CERRO AZUL PLUTONIC COMPLEX: CRETACEOUS ISLAND ARC ROCKS EXPOSED IN RIO MAMONI VALLEY, EASTERN PANAMA

Rocks from the area mapped as the Cerro Azul batholith in eastern Panama vary from gabbro through quartz diorite to hornblende quartz monzonite. This diversity of lithologies suggests the term Cerro Azul plutonic complex is more fitting. These rocks are tholeiitic. Island arc origin for them is indicated by their trace element chemistry. REE’s are slightly fractionated with (La/Sm)_N ranging from1.64 to 3.37 and (La/Yb)_N ranging from 2.34 to 4.94. Some samples show a small positive Eu anomaly. LILE’s (K, Ba, and Th) are enriched while Ta, Nb, Zr, Hf and REE are depleted relative to MORB. Contact relations between these rocks have not been observed, but they were collected from bedrock exposures along a 7 km stretch of the Rio Mamoni in the eastern portion of the Cerro Azul batholith. This body is labeled Cretaceous by Case (1974). These data are consistent with the development of an island arc on the western edge of the Caribbean plate at the end of the Mesozoic Era.