Tectonic evaluation of the Indochina Block during Jurassic-Cretaceous from palaeomagnetic results of Mesozoic redbeds in central and southern Lao PDR Sounthone Singsoupho a,b , Tripob Bhongsuwan b,⇑ , Sten-Åke Elming c a Geophysics Unit, Department of Physics, Faculty of Natural Sciences, National University of Laos, P.O. Box: 7322, Vientiane Capital, Lao Democratic People’s Republic b Geophysics Research Center, Department of Physics, Faculty of Science, Prince of Songkla University, 90112 Hatyai, Thailand c Division of Geosciences and Environmental Engineering, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, SE-97187 Luleå, Sweden article info Article history: Received 3 December 2013 Received in revised form 23 May 2014 Accepted 2 June 2014 Available online 13 June 2014 Keywords: Rock magnetic Palaeomagnetic Mesozoic redbeds Indochina Block Lao PDR abstract Rock magnetic and palaeomagnetic studies were performed on Mesozoic redbeds collected from the cen- tral and southern Laos, the northeastern and the eastern parts of the Khorat Plateau on the Indochina Block. Totally 606 samples from 56 sites were sampled and standard palaeomagnetic experiments were made on them. Positive fold tests are demonstrated for redbeds of Lower and Upper Cretaceous, while insignificant fold test is resulted for Lower Jurassic redbeds. The remanence carrying minerals defined from thermomagnetic measurement, AF and Thermal demagnetizations and back-field IRM measure- ments are both magnetite and hematite. The positive fold test argues that the remanent magnetization of magnetite or titanomagnetite and hematite in the redbeds is the primary and occurred before folding. The mean palaeomagnetic poles for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous are defined at Plat./Plon. = 56.0°N/178.5°E(A 95 = 2.6°), 63. 3°N/170.2°E(A 95 = 6.9°), and 67.0°N/180.8°E(A 95 = 4.9°), respectively. Our palaeomagnetic results indicate a latitudinal translations (clockwise rotations) of the Indochina Block with respect to the South China Block of À10.8 ± 8.8° (16.4 ± 9.0°); À11.1 ± 6.2° (17.8 ± 6.8°); and À5.3 ± 4.7° (13.3 ± 5.0°), for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous, respectively. These results indicate a latitudinal movement of the Indochina Block of about 5–11° (trans- lation of about 750–1700 km in the southeastward direction along the Red River Fault) and clockwise rotation of 13–18° with respect to the South China Block. The estimated palaeoposition of the Khorat Pla- teau at ca. 21–26°N during Jurassic to Cretaceous argues for a close relation to the Sichuan Basin in the southwest of South China Block. These results confirm that the central part of the Indochina Block has acted like a rigid plate since Jurassic time and the results also support an earlier extrusion model for Indochina. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Intercontinental collisions and deformations have taken place in a variety of modes in the Asia continent. The deformations of Southeast Asia have been modeled in a number of laboratory and numerical experiments during the last two decades (e.g. Tapponnier et al., 1982; Cohen and Morgan, 1986; Houseman and England, 1993; Royden et al., 2008). An extrusion tectonic model has been proposed to explain the tectonic of Southeast Asia after the Pre-Tertiary India-Asia collision which occurred in the Lower Eocene (ca. 50 Ma) (e.g. Molnar and Tapponnier, 1975; England and Houseman, 1986; Beck et al., 1995; Rowley, 1996; Tong et al., 2008) or in the Oligocene (ca. 35 Ma) (Aitchison et al., 2007). The southeastward movement of Indochina along the Ailao Shan-Red River (ASRR) shear zone is partly supported by geological evidences (Leloup et al., 1995, 2001; Wang et al., 1998, 2000, 2001; Gilley et al., 2003; Replumaz and Tapponnier, 2003; Replumaz et al., 2004; Ali et al., 2010) and geochronological data (Lacassin et al., 1997; Gilley et al., 2003). Palaeomagnetic studies have been performed in South China and Indochina blocks in attempts to reconstruct tectonic events in these regions (Zhu et al., 1988; Kent et al., 1986; Gilder et al., 1993, 1999; Morinaga and Liu, 2004; Li et al., 2005; Bai et al., 1998; Yokoyama et al., 2001; Enkin et al., 1992; Tanaka et al., 2008; Takemoto et al., 2009; Otofuji et al., 2010, 2012; Cung and Geissman, 2013). On the basis http://dx.doi.org/10.1016/j.jseaes.2014.06.001 1367-9120/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +66 897328670; fax: +66 74558849. E-mail address: tripop.b@psu.ac.th (T. Bhongsuwan). Journal of Asian Earth Sciences 92 (2014) 18–35 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes