A geomagnetic and AMSrecord of the Lower Mammoth (ca. 3.314+/- 0.034 Ma) polarity transition recorded in the Icelandic and Rhyodacite Mauna Kuwale long volcanic sequence Wai’ane Volcano, Oahu, Hawaii

New paleomagnetic measurements, coupled with ⁴⁰Ar/³⁹Ar dating of terrestrial lava sequences, are revolutionizing our understanding of the geodynamo by providing high resolution records of the paleomagnetic field. As part of an investigation of the short-term behavior of the geomagnetic field, we have sampled 25 cooling units of the Mauna Kuwale Wai’anae Volcano, Oahu Hawaii. After the flank collapse of the volcano 22 Icelanditic and 3 Rhyodacitic units were identified and sampled in detail for paleomagnetic, rock magnetic and petrofabric (AMS) studies. We performed both NRM and induced magnetic detailed experiments of the 25 individual cooling units. At least eight samples, collected from each of 25 successive cooling units at Mauna Kuwale, were stepwise demagnetized by both alternating field (5 mT to 100 mT) and thermal (from 28°C to 575–650°C) methods. Mean directions were obtained by principal component analysis. All samples yielded a strong and stable ChRM trending towards the origin of vector demagnetization diagrams based on seven or more demagnetization steps, with thermal and AF results differing insignificantly. Low-field susceptibility vs. temperature (k–T) analysis conducted on individual lava flows indicated approximately half with reversible curves. Curie point determinations from these analyses revealed a temperature close to or equal to 580°C, indicative of almost pure magnetite ranging from single domain (SD) to pseudo-single domain (PSD) grain sizes for most of the flows. FORCs were also determined. The mean directions of magnetization of the entire section sampled indicate a normal polarity, with ∼12 transitional cooling units of the sequence characterized by excursional directions. The record shows paleosecular variation within the transitional portion of the record similar to the Lower Mammoth polarity transition found on 3 adjacent units of the Wai’anae volcano. The ⁴⁰Ar/³⁹Ar isotopic determinations yielded an integrated age obtained from several specimens of 3.314+/- 0.034 Ma.