GEOCHEMISTRY OF CRETACEOUS MAGMATISM IN EASTERN CUBA: RECYCLING OF NORTH AMERICAN CONTINENTAL SEDIMENTS AND IMPLICATIONS FOR SUBDUCTION POLARITY IN THE GREATER ANTILLES PALEO-ARC

Abstract

We present whole-rock major- and trace-element and Nd-Sr-Pb radiogenic isotope data for Cretaceous igneous suites from Eastern Cuba. These rocks are related to the Greater Antilles paleo-island arc magmatism and have three different igneous styles. Group 1 consists of tholeiitic basalts and rare basaltic andesites that have normal mid-ocean ridge basalt (N-MORB)-like compositions similar to those found in back-arc basin basalts (TiO2=1.2-2.9wt%; La/Yb(N)=0-7-0.9, Th/Nb=0.06-0.08, and initial 208Pb/ 204Pb=37.65-37.74). Group 2 comprises basaltic and rare basaltic andesitic subvolcanic dykes with major- and trace-element and isotopic compositions similar to those of island arc tholeiites (TiO2=0.7-1.4 wt%; La/Yb(N)=0.6-0.9, Th/Nb=0.06-0.68, and initial 208Pb/ 204Pb=37.74-38.25). Group 3 is composed of low-Ti (TiO2=0.3-0.9 wt%) calcalkaline igneous rocks that have an unambiguous subduction-related character (La/Yb(N)=1.1-5.0, Th/Nb=0.35-1.55, and initial 208Pb/ 204Pb=37.94-38.39). The parental magmas of the three groups formed by variable melting degrees (<5-25%) of spinel lherzolite, with more depleted mantle sources for Groups 2 and 3 than Group 1.The trace-element and radiogenic isotope compositions of primitive Group 3 samples are strongly bimodal. One subgroup of samples is characterized by low Ta/Yb (0.02-0.03) and Th/La (0.10-0.13), slightly subchondritic Nb/Ta (13.3-17.3), and relatively high initial 206Pb/204Pb (18.57-18.62) and eNd (7.6-9.4). The remaining primitive Group 3 samples have higher Ta/Yb (0.06-0.11) and Th/La (0.24-0.32), and highly subchondritic.