U-Pb ages of zircon,monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Hima- layan tectonic unit are measured using TIMS method. The results show that the magma emplacement ...U-Pb ages of zircon,monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Hima- layan tectonic unit are measured using TIMS method. The results show that the magma emplacement ages for the Kude and the Sajia leu- cogranite are 27.5±0.5 and 14.4±0.2 Ma,respectively. Combined with published U-Pb data from the North Himalayan leu- cogranites,the time-span for the formation of the North Himalayan leucogranites is updated from 27.5 to 10 Ma,instead of previous 15 to 10 Ma.According to the U-Pb ages,the petrogenesis for the North Himalayan leucogranites can be constrained.It is suggested that the North Himalayan leu- cogranites have variety in their petrogenesis.展开更多
A c. 300-year oxygen and carbon isotope record derived from fine-grained and ostracod carbonate from Qinghai Lake testifies to dramatic interannual tointerdecadal limnological change. Fine-grained carbonates, which ar...A c. 300-year oxygen and carbon isotope record derived from fine-grained and ostracod carbonate from Qinghai Lake testifies to dramatic interannual tointerdecadal limnological change. Fine-grained carbonates, which are mainly authigenic, are likely to have formed in the epilimnion of the lake and their isotopic composition reflects the summer temperature and, more importantly, the isotopic composition of the near-surface waters, which is mainly a function of evaporative concentration. Ostracod shells are secreted in the benthos of the lake, and their isotopic composition reflects summer bottom-water conditions, together with fractionation effects, which may differ between species. Differences betweencontemporaneous values from authigenic carbonates and ostracod shells may provide an indication of stratification within the lake and variations in effective precipitation over the northeast part of the Tibetan Plateau over the past 300 years. A period of moderate evaporative concentration, from about 300 to 100 yr BP, was interrupted by a marked wet phase from ～100 to 40 yr BP, which was in turnfollowed by a return to drier conditions in the most recent part of the record.The increase in ? 18O values in the latter part of the record accords well withinstrumental records of lake-level lowering and salinity increase since about 1955 AD.展开更多
文摘U-Pb ages of zircon,monazite and xenotime from the Kude and the Sajia leucogranites in the Sajia dome of the North Hima- layan tectonic unit are measured using TIMS method. The results show that the magma emplacement ages for the Kude and the Sajia leu- cogranite are 27.5±0.5 and 14.4±0.2 Ma,respectively. Combined with published U-Pb data from the North Himalayan leu- cogranites,the time-span for the formation of the North Himalayan leucogranites is updated from 27.5 to 10 Ma,instead of previous 15 to 10 Ma.According to the U-Pb ages,the petrogenesis for the North Himalayan leucogranites can be constrained.It is suggested that the North Himalayan leu- cogranites have variety in their petrogenesis.
基金partly supported by the National Natural Science Foundation of China(Grant No.40125001)the MRes fund from University College London.
文摘A c. 300-year oxygen and carbon isotope record derived from fine-grained and ostracod carbonate from Qinghai Lake testifies to dramatic interannual tointerdecadal limnological change. Fine-grained carbonates, which are mainly authigenic, are likely to have formed in the epilimnion of the lake and their isotopic composition reflects the summer temperature and, more importantly, the isotopic composition of the near-surface waters, which is mainly a function of evaporative concentration. Ostracod shells are secreted in the benthos of the lake, and their isotopic composition reflects summer bottom-water conditions, together with fractionation effects, which may differ between species. Differences betweencontemporaneous values from authigenic carbonates and ostracod shells may provide an indication of stratification within the lake and variations in effective precipitation over the northeast part of the Tibetan Plateau over the past 300 years. A period of moderate evaporative concentration, from about 300 to 100 yr BP, was interrupted by a marked wet phase from ～100 to 40 yr BP, which was in turnfollowed by a return to drier conditions in the most recent part of the record.The increase in ? 18O values in the latter part of the record accords well withinstrumental records of lake-level lowering and salinity increase since about 1955 AD.
