HR: 1340h
AN: GP13A-0026    [Abstracts]
TI: Effects of hydrothermal alteration on the magnetic mineralogy of mid-ocean ridge basalts, IODP Site 1301B, Juan de Fuca Ridge
AU: * Linville, L M
EM: lisa.linville@gmail.com
AF: Geology Dept. Western Washington University, 516 High St., Bellingham, Wa 98225-9080
AU: Housen, B
EM: bernih@cc.wwu.edu
AF: Geology Dept. Western Washington University, 516 High St., Bellingham, Wa 98225-9080
AU: Sager, W
EM: wsager@ocean.tamu.edu
AF: Dept. of Oceanography, Texas A&M, Texas A&M University, College Station, Tx 77843-3146
AB: Pairs of young (3.5 Ma) altered and unaltered MORB from the Juan de Fuca Ridge collected from IODP Expedition 301, Hole 1301B were studied to better understand how hydrothermal alteration affects the magnetization of oceanic crust. Thermomagnetic analysis (performed with both a VSM and Kappabridge) revealed characteristically different Curie temperatures and degree of non-reversibility between altered and unaltered samples. Magnetic contributions outlined by these methods, in addition to IRM and hysteresis parameters, indicate that samples are dominated by single domain titanomagnetite and titanomaghemite, with a titanium content of approximately TM45. Petrological analysis with a SEM confirmed the presence of abundant Fe-Ti oxides. Despite the preponderance of titanomagnetite in unaltered samples, shrinkage cracks, which offer direct evidence of maghemitization, were seen in both altered and unaltered samples, indicating (as do irreversible cooling curves for all samples) that even supposedly unaltered samples have undergone some degree of low temperature oxidation. Preliminary paleomagnetic data in related samples indicates normal polarity and inclinations that are approximately what is expected for this site. The samples also exhibit both streaked and well defined, non-streaked magnetizations. This study intends to utilize the information obtained by procedures described above to test for correlations between characteristic magnetization directions and degree of oxidation, in order to further our understanding of the effect maghemitization has on the paleomagnetism of oceanic rocks.
DE: 1519 Magnetic mineralogy and petrology
DE: 1533 Remagnetization
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005