Zircon LA-ICP-MS U-Pb ages of websterite and basalt in Kudi ophiolite and the implication, West Kunlun

West Kunlun orogen is subdivided into north terrene and south terrene. The known Kudi ophiolite in south terrene of West Kunlun orogen is composed of ultramafic body in Buziwan valley and extrusive rocks in Yixieke valley from the bottom up. There has been a hot debating about age of Kudi ophiolite. This study has collected samples and obtained zircon LA-ICP-MS U-Pb ages of 494. 28 +/- 0. 86Ma and 500. 30 +/- 8. 0Ma respectively for websterite from Buziwan valley ultramafic body and dolerite from lower part of Yixieke valley extrusive rocks in Kudi ophiolite. These two ages are very similar and indicate that the ultramafic body and lower part of the extrusive rocks are composing members of Late Cambrian-Early Ordovician ophiolite, i. e., Kudi ophiolite was the residue of Prototethys Ocean. Previous studies by other researchers got the various age data for ultramafic rocks and extrusive rocks. The reason of large variety of age is that different authors used different dating methods (including Radiolarian) on different samples collected at different localities (especially for extrusive rocks of upper unit of the ophiolit), not to say most of the dating methods used were not fairly reliable. Our reliable in situ method age (500. 30 +/- 8. 0Ma) of dolerite from lowermost part of extrusive stratum is different from the another previously published in situ age datum (also reliable) for massive basalt, which amply demonstrate that the reason of age difference is because of different locality of sampling. Thus, the Yishake Group should be dismembered because it might be tectonicly superimposed stratum.