SHRIMP U-Pb zircon dating of diabase in the La’nga Co ophiolite, Burang, Tibet, and its geological significance

Diabase dikes in ophiolites is the product of the middle ocean ridge spreading, and their age corresponds to the time of the spreading even and also represents the formation age of ophiolites. Zircon SHRIMP U-Pb dating of the diabase dikes in the La’nga ophiolite in the western segment of the Yarlung Zangbo suture zone yielded a 206Pb/238U weighted mean age of 120.2±2.3 Ma（2σ，MSWD=0.71）, which represents the crystallization age of the diabase. Based on the above, combined with the previous reports of the ophiolite ages in the Yarlung Zangbo suture zone (122.3±2.4 Ma for the Xiugugabu ophiolite in the western part, 126.0±1.5 Ma for the Dazhuka ophioilte and 123.0±1.8 Ma for the Jiding ophiolite in the central part and 162.9±2.8 Ma for the Luobusha ophiolite in the eastern part), this age suggests that: the sea-floor spreading age of the Tethys ocean in the La’nga area is consistent with that of the Xiugugabu oceanic basin in the western part; the oceanic basins in the western part and central part of the Yarlung Zangbo suture zone originated synchronously and later than that in the eastern part. From the geochronology data, the authors deduce that the eastern part of the Tethys ocean basin opened earlier than its western part.