Rock Magnetic Properties and Magnetic Petrology of Hawaiian and Icelandic Basalts: a key for the Understanding of high Crustal Magnetizations on Earth and Earth-like Planets?

HR: 14:15h
AN: GP43A-02 [Abstracts]
TI: Rock Magnetic Properties and Magnetic Petrology of Hawaiian and Icelandic Basalts: a key for the Understanding of high Crustal Magnetizations on Earth and Earth-like Planets?
AU: * Kontny, A
EM: agnes.kontny@urz.uni-heidelberg.de
AF: Geologisch-Paläontologisches Institut, Ruprecht-Karls Universität, Im Neuenheimer Feld 234, Heidelberg, D-69120, Germany
AB: The rock magnetic behavior and Fe-Ti oxide petrology of subaerial and submarine basalts have been extensively studied over the last decades because of their importance in understanding Earth's magnetic anomalies. Combined rock magnetic and magneto-mineralogic investigations on different basalt lithologies from scientific drillings on Hawaii and Iceland have shown that multiple processes, related to the geodynamic setting, the emplacement and cooling history and the alteration history affected the texture and composition of the originally homogeneous titanomagnetite and caused significant variation in rock magnetic properties like magnetic susceptibility, Curie temperature, coercivity force or natural remanent magnetization (NRM). Hawaiian basalts from the scientific drillings HSDP-2, SOH-1 and SOH-4 have e.g. NRM intensities between <1 and 13 A/m, which is distinctly lower than those measured on several localities on Iceland. Surface samples from fissure eruptions of the Reykjanes peninsula show 4 - 32 A/m and drill cores from the Stardalur central volcano (subaerial basaltic lava flows) show very high values up to 120 A/m. Although the main controlling factors for these high NRM values seem to be the primary magma composition and cooling history, secondary processes like high-temperature decomposition reactions and hydrothermal alteration can also play a role. During the latter process, titanomagnetite is altered to titanomaghemite and furthermore to (cation-deficient) magnetite. Secondary magnetite can be additionally formed due to hydrothermal activity increasing the total magnetization. Modifications of rock magnetic properties related to these magnetic petrology changes will be discussed for basalts of different strong magnetization in relation to geologic processes.
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly