A series of faulted inland basins were developed in the central Qinghai-Tibet Plateau, among which the Co Ngoin Basin containing thick lacustrine sediments is located in the peripheral area of the Indian monsoon. In t...A series of faulted inland basins were developed in the central Qinghai-Tibet Plateau, among which the Co Ngoin Basin containing thick lacustrine sediments is located in the peripheral area of the Indian monsoon. In this paper, we present the weathering history and paleoclimatic changes in the last 2.8 Ma based on studies of high-resolution temporal distributions of Sr, Rb and Zr concentrations, Rb/Sr and Zr/Rb ratios and δ 13C and TOC for the Co Ngoin sediments, in combination with the sediment properties, grain size distribution and clay mineralogy. The sedimentary records indicate three environmental stages in the last 2.8 Ma. At the core depth of 197?170 m (about 2.8?2.5 Ma), low-intensity chemical weathering in the Co Ngoin catchment was experienced under warm-dry to cool-wet climate conditions with relatively low Sr concentration and high Rb/Sr and Zr/Rb ratios. The sudden occurrence of both subalpine coniferous forest and coarse sand and gravel sediments in the Co Ngoin core reflects a strong tectonic uplift. The high Sr concentrations and low Rb/Sr and Zr/Rb ratios reflect a relatively strong chemical weathering between 2.5 Ma and 0.8 Ma (at the core depth of 170?38.5 m) under a temperate/cool and wet climate, characterized by mud and silt with fine sand, probably indicating a stable process of denudation and planation of the plateau. Above the depth of 38.5 m (about 0.8?0 Ma), the coarsening of sediments indicates a strong tectonic uplift and a relatively low intensity of chemical weathering as supported by the record of sediments having relatively low Sr concentrations and high Rb/Sr and Zr/Rb ratios. Since then, the plateau has taken the shape of the modern topographic pattern above 4000 m a.s.l.展开更多
The g-factors of Ground Rotational Band states of N = 44 isotones 82^Sr, 83^Y, 84^Zr and 85^Nb have been measured by the transient-magnetic-field ion implantation perturbed angular distribution （TMF-IMPAD） method. T...The g-factors of Ground Rotational Band states of N = 44 isotones 82^Sr, 83^Y, 84^Zr and 85^Nb have been measured by the transient-magnetic-field ion implantation perturbed angular distribution （TMF-IMPAD） method. The measured g-factors of 82^Sr increase with the increase of spin I, indicating a proton alignment only. Positive peaks appear in the variation of g-factors with spin for 83^Y and 84^Zzr at spin 21/2^＋ and 10^＋ respectively, indicating a proton alignment followed by a neutron alignment. A negative peak occurs for SSNb at the spin 25/2^＋, indicating a neutron alignment followed by a proton alignment.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.40373004)the National Key Basic Research Science Foundation(Grant No.G199804O810)+1 种基金the UK Royal Society BP Research Fellowshipthe Doctors Foundation of Liaocheng University.
文摘A series of faulted inland basins were developed in the central Qinghai-Tibet Plateau, among which the Co Ngoin Basin containing thick lacustrine sediments is located in the peripheral area of the Indian monsoon. In this paper, we present the weathering history and paleoclimatic changes in the last 2.8 Ma based on studies of high-resolution temporal distributions of Sr, Rb and Zr concentrations, Rb/Sr and Zr/Rb ratios and δ 13C and TOC for the Co Ngoin sediments, in combination with the sediment properties, grain size distribution and clay mineralogy. The sedimentary records indicate three environmental stages in the last 2.8 Ma. At the core depth of 197?170 m (about 2.8?2.5 Ma), low-intensity chemical weathering in the Co Ngoin catchment was experienced under warm-dry to cool-wet climate conditions with relatively low Sr concentration and high Rb/Sr and Zr/Rb ratios. The sudden occurrence of both subalpine coniferous forest and coarse sand and gravel sediments in the Co Ngoin core reflects a strong tectonic uplift. The high Sr concentrations and low Rb/Sr and Zr/Rb ratios reflect a relatively strong chemical weathering between 2.5 Ma and 0.8 Ma (at the core depth of 170?38.5 m) under a temperate/cool and wet climate, characterized by mud and silt with fine sand, probably indicating a stable process of denudation and planation of the plateau. Above the depth of 38.5 m (about 0.8?0 Ma), the coarsening of sediments indicates a strong tectonic uplift and a relatively low intensity of chemical weathering as supported by the record of sediments having relatively low Sr concentrations and high Rb/Sr and Zr/Rb ratios. Since then, the plateau has taken the shape of the modern topographic pattern above 4000 m a.s.l.
基金supported by National Science Foundation of China (Nos.10435010,109751891)
文摘The g-factors of Ground Rotational Band states of N = 44 isotones 82^Sr, 83^Y, 84^Zr and 85^Nb have been measured by the transient-magnetic-field ion implantation perturbed angular distribution （TMF-IMPAD） method. The measured g-factors of 82^Sr increase with the increase of spin I, indicating a proton alignment only. Positive peaks appear in the variation of g-factors with spin for 83^Y and 84^Zzr at spin 21/2^＋ and 10^＋ respectively, indicating a proton alignment followed by a neutron alignment. A negative peak occurs for SSNb at the spin 25/2^＋, indicating a neutron alignment followed by a proton alignment.
