Journal of Geological Research

Research Article

Geochemistry of the Neoarchaean Volcanic Rocks of the Kilimafedha Greenstone Belt, Northeastern Tanzania

Table 1

Major (wt%) and trace (ppm) element composition for the Kilimafedha greenstone belt volcanic rocks.


		Tholeiitic basalts							Transitional intermediate volcanic rocks
	MU 14	MU 15	MU 19	MU 20	MU 43	MU 69	MU 109	MU 12	MU 13	MU 21	MU 27	MU 33	MU 35	MU 36	MU 37	MU 38	MU 39	MU 49	MU 54	MU 57	MU 60	MU 64	MU 65	MU 66	MU 68

SiO₂	50.3	47.4	50.4	50.3	47.8	48.2	49.2	55.2	52.9	52.8	65.3	60.6	53.7	55.1	54.3	54.1	53.5	53.7	53.5	54.1	54.9	56.0	54.9	55.3	62.4
TiO₂	1.36	0.92	0.60	0.66	1.73	1.75	0.62	1.53	1.44	0.84	0.58	0.67	1.45	1.46	1.36	1.54	1.60	1.46	1.26	1.35	1.38	0.91	1.24	1.41	0.84
Al₂O₃	14.7	16.0	14.4	13.5	14.6	14.1	17.3	13.1	15.1	15.0	15.5	16.5	14.0	13.4	14.1	14.3	14.9	14.2	13.7	13.2	13.5	14.7	14.3	13.6	14.2
Fe₂O₃	12.3	12.4	11.9	12.9	13.3	13.5	6.2	9.3	10.8	11.2	4.2	6.7	11.3	12.0	11.2	11.9	12.1	12.1	11.8	11.3	11.7	9.1	10.8	12.0	6.6
MnO	0.27	0.17	0.17	0.18	0.19	0.18	0.08	0.25	0.24	0.16	0.06	0.10	0.11	0.14	0.11	0.14	0.14	0.15	0.12	0.12	0.12	0.19	0.13	0.13	0.09
MgO	5.45	8.09	7.53	7.32	6.62	6.76	8.30	6.00	4.66	5.58	2.68	3.57	3.42	3.71	3.43	3.46	3.62	3.85	4.24	3.53	3.77	5.27	3.80	3.50	2.60
CaO	10.9	10.9	10.7	10.7	10.3	10.5	12.3	7.54	10.94	8.54	3.65	2.73	9.62	6.25	9.49	6.41	5.30	5.69	8.30	6.40	6.94	6.28	7.16	7.43	4.53
Na₂O	2.29	1.84	1.92	1.79	1.96	1.91	2.99	5.14	2.49	1.74	4.91	6.15	3.12	4.96	2.70	4.02	5.00	5.34	2.67	4.69	3.10	3.85	3.01	3.94	4.20
K₂O	0.52	0.17	0.15	0.11	0.03	0.10	0.81	0.79	0.27	1.45	0.83	0.31	1.44	1.09	1.43	1.88	1.77	1.34	2.09	1.44	2.75	0.37	2.20	0.73	1.50
P₂O₅	0.04	0.01	0.01	0.01	0.19	0.09	0.01	0.07	0.06	0.01	0.06	0.08	0.12	0.12	0.12	0.15	0.15	0.13	0.12	0.13	0.03	0.01	0.11	0.13	0.16
LOI	1.46	2.14	2.17	2.45	3.19	2.55	2.15	0.92	1.03	2.29	2.19	2.53	1.39	1.34	1.72	1.81	1.83	1.75	1.97	3.30	1.66	2.93	2.00	1.69	2.80
Total	99.5	100	99.9	100	99.9	99.8	99.9	99.9	99.9	99.6	100	100	99.7	99.6	99.9	99.7	99.9	99.6	99.8	99.5	99.8	99.7	99.6	99.8	100
Mg^#	46.8	56.5	55.6	52.8	49.6	49.7	72.7	56.1	46.1	49.8	56.0	51.2	37.4	38.0	37.7	36.5	37.3	38.7	41.5	38.2	39.1	53.3	41.0	36.7	43.9

Ba	204	27	66			140					1230			418				329		97	763				755
Rb	26	9	5			5					16			35				40		2	97				18
Sr	147	106	101			214					428			236				239		293	320				423
Ni	100	190	90			120					30			80				90		60	90				30
Cr	160	200	240			170					30			40				70		40	90				20
V	342	228	232			249					76			171				154		162	153				108
Th	0.5	0.3	0.2			1					3.9			8				8.7		7	8.9				5.8
Pb	5	5	5			5					7			5				9		42	6				10
U	0.2	0.1	0.1			0.4					1.3			2.1				2.9		1.9	2.5				1.4
Nb	3	2	1			4					4			8				8		7	8				7
Ta	0.3	0.2	0.1			0.3					0.4			0.6				0.8		0.6	0.7				0.5
Zr	80	53	31			88					126			163				177		147	184				176
Hf	2.2	1.4	1			2.4					3.2			4.3				4.9		3.9	4.7				4.6
Y	29	20	16			23					15			23				24		21	24				24

La	4.60	3.00	1.70			9.20					22.1			26.2				28.1		23.8	28.2				33.7
Ce	12.4	8.2	4.6			21.6					42.2			53.5				60		49.4	59.9				69.3
Pr	1.96	1.27	0.75			3.05					4.99			6.46				7.74		6.21	7.49				9
Nd	6.58	6.70	4.10			17.82					17.9			24.4				28.1		22.9	28.5				31.6
Sm	1.63	2.1	1.3			6.1					3.5			5.7				6.4		5.4	6.2				6.5
Eu	1.11	0.84	0.57			1.36					1.06			1.37				1.66		1.68	1.65				1.62
Gd	4.3	3.0	2.0			4.1					3.3			5.7				5.8		4.8	6.1				5.3
Tb	0.8	0.5	0.4			0.7					0.5			0.8				0.9		0.8	0.9				0.8
Dy	5.0	3.4	2.5			4.0					2.6			4.7				4.7		4.0	4.8				4.2
Ho	1.1	0.7	0.6			0.8					0.5			0.9				0.9		0.8	0.9				0.8
Er	3.3	2.1	1.7			2.4					1.5			2.4				2.5		2.1	2.5				2.5
Tm	0.48	0.32	0.26			0.36					0.22			0.34				0.35		0.29	0.34				0.37
Yb	3.10	2.10	1.70			2.30					1.40			2.10				2.20		1.80	2.10				2.30
Lu	0.46	0.31	0.26			0.35					0.22			0.31				0.31		0.26	0.3				0.34

La/Yb	1.5	1.4	1.0			4.0					15.8			12.5				12.8		13.2	13.4				14.7
La/Nb	1.53	1.5	1.7			2.3					5.53			3.28				3.51		3.40	3.53				4.81
Eu/Eu*	0.90	1.02	1.08			1.10					0.95			0.74				0.83		1.01	0.82				0.84
La/Sm_CN	0.90	0.92	0.84			1.70					4.08			2.97				2.83		2.85	2.94				3.35
La/Yb_CN	1.06	1.02	0.72			2.87					11.3			8.95				9.16		9.48	9.63				10.5
Nb/La_pm	0.63	0.64	0.57			0.42					0.17			0.29				0.27		0.28	0.27				0.20

	Transitional intermediate volcanic rocks																						Rhyolites
	MU 76	MU 77	MU 78	MU 79	MU 80	MU 81	MU 82	MU 83	MU 84	MU 85	MU 86	MU 87	MU 89	MU 90	MU 91	MU 92	MU 93	MU 94	MU 95	MU 96	MU 97	MU 100	MU 16	MU 17	MU 18

SiO₂	51.9	51.9	53.2	52.4	53.1	53.3	54.3	53.5	52.2	54.3	55.1	54.3	55.6	55.8	52.8	51.3	52.6	54.9	54.2	53.7	55.4	52.3	74.9	75.5	75.3
TiO₂	1.42	1.38	1.34	1.37	1.49	1.49	0.70	1.51	1.62	1.25	1.35	1.41	1.41	1.43	1.52	0.84	1.20	1.37	1.41	1.09	1.07	1.42	0.03	0.03	0.03
Al₂O₃	14.7	14.2	14.1	14.4	14.2	13.9	15.1	14.0	14.7	13.5	14.4	13.8	13.6	13.4	14.4	14.1	14.2	14.6	14.2	15.1	14.2	15.6	14.28	14.38	14.46
Fe₂O₃	12.4	12.6	12.2	12.4	12.5	12.6	8.2	12.4	13.0	11.3	11.3	12.2	11.8	11.4	13.5	11.6	12.5	11.4	11.6	12.5	11.3	12.9	0.34	0.28	0.34
MnO	0.14	0.14	0.14	0.14	0.14	0.14	0.13	0.14	0.14	0.13	0.14	0.13	0.13	0.12	0.16	0.15	0.19	0.13	0.14	0.15	0.17	0.15	0.02	0.01	0.01
MgO	4.40	4.20	4.04	4.10	3.88	3.92	6.47	3.86	3.89	4.44	3.60	3.68	3.72	3.55	3.82	7.08	4.89	3.66	4.10	4.56	4.26	3.64	0.23	0.22	0.25
CaO	7.36	7.97	8.36	8.38	6.74	7.00	8.87	6.82	6.01	7.40	6.36	7.03	6.39	7.13	6.32	9.37	5.66	5.84	5.56	5.28	5.40	5.97	0.26	0.10	0.15
Na₂O	3.66	2.83	2.88	2.87	4.32	3.92	3.14	4.20	4.63	2.91	5.57	3.79	3.73	3.62	4.63	2.41	4.53	4.55	4.00	4.91	5.04	4.75	5.14	5.17	5.32
K₂O	1.25	1.91	1.48	1.67	1.60	1.52	0.57	1.57	1.79	2.89	1.27	1.47	1.91	0.15	0.95	0.88	2.06	1.66	2.57	1.77	1.62	1.16	3.98	3.61	3.41
P₂O₅	0.11	0.02	0.11	0.11	0.12	0.13	0.11	0.13	0.14	0.11	0.12	0.13	0.14	0.13	0.13	0.03	0.09	0.10	0.13	0.10	0.09	0.12	0.01	0.01	0.01
LOI	2.48	2.35	1.78	1.79	1.59	1.57	2.46	1.52	1.49	1.70	1.40	1.97	1.65	2.94	1.70	2.27	1.87	1.40	1.63	0.94	1.50	1.99	0.75	0.69	0.69
Total	99.8	99.5	99.6	99.7	99.7	99.6	100	99.6	99.6	99.9	101	99.9	100	99.6	100	100	99.8	99.6	99.5	100	100	100	100	100	100
Mg^#	41.3	39.7	39.6	39.5	38.1	38.1	60.9	38.2	37.2	43.9	38.8	37.4	38.4	38.3	35.9	54.8	43.6	38.9	41.2	42.0	42.8	35.8	57.3	60.9	59.3

Ba				504								415	643					626				485	301	220	217
Rb				56								48	61					54				40	91	83	77
Sr				349								398	395					296				312	37	32	31
Ni				160								90	80					80				43	20	20	20
Cr				40								70	70					30				40	20	20	20
V				180								155	149					163				175	5	5	5
Th				7.8								8.9	8.8					7.2				7.5	3.1	2.9	2.7
Pb				5								14	18					5				5	9	5	5
U				2.2								2.5	3.1					2				2.2	2.5	2.1	2
Nb				7								9	8					6				7	5	5	4
Ta				0.6								0.7	0.8					0.6				0.6	0.6	0.6	0.6
Zr				158								179	173					137				155	34	36	33
Hf				4.3								4.6	4.9					3.7				4.1	1.9	2	1.9
Y				25								24	24					23				25	12	9	10

La				23.6								27.4	28.0					22.8				20.1	6.60	3.90	3.70
Ce				50.7								58.3	59.5					47.4				46.6	13.2	9.3	12.3
Pr				6.35								7.2	7.68					5.82				6.24	1.90	1.31	1.12
Nd				24.4								27.3	27.9					22.7				23.6	7.80	5.40	4.60
Sm				5.8								6.2	6.6					5.2				5.7	2.1	1.4	1.4
Eu				1.78								1.6	1.81					1.63				1.62	0.12	0.09	0.1
Gd				6.0								6.2	5.7					5.3				5.5	2.1	1.4	1.5
Tb				0.9								0.9	0.9					0.8				0.9	0.4	0.3	0.3
Dy				4.9								4.7	4.7					4.4				4.7	2.0	1.5	1.5
Ho				0.9								0.9	0.9					0.8				0.9	0.4	0.3	0.3
Er				2.6								2.4	2.5					2.3				2.6	1	0.8	0.9
Tm				0.36								0.34	0.36					0.32				0.36	0.15	0.13	0.14
Yb				2.20								2.00	2.20					2.00				2.20	0.90	0.80	0.90
Lu				0.32								0.3	0.31					0.3				0.33	0.13	0.12	0.12

La/Yb				10.7								13.7	12.7					11.4				9.1	7.3	4.9	4.1
La/Nb				3.37								3.04	3.50					3.80				2.87	1.32	0.78	0.925
Eu/Eu*				0.92								0.79	0.90					0.95				0.89	0.17	0.20	0.21
La/Sm_CN				2.63								2.85	2.74					2.83				2.28	2.03	1.80	1.71
La/Yb_CN				7.69								9.83	9.13					8.18				6.55	5.26	3.50	2.95
Nb/La_pm				0.29								0.32	0.28					0.25				0.34	0.73	1.24	1.04

Mg^# (Magnesium number) = 100 /( + ) as in Section 4.3.1, and Eu/Eu* = Eu/((SmN GdN)^1/2).