[S-IT18] GEOPHYSICAL PROPERTIES AND TRANSPORT PROCESSES IN THE DEEP CRUST AND MANTLE

[SIT18-05] Elastic wave velocity of thermally treated diabase and peridotite and their implications on elastic properties of oceanic lithosphere

*Eranga Gayanath Jayawickrama¹、Yasushi Izuka¹、Ikuo Katayama¹ (1.Department of Earth and Planetary Systems Science Hiroshima University)

キーワード：Thermal cracks, Crack properties, Strength weakening

It is long known that plate tectonics has played a crucial role in the evolution of life on earth and nourishing it. Hence different from other planets such as Mars and Venus where no life exists. This ultimately poses the question of “how was plate tectonics initiated on earth?”. To initiate plate tectonics, flexural bending of the plate is an essential factor that requires a very large lateral stress or significant weakening in the rigidity and other elastic properties of the plate. We hypothesize that thermal cracks formed in the lithosphere of early earth facilitate such weakening of elastic properties assisting breaking and bending of plates. To test our hypothesis, we performed a series of experiments in the laboratory on intact and thermally treated diabase and peridotite (400^oC – 800^oC). The experiments were performed under increasing confining pressures (3-200 MPa) at room temperature. Simultaneous porosity and elastic wave velocity (P and S) measurements were obtained at fully N₂ (dry) and water (wet) saturated conditions. The velocity and porosity inversions indicate a significant variation in crack properties (crack density, aspect ratio) and reduction in the bulk modulus, Young's modulus, and shear modulus of thermally treated samples in comparison to intact samples. Our results thus indicate significant strength weakening of the oceanic lithosphere due to the effect of thermal cracks.