Paleomagnetism of Upper Cretaceous Red-Beds from the Eastern

Journal of Asian Earth Sciences 114 (2015) 732–749

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Journal of Asian Earth Sciences

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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 paleomagnetic 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 magnetic carriers. The progressive acquisition of isothermal remanent 2. Regional geology and sampling magnetization (IRM) was used to determine the coercivity of magnetic 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. Subsequently, the Thai Block. As the southern and northern boundaries of the remanence of all four specimens increased rapidly but without Qiangtang Block, the west–northwest-trending Jinshajiang Suture reaching saturation up to the maximum DC field of up to Zone and the Bangong-Nujiang Suture Zone are, respectively, also 2400 mT, indicating the existence of goethite and/or hematite. altered in a south-southeastern direction (Fig. 1A). The Mangkang The remanence decreased rapidly when a reversed field of 400– area is located in the southeastern part of the Qiangtang Block. 700 mT was applied, indicating the presence of high coercivity The oldest rocks exposed in the Mangkang area are of Early magnetic minerals (Fig. 2A). Thermal demagnetization of a three- Ordovician in age. Middle Devonian to Upper Permian littoral component IRM revealed that the hard component in samples and shallow marine limestone and dolomite unconformably over- MK8-7 and MK12-8 samples were reduced dramatically at around lie the Lower Ordovician strata. Triassic strata are mainly com- 100 °C, indicating the existence of goethite. The soft and medium posed of littoral-shallow marine clastic rocks and limestone components of four specimens began to be reduced around with intercalated latite and amygdaloidal basalt, conformably 500 °C(Fig. 2B) and the soft component unblocked at 580–600 °C overlain by Jurassic to Cretaceous red-beds (Huang et al., 1992; (Fig. 2C). In addition, the hard component of samples MK8-7, BGMRX, 1993). Previously stratigraphic studies divided the Creta- MK12-8 and MK16-2 was also reduced slightly at 500–600 °C. ceous red-beds of the Mangkang area into the Lower Cretaceous These characteristics indicate the presence of magnetite (Fig. 2B). Laoran Formation and the Upper Cretaceous Zonggu Formation As the thermal demagnetization temperature continuously and the Xuzhong Formation, with the Zonggu Formation con- increased, the medium and hard components of all four specimens formably overlying the Laoran Formation. The Laoran Formation finally unblocked at 680 °C(Fig. 2B), indicating the presence of has a total thickness of about 800 m in the Mangkang area, and abundant hematite. Thus, we conclude that hematite and mag- is mainly composed of calcareous siltstone, mudstone, yellow– netite are the dominant magnetic carriers of the Upper Cretaceous green feldspathic quartz sandstone, and interbedded purple–red Zonggu Formation in the Mangkang area, with goethite also being sandstone and conglomerate. Abundant vertebrate fossils (e.g., present in some cases. Prodeinodon tibetensis, Mangkamosaurus lawulacus) have been found in this formation, indicating an Early Cretaceous age (BGMRX, 1993). The Zonggu Formation is about 1700 m thick in 4. Paleomagnetic results total and is mainly composed of purple-red mudstone, argilla- ceous siltstone and interbedded coarse red sandstone and quartz The paleomagnetic experiments were carried out in the Key sandstone. The presence of abundant dinosaur fossils (Megacer- Laboratory of Paleomagnetism and Tectonic Reconstruction, the uixosaurus tibetensis, Ornithomimus sp., and Hadrosauridae spe- Ministry of Land and Resources in Beijing. All the core samples cies) and the ostracodes (Eucypris profunda, E. angulata Ye, were cut into specimens of length 2.2–2.3 cm in the laboratory. Darwinula contracta Mandelstam, Cypridea sp., and Quadro- All specimens were subjected to stepwise thermal demagnetiza- cypridea regularis) indicate a Late Cretaceous age (Huang et al., tion in an ASC TD-48 thermal demagnetizer, and remanent magne- 1992; BGMRX, 1993). tization was measured using a 2G-755 cryogenic magnetometer. The section from which paleomagnetic samples were obtained Stepwise thermal demagnetization was carried out up to 680 °C, is located in the Upper Cretaceous Zonggu Formation in the west- the temperature interval for thermal demagnetization was ern part of Mangkang County (Fig. 1B). The sampling section 50–100 °C at the beginning, then 10–20 °C at higher temperatures. stretches across an approximate northwest axial-trending fold The magnetic behavior of each specimen during thermal demagne- belt. A total of 18 sites (223 samples) were sampled in the Upper tization was plotted on a Zijderveld diagram (Zijderveld, 1967; Cretaceous Zonggu Formation (Fig. 1B), and each sampling site Cogné, 2003). The directions of magnetization components of spec- spans several meters of the strata to ensure that a sufficient length imens were determined using principal component analysis of time is represented. Sampling sites MK3–MK18 were obtained (Kirschvink, 1980). Site-mean directions were calculated using from purple-red mudstone and siltstone, and the other two sam- Fisher’s statistics (Fisher, 1953). pling sites (MK1, MK2) were obtained from coarse red sandstone All of the specimens exhibited similar magnetic behavior dur- and quartz sandstone. All samples were collected with a portable ing thermal demagnetization (Fig. 3). The low-temperature mag- drill and oriented with a magnetic compass. The location of each netization components (LTC) could be isolated from only 43 sampling site was determined using a portable GPS. The present- specimens when the thermal demagnetization temperature day geomagnetic direction value at the sampling section was esti- reached 200 °C. The site-mean direction of the LTC before tilt mated using the International Geomagnetic Reference Field (2010) correction is Dg = 357.6°, Ig = 34.3°, k = 22.2, a95 = 4.7°, n =43 (International Association of Geomagnetism and Aeronomy, 2010). samples, which is close to the Earth’s magnetic field in the Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749 735

Fig. 2. Rock magnetic results for representative specimens from Upper Cretaceous red-beds. (A) IRM acquisition curve and back-field demagnetization. (B) Thermal demagnetization of IRM. Thermal demagnetization of a three component IRM produced by applying a different DC field (2.5 T, 0.4 T and 0.12 T) to each of three perpendicular axes of a specimen. (C) Thermal demagnetization of the soft components of the IRM. sampling area (D = 358.3°, I = 35.9°), and the mean direction after the 95% confidence limits, which may be caused by the small num- tilt correction is Ds = 21.6°, Is = 56.9°, k = 5.6, a95 = 10.2°(Fig. 4A). ber of reversed polarity sites (MK3–MK5), which were sampled at The precision parameter (k) decreases from 22.2 to 5.6 after tilt the similar stratigraphic levels, and represented probably a short correction, suggesting that the LTC is a viscous remanent time of deposition. magnetization. The high-temperature component (HTC) was defined by a linear Although the thermal demagnetization results from most of the decay toward the origin from 600 to 685 °C, observed in 17 sam- specimens indicate that the remanence behaves as a single linear pling sites (Fig. 3), which was carried by hematite, as demonstrated magnetization component after heating to 300 °C, the demagneti- by the rock magnetic results. Sites MK1 is mainly composed of zation intensities fall rapidly after heating to 600 °C and 680 °C. coarse red sandstone, which gave a site-mean direction with a

These characteristics indicate the presence of two magnetization large degree of uncertainty (a95 = 19.6°) and which also deviates components carried probably by magnetite and hematite, respec- from the HTC directions of sampling sites. Consequently, we tively. The middle-temperature magnetization component (MTC) rejected the direction of MK1 for further consideration. Three sites could be isolated between 350 °C and 580 °C for specimens from (MK3, MK4, and MK5) exhibit reversed polarity directions, and the sampling sites MK2–MK18 (Fig. 3). Three sites (MK3, MK4, and other 14 sites exhibit normal polarity (Table 2 and Fig. 4C). The

MK5) exhibit a reversed polarity MTC, and the other 14 sites exhi- site-mean direction is Dg = 49.3°, Ig = 25.7°, kg = 4.3, a95 = 19.5° bit a normal polarity MTC (Table 1 and Fig. 4B). The site-mean (N = 17 sites) before tilt correction, and Ds = 51.3°, Is = 56.1°, direction is Dg = 48.4°, Ig = 26.1°, kg = 4.0, a95 = 20.4°, N = 17 sites ks = 31.0, a95 = 6.5° after tilt correction. The fold test of before tilt correction, and Ds = 49.9°, Is = 56.9°, ks = 41.8, McElhinny (1964) gave ks/kg = 7.18 > F [32, 32] = 1.81, indicating a95 = 5.6° after tilt correction. The fold tests are positive at the a positive fold test at the 95% confidence level. The fold test of 95% confidence level, according to the methods of McElhinny McFadden (1990) is also positive at the 95% confidence level,

(1964) (ks/kg = 10.37 > F [32, 32] = 1.81), and McFadden (1990) according to the calculated values nin situ = 13.60 in geographic (the calculated values are nin situ = 11.69 in geographic coordinates coordinates and ntilt corrected = 1.57 after tilt correction, while the and ntilt corrected = 2.26 after tilt correction, while the critical value is critical value nC = 4.80. While applying progressive unfolding, the nC = 4.80 at the 95% confidence level). In addition, on applying pro- precision parameter (k) reaches a maximum at 98.6% unfolding gressive unfolding, the precision parameter (k) reaches a maxi- (Fig. 4C). The reverse test is positive at the 95% confidence limit mum at 103.0% unfolding (Fig. 4B). The positive fold tests with a classification C (averages Gamma = 14.2 < Critical confirm that the MTC is the pre-folding original magnetization. Gamma = 16.2) (McFadden and Lowes, 1981). Therefore, we con- The reverse test (McFadden and Lowes, 1981) was negative at clude that the HTC remanence is the primary magnetization. 736 Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749

Fig. 3. Orthogonal projections of magnetization vector end-points for representative specimens of Upper Cretaceous red-beds. Solid/open symbols are the horizontal/vertical projection in geographic coordinates. The red points show the thermal temperature interval which resulted in the isolation of the MTCs. The blue points show the thermal temperature which resulted in the isolation of the HTCs. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.) Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749 737

Fig. 4. (A) Equal-area projections of the site mean directions for low-temperature components before and after tilt correction. (B) Equal-area projections of the site mean direction for middle-temperature components before and after tilt correction, and progressive unfolding of the mean direction. (C) Equal-area projections of the site mean direction for high-temperature components before and after tilt correction, and progressive unfolding of the mean direction. Gray circles around the red stars in the (A), (B) and (C) denote the 95% conﬁdence limit and mean direction of the sampling section. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.)

Careful analysis of the thermal demagnetization results indi- both acquired very shortly after sediment deposition. The positive cates that the site-mean direction of the MTC is insigniﬁcantly dif- fold test suggests that both the MTC and HTC magnetizations were ferent with that of the HTC, which implies that the magnetic formed prior to the formation of fold belts, and the positive reverse carriers of MTC and HTC are very probably detrital magnetite and tests results for the HTC suggests that the HTC magnetizations were hematite, respectively, and that their respective remanences were acquired during the formation of the red-beds. 738 Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749

Table 1 Middle temperature magnetic components of Upper Cretaceous red-beds samples collected from the Mangkang.

Site Locality Bedding n/N In situ Tilt-corrected k a95 (°) Paleopole A95 (°) N/E (°) Strike/dip (°) Dec. (°) Inc. (°) Dec. (°) Inc. (°) Lat. (°N) Lon. (°E) *MK1 29°430/98°250 140/76 5/12 336.8 40.4 306.8 46.2 20.6 14.7 – – – MK2 29°430/98°250 140/76 11/12 60.4 49.4 99.1 65.0 39.1 7.4 – – – MK3 29°430/98°250 140/76 12/14 222.9 21.9 220.4 47.2 27.2 8.5 – – – MK4 29°430/98°250 137/68 11/12 219.2 21.0 216.3 45.7 71.2 5.4 – – – MK5 29°430/98°250 138/78 10/13 216.0 29.9 214.6 38.9 43.6 7.4 – – – MK6 29°420/98°300 171/54 11/12 73.2 7.0 65.4 60.1 86.7 4.9 – – – MK7 29°420/98°300 184/51 11/12 86.1 8.7 81.1 58.1 212.0 3.1 – – – MK8 29°420/98°320 253/36 8/11 119.3 52.7 56.8 63.1 111.0 5.3 – – – MK9 29°420/98°320 245/45 10/12 106.3 51.0 37.3 58.8 67.8 5.9 – – – MK10 29°420/98°340 161/60 11/12 64.5 8.0 49.2 65.9 55.3 6.2 – – – MK11 29°420/98°340 173/45 7/14 62.2 13.4 45.1 56.4 39.1 9.8 – – – MK12 29°420/98°340 183/45 9/14 66.5 24.8 37.5 60.6 135.5 4.4 – – – MK13 29°420/98°340 206/34 11/12 66.6 31.4 40.6 48.0 126.5 4.1 – – – MK14 29°420/98°350 28/41 9/13 358.9 39.5 39.3 46.6 140.9 4.4 – – – MK15 29°420/98°350 40/43 9/12 354.1 36.3 37.3 55.0 91.1 5.4 – – – MK16 29°420/98°350 53/47 8/12 358.5 37.7 54.0 62.7 152.9 4.5 – – – MK17 29°420/98°350 54/50 8/12 7.4 33.8 57.7 55.1 156.1 4.4 – – – MK18 29°420/98°350 53/52 7/12 359.3 42.7 74.4 62.2 160.6 4.8 – – – Group mean direction of Upper Cretaceous 17/18 48.4 26.1 4.0 20.4 red-beds 17/18 49.9 56.9 41.8 5.6 Fold Test and reversal Test: (A) positive fold test at 95% confidence limits; (B) positive fold test at 95% confidence limits Reversal Test: (C) Negative at 95% confidence limits (A) McElhinny’s Test (1964): N = 17, ks/kg = 10.37 > F [32,32]= 1.81 at 95% confidence limit

(B) McFadden’s Test (1990): N = 16, n(2)in-situ = 11.69 > nC = 4.80 > n(2)tilt-corrected = 2.26 at 95% conﬁdence limit (C) McFadden and Lowes (1981): Statistics R = 0.12, averages Gamma = 7.8, F [26,4] = 5.76, Critical Gamma = 12.2, Critical R at 95% = 0.2

N and n are number of samples collected and used for paleomagnetic calculation, respectively. Dec. and Inc. are declination and inclination, respectively; k is the Fisherian precision parameter for samples (Fisher, 1953); a95 and A95 are the radius of cone at 95% conﬁdence level about the mean direction. Lat. and Lon. are latitude and longitude of paleopole.

5. Inclination shallowing of the Cretaceous red-beds of the (36.7 ± 6.7°)(Fig. 5A). Next, only sites where the attitudes of the Mangkang area sampling strata were uniform were selected for E/I correction. According to these stricter criteria, only samples from sites MK8, The results of statistical analyses and comparison of the paleo- MK9 and MK14–MK18 were selected. In this case, the corrected magnetic data from red-beds with those from volcanic rocks con- inclination for the Late Cretaceous is 62.8°, with an error range firm that depositional and/or compaction-induced inclination from 55.4° to 76.3°. Although the latter was smaller than that for shallowing in hematite-bearing red-beds may result in inclination the former estimation, the corresponding paleolatitude of deviation in East Asia (Bazhenov et al., 2002; Gilder et al., 2003; 44.2 ± 7.4°, is still higher than that of the observed paleolatitude Tan et al., 2003; Tauxe and Kent, 2004; Huang et al., 2005; Wang (36.7 ± 6.7°)(Fig. 5B). Paleomagnetic data from volcanic rocks and Yang, 2007). Therefore the elongation/inclination (E/I) correc- and red-beds indicate that the Tarim Block was situated in a range tion method (Tauxe and Kent, 2004), and the inclination shallow- of paleolatitudes between 30.6 ± 6.4°N and 35.0 ± 4.4°N during ing correction experiments described by Hodych and Buchan Cretaceous to Eocene time (Gilder et al., 2003; Huang et al., (1994), were used to test whether inclination shallowing is evident 2005; Bazhenov et al., 2002). In addition, Late Cretaceous paleo- in the paleomagnetic results. magnetic data from volcanic rocks from the Qaidam Basin indicate The main principle of the elongation/inclination (E/I) correction that the eastern edge of the Qaidam Basin, to the north of the method (Tauxe and Kent, 2004) is that while the deposition and Qiangtang Block, was situated at a paleolatitude of 34.4 ± 5.4°N compaction of red-beds may systematically compress the distribu- (the reference point is 35.2°N, 101.8°E) during the Late Cretaceous tion range of the observed inclination data, the distribution range (Sun et al., 2006). It is therefore impossible for the Qiangtang Block of the declination data should remain stable. This should lead to to have been situated on the northern side of the Tarim Block and the elongation of the distribution of the paleomagnetic data along the Qaidam Basin during the Late Cretaceous. Therefore, we con- the latitudinal direction. Local differences in vertical-axis rota- clude that correction of the inclination data using the E/I method tional deformation, or in plunging fold movement of the sampling may produce an excessively high estimate based on the potentially strata, can also induce a similar deviation of the paleomagnetic only slight local deformation and the wide distribution of the sam- data along the latitudinal direction. In this case, it is impossible pling sites. to determine if this effect was caused by the deposition and com- The rock magnetic results demonstrate that hematite is the paction or by regional differences in rotational deformation. Varia- main magnetic carrier of the HTC in Upper Cretaceous red-beds tions in the attitude of the sampling strata may indicate that they in the Mangkang area, and therefore the method of Hodych and are affected by local rotational deformation, which may have Buchan (1994) can be used to determine quantitatively the caused the deviation of the magnetic declinations. Thus, the sam- possibility of inclination deviation. Fifteen specimens were drilled ples from sites MK6–MK18 were selected for elongation/inclina- in the direction perpendicular to the bedding from five oriented tion (E/I) correction based firstly on the relatively similar attitude hand samples from sites MK3, MK7, MK10, MK12, and MK15. of the sampling strata. The E/I correction shows that the corrected The IRM parallel (IRMx) and perpendicular (IRMz) to the bedding inclination for the Late Cretaceous is 66.8°, with an error range plane for the 15 specimens were measured in successive DC from 58.2° to 79.0°, corresponding to a paleolatitude of fields applied at angle of 45° to the bedding, and then thermal 49.4 ± 9.9°. This is clearly higher than the observed paleolatitude demagnetizations were performed on the same specimens. The Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749 739

Table 2 High temperature magnetic components of Upper Cretaceous red-beds samples collected from the Mangkang.

Site Locality Bedding n/N In situ Tilt-corrected k a95 (°) Paleopole A95 (°) N/E (°) Strike/dip (°) Dec. (°) Inc. (°) Dec. (°) Inc. (°) Lat. (°N) Lon. (°E) This study *MK1 29°430/98°250 138/57 6/12 271.8 0.7 287.2 35.5 12.7 19.6 – – – MK2 29°430/98°250 111/28 12/12 61.5 58.7 119.7 70.0 75.5 5.0 8.5 129.5 8.0 MK3 29°430/98°250 140/76 13/14 226.5 18.5 224.8 51.4 25.2 8.4 51.8 173.1 9.4 MK4 29°430/98°250 137/68 12/12 221.4 15.6 218.2 51.4 33.8 8.0 57.3 174.4 9.0 MK5 29°430/98°250 138/78 11/13 216.0 29.9 214.6 38.9 43.6 7.4 58.0 194.2 6.8 MK6 29°420/98°300 171/54 12/12 75.9 5.5 71.1 59.2 119.9 3.8 32.3 157.5 4.9 MK7 29°420/98°300 184/51 11/12 87.9 6.6 84.9 56.1 151.1 3.9 21.0 157.3 4.8 MK8 29°420/98°320 253/36 8/11 107.4 49.9 56.2 55.5 132.7 5.8 43.0 165.3 7.0 MK9 29°420/98°320 245/45 11/12 104.2 52.3 34.7 57.9 67.9 5.6 60.1 161.9 7.1 MK10 29°420/98°340 161/60 11/12 62.5 4.6 47.6 62.0 66.2 6.0 50.0 155.4 8.2 MK11 29°420/98°340 173/45 12/14 63.4 19.2 41.8 62.2 27.0 11.8 54.2 154.3 16.2 MK12 29°420/98°340 183/45 13/14 62.0 23.4 33.2 56.9 116.5 4.8 61.4 163.9 5.9 MK13 29°420/98°340 206/34 11/12 64.3 23.4 45.1 40.3 79.1 5.2 49.3 187.1 4.9 MK14 29°420/98°350 28/41 9/13 1.8 39.1 40.5 44.5 111.9 4.9 54.2 184.2 4.9 MK15 29°420/98°350 40/43 9/12 350.3 41.2 42.4 59.8 43.0 8.5 37.3 178.3 8.3 MK16 29°420/98°350 53/47 10/12 348.9 37.6 46.5 69.6 49.0 10.1 49.0 139.8 16.0 MK17 29°420/98°350 54/50 11/12 25.5 29.7 62.4 39.5 18.3 16.1 34.1 180.3 14.9 MK18 29°420/98°350 53/52 10/12 10.1 39.6 70.6 53.7 104.5 5.9 31.2 164.2 6.9 Group mean direction of Upper Cretaceous 17/18 49.3 25.7 4.3 19.5 red-beds 17/18 51.3 56.1 31.0 6.5 Fold Test: (A) positive fold test at 95% confidence limits; (B) positive fold test at 95% confidence limits Reversal Test: (C) positive at 95% confidence limits in classification C (A) McElhnny’s Test (1964): N = 17, ks/kg = 7.18 > F [32,32] = 1.81 at 95% confidence limit

(B) McFadden’s Test (1990): N = 17, n(2)in-situ = 13.60 > nC = 4.80 > n(2)tilt-corrected = 1.57 at 95% confidence limit (C) McFadden and Lowes (1981): Statistics R = 0.17, averages Gamma = 14.2, F26,4] = 5.76, Critical Gamma = 16.2, Critical R at 95% = 0.22 Huang et al., 1992 B29°420/98°420 174/60 5/5 45.7 9.3 34.8 36.2 232.7 5.0 57.2 197.5 4.4 C29°420/98°420 130/60 5/5 21.5 2.6 3.9 57.5 93.6 8.0 91.0 118.8 10.0 D29°420/98°420 353/62 5/5 298.9 44.2 32.3 57.2 359.2 3.9 62.1 163.1 4.9 E29°420/98°420 30/45 5/5 9.8 38.7 49.0 39.3 433.6 3.7 45.7 186.3 3.4 F29°420/98°420 30/47 5/5 337.4 45.2 47.8 63.3 52.4 10.7 49.7 153.0 15.0 G29°420/98°420 56/46 5/5 5.5 28.7 43.4 55.1 66.3 9.5 53.3 167.7 11.4 H29°420/98°420 40/50 5/5 10.8 36.8 56.6 43.3 91.3 8.1 40.1 179.4 7.9 I29°420/98°420 10/52 5/5 151.2 60.5 242.3 51.0 1233.6 3.2 37.2 169.5 3.6 J29°420/98°420 2/60 5/5 325.2 49.7 44.1 45.8 513.4 3.4 51.4 181.1 3.5 K29°420/98°420 2/60 9/10 323.2 52.1 47.6 46.7 178.3 3.9 48.5 178.8 4.0 M29°420/98°420 176/49 5/5 44.6 32.1 357.6 55.9 102.3 7.6 50.0 165.9 9.2 The mean direction of Upper Cretaceous 28 31.8 54.8 3.9 15.9 red-beds of this study and Huang et al. 28 46.8 54.5 29.4 5.1 (1992) Fold Test: (A) positive fold test at 95% confidence limits; (B) positive fold test at 95% confidence limits Reversal Test: (C) positive at 95% confidence limits in classification C (A) McElhinny’s Test (1964): N = 28, ks/kg = 7.513 > F [54,54] = 1.57 at 95% confidence limit

(B) McFadden’s Test (1990): N = 28, n(2)in-situ = 22.99 > nC = 6.15 > n(2)tilt-corrected = 1.53 at 95% conﬁdence limit (C) McFadden and Lowes (1981): Averages Gamma = 7.0, F [46,6] = 3.76, Critical Gamma = 14.6, Critical R at 95% = 0.12

results of ﬁve representative specimens are shown in Fig. 6. The 6. Cretaceous paleopoles of the Mangkang area value of IRMz is approximately equal to that of IRMx when the ﬁeld was applied in the range of 200–1000 mT (Fig. 6B). Paleopoles were calculated for each sampling site (Table 2), and Because the HTCs were isolated in the temperature interval from then Fisher’s statistics (Fisher, 1953) were used to calculate the 600 °C to 680 °C, the values of IRMz and IRMx demagnetized average Late Cretaceous paleopole (paleolatitude = 45.6°, longi- between 600 °C and 680 °C were also selected for comparison tude = 164.6°) of the studied section in the Mangkang area. (Fig. 6C), and these values were roughly equal. The mean ratios Huang et al. (1992) carried out paleomagnetic studies in the of IRMz/IRMx of thermal demagnetization between 600 °C and Upper and Lower Cretaceous red-beds in the Mangkang area, adja- 680 °C and those acquired between 200 and 1000 mT for the 15 cent area to the present study area. Otofuji et al. (1990) also specimens are 0.980 and 0.989, respectively. The mean ratio of obtained paleomagnetic data from the Lower Cretaceous red- IRMz/IRMx calculated from higher-temperature demagnetizations beds in the Mangkang area. In most of the sampling sites used in (600–680 °C) was used to correct the inclination of the sampling these two studies, the number of specimens sampled at each site sites. The corrected site-mean inclination for the HTC is 56.6°, was less than 6. Although no fold test was conducted due to the which is almost the same as the observed inclination (56.1°) fact that a single limb was sampled in the study of Otofuji et al. (Table 3). Thus, this result indicates that inclination shallowing (1990), the HTC directions of the Early Cretaceous obtained by is not present in the Upper Cretaceous red-beds of the Mangkang Otofuji et al. (1990) and Huang et al. (1992) are similar (Table 4). area. The Late Cretaceous HTC directions obtained by Huang et al. 740 Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749

Fig. 5. Results of E–I (elongation–inclination) correction of Paleogene paleomagnetic data from the southeastern part of Simao Terrane. (A) For samples MK6–MK18, the corrected inclination is 66.8°, with an error range of 58.2–79.0°. (B) For samples MK8, MK9 and MK14–MK18, the corrected inclination is 62.8°, with an error range of 55.4– 76.3°. (A-a) and (B-a): Paleomagnetic directions. (A-b) and (B-b): Elongation direction of the curve with respect to inclination. (A-c) and (B-c): Elongation/inclination as a function of f. (A-d) and (B-d): Cumulative distribution of the corrected inclination.

(1992) are also very similar to those obtained in our study mean Early Cretaceous paleopole for the Mangkang area is at

(Table 2). Plat. = 43.0°, Plong. = 171.8°, A95 = 9.2°. The Late Cretaceous paleomagnetic data of the present study The Master Apparent Polar Wander Path (APWP) for Eurasia were combined with those of Huang et al. (1992) to obtain an over- (Besse and Courtillot, 2002, 2003) is usually employed as reference all mean direction for the Mangkang area (Table 2). The result was paleopoles for Late Mesozoic–Cenozoic paleomagnetic studies of as follows: Dg = 31.8°, Ig = 54.8°, kg = 3.9, a95 = 15.9° (N = 28 sites) the Tibetan Plateau. However, recent geological studies show that before tilt correction, and Ds = 46.8°, Is = 54.5°, ks = 59.4, the Eurasian plate was probably not a rigid plate during the Ceno- a95 = 5.1° after tilt correction (Fig. 7A). The fold test of McElhinny zoic, and relative tectonic movements may still have occurred (1964) shows that ks/kg = 7.513 > F [54, 54] = 1.57, indicating a between the European and the Siberian blocks. Thus the use of positive fold test at the 95% conﬁdence level. The McFadden fold European poles would induce a greater intracontinental shortening test (McFadden, 1990) is also positive at the 95% conﬁdence level estimate in Asia when paleomagnetic data are compared (Yegorova

(nin situ = 22.99 in geographic coordinates and ntilt corrected = 1.53 and Starostenko, 1999; Trifonov, 2004; Dupont-Nivet et al., 2010a, after tilt correction, critical value nC = 6.15). The results pass the b; Cogné et al., 2013). Cogné et al. (2013) constructed a new APWP reversal test with classiﬁcation C (average Gamma = 7.0 < Critical for Eastern Asia using the paleomagnetic data obtained from the Gamma = 14.6) (McFadden and Lowes, 1981). The grand mean of Siberian Craton, Amuria, the Korean Peninsula and the North and Late Cretaceous paleopoles is: Plat. = 48.7°, Plong. = 167.7°, South China blocks. However, the Cretaceous reference poles for

A95 = 6.1° (N = 28 sites). Eastern Asia of Cogné et al. (2013) are indistinguishable from the The grand mean of the Early Cretaceous paleomagnetic data of Eurasian Cretaceous reference poles of Besse and Courtillot Huang et al. (1992) and Otofuji et al. (1990) for the Mangkang area (2002, 2003), indicating that Eurasia remained relatively stable is Dg = 305.3°, Ig = 40.9°, kg = 1.8, a95 = 40.2° (N = 17 sites) before and approximated a rigid block during the Cretaceous. Therefore, tilt correction, and Ds = 54.8°, Is = 49.9°, ks = 21.9, a95 = 7.8° after the Cretaceous APWP of Eurasia constructed by Besse and tilt correction (Fig. 7B and Table 4). The fold test is positive with Courtillot (2002, 2003) was still used in the present study to esti- ks/kg = 12.31 > F [32, 32] = 2.05 at the 95% conﬁdence level mate the intracontinental crustal deformation of the Tibetan pla-

(McElhinny, 1964), and nin situ = 20.07 in geographic coordinates teau. To restrict the reference paleopoles accurately, we divided and nilt corrected = 2.03 after tilt correction (critical value of the Cretaceous paleopoles selected from the APWP of Eurasia into nC = 4.04) (McFadden, 1990). Reference to Fig. 7B shows that the two groups according to the geomagnetic polarity time scale, and site-mean directions of Huang et al. (1992) and Otofuji et al. then calculated the average paleopoles for the Early and Late Cre- (1990) are elongated in the longitudinal (W–E) direction, indicat- taceous using Fisher statistics (Table 5). The average Paleocene ing the probable occurrence of rotational deformation between paleopole was also calculated using the same method (Table 5). the sampling sections. The mean of inclination values is only The average paleopoles for each geological stage of Eurasia were 47.8 ± 5.8° after tilt correction, which is indistinguishable from used as reference paleopoles to calculate the latitudinal displace- that calculated using Fisher’s statistics (Is = 49.9°). The overall ment and rotations of the Lhasa Block and the Qiangtang Block Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749 741

Fig. 6. (A) Plots of IRMx (parallel to bedding) and IRMz (perpendicular to bedding) acquisitions produced by applying a magnetic field at an angle of 45° to the bedding as a function of increasing field. (B) The slope (IRMz/IRMx) of the least-squares-fit for the data points between 200 mT and 1000 mT was used to estimate the magnetic anisotropy of hematite. (C) The slope of the thermal demagnetization of IRMz and IRMx between 600 °C and 680 °C was used to estimate the inclination shallowing ratio for the inclination correction of the red-bed samples. 742 Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749

Table 3 latitudinal displacement (3.2 ± 7.8°), and at a paleolatitude of Anisotropy of isothermal remanent magnetization for Lower Cretaceous red-beds of 35.0 ± 5.1°N in the Late Cretaceous with southward latitudinal dis- the Mangkang area. placement (7.3 ± 5.2°) with respect to Eurasia.

ID NIobs IF Mean IRMz/IRMx Mean IRMz/ The paleomagnetic results of Halim et al. (1998) suggested that (sampling (acquired between IRMx the Qiangtang Block was situated at a paleolatitude of 18.9 ± 5.9°N sites) 200 and 1000 mT) (acquired in the Paleocene, and experienced 16.7 ± 7.3° northward latitudi- above 600 °C) nal displacement relative to Eurasia since the Paleocene. Chen et al. Mk3 3 51.4 52.7 0.956 0.951 (1993) suggested that the western part of the Qiangtang Block was MK7 3 56.1 56.8 0.985 0.971 ° Mk10 3 62.0 61.6 1.056 1.018 situated at a paleolatitude of 11.3 ± 5.6 N in the Cretaceous, based Mk12 3 56.9 57.1 1.023 0.994 on paleomagnetic results obtained from the Cretaceous red-beds at MK15 3 59.8 60.7 0.923 0.965 the western end of the Qiangtang Block, and this may indicate that Group mean 56.1 56.6 0.989 0.980 western Qiangtang experienced 18.9 ± 4.9° northward latitudinal direction displacement relative to Eurasia since the Cretaceous. Lippert et al. N: the number of specimens performed the measurement of thermal demagneti- (2011) obtained Eocene paleomagnetic results from three volcanic zation and AIR, respectively; Iobs: means observed inclination; IF: means inclination sampling sections in the central part of the Qiangtang Block calculated from the IRMz/IRMx acquired above 600 °C. (Table 6 and Fig. 8A), which gave a mean paleolatitude of 28.7 ± 3.7°N at a reference point (33.0°N/88.0°E), suggesting that ° which comprise the southern and central parts of the Tibetan the central part of the Qiangtang Block experienced 6.2 ± 4.6 Plateau. northward displacement relative to Eurasia (Lippert et al., 2014). Although inclination shallowing tests were not conducted in studies of red-beds by Chen et al. (1993) and Halim et al. (1998), 7. Discussion our present Cretaceous result, and those obtained from Cretaceous volcanic rocks from the Lhasa Block and from Eocene volcanic 7.1. The discrepancy between the Cretaceous and Eocene rocks in the Qiangtang Block (Table 6), indicate the existences of paleomagnetic data of the Qiangtang Block inclination shallowing in the Cretaceous red-beds in the western and central part of the Qiangtang Block (Chen et al., 1993; Halim In the last three decades, several paleomagnetic studies have et al., 1998). Thus, the paleomagnetic data of Chen et al. (1993) been conducted on the Cretaceous and Cenozoic red-beds or vol- and Halim et al. (1998) were not used in the following discussion. canic rocks of the Qiangtang Block, most of them from the middle and eastern parts (Table 6). However, relatively few paleomagnetic studies have been made of the western areas of the Qiangtang 7.2. The discrepancy between the Cretaceous and Paleocene–Eocene Block. The Cretaceous results from the Mangkang area in the east- paleomagnetic data from the Lhasa Block ern part of Qiangtang Block are very consistent (Huang et al., 1992; Otofuji et al., 1990; this study), which indicate that the eastern part Many paleomagnetic studies have been carried out on Creta- of the Qiangtang Block was once situated at a paleolatitude of ceous red-beds and volcanic rocks to constrain the age of the 30.7 ± 6.9°N in the Early Cretaceous with insigniﬁcant southward India–Asia collision and crustal shortening in south Eurasia

Table 4 High temperature magnetic components of Lower Cretaceous red-beds samples collected from the Mangkang area.

Site Locality Bedding n/N In situ Tilt-corrected k a95 (°) Paleopole A95 (°) N/E(°) Strike/dip (°) Dec. (°) Inc.(°) Dec. (°) Inc. (°) Lat. (°N) Lon. (°E) Huang et al., 1992 A29°420/98°240 350/80 4/5 268.6 46.6 70.2 52.7 104.5 9.0 31.2 165.3 10.3 B29°420/98°240 0/84 4/5 279.2 42.1 78.6 53.0 73.1 9.0 24.7 162.4 10.4 D29°420/98°240 335/120 5/5 259.7 5.6 40.9 51.7 46.2 11.4 55.0 173.3 12.8 E29°420/98°240 336/125 5/5 265.4 5.8 38.1 45.3 198.9 5.4 56.5 183.9 5.5 G29°420/98°240 330/120 5/5 280.6 16.5 14.4 29.3 32.2 13.7 70.7 231.9 11.2 I29°420/98°240 324/120 5/5 276.1 23.7 46.0 31.6 95.1 7.9 46.2 194.5 6.6 J29°420/98°240 351/83 5/5 248.2 47.2 94.1 48.3 41.0 12.1 10.9 160.7 12.8 K29°420/98°240 350/85 5/5 250.9 55.0 86.8 39.5 29.1 14.1 13.5 170.3 13.4 A1 29°420/98°360 208/115 3/5 64.3 51.6 75.9 41.7 2272.3 2.6 23.3 173.3 2.5 B1 29°420/98°360 200/115 4/5 76.2 50.1 72.7 53.8 138.3 7.8 29.5 163.6 9.1 C1 29°420/98°360 186/107 5/5 70.6 33.9 47.4 61.7 152.7 6.2 50.2 156.1 8.4 D1 29°420/98°360 190/113 5/5 67.9 29.4 29.4 60.6 839.6 3.3 63.5 153.9 4.4 Otofuji et al., 1990 70 29°420/98°360 13/49 6/6 30.2 53.9 47.3 49.2 211.0 4.6 49.3 175.9 8.0 71 29°420/98°360 17/46 6/6 22.2 53.6 51.8 56.0 20.1 15.3 46.6 165.4 18.6 72 29°420/98°360 12/52 6/6 30.8 54.4 54.8 54.3 128.0 6.0 43.9 167.3 7.1 73 29°420/98°360 7/58 6/6 23.8 56.2 26.2 42.9 119.7 6.2 40.3 179.8 6.0 74 29°420/98°360 5/49 6/6 16.4 44.5 33.3 40.9 124.0 6.0 59.7 192.5 5.7 The mean direction of Lower Cretaceous 17 305.3 40.9 1.8 40.2 red-beds of Huang et al. (1992) and 17 54.8 49.9 21.9 7.8 Otofuji et al. (1990) Fold Test: (A) positive fold test at 95% confidence limits; (B) positive fold test at 95% confidence limits (A) McElhinny’s Test (1964): N = 17, ks/kg = 12.31 > F [32,32] = 2.05 at 95% confidence limit

(B) McFadden’s Test (1990): N = 17, n(2)in-situ = 20.07 > nC = 4.04 > n(2)tilt-corrected = 2.03 at 95% conﬁdence limit

Fig. 7. (A) Equal-area projections of Late Cretaceous paleomagnetic data and mean direction of this study and that of Huang et al. (1992), before and after tilt correction. (B) Equal-area projections of Early Cretaceous paleomagnetic data and mean direction of Otofuji et al. (1990) and Huang et al. (1992), before and after tilt correction. Gray circles around the red stars in (A) and (B) denote the 95% conﬁdence limit and mean direction of the sampling section. Blue circle with blue dashed line is the average inclination and error of the average inclination for the sampling section. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web version of this article.)

Table 5 The Cretaceous and Paleogene reference paleopole of the Eurasia calculated from the Master Apparent Polar Wander Path of Eurasia (Besse and Courtillot, 2002, 2003).

Name Time Age (Ma) VGP Average VGP

Plat. (°) Plon. (°) A95 (°) K Plat. (°) Plon. (°) A95 (°) Eurasia-E Eocene 40.0 81.3 162.4 3.3 81.9 – – – Eurasia-P Paleocene 52.2 80.9 164.4 3.4 59.4 81.3 172.4 3.7 59.7 81.1 190.5 2.9 56.1 Eurasia-K2 Late Cretaceous 67.3 80.3 204.3 3.2 61.0 81.5 198.5 2.2 77.9 81.4 206.1 5.9 47.2 90.0 82.2 202.1 5.2 65.2 97.6 81.7 180.1 6.7 43.0 Eurasia-K1 Early Cretaceous 113.6 80.0 183.6 4.2 74.8 77.0 191.8 3.4 119.1 78.2 189.4 2.4 182.9 126.4 75.8 192.9 2.8 205.5 136.8 73.8 197.6 6.0 103.2 Eurasia-K Cretaceous 79.3 194.4 2.4

Plat.: Latitude of paleopole; Plon.: Longitude of paleopole; K: the Fisherian precision parameter for samples (Fisher, 1953); A95 is the radius of cone at 95% conﬁdence level about the average paleopole.

(Achache et al., 1984; Chen et al., 2010; Dupont-Nivet et al., 2010a; paleolatitude of 24.2 ± 4.2°N and that only 2.9 ± 3.8° Liebke et al., 2010; Ma et al., 2014; Yang et al., 2014; Chen et al., intracontinental shortening occurred within Asia, according to 2012; Tan et al., 2010; Sun et al., 2010, 2012; Huang et al., 2013). paleomagnetic data from Upper Cretaceous lava ﬂows at Linzhou. Tan et al. (2010) point out the Lhasa Block was situated at a Their paleomagnetic results indicate the possible occurrence of 744

Table 6 The Cretaceous and Paleocene paleomagnetic data from the Qiangtang Block and the Lhasa Block.

Location Time N Observed Paleopole Relative movement Rock type Test Relative to Reference (°N/°E) (Ma) Dec. Inc. a95 Paleolatitude Plat. Plon. A 95 Rotation Displacement (°) (°) (°) (°) (°) (°) (dp/dm) (°) (°) Qiangtang Block 34.5/90.2 38.6 ± 0.5 7 356.6 45.9 3.4 27.3 ± 2.8 82.2 293.1 2.8/4.3 14.0 ± 4.9 8.0 ± 3.4 V PFT Eurasia-E Lippert et al., 2011 32.2/86.6 34.2 ± 1.3 13 120.5 56.8 3.7 37.4 ± 3.9 41.7 21.1 3.9/5.4 69.8 ± 7.4 5.0 ± 4.8 V PFT Eurasia-E Lippert et al., 2011 32.7/85.6 35.4 ± 2.4 13 19.5 36.1 7.2 20.0 ± 4.9 68.5 206.8 4.9/8.4 9.1 ± 8.5 12.7 ± 6.2 V PFT Eurasia-E Lippert et al., 2011 Mean inclination after tilt correction = 46.0 ± 5.3° Paleolatitude = 28.7 ± 3.7°N Indicating 6.2 ± 4.6° northward displacement relative to the paleopoles of Eurasia Reference point: 33.0°N/88.0°E

#34.5/92.8 E1 7 9.5 34.3 8.9 18.9 ± 5.9 72.3 242.0 5.9/10.2 1.1 ± 9.9 16.7 ± 7.3 Rb PFT Eurasia-P Halim et al., 1998 732–749 (2015) 114 Sciences Earth Asian of Journal / al. et Tong Y.-B. 29.7/98.4 K2 17 51.3 56.1 6.5 36.7 ± 6.7 47.0 165.1 6.7/9.3 41.8 ± 10.4 8.8 ± 6.7 Rb PFT Eurasia-K2 This study 29.7/98.7 K2 11 39.5 51.6 8.5 32.2 ± 7.9 56.7 172.7 10.6 30.0 ± 12.8 4.3 ± 8.7 Rb PFT Eurasia-K2 Huang et al., 1992 Mean direction K2 28 46.8 54.5 5.1 35.0 ± 5.1 48.7 167.7 6.1 39.5 ± 7.9 7.3 ± 5.2 Rb PFT Eurasia-K2 This study + Huang et al., 1992 29.7/98.4 K1 12 57.7 50.2 10.9 31.0 ± 10.9 40.6 170.5 13.0 43.4 ± 15.8 3.6 ± 10.7 Rb PFT Eurasia-K1 Huang et al., 1992 29.7/98.6 K1 5 48.2 49.0 8.8 29.9 ± 9.5 48.5 175.9 9.5 33.4 ± 11.6 1.7 ± 8.1 Rb No FT Eurasia-K1 Otofuji et al., 1990 Mean direction K1 17 54.8 49.9 7.8 30.7 ± 6.9 43.0 171.8 9.2 40.4 ± 11.4 3.2 ± 7.8 Rb PFT Eurasia-K1 Huang et al., 1992 + Otofuji et al., 1990 #35.0/79.7 K 7 1.3 21.8 6.6 11.3 ± 5.6 66.3 256.5 3.7/7.0 9.9 ± 6.3 18.9 ± 4.9 Rb PFT Eurasia-K Chen et al., 1993 Lhasa Block 32.3/82.6 K1 52 28.2 34.5 2.3 19.0 ± 1.5 61.4 192.9 2.1 14.6 ± 4.4 8.1 ± 3.2 La PFT Eurasia-K1 Ma et al., 2014 31.3/85.1 K1 12 350.5 25.5 7.7 13.4 ± 4.5 70.1 293.2 7.4 23.5 ± 8.5 13.4 ± 6.5 V PFT Eurasia-K1 Yang et al., 2014 31.3/85.1 K1 18 327.0 35.7 4.6 19.8 ± 3.1 58.2 341.8 4.6 47.0 ± 6.2 7.1 ± 4.6 La, T PFT Eurasia-K1 Chen et al., 2012 #29.9/91.2 K2 21 22.6 41.9 4.4 24.2 ± 4.2 69.1 191.7 4.2 13.5 ± 5.2 2.9 ± 3.8 La PFT Eurasia-K2 Tan et al., 2010 29.9/90.7 K2 20 350.8 32.1 8.1 17.5 ± 6.8 75.0 306.7 6.8 18.3 ± 7.5 9.5 ± 5.7 Rb, A PFT Eurasia-K2 Sun et al., 2012 31.2/84.9 K2 33 316.8 30.2 5.4 16.2 ± 3.3 48.0 344.3 5.3 52.0 ± 6.1 11.3 ± 4.6 Rb PFT Eurasia-K2 Yang et al., 2014 northward displacement relative to the paleopoles of Eurasia Reference point: 31.2°N/85.7°E Mean Inclination after tilt correction = 31.6 ± 5.3° Paleolatitude = 17.1 ± 3.3°N Indicating 10.2 ± 4.3° 30.0/91.2 E(45–65) 10 359.5 51.8 5.2 32.5 ± 5.9 87.5 81.4 5.9 10.5 ± 8.2 1.5 ± 5.6 V PFT Eurasia-P Tan et al., 2010 30.0/91.1 E(47–54) 24 12.5 39.4 5.3 22.3 ± 5.5 76.4 212.6 4.0/6.7 2.5 ± 7.6 8.6 ± 5.5 V PFT Eurasia-P Dupont-Nivet et al., 2010a 30.0/91.1 E(53) 10 15.4 27.2 8.3 14.4 ± 8.5 68.9 225.4 5.8/10.6 5.4 ± 10.2 16.5 ± 7.7 D PFT Eurasia-P Liebke et al., 2010 30.0/91.2 E(43–54) – 10.2 20.5 2.6 10.6 ± 1.9 68.4 243.0 1.9 0.2 ± 4.7 20.4 ± 3.3 Rb, T DP Eurasia-P Huang et al., 2013 30.1/90.9 E(55) 14 359.0 26.1 9.2 13.7 ± 7.3 73.6 274.3 7.3 13.5 ± 6.9 20.0 ± 5.2 V PFT Eurasia-P Sun et al., 2010 29.9/90.2 E(44–60) 23 355.9 20.2 6.9 10.4 ± 5.3 70.6 281.0 5.3 13.7 ± 6.9 19.9 ± 5.2 V PFT Eurasia-P Chen et al., 2010 29.9/90.2 E(60–64) 15 354.0 13.0 8.8 6.6 ± 8.5 66.0 284.9 8.5 16.0 ± 9.6 24.1 ± 7.4 V PFT Eurasia-P Chen et al., 2010 30.0/91.0 E(45–65) 8 350.9 25.5 11.0 13.4 ± 11.0 71.4 299.8 11.0 19.1 ± 12.1 17.5 ± 9.3 V PFT Eurasia-P Achache et al., 1984 ° Mean paleomagnetic pole: Plat. = 80.2°N, Plon. = 230.4°N, K = 30.5, A95 = 4.1 (Lippert et al., 2014) Paleolatitude = 22.3 ± 4.4°N Indicating 8.5 ± 4.1° northward displacement relative to the paleopoles of Eurasia Reference point: 30.0°N/90.5°E

N is the number of sampling sites used for paleomagnetic calculation. Dec. and Inc. are declination and inclination, respectively. Plat. and Plon. are latitude and longitude of paleopole. a95 and A95 is the radius of cone at 95% conﬁdence level about the mean direction. K2, Late Cretaceous. K1, Early Cretaceous. Rotation: the negative and positive value means counterclockwise and clockwise rotation, respectively. Translation: the negative and positive value means southward latitudinal displacement and northward latitudinal displacement, respectively. Rb. Red-beds; A, andesite; La, lava ﬂows; V, volcanic rock; T, tuff; D, dykes. FT, fold test; PFT, positive fold test. # means the data are not used in the following discussion. Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749 745

Fig. 8. (A) Equal-area projection of Cretaceous and Paleogene paleopoles from the Lhasa Block and Qiangtang Block. Paleomagnetic data are shown in Table 6. Black circles denote the 95% confidence limit. Paleopole and corresponding 95% confidence limits are plotted onto the northern hemisphere. Small circle with its 95% errors passing through 17.1 ± 3.3°N is calculated from the Cretaceous volcanic paleomagnetic results obtained from the Lhasa Block and centered at the reference point of 31.2°N, 85.7°E. (B) Equal-area projection of Cretaceous volcanic paleomagnetic data obtained from the Lhasa Block. Blue circle with blue dashed line is the average inclination and the error of the average inclination for the sampling section. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

inclination shallowing in the Cretaceous red-beds of the Lhasa occurred between different sampling sections, the average inclina- Block. However, the paleomagnetic data obtained from Lower Cre- tion (31.6 ± 5.3°) of the Lhasa Block was used for the following dis- taceous lava flows and tuffs show that the Lhasa Block was situated cussion (Fig. 8B). at a paleolatitude of 19.8 ± 3.1°N, in addition, 7.1 ± 4.6° of north- Compared with the consistent Cretaceous paleomagnetic data ward intracontinental shortening was suggested within Asia rela- obtained from Cretaceous volcanic rocks, and from some red- tive to Eurasia since the Early Cretaceous (Chen et al., 2012). The beds, the Paleocene to Eocene paleomagnetic data obtained from paleomagnetic data of Sun et al. (2012), from the Upper Cretaceous volcanic rocks in the Lhasa Block exhibit a greater degree of dis- red-beds and interbedded andesite, show a similar paleolatitude crepancy (Tan et al., 2010; Dupont-Nivet et al., 2010a; Liebke (17.5 ± 6.8°N) for the Lhasa Block, indicating a large 9.5 ± 5.7° lati- et al., 2010; Huang et al., 2013; Chen et al., 2010; Achache et al., tudinal intracontinental shortening within Asia. Ma et al. (2014) 1984; Sun et al., 2010). The Paleocene–Eocene paleolatitude of obtained paleomagnetic data from the Lower Cretaceous Lava the Lhasa Block estimated from the volcanic rocks changed from flows in the central part of the Lhasa Block, which also show a pale- 6.6 ± 8.5°N to 32.5 ± 5.9°N, implying that the intracontinental olatitude of 19.0 ± 1.5°N, and 8.1 ± 3.2° northward intracontinen- shortening within Asia varied from 1.5 ± 5.6° to 20.4 ± 3.3° relative tal shortening within Asia relative to Eurasia since the Early to Eurasia (Table 6). Sun et al. (2012) speculated that the large Cretaceous. These estimates of crustal shortening are significantly range of paleolatitudes estimated from the Linzizong volcanic larger than that of the upper limit of the estimate of Tan et al. rocks may reflect the fact that some of the magnetizations have (2010) (2.9 ± 3.8°). Recently, Yang et al. (2014) obtained very con- recorded geomagnetic secular variation. Ma et al. (2014) and Yi sistent paleomagnetic results from Lower Cretaceous volcanic et al. (2011) also pointed out that the true spot recording of poles rocks and Upper Cretaceous red-beds in the Lhasa Block, which during such as long interval of eruption (from 64 to 40 Ma) indicated that inclination shallowing is negligible within the Upper recorded by volcanic rocks of the Linzizong Group may be respon- Cretaceous red-beds. This result is also consistent with previous sible for the diversity of the paleolatitudes estimated from paleo- results obtained from Cretaceous volcanic rocks. However, the magnetic data. Recently, Lippert et al. (2014) reviewed the inclination shallowing corrections were rarely applied to previous paleomagnetic data obtaining from Paleocene–Eocene volcanic paleomagnetic data from the Cretaceous red-beds (Tan et al., 2010; rocks in the Lhasa Block and calculated a mean Paleocene–Eocene Achache et al., 1984), and therefore we chose to ignore them. paleomagnetic pole (Plat. = 80.2°N, Plon. = 230.4°N, K = 30.5,

The Early and Late Cretaceous paleopoles of the Lhasa Block are A95 = 4.1°) that averaged out the secular variation of the geomag- distributed along a small circle (Fig. 8A) (Chen et al., 2012; Sun netic ﬁeld. The result indicates that the Lhasa Block (reference et al., 2012; Ma et al., 2014; Yang et al., 2014), and the average point at 30.0°N/90.5°E) was situated at a paleolatitude of Cretaceous paleolatitude of the Lhasa Block (17.1 ± 3.3°N) can be 22.3 ± 4.4°N, indicating that it experienced 8.5 ± 4.1° northward calculated using a small circle centered on the reference point of displacement relative to Eurasia since the Paleocene–Eocene. In 31.2°N/85.7°E. Because intense local rotational deformation summary, the available paleomagnetic results obtained from 746 Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749

Fig. 9. (A) Paleolatitude evolution of the Lhasa Block and the Qiangtang Block. (B) The latitudinal displacement with error bars versus the longitudes of the paleomagnetic sampling section of the Lhasa Block and the Qiangtang Block. Paleomagnetic data from the present study and from previous studies are also shown in Table 6. (C) The rotational movement with error bars versus longitudes of the paleomagnetic sampling section of the Lhasa Block and the Qiangtang Block. Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749 747

Cretaceous and Paleocene volcanic rocks show an approximately eastern end of Tibetan Plateau and formed the Eastern Himalaya consistent paleolatitude of 20° for the Lhasa Block. Syntaxis since the Oligocene/Miocene (Lee et al., 2003; Ding et al., 2001), the crustal material was extruded to the southeast 7.3. Implications of the paleomagnetic results for the tectonics history along several large strike-slip faults systems in the eastern part of the central and eastern parts of the Qiangtang Block since the Early of Tibet (Tapponnier et al., 1982; Replumaz and Tapponnier, Cretaceous 2003; Otofuji et al., 2007; Tanaka et al., 2008; Tong et al., 2013). Paleomagnetic and geological studies in the Indochina Block and Previous paleomagnetic results show there is not a large differ- Shan-Thai Block in the southeastern edge of Tibetan Plateau favor ence between the Cretaceous paleolatitude (17.1 ± 3.3°N) and the the conspicuous lateral extrusion movement of these two blocks Paleocene–Eocene paleolatitude (22.3 ± 4.4°N) of the Lhasa Block since the Oligocene (Leloup et al., 1995, 2001; Gilley et al., 2003; (Fig. 9A), indicating that the Lhasa Block did not experience signif- Otofuji et al., 2007; Yang and Besse, 1993; Yang et al., 1995, icant latitudinal displacement (5.2 ± 4.4°) during the interval from 2001; Zhang et al., 2012). Furthermore, the Indochina and Shan- the Cretaceous to the Paleocene–Eocene. However, our results indi- Thai Blocks underwent 35° clockwise rotational movement rela- cate that the eastern end of Qiangtang Block was located at a mod- tive to the South China Block in the process of southeastward erate paleolatitude of 30.7 ± 6.9°N in the Early Cretaceous and at escape movement (Sato et al., 2007; Otofuji et al., 2007; Tanaka 35.0 ± 5.1°N in the Late Cretaceous. In addition, the central part et al., 2008; Tong et al., 2013; Yang et al., 1995; Zhang et al., of the Qiangtang Block was situated at a paleolatitude of 2012; Kornfeld et al., 2014). The Mangkang area also experienced 28.7 ± 3.7°N in the Eocene. These data may indicate that the Qiang- obvious southward displacement (7.3 ± 5.2° to 3.2 ± 7.8°) and tang Block maintained a relatively stable paleoposition, and signif- clockwise rotation since the Cretaceous (Fig. 9B and C). The crustal icant latitudinal displacement did not occur from the Cretaceous to deformation of the Mangkang area is very consistent with that of the Eocene, given the possible systematic errors which may affect the Indochina and Shan-Thai Blocks since the collision of the Indian the paleomagnetic data (Fig. 9A). plate and Tibetan Plateau in the Early Paleogene, which indicates The difference between its observed and expected paleolati- that the Indian Plate penetrated into Eurasia at the eastern end tudes indicates that the Lhasa Block experienced 10.2 ± 4.3° of the Tibetan Plateau and that the formation of the Eastern Hima- northward displacement since the Cretaceous, and 8.5 ± 4.1° laya Syntaxis since the Oligocene/Miocene was the main cause of northward displacement since the Paleocene–Eocene. The central this type of crustal deformation of the eastern part of the Qiang- part of the Qiangtang Block also experienced 6.2 ± 4.6° northward tang Block. displacement since the Eocene, relative to Eurasia. Thus, only a few degree of latitudinal displacement occurred between the Qiang- tang Block and the Lhasa Block, which may have formed the stable 8. Conclusions southern edge of Eurasia and together experienced north-south intracontinental shortening with respect to Eurasia since the onset (1) Paleomagnetic data from the Cretaceous red-beds in the of the collision of India–Eurasia in the early Cenozoic (Fig. 9B). Mangkang area indicates that the Qiangtang Block was situ- However, the difference between the observed and expected pale- ated at paleolatitudes of 35.0 ± 5.1°N during the Late Creta- olatitude of the Mangkang area, in the eastern part of Qiangtang ceous and at 30.7 ± 6.9°N during the Early Cretaceous. Block, indicates that this area experienced 3.2 ± 7.8° southward Inclination shallowing correction experiments show no displacement since the Early Cretaceous and 7.3 ± 5.2° southward obvious inclination shallowing, which may have been displacement since the Late Cretaceous. induced by depositional and/or compaction process in the Previous geological studies indicate that the Qiangtang Block Cretaceous red beds of the eastern area of the Qiangtang and the Lhasa Block were sutured together before the Early Creta- Block. ceous (Yin and Harrison, 2000; Tapponnier et al., 2001; Kapp et al., (2) The Lhasa Block and Qiangtang Block have formed the stable 2003, 2007; Guynn et al., 2006; Qiangba et al., 2009; Zhu et al., southern edge of Eurasia and together have experienced 2013). Thus, about 10° paleolatitudinal difference between the north–south intracontinental shortening since the Cenozoic eastern part of the Qiangtang Block and the central Qiangtang- collision of India and Eurasia. Since the early Paleogene, Lhasa Block is not supported by geological data related to later because of the collision of the Indian plate with the Tibetan intracontinental shortening due to the India/Eurasia collision. Plateau, the Lhasa Block and the central part of the Qiang- Two possible interpretations are proposed, as follows, 1) 10° tang Block have experienced a very large northward dis- northward displacement and clockwise rotation of the central part placement. However, the eastern end of the Qiangtang of the Qiangtang and Lhasa Blocks with respect to Eurasia have Block experienced southward displacement and clockwise occurred since the collision between India and Eurasia. However, rotation, which is uniform with the crustal deformation of the eastern part of the Qiangtang Block experienced 7° south- the Indochina and Shan-Thai Block in the southeastern edge ward extrusion movement relative to Eurasia during the Cenozoic. of the Tiabetan Plateau. All of this crustal deformation in the In consequence, a large tectonic boundary is speculated to separate eastern part of the Qiangtang Block was likely induced by the Mangkang area in the eastern part of the Qiangtang Block from the Indian Plate penetrating into Eurasia at the eastern end the Central part of the Qiangtang block, implying that the eastern of the Tibetan Plateau and the formation of the Eastern most of the Qiangtang was an independent terrane. However, such Himalaya Syntaxis since the Oligocene/Miocene. a tectonic boundary has not so far been found in the Qiangtang Block. 2) Inclination shallowing and/or secular variation affects are still present in the Cretaceous paleomagnetic results obtained from red-beds and/or volcanic rocks of the Lhasa block. If this is Acknowledgments the case, clearly more Cretaceous paleomagnetic data are needed to address the problem. This work was supported by the Chinese Geological Survey The Lhasa Block and Qiangtang Block were possible aligned (Grant 1212011120164) and the National Natural Science Founda- approximately E–W prior to the initial collision of India and Eura- tion of China (Grant 41202162). We thank three anonymous sia (Liebke et al., 2010; Najman et al., 2010; Ma et al., 2014). Sub- reviewers and guest editor Dr. Shuwen Dong for suggestions which sequently, because the Indian Plate penetrated into Eurasia at the have greatly improve the manuscript. 748 Y.-B. Tong et al. / Journal of Asian Earth Sciences 114 (2015) 732–749

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