Full vector paleosecular variation (PSV) recorded on the Koolau Volcano, Oahu, Hawaii during the Matuyama Chron at Makapuu Point (ca. 2.6 to ~2.2 Ma).

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Paleomagnetic (i.e. fossil magnetism) data are the unique source of observations to understand the geomagnetic transitions and hence the geodynamo processes involved in field generation. Due to the fact that there is a need to obtain reversal records from volcanic sequences in order to have a better understanding of the generation of the Earth's magnetic field, it is proposed to study a long sequence (about ~191 meters) of lavas from the island Oahu, Hawaii at a site known as Makapuu Point, Koolau Volcano with the main objective of investigating the full range of paleomagnetic signals recorded before during and after several successive polarity transitions. The section covering ~410,000 years of field changes includes the possibility of studying the detailed recording of the successive magnetic field reversals such as the Gauss-Matuyama, Cryptochron C2r.2r-1 and the onset of the Reunion Subchron, since the base of the section is 2.60+/-0.13 million years old, the middle part is 2.49+/-0.07 million years old and about 10 m below the top of the section the age is ~2.19+/-0.12 million years old. The objectives of this 2 year research study are related to the knowledge of field variations during periods like reversals and excursions and related to the critical time intervals that precede and follow reversals that so far have only been documented from a few sedimentary sequences, for the interval between 2.6 to ~2.012 Ma. Reversal studies cannot be separated from the surrounding polarity intervals and most records published so far were not long enough to provide complete information. The sequence offers the exceptional opportunity to study changes over a time period that includes several polarity intervals and thus documents the paleofield behavior over various time constants. This is a basic condition to extract and bring up significant constraints for the theoretical and numerical modeling of the generation of the paleofield. This research will have impacts on field like magnetostatigraphy, rock magnetism, geomagnetism and physical volcanism. Several undergraduate students will be supported and involved in all aspects of the research.The proposal is focused on full vector studies in order to determine the total field vector and Paleosecular Variation (PSV) of the "stable" polarities. The study will focus on the successive periods of polarity and their associated reversals. The paleointensity experiments will be conducted using a version of the Thellier-Coe as well as the differential pTRM "multi-specimen" methods. The PIs have imposed severe criteria to discard samples affected by magneto-mineralogical transformations and with magnetization components involving multi-domain grains. It is important to deal with paleointensity values that rely on a minimum number of 5 to 8 determinations per flow in order to perform suitable statistical treatment. Given the time consuming aspect of paleointensity studies, a two-year period is envisaged to achieve the goals of this proposal including 10 more radiometric 40Ar/39Ar age determinations. The principal investigator and four undergraduate students will carry out the entire research project. The involvement of undergraduate students will be a priority in this project, from fieldwork, laboratory work, analysis and publication of the results. Data will be disseminated through publication and on the web and community maintained paleomagnetic and geochronologic databases. This project will provide the stimulus to maintain the paleomagnetics operation at UH and the Rare Gas Lab. at the Univ. of Wisconsin at Madison both of which are used by a diverse group of students and researchers from all over the world.