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Abstract: Based on field mapping, section measurement and magnetostratigraphy, ∼1700m of sedimentary rocks have accumulated in the Wushan basin between ∼16Ma and ∼6Ma. Basin geometry, sedimentation characteristics and the early syn-depositional deformation along the northern margin of the basin indicate that formation of the Wushan basin was related to tectonic deformation along the West Qinling fault zone during the middle Miocene. A series of basins of similar age to the Wushan basin were generated along and to the south of the West Qinling fault zone while basalts also erupted in this region at this time. We suggest that the middle Miocene (∼16Ma) may represent a change in kinematics and deformation style in the region along and to the south of the West Qinling fault zone. At this time, there was a transition from NNE–SSW compressional deformation, that dominated the region since the late Paleogene, to the development of WNW–ESE and/or E–W trending strike-slip movement and associated transpressional and transtensional activity that continues today. The Miocene Wushan basin may have developed in association with transpression along the West Qinling fault zone. Whether this transition was related to the onset of strike-slip along the east Kunlun fault and related deformation transfer, lower crustal flow, or removal of mantle lithosphere, the middle Miocene provides direct evidence for a change in the kinematic style along the plateau margin. [Copyright &y& Elsevier]

SUMMARY High-grade metamorphic rocks of the upper amphibolite to granulite facies in the Higher Himalayan crystalline (HHC) were studied for their appropriateness for palaeomagnetic investigations. Sampling and fieldwork was accomplished on a south-north transect at ∼87°E in the Khumbu region south of Everest. Paragenesis of iron-sulphides and oxides was found to be variable due to different source rocks and metamorphic conditions in this area. Unblocking temperature ranges, isothermal remanence acquisition, low-temperature magnetic properties and microscopic observations confirm the presence of pyrrhotite and magnetite. Two remanence components were separated with unblocking temperature intervals of 250-330 °C and 370-550 °C, which can be attributed to characteristic remanent magnetizations (ChRM) of monoclinic pyrrhotite (ChRMpyr) and magnetite (ChRMmag), respectively. Mainly the ChRMpyr showed a consistent demagnetization behaviour, probably residing in pyrrhotite particles within the single domain to pseudo-single domain range. Normal and reverse polarities were observed, partly co-existing within the unblocking spectrum of single specimens; this (i) supports a thermoremanent (TRM) origin of the ChRMpyr and (ii) indicates that the time span of remanence acquisition was long enough to average out palaeosecular variation. The age of the ChRMpyr can be related to the last metamorphic cooling event at the Early to Late Miocene boundary (16 Ma). The ChRMmag is probably a secondary chemical or thermochemical remanence acquired by hydrothermal processes during retrogression. ChRMpyr and ChRMmag directions are similar suggesting that pyrrhotite and magnetite were magnetized approximately contemporaneously. Separation of the sampling area into three sectors reveals a south-north trend with (i) variable block rotations in the southernmost part close to the Main Central Thrust (five sites), (ii) no rotation in the area between Lukla and Namche (10 sites) and (iii) a significant clockwise rotation ( N= 5 sites, D/ I= 42.3°/29.4°, k= 20.7, α95= 17.2°) along the Imja Khola north of Namche. We interpret the clockwise rotation as an apparent rotation due to tilting by crustal doming in the Everest region. This doming obviously occurred north of a fault zone located at around Namche and was not affecting the region south of it. The clockwise sense of the apparent vertical-axis rotation indicates that the area north of Namche is located at the western side of the dome structure where westward tilting around a subhorizontal axis occurred (best fit: tilt direction 277°, tilt angle 51°). [ABSTRACT FROM AUTHOR]

Abstract: A continuous fluviolacustrine record provides the geochronological framework to reconstruct the fluvial landscape evolution of the middle reach of the Huanghe (Yellow River). Magnetostratigraphic records from six sections at the north of the Jinshaan Gorge indicate that an isolated fluviolacustrine system occupied this gorge from 8.3 to 3.7Ma. Local fluvial incision initiated at the lake margin around 5.3-4.9Ma, and concomitant fluvial deposits intruded laterally into fine lacustrine strata increasing the sedimentation rate (ca. 3.1cm/ky) within the isolated lake. The temporal coincidence of the onset of uplift-driven valley incision at 3.7Ma along the Yellow River and the onset of basin excavation suggest that uplift possibly played an important role in the late Pliocene-Quaternary drainage evolution. Consequently, incision of the Yellow River upstream in the Jinshaan Gorge initiated at 3.7Ma. [Copyright &y& Elsevier]

Abstract: Crustal movement around and away from the Namche Barwa syntaxis is indicated in the Asian velocity field inferred from GPS data and Quaternary fault slip rates. Nevertheless, there is a limited field-based control on the rotational history of the north-eastern Himalayan arc. Exploring the poly-phase nature of deformation, within the Cretaceous diorite dykes and their host-rock (Triassic flysch), in the eastern Tethyan Himalaya (90°–92°E), combined with new remote sensing data and existing thermo-geochronological data, allow us to unravel the kinematic relationship between paleomagnetic remanence vectors and the deformation phases. Decay at 325°C in high temperature susceptibility curves and in the thermal demagnetization of the SIRM indicate that the characteristic remanent magnetization in the Cretaceous diorite dykes is carried by pyrrhotite. The pyrrhotite component unblocks at 280–350°C, revealing normal and reverse polarities. It is of post-folding origin with a mean remanence direction of 019°/28° and 001°/20° in the eastern (Qonggyai valley) and western (Nagarze) part of the sampling area, respectively. The ~22Ma K–Ar age of the last metamorphic event support that the remanence is post-Eohimalayan folding and likely of thermoremanent or thermo-chemical origin. Comparison of the declination with respect to the Early-Miocene reference direction, yields a trend from no apparent rotation in the west to 20° clockwise rotation in the east with respect to the stable Indian plate. This result can be kinematically related to the Middle to Late-Miocene strain partitioning between far-field southeast extrusion of SE Tibet and near-field strike-slip faulting and E–W extension. Furthermore the observed pattern of tilting around horizontal axis may reflect concealed North Himalayan doming. [ABSTRACT FROM AUTHOR]