衝撃圧縮に伴う温度変化の重要性と衝突現象

広島大学大学院理学研究科

地球惑星システム学専攻 関根 利守

[日本における超高速衝突 　　　　　実験の現状と展望] 2011.12.13 惑星科学研究センター HIROSHIMA UNIVERSITY

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

Regolith

Fractured bedrock

High-velocity Impacts

breccias

Difference between volcanic craters and impact craters

•  Mechanism　 - Energy; external （shock waves=SW） or Internal

（explosive eruptions=EE） - Strain rate; 104-106/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　ー　Breccias and regolith on

the surface, Pt group elements, and isotope ratios •  Petrological, Mineralogical　ー　Shutter cones, Planar and

planar deformation feature(PDF), HP minerals, and HP glasses

•  No Morphological difference

S1�

S2�

S3�

S4�

S5�

S6�

Shock Melting�

Shock Vaporization �

Shock stage

75-90

45-60

20-30

10-15

5-10

4-5 Planar fractures

Undulatory extinction �(Cpx lamera)

Ir-cracks

Mosaicism R-cracks

Rep. minerals Whole rock Shock Pressure (GPa)

Melt pockets

Dark shock veins

Whole rock melting

Maskelynite

Recrystallization HP phase

Melt HP phase

Melt HP phase

Ol Opx Pl

HP phase β

Current status for shock metamorphism

？15~25 GPa based on the phase equilibrium

Feldspar Hugoniots

Compiled by Sekine and Ahrens (1991)

NaCaK Hollandite LPP

HPP

maskelynite

Release paths from Hugoniot states

Oligoclase Ab75An19Or5 Ahrens et al.1969

Orthoclase Ab25Or75 Grady & Murri (1976)

HEL HEL

HP feldspar (hollandite) is unquenchable! Why does Hol exist in some meteorites?

The system KAlSi3O8-NaAlSi3O8 at HPHT Static pressure data by Liu (2006)

Cf. DAC Exp. Liu (1978) and Tutti (2007)

Limit

No Ab-rich Hollandite

Pl-Msk-Hol

1

2 3r

3c

4 5 6

7 4

6 5

7 7 7

W W

W

W 8

飛翔体

金属板

ネジ試料

容器

回収実験�

その場観察実験�

圧縮法の相違点

1. 衝撃圧縮 2. 静的圧縮 （準静的圧縮） 3. 等エントロピー圧縮

衝撃波の立たない動的圧縮

ー圧力発生原理と熱力学的相違ー

Volume

Pre

ssur

e

V0 V

PH

PS

P

Shock temperature calculation

Hugoniot

Isentrope

V0 V1

PH PS

€

TS = Ti exp ( γV)dV

Va

Vb

∫

TS : temperature along the isentropeTi : initial temperatureTH : shock temperature

Vγ(PH − PS ) = CV

TS

TH

∫ dT

PH2(V0 −V1) = − PdV +

V1γV0

V1

∫ (PH − PS ) + ETR

P = d0UpUs = d0Up(C0+SUp)

Impedance match diagram

Pres

sure

Particle velocity

Sample

ContainerFlyer

Reflection

P1

P0

Vimp

P2

Us Us

Ur

P0

P1 P2

Shock pressure, internal energy, and residual temperature

Multiple shock process

Single shock process

(Porous samples)

P, T

PH

TH

Ris

ing

Rel

ease

TR

(a) Ideal solid

Thermal conduction

P, T

PH

TH

Ris

ing

Rel

ease

TR

(b) Porous body

Thermal conduction

Surface of grain

Center of grain Average

PT profiles during impact process

Shear Band A region where plastic deformation in a material is highly concentrated

•  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

Fracture surface of a metallic glass along shear band (Chou & Spaepen, 1975)

Shear bands

Shear band formation mechanism

τ

γ<γc

τ

γ>γc

γ

τ

γc

γ γc

initial

Temperature increase by shear bands Stress τ, strain γ, work W

Density ρ, heat capacity Cv Efficiency of conversion of work β

Wright & Walter

γ (or time)

τ Temp

dγ/dt Perturbed

γ at

seve

re lo

catio

n

dγ/dt

101 102 103 104 105 /s

s t a b l

e

€

dW = τdγ

dT =βρCv

dW =βρCv

τdγ

T =βρCv

τdγ0

γ

∫

Local heating at a shear band, calculated by heat diffusion equation

ns

Heat content Heat content

N2 reduction to NH3 by impacts

Fe 

N2

Ocean

N2 + H2 Hot

NH3

Fe + H2O = FeO + H2 

2 mm

30 mm

Sample Fe, Ni,  H2O, N2 (NH3) , 13C（Solid）

30 mm

Pb gasket

Propellant gun

Shock P; 6 GPa, duraBon; 0.7 μs、T; 5,000～3,000 K 

projecBle Container

Sample

Experimental method

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 + H2O

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