Extremely magnetized abyssal lavas erupted in active back-arc of the Okinawa Trough
Abstract
Although high-amplitude of marine magnetic anomalies have been utilized for understanding for seafloor dynamics, the causal link between intensity of natural remanent magnetization and physical and chemical processes of extrusive rocks are still unclear. In addition, we essentially lack rock magnetic data of arc-back-arc lavas, which potentially provide strong constraints for understanding time- and spatial-dependent diversity of lava magnetization including mid-ocean ridge basalts. Here, we present new rock magnetic data of strongly magnetized basaltic rocks, which rank among the most magnetized in known oceanic basaltic rocks, from active back-arc region of the Okinawa Trough. We analyzed 27 non-oxidized (fresh) basaltic rock samples obtained from the active back-arc volcanoes, located at the segment boundary along back-arc rift. Their natural remanent magnetization ranges 7 A/m to >200 A/m, and has clear nonlinear relationship with both magnetic hysteresis signatures and titanomagnetite amount. The strongly magnetized lavas show large contribution of appropriate amount of SD titanomagnetite grains formed in proper crystal growth environments. The high-temperature thermomagnetic experiments demonstrate reversible curves in both heating and cooling with single Curie temperature. The Curie temperature shows up to 480°C for strongly magnetized lavas, which is much higher than that of mid-ocean ridge basalts mainly containing TM60, indicating that rich Fe and low Ti contents of titanomagnetite grains are main magnetic carrier. These observations clearly demonstrate that intensity of natural remanent magnetization is primarily controlled by cooling rate of lavas and ratio of Fe to Ti of titanomagnetite grains as well as bulk iron contents, with important implications towards marine magnetic anomalies and arc-back-arc volcanism.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMGP44A..05F
- Keywords:
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- 1518 Magnetic fabrics and anisotropy;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1519 Magnetic mineralogy and petrology;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1525 Paleomagnetism applied to tectonics: regional;
- global;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1527 Paleomagnetism applied to geologic processes;
- GEOMAGNETISM AND PALEOMAGNETISM