The 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.
