Formation of lower fast-spread oceanic crust: a structural and geochemical study of troctolites in the Hess Deep Rift (East Pacific Rise)

Akizawa, Norikatsu; Godard, Marguerite; Ildefonse, Benoît; Arai, Shoji

doi:10.1186/s40645-023-00560-4

Progress in Earth and Planetary Science

Table 1 Details of troctolite samples from Hess Deep

From: Formation of lower fast-spread oceanic crust: a structural and geochemical study of troctolites in the Hess Deep Rift (East Pacific Rise)

Petrography	Hole	Core section	TI (cm)	Rock type	Note	MGS (mm)			Parameters and aquired values by EBSD analysis												T_REE (°C)		T_BKN (°C)
Sample name						Ol	Pl	SS (µm)	Ol			Pl			Area fraction (%)							1σ
Sample name						Ol	Pl	SS (µm)	N	J	M	N	J	M	NIA	Ol	Pl	Cpx	Opx	IA total		1σ
FGT1	U1415I	4R2	9	FGT	Cpx oikocryst-bearing	2	2	25	34,750	3.26	0.02	3E + 05	1.76	0.03	14.8	6.0	45.6	33.6	0.02	85.2			968
FGT2	U1415J	5R1	111	FGT	Cpx oikocryst-bearing	2	2	30	21,426	12.6	0.11	3E + 05	2.96	0.05	12.0	4.5	64.7	18.6	0.14	88.0	1182	33	939
FGT3	U1415J	6G1	11	FGT	Cpx oikocryst-bearing	2	2	30	36,392	3.39	0.05	2E + 05	2.47	0.05	23.1	8.2	50.7	17.9	0.06	76.9	1201	27	965
FGT4	U1415J	7G1	28	FGT	Cpx oikocryst-bearing	2	2	30	5531	5.91	0.05	1E + 05	3.94	0.12	22.6	2.4	58.2	14.8	2.03	77.4	1200	32	976
FGT5	U1415J	8R1	99	FGT	Cpx oikocryst-bearing	2	2	30	38,218	2.97	0.03	3E + 05	2.58	0.07	12.8	7.2	59.1	20.6	0.35	87.2	1245	15	901
FGT6	U1415J	8R2	5	FGT	Cpx oikocryst-bearing	2	2	30	52,992	2.28	0.03	3E + 05	4.46	0.12	19.9	10.5	62.1	7.6	0.02	80.1			1059
FGT7	U1415J	8R2	45	FGT		2	2	25	60,647	2.38	0.04	3E + 05	6.39	0.19	22.8	12.2	64.7	0.4	–	77.2
SOBT1	U1415J	10R1	20	SOBT		8	2	35	56,313	18.6	0.21	84,155	2.14	0.01	36.0	25.1	37.6	1.3	0.06	64.0
FGT8	U1415J	10R1	45	FGT		2	2	30	87,192	2.18	0.05	3E + 05	2.81	0.10	13.6	18.3	67.3	0.6	0.17	86.4			883
FGT9	U1415J	11R1	29	FGT		2	2	50	28,042	3.33	0.09	1E + 05	2.33	0.07	23.3	16.2	59.2	1.3	–	76.7	1196	45
CGT1	U1415J	13R1	44	CGT		5	4	50	19,237			17,973			73.4	13.7	12.8	–	–	26.6
FGT10	U1415J	15G1	1	FGT	Cpx oikocryst-bearing	2	2	30	47,640	1.90	0.03	3E + 05	2.11	0.04	17.1	9.2	50.4	23.2	0.09	82.9			957
CGT2	U1415J	18R1	77	CGT		5	4	50	5129			1124			94.6	4.2	0.9	0.3	–	5.4
CGT3	U1415J	18R1	146	CGT		7	4	50	8678			16,232			85.4	5.1	9.5	0.0	–	14.6
CGT4	U1415J	19R1	15	CGT		4	3
CGT5	U1415P	16R1	21	CGT		4	3	50	26,390			44,581			62.6	13.9	23.5	0.1	–	37.4
CGT6	U1415P	16R1	41	CGT		7	6	50	38,691			60,540			41.1	22.6	35.4	0.9	–	58.9
CGT7	U1415P	18R1	57	CGT		7	5	50	6491			18,869			69.1	7.8	22.8	0.3	–	30.9
CGT8	U1415P	18R1	98	CGT		5	4
CGT9	U1415P	21G1	4	CGT	Cpx-rich	10	5	50	28,547			20,965			58.3	16.5	12.1	13.0	–	41.7
CGT10	U1415P	22R1	7	CGT		6	4	50	3199			49,116			51.8	2.9	45.1	0.2	–	48.2
CGT11	U1415P	22R1	13	CGT		10	5	50	11,745			30,650			68.6	8.5	22.2	0.7	–	31.4
CGT12	U1415P	22R1	108	CGT		4	4
CGT13	U1415P	23R1	118	CGT		7	5	50	10,811			26,755			74.4	7.1	16.9	1.6	–	25.6
CGT14	U1415P	23R2	41	CGT		8	4	50	17,165			46,402			53.6	12.3	33.2	1.0	–	46.4

Three coarse-grained troctolites, CGT4, CGT8, and CGT12 are not suitable for fabric analysis by EBSD because of their severe alteration, but we could analyze their primary chemical compostions of minerals. N represents number of grains detected by EBSD analysis. Refer to text for further explanations of J-index (J) and M-index (M). REE-in-plagioclase-clinopyroxene thermometer formulated by Sun and Liang (2017) and two pyroxene thermometer formulated by Brey and Köhler (1990) were applied for temperatrue estimates as T_REE and T_BKN, respectively
CGT Coarse-grained troctolite, Cpx Clinopyroxene, FGT Fine-grained troctolite, IA Indexed area, MGS Maximum grain size, NIA Not indexed area, Ol Olivine, Opx Orthopyroxene, Pl Plagioclase, SOBT Skeletal ol-bearing troctolite, SS Step size of EBSD analysis, TI Top interval. -: Not detected

Back to article page