【摘要】 蛇绿岩中的辉绿岩岩墙是洋脊扩张的产物,其形成年龄代表了扩张事件的时间,也代表了蛇绿岩的形成时代。对雅鲁藏布江缝合带西段拉昂错蛇绿岩中的辉绿岩岩墙进行锆石SHRIMP U-Pb定年,得出加权平均年龄为120.2Ma±2.3Ma,代表辉绿岩的结晶年龄。结合已有的关于雅鲁藏布江蛇绿岩的形成年龄(西段休古嘎布122.3Ma±2.4Ma,中段大竹卡126.0Ma±1.5Ma、吉定123.0Ma±1.8Ma,东段罗布莎162.9Ma±2.8Ma)的报道,表明拉昂错地区特提斯洋海底扩张的时代与休古嘎布地区一致,雅鲁藏布江西段与中段地区洋盆的形成时代一致,但晚于东段的发育时代。这意味着整个东提斯洋盆的发育时代存在东早西晚的特点。更多还原

【Abstract】 Diabase dikes in ophiolites is the product of the middle ocean ridge spreading, and their age corresponds to the time of the spreading event 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 forthe 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.更多还原