Tracing Pre-Mesozoic Tectonic Sutures in the Crystalline Basement of the Protocarpathians: Evidence from the Exotic Blocks from Subsilesian Nappe, Outer Western Carpathians, Poland

Abstract

Pre-Mesozoic exotic crystalline blocks within the Outer Carpathian flysch have potential to unravel the nature of their eroded basement source(s) and to reconstruct the Paleozoic–Precambrian history of the Protocarpathians. Strongly tectonized Campanian–Maastrichtian grey marls in the Subsilesian Nappe of the Outer Western Carpathians in Poland contain a variety of different lithology types, including granitoids and andesites. Petrological investigations coupled with zircon and apatite U-Pb dating were performed on crystalline (subvolcanic) exotic blocks from a locality in the Subsilesian Nappe. U-Pb zircon dating yields magmatic crystallization ages of c. 293 Ma for the microgranitoid and c. 310 Ma for the andesite block, with inherited zircon cores yielding Archean, Paleoproterozoic, Mesoproterozoic and Cadomian ages. Whole rock trace element and Nd isotope data imply that the melt source was composed of a significant Neoproterozoic crustal component in both the microgranite and andesite. The Late Carboniferous–Permian magmatic activity likely continues outside the Carpathian Belt and can be linked to a Late Paleozoic transtensional zone, which is a continuation of the Lubliniec–Kraków Zone that extends under the Carpathians to Moesia. This Late Paleozoic transtensional zone was probably reactivated during the Late Cretaceous under a transpressional regime within the Żegocina tectonic zone, which caused the uplift of the Subsilesian Ridge and intensive erosion.

1. Introduction

The presence of Pre-Mesozoic basement within the Alpine orogens was first identified c. 200 years ago [1]. In most of the Alpine orogens of Europe, such as the Alps and Carpathians, Pre-Mesozoic basement is present as exotic blocks inside the sedimentary or metasedimentary successions or as uplifted crystalline massifs, termed “core mountains” [2,3]. Investigating the Pre-Alpine basement and constraining the timing of its main tectonic events remain active problems in European geology. The Carpathian Mountains are an orogen of Alpine (Cretaceous–Neogene) age, but their structure reflects a prolonged Neoproterozoic and Phanerozoic history. While the crystalline massifs in the Central Carpathians are relatively well-studied ([3] and references therein), the presence of pre-Alpine components in the Outer Carpathians are less understood. Pre-Alpine basement is present in the form of exotic blocks and interpreted as remnants of the Protocarpathian crystalline basement, which is inferred to underlay the Mesozoic and Cenozoic basins of the Carpathian orogenic system [4,5]. During the syn-orogenic (Cretaceous–Neogene) stage of the evolution of the Carpathians, several ridges were formed inside the Tethys marginal basins [6]. These ridges were cored by Pre-Mesozoic crystalline basement and were uplifted during Alpine closure of the Tethys Ocean. Subsequent erosion of the uplifted ridges resulted in the transportation of large amounts of basement material (often as olistostromes) into the Carpathian basins [7]. These crystalline blocks likely represent remnants of the Protocarpathian basement and afford the opportunity to reconstruct the Neoproterozoic to Paleozoic–Precambrian history of the Protocarpathians. This paper investigates and interprets crystalline plutonic and volcanic exotic blocks, found at a locality in the Subsilesian Nappe of the Outer Western Carpathians in Poland (Figure 1).

2. Geological Setting and Sampling

The Carpathian Mountains in the Czech Republic, Poland, Slovakia, Ukraine and Romania are geographically divided into the Western, Eastern and Southern Carpathians (Figure 1a). The Western Carpathians in Poland are traditionally subdivided into the Central and Outer Carpathians, separated by the Pieniny Klippen Belt ([3] and references therein; [10]). The Outer Western Carpathians are built of Jurassic–Neogene sedimentary rocks that were thrust over the European Platform (Figure 1a,b). This resulted in the formation of nappe sequences that detached from their basement [11,12] and comprise the Magura Nappe, Fore–Magura Group of nappes, Silesian Nappe, Subsilesian Nappe and Skole (Skiba) Nappe (Figure 1b). These sedimentary sequences often contain crystalline exotic blocks. In the Subsilesian and Silesian nappes, most of the exotic blocks are of Neoproterozoic age [5,13,14], while the basement of Magura Nappe, as deduced from exotic blocks, is primarily late Variscan with Neoproterozoic remnants [15]. The analysed exotic blocks are shown in Figure 2.

The study area is located within the Subsilesian Nappe. Originally occupying a structural position between the Silesian and the Skole nappes, the Subsilesian Nappe exposures south of Kraków are limited to small tectonic windows forming belts within the Silesian Nappe and along the northern boundary of the Magura Nappe (Figure 1c). The sampled area is located in a belt stretching over a distance of several kilometers along the boundary of the Magura Nappe and is known as the Żegocina Zone sensu Skoczylas–Ciszewska [16]. In the Żegocina Zone, a series of E–W trending structures are associated with the exposure of the Subsilesian nappe [9,16], and the zone is interpreted to represent a tectonic mélange. The Subsilesian Nappe is composed mainly of Upper Cretaceous and Lower Paleogene carbonate deposits, which were deposited in the Subsilesian Sedimentary Zone, an uplifted high that separates the Silesian and Skole basins [4,17,18]. The central part of this high is inferred to have been composed of crystalline basement rocks and is termed the Subsilesian Ridge. This paleogeographic entity, which is now destroyed, supplied crystalline basement blocks to the slope and basinal areas. The crystalline blocks occur within marly slope deposits. These strongly tectonized Campanian–Maastrichtian grey marls contain different types of lithology, including limestones, gneisses, granitoids and andesites [19]. Two samples of c. 10 kg each were extracted from large rounded blocks of grey andesite (3 m in diameter) and a pale, fine-grained granitoid (4 m in diameter), in the Pluskawka Stream valley near the villages of Nowe Rybie and Kamionna in the Beskid Wyspowy Range (Figure 1c, N 49°47 15,8″, E 20°21 03,4″).

3. Analytical Techniques

3.1. Microscopy

Petrographic analyses of thin sections were undertaken at the Institute of Earth Sciences in the University of Silesia using an Olympus BX-51 microscope to constrain textural and microstructural relationships and to determine the presence of zircon.

3.2. Electron Probe Micro-Analyses (EPMA)

Microprobe analyses of the main rock-forming and accessory minerals were carried out at the Inter-Institutional Laboratory of Microanalyses of Minerals and Synthetic Substances, Warsaw, using a CAMECA SX-100 electron microprobe. The analytical conditions employed an accelerating voltage of 15 kV, a beam current of 20 nA, counting times of 4 s for peak and background and a beam diameter of 1–5 µm. Reference materials, analytical lines, diffracting crystals, mean detection limits (in wt%) and uncertainties were as follows: rutile—Ti (Kα, PET, 0.03, 0.05), diopside—Mg (Kα, TAP, 0.02, 0.11), Si—(Kα, TAP, 0.02, 0.21), Ca—(Kα, PET, 0.03, 0.16), orthoclase—Al (Kα, TAP, 0.02, 0.08), and K (Kα, PET, 0.03, 0.02), albite—Na (Kα, TAP, 0.01, 0.08), hematite—Fe (Kα, LIF, 0.09, 0.47), rhodonite—Mn (Kα, LIF, 0.03, 0.10), phlogophite—F (Kα, TAP, 0.04, 0.32), tugtupite—Cl (Kα, PET, 0.02, 0.04), Cr₂O₃—Cr (Kα, PET, 0.04, 0.01), ZirconED2—Zr (Lα, PET, 0.01, 0.01), Nb₂O₃-MAC—Nb (Lα, PET, 0.09, 0.01), V₂O₅—V (Kα, LIF, 0.02, 0.01), YPO₄—Y (Lα, TAP, 0.05, 0.05), CeP₅O₁₄—Ce (Lα, LPET, 0.09, 0.02), NdGaO₃—Nd (Lβ, LIF, 0.31, 0.24), ThO₂—Th (Mα, LPET, 0.09, 0.09), UO₂—U (Mα, LPET, 0.16, 0.13).

3.3. Whole-Rock Chemical and Isotope Analyses

Whole-rock analyses were undertaken by X-ray fluorescence (XRF) for major and large ion lithophile trace elements (LILE), and by fusion and ICP-MS for high field strength elements (HFSE) and rare earth elements (REE) at Bureau Veritas Minerals (Canada). Preparation involved lithium borate fusion and dilute digestions for XRF and lithium borate decomposition or aqua regia digestion for ICP-MS. LOI was determined at 1000 °C. Uncertainties for most of the major elements are 0.01%, except for SiO₂, which is 0.1%. REE were normalized to C1 chondrite [20].

The Sm-Nd analytical work was performed at the Laboratory of Geochronology, Department of Lithospheric Research, University of Vienna. Results are based on ion chromatography TIMS procedures. Sample digestion for Nd–Sr analysis was performed in Savillex^® beakers using an ultrapure 4:1 mixture of HF and HNO₃ for 10 days at 110 °C on a hot plate. For whole rock powders, a minimum dissolution time of 3 weeks was applied to ensure maximum leaching of the REEs from refractory material such as zircon. After evaporating the acids, repeated treatment of the residue using HNO3 and 6.0 N HCl resulted in clear solutions for all samples. The REE fraction was extracted using AG® 50W-X8 (200–400 mesh, Bio-Rad) resin and 4.0 N HCl. Nd was separated from the REE fraction using Teflon-coated HdEHP, and 0.22 N HCl as the elution media. Maximum total procedural blanks were 50 pg for Nd and were taken as negligible. Nd was run as metal on an Re double filament, using a ThermoFinnigan® Triton MC TIMS. A ¹⁴³Nd/¹⁴⁴Nd ratio of 0.511841 ± 0.000005 (n = 5) was determined for the La Jolla (Nd) international standard, during the period of investigation. Within-run mass fractionation for Nd isotope compositions was corrected to ¹⁴⁶Nd/¹⁴⁴Nd = 0.7219. Uncertainties on the Nd isotope ratio are quoted as 2 σm.

3.4. Mineral Separation and Imaging

Zircon crystals were separated using standard techniques (crushing, hydro-fracturing, washing, Wilfley shaking table, Frantz magnetic separator and hand picking). Mineral separation was carried out at the Institute of Geological Sciences at the Polish Academy of Sciences, Kraków, Poland. The crystals were cast in 25 mm diameter epoxy resin mounts, ground and polished to half-thickness to expose the grain interiors. Internal mineral textures were then characterized by back-scattered electron (BSE) and cathodoluminescence (CL) imaging, using a FET Philips 30 scanning electron microscope with a 15 kV accelerating voltage and a beam current of 1 nA at the Institute of Earth Sciences, University of Silesia, Sosnowiec, Poland.

3.5. LA-ICP-MS U-Pb Dating

LA-ICPMS U-Pb age zircon and apatite data were acquired using a Photon Machines Analyte Excite 193 nm ArF excimer laser-ablation system with a HelEx 2-volume ablation cell coupled to an Agilent 7900 ICPMS at the Department of Geology, Trinity College Dublin, Ireland. The instruments were tuned using NIST612 standard glass to yield Th/U ratios of unity and low oxide production rates (ThO+/Th+ typically <0.15%). A quantity of 0.4 l min⁻¹ He carrier gas was fed into the laser cell, and the aerosol was subsequently mixed with 0.6 l min⁻¹ Ar make-up gas and 11 mL min⁻¹ N₂. For zircon, data reduction of the raw U-Pb isotope data was performed through the “VizualAge” data reduction scheme [21] in the freeware IOLITE package [22]. For apatite, the “VizualAge_UcomPbine” data reduction scheme [23], which can account for variable common Pb in the apatite standards, was employed. Sample-standard bracketing was applied after the correction of downhole fractionation to account for long-term drift in isotopic or elemental ratios by normalizing all ratios to those of the U-Pb reference standards. Final age calculations were made using the Isoplot add-in for Excel [24].

3.5.1. U-Pb Zircon Dating

For zircon dating, a repetition rate of 11 Hz and a circular spot of 24 μm were employed. Eleven isotopes (⁴⁹Ti, ⁹¹Zr, ¹⁷⁵Lu, ²⁰²Hg, ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb, ²³²Th, ²³⁵U and ²³⁸U) were acquired during each analysis, which comprised 27 s of ablation and 12 s washout, the latter portions of which were used for the baseline measurement. In addition, 91500 zircon (²⁰⁶Pb/²³⁸U TIMS age of 1065.4 ± 0.6 Ma; [25]) was used as the primary U-Pb calibration standard. The secondary standards GZ-7 zircon (²⁰⁶Pb/²³⁸U TIMS age of 530.26 Ma ± 0.05 Ma; [26]), Plešovice zircon (²⁰⁶Pb/²³⁸U TIMS age of 337.13 ± 0.37 Ma; [27]) and WRS 1348 zircon (²⁰⁶Pb/²³⁸U TIMS age of 526.26 ± 0.70; [28]) yielded LA-ICPMS ages of 532.0 ± 2.2 Ma, 337 ± 1.6 Ma and 528.4 ± 3.2 Ma respectively.

3.5.2. U-Pb Apatite Dating

Apatite crystals were prepared as separates on polished epoxy mounts. A total of 29 isotopes (³¹P, ³⁵Cl, ⁴³Ca, ⁵¹V, ⁵⁵Mn, ⁸⁸Sr, ⁸⁹Y, ⁹⁰Zr, ¹³⁹La, ¹⁴⁰Ce, ¹⁴¹Pr, ¹⁴⁶Nd, ¹⁴⁷Sm, ¹⁵³Eu, ¹⁵⁷Gd, ¹⁵⁹Tb, ¹⁶³Dy, ¹⁶⁵Ho, ¹⁶⁶Er, ¹⁶⁹Tm, ¹⁷²Yb, ¹⁷⁵Lu, ²⁰²Hg, ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb, ²³²Th and ²³⁸U were acquired using a 60 µm laser spot, an 11 Hz laser repetition rate and a fluence of 2.5 J/cm². A ~1 cm sized crystal of Madagascar apatite that has yielded a weighted average ID-TIMS concordia age of 473.5 ± 0.7 Ma was used as the primary apatite reference material in this study. McClure Mountain syenite apatite (the rock from which the ⁴⁰Ar/³⁹Ar hornblende standard MMhb is derived) and Durango apatite were used as secondary standards. McClure Mountain syenite has moderate but reasonably consistent U and Th contents (~23 ppm and 71 ppm, [29]), and its thermal history, crystallization age (weighted mean ²⁰⁷Pb/²³⁵U age of 523.51 ± 2.09 Ma) and initial Pb isotopic composition (²⁰⁶Pb/²⁰⁴Pb = 17.54 ± 0.24; ²⁰⁷Pb/²⁰⁴Pb = 15.47 ± 0.04) are known from high-precision ID-TIMS analyses [30]. NIST 612 standard glass was used as the apatite trace-element reference material, and a crushed aliquot of Durango apatite that has been characterized by solution quadrupole-ICP-MS analyses [31], was used as the apatite trace-element secondary standard.

Common Pb in the apatite standards was corrected using a ²⁰⁷Pb-based correction in VizualAge_UcomPbine and includes the propagation of the uncertainties in the age of the reference materials. Over the course of the analyses, McClure Mountain apatite (²⁰⁷Pb/²³⁵U TIMS age of 523.51 ± 2.09 Ma; [30]) and Durango apatite (31.44 ± 0.18 Ma; [32]) yielded weighted average 207Pb-corrected ages of 517.5 ± 3.5 Ma (MSWD = 2.3) and 31.82 ± 0.41 Ma (MSWD = 1.9), respectively. The McClure Mountain apatite age was anchored using a ²⁰⁷Pb/²⁰⁶Pb value of 0.88198 derived from an apatite ID-TIMS total U-Pb isochron [30]. All apatite REE contents were normalized to C1 chondrite [20].

4. Results

4.1. Petrography, Mineral Chemistry and Whole-Rock Chemistry of Exotic Blocks

4.1.1. Microgranite

Approximately 10 kg of microgranite (sample Pl-2) was extracted from a 4 m diameter block of fine-grained equigranular granitoid from Pluskawka Stream. Sample PL-2 is composed of quartz, zoned plagioclase (An_24-12), K-feldspar (Figure 2b), magmatic muscovite (Ti = 0.9–0.14 a.p.f.u;

Table 1. Representative microprobe analyses of biotite and muscovite with their crystal-chemical formulas recalculated for 22 O²⁻.

Compound		PL 2–Biotite (Bt)				PL 2–Muscovite (Ms)
	LoD	Bt-1	Bt-2	Bt-3	Bt-4	Ms-1	Ms-2	Ms-3	Ms-4
SiO2 (wt.%)	0.04	34.45	34.24	34.72	33.67	46.29	46.90	46.40	46.56
TiO2	0.06	3.26	3.17	3.26	3.22	1.35	1.28	0.91	0.97
Al2O3	0.03	18.09	18.16	18.44	18.09	33.06	33.88	35.38	35.30
Cr2O3	0.01	0.08	0.18	0.30	0.03	0.12	0.03	0.07	b.d.l
FeO	0.08	25.98	25.74	25.08	26.38	2.12	2.15	1.47	1.92
MgO	0.02	3.85	3.97	3.90	3.66	0.67	0.70	0.46	0.50
MnO	0.02	0.62	0.56	0.51	0.71	b.d.l.	0.07	0.06	b.d.l.
Na2O	0.04	0.03	0.05	0.05	0.07	0.33	0.28	0.61	0.46
K2O	0.05	9.28	9.56	9.26	9.39	10.55	10.28	10.30	10.58
Total		95.64	95.63	95.52	95.22	94.49	95.50	95.66	96.29
Si (apfu)		5.423	5.395	5.437	5.351	6.247	6.238	6.152	6.152
Aliv		2.577	2.605	2.563	2.649	1.753	1.762	1.848	1.848
Alvi		0.778	0.768	0.841	0.739	3.505	3.548	3.681	3.648
Ti		5.423	5.395	5.437	5.351	0.137	0.128	0.090	0.096
Cr		0.002	0.022	0.037	0.004	0.013	0.004	0.007	-
Fe		3.42	3.392	3.285	3.507	0.240	0.239	0.163	0.212
Mg		0.904	0.933	0.911	0.867	0.135	0.138	0.091	0.098
Mn		0.083	0.075	0.067	0.096	-	0.008	0.007	-
Na		0.009	0.016	0.015	0.022	0.086	0.073	0.157	0.119
K		1.863	1.921	1.85	1.904	1.817	1.745	1.742	1.783
#mg		0.20	0.21	0.21	0.19	0.36	0.36	0.35	0.32

#mg = Mg/(Fe + Mg + Mn); b.d.l.—below detection limit.

) and biotite (#mg = 0.19–0.21; Ti ~0.38 a.p.f.u.; Table 1), which is locally chloritized. Accessory minerals are ilmenite, REE-rich epidote (

Table 2. Selected microchemical analyses and crystal chemical formulae of epidote and ilmenite from Pluskawka (Pl 2) microgranite.

		Epidote (Ep)			Ilmenite (Ilm)
Compound	LoD	Ep-1	Ep-2	Ep-3	Ilm-1	Ilm-2
Nb2O5 (wt.%)	0.10	-	-	-	0.36	0.25
SiO2	0.02	32.15	33.84	33.27	0.04	0.03
TiO2	0.04	0.15	0.56	0.13	50.99	50.82
ThO2	0.07	0.23	0.31	0.17	-	-
UO2	0.01	b.d.l.	0.01	0.03	-	-
Al2O3	0.03	19.74	20.11	20.13	b.d.l.	b.d.l.
Fe2O3	0.10	11.76	10.91	11.19	11.69	10.67
V2O3	0.05	-	-	-	0.07	0.15
Y2O3	0.06	0.77	1.43	1.25	-	-
La2O3	0.04	4.46	2.99	3.25	-	-
Ce2O3	0.06	9.54	7.24	8.05	-	-
Pr2O3	0.28	0.77	0.99	0.73	-	-
Nd2O3	0.40	3.30	3.54	3.46	-	-
Sm2O3	0.20	0.55	0.85	0.46	-	-
Gd2O3	0.18	1.39	1.56	1.61	-	-
FeO	0.10	-	-	-	26.01	27.13
MnO	0.10	1.28	1.67	1.62	9.87	10.04
ZnO	0.02	-	-	-	0.06	0.10
MgO	0.02	0.08	0.08	0.06	-	-
CaO	0.04	11.49	10.91	11.77	-	-
Na2O	0.03	0.04	0.15	0.04	-	-
H2Ocalc	-	1.65	1.69	1.65
Total		99.35	98.84	98.87	99.09	99.19
crystal-chemical formulea based on
		25 O2−			6 O2−
Nb (apfu)		-	-	-	0.009	0.006
Si		5.828	6.016	5.851	0.002	0.002
Ti		0.021	0.075	0.017	2.000	1.909
Th		0.010	0.013	0.007	-	-
U		0.000	0.000	0.001	-	-
Al		4.217	4.213	4.301	-	-
Fe3+		1.604	1.459	1.527	0.311	0.289
V		-	-	-	0.002	0.006
Y		0.074	0.135	0.121	-	-
La		0.298	0.196	0.217	-	-
Ce		0.633	0.471	0.534	-	-
Pr		0.051	0.064	0.048	-	-
Nd		0.215	0.225	0.224	-	-
Sm		0.034	0.052	0.054	-	-
Gd		0.084	0.092	0.970	-	-
Fe2+		-	-	-	1.246	1.252
Mn		0.197	0.251	0.248	0.436	0.442
Zn		-	-	-	0.002	0.004
Mg		0.021	0.020	0.017	-	-
Ca		2.233	2.077	2.287	-	-
Na		0.015	0.054	0.014	-	-
ΣREE		1.315	1.100	2.047	-	-

) and zircon. The equilibrium temperature of ternary feldspar is in the range of 392 °C to 455 °C (according to the Fuhrman and Lindsley model, [33] was (

Table 3. Modal composition and temperature estimate obtained using the Fuhrman and Lindsley [33] ternary feldspars geothermometry for feldspars from the exotic block from Pluskawka microgranite (Pl 2).

Feldspar Type/Composition	Ab	Or	An
K-feldspar and plagioclase
plagioclase original/adjusted	0.822/0.808	0.008/0.010	0.163/0.182
alkali feldspar original/adjusted	0.031/0.100	0.904/0.899	0.004/0.001
Concordant temperature [°C]	412	412	412
Average temperature [°C]	412
plagioclase original/odjusted	0.828/0.806	0.011/0.020	0.153/0.175
alkali feldspar original/adjusted	0.076/0.116	0.894/0.883	0.002/0.001
Concordant temperature [°C]	426	470	470
Average temperature [°C]	455

), assuming 200 MPa pressure.

This granitoid is weakly peraluminous (ASI = 1.065;

Table 4. Chemical composition and selected petrological indices of the whole-rock samples of crystalline exotic blocks from the Pluskawka Stream.

		PLUSKAWKA
Sample No.	LoD	Pl 2	And-J	And-C
SiO2 (wt.%)	0.01	76.8	64.91	58.11
TiO2	0.01	0.1	0.54	0.73
Al2O3	0.01	12.7	12.22	17.75
Fe2O3T	0.04	1.02	3.50	5.82
MnO	0.01	0.03	0.06	0.07
MgO	0.01	0.12	0.39	0.49
CaO	0.01	1.04	5.75	3.18
Na2O	0.01	3.19	2.93	4.13
K2O	0.01	4.49	3.45	5.38
P2O5	0.01	0.03	0.25	0.35
LOI	-	0.25	5.90	3.80
Total		99.77	99.90	99.81
Sr	0.5	72.5	218.00	275.60
Ba	1.0	593.00	714.00	1000.00
Rb	0.1	169.7	40.20	59.90
Th	0.2	17.10	12.00	16.60
U	0.1	5.10	3.50	2.60
Ga	0.5	13.40	12.30	17.00
Ni	0.1	1.10	20.00	32.00
Cr	5.0	-	62.00	90.00
Zr	0.1	96.00	138.10	196.30
Hf	0.1	3.30	3.30	4.90
Y	0.1	20.30	10.20	13.90
Nb	0.1	7.80	11.90	16.30
Ta	0.1	0.90	0.80	1.30
La	0.1	35.10	52.80	75.30
Ce	0.1	65.20	89.50	123.80
Pr	0.02	7.10	9.99	14.00
Nd	0.30	26.50	35.30	49.00
Sm	0.05	4.48	5.27	7.12
Eu	0.02	0.43	1.27	1.68
Gd	0.05	4.05	3.53	4.79
Tb	0.01	0.65	0.41	0.56
Dy	0.05	3.86	1.96	2.86
Ho	0.02	0.73	0.35	0.50
Er	0.03	2.06	0.96	1.42
Tm	0.01	0.3	0.13	0.18
Yb	0.05	2.27	0.92	1.17
Lu	0.01	0.32	0.14	0.19
ASI		1.07	0.66	1.01
Rb/Sr		2.34	0.18	0.22
#mg		0.32	0.31	0.25
Nd/Th		1.55	2.94	2.95
ΣREE		153.05	202.53	282.57
Eu/Eu*		0.31	0.90	0.88
CeN/YbN		7.54	25.55	27.79
TZr [°C]		758	N.A.	N.A.

#mg = Mg/(Fe + Mg + Mn).

), plotting on the high-K–calc-alkaline trend and within the volcanic arc granite field (Figure 3a,b).

The granite yields a relatively low Zr saturation temperature (758 °C), high Rb/Sr ratio (2.34) and low Th/U ratio (3.35; Table 3). Chondrite (C1)-normalized REE patterns are characterized by a distinct negative Eu anomaly (Eu/Eu* = 0.31) and weak REE fractionation (Ce_N/Yb_N = 7.54; Table 4; Figure 4a). On a primitive mantle-normalized multi-element plot, enrichment in large ion lithophile elements (LILE) and negative Ti and P anomalies are noted (Figure 4b).

4.1.2. Andesite

Two samples (And-J and And-C), weighting approximately 10 kg each, were extracted from a 1.5 m in diameter block of andesite. Two different rock types were recognized in the samples—a light-grey variety with porphyritic texture and a dark-reddish, equigranular, fine-grained facies containing several small fragments of mudstone (1–3 cm in size). The mineral composition of both rock types is similar and consists of albitized plagioclase, chloritized biotite, spinel and sporadic remnants of pyroxene (Figure 2b) [38].

On a Zr/TiO₂ vs Nb/Y diagram [35], both samples plot within the trachyandesite field (Figure 3c). On a multi-element plot, Nb and Ta negative anomalies are noted (Figure 4b). Chondrite (C1)-normalized REE patterns show moderate fractionation (Ce_N/Yb_N = 26.8–29.15) and very flat Eu anomalies (Eu/Eu* = 0.88–0.90; Table 4; Figure 4a). Due to the secondary alteration, the relatively mobile LILE were not used for geochemical discrimination purposes.

The cathodoluminescence images of zircons and apatites are shown in Figure 5.

4.2. Zircon and Apatite Characteristics and U-Pb Dating

4.2.1. Microgranitoid

Zircon crystals from the fine-grained granite sample from Pluskawka Stream (Pl 2) are colorless, short-prismatic, with aspect ratios of 1:1 to 2:1. Cathodoluminescence imaging reveals the presence of magmatic oscillatory zoning, locally overgrowing inherited cores showing very weak luminescence. We undertook 22 spot analyses on 19 zircon grains (Figure 5a and Figure 6a). Seven magmatically zoned grains yielded a concordia age of 293.2 ± 4.1 (MSWD = 0.31; Figure 6b,c). Five subconcordant Neoproterozoic ²⁰⁶Pb/²³⁸U ages ranging from 587 Ma to 659 Ma were detected in both inherited cores and single crystals; older ²⁰⁶Pb/²³⁸U ages of 1138 Ma, 1471 Ma, 1856 Ma, 1973 Ma, 2001 Ma, 2003 Ma, 2574 Ma were also found in both inherited cores and single crystals (

Table 5. LA-MC-ICP-MS U–Pb zircon data from Pluskawka microgranite and andesite.

Sample No.	Pb207/U235	2σ	Pb206/U238	2σ	Rho	207Pb/235U Age [Ma]	2σ	206Pb/238U Age [Ma]	2σ	U [ppm]	Th [ppm]	Th/U
Microgranitoid
Magmatic zircon crystals—Variscan
PL2_1	0.335	0.026	0.0449	0.0019	0.024733	293	10	283.4	7.1	219	384	1.75
PL2_2	0.341	0.026	0.0472	0.0019	0.19609	297	10	297.4	6.3	202	262	1.42
PL2_4	0.323	0.028	0.046	0.0019	0.14079	282	14	289.7	6.5	124.2	213	1.71
PL2_6	0.338	0.034	0.0472	0.002	0.11162	301	19	297.3	7.3	69.1	84	1.22
PL2_10	0.343	0.03	0.0461	0.0019	0.096029	299	15	290.5	6.5	322	691	2.15
PL2_13	0.329	0.029	0.0468	0.0019	0.011323	290	15	294.6	6.5	151.2	374	2.47
PL2_19	0.367	0.035	0.0474	0.002	0.23971	318	19	298.7	6.7	176.3	260.9	1.48
Concordia age = 293.2 ± 4.1 Ma; MSWD = 0.31
Inherited zircon crystals—Neoproterozoic
PL2_3	0.94	0.068	0.1074	0.0042	0.1809	673	15	659	11	227	157	0.69
PL2_16	0.804	0.067	0.097	0.004	0.22032	597	24	596	13	64.8	40.4	0.62
PL2_18	0.854	0.071	0.0989	0.0047	0.25292	632	21	608	19	284.9	129.2	0.45
PL2_20 *	0.932	0.079	0.0953	0.0045	0.82171	673	27	587	18	301.2	302.6	1.00
PL2_22 *	0.903	0.068	0.0935	0.0042	0.47181	662	22	576	16	423	150.8	0.36
Inherited zircon crystals–Archean
PL2_7	6.376	0.42	0.3646	0.013	0.51946	2028	10	2003	21	427	410	0.97
PL2_8	5.628	0.38	0.3339	0.013	0.67559	1921	13	1856	27	392	318	0.81
PL2_9	6.403	0.43	0.3641	0.014	0.59429	2031	12	2001	22	563	665	1.18
PL2_11 *	8.68	0.68	0.358	0.017	0.86632	2299	39	1973	54	117	157	1.34
PL2_14 *	5.93	0.44	0.2566	0.011	0.83782	1961	30	1471	33	229	39.6	0.17
PL2_17	12.36	0.83	0.491	0.019	0.63744	2634	14	2574	31	658	376	0.57
PL2_21	2.155	0.17	0.1932	0.011	0.64341	1165	28	1138	45	469	119.4	0.25
Andesite
Rims—Variscan
And_9	0.343	0.025	0.0493	0.0011	0.2744	310.2	6.9	299.4	21.8	111.2	200.7	1.81
And_12	0.373	0.021	0.049	0.0012	0.1797	308.4	7.6	321.9	18.1	73.8	114.8	1.56
Concordia age = 310 ± 4.9 Ma; MSWD = 0.22
Inherited cores and crystals—Neoproterozoic
And_15	0.751	0.043	0.0904	0.0025	0.1835	557.9	15.4	568.8	32.6	38.3	29.55	0.77
And_5	0.834	0.041	0.1003	0.002	0.1204	616.2	12.3	615.8	30.3	61.4	50.5	0.82
And_6	0.84	0.043	0.1018	0.0027	0.1315	624.9	16.6	619.1	31.7	113	52	0.46
And_7	0.833	0.045	0.0979	0.0022	0.1854	602.1	13.5	615.3	33.2	45.8	25.65	0.56
And_8	0.881	0.04	0.1036	0.0028	0.3205	635.5	17.2	641.5	29.1	60.7	42.6	0.70
And_16	0.812	0.034	0.1017	0.0021	0.2615	624.4	12.9	603.6	25.3	104.4	80	0.77
And_17	0.864	0.04	0.0988	0.0032	0.2590	607.4	19.7	632.3	29.3	73.6	76.5	1.04
Concordia age = 618.4 ± 8.3 Ma; MSWD = 0.18
And_1	1.025	0.044	0.1171	0.0024	0.2701	713.9	14.6	716.4	30.8	71.4	107.6	1.51
And_2	1.033	0.038	0.1175	0.0024	0.2079	716.2	14.6	720.4	26.5	73.4	115.5	1.57
And_3	1.04	0.039	0.1176	0.0024	0.3231	716.7	14.6	723.9	27.1	74.3	115.8	1.56
Concordia age = 716.9 ± 7.3 Ma; MSWD = 0.66
Inherited zircon crystals—Archean
And_4	13.36	0.25	0.4982	0.009	0.4992	2606.1	47.1	2705.4	50.6	206.6	183.9	0.89
And_10	11.4	0.36	0.441	0.013	0.6003	2355.1	69.4	2556.4	80.7	61.4	83.4	1.36
And_11	5.626	0.084	0.2261	0.004	0.3906	1314.0	23.2	1920.1	28.7	1095	113	0.10
And_13	17.48	0.29	0.5863	0.0098	0.7073	2974.4	49.7	2961.6	49.1	775	485	0.63
And_14	16.46	0.56	0.564	0.019	0.6219	2883.1	97.1	2903.9	98.8	413	278	0.67

; Figure 6a).

Apatite crystals are clear, translucent and idiomorphic hexagonal prisms, with aspect ratios ranging from 1.5:1 to 2.5:1 and long axes ranging from 100 to 250 µm (Figure 5b). We undertook 54 spot analyses on 42 apatite crystals. They are chemically zoned and rich in Mn (381–1317 ppm), Sr (656–3449 ppm), zoned with respect to REE, with ∑_REE ranging from 3 192 ppm to 13 246 ppm (at rims and in cores, respectively) (Table S1). Their chondrite (C1)-normalized REE patterns show LREE enrichment (Ce/Yb = 12.7–99.9) and mostly negative Eu anomalies (Eu/Eu* = 0.21–0.87, with one exception at 1.43; Table S1; Figure 4a). Our 54 analyses from 42 grains yielded an unanchored Tera–Wasserburg lower intercept age of 290.2 ± 5.6 Ma with a ²⁰⁷Pb/²⁰⁶Pb initial ratio of 0.839 ± 0.0050 (MSWD = 1.16; Figure 6d; Table S2). The apatite grains plotted close to the intersection of the mafic I-type, alkaline and ultramafic fields on a Sr/Y vs ∑_LREE biplot [39], with the majority of the grains plotting just inside the alkaline field.

4.2.2. Andesite

Nine zircon crystals from the andesite facies lacking visible mudstone clasts (And) were analyzed. The zircons are subhedral to anhedral, short-prismatic, with aspect ratios ranging from 1:1 to 2:1. We carried out 17 spot analyses (Table 5). Six analyses from magmatically zoned crystals (Figure 5c) showing moderate luminescence yielded a concordia age of 618.4 ± 8.3 Ma (Figure 6e,f). One zircon crystal with a homogeneous internal structure and weak luminescence yielded an age of 560.2 ± 13.7 Ma. One crystal exhibited homogeneous weak luminescence, typical of metamorphic zircon crystals; 3 analyses located within this grain yielded concordant age of 716.9 ± 7.3 Ma. Cathodoluminescence imaging reveals the presence of two inherited cores, mostly with weak luminescence, and these yield concordant ages of 2958 and 2907 Ma, as well as discordant ages (Figure 6e, Tables S1 and S2). Two CL-bright, magmatically zoned rims which are 20 to 40 µm thick (Figure 5) yielded an age of 310 ± 4.9 Ma (Table 5).

5. Discussion

5.1. Petrogenetic Interpretation

The microgranite and andesite from Pluskawka share a volcanic arc affinity and positive Th and negative P and Ti anomalies on a primitive-mantle-normalized multi-element diagram (Figure 3b and Figure 4b). These characteristics imply a crustal origin for the parent magma for both rock types. This is supported by the negative εNd²⁹³ value (−5.5,

Table 6. Whole-rock Rb-Sr and Sm-Nd isotopic composition of the Pl 2 microgranite. T_DM calculated according to Liew and Hofmann [50] procedure.

Scheme 147.	Sm [ppm]	Nd [ppm]	147Sm/144Nd	143Nd/144Nd	±	εNd316	TDM
Pl 2	4.48	26.5	0.102196	0.512175	0.000003	5.50	1.45

) and T_DM age of 1.45 Ga (Table 6) for the microgranite. This Nd isotope systematics are typical of granitoid rocks of the European Variscan belt and are interpreted to represent the Archean/Neoproterozoic basement that melted during Variscan orogenesis [40,41]. The mixed Paleoproterozoic /Neoproterozoic protolith is inferred from the U-Pb ages of inherited zircon crystals from the microgranite (PL 2) and andesite (AND), which both show Neoproterozoic and Paleoproterozoic (>2000 Ma) age ranges (Table 5). However, it may be unwise to assume that these samples represent Variscan magmatic rocks of volcanic arc affinity, as the geochemical characteristics could also have been inherited from the protolith ([42] and references therein). The very similar zircon and apatite ages (Figure 6) in microgranite sample Pl-2 (293.2 ± 4.1 Ma and 290.2 ± 5.6 Ma) imply very rapid cooling from crystallization temperatures to temperatures below the apatite closure temperature window (c. 450 °C) and thus support a hypabyssal origin.

5.2. Implications for Paleozoic Paleogeology

The analyzed rocks represent Late Carboniferous–Permian bimodal volcanic–plutonic activity (Figure 3a,b). The samples show lithological, geochemical and age similarities to the magmatic rocks from the Kraków–Lubliniec tectonic zone [36,41,43] as well as to the Carboniferous–Permian intraplate volcanic rocks that are widespread in the Romanian Moesia [43]. As the exotic blocks represent the basement that was eroded during the uplift of the Subsilesian Ridge, we assume that these magmatic rocks continued in the Protocarpathians to both the north-west and south-east (Figure 7).

The lineament connecting Tenczynek, Pluskawka and Moesia is related to the southeastern extension of the Kraków–Lubliniec tectonic lineament as well as to the boundary between the Brunovistulia and Małopolska blocks [41,42,43,44,45]. According to Mazur et al. [46], this zone formed during the latest Carboniferous–Permian transtensional tectonic activity, contemporaneous with the Liplas–Tarnawa pull-apart basin located south of Kraków [47]. This lineament cuts across the Variscan structures within the Neoproterozoic basement of central Pangea (Figure 7). The Protocarpathian region is characterized by the Neoproterozoic basement overlain by Upper Paleozoic sedimentary sequences, similar to the Brunovistulia and Małopolska massifs [5,48,49]. As was previously mentioned, the other analyses of the Subsilesian exotics indicate the prevailing Neoproterozoic (Cadomian) age of the substratum in this area [5,13,14].

The Neoproterozoic rocks of the Protocarpathian basement were the source for the Variscan magmas formation, which subsequently was emplaced within this Late Variscan transpressional zone. The occurrence of the Late Paleozoic magmas is probably limited to this transpressional zone. The Neoproterozoic Outer Protocarpathian basement adjacent to the Laurussian margin was covered by the Paleozoic sedimentary rocks, including Carboniferous coal-bearing strata (Figure 7) [50,51,52,53,54,55]. The Central Pangean Mountain Belt [54] was located west of the Outer Protocarpathian area (Figure 7). It included the Central Carpathian collisional zone

5.3. Implications for Cretaceous–Paleogene Paleogeology

Epicontinental sedimentation continued in the Outer Protocarpathian region during Permian to Jurassic times [53]. The Protosilesian back-arc basin, containing syn-rift, post-rift and synorogenic deep-water sedimentary sequences was initiated during Late Jurassic times [3,18,54]. There is no evidence indicating the oceanic crust within this back-arc basin. The northward movement of the Central Carpathian plate, part of the larger ALCAPA (ALpine-CArpathian-PAnnonian) plate, caused progressive inversion and emergence of ridges during the Late Cretaceous. These ridges separated a series of newly formed basins [3,18,56]. The Subsilesian Ridge (Figure 8) separated the Silesian and Skole basins, which were later inverted to form the Silesian and Skole Nappes.

The Subsilesian Ridge, the source of the exotic clasts, was surrounded by a slope region characterized by mixed pelagic and turbiditic sedimentation that corresponds to the Subsilesian Sedimentary Zone. The large size of these blocks (more than 1 m in diameter, locally up to some tens of meters or even more than 100 m in diameter—see [14])—indicates short transport distances and intense tectonic activity during the deposition of the host Campanian–Maastrichtian grey marls [57] on the slope of the Subsilesian Ridge. This tectonic activity may have triggered earthquakes (see e.g., [58]) and produced mélange complexes.

This transpressional tectonic zone (Żegocina Zone) is regarded as a segment of the Kraków–Moesia fault zone in the basement and indicates rejuvenation of an older Paleozoic tectonic lineament. The position of the Żegocina Zone 100 km south of Kraków (see also [51]) and its link to the Kraków–Moesia lineament allow for a more precise palinspastic reconstruction of the Late Cretaceous–Paleocene Outer Carpathian basins (Figure 8). The suggested orientation of the Subsilesian Ridge (Figure 8) is consistent with the geometry of the Skole Basin that is quite narrow south of Kraków yet wide in eastern Poland, Ukraine and Romania [12,18,52,56]. According to Kováč et al. [59], two units related to the Subsilesian Nappe existed during Paleogene times: the Subsilesian Basin and the Subsilesian Ridge. The orientation of their ridge is similar to our paleogeography (Figure 8). According to Golonka et al. [18], the Subsilesian Ridge and slope constituted the Subsilesian Sedimentary Area. The Pluskawka exotics were deposited within the marly facies in the Subsilesian Sedimentary Area/Subsilesian Basin located next to the European Platform with Neoproterozoic basement. This area was situated around 100 km south of Kraków. It moved and now is about 30 km south of Kraków.

6. Conclusions

• Exotic blocks of Late Carboniferous–Permian magmatic rocks are found in Campanian–Maastrichtian grey marls of the Subsilesian Nappe. This magmatic activity is also found outside the Carpathian Belt and can be linked to a Late Paleozoic transtensional zone, which is a continuation of the Lubliniec–Kraków Zone that extends under the Carpathians to Moesia.
• This Late Paleozoic transtensional zone was probably reactivated during the Late Cretaceous under a transpressional regime within the Żegocina tectonic zone, which caused the uplift of the Subsilesian Ridge and intensive erosion.