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The origin and development of the major rivers in the eastern Tibetan Plateau have been a special focus of research because of the close links recognized between river formation, tectonic uplift, and climate change. In this article, we review a number of sedimentary provenance investigations aiming to constrain the drainage evolution of the main rivers draining eastern Tibet, including the Mekong, Red, Pearl, Yangtze, and Yellow rivers. The Mekong River was formed no later than ~17 Ma, likely triggered by a period of enhanced East Asian summer monsoon precipitation during the middle Miocene. A single large paleo-Red River draining the southeastern Tibetan Plateau into the Song Hong - Yinggehai Basin had been proposed to explain the unusual drainage pattern. However, this is not compatible with the distinctive provenance signals in the southeastern Tibetan river sands compared with the Song Hong - Yinggehai Basin, indicating that there has been no large-scale paleo-Red River since the late Eocene. The Pearl River has formed during the late Oligocene, as there was a sharp provenance change in the Pearl River Mouth Basin. Moreover, rivers draining southeast coastal China (e.g., Min River) migrated westward at the same time. These clues highlight that paleo-rivers in southeastern China started to migrate inland during the Late Oligocene. In contrast, the formation timing of the Yangtze River is still under intensively debated, ranging from late Cretaceous to Holocene, mainly due to the complex evolution history of this trans-continental river. The formation of the First Bend of the Yangtze River likely happened during the late Eocene, resulting from changes in the regional topographic gradient triggered by local magmatic activity and/or movement of the Ailao Shan-Red River Fault. Onshore and offshore provenance evidence indicate that incision of the Three Gorges happened no later than the late Miocene. Formation of the Square Bend of the Yellow River occurred prior to the late Pliocene, while incision of the Sanmen Gorge, a key capture point connecting the upper-middle and lower Yellow River likely occurred in the early Pleistocene (~1.2 Ma). Multi-provenance proxies on well-dated and continuous sedimentary records can provide objective information in terms of the origin and evolution of the major rivers flowing from eastern Tibet. Although the evolution of these rivers remains debatable, a comparison among the river evolution, climatic and tectonic events suggests that Eocene local and isolated drainage patterns is likely related to the dry climate condition in the East Asia. Oligocene and late Miocene inlandward expansion and integration of rivers coincides with both the formation of the East Asian Monsoon and the timing of major tectonic events, such as the growth of the Tibetan Plateau and the rifting and opening of the eastern Asian marginal basins, highlighting the importance of climate and tectonics in controlling the evolution of major rivers. [ABSTRACT FROM AUTHOR]

Abstract: V p and V s values have been measured experimentally and calculated for granulite-facies lower crustal xenoliths from central Ireland close to the Caledonian Iapetus suture zone. The xenoliths are predominantly foliated and lineated metapelitic (garnet–sillimanite–K-feldspar) granulites. Their metapelitic composition is unusual compared with the mostly mafic composition of lower crustal xenoliths world-wide. Based on thermobarometry, the metapelitic xenoliths were entrained from depths of c. 20–25±3.5 km and rare mafic granulites from depths of 31–33±3.4 km. The xenoliths were emplaced during Lower Carboniferous volcanism and are considered to represent samples of the present day lower crust. V p values for the metapelitic granulites range between 6.26 and 7.99 km s−1 with a mean value of 7.09±0.4 km s−1. Psammite and granitic orthogneiss samples have calculated V p values of 6.51 and 6.23 km s−1, respectively. V s values for the metapelites are between 3.86 and 4.34 km s−1, with a mean value of 4.1±0.15 km s−1. The psammite and orthogneiss have calculated V s values of 3.95 and 3.97 km s−1, respectively. The measured seismic velocities correlate with density and with modal mineralogy, especially the high content of sillimanite and garnet. V p anisotropy is between 0.15% and 13.97%, and a clear compositional control is evident, mainly in relation to sillimanite abundance. Overall V s anisotropy ranges from 1% to 11%. Poisson''s ratio (σ) lies between 0.25 and 0.35 for the metapelitic granulites, mainly reflecting a high V p value due to abundant sillimanite in the sample with the highest σ. Anisotropy is probably a function of deformation associated with the closure of the Iapetus ocean in the Silurian as well as later extension in the Devonian. The orientation of the bulk strain ellipsoid in the lower crust is difficult to constrain, but lineation is likely to be NE–SW, given the strike-slip nature of the late Caledonian and subsequent Acadian deformation. When corrected for present-day lower crustal temperature, the experimentally determined V p values correspond well with velocities from the ICSSP, COOLE I and VARNET seismic refraction lines. Near the xenolith localities, the COOLE I line displays two lower crustal layers with in situ V p values of 6.85–6.9 and 6.9–8.0 km s−1, respectively. The upper (lower velocity) layer corresponds well with the metapelitic granulite xenoliths while the lower (higher velocity) layer matches that of the basic granulite xenoliths, though their metamorphic pressures suggest derivation from depths corresponding to the present-day upper mantle. [Copyright &y& Elsevier]

The unusual drainage pattern in the southeastern Tibetan Plateau has been proposed to result from the breakup of a single paleo-Red River system. However, whether there or not was a major early Cenozoic "paleo-Red River" flowing from southeastern Tibet to the South China Sea is still highly debated. In this study, we have used Pb isotopic analyses of detrital K-feldspar to constrain the sedimentary provenance of the Cenozoic deposits from the onshore Jianchuan Basin and offshore Yinggehai and Qiongdongnan basins, and further to decipher the drainage evolution of the upper-middle Yangtze and Red Rivers. Detrital K-feldspar from the Baoxiangsi Formation in the Jianchuan Basin shows an apparent mixture of sand delivery from both the upper Yangtze and Yalong rivers, indicating that there was a river draining the Qiangtang Block and Songpan-Ganzi that used to flow through the Jianchuan Basin during the Eocene. In contrast, K-feldspar Pb isotopes from the Eocene to Pliocene deposits of the Yinggehai and Qiongdongnan basins are different from those of the Jianchun Basin and Yangtze, Salween, and Mekong rivers, but similar to that of the modern Red River. These lines of evidence suggest that major rivers draining southeastern Tibet have not been tributaries of the paleo-Red River and hence, there has been no fluvial connection between southeastern Tibet and the South China Sea since at least the late Eocene. • Sedimentary provenance of the Jianchuan,Yinggehai and Qiongdongnan basins were constrained by Pb-in-K-feldspar. • There was a river draining the Qiangtang and Songpan-Ganzi that used to flow through the Jianchuan Basin during the Eocene. • Sedimentary provenance of the YGHB and QDNB has been similar to the modern Red River since the late Eocene. • No fluvial connection between southeastern Tibet and the South China Sea since at least the late Eocene. [ABSTRACT FROM AUTHOR]

This study used signal-to-noise ratios to assess the effects of increasing Itrax XRF instrument parameters, namely tube voltage, tube current and exposure time, on XRF spectra and measurement repeatability. Tests were performed on cores from British and Irish floodplains. Seven combinations of tube voltage and current and six exposure times were compared using signal-to-noise ratios for eight target elements. Signal-to-noise ratios may be substantially improved by selecting instrument parameters, particularly tube voltage, for specific target elements. They can also be used to assess element profile suitability for interpretation by comparison with the limit of quantification. Repeatability was assessed using the standard deviation of measurements in nine repeat scans. The variation in element levels in the majority of profiles is considerably greater than the variability in individual measurements. [ABSTRACT FROM AUTHOR]

Abstract Quantitative reconstruction of high-temperature thermal histories (>350 °C) has applications in metamorphic studies, processes which exhume deep crust, the evolution of active margins over hundreds of millions of years, and the study of extra-terrestrial rocks. Previous studies have demonstrated that apatite U-Pb data can be used to recover thermal history information at T > 350 °C from single crystal (bulk) dates. We present U-Pb bulk grain (ID-TIMS) and intra grain (LA-MC-ICP-MS) U-Pb data from apatites to evaluate the importance of parent isotope (U) distribution when extracting thermal history information from apatites that have experienced partial Pb loss. We find that parent U zonation can cause considerable scatter when single (bulk) grain dates are compared with their grain size, and therefore U zonation must be taken into account when inverting U-Pb dates and grain sizes to seek thermal history solutions. We show that accurate thermal history solutions can be obtained from apatites which have zoned concentrations when in-situ variations in U concentration and U-Pb dates are modelled. This observation validates the hypothesis that Pb is lost by thermally driven volume diffusion. In-situ analytical techniques yield significantly more accurate thermal history solutions than bulk grain ID-TIMS analyses when investigating rocks which contain compositionally zoned apatites. [ABSTRACT FROM AUTHOR]

We report on the first zircon hafnium-oxygen isotope and trace element study of a transect through one of the largest terrestrial impact melt sheets. The differentiated melt sheet at the 1.85 Ga, originally ca. 200 km in diameter Sudbury impact crater, Ontario, Canada, yields a tight range of uniform zircon Hf isotope compositions (ε Hf(1850) of ca. −9 to −12). This is consistent with its well-established crustal origin and indicates differentiation from a single melt that was initially efficiently homogenised. We propose that the heterogeneity in other isotopic systems, such as Pb, in early-emplaced impact melt at Sudbury is associated with volatility-related depletion during the impact cratering process. This depletion leaves the isotopic systems of more volatile elements more susceptible to contamination during post-impact assimilation of country rock, whereas the systems of more refractory elements preserve initial homogeneities. Zircon oxygen isotope compositions in the melt sheet are also restricted in range relative to those in the impacted target rocks. However, they display a marked offset approximately one-third up the melt sheet stratigraphy that is interpreted to be a result of post-impact assimilation of 18 O-enirched rocks into the base of the cooling impact melt. Given that impact cratering was a more dominant process in the early history of the inner Solar System than it is today, and the possibility that impact melt sheets were sources of ex situ Hadean zircon grains, these findings may have significance for the interpretation of the early zircon Hf record. We speculate that apparent ε Hf -time arrays observed in the oldest terrestrial and lunar zircon datasets may be related to impact melting homogenising previously more diverse crust. We also show that spatially restricted partial melting of rocks buried beneath the superheated impact melt at Sudbury provided a zircon crystallising environment distinct to the impact melt sheet itself. [ABSTRACT FROM AUTHOR]

Abstract: The island of South Georgia exposes remnants of a Late Jurassic to Early Cretaceous Andean magmatic arc and marginal basin system that was compressively deformed during the mid-Cretaceous main Andean Orogeny forming widespread NW-SE trending folds and a coaxial penetrative cleavage displaying a predominantly NE-SW stretching lineation. Detailed structural studies of the Cooper Bay to Cape Vahsel area of South Georgia reveal that intense, mid-Cretaceous, polyphase deformation was strongly influenced by sinistral strike-slip shear parallel to the NW-SE regional structural grain, and along a major pre-existing fault, which we interpret as the partitioned wrench component of bulk transpressional deformation. The relationship between fold axial plane orientation and interlimb angle of widely distributed mesoscale folds is consistent with counter-clockwise rotation and fold appression as a result of sinistral simple shear deformation, suggesting kinematic strain partitioning of the wrench component was on the whole highly efficient. Locally, the modification of steep tectonic anisotropies to shallow inclinations during D2 deformation induced imperfect or inefficient partitioning with fold arrays exhibiting fold appression characteristic of a transpressional deformation path. Our partitioned transpression model for main Andean deformation of South Georgia fits well with tectonic interpretations of the Cordillera Darwin, Patagonia. [Copyright &y& Elsevier]