Permo-Triassic granitoids in the northern part of the Truong Son belt, NW Vietnam: Geochronology, geochemistry and tectonic implications Junlai Liu a, ⁎, My-Dung Tran a, b , Yuan Tang a, c , Quang-Luat Nguyen b , Thanh-Hai Tran b , Wenbin Wu a , Jiafu Chen a , Zhaochong Zhang a , Zhidan Zhao a a State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China b Hanoi University of Mining and Geology, Hanoi, Vietnam c Chengdu Institute of Geology and Mineral Resources, Chengdu 610081, China abstract article info Article history: Received 1 March 2011 Received in revised form 18 October 2011 Accepted 18 October 2011 Available online 7 November 2011 Keywords: Truong Son granitoids LA-ICP-MS zircon geochronology Eastern Tethys Subduction Post-collisional extension NW Vietnam The northern segment of the Truong Son belt of northwestern Vietnam is composed of three granitoid com- plexes (Chieng Khuong, Dien Bien, and Song Ma, respectively). Our new LA-ICP-MS U–Pb dating results of magmatic zircons from five granitoid samples in the Dien Bien and the Chieng Khuong complexes reveal the existence of three age populations of magma emplacement and crystallization from 276 to 202 Ma. The new data show that the quartz diorite of the Chieng Khuong complex is dated to be 271 Ma. However, the previously named Dien Bien complex, exposed at different localities, has various ages (from 281 to 202 Ma) of magmatic crystallization. The Chieng Khuong quartz diorite exhibits high Mg-value (60.7) and enriched Sr–Nd isotopic features (I Sr = 0.713822, εNd (t)=-11.34), with subduction-related geochemical features (e.g., depletion in Nb, Ta and Ti and enrichment in Rb and La). The Dien Bien gabbroic diorite at Muong Lay is characterized by relatively depleted isotopic data (I Sr = 0.705050, εNd (t) = + 0.09) and exten- sive depletion in Nb and Ta. By contrast, the Dien Bien granodiorite and quartz monzonite at Dien Bien are high-K calc-alkaline to calc-alkaline, with high Mg-values (45.5 to 54.4), and they display enriched Sr–Nd iso- topic data (I Sr = 0.714912 to 0.716430, εNd (t) =-9.58 to -8.85) and post-collisional geochemical charac- teristics (e.g., enrichment in total alkali, LILE and LREE and depletion in Eu, Sr, P, Ti and Nb). Under the framework of regional tectonic evolution, the Permo-Triassic magmatism along the northern Truong Son belt is thus grouped into an early stage from ca. 280 to 250 Ma and a late stage from 229 to 202 Ma. The early Permian-early Triassic arc magmatism (280–270 Ma and 250–245 Ma), which is widely distributed in the Truong Son belt, provides reliable information on the continuous subduction of the Song Ma oceanic plate beneath the Indochina block. Furthermore, the magmatism of the Dien Bien complex at Dien Bien was formed during post-collisional extension at ca. 229 to 202 Ma. Diachronous suturing of the eastern Tethyan evolution is characterized by the differences in the ages of subduction/post-collisional evo- lution along the Ailaoshan and the Song Ma belts. © 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. 1. Introduction As a part of the eastern Tethyan orogenic belt, the Southeast Asian continent is constituted by continental blocks separated by suture zones. In a fan-shaped area between the Red River and the Sagaing fault zones are several such blocks, including the Sibumasu, the Sukhothai, the Simao and the Indochina blocks (Hutchison, 1989; Metcalfe, 1996a, 1996b, 1998; Lepvrier et al., 2004; Feng et al., 2005; Sone and Metcalfe, 2008). The suture zones between the blocks include the Changning–Menglian–Chiangmai, Jinghong, Ailaoshan, and Song Ma sutures (Mo et al., 1993, 1998). The Song Da rift is a different tectonic unit located between these blocks (Poliakov et al., 1998). The Changning–Menglian–Qiangmai suture zone is thought to be derived from the major Tethyan Ocean between the Eurasian and Gondwanan continents during the late Paleozoic and early Meso- zoic (Liu et al., 1991; Zhang, 2000; Zhong and Zhao, 2000; Charusiri et al., 2002; Sone and Metcalfe, 2008). Most authors agree that the Ailaoshan–Song Ma belt is a suture zone that separates the South China block from the Indochina block (Zhang et al, 1994; Chung et al., 1997; Wang et al., 2000, Metcalfe, 2006; Yumul et al., 2008), but there is still controversy regarding the nature of the primary ocean basin and the present boundary between the two blocks. Wang et al. (2000), on the basis of integrated tectonic, biostratigraphic, chemostratigraphic and geochronological studies of the different tectonic units along the Ailaoshan suture zone, suggested that this suture zone represents a back-arc basin because of the con- tinued extension and subduction of the Changning–Menglian ocean, Gondwana Research 22 (2012) 628–644 ⁎ Corresponding author. Tel.: + 86 13810306276. E-mail address: jliu@cugb.edu.cn (J. Liu). 1342-937X/$ – see front matter © 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2011.10.011 Contents lists available at SciVerse ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr