GEOCHEMISTRY AND GEOCHRONOLOGY OF THE MESOZOIC VOLCANIC ROCKS IN THE SOUTHERN GREAT XINGGAN RANGE, NE CHINA

Mesozoic volcanic rocks are widespread throughout the Great Xing’an range, NE China. Their ages formed from about 180 Ma to 120 Ma, with a strong peak about 125 Ma, and several weak peaks at ∼116 Ma, ∼140 Ma and ∼156 Ma respectively in age histogram. These complicated age spectrum points out that the volcanism may be related not only with the subduction of the Pacific plate, but also with closure of the Okhotsk ocean.Mesozoic volcanic rocks are widespread throughout the Great Xing’an range, NE China. Their ages formed from about 180 Ma to 120 Ma, with a strong peak about 125 Ma, and several weak peaks at ∼116 Ma, ∼140 Ma and ∼156 Ma respectively in age histogram. These complicated age spectrum points out that the volcanism may be related not only with the subduction of the Pacific plate, but also with closure of the Okhotsk ocean

GEOCHEMISTRY AND GEOCHRONOLOGY OF THE MESOZOIC VOLCANIC ROCKS IN THE SOUTHERN GREAT XINGGAN RANGE, NE CHINA

Mesozoic volcanic rocks are widespread throughout the Great Xing’an range, NE China. Their ages formed from about 180 Ma to 120 Ma, with a strong peak about 125 Ma, and several weak peaks at ∼116 Ma, ∼140 Ma and ∼156 Ma respectively in age histogram. These complicated age spectrum points out that the volcanism may be related not only with the subduction of the Pacific plate, but also with closure of the Okhotsk ocean

Zircon U-Pb dating and trace elements geochemistry of the Gaotan gabbro from Ziyang County, Shaanxi Province

Basic dike swarms are widely distributed in the Ziyang-Langao-Zhenping area of Ankang in Shaanxi Province and Zhuxi area in Hubei Province, intruding the Early Paleozoic strata which characterized by bimodal volcanic association. The gabbro dikes emplacement dated 410±5 Ma by the LA-ICP-MS zircon U-Pb dating. They show the patterns of enriched LREE with high fractionation of light and heavy REE, and enrichment of incompatible elements in the primitive mantle-normalized spider-diagrams with peaks of Ba, Nb and Ti and valleys of Pb and U. The ratios of Th/Nb is less than 0.11 and those of Nb/Zr more than 0.15, indicating that they were derived from enriched mantle source closely related to the plume. The ratios of Nb/U, Ce/Pb and concentration of U, Th, Pb and Ni in the gabbro dikes indicate that the pyroxenes and olivines were main fractional minerals in the fractional crystallization during the magma evolution, and they were not affected by contamination of continental crust from the mantle to crust. These helps to infer that the extensional tectonics developed constrainedly in the Early Paleozoic by the mantle plume activities that happened at the boundary of paleocontinent on the northern margin of Yangtze Plate, thus producing the large group of basic dike swarms in these areas. The deep thermodynamic condition is responsible for the crustal extension and end. Thus the age of 410±4.5 Ma not only represents the magma emplacement, but also the extension evolution history of this continent crust rift from beginning to end in Silurian

Topology characterization of a benzodiazepine-binding β-rich domain of the GABAA receptor α1 subunit

Structural investigation of GABAA receptors has been limited by difficulties imposed by its trans-membrane-complex nature. In the present study, the topology of a membrane-proximal β-rich (MPB) domain in the C139–L269 segment of the receptor α1 subunit was probed by mapping the benzodiazepine (BZ)-binding and epitopic sites, as well as fluorescence resonance energy transfer (FRET) analysis. Ala-scanning and semiconservative substitutions within this segment revealed the contribution of the phenyl rings of Y160 and Y210, the hydroxy group of S186 and the positive charge on R187 to BZ-binding. FRET with the bound BZ ligand indicated the proximity of Y160, S186, R187, and S206 to the BZ-binding site. On the other hand, epitope-mapping using the monoclonal antibodies (mAbs) against the MPB domain established a clustering of T172, R173, E174, Q196, and T197. Based on the lack of FRET between Trp substitutionally placed at R173 or V198 and bound BZ, this epitope-mapped cluster is located on a separate end of the folded protein from the BZ-binding site. Mutations of the five conserved Cys and Trp residues in the MPB domain gave rise to synergistic and rescuing effects on protein secondary structures and unfolding stability that point to a CCWCW-pentad, reminiscent to the CWC-triad “pin” of immunoglobulin (Ig)-like domains, important for the structural maintenance. These findings, together with secondary structure and fold predictions suggest an anti-parallel β-strand topology with resemblance to Ig-like fold, having the BZ-binding and the epitopic residues being clustered at two different ends of the fold