ZIRCON δ18O EVIDENCE FOR CRUSTAL RECYCLING IN ISLAND ARCS: THE CIALES AND MOROVIS STOCKS OF PUERTO RICO
Ciales and Morovis are small (2 to 20 km2) granodiorite stocks located 1 km apart. Both contain zircons that yield elevated δ18O values of 6.73±0.04 and 6.69±0.04‰, VSMOW, respectively (Pérez, 2008). Grain imaging with back scattered electrons (BSE) and transmitted light (TL) shows that zircons from the Ciales and Morovis stocks are mostly euhedral and do not show internal complexities. Likewise, CL imaging shows simple oscillatory zoning and sector zoning with no evidence of inherited cores. The BSE, TL, and CL results all indicate a simple crystallization history with no evidence of inheritance; these data are consistent with simple U-Pb spectra for these samples, which yield U-Pb ages of 83.9±1.7 Ma (Ciales) and 85.3±1.8 Ma (Morovis) (Cavosie, unpublished). The similarities in data between the Ciales and Morovis stocks indicate that they are two surface exposures of a single pluton, whose δ18O(Zrc) values, grain morphologies, and internal structure demonstrate evidence of crustal recycling during the formation of Puerto Rico.