Peri-Gondwanan Ordovician crustal fragments in the high-grade basement of the Eastern Rhodope Massif, Bulgaria: evidence from U-Pb LA-ICP-MS zircon geochronology and geochemistry

Figures & data

Figure 1. Tectonic sketch map of Variscan and the Alpine orogenic belts in Europe. Box in 1(a): outline of map area in 1(b) depicting the Alpine tectonic framework around the Aegean region of the Eastern Mediterranean. Data sources used for map construction in 1(a) of pre-Variscan and Variscan basement areas from Neubauer (2002), Von Raumer et al. (2003), Carrigan et al. (2006), and Anders et al. (2006). Abbreviations: AA, Austroalpine; AM, Armorican Massif; AT, Anatolia; BF, Black forest; BM, Bohemian Massif; B-SG, Balkan-Sredna Gora; F, Flamborun; H, Harz; Hel, Helvetic; Ib, Iberia; MC, Massif Central; Mo, Moesia; OM, Ossa-Morena; Pen, Peninic; Rh, Rhenohercinian; S, Strandzha; Sax, Saxoturingian; SC, South Carpathians; Sd, Sardinia; Sk, Sakarya; SMM, Serbo-macedonian; Rh, Rhodope.

Figure 2. Simplified tectonic map of the eastern Rhodope-Thrace region in southern Bulgaria and northern Greece modified after Bonev et al. (2010). Available geochronology (inset, see also text and references) and the location of samples used in this study for U-Pb LA-ICP-MS geochronology are shown.

Figure 3. Lithologic context and field relations of the studied metamorphic basement rocks and volcanic rocks: (a) columnar section of the rock succession in sampled fragment of the upper unit of the high-grade basement and the sedimentary-volcanic unit, showing the location of U-Pb LA-ICP-MS geochronology samples, (b) metamorphic succession of alternating different metasedimentary lithologies hosting lenses of metaultramafic-mafic rocks, (c) metagabbros intruded by irregular metaplagiogranite veins, (d) garnet amphibolite (sample EG 06-12a) cross-cut by numerous multi-generation aplite veins, (e) alkaline basalt dyke fragment depicting the texture and the occurrences of xenoliths and xenocrysts within the rock. Coin for scale is 4 cm in diameter. This rock, devoid of xenoliths, is representative for the sample EG 06-1.

Figure 4. Field photographs and microphotographs of the studied metamorphic basement rocks: (a) quartzite in the metasedimentary succession shown in a box of Figure 3(b), (b) marble xenolith included in the metagabbros, both deformed foliation-parallel and sub-isoclinally folded (F), (c) coarse granular metagabbros preserving original lamellar plagioclase, metamorphic hornblende, and minor quartz. Note that the regional foliation is deduced by planar alignment of hornblende and plagioclase, (d) metaplagiogranite consisting of recrystallized quartz, primary lamellar plagioclase, metamorphic biotite, and epidote developed at expense of plagioclase. Abbreviations: amph, amphibole; bt, biotite; pl, plagioclase; fs, alkali feldspar; ep, epidote. Scale bar = 2 mm.

Table 1. Representative microprobe analyses for chemistry of mineral phases in the samples of the high-grade basement rocks.

Sample	EG06-11	EG06-12a	EG06-12a	EG06-7	EG06-11	EG06-11	EG06-9	EG06-9	EG06-7	EG06-7	EG06-7
Mineral	grt	grt	amph	amph	amph	fs	fs	fs	fs	bt	ep
Rocktype	mgb	mgb	mgb	md	mgb	mgb	mplg	mplg	md	md	mgb
SiO2	44.06	38.19	43.49	42.87	43.52	63.92	62.51	46.54	63.51	36.25	38.00
TiO2	0.65	0.05	0.43	0.51	0.63	–	–	1.36	–	2.77	0.04
Al2O3	12.43	21.61	13.77	13.00	12.43	22.99	23.65	30.57	22.92	15.56	27.03
Cr2O3	0.04	0.02	0.00	0.02	0.06	–	–	–	–	0.05	0.02
Fe2O3	0.00	1.88	7.08	8.86	7.44	0.00	0.03	3.67	0.13	–	8.37
FeO	14.32	22.17	6.63 25.06	7.21	7.49	0.03	–	–	–	15.45	–
MnO	0.29	1.63	0.10	0.32	0.27	0.03	–	–	–	0.14	0.19
MgO	11.98	6.72	12.29	11.39	11.96	–	0.01	1.61	–	14.40	–
CaO	11.12	7.73	11.08	10.73	11.04	3.77	4.61	–	3.96	0.02	23.69
Na2O	–	–	1.89	2.10	1.93	9.26	8.59	0.27	9.42	0.17	–
K2O	–	–	0.64	0.50	0.49	0.21	0.48	10.69	0.30	9.53	–
H2O	–	–	2.06	2.04	2.04	–	–	–		3.95	1.90
Total	94.96	100.00	99.47	99.55	99.30	102.58	99.86	94.72	100.5	98.28	99.13
Si	3.452	2.956	6.330	6.295	6.386	8.092	2.772	2.287	2.803	5.501	2.991
Ti	0.038	0.003	0.047 0.009	0.057	0.070	–	–	0.050	–	0.316	0.002
Al^IV	0.000	0.044	1.670	1.705	1.862	0.000	1.236	1.770	1.192	2.499	0.009
Al^VI	1.147	1.928	0.692	0.544	0.578	3.430	0.000	–	–	0.282	2.499
Cr	0.002	0.001	0.000	0.002	0.001	0.000	0.000	–	–	0.007	0.001
Fe^3+	0.000	0.011	0.776	0.979	0.793	0.000	0.001	0.136	0.004	–	0.496
Fe^2+	0.938	1.435	0.807	0.885	1.530	0.004	–	–	–	1.960	–
Mn^2+	0.019	0.107	0.012	0.040	0.028	0.003	–	–	–	0.018	0.006
Mg	1.399	0.776	2.667	2.493	1.970	–	0.001	0.118	–	3.256	–
Ca	0.940	0.641	1.728	1.688	1.782	0.511	0.219	–	0.187	0.004	1.998
Na	–	–	0.534	0.597	0.644	2.273	0.738	0.026	0.806	0.051	–
K	–	–	0.119	0.093	0.083	0.033	0.027	0.670	0.017	1.844	–
OH	–	–	2.000	2.000	2.000	–	–	–	–	4.000	1.000
Py	42.447	26.221
Alm	28.457	48.497
Sp	0.579	3.605
And	0.000	5.372
Uv	0.186	0.065
Gro	28.331	16.240
#Mg	59.9	35.1	76.8	73.8	56.3					62.4
Ab						80.700	75.011	3.724	79.760
An						18.100	22.243	–	18.544
Or						1.200	2.740	96.276	1.696

Notes: Structural formula based on 23 and 24 oxygen atoms, respectively for amphiboles and garnets, and 32 and 22 oxygen atoms for feldspar and micas. Abbreviations: amph, amphibole; bt, biotite; grt, garnet; ep, epidote; fs, feldspar; mgb, matagabbro; md, metadiorite; mplg, metaplagiogranite.

Figure 5. Mineral compositions of the studied metamorphic basement rock samples: (a) amphibole compositions diagram (after Leake, 1978), (b) feldspar compositions ternary diagram.

Table 2. Whole-rock chemical analyses of metamafic and associated evolved rocks in the high-grade metamorphic basement of the eastern Rhodope Massif and Oligocene volcanic rocks.

Sample	EG06-6	EG06-7	EG06-9	EG06-9a	EG06-10	EG06-11	EG06-12a	EG06-12c	EG06-1	PK-20
Rock type	mgb	md	mplg	mplg	lmd	mgb	mgb	apl	alkbas	and
SiO2	49.30	61.13	68.22	60.75	70.09	52.26	43.33	73.55	46.76	57.13
TiO2	1.21	0.80	0.66	0.73	0.53	1.19	0.49	0.97	2.05	0.80
Al2O3	15.88	15.19		15.02		14.15	24.90	8.37	16.84	17.06
Fe2O3	10.03	6.70	4.75	7.18		10.41	10.96	6.55	8.75	6.72
MnO	0.16	0.16	0.10	0.15		0.20	0.17	0.08	0.16	0.14
MgO	7.47	3.38	1.83	4.14	2.02	7.48	4.04	3.66	7.25	3.36
CaO	9.20		2.80	5.24		8.56	12.84	4.41	9.48	6.38
Na2O	4.25		3.54	3.32		3.80	1.83	1.53	4.43	3.47
K2O	0.35		2.11	2.15		0.37	0.41	0.40	1.40	2.90
P2O5	0.12		0.15	0.14		0.08	0.11	0.02	0.73	0.37
Cr2O3	0.05	0.01	n.d.	0.01	0.01	0.03	n.d.	0.01	0.03	n.d.
NiO	0.01	n.d.	n.d.	n.d.	n.d.	0.01	n.d.	n.d.	0.01	n.d.
LOI	1.08	0.50	0.54	0.79	0.21	0.53	0.54	0.54	1.65	1.06
Total	99.09	99.67	99.01	99.63	99.82	99.08	99.62	100.10	99.52	99.39
Nb	3		10	8	9	5	<1<	17	75	14
Zr	82	114	181	130	140	88	21	39	223	204
Y		34	32	29	33	29	10	18	28	26
Rb				55	4	5	18	6	54	182
Sr	231	284	307	273	270	111	301	250	813	518
	88	150	495	348	89	14	86	111	795	1022
U	2	3	4		4	<2<	3	<2<	2	10
Th	<2<	7	7		8	<2<	<2<	43	7	19
Pb	4	24		12	30	<2<	6	5	4	32
Hf	3		7	6	7	6	<1<	7	8	9
Sc	49	25	14		19	49	21	20	20	14
Cr	304	42	16	65	32	230	23	25	171	27
V	282	126	72	144	82	273	305	165	216	157
Ni	59	10	4	17	9	42	8	10	103	13
Ga	17	17	15	16	14	18	23	13	18	18
Zn	43	62	53	71	42	38	66	68	76	73
Cu	20	66	96	53	19	27	26	85	42	30
Co	42	22	12	21	11	37	27	25	30	17
La	13	15	16	14	12	7	<4<	38	43	38
Ce	23	31	44	44	32	18	15	39	90	66
Nd	14	13	20	23	14	9	7	25	42	28

Notes: elements (wt.%), trace elements and rare earth elements (ppm) analysed by XRF. Abbreviations: abas, alkaline basalt; and, andesite; apl, aplite vein; lmd, leucocratic metadiorite; mgb, matagabbro; md, metadiorite; mplg, metaplagiogranite; n.d. = not detected.

Figure 6. Geochemical and tectono-magmatic discrimination diagrams of the studied metamorphic basement rock samples. (a, b) chondrite and N-MORB-normalized trace elements diagrams, respectively. Normalization values after Sun and McDonough (1989). BABBs compositions used in comparison in b are taken from Saunders and Tarney (1991), (c) Ti-V diagram showing fields of IAT, volcanic arc CAB, MORB and BABB and OIB, oceanic island basalts after Shervais (1982), (d) Zr/Y-Zr diagram after Pearce and Norry (1979), (e) Nb-Zr-Y diagram after Meschede (1986), (f) Ti–MnO–P₂O₅ diagram after Mullen (1983).

Table 3. U-Pb LA-ICP-MS analytical data for zircons in samples used in the study.

	Isotopic ratios							Apparent ages (Ma)
Sample/analysis	^207Pb/^206Pb	±2s %	^207Pb/^235U	±2s %	^206Pb/^238U	±2s %	Rho	^206Pb/^238U	±2s	^207Pb/^235U	±2s	^207Pb/^206Pb	±2s
EG06-1 alkaline basalt		Lat. N 41°18′46.30′′, Long. E 25°38′19.76′′
EG06-1/1r1	0.0517	2.0	0.3417	1.8	0.0479	1.0	0.09	301.6	2.9	298.4	4.9	270	46
EG06-1/1r2	0.0524	2.6	0.3431	3.0	0.0473	1.1	0.43	298.0	3.3	299.5	7.5	300	60
EG06-1/2r1	0.0562	2.6	0.5686	3.4	0.0729	1.0	0.82	453.8	4.6	457.1	12.6	458	60
EG06-1/2r2	0.0556	2.0	0.5640	2.4	0.0736	0.8	0.59	457.8	3.6	454.1	8.8	436	46
EG06-1/2rc	0.0557	2.3	0.5801	2.6	0.0747	0.9	0.49	464.4	4.0	464.5	9.7	442	50
EG06-1/2cr	0.0561	1.2	0.5700	1.4	0.0742	0.6	0.50	461.2	2.8	458.0	5.3	454	26
EG06-1/4r1	0.0517	2.3	0.3501	2.8	0.0489	1.0	0.63	308.0	3.0	304.8	7.4	272	52
PK20 andesite Iran tepe		Lat. N 41°32′45.75′′, Long. E 25°40′20.52′′
PK20/1r1	0.0515	2.5	0.3383	3.0	0.0483	1.5	0.55	304.1	4.4	295.9	7.6	264	58
PK20/1r2	0.0528	1.9	0.3572	2.0	0.0490	1.3	0.38	308.6	3.9	310.1	5.4	318	44
PK9 dacite Iran tepe		Lat. N 41°29′20′′, Long. E 25°43′33′′
PK9/1rc1	0.0528	1.7	0.3291	1.8	0.0457	0.9	0.35	288.0	2.7	288.9	4.6	320	40
PK9/1rc2	0.0529	1.1	0.3287	2.4	0.0452	1.0	0.47	285.2	2.8	288.6	6.1	322	48
PK9/1r	0.0529	2.5	0.3079	2.4	0.0422	1.4	0.45	266.5	3.6	272.6	6.6	322	56
PK9/2r1	0.0460	5.6	0.0263	5.4	0.0042	0.4	0.04	26.9	0.4	26.3	1.4	0	64
PK9/2r2	0.0481	5.6	0.0276	3.0	0.0042	1.6	0.15	26.9	0.4	27.6	1.4	100	130
PK9/2c	0.0594	5.0	0.0351	3.0	0.0043	1.3	0.10	27.7	0.4	35.0	1.7	580	108
PK9/3c	0.0520	2.1	0.1888	2.0	0.0264	0.8	0.10	168.0	1.3	175.6	3.3	286	48
PK9/3r1	0.0514	1.4	0.2568	1.6	0.0361	0.9	0.47	228.6	2.1	232.1	3.3	258	32
PK9/3r2	0.0517	1.5	0.2754	1.6	0.0391	0.8	0.27	247.1	1.9	247.0	3.4	270	34
PK9/5r	0.0577	2.2	0.5789	2.2	0.0734	0.9	0.32	456.7	4.2	463.8	8.4	518	48
PK9/5rc	0.0605	1.8	0.7160	2.4	0.0866	0.8	0.90	535.5	4.0	548.3	10.6	620	38
PK9/5c	0.0635	1.6	0.9127	2.2	0.1045	0.8	0.84	640.9	4.9	658.5	10.6	722	32
PK9/6r1	0.0538	2.4	0.3397	2.2	0.0467	1.0	0.14	294.1	2.8	296.9	5.8	360	54
PK9/6r2	0.0542	1.7	0.3484	2.2	0.0469	0.9	0.57	295.3	2.6	303.5	5.5	376	38
PK9/6c	0.0540	2.3	0.3398	2.6	0.0461	1.1	0.46	290.4	3.0	297.0	6.6	370	52
EG06-9 metagranodiorite Egrek		Lat. N 41°19′54.39′′, Long. E 25°37′49.39′′
EG06-9/1c	0.0564	1.9	0.5834	2.6	0.0748	1.6	0.70	465.3	7.0	466.7	9.8	466	42
EG06-9/1r1+c	0.0563	2.1	0.5790	2.6	0.0744	0.9	0.62	462.6	3.9	463.8	9.3	464	46
EG06-9/1r2+c1	0.0560	2.6	0.5567	3.2	0.0722	1.3	0.61	449.5	5.7	449.4	11.4	450	58
EG06-9/2r2+c	0.0556	2.6	0.5586	3.2	0.0730	1.0	0.71	454.0	4.6	450.6	11.3	436	56
EG06-9/3r1+c	0.0563	1.9	0.5452	2.4	0.0710	1.0	0.57	442.0	4.2	441.9	8.3	462	42
EG06-9/3r2+c	0.0565	1.6	0.5511	1.8	0.0711	1.0	0.46	442.7	4.1	445.7	6.6	470	36
EG06-9/4r1c	0.0580	2.0	0.6611	2.6	0.0827	1.5	0.62	512.4	7.4	515.3	10.5	528	44
EG06-9/4c	0.0582	2.2	0.6460	3.2	0.0811	2.4	0.76	502.8	11.5	506.0	13.1	534	46
EG06-9/4r2c	0.0570	1.9	0.6498	1.4	0.0830	2.4	0.70	513.9	12.0	508.3	9.7	492	42
EG06-9/5rc	0.0554	3.0	0.5487	3.6	0.0728	1.6	0.57	453.1	6.9	444.1	12.8	428	66
EG06-9/5c	0.0547	2.8	0.5669	3.0	0.0740	1.2	0.41	460.2	5.1	456.0	11.3	400	62
EG06-9/6r2c1	0.0554	2.1	0.5520	2.6	0.0736	1.3	0.57	457.7	5.9	446.3	9.3	426	46
EG06-9/7r1	0.0560	2.1	0.5838	2.8	0.0753	1.9	0.70	468.0	8.4	466.9	10.8	452	46
EG06-7 metagabbro Egrek		Lat. N 41°19′55.11′′, Long. E 25°37′47.01′′
EG06-7/2r	0.0524	2.7	0.3653	1.4	0.0506	0.6	0.36	318.5	3.5	316.2	7.9	302	60
EG06-7/3r	0.0460	6.1	0.0473	3.0	0.0074	0.9	0.07	47.8	0.8	46.9	2.7	0	70
EG06-7/3c	0.0490	9.6	0.0519	4.4	0.0076	1.3	0.15	49.1	1.3	51.4	4.4	146	228
EG06-7/4r	0.0562	1.5	0.5679	1.0	0.0733	0.5	0.73	456.1	4.2	456.7	7.7	458	34
EG06-7/4c	0.0569	2.6	0.6038	1.5	0.0764	0.6	0.46	474.3	5.9	479.6	11.4	486	58
EG06-7/5r1+2	0.0510	5.2	0.0352	2.5	0.0051	1.2	0.16	32.6	0.8	35.1	1.7	238	120
EG06-7/5r1	0.0469	6.6	0.0312	3.4	0.0049	1.0	0.24	31.5	0.6	31.2	2.1	44	120
EG06-12a garnet-amphibolite		Lat. N 41°22′57′′, Long. E 25°42′40.8′′
EG12a/1r1+2	0.0563	2.0	0.5543	2.4	0.0718	1.1	0.61	446.8	4.8	447.8	8.9	464	44
EG12a/1r1+2b	0.0563	2.0	0.5572	2.2	0.0718	1.3	0.49	447.2	5.4	449.7	8.2	462	44
EG12a/1r1	0.0569	2.7	0.5616	3.2	0.0721	1.1	0.59	448.9	4.9	452.6	11.8	488	60
EG12a/2r1	0.0552	2.2	0.5663	2.4	0.0738	0.8	0.49	459.0	3.7	455.7	9.1	418	48
EG12a/2r2	0.0565	1.6	0.5655	2.0	0.0724	1.2	0.58	450.4	5.2	455.1	7.1	472	36
EG12a/3r1	0.0558	1.8	0.5431	2.2	0.0711	0.9	0.56	442.7	3.9	440.5	7.6	444	40
EG12a/3r2	0.0550	2.0	0.5464	2.2	0.0722	0.9	0.42	449.3	3.9	442.6	7.9	412	46
EG12a/4r1	0.0521	3.2	0.3507	3.6	0.0491	1.2	0.46	308.7	3.5	305.2	9.5	286	74
EG12a/4c	0.0524	3.9	0.3470	4.2	0.0488	1.2	0.37	307.1	3.5	302.5	10.9	302	88
EG12a/4r2	0.0531	3.2	0.3605	3.8	0.0490	1.2	0.66	308.3	3.6	312.6	10.4	332	74
EG12a/5r1+2	0.0568	2.6	0.5412	3.0	0.0697	0.9	0.65	434.2	3.9	439.2	10.8	484	56
EG12a/5r1+2b	0.0557	2.5	0.5390	2.8	0.0704	0.9	0.41	438.4	4.0	437.8	9.8	438	56
EG12a/6r1	0.0558	1.8	0.4974	2.2	0.0660	0.9	0.53	412.2	3.4	409.9	7.2	444	42
EG12a/6r2	0.0565	2.7	0.5495	3.4	0.0716	1.0	0.74	445.7	4.5	444.7	12.3	472	60
EG12a/6c	0.0568	2.8	0.5658	2.8	0.0726	1.0	0.26	452.1	4.2	455.3	10.6	484	62

Figure 7. Representative cathodoluminescence images of dated zircons in metamorphic and volcanic rocks. Sample numbers indicated. Circled areas represent location of spot analyses, together with corresponding ages given with 2σ. For samples’ location see Figures 2 and 3.

Figure 8. Concordia plots for dated metamorphic and volcanic rock samples.

Figure 9. Regional frame of unpublished and published U-Pb zircon geochronology in the Rhodope metamorphic basement and adjacent terranes (zones) and derived from this study. Map constructed using Ricou et al. (1998) and Bonev, Marchev, and Singer (2006a). See the text for details and Figure 2. Geochronology data sources and methods: (1) Himmerkus et al. (2006) Pb/Pb evaporation, (2) Himmerkus, Reischmann, and Kostopoulos (2009) Pb/Pb evaporation, (3) Macheva et al. (2006) ID TIMS/LA-ICP-MS, (4) Zidarov et al. (2003) ID TIMS, (5) Peytcheva et al. (2009) ID TIMS/LA-ICP-MS, (6)Graf et al. (1998) ID TIMS, (7) Zagorchev et al. (2011) LA-ICP-MS, (8) Naydenov et al. (2009) LA-ICP-MS, (9) Arkadakskiy et al. (2003) ID TIMS, (10) Ovtcharova (2005) ID TIMS, (11) Carrigan et al. (2003) HR SIMS, (12) Carrigan et al. (2005, 2006) HR SIMS, (13) Şahin et al. (2011) SHRIMP/LA-ICP-MS, (14) Anders et al. (2006) ID TIMS/SHRIMP, (15) Okay et al. (2008) LA-ICP-MS/TIMS Pb evaporation. Concordant ages in metamorphic rocks derived from this study are shown.

Figure 10. (a–b) Paleotectonic reconstructions after Stampfli and Borel (2002) for Early Ordovician and Early Silurian. (c) A scenario depicting tectonic setting of origin, compositions, and protolith age of metamorphic rocks in the eastern Rhodope and the link to adjacent terranes.

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