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Geochemical data for volcanic samples recovered at Site 862 of Leg 141 of the Ocean Drilling Program show that a wide diversity of magma types were generated in the region of tie Taitao Ridge. We have divided the data into seven groups. Numerous samples belong to three groups of basaltic glasses—our Groups 1, 2, and 5. Relative few samples of Groups 3, 4, and 6 were collected. Group 7 includes silicic samples that range from andesites to rhyolites. Group 1 samples conform in most aspects of their major and trace element and isotopic chemistry and in their liquid line of descent to N-type mid-ocean ridge basalts (MORB) saturated in olivine and Plagioclase. Group 2 samples differ from those of Group 1 in several features of their chemistry. They have higher contents of K2O and incompatible trace elements and are mildly light rare earth element (LREE)-enriched. Their Nb depletions and low values of Ce/Pb and K/Pb are consistent with addition of a subducted sediment-like component. Sr-Nd and Pb isotopic compositions also indicate the presence of a component with higher time-integrated Rb/Sr, U/Pb, and Th/U and lower Sm/Nd than typical for the sources of MORBs. In addition, the Group 2 glasses define a trend of very limited Fe-enrichment, as for calc-alkaline rather than tholeiitic suites. Group 5 glasses have compositions intermediate between those of Group 1 and Group 2 glasses and suggest that there was a broad continuum of primary magmas depending upon the amount of sediment introduced into the mantle. Group 1 glasses with MgO = 8.0% fall on the global array of Klein and Langmuir (1987) between Na8 0 and Fe8 0, but lie off the arrays of Na8 0 and Fe8 0 against axial depth. If the glasses originally did conform to these arrays, the Taitao Ridge has been uplifted 2000-4000 m. The glassy plagioclase-homblende-phyric rhyolites are plausibly melts of metamafic sources. Trace-element patterns and Pb isotopic compositions indicate that this source was chemically similar to Group 2 rocks. The higher Sr/Sr of the rhyolites probably results from incorporation of seawater-derived fluids in these sources. Incompatible-element enrichments and REE patterns of the rhyolites are consistent with 10% melting of a Group 2-like source to leave a residue of Plagioclase and hornblende. In this case, phenocrysts in the rhyolites are probably restite.

Geochemical Data on Volcanic Rocks and Glasses Recovered from Site 862: Implications for the Origin of the Taitao Ridge, Chile Triple Junction Region