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2006
Bowles, J, Gee JS, Kent DV, Perfit MR, Soule SA, Fornari DJ.  2006.  Paleointensity applications to timing and extent of eruptive activity, 9 degrees-10 degrees N East Pacific Rise. Geochemistry Geophysics Geosystems. 7   10.1029/2005gc001141   AbstractWebsite

[ 1] Placing accurate age constraints on near-axis lava flows has become increasingly important given the structural and volcanic complexity of the neovolcanic zone at fast spreading ridges. Geomagnetic paleointensity of submarine basaltic glass (SBG) holds promise for placing quantitative age constraints on near-axis flows. In one of the first extensive tests of paleointensity as a dating tool or temporal marker we present the results of over 550 successful SBG paleointensity estimates from 189 near-axis (< 4 km) sites at the East Pacific Rise, 9 degrees - 10 degrees N. Paleointensities range from 6 to 53 mu T and spatially correspond to the pattern expected from known temporal variations in the geomagnetic field. Samples within and adjacent to the axial summit trough (AST) have values approximately equal to or slightly higher than the present-day. Samples out to 1 - 3 km from the AST have values higher than the present-day, and samples farther off axis have values lower than the present-day. The on-axis samples (< 500 m from the AST) provide a test case for using models of paleofield variation for the past few hundred years as an absolute dating technique. Results from samples collected near a well-documented eruption in 1991 - 1992 suggest there may be a small negative bias in the paleointensity estimates, limiting resolution of the dating technique. Possible explanations for such a bias include local field anomalies produced by preexisting magnetic terrain; anomalously high magnetic unblocking temperatures, leading to a small cooling rate bias; and/or the possibility of a chemical remanence produced by in situ alteration of samples likely to have complicated thermal histories. Paleointensity remains useful in approximating age differences in young flows, and a clear along-axis paleointensity contrast near 9 degrees 50'N is suggestive of a similar to 150 - 200 year age difference. Paleointensity values of off-axis samples are generally consistent with rough age interpretations based on side scan data. Furthermore, spatial patterns in the paleointensity suggest extensive off-axis flow emplacement may occur infrequently, with recurrence intervals of 10 - 20 kyr. Results of a stochastic model of lava emplacement show that this can be achieved with a single distribution of flows, with flow size linked to time between eruptions.

2003
Bowles, J, Tauxe L, Gee J, McMillan D, Cande S.  2003.  Source of tiny wiggles in Chron C5: A comparison of sedimentary relative intensity and marine magnetic anomalies. Geochemistry Geophysics Geosystems. 4   10.1029/2002gc000489   AbstractWebsite

[1] In addition to the well-established pattern of polarity reversals, short-wavelength fluctuations are often present in both sea-surface data ("tiny wiggles'') and near-bottom anomaly data. While a high degree of correlation between different geographical regions suggests a geomagnetic origin for some of these wiggles, anomaly data alone cannot uniquely determine whether they represent short reversals or paleointensity variations. Independent evidence from another geomagnetic recording medium such as deep-sea sediments is required to determine the true nature of the tiny wiggles. We present such independent evidence in the form of sedimentary relative paleointensity from Chron C5. We make the first comparison between a sedimentary relative paleointensity record (ODP Site 887 at 54degreesN, 148degreesW) and deep-tow marine magnetic anomaly data (43degreesN, 131degreesW) [ Bowers et al., 2001] for Chron C5. The sediment cores are densely sampled at similar to2.5 kyr resolution. The inclination record shows no evidence for reverse intervals within the similar to1 myr-long normal Chron C5n.2n. Rock magnetic measurements suggest that the primary magnetic carrier is pseudo-single domain magnetite. We choose a partial anhysteretic magnetization (pARM) as our preferred normalizer, and the resulting relative paleointensity record is used as input to a forward model of crustal magnetization. We then compare the results of this model with the stacked deep-tow anomaly records. The two records show a significant degree of correlation, suggesting that the tiny wiggles in the marine magnetic anomalies are likely produced by paleointensity variations. An analysis of our sampling density suggests that if any reverse intervals exist at this site, they are likely to be <5 kyr in duration. Furthermore, we suggest that reverse intervals during Chron C5n.2n documented in other locations are unlikely to be global.