scale = 0.02 A/m Scale = 0.2 A/m S Down S Down N Up N Up CD19LL01J2 19LL06G1 580ć N N W E Down E Down Up W ć 500ć 580 Up 500ć 370ć NRM NRM W E W 580ć 580ć 570ć 550ć 560ć Scale = 0.1 A/m S Scale = 0.1 A/m S NRM S Down NRM S Down Figure 2. Equal-area projections and orthogonal plots of progressive demagnetization results for representative ca. 775 Ma dike specimens, in geographic coordinates. Solid (open) circles in orthogonal plots represent the horizontal (vertical) components of magnetization. NRM— natural remanent magnetization. thermomagnetic and hysteresis curves (Fig. S2) test at 95% confidence level (class C; McFadden The 15 VGPs yield an angular dispersion of that demonstrate the main magnetic carriers in and McElhinny, 1990), with the observed angu- 11.0° with confidence interval 9.2°–12.8° (1σ). the samples are single-domain and pseudo-sin- lar difference (γ0 = 10.7°) less than the critical That value and its confidence interval overlap gle-domain magnetite grains. Some specimens angle (γc = 12.9°) (Table S1).