Mineral Geochemistry of Basaltic Rocks from IODP Expeditions 334 and 344: Implications for Magmatic Processes of Cocos Ridge Segment Being Subducted Beneath the Middle America Trench

The Cocos Ridge, which is subducted beneath the Central American Volcanic Arc, has a complex tectonic evolution history due to plume-ridge interaction between Galápagos plume and Cocos—Nazca spreading center. This study presents major trace element analyses of plagioclase clinopyroxenes hosted by Ridge basaltic rocks that were drilled in three holes (U1381A, U1381C U1414A) Sites U1381 U1414 on close Middle America Trench during Integrated Ocean Drilling Program (IODP) Expeditions 334 344. results show (1) plagioclases are mainly bytownite labradorite with subordinate andesine, enriched light rare earth elements (LREE) some large-ion lithophile (LILE) exhibit marked positive Eu anomalies; (2) augites, depleted highly incompatible such as LREE LILE, have nearly flat heavy patterns (HREE) lack anomalies chondrite-normalized (REE) diagrams. During ascent surface, primary magmas experienced fractional crystallization plagioclase, clinopyroxene, Ti-Fe oxides possibly olivine (complete replacement secondary minerals). temperatures phenocrysts microlites 1050 1269 °C, 866 1038 respectively, pressures 0.3–0.7 GPa. clinopyroxene phenocrysts/micro-phenocrysts 1174–1268 similar those phenocrysts, suggesting cotectic crystallized early stage magmatic evolution. In addition, equilibrium phenocrysts/micro 0.02–0.97 GPa, implying started crystallize within mantle, magma undergone an no plagioclase.