Nd and Sr isotopic signatures of Mesozoic plutons in northeastern North America

Nd and Sr initial isotope ratios are reported for 17 Mesozoic plutons of the Monteregian Hills and White Mountain series provinces in northeastern North America. Some variation in the isotopic ratios at most localities is caused by crustal-contamination processes. When the crustal assimilation effects are taken into account, the initial ratios for apparently uncontaminated, mantle-derived parental magmas show only restricted range in ⁸⁷Sr/⁸⁶Sr (0.7032 to 0.7040) and ε_Nd (T) (+5.4 to +2.3), which are inversely correlated. These ratios characterize alkaline to subalkaline magmas emplaced over more than 400 km² and about 80 m.y. The isotopic and trace-element characteristics are broadly similar to those of many modern ocean-island basalts, specifically the New England Seamounts, suggesting similar time-integrated, lithophile-element-depleted mantle sources. The results are consistent with plume-related mantle sources deeper than the subcontinental mantle.