High-pressure mafic granulites in the Trans-North China Orogen: Tectonic significance and age Jian Zhang a , Guochun Zhao a, * , Min Sun a , Simon A. Wilde b , Sanzhong Li c , Shuwen Liu d a Department of Earth Sciences, James Lee Science Building, The University of Hong Kong, Pokfulam Road, Hong Kong, China b Department of Applied Geology, Curtin University of Technology, Bentley 6102, Western Australia c College of Marine Geosciences, Ocean University of China, 266003, Qingdao, China d School of Earth and Space Sciences, Peking University, Beijing 100871, China Received 19 February 2005; accepted 5 October 2005 Available online 18 January 2006 Abstract High-pressure mafic granulites (including retrograded eclogites) have been reported from the Trans-North China Orogen, a Paleoproterozoic orogenic belt along which two discrete continental blocks, referred to as the Eastern and Western Blocks, were amalgamated to form the North China Craton. Extensive metamorphic investigations and geochronology carried out over the last few years provide important insights into the age and significance of these high-pressure granulites, which are critical in understanding of the timing and tectonic processes involved in the assembly of the North China Craton. Most high-pressure mafic granulites in the Trans-North China Orogen preserve the high-pressure granulite facies assemblage garnet + plagioclase + clinopyroxene + quartz, the medium-pressure granulite facies assemblage garnet + plagioclase + clinopyroxene + orthopyrox- ene T quartz, the low-pressure granulite facies assemblage orthopyroxene + clinopyroxene + plagioclase T quartz, and the amphibolite facies assemblage hornblende + plagioclase. Minor high-pressure granulites preserve the early eclogite facies mineral assemblage of garnet + quartz + om- phacite pseudomorph (clinopyroxene + Na-rich plagioclase), indicating that they are retrograded eclogites. These mineral assemblages and their P – T estimates define a clockwise P – T path involving near-isothermal decompression and cooling following the peak high-pressure metamorphism, which suggests that they formed during continent – continent collision. Field mapping and geochronology indicate that the precursors of these high- pressure granulites were mafic dykes which were emplaced at ¨1915 Ma and underwent high-pressure granulite facies metamorphism at ¨1.85 Ga. Taken together, the high-pressure granulites in the Trans-North China are considered to have resulted from final collision between the Eastern and Western Blocks to form the North China Craton at ¨1.85 Ga, not at ¨2.5 Ga as recently proposed by some authors. D 2005 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Keywords: High-pressure granulite; Trans-North China Orogen; P– T paths; North China Craton; Paleoproterozoic tectonics 1. Introduction One of the main arguments against the operation of plate tectonic processes in the early Precambrian has been the apparent lack of high-pressure rock assemblages. In recent years, however, such rocks of Paleo- to Mesoproterozoic age have been discovered in the Canadian Shield (Snoeyenbos et al., 1995; Baldwin et al., 2003; Indares, 2003), NW Scotland (Baba, 1998), North China (Zhai et al., 1992, 1993, 1995, Dirks et al., 1997; Guo et al., 1993, 2001, 2002; Guo and Zhai, 2001; Zhao et al., 2001a; O’Brien et al., 2005), Tanzania (Mo ¨ller et al., 1995; Boven et al., 1999), India (Bhowmik and Roy, 2003), Brazil (Del Lama et al., 2000), Siberia (Smelov and Beryozkin, 1993) and the Baltic Shield (Mo ¨ller, 1998, 1999). Studies of the metamorphic and structural evolution of such high-pressure rocks occurring in former mountain belts provides valuable information on possible subduction and collision events as well as on the subsequent exhumation and cooling processes (Carswell, 1990; O’Brien, 2001; O’Brien and Rotzler, 2003; Carswell et al., 2003). High-pressure mafic granulites (including retrograded eclo- gites) have been widely reported in the Trans-North China 1342-937X/$ - see front matter D 2005 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2005.10.005 * Corresponding author. Tel.: +852 28578203; fax: +852 25176912. E-mail address: gzhao@hkucc.hku.hk (G. Zhao). Gondwana Research 9 (2006) 349 – 362 www.elsevier.com/locate/gr