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Pringle, Staudigel H, Gee J.  1991.  Jasper Seamount: Seven million years of volcanism. Geology. 19:364-368.   10.1130/0091-7613(1991)019<0364:jssmyo>2.3.co;2   AbstractWebsite

Jasper Seamount is a young, mid-sized (690 km super(3)) oceanic intraplate volcano located abut 500 km west-southwest of San Diego, California. Reliable super(40)Ar/ super(39)Ar age data were obtained for several milligram-sized samples of 4 to 10 Ma plagioclase by using a defocused laser beam to clean the samples before fusion. Gee and Staudigel suggested that Jasper Seamount consists of a transitional to tholeiitic shield volcano formed by flank transitional series lavas, overlain by flank alkalic series lavas and summit alkalic series lavas. Twenty-nine individual super(40)Ar/ super(39)Ar laser fusion analyses on nine samples confirm the stratigraphy: 10.3-10.0 Ma for the flank transitional series, 8.7-7.5 Ma for the flank alkalic series, and 4.8-4.1 Ma for the summit alkalic series. The alkalinity of the lavas clearly increases with time, and there appear to be 1 to 3 m.y. hiatuses between each series. The age data are consistent with the complex magnetic anomaly of Jasper; however, the dominant reversed polarity inferred from the anomaly suggests that most of the seamount formed at ca. 11 Ma, prior to the onset of Chron C5N.

R
Gee, J, Varga R, Gallet Y, Staudigel H.  1993.  Reversed-polarity overprint in dikes from the Troodos ophiolite: Implications for the timing of alteration and extension. Geology. 21:849-852.: Geological Society of America   10.1130/0091-7613(1993)021<0849:rpoidf>2.3.co;2   AbstractWebsite

Paleomagnetic analysis of dikes from the Troodos ophiolite indicates the presence of a well-defined reversed-polarity overprint, an unexpected result given the currently accepted Cenomanian-Turonian age (88-91 Ma) suggesting formation during the Cretaceous Long Normal Period (83-118 Ma). This reversed- polarity component was apparently acquired prior to tectonic tilting of the dikes, implying that extensional tectonism occurred significantly (>5 m.y.) off axis. Alternatively, the paleomagnetic and field observations may be reconciled if parts of the ophiolite are significantly younger.