Inverse thermoremanent magnetization

摘要: [1] Inverse thermoremanent magnetization (ITRM) is reversed to the (TRM) process: ITRM results from warming low temperature T in a magnetic field, while TRM field cooling high T. The development of was studied magnetites grain sizes submicron 135 μm, pyrrhotites and hematite crystals. All three minerals acquired after through their transitions (35 K for pyrrhotite, 120 130 magnetite, 250 hematite). However, when an impacting meteorite's cold interior warms ambient geomagnetic magnetite most likely candidate acquiring ITRM. blocking distribution determined 12 neighboring partial ITRMs nested field-on plus field-off cycles (300–20 K). largest are produced intervals around magnetite's Verwey transition (TV = 110–120 K) isotropic point (TK Both involve large changes crystalline anisotropy renucleation domains. blocked initially broad domain walls narrow pinned by dislocations. has contrasting properties TRM, which mainly due single-domain moments. strongest 3- 20-μm grains, whereas peaks magnetites. Only 10–20% survives low-temperature demagnetization (LTD) at 77 or AF 10–15 mT, compared 30–90% TRM. decreases quasi-linearly with thermal demagnetization. median unblocking TUB ≈300°C 20–25% 550°C. low-TUB part could mimic extraterrestrial NRM TUB, cited as evidence negligible heating meteorites transfer Earth. high-TUB would contaminate paleointensity determinations up highest steps. best cure contamination LTD pretreatment.