Samarium-Neodymium and Strontium Systematics Applied to Calcite Veins in Dabashan Thrust and Fold Belt in China: Dating and Tracing of the Fluid

Dabashan Thrust and Fold Belt is situated in the transfer zone between Qinling Orogen and Sichuan Basin, where multi-generation calcite veins were developed. Two kinds of veins, bedding-parallel and fracture-filled veins, were collected for analyses of rare-earth elements (REE), samarium-neodymium and strontium isotopes. The total REE contents of the calcites from the bedding-parallel vein are much higher than those from fracture-filled veins and are rich in light REE (LREE). The chondrite-normalized patterns of REE curves of the calcites from fracture-filled veins are flatten. The 87Sr/86Sr and 143Nd/144Nd ratios of calcites from bedding-parallel vein are from 0.71068 to 0.71115 and from 0.51192 to 0.512058, respectively. On the 147Sm/143Nd vs 143Nd/144Nd diagram, the six samples from the bedding-parallel vein give a Sm-Nd isochron age of 357±230 Ma (2σ)( MSWD = 24) with an initial 143Nd/144Nd ratio of 0.51168±0.00019. However, the plots of the four samples from fracture-filled veins are rather scatter either on 147Sm/143Nd vs 143Nd/144Nd or on 87Sr/86Sr vs 143Nd/144Nd diagram. The fluids, from which the two kinds of veins precipitated, are different in origin and flowing.