Characterization of olivine fabrics and mylonite in the presence of fluid and implications for seismic anisotropy and shear localization

Earth, Planets and Space

Table 1 Sample description and results

Sample		372	373	374	379			380			381
Sample		372	373	374	L	M	S	L	M	S	381
Modal composition (%)^a	ol	10	33	18	61	97	64	35	57	50	30
	opx	76	14	33	3	3	3	7	4	5	6
	cpx	13	50	45	35	0	33	55	39	45	61
	sp	1	3	4	1	0	0	3	0	0	3
LPO of olivine^b		E	A + B	B	A + B	(100) [010]	B	A + B	E	-	A + B
M-index^c		0.27	0.08	0.17	0.1	0.06	0.04	0.06	0.04	0.04	0.1
Water content 3,620 to 3,500 cm^-1d (ppm H/Si)		240	230	240	90	280	-	90	210	-	110
Water content 3,750 to 3,400 cm^-1e (ppm H/Si)		400	430	370	110	600	-	320	400	-	320
Average grain size^f (μm)		2,090	1,470	1,620	1,270	53	9	1,670	50	10	1,240
Max. Vp anisotropy (%)		3.2	4.7	4.2	6.8	7.5	2.2	3.4	2.9	1.4	3.5
Max. Vs anisotropy (%)		2.37	2.94	2.43	3.77	5.20	1.33	1.94	1.86	0.92	3.19
Vp/Vs ratio		1.7	1.74	1.72	1.77	1.75	1.73	1.71	1.73	1.73	1.73

Ol, olivine; sp, spinel. L, M, and S represent large-grained (wall rock), medium-grained, and small-grained areas, respectively. Medium- and small-grained areas belong to the mylonite zone. ^aGarnet grains were found as an accessory mineral in the small-grained area. ^bThe LPO of olivine classified in a previous experimental study (Jung et al. 2006). ^cThe M-index represents the fabric strength of olivine (Skemer et al. 2005). ^d,eThe water content of olivine was calculated using Paterson's calibration (Paterson 1982), using the IR bands between 3,620 to 3,500 cm^-1 (d) and 3,750 to 3,400 cm^-1 (e). Each result for water content is an average of 10 grains and excludes cracks and inclusions and uncertainty of water content is ±50 ppm H/Si. ^fGrain sizes for both the medium- and small-grained areas were determined by the linear intercept method (Gifkins 1970).