Preliminary measurements of boundary layer reactive halogens based on MAXDOAS technique over Salt Lake in West China

正The reactive halogens play key roles in the destruction of boundary layer ozone by catalytic reactions and provide a fast pathway to the sedimentation of elemental gaseous mercury.The presence of bromine oxides in the lower     

Distinct continental margins and associated stratigraphic architecture patterns during the seafloor spreading of South China Sea

In this paper we compare four types of stratigraphic architectures around the continental margins in the South China Sea (SCS) based on a plentiful of seismic profiles. The results indicate that stratigraphic patterns are not only related closely to structure regimes of peripheral of the SCS, but also are restrained by crust structure from continental crust to oceanic crust. In the extensional setting, depositional centres during the syn‐spreading stage are located in the strong extensional area. A wedge‐decrease continental crust represented by the Pearl River Mouth type is characterized by high deposition and subsidence rate during the syn‐rifting and syn‐spreading stages in the distal zone. And in the Zhongjiannan type with a continental ribbon, high deposition and subsidence rate during the syn‐rifting and syn‐spreading stages are present in the proximal zone. However, in the southern and eastern margins with compressional setting, the Liyue and Zengmu microcontinent blocks are separated from the South China with the seafloor spreading of SCS, in which a confined or relative thin syn‐spreading deposits are presence. High deposition and subsidence rate is closely related to the collision or subduction condition during the post‐spreading stage in the Liyue bank type and the Zengmu type, a huge progradational clinoforms are present along the subduction and collision margin. Therefore, this study shows distinct stratigraphic architecture in different continental rifted margins, distinct depositional and subsidence characteristics formed during the process of lithospheric rupture can provide an effective method for the study on the continental marginal sea in the western Pacific.     

Recognition of Early Paleozoic Magmatisms in the Supposed Proterozoic Basements of Zhalantun, Great Xing’an Range, NE China

The Zhalantun terrane from the Xing'an massif, northeast China, was used to be considered as Proterozoic basements. However, amounts of detrital zircon ages from the meta-sedimentary rocks deny the existence of Precambrian basements recently. Notably, magmatic rocks were barely reported to limit the exact ages of the Zhalantun basements. In this study, we collected rhyolite, gabbro and quartz diorite for zircon in-situ U-Pb isotopic dating, which yield crystallization ages of ～505 Ma, ～447 Ma and ～125 Ma, respectively. Muscovite schist and siltstone define maximum depositional ages of ～499 Ma and ～489 Ma, respectively. Additionally, these dated supracrustal rocks and plutons also yield ancient detrital/xenocryst zircon ages of ～600–1000 Ma, ～1600–2220 Ma, ～2400 Ma, ～2600–2860 Ma. Based on the whole-rock major and trace element compositions, the ～505 Ma rhyolites display high SiO_2 and alkaline contents, low Fe_2O_3T, TiO_2 and Al_2O_3, and relatively high Mg O and Mg#, which exhibit calc-alkaline characteristics. These rhyolites yield fractionated REE patterns and negative Nb, Ta, Ti, Sr, P and Eu anomalies and positive Zr anomalies. The geochemistry, petrology and Lu-Hf isotopes imply that rhyolites were derived from the partial melting of continental basalt induced by upwelling of sub-arc mantle magmas, and then experienced fractional crystallization of plagioclase, which points to a continental arc regime. The ～447 Ma gabbros exhibit low Si O2 and alkaline contents, high Fe2 O3 T, Ti O2, Mg O and Mg#. They show minor depletions of La and Ce, flat MREE and HREE patterns, and negative Nb, Ta, Zr and Hf anomalies. Both sub-arc mantle and N-MORB-like mantle were involved in the formation of the gabbros, indicative of a probable back-arc basin tectonic setting. Given that, the previously believed Proterozoic supracrustal rocks and several plutons from the Zhalantun Precambrian basements were proved to be Paleozoic to Mesozoic rocks, among which these Paleozoic magmatic rocks were generally related to subduction regime. So far, none Proterozoic rocks have been identified from the Zhalantun Precambrian basement, though some ～600–3210 Ma ancient detrital/xenocryst zircons were reported. Combined with ancient zircon ages and newly reported ～2.5 Ga and ～1.8 Ga granites from the south of the Zhalantun, therefore, the Precambrian rocks probably once exposed in the Zhalantun while they were re-worked and consumed during later long tectonic evolutionary history, resulting in absence of Precambrian rocks in the Zhalantun.     

FAUNE DES MOLLUSQUES UTILES ET NUISIBLES DE LA MER SUD DE LA CHINE

La Mer Sud de la Chine est une mer chaude et formée par une partie de l'Océan Pacifique occidentale. Par ses latitudes basses, par ses immenses plages à mangroves, par ses myriades d'(?)les montagneuses et nombreux archipels à coraux, elle fournit une faune plus variée et bien différente de celle de la Met Est surtout de la Mer Jaune et du golfe de Pohai. Les espèces de mollusques de la Mer Sud sont aussi un peu différentes de celles de l'Indochine et de l'Indonésie, à cause de débit des fleuves qui apportent de grandes quantités de limon et matière organique dans cette mer, et emp(?)chent, en bien des points, le développement de certaines espèces de mollusques qui exigent une eau pure, d'une part, et favorisent le dévetoppement de certaines     

A Statistical Algorithm for Retrieving Background Value of Absorbing Aerosol Index Based on TROPOMI Measurements

The ultraviolet aerosol index(UVAI) is essential for monitoring the absorbing aerosols during aerosol events. UVAI depends on the absorbing aerosol concentration, the viewing geometry, and the temporal drift of radiometric sensitivity. To efficiently detect absorbing aerosols with the highest precision and to improve the accuracy of long-term UVAI estimates,the background UVAI must be examined through the UVAI retrieval. This study presents a statistical method that calculates the background val...     

Prevalent thickening and local thinning of the mantle transition zone beneath the Baikal rift zone and its dynamic implications

The Baikal rift is the most seismically active continental rift in the world and is significant for studying the dynamics of continental rifts, although its precise dynamic mechanisms remain controversial. We calculated receiver functions (1748) from Global Seismographic Network seismic stations TLY and ULN and stacked receiver functions in different bins. Here we present discontinuities at depths of 410km and 660km and thickness of the mantle transition zone (MTZ) beneath the study area. The MTZ structure shows an obvious thickening (292km) in the Baikal rift zone except for an area of limited thinning (230km), whereas it is basically normal (250km) beneath the Mongolian area, to the southeast of the Baikal rift. Combining these results with previous findings, we propose that the large-scale thickening beneath the Baikal rift zone is likely to be caused by the Mesozoic collision between the Siberian Platform and the Mongolia-North China Block or magmatic intrusion into the lower crust, which would result in crust and lithosphere thickening. Thus, the lower crust becomes eclogitized and consequently detached into the deep mantle because of negative buoyancy. The detachment not only induces asthenosphere upwelling but also accelerates mantle convection of water detached from the subducted slab, which would increase mantle melting, while both processes promote the development of the rift. Our preliminary results indicate that the detachment and the consequent hot upwelling have an important influence on the development of the Baikal rift, and a small-scale mantle upwelling indicated by the located thinning may have destroyed the lithosphere and promoted this development.     

Characteristics of Temperature Distribution and Control factors in Geothermal Field

In recent years, China has carried out large‐scale exploration, exploitation and utilization of geothermal resources, but there is no unified understanding of the distribution characteristics of geothermal field and the controlling factors of forming geothermal field. As for the heat source, some scholars think it is the contribution of radioactivity, fault, magma chamber, or an abnormal heat source, and even the heat generated by the influence of the tectonic movement. As a result, many exemplary geothermal explorations have made great mistakes. After drilling at a depth of 3000‐5000m, the temperature obtained is not as good as the common low‐temperature sedimentary basin, and the losses are huge and extremely uneconomical.