Geochemistry of Paleoproterozoic (1770 Ma) mafic dikes from the Trans-North China Orogen and tectonic implications Yuejun Wang a,d, * , Guochun Zhao b , Peter A. Cawood c , Weiming Fan a , Touping Peng a , Linhua Sun a a Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, P.O. Box 1131, Guangzhou 510640, People’s Republic of China b Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong c Tectonics Special Research Centre, The University of Western Australia, Crawley, WA 6009, Australia d Department of Earth Sciences, Northwest University, Xi’an 710069, China Received 14 July 2007; received in revised form 5 October 2007; accepted 23 October 2007 Abstract Paleoproterozoic (1770 Ma) mafic dikes occur throughout the Trans-North China Orogen. These dikes can be divided into three geochemically distinct groups. Group 1 with FeOt of 12.73–18.06%, (Nb/La) N 0.18–0.39, (Th/La) N of, 0.60–1.24, e Nd (t) of 5.1 to 2.4, and an enrichment in LILE’s and a depletion in HFSE’s. Group 2 has flat REEs and incompatible elements patterns, and possesses (Nb/La) N = 0.64–0.87, (Th/La) N = 0.61–1.20 and e Nd (t)= 1.7 to 1.1. Group 3 has low FeOt contents (8.19–11.57%) and (Th/La) N ratios (0.29–0.72), but similar (Nb/La) N ratios and e Nd (t) values to those of Group 1. Petrological and geochemical data suggest that these dikes may have originated from different sources. Group 1 could be derived from a ‘‘re-fertilized’’ lithospheric source incorporating a continental basaltic component trapped from a earlier phase of subduction. Group 2 was likely a product of a subduction-modified lithospheric mantle hybridized by recycled gabbroic lower crust. By contrast, Group 3 originated from a mixture of subduction-modified lithospheric mantle with a MORB component. In combination with the available data, we propose that the sources of the mafic dikes were initially modified by the 1.85 Ga subduction/collision event that assembled the North China Craton, and partially melted under subsequent rifting in response to the upwelling convective mantle. Ó 2007 Published by Elsevier Ltd. Keywords: Geochemistry; Mafic dikes; Subduction-related lithospheric mantle; Paleoproterozoic; Trans-North China Orogen 1. Introduction In the last decade, numerous structural, lithological, metamorphic, geochemical and geochronological investi- gations have been carried out to probe into the Precam- brian evolution of the North China Craton (e.g. Cawood et al., 1998; Kro ¨ner et al., 2005, 2006; Zhao et al., 2000, 2003, 2005; Zhai and Liu, 2003; Wang et al., 2003, 2004). It is generally agreed that the North China Craton is composed of two different blocks that developed inde- pendently and finally collided to form a coherent craton (Fig. 1a) (e.g. Zhao et al., 2005 and references therein). However, timing of the final amalgamation of the North China Craton is still debated. Li et al. (2000) and Kusky and Li (2003) argued that the two Achaean blocks of the North China Craton (the Eastern and Western Blocks) were amalgamated by a 2.5 Ga collisional event, and that the 1.85 Ga Lu ¨ liang event (traditionally named the ‘‘Lu ¨ liang Movement’’) represents an intra-continental rifting event in the craton, whereas others favor the 1367-9120/$ - see front matter Ó 2007 Published by Elsevier Ltd. doi:10.1016/j.jseaes.2007.10.018 * Corresponding author. Present address: Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, P.O. Box 1131, Guangzhou 510640, People’s Republic of China. Tel.: +86 20 85290527; fax: +86 20 85291510. E-mail address: yjwang@gig.ac.cn (Y. Wang). www.elsevier.com/locate/jaes Available online at www.sciencedirect.com Journal of Asian Earth Sciences xxx (2007) xxx–xxx ARTICLE IN PRESS Please cite this article in press as: Wang, Y. et al., Geochemistry of Paleoproterozoic (1770 Ma) mafic dikes ..., Journal of Asian Earth Sciences (2007), doi:10.1016/j.jseaes.2007.10.018