Electron microprobe chemical ages of monazite from Qinling Group in the Qinling Orogen： Evidence for Late PanAfrican metamorphism？

Electron microprobe chemical dating was carried out on monazites enclosed in two gen-erations of mineral paragenesis of St Ky Grt and Sil And Grt St, respectively, from the Qinling Group. Two different ages, 520±23 Ma and 435±9 Ma, were obtained from these monazites. This indicates that the Qinling Group experienced a metamorphism during the Early Cambrian, which is probably in response to the Late Pan-African subduction-accretion tectonothermal event.     

Occurrences of Permian radiolarians in central and eastern Nei Mongol （Inner Mongolia） and their geological significance to the Northern China Orogen

The Zhesi (Jisu) Formation of the Middle Permian in Nei Mongol (Inner Mongolia) was commonly considered to be a shallow marine sequence. Here I report the radiolarians found in the argillite bed of that formation in Zhesi and Xilinhot areas. This fact indicates a deep marine sedimentary facies persisted during the Middle Permian, and suggests that the ocean between the North China Block and Siberian Craton was not closed until the Late Guadalupian. The suture of this two blocks is probably extends along the Linxi ophiolite belt, south of the Hegenshan ophiolite belt.     

Initial movement of the Karakorum Fault in western Tibet： constraints from SHRIMP U-Pb dating of zircons

The Karakorum Fault zone(KFZ)plays an important role in understanding the formation,evolvement and deformation of the Tibetan Plateau.The high-T dextral shearing metamorphic rocks,e.g.,mylonites or mylonitized gneisses-granites,locally crop out along the southeastern part of the KFZ in the Ayila Ri’gyüRange area.The SHRIMP U-Pb dating of the syn-kinematic crystallized zircons indicates that the initial age of the KFZ is~27 Ma,~10 Ma older than previous results.The extensive high-T dextral shearing along the KFZ started at least at 27-20 Ma,accompanied by the syn-kinematic emplacement of leuco-granites.Deformation and concomitant fluid circulation during shearing most likely occurred as early as at 25-13 Ma.The KFZ probably grew from southeast to northwest along the fault as a result of continuous convergence between the India plate and Eurasia plate.     

Growth ages of ferromanganese crusts from the western and central Pacific： Comparison between nannofossil analysis and ^10Be dating

Based on results of nannofossil analysis and 10Be dating in ferromanganese crusts M1-1 and A1-1 (no nannofossils were found in it),from the western and central Pacific respectively,it is found that the crust growth ages from nannofossil biostrati-graphy agree well with those based on 10Be isotope analysis. Both crusts have three growth layers,and the oldest layer was deposited in Miocene at about 12.80 Ma. The maximum,minimum,and average growth rates of crust A1-1 (from the central Pacific) are 8.11,1.92 and 3.47 mm/Ma,and those of crust M1-1 (from the western Pacific) are 2.93,0.47,and 0.94 mm/Ma.