Modelling the internal structure of Ceres: Coupling of accretion with compaction by creep and implications for the water-rock differentiation

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Table 1

Composition, mass, and volume fractions of the constituents, and further key parameters for modelling Ceres’ compaction.


Model	Mineral	Mass fraction	Vol. fraction	Intrinsic density	Act. energy	Por. interval
−	−	x_j	v_j	ρ_i	E_j
−	−	[%]	[%]			[%]



CIa	Serpentine	49.20	46.98	2576	88^a	48−30
high-	Pyrene	3.10	6.00	1270	88^b	48−30
density	Montmorillonite	17.00	17.60	2320	105⁽³⁾^c	30−18
model	Halite	4.20	4.99	2070	105⁽⁴⁾	30−18
from (1)	Mirabilite	4.50	7.05	1570	128⁽⁵⁾	18−13
and (2)	Magnetite	15.00	7.13	5175	188⁽⁶⁾	13−8
	Epsomite	7.00	10.25	1680	270⁽⁵⁾	8−0


Average	−	100.00	100.00	2460	−	−


CIb	Pyrene	6.20	10.94	1270	88^b	48−33
low-	Saponite	36.30	35.05	2320	105^d	48−33
density	Mirabilite	7.90	11.27	1570	128⁽⁵⁾	33−28
model	Gypsum	5.90	5.60	2360	145⁽⁷⁾^e	28−25
from (1)	Hematite	23.20	9.81	5300	251⁽⁸⁾	25−20
and (2)	Epsomite	20.50	27.33	1680	270⁽⁵⁾	20−0


Average	−	100.00	100.00	2240	−	−

Notes. These mineralogical compositions have been proposed by Zolotov (2009) assuming accretion of Ceres from small aqueously altered planetesimals (with a nearly CI chondritic initial composition) that contain hydrated minerals. The relative abundances of species differ slightly from those shown in Zolotov (2009) and Castillo-Rogez (2011), since the latter were completed to obtain a mass/volume fraction of 100%.

^(a)

Based on the deformation experiments on serpentine at pressures above 1 GPa and temperatures of 470−770 K, the creep activation energy is expected to be <20 kJ mol^-1 (Hilairet et al. 2007). We use an upper bound of 88 kJ mol^-1, since the internal pressure of Ceres is approximately below 0.2 GPa and since the strength of serpentine is a matter of debate.

^(b)

A lower value of 84 kJ mol^-1 has been reported by Ripple & Day (1966).

^(c)

This is an upper bound of E because we lack reliable data. We note, however, that activation values of 10−50 kJ mol^-1 have been reported by McLaughlin & Ubbelohde (1956) and Martinho et al. (2001).

^(d)

Because we lack data and since saponite and montmorillonite are both members of the smectite group, the same activation energy is used.

^(e)

Here, diffusion creep activation energy of anhydrite is used. A lower activation energy of 130 kJ mol^-1 has been reported by Baumann (1984) for the dislocation creep of gypsum.

Reference. (1) Zolotov (2009); (2) Castillo-Rogez (2011); (3) Pusch & Yong (2005); (4) Durham et al. (2005); (5) Heard (1972); (6) Till & Moskowitz (2013); (7) Dell’Angelo & Olgaard (1995); (8) Siemes et al. (2011).

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