Rare earths (RE) are critical materials in many high-technology products. Due to the uneven distribution and important functions for industrial development, most countries import RE from a handful of suppliers that are rich in RE, such as China. However, because of the rapid growth of RE exploitation and pollution of the mining and production process, some of the main suppliers have gradually tended to reduce the RE production and exports. Especially in the last decade, international RE trade has been changing in the trade community and trade volume. Based on complex network theory, we built an unweighted and weighted network to explore the evolution of the communities and identify the role of the major countries in the RE trade. The results show that an international RE trade network was dispersed and unstable because of the existence of five to nine trade communities in the unweighted network and four to eight trade communities in the weighted network in the past 13 years. Moreover, trade groups formed due to the great influence of geopolitical relations. China was often associated with the South America and African countries in the same trade group. In addition, Japan, China, the United States, and Germany had the largest impacts on international RE trade from 2002 to 2014. Last, some policy suggestions were highlighted according to the results.
The sedimentary sequences since 33 ka B.P. to 10 ka B.P. have been established in the Re'nacuo‐Lake, Gaize area of north Tibet, through a study of a lacustrine section. The climate since 33 ka B.P. to 10 ka B.P. may be divided into two cycle include 5 dry phases and 5 moist phases from reconstructing the paleoclimate through a study of sporopollen analysis. It mainly reflects the general regularity of global climatic change through contrasting with the pale environment in northern hemisphere. Our pollen record reveals a regional climate history similar to those from the neighboring sites, including the GISP2, the Guliya ice core and core RM in Zoige, and thus supports the notion that the Qinghai‐Tibetan Plateau acts as an important link between climatic events in the North Atlantic realm and the Asian monsoon domain. The response of the Qinghai‐Tibet Plateau to the global climatic change is relatively sensitive.
Subduction of Bangong Suture Ocean and collision between the Lhasa and Qiangtang blocks were keys to better understand the development of central Tibet. However, the initiation and closure timing, and nature and structure of the Bangong suture are still poorly constrained. Mesozoic intrusions are widely distributed in central Tibet. Petrology, geochronology and geochemistry of the Renacuo pluton and their microgranular enclaves in the Gaize area to the north of the Bangong–Nujiang suture zone, south of the Longmu Co–Shuanghu suture zone, are used to constrain the tectonic history of the Bangong suture. Results of our SHRIMP U–Pb dating of the zircons are as follows: quartz diorite is 139 ± 4 Ma, MSWD = 1.6; the microgranular enclave is 147.3 ± 3.3 Ma, MSWD = 0.45. The evolutionary trend of the major elements, trace elements and rare earth elements of the microgranular enclaves and the host rocks are almost similar, suggesting that the enclaves and the host rocks may have had the same source. They most likely originated from magma mixing between mantle‐derived and crust‐derived melts. On the basis of our mapping and geochronologic studies, we suggest that the formation of the Renacuo pluton is consistent with previously suggested northward subduction of the Bangong Suture Ocean, which occurred in the Late Jurassic–Early Cretaceous. Copyright © 2015 John Wiley & Sons, Ltd.
The Taolaituo porphyry-type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. The mineralization occurs mainly as veins, lenses and layers within the host porphyry. To better understand the link between the mineralization and the host igneous rocks, we studied samples from the underground workings and report new SHRIMP II zircon U-Pb and Re-Os molybdenite ages, and geochemical data from both the molybdenites and the porphyry granites. Five molybdenite samples yield a Re-Os isochron weighted mean age of 133.0 ± 0.82 Ma, whereas the porphyry granitoids samples yield crystallization ages of 133 ± 1 Ma and 130.4 ± 1.3 Ma. The U-Pb and Re-Os ages are similar, suggesting that the mineralization is genetically related to the Early Cretaceous porphyry emplacement. These observations indicate that the molybdenites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lithospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Taolaituo deposit occurred contemporaneously with the Early Cretaceous tectonothermal events associated with lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere associated with intra-continental extension in northeast China.
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