Petrology and geochemistry of granitoids and their mafic micogranular enclaves (MME) in marginal part of the Małopolska Block (S Poland)

Abstract

Granitic plutons (the Dolina Będkowska valley and Pilica area) were found in a few boreholes in the Małopolska Block (MB). These granitic rocks may represent apical parts (apophyses) of a great magmatic bodies (batholiths) located in deeper level of the Ediacaran/Paleozoic basement. They are described as 'stitching intrusions', generated during/after collision in Carboniferous/Permian period (~300 Ma) between the Upper Silesian Block (USB) and the Małopolska Block (MB). These rocks are fresh, unaltered granodiorites that are pale grey in colour. They have holocrystalline, medium-to coarse-grained structure and massive texture. For the first time, several mafic microgranular enclaves (MME), varying in size and colour, were found in the granodioritic host (HG). The occurrence of MME in the host granodioritic rocks is evidence of a mingling process between mafic and felsic magmas. The MME are pale/dark grey in colour, fine-grained rocks with 'porphyritic' textures. They consist of large megacrysts/xenocrysts of plagioclase, quartz, alkali feldspars and the fine-grained groundmass of pseudo-doleritic textures (lath-shaped plagioclases, blade-shaped amphiboles/biotites). According to their modal/mineral composition, they represent Q-diorites and tonalites. The MME, similar to the host granodiorites (HG), are I-type rocks, exhibit high Na2O content >3.2 wt%; normative diopside or normative corundum occurs (mainly <1%). They are metaluminous to slightly peraluminous (ASI <1.1) and have calc-alkaline, medium-K to high-K character. They generally belong to magnesian series (#Mg=0.20-0.40) and have low agpaitic index (<0.87). They are low evolved magmatic rocks. The rocks studied are enriched in LREEs (La, Ce, Sm) compared to HREEs. The Eu* negative anomaly and high Sr contents point to varying degrees of plagioclase fractionation connected to the mixing process rather than simple fractional crystallization. Both rocks studied (HG and MME) are characterized by a high content of LILEs (K, Ba, Rb) in normalized patterns and a low HFS/LIL elements ratio (Ta, Nb)/(K, Rb, La). The projection points of the rocks 4 studied plot in different fields of various petrochemical diagrams: mainly in the arc granites that are rare in the pre-collisional granites as well as the syn-subductional to post-collisional granites fields. For the first time, inner textures in rock-forming minerals related to mixing processes are described both in the granodioritic host (HG) and in the MME. Mantled boxy cellular plagioclase megacrysts with 'old cores' of labradorite composition, and amphibole aggregates with titanite and opaque minerals, represent peritectic rather than primary residual minerals. The plagioclase, quartz and alkali feldspar megacrysts/xenocrysts were mechanically transferred from the granodioritic host (HG) to MME. The presence of lath-shaped plagioclases, blade-shaped amphiboles/biotites and acicular-shaped apatites in the groundmass of the MME is evidence of undercooling of hot mafic blobs in a relatively cold granodioritic magma ...

Cogenetic origin of mafic microgranular enclaves in calc-alkaline granitoids: The Permian plutons in the northern North China Block

“…There is an essential need for caution in using the MMEs as evidence for crustal-mantle interaction or mixing and/or mingling between crustal-derived felsic and mantle-derived mafic magmas during formation of granitic rocks, especially where no independent evidence is found for such a process. In some previously studied granitoid plutons with enclaves that are in the intermediate composition range and exhibit similar mineral assemblage and isotopic compositions (e.g., Holden et al, 1991;Barbarin and Didier, 1992;Sergi, 1997;Asrat et al, 2004;Barbarin, 2005;Kaygusuz and Aydınçakır, 2009;Turnbull et al, 2010;Wolska, 2012;Xiong et al, 2012), the role of MMEs in evaluating the mixing and/or mingling processes between crustal-derived felsic and mantle-derived mafic magmas may have been overestimated. Instead, the MMEs in this setting can provide valuable information on emplacement mechanisms and incremental growth of granitoid plutons in continental crust (e.g., Paterson et al, 2003Paterson et al, , 2004Donaire et al, 2005;Paterson, 2005, 2010;, 2013Barbey et al, 2008;Economos et al, 2009;Caricchi et al, 2012;Zhang and Zhao, 2013).…”

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

“…During the Carboniferous to Permian, there was extensive plutonic and volcanic activity in the Małopolska and Brunovistulian terranes along the Kraków-Lubliniec regional fault zone. This Kraków-Lubliniec igneous belt comprises deepseated, calc-alkaline, granodiorite-diorite to quartz monzonite-monzogranite intrusions (e.g., Wolska 2012 and references therein) and a bimodal suite of sub-volcanic and volcanic rocks represented by mafic-intermediate (trachybasalts-trachyandesites with minor lamprophyres) and felsic (dacites-trachydacites-rhyolites) rocks (Ryka 1974;Wolska 1984;Heflik et al 1992;Słaby 1987;Muszyński 1991Muszyński , 1995Muszyński and Pieczka 1996;Muszyński and Czerny 1999;Truszel et al 2006;Żelaźniewicz et al 2008;Słaby et al 2010;Wolska 2012). It is likely that the bimodal igneous suite formed from magmas is derived from different types of sources, some of which might have been evolved by fractional crystallization (e.g., Czerny and Muszyński 1997).…”

“…Granitoids with extrusive rocks have been intersected in about 260 boreholes. Granitoids from the boreholes are metaluminous to slightly peraluminous (ASI < 1.1), I-type rocks of calc-alkaline, medium-to high-K character (Wolska 2012, and references therein) with high Na 2 O content (> 3.2 wt%) and normative diopside and corundum (mainly < 1%). Most are multiphase intrusions into a variety of rocks ranging in age from Precambrian to late Carboniferous.…”

“…Several of the analysed samples were highly altered and mineralized (PZ11/24, KH2/13, RK2/37, DB4/10, 25WB/26, 25WB/27 and KO4/15), excluding them from being plotted on the geochemical diagrams presented here. In the following diagrams, the compositions of the least altered samples are compared with those of igneous rocks collected by other researchers from boreholes (Ryka 1974;Muszyński 1991;Wolska 2012) and outcrops in the southern part of the KLFZ (Słaby et al 2010) (Appendix 2). According to Słaby et al (2010), the data for the felsic and intermediate suites from the KLFZ indicate two different unrelated trends which show a negative correlation with SiO 2 (Appendix 3).…”

“…Our lamprophyre and diabase samples have alkaline and shoshonitic characteristics with a range of K 2 O, Fe 2 O 3 and transition element (Cr, V, Ni and Co) contents (Table 2). Chemical compositions of our least altered granodiorite samples are plotted on Harker diagrams for the major oxides (Appendix 3a-g) for comparison with granitoid compositions reported by Wolska (2012) and Żelaźniewicz et al (2008). These plots show negative correlations with SiO 2 for Pearce et al (1984), the felsic igneous rocks plot in the island arc (VAG) and syn-collisional (syn-COLG) granite fields (Fig.…”