[SIT22-P31] Magnetic mineral inclusions in single zircon crystals from the Tanzawa tonalite and the river of Yangtze and Mississippi
Keywords:paleointensity, zircon, inclusion
Sato et al. (2015) and Sato (2018, JpGU) reported the rock-magnetic properties of the single zircon crystals sampled from the the Tanzawa tonalite (4-5 Ma) and from the Yangtze and Mississipi river. They demonstrated that the various rock-magnetic properties such as natural remanent magnetization (NRM), isothermal remanent magnetization (IRM), hysteresis parameters, and transition temperature could be measured using the standard magnetometers (SQUID magnetometer, MPMS, and AGM). During their rock-magnetic measurements, many of single zircon crystals are below the limits of the sensitivity of the magnetometers employed, but a few % zircons had values of M NRM > 4 x 10−12 Am2 And M IRM > 4 x 10−12 Am2, containing enough magnetic minerals to be measured in the DC SQUID magnetometer. The main remanence carriers seem to be nearly pure magnetite with pseudo-single-domain grain sizes. These samples are expected to appropriate for the paleointensity study, but identification of mineral inclusions in those zircons are not yet investigated.
Here, we report mineral inclusions in zircons from 1) Tanzawa tonalite, 2) the Yangtz river, and 3) the Mississippi river, with an optical microscope, Laser-Raman microspectroscopy and SEM-EDS system. Results indicate that zircon crystals appropriate for the paleointensity study contain magnetic minerals, such as titano-magnetite and pyrrhotite. Significantly, titano-magnetite inclusions display fine exsolution lamellae indicating single- or pseudo-single-domain size. In this presentation, we will discuss on the results of rock-magnetic measurements and magnetic mineral inclusions in zircons.