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.

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that distinguish it from the rest of the system. Geochemical modelling indicates that magmatic differentiation through crystal fractionation and minor crustal assimilation occurred in crustal and shallow sub-volcanic magma reservoirs. In the central part of the system, a number of vertically spaced reservoirs acted as a filter, capturing basaltic dykes and hindering their ascent. In the outer region, dykes either reached the surface unhindered and erupted to form the basaltic/trachybasaltic succession or stalled at crustal levels and differentiated to trachyte before forming dispersed domes/flows. The central plumbing system "filter" resulted in a nest-shaped volcano, with a trachytic core surrounded by basaltic products, and stopped direct injection of basaltic magmas into the shallow syenitic magma reservoir, likely preventing its destabilization and explosive eruption.

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