Neodymium and strontium isotopic constraints on the origin of the peraluminous granitoids of the South Mountain Batholith, Nova Scotia, Canada

Abstract

Nd isotopic data from the South Mountain batholith show that its peraluminous granitic rocks have considerably higher [epsilon]tNd (t=372 Ma) values (-5.2 to -1.4) than the extensive flyschoid country rocks (-11.2 to -8.7). These isotopic data are combined with Sr isotopic measurements to estimate the involvement of the country rocks, either as source materials or as contaminants, in the batholith. Metasedimentary enclaves in the batholith generally have Nd and Sr isotopic compositions intermediate between those of the batholith and the country rocks, and provide evidence of contamination by the country rocks. Integrated with other geochemical data, the isotopic results show at least two possible origins for the South Mountain batholith: either this large batholith is a hybrid of mantle and crustal materials and contains a large proportion of mantle-derived Nd and Sr, or the magma is derived from deeper metasedimentary crustal material, with younger model ages or higher Sm/Nd ratios than the upper crust.