A possible mechanism for spontaneous cyclic back-arc spreading

Progress in Earth and Planetary Science

Table 2 Rheological parameters of rocks

	Viscous flow			Frictional stress^*1
		Activation energy	Activation volume	Cohesion	Effective frictional coefficient
	A_N	E_N	V_N	c	ϕ
	/s/MPa	kJ/mol	cm³/mol	MPa
Continental upper crust	10^–11	54^*2	0	30 (1)	0.4 (ϕ _AL)
Continental lower crust	10^–7	118^*3	0	30 (1)	0.4 (ϕ _AL)
Oceanic crust	10^–7	118^*3	0	1	0.005
Mantle wedge	2 × 10^–8	150	4	1	ϕ _AL
Upper mantle	5 × 10^–7	215^*4	4	30 (1)	0.4 (ϕ _AL)
Upper mantle for SP^*5	5 × 10^–7	215^*4	4	30 (1)	0.4 (0.1)
Transition zone	5 × 10^–7	215^*4	4	30 (1)	0.6 (0.4)
Lower mantle	6 × 10^–10	200	2.5–1.3^*6	30 (1)	0.6 (0.4)

*1 Values in brackets denote friction coefficient and cohesion in weakened state for strain larger than 0.5 (c_weakened, ϕ _weakened)
*2 Dislocation creep of wet quartz (n = 4, E_dis = 135 kJ/mol, Hirth et al. 2001)
*3 Dislocation creep of wet plagioclase (n = 3, E_dis = 235 kJ/mol, Rybacki and Dresen 2004)
*4 Dislocation creep of wet olivine (n = 3, E_dis = 430 kJ/mol, Karato and Wu 1993)
*5 Upper mantle for subducting plate (purple in Figs. 1b and 2)
*6 Linearly decrease with the depth of 660–2900 km