Radiometric Ages of Basement Lavas Recovered at Loen, Wodejebato, MIT, and Takuyo-Daisan Guyots, Northwestern Pacific Ocean

Abstract

The best estimate for the age of the oldest volcanism recovered from the summits of Loen, Wodejebato, MIT, and TakuyoDaisan guyots, northwestern Pacific Ocean, is 113, 83, 123, and 118 Ma, respectively. All of these sites originated in the central and western regions of the South Pacific Isotopic and Thermal Anomaly (SOPITA). The 113-Ma age for Loen Guyot is significantly different from the 76-Ma age of volcanism under the carbonate platform of its neighbor, the living Anewetak Atoll, and suggests that drowned guyot/living atoll seamount pairs may have no genetically significant relationship other than geographic proximity. Although all of the basalts recovered from the top of Wodejebato Guyot were erupted during polarity Chron 33R (ca. 79-85 Ma), both the occurrence of reworked Cenomanian calcareous nannofossils in one of the summit cores and the existence of a thick Cenomanian volcaniclastic sequence, including 94-Ma basaltic clasts, in the archipelagic apron indicate that there must have been a Cenomanian or older edifice beneath the drilled summit volcanics. AT MIT Guyot, two late-stage periods of volcanism can be recognized: late Aptian (ca. 115 Ma) phreatomagmatic eruptions through the existing volcanic and carbonate platform, and 120-Ma hawaiites seen both as exotic clasts in the 115-Ma tuffs and as lava flows at the top of the basement sequence. Also, the 122.9 ± 0.9 Ma age of two lavas in the basement lava sequence date the upper boundary of the reversed polarity Chron MIR, providing an important calibration point for the Cretaceous Geological Reversal Time Scale. The 118-Ma age of volcanism at Takuyo-Daisan Guyot is best constrained by the age of dredge basalts from its flanks and those of its neighbor to the southwest, Takuyo-Daini Seamount, but agrees well with the oldest sediments recovered at Hole 879A.