Cretaceous geomagnetic paleointensities; Thellier experiments on pillow lavas and submarine basaltic glass from the Ontong Java Plateau

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doi: 10.1029/2003GC000611
Author(s): Riisager, Peter; Riisager, Janna; Zhao, Xixi; Coe, Robert S.
Author Affiliation(s): Primary:
University of California at Santa Cruz, Earth Sciences Department, Santa Cruz, CA, United States
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 4(12). Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. Accessed on Feb. 2, 2004. 44 refs.; illus., incl. 2 tables, sketch map
Summary: We present new Thellier paleointensity results on pillow lavas and pillow-rim submarine basaltic glass (SBG) from 120 Ma basalts erupted on the Ontong Java Plateau. All pillow lavas have suffered low-temperature alteration and are unsuitable for Thellier paleointensity experiments. In contrast, pillow-rim SBG is virtually impermeable to seawater and therefore has suffered little or no low-temperature alteration. Out of 21 selected SBG samples with magnetic moment larger than 10-10 Am2, 18 samples (from 12 chilled SBG margins) yielded paleointensity estimates of good technical quality. Rock magnetic measurements show the primary carrier of remanence is low-Ti titanomagnetite occurring in a continuous range of compositions starting from nearly pure magnetite. As suggested by a recent study, magnetic hysteresis parameters were monitored during the entire paleointensity experiment and a drastic change of parameters was observed above 400-440°C, which is in accordance with the partial thermoremanent magnetization checks failing significantly above the same temperature. We suggest that paleointensity estimates obtained below this critical temperature represent true determination of the paleomagnetic field strength. For several pillow margins two to three samples were measured, and in such cases the data agree well. Altogether we obtain reliable estimates from 12 SBG pillow-rims, yielding a mean paleointensity of 27.1±13.4 µT and a corresponding virtual axial dipole moment of 5.8±2.8·1022 Am2. This value is slightly higher than whole rock data from similar aged subaerial lava flows. The paleosecular variation of the intensity estimates is slightly larger than previously reported for paleointensity determinations for the Cretaceous Normal Superchron.
Year of Publication: 2003
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Basalts; Cretaceous; Dipole moment; Glasses; Igneous rocks; Lava; Leg 192; Magnetic properties; Mesozoic; Ocean Drilling Program; Ontong Java Plateau; Oxides; Pacific Ocean; Paleomagnetism; Pillow lava; Secular variations; Submarine volcanoes; Titanomagnetite; Volcanic rocks; Volcanoes; West Pacific
Coordinates: S100000 N100000 E1750000 E1500000
Record ID: 2004067096
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