Application of REE and Nd-isotope characteristics to distinguish protolith provenances of sedimentary and metasedimentary rocks in complex accretionary continental margins, such as the North American Cordillera. REE are not very mobile during metamorphic processes. Furthermore, the Sm-Nd isotope system is ideal for studying metamorphic rocks like schist, since their similar chemical properties prohibit relative loss of radiogenic daughter isotopes due to weathering. Also, Nd is relatively enriched over Sm during fractional crystallization of magma, resulting in lower Sm/Nd ratios in crustal rocks and lower radiogenic 143Nd. Comparison of the 143Nd/144Nd ratio with a chondritic reservoir results in the so-called epsilon parameter. Positive epsilon-values indicate a juvenile source, while a negative value means that the rocks were derived from old crustal rocks with orginally low Sm/Nd ratio. This is particular helpful when testing terrane affinity of metamorphic assemblages, whose rocks are otherwise indistinguishable from eachother.
Neodymium isotope analyses were done at the Radiogenic Isotope Facility of the University of Alberta.
Epsilon Nd-values over various REE-ratios show the correlation of Dezadeash Formation slates (diamonds) with juvenile island arc volcanics (IAV, after Taylor & McLennan 1985) and Aishihik metamorphic suite schists (triangle) with evolved continental crust (PUCC: Precambrian Upper Continental Crust, after Taylor & McLennan 1985). The schist and gneiss samples of the Kluane metamorphic assemblage (circles) fall on a mixing line indicating possible protolith origin from mixing of juvenile and evolved sedimentary sources. DRB: Dawson Range Batholith granitoids (Selby et al. 1999, Can.J.Earth Sci. 36).
Epsilon Nd-values and depleted mantle model ages of metasedimentary rocks of the Kluane metamorphic assemblage (KMA) and the Aishihik metamorphic suite (AMS), and sedimentary rocks of the Dezadeash Formation (DF).
