There is an ophiolite zone along Yiyang-Dexing-Wuyuan i.n northeastern Jiangxi at the southeastern margin of the Jiangnan oldland.It is widely Held that the ophiolites is a boundary between two first-order tectonic units, the Yangtze and South China blocks, consisting of fragments of ocea- nic crust squeezed up during its subduction in Proterozoic, but some consi- der that it is a Mesozoic suture between the two great old masses. The mineral Sm-Nd isochron gives an age of 1034±16 Ma (MSWD=1.0)，thus suggesting that the ophioliaic blocks may be a product of the Proterozoic subduction of the oceanic crust rather than a Mesozoic suture.