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The components and evolution of subcontinental lithospheric mantle beneath the North China Craton and the Yangtze Craton is a current topic in the geological study of China and the carbon isotopic composition of diamond is one of the most direct probes into cratonic lithospheric mantle processes. In this paper, in-situ SIMS (Secondary Ion Mass Spectrometry) techniques were used to analyze the carbon isotope compositions at different internal growth zones of diamonds from Shandong and Liaoning in the North China Craton and Hunan in the Yangtze Craton. It was found that the carbon isotopic range of diamonds from the North China Craton are rather distinct from those of the Yangtze Craton; the former has a range of −6.0/‰ to −2.0‰ (relative to VPDB) with an average value of −3.0‰ in their core areas, which is consistent with global peridotitic diamonds; the diamonds from the Yangtze Craton, however, have a carbon isotopic range from −8.6‰ to −3.0‰ with an average value of −7.4‰ in their core areas, being more consistent with global eclogitic diamonds. The variations of carbon isotope ratios between different internal growth zones in individual diamonds were different in the three diamond localities studied. There was a clear correlation between changes in carbon isotopic composition and phases of diamond dissolution and new growth, while no correlation was observed between δC and internal inclusions. The variations suggest that the carbon isotopic compositions of mantle fluids were changing during the process of diamond crystallization, and that the heterogeneity of the carbon isotopic composition in mantle carbon reservoirs was a more important factor than carbon isotope fractionation in controlling the carbon isotopic compositions and their variation in diamonds. In addition, the preliminary results of in-situ nitrogen analyses demonstrated that the variation of carbon isotopic compositions between the core and outer growth zones does not correlate with nitrogen abundances, implying either that diamonds crystallized in an open environment or that the carbon isotopic composition and nitrogen contents in mantle fluids were controlled by other, not yet understood factors. The experimental results provide hints that the isotopic composition of carbon and its original sources were different in metasomatic fluids controlling diamond formation in the mantle beneath the North China Craton and the Yangtze Craton. [ABSTRACT FROM AUTHOR]

Climate and tectonism are both particularly intense in the Yarlung Zangbo (Tsangpo) Great Canyon in the eastern Himalayan syntaxis, which is characterized by the most rapid landscape evolution of anywhere in the world. Thus, the eastern Himalayan syntaxis is one of the best locations to study the interactions between climate and tectonics. This paper investigates the cooling ages of the Doxong La-Baibung profile using apatite fission track (AFT) dating on 11 bedrock samples at elevations ranging from 4210 to 710 m. There are topographic, climatic, metamorphic, and thermochronological gradients in the profile, providing good conditions to study interactions between climate and tectonics. AFT ages ranged from 4.6±0.6 Ma to 1.7±0.3 Ma, and the mean fission track lengths ranged from 11.0 to 12.4 µm. It was found that the cooling rates revealed by AFT ages increased with decreasing elevation. However, the tendency of the cooling rates revealed by the 40Ar-39Ar ages was different from that indicated by the AFT ages. Moreover, for most districts of the eastern Himalayan syntaxis, the compiled AFT age distribution correlates well with the annual average precipitation, indicating the coupling of the cooling and erosion rates of the near-surface rock and precipitation. The geothermal history modeling results indicate an obvious increase in the cooling and erosion rate between 1.0 and 0.5 Ma. This age is consistent with other research findings for this time, when the vapor channel of the Yarlung Zangbo Great Canyon began to take effect. These evidences suggest that climate, especially precipitation, has acting as a key factor influencing the rapid cooling and erosion in the Yarlung Zangbo Great Canyon since 1-0.5 Ma. [ABSTRACT FROM AUTHOR]