In the upper Silurian Cadillac Mountain intrusive complex (Maine), basaltic injections have produced a thick, layered gabbro-diorite unit (GDU) that now separates the I-type lower Cadillac Mountain Granite (LCMG, eNdi =+1.6 to +2.7) from the A-type upper granite (UCMG, eNdi =+2.5 to +2.8). The GDU is the result of multiple infusions of tholeiitic magma into the granitic magma chamber producing macrorythmic units of chilled gabbro at the bottom (87Sr/86Sri=0.7026-0.7032, eNdi =+4.5 to +7.2), medium-grained gabbro in the middle (87Sr/86Sri= 0.7028-0.7042, eNdi =+2 to +6), and dioritic to granitic rocks at the top (87Sr/86Sri>0.7036, eNdi =+2.4 to +2.9). Trace element and isotopic compositions of evolved rocks at the top of GDU macrorythmic units are consistent with the notion that these rocks reflect mixing of basaltic and LCMG or UCMG magma with simultaneous fractional crystallization, resulting in the formation of gabbroic cumulates. The restricted eNdi of the evolved rocks in the GDU contrasts with the larger variability of eNdi in the cumulates, suggesting further contamination of residual GDU liquids with LCMG or UCMG and subsequent homogenization. Covariations of eNdi with Sm/Nd, Sr/Nd and Nb suggest contamination of portions of the LCMG with evolved liquids of the type found in the GDU, rather than with unmodified basalt. The compositional variation of the UCMG can be roughly explained by a mixture of minor mafic enclaves and a granitic component that is high in SiO2 and K2O. The mafic enclaves in the UCMG show strong enrichments in Nb, Zr, and Y that anticorrelate with SiO2, K and Rb, but show hardly any correlation with eNdi (+1.9 to +3.4). The Nd isotopic compositions of all analyzed enclaves appears to be dominated by a granite-like component, suggesting hybridization of basaltic and granitic melts at some stage in their evolution (1).

(1) Wiebe, R. A. et al. (1997) J. Petrol. 38, 393-423.