SHRIMP U-Pb zircon dating for Qiashikansayi granodiorite, the Northern Altyn Tagh Mountains and its geological implications

The Qiashikansayi granodiorite is foliated resulting in a granodioritic gneiss. Its geochemical features, such as alumina saturation index(A/CNK) of 0.81-0.99, Na2O/K2O values>1, TiO2 contents <1.0%, LREE enrichment with high fractionation factors, weakly negative or no Eu anomalies, and significant Ba and Ti negative anomalies, suggest that it is similar to a typical island arc pluton. The trace elements of the Qiashikansayi granodiorite are plotted in the island arc field in the tectonic setting discrimination diagrams as well. Cathodoluminescence images demonstrated that the zircons have clear rhythmic crystallized zoning, without any remnant core and new crystallized rim, suggesting the zircons be magmatic ones. Their U and Th contents vary in the range of 574-870 μg/g, and 279-556μg/g respectively, with the Th/U ratio in the range of 0.52-0.68. SHRIMP zircon U-Pb dating yielded the 481.5±5.3 Ma age for the intrusion of the granodiorite, which is coeval with the island arc volcanic rocks in the no     

Evidence for UHP metamorphism of eclogites from the Altun Mountains

Ultrahigh pressure (UHP) metamorphism refers to metamorphism that has occurred at pressures for the stability of coesite. The polycrystalline quartz inclusions showing the characteristic texture within garnets of eclogites indicates the pre-existence of coesites under the peak metamorphic condition. The unusual exsolution textures in ompacites and apatites, and the pressure estimations of phengite-bearing eciogites have been taken to provide further proof of eclogite formation under the UHP conditions.Combined with the fact that coesites have been observed in country rocks of eclogites in North Qaidam Mountains, another UHP metamorphic belt cut by the large-scale strikeslip fault in the AItun-North Qaidam area of China is confirmed.``     

Sapphirine-bearing high pressure mafic granulite and its implications in the south Altyn Tagh

Sapphirine is a relatively uncommon mineral whichgenerally occurs in granulite with bulk compositions richin both Mg and Al. It was mainly recognized in Al-richrocks of Precambrian granulite terrane[1]. Recently, it wasalso reported from the HP/HT metamorphic rocks in thePhanerozoic collision orogens[2,3]. In China, up to now,sapphirine was only reported in Precambrian Al-richgneisses from the Daqingshan area, Inner Mongolia[4].Sapphirine often forms from the breakdown of earlieraluminou…     

Lawsonite-bearing eclogites in the north Qilian and north Altyn Tagh： Evidence for cold subduction of oceanic crust

Laboratory experiments and thermal models predic that lawsonite-bearing eclogite should be the dominan rock types for typical oceanic subduction zone[1,2] However, eclogite containing unaltered lawsonite is rare in nature and has been described only from …     

球磨时间对片型羰基铁粉微波吸收剂结构和性能的影响

用湿法球磨制备微米片状羰基铁粉,研究形成产物的微观结构、演化过程以及静磁性能和2~18 GHz微波电磁参数。利用扫描电子显微镜(SEM)和X线衍射(XRD)进行分析。研究结果表明:随着球磨时间的延长,羰基铁粉片型化程度增加,晶粒尺寸逐渐减小,矫顽力明显增大。在比饱和磁化强度相近时,粒子的各向异性提高了片状羰基铁粉的磁损耗和介电损耗性能;随着片状结构厚度的减小,磁导率实部μ′以6 GHz为支点,在2~6 GHz之间逐渐增大,而在6~18 GHz之间逐渐减小,形成典型的"跷跷板"现象;磁导率虚部μ′′持续增大,峰值出现在6 GHz左右并向低频移动。     

Zircon SHRIMP dating of granite from Qaidamshan, NW China

Zircon SHRIMP dating from Qaidamshan granite shows that the granite age is 446 Ma, similar to that of eclogite in the UHP belt. We think that both granite and eclogite may be formed at different stages during tectonic evolution of this area. Together with other studies we suggested that the collision of ocean and continent plates may occur at the early Caledonian in this area, forming the eclogite, and the collision of continent and continent plates at the late Caledonian, forming the Qaidamshan granite with the zircon SHRIMP age of 446 Ma.