Investigation of Cretaceous East Thethyan Mantle Sources Through An Isotopic Study of Yarlung-Zangpo Suture Zone Basalts, Tibet

印度洋海脊玄武岩的地幔来源具有与太平洋和北大西洋海脊不同的铅-钕-锶同位素特征。印度洋地幔签名的原因尚不清楚：它可能起源于冈瓦那超大陆的解体，也可能是从中生代位于冈瓦那以北的现已消失的特提斯洋的地幔继承而来的更古老的特征。然而，人们对特提斯地幔的性质知之甚少，因为从这个地幔来源获得的物质在今天暴露的有限，所以几乎没有同位素或微量元素数据。为了解决我们知识中的这一差距，进而解决印度洋地幔独特的同位素特征这一更大的问题，将对特提斯洋壳进行系统调查，其碎片保存在南亚南特提斯缝合带的陆地上。一次难得的机会是，美国调查人员受邀参加一个中国考察队，在西藏南部雅鲁藏布江缝合带暴露的特提斯海底碎片上工作。雅鲁藏布缝合带是南特提斯缝合带最长的地段之一。美国研究人员将对采集到的玄武岩和辉长岩样品进行年龄校正后的Nd、Pb、Sr同位素比值和各种微量元素的分析。这些数据将与中国团队的岩石学、构造和地质年代学研究结合起来获得。该项目将为地幔演化和动力学的基本问题提供新的见解，同时也促进了美中研究人员和学生之间的合作和科学交流。

9805318MahoneyThe mantle sources of Indian Ocean ridge basalts have a Pb-Nd-Sr isotopic signature distinct from those of the Pacific and North Atlantic ridges. The reason for the Indian Ocean mantle signature is unknown: it may have originated with the breakup of the supercontinent of Gondwana, or it may be an older feature inherited from the mantle of the now-vanished Tethyan Ocean which lay to the north of Gondwana in the Mesozoic. However, the nature of Tethyan mantle is poorly known as few isotopic or trace element data exist for the limited present-day exposures of materials derived from this mantle source. To address this gap in our knowledge, and in turn the larger issues of the unique isotopic signature of the Indian Ocean mantle, a systematic investigation of Tethyan Ocean crust, fragments of which are preserved on land in the South Tethyan suture belt of southern Asia, will be conducted. In a rare opportunity, the American investigators have been invited to join a Chinese expedition working on Tethyan seafloor fragments exposed in the Yarlung-Zangpo suture zone of southern Tibet, one of the longest stretches of the South Tethyan suture belt. Age-corrected Nd, Pb, and Sr isotopic ratios and a variety of trace elements will be analyzed by the US researchers on basalt and gabbro samples collected. These data will be obtained in conjunction with petrological, structural, and geochronological studies by the Chinese team. This project will provide new insights on fundamental questions of mantle evolution and dynamics while also promoting cooperation and scientific exchange between US and Chinese researchers and students.