S U M M A R YLower to Middle Cretaceous red sandstones were sampled at four localities in the LanpinSimao fold belt of the Shan-Thai Block to describe its regional deformational features. Most of the samples revealed a characteristic remanent magnetization with unblocking temperatures around 680 • C. Primary natures of magnetization are ascertained through positive fold test. A tilt-corrected formation-mean direction for the Jingdong (24.5 • N, 100.8 • E) locality, which is located at a distance of 25 km from the Ailaoshan-Red River Fault, revealed northerly declination with steep inclination (Dec./Inc. = 8.3 • /48.8 • , α 95 = 7.7 • , N = 13). However, mean directions obtained from the Zhengyuan (24.0 • N, 101.1 • E), West Zhengyuan (24.0 • N, 101.1 • E) and South Mengla (21.4 • N, 101.6 • E) localities indicate an easterly deflection in declination; such as Dec./Inc. = 61.8 • /46.1 • , α 95 = 8.1 • (N = 7), Dec./Inc. = 324.2 • /−49.4 • , α 95 = 6.4 • (N = 4) and Dec./Inc. = 51.2 • /46.4 • , α 95 = 5.6 • (N = 13), respectively. The palaeomagnetic directions obtained from these four localities are incorporated into a palaeomagnetic database for the Shan-Thai Block. When combined with geological, geochronological and GPS data, the processes of deformation in the Shan-Thai Block is described as follows: Subsequent to its rigid block clockwise rotation of about 20 • in the early stage of India-Asia collision, the Shan-Thai Block experienced a coherent but southward displacement along the Red River Fault prior to 32 Ma. This block was then subjected to a north-south compressive stresses during the 32-27 Ma period, which played a key role in shaping the structure of Chongshan-Lancang-Chiang Mai Belt. Following this some local clockwise rotational motion has occurred during the Pliocene-Quaternary time in central part of the Shan-Thai Block as a result of internal block movements along the reactivated network of faults.

We report palaeomagnetic results obtained from Cretaceous red bed samples, collected from the eastern Hindukush mountains, northern Pakistan. Rock magnetic studies revealed specular haematite as the dominant remanence carrier, while pigmentary haematite, magnetite and goethite are responsible for the acquisition of secondary magnetizations. Thermal treatment generally revealed three components of magnetization. The most unstable component (A) was removed between 200°C and 500°C, which corresponds to the local present field direction. The intermediate component (B) was generally separated between 200°C and 660°C. The omnipresence of this complex secondary component across the Northern Suture Zone suggests that movement of chemically active orogenic fluids at, or slightly before, the time of the India-Asia collision was probably responsible for the authigenic remagnetization processes. The characteristic component (C) was generally unblocked between 600°C and 685°C. The characteristic directions from 12 sites fall into two groups. The sites from the Purit Formation give a tilt-corrected mean direction of D=311.2°, I=-4.4°, k=12.4, a 95 =17.8°, indicating a counter-clockwise rotation of about 66°and 15°relative to Eurasia and India, respectively. The tilt-corrected mean direction for the Reshun and Drosh formations is D=263.0°, I=2.2°, k=52.7, a 95 =10.6°, which indicates that the sampling area experienced a counter-clockwise rotation of about 114°and 63°with respect to Eurasia and India, respectively. In both cases the palaeomagnetic rotation is consistent with the regional superstructure of the Hindukush-Pamir-Karakoram syntaxial bend. The difference in rotation between these two groups is probably due to local tectonic movement caused by the net rotation of thrust sheets along the Northern Suture Zone. The palaeolatitudes calculated for Purit and Reshun+Drosh formations are 2.2°S and 1.1°N, respectively. This indicates that about 4000 km of convergence has taken place since the mid-Cretaceous, of which about 90 per cent post-dates the India-Asia collision. The Late Cretaceous inclination values across the Northern Suture Zone are almost identical, which indicates that suturing had been completed at the time of ChRM acquisition.

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SUMMARY We present palaeomagnetic results from Late Cretaceous welded tuffs in the Kisin Group (Monastirskaya Suite, Primorskaya Series) collected at 27 sites from the Sikhote Alin mountain range. A high unblocking temperature magnetization component (>590°C) was isolated after stepwise thermal demagnetization from 25 sites. Combined with previously reported data, reliable characteristic remanence directions from 39 sites are distributed at eight areas ranging from 46.7°N, 138.1°E to 43.4 °N, 134.8°E in the Sikhote Alin Block. The bedding‐tilt test is positive for two area mean directions and inconclusive for the remaining six areas. The data set for all 39 sites reveals a positive bedding‐tilt test at the 99 per cent confidence level, and their tilt‐corrected mean direction is D= 335.6°, I= 54.4° (α95= 8.5°), corresponding to a palaeopole at 71.5°N, 38.9°E with A95= 9.9°. This westerly direction is ascertained through the tilt‐corrected mean direction (D= 331.1°, I= 53.5°, α95= 8.5°) based on the 25 data selected from four areas (Kema river, Terney, Plastun and Moryak‐Rybolov) where each data set passes the positive bedding‐tilt test or reveals an increase in the precision parameter after tilt correction. Palaeomagnetic declination indicates that the Sikhote Alin Block has rotated counterclockwise by 41°± 16° with respect to the Eurasian continent between Late Cretaceous times and 53–50 Ma. Compared with palaeomagnetic data from the surrounding regions, we find that the rotation recorded in Sikhote Alin extends westward into the interior of the Mongolia Block. The eastern margin of the Asian continent experienced both counterclockwise rotation of the eastern part of the Mongolia Block and clockwise rotation of the eastern part of the North China Block over the Cretaceous. We interpret these data in terms of a strong net horizontal force towards the ocean side, acting on the lithosphere at the eastern margin of the Asian continent between the Late Cretaceous and 53–50 Ma. Intermittently occurring upwellings of mantle and associated horizontal flows may have played an important role in producing the net horizontal force acting on the continental block during Late Cretaceous times.

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SUMMARY An active oroclinal bending is discovered in the Shan‐Thai Block to the south of the eastern Himalayan syntaxis. To investigate the evolution of the Simao Arc using palaeomagnetic techniques, the Middle Cretaceous red beds of the Nanxin Formation were sampled at the Zhengwan (22.8°N, 100.9°E) and Dadugang (22.4°N, 101.0°E) localities in the southern Simao Basin. Most of the studied samples revealed the presence of characteristic remnant magnetization with unblocking temperatures around 680 °C. A primary nature for this magnetization is interpreted on the basis of a positive fold and reversal test. Tilt‐corrected mean directions calculated for Zhengwan and Dadugang localities are characterized by large easterly deflected declination; D= 51.8°, I= 47.9°, ks= 45.0, α95= 6.9°, N= 11 and D= 64.1°, I= 48.1°, ks= 36.0, α95= 7.3°, N= 12, respectively. Steep inclination values at both these localities with respect to those expected are in the range previously reported from the Shan‐Thai Block, confirming their southward displacement by 6.2°± 1.7° as part of the Shan‐Thai Block. Combination of the present data (two localities) with those previously reported from Simao Basin (seven localities) reveals a positive palaeomagnetic oroclinal test, indicating that the present‐day arc‐like geometry of the Simao Basin was formed by oroclinal bending. Comparison with recent GPS and structural data suggest that formation of the Simao curvature started after the early Pliocene (after 4 Ma) and continuing until the present. Origin of the Simao Arc is ascribed to southwestward movement of the crustal material across the Ailao Shan‐Red River Fault (around the eastern Himalaya syntaxis), which was formed by westward movement of the decollement with progressive eastward deepening of the Lanping‐Simao Basin. Decoupling between the upper and the middle–lower crusts is a requisite condition for the arc formation on the continent.

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S U M M A R YCretaceous red sandstones of the Feitianshan Formation and the Xiaoba Formation were sampled at 33 sites from the Dadeli and Mishi synclines of Xichang (27.9 • N, 102.3 • E). The study area is a part of the Chuan Dian fragment bounded by the Xianshuihe-Xiaojiang and the Red River fault systems, which in turn constitute the southwestern part of the Yangtze Block. Almost all the samples give a characteristic palaeomagnetic direction with unblocking temperatures up to 680 • C. The primary nature of magnetization is ascertained by a positive fold test with a 99 per cent confidence level for the Dadeli Syncline. The tilt corrected overall mean direction of the 33 sites is D = 3.7 • , I = 41.5 • (α 95 = 3.4 • ), with a corresponding palaeopole at 85.2 • N, 241.7 • E(A 95 = 3.5 • ). This pole occupies the near-sided position with respect to the estimate of the Cretaceous pole of the Sichuan Basin, indicating that the Xichang area experienced a significant southward displacement. Combined with earlier reported palaeomagnetic data from the Chuan Dian fragment, a significant southward displacement of 6.7 • ± 3.5 • in latitude is estimated for the whole fragment with respect to the Sichuan Basin since the Late Cretaceous. Extrusion dynamics in the Asian continent due to its collision with India brought about the southward displacement of the Chuan Dian fragment. Declination data indicate that the southern part of the Chuan Dian fragment was subjected to clockwise sense rotation of up to 45 • . This significantly large tectonic rotation probably occurred during extrusion of this fragment from the north.