| dc.description | The South Mountain Batholith (SMB) of southern Nova Scotia is a large, peraluminous granitoid complex, intruded dominantly into rocks of the Meguma Group. Field and textural relations reveal evidence for contamination of the SMB by rocks of the Meguma Group in the form of xenoliths, xenocrysts, and former partial melt, and assimilation of the country-rock material through fracturing, dispersal, partial melting, dissolution, and ion exchange reactions. Assimilation of the metapsammitic rocks released xenocrystic quartz, biotite, and plagioclase, and ≤50 vol% of partial melt into the SMB magmas, whereas assimilation of the metapelitic rocks released xenocrystic garnet and cordierite, and ≤80 vol% of partial melt. In the SMB rocks remote from contacts with Meguma Group rocks, textural relations, chemical compositions, and zoning patterns permit the identification of xenocrystic garnet and cordierite with confidence. On the other hand, deciphering the origin of single quartz, biotite, and plagioclase crystals in the SMB has a considerable uncertainty, because textures and compositions of country rock-derived and small magmatic crystals are similar. Despite these difficulties, assuming that all suspect crystals are true xenocrysts, and that all xenocrysts are physically detectable, xenocrysts make up ≤4 vol% and ≤3 vol% in the marginal and more central rocks of the SMB. Using ratios of xenocrysts to partial melt determined in melting experiments employing rocks of the Meguma Group, the abundance of xenocrysts suggests that ≤10 vol% of physically invisible, complementary former country-rock partial melt is present in the SMB rocks. Together, ≤16 and ≤8 vol% of country-rock material appears to occur in the marginal and more central rocks of the SMB, respectively. However, existing whole-rock isotopic data indicate that at least the most evolved rocks of the SMB may have ≤56 vol% of additional former Meguma Group partial melt. Energy-constrained numerical modelling of the assimilation of Meguma Group rocks in the SMB magmas through partial melting shows that selective contamination of the exposed SMB rocks by Meguma Group-derived partial melt may explain the presence of the additional former partial melt, but cannot rule out that the partial melt was added to the SMB as part of the source. | en_US |
