Journal of Asian Earth Sciences 114 (2015) 732–749 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Paleomagnetism of Upper Cretaceous red-beds from the eastern Qiangtang Block: Clockwise rotations and latitudinal translation during the India–Asia collision ⇑ Ya-Bo Tong a,b, Zhenyu Yang c, , Liang Gao a, Heng Wang a, Xu-Dong Zhang d, Chun-Zhi An a, Yin-Chao Xu a, Zhi-Rui Han a a Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China b Key laboratory of Paleomagnetism and Tectonic Reconstruction, The Ministry of Land and Resources, Beijing 100081, China c College of Resources, Environment and Tourism, Capital Normal University, Beijing 100048, China d East China Mineral Exploration and Development Bureau, Nanjing 210007, China article info abstract Article history: High-temperature magnetization component was isolated between 600 °C and 680 °C from Upper Received 13 June 2014 Cretaceous red-beds in the Mangkang area, in the eastern end of the Qiangtang Block, Tibetan Plateau. Received in revised form 6 August 2015 The tilt-corrected site-mean direction is Ds/Is = 51.3°/56.1°, with k = 31.0 and a95 = 6.5°, corresponding Accepted 14 August 2015 to a paleolatitude of 36.7 ± 6.7°N. Positive fold and reversal tests indicate a primary magnetization. Available online 17 August 2015 Inclination shallowing tests show that inclination bias is not present in the Upper Cretaceous red-beds of the Qiangtang Block that might induce through depositional and/or compaction process. However, pre- Keywords: vious paleomagnetic data obtained from Cretaceous and Paleocene–Eocene volcanic rocks show that the Qiangtang Block paleolatitudes of the Lhasa Block were 17.1 ± 3.3°N and 22.3 ± 4.4°N, respectively, and 28.7 ± 3.7°N for Lhasa Block Paleomagnetism the central Qiangtang Block yielded from Eocene volcanic rocks. These results show that there was a Cretaceous 10° latitudinal discrepancy between the Lhasa Block and Qiangtang relative to Eurasia. However, the Inclination shallowing Mangkang area of the southeastern Qiangtang Block experienced 3.2 ± 7.8° to 7.3 ± 5.2° southward extrusion and 40° clockwise rotational movement relative to Eurasia since the Cretaceous, which coin- cided with the Early Cenozoic rotational extrusion of the Indochina and Shan-Thai Blocks. The crustal deformation in the eastern Qiangtang Block should have been caused by the Indian Plate penetrating into Eurasia in the eastern end of Tibetan Plateau and the formation of the Eastern Himalaya Syntaxis since the Oligocene/Miocene. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Jinshajiang Suture Zone during the Late Triassic to Early Jurassic (Yin and Harrison, 2000; Haines et al., 2003; Schneider et al., The current Tibetan Plateau is an amalgamation of several crus- 2003; Pullen et al., 2008; Zhu et al., 2013). From the Middle to Late tal blocks, comprising from north to south, the Songpan-Ganzi Triassic the Lhasa Block began to separate from northern Australia Block, the Qiangtang Block, the Lhasa Block and the Tethyan Hima- (Metcalfe, 2009, 2011; Zhu et al., 2011), and subsequently drifted laya (Fig. 1A). The Qiangtang Block is situated between the Lhasa northward and accreted onto the Qiangtang Block along the Block and the Songpan-Ganzi Block. The Bangong-Nujiang Suture Bangong-Nujiang Suture Zone during the Late Jurassic and Early Zone and the Jinshajiang Suture Zone comprise the southern and Cretaceous (Yin and Harrison, 2000; Tapponnier et al., 2001; northern boundaries of the Qiangtang Block, respectively Kapp et al., 2003, 2007; Guynn et al., 2006; Qiangba et al., 2009; (Fig. 1A). The Qiangtang Block is generally thought to have sepa- Zhu et al., 2013). Finally, the Songpan-Ganzi Block, Qiangtang Block rated from Gondwana in the Late Paleozoic (Allégre et al., 1984; and Lhasa Block constituted the southern margin of Eurasia prior to Sengör, 1987; Yin and Harrison, 2000; Xu et al., 2014), and the Cenozoic India–Eurasia collision. then to have accreted onto the Songpan-Ganzi Block along the During the past three decades many geological and paleomag- netic studies of the Lhasa Block have argued that the Indian Plate collided with the southern edge of Eurasia along the Indus- ⇑ Corresponding author. E-mail address: [email protected] (Z. Yang). Yalung-Zangbo Suture Zone during the Early Eocene, and that http://dx.doi.org/10.1016/j.jseaes.2015.08.016 1367-9120/Ó 2015 Elsevier Ltd. All rights reserved. Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749 733 Fig. 1. (A) Schematic tectonic-geographical map of South Asia. (B) Tectonic map of the paleomagnetic sampling section in the Mangkang area. (C) Strike and dip of the strata for each sampling sites. (D) Geological profile of the paleomagnetic sampling section of the Mangkang area. JSSZ, Jinshajiang Suture Zone. LSSZ, Longmu Tso-Shuanghu Suture Zone. BG-NJSZ, Bangong-Nujiang Suture Zone. IYZSZ, Indus-Yarlung Zangbo Suture Zone. subsequently the Indian Plate penetrated into Eurasia and induced proposition for the existence of inclination shallowing in all of a tremendous amount of north to south convergence and intense the Cretaceous red-beds in the Tibetan Plateau (Tan et al., 2010). crustal deformation within the southern part of Eurasia (Peltzer Although the possible inclination shallowing of red-beds would and Tapponnier, 1988; Tapponnier et al., 1982, 2001; Replumaz result in an inaccurate estimation of paleo-latitudes from Creta- and Tapponnier, 2003; Molnar and Stock, 2009; Copley et al., ceous red-beds, several paleomagnetic data obtained from Creta- 2010; Canda and Stegman, 2011; Van Hinsbergen et al., 2011; ceous to Paleocene–Eocene volcanic rocks in the Lhasa Block can Sun et al., 2010, 2012; Ma et al., 2014; Yang et al., 2014). Most of still provide reliable constraints on the paleo-positions and crustal the paleomagnetic data obtained from Cretaceous red-beds in the convergence of southern Eurasia. For the Qiangtang Block, almost Lhasa Block indicate that the south to north crustal convergence all the paleomagnetic data were obtained from the Cretaceous which occurred in the southern Eurasia was greater than red-beds in the eastern and western parts (Huang et al., 1992; 1500 km since the initial collision of India and Eurasia (Achache Otofuji et al., 1990; Chen et al., 1993), and none of these data were et al., 1984; Lin and Watts, 1988; Sun et al., 2010). However, con- evaluated for possible inclination shallowing. Recently Lippert trasting viewpoints also exist. For example, Tan et al. (2010) et al. (2011) obtained paleomagnetic data from the Eocene volcanic obtained paleomagnetic data from Upper Cretaceous and Eocene rocks in the central part of the Qiangtang Block, and suspected the volcanic rocks and suggested that only a few hundred kilometers occurrence of inclination shallowing in the Cretaceous red-beds in of crustal convergence occurred in southern Eurasia. Moreover, the Qiangtang Block. It is therefore very difficult to constrain the they proposed that Cretaceous red-beds in the Lhasa Block were crustal deformation characteristics, and north to south intraconti- affected by inclination shallowing due to deposition/compaction nental convergence, in southern Eurasia based solely on the cur- processes. In addition, Ma et al. (2014) and Yang et al. (2014) rent paleomagnetic data from the Qiangtang Block. obtained very consistent paleomagnetic data from Lower Creta- Here, we report the results of a new paleomagnetic study and ceous volcanic rocks and Upper Cretaceous red-beds in the Lhasa inclination shallowing tests of the Upper Cretaceous red-beds in Block, respectively, indicating that 1000 km south to north crus- the eastern part of the Qiangtang Block, on the northern side of tal convergence has taken place in southern Eurasia since the late the Eastern Himalayan Syntaxis. A combination of reliable Creta- Cretaceous. It seems that the paleomagnetic results of Ma et al. ceous and Paleocene–Eocene paleomagnetic data from the Qiang- (2014) and Yang et al. (2014) are incompatible with the tang and the Lhasa Blocks was used to estimate latitudinal 734 Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749 crustal convergence and crustal material movement characteristic 3. Rock magnetism of the central and eastern part of the Tibetan Plateau. Rock magnetic characteristics can be used to identify the mag- netic carriers. The progressive acquisition of isothermal remanent 2. Regional geology and sampling magnetization (IRM) was used to determine the coercivity of mag- netic minerals, and the thermal demagnetization of three- The Eastern Himalayan Syntaxis and surrounding area have component IRM was used to reveal the unblocking temperatures been located in a structural position between two tectonic of different magnetic minerals (applied successively to each of domains since the Miocene: N–S crustal shortening combined the three axes with different DC field of 2.5 T for the Z axis, 0.4 T with E–W extension (Armijo et al., 1986; Jessup et al., 2008), for the Y axis, and 0.12 T for the X axis) (Lowrie, 1990). Based on and southeastward and eastward movement of the crustal mate- the lithologic characteristics of the samples, four representative rial of Tibet (Tapponnier et al., 1982; Royden et al., 1997; Wang specimens (MK3-5, MK8-7, MK12-8, MK16-2) were selected for and Burchfiel, 2000; Zhang et al., 2004). Significant arcuate rock magnetic experiments strike-slip fault belts and compact linear fold systems are widely The rock magnetic properties of the four representative speci- developed around the Eastern Himalayan Syntaxis (Fig. 1A). The mens were similar (Fig. 2). The IRM acquisition curves of MK3-5 east–west-trending Qiangtang Block exhibits a 90° turn around and MK16-2 increased slowly between DC fields from 0 to the Eastern Himalayan Syntaxis and becomes a southeastern- 150 mT, however, the magnetic remanence of MK8-7 and MK12- trending belt, and then is gradually superseded by the Shan- 8 increased more rapidly from 0 to 150 mT.