HIROSHIMA UNIVERSITY [ ] 2011.12.13
Objectives of this study Impact phenomena; Planetary formation and evolution, origin of meteorites, and origin of life How we reveal the shock strength in impacts from shocked meteorites and impactites Currently we have no full knowledge for that We need to understand impact phenomena comprehensively, but not individual changes in them It is important to understand totally physical changes during impact to improve the basic knowledge including temperature
High-velocity Impacts breccias Regolith Fractured bedrock
Difference between volcanic craters and impact craters Mechanism - Energy; external shock waves=sw or Internal explosive eruptions=ee - Strain rate; 10 4-10 6 /s (SW) or 10-3 -10-6 /s(ee) - Stress level; ~5 GPa-100 GPa (SW) or < 2 GPa(EE) - Deformation; uniaxis or not Geophysical - Negative anomaly and - Positive anomaly Geological, Geochemical Breccias and regolith on the surface, Pt group elements, and isotope ratios Petrological, Mineralogical Shutter cones, Planar and planar deformation feature(pdf), HP minerals, and HP glasses No Morphological difference
Current status for shock metamorphism Shock stage Rep. minerals Whole rock Shock Pressure (GPa) Ol Opx Pl Ir-cracks Planar fractures Undulatory extinction Mosaicism R-cracks HP phase β Recrystallization Melt HP phase HP phase Maskelynite Melt HP phase Dark shock veins Melt pockets Whole rock melting 4-5 5-10 10-15 20-30 45-60 15~25 GPa based on the 75-90 phase equilibrium
Feldspar Hugoniots Compiled by Sekine and Ahrens (1991) HPP LPP maskelynite NaCaK Hollandite
Release paths from Hugoniot states Orthoclase Ab 25 Or 75 Grady & Murri (1976) Oligoclase Ab 75 An 19 Or 5 Ahrens et al.1969 HEL HEL HP feldspar (hollandite) is unquenchable! Why does Hol exist in some meteorites?
The system KAlSi 3 O 8 -NaAlSi 3 O 8 at HPHT Static pressure data by Liu (2006) Cf. DAC Exp. Liu (1978) and Tutti (2007) No Ab-rich Hollandite Limit
Pl-Msk-Hol 1 3c 2 3r 77 74 7 6 5 6 5 4 W W W W 8
1. 2. 3. Pressure PH PS P V Volume V 0
Shock temperature calculation T S = T i exp V b V a ( γ V )dv T S : temperature along the isentrope T i : initial temperature T H : shock temperature V γ (P H P S ) = P H T H T S C V V 1 dt 2 (V 0 V 1 ) = PdV + V 1(P H P S ) + E TR γ V 0 P H P S Isentrope Hugoniot V 1 V 0
Impedance match diagram P = d 0 UpUs = d 0 Up(C 0 +SUp) Flyer Container P 0 Sample Ur Pressure P 2 P 1 Us Us Reflection P 0 V imp P 1 P 2 Particle velocity
Shock pressure, internal energy, and residual temperature Multiple shock process (Porous samples) Single shock process
Release Release PT profiles during impact process (a) Ideal solid (b) Porous body P H Surface of grain P, T P, T T H Average Center of grain T H T R P H Thermal conduction T R Thermal conduction Rising Rising
Shear Band A region where plastic deformation in a material is highly concentrated Fracture surface of a metallic glass along shear band (Chou & Spaepen, 1975) Ductile materials ( metals, alloys, plastic, polymers, granular materials, and soils) Quasi-brittle materials (concrete, rock, ice, and some ceramics) not observed in brittle materials such as glass at room temperature
Shear bands
Shear band formation mechanism τ τ γ initial γ<γ γ τ γ>γ γ γ
Temperature increase by shear bands dw = τdγ dt = T = β ρc v dw = β ρc v γ 0 τdγ β ρc v τdγ Stress τ, strain γ, work W Density ρ, heat capacity Cv Efficiency of conversion of work β Perturbed dγ/dt Wright & Walter τ Temp γ at severe location s t a b l e 10 1 10 2 10 3 10 4 10 5 /s γ (or time) dγ/dt
Local heating at a shear band, calculated by heat diffusion equation Heat content Heat content ns
N 2 reduction to NH 3 by impacts N 2 N 2 + H 2 Hot Fe NH 3 Ocean Fe + H 2 O = FeO + H 2
Propellant gun Experimental method projecble Container 2 mm 30 mm 30 mm Sample Fe, Ni, H 2 O, N 2 (NH 3 ), 13 C Solid Shock P; 6 GPa, durabon; 0.7 μs T; 5,000 3,000 K Sample Pb gasket
Containers to recover aqueous solutions 0.68 km/s 0.80 km/s 0.82 km/s 0.90 km/s 1.01 km/s 1.04 km/s
Shock process in Ol + H 2 O SUS304 Olivine Aqueous sol Air
Summary HV impacts generate shock wave and rarefaction wave in materials at high strain rates They affect the state with a time lag, and interact each other to change local conditions of P and T The initial physical state of target is important, but in most case remains unknown Crystal sliding systems and pore distribution in the initial state generate higher T locally Adiabatic shear bands may play a key role to form shock veins where the T is locally higher than that of the host rock