EVOLUTION OF SM-ND ISOTOPIC SYSTEM IN CLASTIC ROCKS OF FORELAND BASINS: COMPARISON OF PRIVERKHOYANSK (NE SIBERIA) AND FOOTHILLS (SW ALBERTA)

The Priverkhoyansk and Rocky Mountain foreland basins formed in response to thrusting that began in the Late Jurassic in Verkhoyansk fold and thrust belt and Cordillera accordingly. Sm-Nd isotopic system of 56 samples from NE Siberia and 23 samples from SW Alberta were studied to compare the provenances and evolution of the orogens.

In SW Alberta, results of our study are in agreement with those by Ross et al. (2005). Wide range of e_Nd(t) values (from -15 to -1) is typical for Cretaceous foreland basin clastics. Upper Jurassic and Lower Cretaceous samples show less variation in e_Nd(t) (from -15 to -19). Provenance of clastic rocks with such variation in e_Nd(t) is located within the fold and thrust belt. More negative e_Nd(t) values of Upper Cretaceous samples show increasing influence of the old crust erosion, whereas The almost zero e_Nd(t) values in some Cretaceous samples indicate that western accreted juvenile terranes probably contributed to clastic sedimentation in the Alberta foreland basin.

In northeastern Siberia Cretaceous foreland basin samples show significant variations in e_Nd(t) values within the Carboniferous – Jurassic passive margin succession. Unlike Cordillera, e_Nd(t) values for Cretaceous samples of Priverkhoyansk foreland basin range from -19 to -15 and are significantly more negative than those of the Carboniferous through Jurassic succession. Such low e_Nd(t) values are typical for Siberian Craton basement, and the Anabar Shield, Aldan Shield and Olenek Uplift were most likely source of Cretaceous clastic rocks. Erosion of the Verkhoyansk Ridge did not significantly contribute to the foreland basin sedimentation as e_Nd(t) values for Carboniferous to Triassic succession in fold and thrust belt range from -12 to -2 and are more positive than those in Cretaceous clastics. Thus, unlike Cordilleran foreland basin, Priverkhoyansk foreland basin was infilled by sediments eroded from the distal basement source with almost no input from the Verkhoyansk fold and thrust belt.