U-Pb zircon dating constraints on formation time of Qilian high-grade metamorphic rock and its tectonic implications

In order to constrain the formation time of high-grade metamorphic rocks in the Qilian Mountains, U-Pb zircon dating was carried out by using LA-ICPMS technique for a paragneiss of the Hualong Group in the Qilian Mountains basement series and a weakly foliated granite that intruds into the Hualong Group. Zircons from the paragneiss consist dominantly of detrital magma zircons with round or sub-round shape. They have 207Pb/206Pb ages mostly ranging from 880 to 900 Ma, with a weighted mean age of 891 ±9 Ma, which is interpreted as the magma crystallization age of its igneous provenance and can be taken as a lower age limit for the Hualong Group. Magma crystallization age for the weak-foliated granite is 875±8 Ma, which can be taken as an upper age limit for the Hualong Group. Accordingly, the formation time of the Hualong Group is constrained at sometime between 875 and 891 Ma. A few zir- cons from both paragneiss and weak-foliated granite display old inherited ages of 1000 to 1700 Ma and young metamorphic ages of Early Paleozoic. The zircon age distribution pattern confirms that the Qilian Mountains and the northern margin of Qaidam Basin had a united basement, with geotectonic affinity to the Yangtze Block. The results also reveal that sediments of the Hualong Group formed by rapid accumulation due to rapid crustal uplift-erosion. This process may result from intensive Neoproterozoic orogenesis due to assembly of the suppercontinent Rodinia.     

皖南尖吻蝮蛇毒出血毒素Ⅰ氨基酸序列初步研究

中国皖南尖吻蝮蛇（Ａｇｋｉｓｔｒｏｄｏｎａｃｕｔｕｓ）毒出血毒素Ｉ（ＡａＨＩ）氨基酸序列得到初步测定．ＡａＨＩ的Ｎ端１３个残基序列为ＳＴＥＦＱＲＹＭＥＩＶＩＶ．序列比较表明ＡａＨＩ与其它种属来源的低分子量（２０～２４ｋＤ）蛇毒出血毒素和金属蛋白酶有较高的同源性．