Fig. 10. N-MORB-normalized trace-element plots for mafic and ultramafic rocks of the Rio Boba plutonic sequence, as well as for other regionally related volcanic rocks. (a) Pyroxenites, (b)troctolites, (c) olivine gabbronorites, (d) gabbronorites, (e) oxide gabbronorites, (f) Puerca Gorda Schists, (g) main geochemical groups of Lower Cretaceous volcanic rocks in Hispaniola, and (h) mafic volcanic rocks from El Cacheal complex and Los Caños Fm of Puerto Plata ophiolitic complex (data from Escuder-Viruete et al., 2006, 2011c, 2014, and this work). MORB-normalizing values are from Sun and McDonough (1989). Boninite compositions are from the ODP Leg 125 (Pearce et al., 1992; Pearce and Peate, 1995; Taylor and Nesbitt, 1995; Pearce and Reagan, 2019). See text for explanation.

Overall, the major element composition of the gabbronorites is similar to the Talkeetna Arc rocks, though some of the more evolved Talkeetna samples have lower CaO, TiO₂ and FeO_Tfor similar Mg#. The pyroxenites display a restricted compositional range and can be compared with the pyroxenites of the Solomon Islands, although they have a lower Mg#.

The experimental models for anhydrous fractional crystallization of primitive tholeiitic basalt at the base of the crust (1.0 GPa) and at shallover crustal conditions (0.7 GPa) show a continuous differentiation trend from high Mg# cumulates (dunite, lherzolite and websterite) to evolved, low Mg# liquids. Gabbroic samples follow a trend subparallel to the experimental liquid line of descent in the Mg# 80-40 interval. This trend is continuous with no gaps in Mg#. The Rio Boba gabbroic rocks plot away from the experimental crystallization lines at 0.7 and 1.0 Gpa in the CaO, TiO₂ and FeO_T vs. Mg# diagrams, reflecting a variability that may be related to fractional crystallization. These differences may be due to a different starting basalt composition and/or the elimination of all solid phases in each single fractionation step and/or the constant pressure conditions followed in the modeling. With some exception, the dunite-wehrlite-pyroxenite cumulates obtained in the modeling of anhydrous fractional crystallization have higher Mg# values than the Rio Boba pyroxenites, suggesting that these pyroxenites are products of the crystallization of already evolved mantle-derived magmas. This is consistent with the lower Mg# values with respect to the SSZ mantle pyroxenites of the Solomon Islands.

The concentrations of Cr, Ni, V and Sc are higher in pyroxenites and progressively decrease from the gabbronorites to the oxide gabbronorites (Appendix E). The concentrations of these elements in the Puerca Gorda mafic metavolcanic rocks are similar to those in the gabbronorites. With some exception of the more evolved oxides gabbronorites, the mafic plutonic rocks of the Rio Boba sequence and the metavolcanic rocks of Puerca Gorda have Ti/V values equal to, and lower than, chondrite (<10), which values are similar to those of the boninites, suggesting high depletion in the mantle source. Zr concentration shows an incompatible behavior increasing from very low levels in the pyroxenites and gabbronorites to higher concentrations in the mafic metavolcanic rocks.