Revised Chronostratigraphic Framework of the Metamorphic Strata in the Jiangnan Orogenic Belt,South China and its Tectonic Implications

In a re-study of regional geology by the China Geological Survey （CGS）, the key problem is in the stratigraphical division and correlation. According to the new isotopic dating of the Mesoand Neoproterozoic in China, there have been great changes in the strata correlation and tectonic explanation. The authors obtained four zircon sensitive high resolution ion micro-probe （SHRIMP） U- Pb datings from the bentonite of the Lengjiaxi Group （822±10 Ma, 823±12 Ma and 834±11 Ma） and Banxi Group （802.6±7.6 Ma） in north Hunan Province, which is considered to be the middle part of the Jiangnan Orogenic Belt. On the basis of the zircon dating mentioned above, the end of the Wuling orogen is first limited in the period from 822 Ma to 802 Ma in one continued outcrop （Lucheng section） in Linxiang city, Hunan Province. Combining a series of new zircon U-Pb datings in the Yangtze and Cathaysia blocks, several Neoproterozoic volcanic events and distribution of the metamorphic rocks in the Jiangnan Orogenic Belt have been distinguished. In the context of the global geodynamics, it is useful to set up a practical and high precision chronological framework and basic and unified late Precambrian section in South China.

Response of revegetation to climate change with meso- and micro-scale remote sensing in an arid desert of China

The revegetation protection system(VPS)on the edge of the Tengger Desert can be referred to as a successful model of sand control technology in China and even the world,and there has been a substantial amount of research on revegetation stability.However,it is unclear how meso-and micro-scale revegetation activity has responded to climatic change over the past decades.To evaluate the relative influence of climatic variables on revegetation activities in a restored desert ecosystem,we analysed the trend of revegetation change from 2002 to 2015 using a satellite-derived normalized difference vegetation index(NDVI)dataset.The time series of the NDVI data were decomposed into trend,seasonal,and random components using a segmented regression method.The results of the segmented regression model indicate a changing trend in the NDVI in the VPS,changing from a decrease(−7×10−3/month)before 2005 to an increase(0.3×10−3/month)after 2005.We found that precipitation was the most important climatic factor influencing the growing season NDVI(P<0.05),while vegetation growth sensitivity to water and heat varied significantly in different seasons.In the case of precipitation reduction and warming in the study area,the NDVI of the VPS could still maintain an overall slow upward trend(0.04×10−3/month),indicating that the ecosystem is sustainable.Our findings suggest that the VPS has been successful in maintaining stability and sustainability under current climate change conditions and that it is possible to introduce the VPS in similar areas as a template for resistance to sand and drought hazards.

The effect of melt flow induced by RMF on the meso-and micro-structure of unidirectionally solidified Al–7wt.%Si alloy Benchmark experiment under magnetic stirring

During the last two decades,many algorithms were developed to simulate the solidification process for different casting methods like ingots,continuous casting of steel and the direct chill cast of aluminum.Experiments performed under exactly known conditions and with the detailed knowledge of meso-and micro-structures are required for validating these simulations.The aim of this paper is to give a data set to validate these simulations.Unidirectional solidification experiments were performed by using a rotating magnetic field(RMF)to study the effect of melt flow on the solidified micro-and meso-structure of the Al-7wt.%Si binary alloy.The first and the third 1/3 parts of samples were solidified without magnetic stirring,and the second(middle)1/3 part was solidified by using magnetic stirring.The magnetic induction was 10 m T,the temperature gradient was~7 K/mm,and the sample movement velocity was 0.1 mm/s.On the longitudinal section of the sample,the columnar/equiaxed transition(CET),the equiaxed/columnar transition(ECT),the secondary dendrite arm spacing(SDAS),and the macrosegregation(concentration distribution and the amount of eutectic)were investigated.The primary dendrite arm spacing(PDAS)and the grain structure were studied on the cross-section after color etching.