Paleointensity applications to timing and extent of eruptive activity, 9°-10°N East Pacific Rise
Julie Bowles; Jeffrey S. Gee; Dennis V. Kent; Michael R. Perfit; S. Adam Soule; Daniel J. Fornari
- Paleointensity applications to timing and extent of eruptive activity, 9°-10°N East Pacific Rise
Gee, Jeffrey S.
Kent, Dennis V.
Perfit, Michael R.
Soule, S. Adam
Fornari, Daniel J.
- Lamont-Doherty Earth Observatory
- Book/Journal Title:
- Geochemistry, Geophysics, Geosystems
- 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 (<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°50′N is suggestive of a ~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.
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