Carboniferous–Permian magmatism and Mo–Cu (W) mineralization in the contact zone between the Małopolska and Upper Silesia Blocks (south Poland): an echo of the Baltica–Gondwana collision

Abstract

The Kraków-Lubliniec tectonic zone (KLFZ) in southern Poland, which divides the Małopolska Block (MB) from the Upper Silesia Block (USB), is a portion of the SW margin of the Trans-European Suture Zone. Zircon U-Pb dating of a variety of igneous rocks (granodiorites, dacites, lamprophyre and diabase) from the subsurface Kraków-Lubliniec igneous belt along the KLFZ shows that magmatism spanned within a narrow time period (ca. 10 Ma) between 303.8 ± 2.2 and 292.7 ± 4.9 Ma. The earlier magmatism (303.8 ± 2.2-294.7 ± 2.3 Ma) was felsic calc-alkaline, and the contemporaneous or/and slightly later alkaline volcanism (294.4 ± 4.9-292.7 ± 4.9 Ma) was of mafic-intermediate composition. The felsic rocks (granitoids and dacitoids) are weakly peraluminous, medium to high K, moderate Mg# (0.39-0.46), weakly evolved and I-type rocks. Due to the intensive development of hydrothermal alteration, these rocks are commonly strongly altered and locally mineralized by porphyry and other types of Mo-Cu (W) ores that are closely related to the felsic magmatism in space and time. The zircon U-Pb dating yielded ages which are similar to the previously measured Re-Os ages of molybdenites from the KLFZ. Felsic magmatism at the Myszków Mo-Cu-W deposit yielded ages in the range 301.0 ± 2.1-295.9 ± 2.9 Ma. The youngest rocks dated are from the Mysłów area in the USB-volcanic alkaline rocks (lamprophyre and diabase) of shoshonitic character, with low Mg# (0.49 and 0.69, respectively) and Ni contents (< 62 ppm), indicative of a relatively juvenile magma composition. Inherited zircon cores, remnant detrital zircon from a sediment component in the source rocks, were dated to be ranging from ca. 2775 to 575 Ma. Inheritance of ca. 600 Ma (Cadomian basement) and ca. 1.40 Ga (Mesoproterozoic) is common in the rocks from both blocks, but those from the MB contain additional inheritance with dates of 2.78-2.67 and 2.05-1.92 Ga, both ages characteristic of zircon from the Svecofennian of northern Europe (Baltica). The inherited zircon from the youngest alkaline rocks provided evidence for Mesoproterozoic (ca. 1.55-1.44 and 1.09 Ga) and Palaeoproterozoic (1.96 Ga) thermal events in the USB, and its possible affinity to Avalonian cratonic crust as a source for its igneous protolith. U-Pb isotopic studies of zircons from KL igneous belt indicate its inherited signatures from the crustal sources and magma emplacements during the KLFZ wrenching which allowed channels and room for magma emplacement along the MB and USB in upper Carboniferous-lower Permian on SW margin of the East-European Craton. Mo-Cu (W) ore mineralization, associated with the ~ 300 Ma felsic magmatism, represents rather the product of decompression melting induced in the areas of decreased pressure, undergone in the regional wrench fault zones than the classic Mo-Cu porphyry-style mineralization.

A reappraisal of K-Ar and new U-Pb age data for felsic rocks in the vicinity of the Kraków-Lubliniec Fault Zone (southern Poland)

“…These in her ited zir cons are rare and there is no clear age pat tern to ex plain rea son ably their or i gin. Mikulski et al (2019) tried to re late in her ited age val ues from the Ma³opolska Block, i.e. those much "older" zir con re sults, to the de vel op ment of Baltica.…”

“…Bore hole cores from four bore holes were se lected for this study: PZ-10, PZ-13, Z-13 and WB-115. Their lithological logs can be found in Nawrocki et al (2010) and Mikulski et al (2019). In these bore holes, mag matic rocks oc cur as com plex bod ies some hun dreds to >1000 metres thick.…”

“…The de tailed petrographic char ac ter is tics of these rocks in the Up per Silesia Ba sin and ad ja cent re gions in Po land and Czech have been widely de scribed [e.g., Homola, 1960;Papalová and Tomšík, 1970;Martinec et al, 1994 and ref er - A-F -petrographic pro file of granitoids in the PZ-10 bore hole (depth from 412.4 to 1149.5 m); G, H -WB-116 sam ple; Q -quartz, Sk -feld spar, Bio -bi o tite, Se -seri cite ences therein; Markiewicz and Markowiak, 1998;Truszel and Karwowski, 2003;Markowiak, 2005;Truszel et al, 2006;Nawrocki et al, 2008 (diabases) and¯elaŸniewicz et al, 2008 (granitoids)]. The most re cent petrographic geo chem i cal descrip tion is by Mikulski et al (2019). The pres ent study con cerns dat ing by two meth ods: K-Ar on bi o tite (ar chi val de ter mi na tions; re-ap praised) and U-Pb SHRIMP on zir con.…”

“…Some re sults of SHRIMP U-Pb dat ing of the granodiorite from the WB-102A bore hole were also then reported (¯elaŸniewicz et al, 2008), and from the Zalas por phyry. More re cently, the age de ter mi na tion sum ma ries and SHRIMP U-Pb val ues were pub lished (Mikulski et al, 2019).…”

The Variscan foreland in Poland revisited: new data and new concepts

“…A chain of calc-al ka line granitoid in tru sions north-east of the fault was pre vi ously as cribed to a phase of subhorizontal ex tension and block up lift in the late Namurian and Westphalian (¯aba, 1999). The re cent ra dio met ric data, how ever, in di cate a later age, at ap prox i mately the Gzhelian-Asselian bound ary in ter val (¯elaŸniewicz et al, 2008;Mikulski et al, 2019) which sug gests post-orogenic em place ment.…”