Geochemical Characteristics and Tectonic Setting of Meta-mafic Volcanic Rocks from Jixian Group in Liujiaping,Wenxian County, Gansu Province

doi:10.19657/j.geoscience.1000-8527.2018.06.13

Abstract

Abstract:

Detailed field geological survey suggested that the Jixian Group volcanic rocks in Liujiaping are mainly meta-basalts. Geochemical analysis showed that the rocks are aluminum unsaturated (average A/CNK=0.59%) and sodic (Na₂O/K₂O=47.00-144.00). In the TAS diagram, the basalts are sub-alkaline. In the AFM diagram, the samples fall into the tholeiitic basalt field. The total REE contents (∑REE) vary in the range of 58.22×10^-6-95.59×10^-6(average 67.81×10^-6 ). The rocks show anomalies of Eu (δEu=0.83-1.17) and Ce (δCe=0.88-0.95), with flat chondrite-normalized REE distribution pattern. The trace element geochemistry is characterized by distinct depletions of Zr, P, Y and Yb, and relative enrichments of Th, Hf and Nb. There is also strong depletion in K and relative enrichments in Rb and Ba. The values of Zr/Y are 2.38-3.91; Ti/Zr are 92.30-147.23; and Th/Ta are 1.77-2.21, more than 1.60. The meta-basalt yielded a whole-rock Sm-Nd isochron age of (1,387±32) Ma. Based on geochemical tectonic discrimination and regional geological background, it is considered that the Jixian Group meta-basalts in Liujiaping were formed in an island arc setting, which is important to the tectonic evolution study of the Bikou terrane.

Key words: Jixian Group, meta-basalt, Sm-Nd age, geochemical characteristic, tectonic setting

CLC Number:

MAO Yanli, WANG Tao, LI Hongrui, PAN Zhongkui. Geochemical Characteristics and Tectonic Setting of Meta-mafic Volcanic Rocks from Jixian Group in Liujiaping,Wenxian County, Gansu Province[J]. Geoscience, 2018, 32(06): 1254-1262.

Figures/Tables 12

References 39

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样品编号	SiO₂	TiO₂	Al₂O₃	Fe₂O₃	FeO	MnO	MgO	CaO
PM26-23	50.02	1.60	14.70	2.19	8.58	0.20	7.58	10.59
PM26-35	48.78	0.96	14.12	2.75	8.53	0.17	7.73	12.44
PM26-58	48.53	1.13	13.54	2.19	9.83	0.20	7.91	11.72
PM26-76	46.93	1.05	13.12	2.39	10.28	0.22	8.11	10.42
PM26-82	49.13	1.09	13.48	5.00	7.93	0.18	5.62	12.75
PM26-110	48.16	1.11	14.27	3.48	9.77	0.19	6.42	11.60
样品编号	Na₂O	K₂O	P₂O₅	烧失量	总量	A/CNK	FeO^T	Mg^#
PM26-23	2.22	0.02	0.18	3.04	100.92	0.64	10.55	56.15
PM26-35	1.44	0.01	0.09	2.38	99.39	0.56	11.00	55.60
PM26-58	1.45	0.03	0.09	2.69	99.31	0.57	11.80	54.44
PM26-76	1.57	0.02	0.08	5.57	99.75	0.61	12.43	53.77
PM26-82	0.47	0.01	0.08	5.10	100.82	0.56	12.43	44.63
PM26-110	1.69	0.02	0.10	3.60	100.40	0.60	12.90	47.01

样品编号	SiO₂	TiO₂	Al₂O₃	Fe₂O₃	FeO	MnO	MgO	CaO
PM26-23	50.02	1.60	14.70	2.19	8.58	0.20	7.58	10.59
PM26-35	48.78	0.96	14.12	2.75	8.53	0.17	7.73	12.44
PM26-58	48.53	1.13	13.54	2.19	9.83	0.20	7.91	11.72
PM26-76	46.93	1.05	13.12	2.39	10.28	0.22	8.11	10.42
PM26-82	49.13	1.09	13.48	5.00	7.93	0.18	5.62	12.75
PM26-110	48.16	1.11	14.27	3.48	9.77	0.19	6.42	11.60
样品编号	Na₂O	K₂O	P₂O₅	烧失量	总量	A/CNK	FeO^T	Mg^#
PM26-23	2.22	0.02	0.18	3.04	100.92	0.64	10.55	56.15
PM26-35	1.44	0.01	0.09	2.38	99.39	0.56	11.00	55.60
PM26-58	1.45	0.03	0.09	2.69	99.31	0.57	11.80	54.44
PM26-76	1.57	0.02	0.08	5.57	99.75	0.61	12.43	53.77
PM26-82	0.47	0.01	0.08	5.10	100.82	0.56	12.43	44.63
PM26-110	1.69	0.02	0.10	3.60	100.40	0.60	12.90	47.01

样品编号	Sr	Rb	Ba	Th	Ta	Nb	Zr	Hf	Ti	Sc	Cr
PM26-23	86.30	6.00	10.50	8.00	4.00	8.20	108.00	7.50	9 968.00	33.60	254.00
PM26-35	230.00	9.00	22.80	10.10	5.00	14.00	51.00	8.10	6 394.00	35.00	184.00
PM26-58	133.00	16.60	25.10	7.80	4.30	10.10	59.00	2.80	6 498.00	40.40	214.00
PM26-76	125.00	45.90	28.00	9.90	5.30	9.90	48.00	5.60	7 067.00	37.20	131.00
PM26-82	226.00	72.30	8.30	8.40	3.80	8.60	56.10	9.70	7 493.00	31.40	130.00
PM26-110	164.00	77.30	10.50	7.80	4.40	12.00	58.00	8.80	7 329.00	36.60	170.00
样品编号	La	Ce	Pr	Nd	Sm	Eu	Gd	Tb	Dy	Ho	Er
PM26-23	7.20	17.80	2.90	14.80	4.30	1.20	4.59	0.92	5.91	1.15	3.29
PM26-35	3.90	9.60	1.60	8.20	2.60	0.92	2.83	0.62	4.07	0.82	2.39
PM26-58	4.80	11.40	1.90	9.70	2.90	1.08	3.20	0.68	4.37	0.89	2.55
PM26-76	3.60	9.50	1.60	8.30	2.60	1.04	2.88	0.63	4.12	0.85	2.46
PM26-82	3.40	9.40	1.60	8.20	2.50	0.95	2.75	0.61	3.98	0.81	2.31
PM26-110	4.10	10.70	1.70	9.00	2.80	0.94	2.99	0.66	4.31	0.88	2.56
样品编号	Tm	Yb	Lu	Y	∑REE	∑Ce/∑Y	δEu	δCe	(La/Yb)_N	(Ce/Yb)_N
PM26-23	0.49	3.02	0.42	27.60	95.59	2.44	0.83	0.91	1.39	1.33
PM26-35	0.36	2.36	0.34	19.90	60.51	1.94	1.04	0.90	0.96	0.92
PM26-58	0.37	2.28	0.34	20.90	67.36	2.16	1.09	0.88	1.22	1.13
PM26-76	0.36	2.24	0.32	20.20	60.70	1.92	1.17	0.92	0.93	0.96
PM26-82	0.35	2.15	0.31	18.90	58.22	1.96	1.11	0.94	0.92	0.98
PM26-110	0.38	2.41	0.36	20.70	64.49	2.01	1.00	0.95	0.99	1.00

样品编号	Sr	Rb	Ba	Th	Ta	Nb	Zr	Hf	Ti	Sc	Cr
PM26-23	86.30	6.00	10.50	8.00	4.00	8.20	108.00	7.50	9 968.00	33.60	254.00
PM26-35	230.00	9.00	22.80	10.10	5.00	14.00	51.00	8.10	6 394.00	35.00	184.00
PM26-58	133.00	16.60	25.10	7.80	4.30	10.10	59.00	2.80	6 498.00	40.40	214.00
PM26-76	125.00	45.90	28.00	9.90	5.30	9.90	48.00	5.60	7 067.00	37.20	131.00
PM26-82	226.00	72.30	8.30	8.40	3.80	8.60	56.10	9.70	7 493.00	31.40	130.00
PM26-110	164.00	77.30	10.50	7.80	4.40	12.00	58.00	8.80	7 329.00	36.60	170.00
样品编号	La	Ce	Pr	Nd	Sm	Eu	Gd	Tb	Dy	Ho	Er
PM26-23	7.20	17.80	2.90	14.80	4.30	1.20	4.59	0.92	5.91	1.15	3.29
PM26-35	3.90	9.60	1.60	8.20	2.60	0.92	2.83	0.62	4.07	0.82	2.39
PM26-58	4.80	11.40	1.90	9.70	2.90	1.08	3.20	0.68	4.37	0.89	2.55
PM26-76	3.60	9.50	1.60	8.30	2.60	1.04	2.88	0.63	4.12	0.85	2.46
PM26-82	3.40	9.40	1.60	8.20	2.50	0.95	2.75	0.61	3.98	0.81	2.31
PM26-110	4.10	10.70	1.70	9.00	2.80	0.94	2.99	0.66	4.31	0.88	2.56
样品编号	Tm	Yb	Lu	Y	∑REE	∑Ce/∑Y	δEu	δCe	(La/Yb)_N	(Ce/Yb)_N
PM26-23	0.49	3.02	0.42	27.60	95.59	2.44	0.83	0.91	1.39	1.33
PM26-35	0.36	2.36	0.34	19.90	60.51	1.94	1.04	0.90	0.96	0.92
PM26-58	0.37	2.28	0.34	20.90	67.36	2.16	1.09	0.88	1.22	1.13
PM26-76	0.36	2.24	0.32	20.20	60.70	1.92	1.17	0.92	0.93	0.96
PM26-82	0.35	2.15	0.31	18.90	58.22	1.96	1.11	0.94	0.92	0.98
PM26-110	0.38	2.41	0.36	20.70	64.49	2.01	1.00	0.95	0.99	1.00

样号	岩性	w(Sm)/10^-6	w(Nd)/10^-6	¹⁴⁷Sm/¹⁴⁴Nd	¹⁴³Nd/¹⁴⁴Nd±1σ	T_DM±1σ/Ma
1	变玄武岩	8.951	40.170	0.134 8	0.512 317±0.000 004	1 606±8
2	变玄武岩	8.111	37.130	0.132 2	0.512 318±0.000 004	1 554±7
3	变玄武岩	2.343	7.601	0.186 5	0.512 800±0.000 003	1 956±17
4	变玄武岩	2.356	7.460	0.191 1	0.512 826±0.000 004	2 177±27
5	变玄武岩	2.887	9.254	0.188 7	0.512 832±0.000 010	1 933±60
6	变玄武岩	3.207	10.390	0.186 8	0.512 826±0.000 004	1 831±22
7	变玄武岩	2.633	8.461	0.188 3	0.512 815±0.000 005	2 004±30
8	变玄武岩	2.489	7.922	0.190 1	0.512 827±0.000 004	2 079±26