Age, provenance and tectonic setting of the high-grade Jequitinhonha Complex, Araçuaí Orogen, eastern Brazil

Dias, Tatiana Gonçalves; Caxito, Fabrício de Andrade; Pedrosa-Soares, Antônio Carlos; Stevenson, Ross; Dussin, Ivo; Silva, Luiz Carlos da; Alkmim, Fernando; Pimentel, Márcio

doi:10.1590/2317-4889201620160012

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Brazilian Journal of Geology

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ARTICLES • Braz. J. Geol. 46 (02) • Apr-Jun 2016 • https://doi.org/10.1590/2317-4889201620160012 copy

Age, provenance and tectonic setting of the high-grade Jequitinhonha Complex, Araçuaí Orogen, eastern Brazil

Idade, proveniência e ambiente tectônico do Complexo Jequitinhonha de alto grau, Orógeno Araçuaí

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT:

The Jequitinhonha Complex of the northeastern Araçuaí orogen is an extensive sedimentary unit metamorphosed in the amphibolite-granulite facies transition around 580-545 Ma. The unit consists of Al-rich (kinzigitic) paragneisses with decametric intercalations of graphite gneisses and quartzites, and centimetric to metric lenses of calcsilicate rocks. A new detrital zircon U-Pb age spectrum is reported for a sample of quartzite, and whole-rock geochemical (major and trace elements, 9 samples) and Sm-Nd isotope data (10 samples) for Jequitinhonha Complex paragneiss. Together with published data these show that: (1) the geochemistry of paragneiss samples of the Jequitinhonha Complex are similar to those of passive margin sedimentary protoliths; (2) detrital zircon data yield U-Pb age populations between ca. 0.9 and 2.5 Ga; and (3) Sm-Nd T_DM model ages range from 1.6 to 1.8 Ga and εNd_{(575 Ma)} around -7.5. The data reveal a mixture of Cryogenian to Mesoproterozoic rift-related igneous rocks with the Palaeoproterozoic-Archaean basement rocks of the São Francisco-Congo palaeocontinent as the main source areas, and also support the correlation between the Jequitinhonha Complex and the passive margin units of the upper Macaúbas Group, constituting the precursor basin of the orogen. Our results, with the absence of ophiolites in the Jequitinhonha Complex, reinforce the interpretation that the São Francisco-Congo palaeocontinent was not divided to the north of the focused region, suggesting an ensialic termination of a gulf during the Neoproterozoic.

KEYWORDS:
Kinzigite gneiss; Jequitinhonha Complex; Araçuaí Orogen; West Gondwana

Sample	AL01	AL27	AL21	AL03	RP64	JE08	RP51	JE06	AL16A
UTM coord.	335405 /8215547	322357/ 8226222	310029/ 8211137	318673/ 8213968	340509/ 8152465	285271/ 8182872	315062/ 8144209	285390/ 8182951	327292/ 8194091
Major elements (wt %)					340509/ 8152465	285271/ 8182872	315062/ 8144209	285390/ 8182951	327292/ 8194091
SiO₂	58.47	58.50	58.94	59.72	59.90	60.45	61.30	64.13	73.69
TiO₂	1.07	1.00	1.12	1.02	1.04	1.01	1.06	0.96	0.80
Al₂O₃	19.06	18.95	17.59	17.95	17.67	17.94	17.93	16.24	11.49
Fe₂O₃	9.83	9.96	10.31	10.12	7.93	9.03	9.03	7.69	5.56
MnO	0.16	0.15	0.15	0.18	0.10	0.14	0.11	0.13	0.09
MgO	4.00	4.15	4.19	3.52	3.67	3.60	3.73	3.02	1.75
CaO	0.72	0.66	0.71	0.48	2.28	0.69	0.59	0.87	1.19
Na₂O	1.60	1.46	1.63	1.46	2.86	1.75	1.51	2.12	2.55
K₂O	4.05	3.94	3.97	4.26	2.53	3.53	3.33	3.24	2.09
P₂O₅	0.09	0.11	0.07	0.10	0.17	0.13	0.09	0.15	0.08
Cr₂O₃	0.019	0.019	0.019	0.034	0.015	0.016	0.017	0.014	0.011
LOI	0.7	0.9	1.1	0.8	1.6	1.5	1.1	1.3	0.6
TOT/C	0.10	0.12	0.14	0.08	0.19	0.15	0.05	0.11	0.07
TOT/S	0.06	0.04	0.07	0.06	0.16	<0.02	0.22	<0.02	0.09
Sum	99.76	99.79	99.78	99.65	99.78	99.78	99.79	99.84	99.92
Trace elements (ppm)					99.78	99.78	99.79	99.84	99.92
Ba	625	548	557	702	482	639	529	382	147
Rb	191.1	199.2	196.8	194.0	188.9	194.3	143.6	199.0	176.7
Sr	100.4	86.2	126.7	79.7	201.0	83.8	77.2	80.7	89.0
Cs	6.3	5.4	6.5	6.7	7.1	10.8	5.6	9.2	9.1
Tl	0.5	0.9	1.1	0.9	0.9	1.0	0.5	1.0	0.9
Ta	0.8	0.8	1.2	2.7	2.0	1.1	1.0	1.4	1.7
Nb	18.1	14.3	19.7	20.9	44.1	15.6	16.6	17.8	23.1
Hf	6.2	5.0	5.7	6.1	5.4	5.4	5.9	6.7	5.7
Zr	200.3	169.0	192.7	208.3	183.1	187.3	206.3	211.0	212.7
Y	34.6	31.2	30.7	34.1	22.3	32.2	33.4	33.5	14.3
Th	17.3	14.1	14.0	15.2	16.2	15.1	15.3	15.0	11.5
U	2.8	2.5	2.8	4.4	3.5	3.3	3.2	4.0	3.9
Co	27.7	22.8	22.2	163.4	19.2	21.8	23.1	18.5	11.1
Sc	24	24	24	25	15	20	19	17	13
V	211	164	171	184	156	158	166	135	94
Cu	47.9	29.8	23.0	30.3	37.1	34.7	84.6	11.7	19.5
Pb	1.3	1.2	2.0	1.4	2.0	1.5	1.4	1.3	1.9
Zn	111	112	139	123	141	105	100	94	97
Bi	<0.1	<0.1	<0.1	0.2	<0.1	0.4	<0.1	0.6	0.2
Be	1	<1	2	2	4	2	2	2	1
Ga	25.6	23.7	25.7	26.1	29.3	24.7	23.5	20.5	18.7
Sn	<1	2	2	1	1	3	1	3	3
W	<0.5	<0.5	<0.5	828.2	0.6	0.7	<0.5	<0.5	0.6
As	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5	<0.5
Au	0.9	0.6	0.6	<0.5	<0.5	<0.5	<0.5	0.6	2.1
Mo	0.6	0.4	0.6	3.8	0.5	0.4	0.5	0.3	0.5
Ni	63.0	60.6	58.3	59.2	47.0	55.0	56.4	45.2	27.9
Th/Sc	0.72	0.59	0.58	0.61	1.08	0.76	0.81	0.88	0.88
Rare earth elements (ppm)					1.08	0.76	0.81	0.88	0.88
La	40.4	36.7	39.3	41.5	39.5	38.1	40.1	38.7	22.4
Ce	91.3	77.4	82.5	97.4	86.8	86.7	92.7	88.8	47.5
Pr	9.89	8.88	9.44	10.19	9.07	9.33	9.72	9.57	5.52
Nd	37.0	34.7	36.2	38.1	34.0	34.8	37.8	36.0	20.1
Sm	7.10	6.30	6.48	7.33	6.07	6.79	7.17	7.21	3.44
Eu	1.49	1.30	1.04	1.38	1.10	1.29	1.36	1.26	0.78
Gd	6.25	5.63	5.70	6.68	5.32	6.25	6.59	6.44	2.55
Tb	1.05	0.96	0.94	1.07	0.82	1.04	1.06	1.08	0.43
Dy	5.68	5.13	5.00	6.00	4.40	5.76	5.66	6.02	2.14
Ho	1.20	1.10	1.06	1.24	0.81	1.12	1.16	1.18	0.48
Er	3.63	3.29	3.38	4.00	2.11	3.40	3.28	3.44	1.76
Tm	0.55	0.52	0.54	0.61	0.33	0.52	0.50	0.54	0.33
Yb	3.49	3.32	3.62	3.92	1.97	3.27	3.20	3.30	2.41
Lu	0.54	0.51	0.52	0.58	0.30	0.50	0.48	0.50	0.38
∑REE	209.57	185.74	195.72	220.00	192.60	198.87	210.78	204.04	110.22
La_N/Yb_N	8.3	7.9	7.8	7.6	14.4	8.4	8.9	8.4	6.7
Eu/Eu*	0.7	0.7	0.5	0.6	0.6	0.6	0.6	0.6	0.8

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