Abstract

The Nauru Basin contains a well-documented pattern of Late Jurassic magnetic anomalies and a Cretaceous volcanic complex that has not disturbed the older magnetic structure. The following hypotheses are offered to explain this paradox. The Cretaceous basalts are normally and uniformly magnetized, making them invisible to a surface-towed magnetometer. Tension cracks and fractures associated with thermal uplift and/or magma wedging provided pathways for the Cretaceous magma through the Jurassic basement without disrupting the Jurassic magnetic structure. The same tension cracks admitted sea water that convectively removed heat from the magnetic layer and thus maintained the Jurassic basement below its magnetic blocking temperature for extended periods of time during intrusive thermal episodes. Finally, the maximum uplift associated with Cretaceous volcanism in the Nauru Basin could have been equal to, but was probably something less than, that associated with nearby seamount and atoll chains.

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