Mechanisms of granite alteration into grus, Karkonosze granite, SW Poland

Catena 150 (2017) 230–245

Contents lists available at ScienceDirect

Catena journal homepage: www.elsevier.com/locate/catena

Mechanisms of granite alteration into grus, Karkonosze granite, SW Poland☆ Bartłomiej Kajdas a,⁎, Marek J. Michalik b, Piotr Migoń c a b c

Department of Soil Science and Soil Protection, University of Agriculture in Krakow, Mickiewicza 21, 31-120 Kraków, Poland Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, Kraków, Poland Institute of Geography and Regional Development, University of Wroclaw, pl. Uniwersytecki 1, 50-137 Wroclaw, Poland

a r t i c l e

i n f o

Article history: Received 9 August 2016 Received in revised form 21 November 2016 Accepted 23 November 2016 Available online xxxx Keywords: Grus Granite Clay minerals Weathering Hydrothermal alteration

a b s t r a c t Granitic gruses are usually considered as a product of deep weathering, but the influence of hydrothermal fluids was also noticed. In this work, a wide range of mineralogical and chemical methods performed on 43 samples from three representative outcrops and a reference site is used to determine the influence of hydrothermal and weathering fluids on the development of granitic gruses from the coarse grained Karkonosze granite. Four types of altered granites have been distinguished, including compact and friable granite, typical grus, and localized heavy altered zones. Mineralogical observations such as complete albitization of plagioclase and crystallization of secondary quartz revealed an important role of hydrothermal alteration at the early stage of grusification. The origin of smectite and alteration of biotite into muscovite are likely to be connected with circulation of hydrothermal fluids too. Grusification sensu stricto was primarily caused by vermiculitization of biotite which resulted in volumetric expansion and the development of transmineral microcracks with non-accordant pore surfaces. Thus, it requires hydrothermal alteration to be relatively minor, confined to postmagmatic changes, since more advanced alteration of biotite into muscovite rather than vermiculite arrests further development of microcracks and leads to the development of friable granite. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Among products of near-surface disintegration of crystalline rocks grus (also spelled gruss) is particularly common and has been reported from many localities worldwide and every climatic zone. The term was defined as fragmental product of in-situ granular disintegration of granitic rocks (Bates and Jackson, 1987) or, without too narrow regard to lithology, as a product of granular disintegration of parent rock. It contains mainly gravel- and sand-size grains, while the amount of silt and clay fraction is usually smaller than 25% by weight and the amount of clay itself is lower than 10% by weight. Gruses typically develop from medium to coarse granite and show rather small mineralogical and chemical alterations in comparison to the parent rock (Migoń and Thomas, 2002). However, an accumulation of poorly sorted quartz grains and clayey material derived from weathered granite was also subsumed under the term ‘grus’ (Goudie et al., 1994). Over the years, ideas of processes and mechanisms behind grus formation have evolved. Some authors considered granitic gruses as a product of physical weathering, either insolation (Johannsen, 1934) or frost weathering (Marchand, 1974). Although shallow grus mantles ☆ This work was supported by the Polish National Science Center [grant number N N307 426993]. ⁎ Corresponding author. E-mail address: [email protected] (B. Kajdas).

http://dx.doi.org/10.1016/j.catena.2016.11.026 0341-8162/© 2016 Elsevier B.V. All rights reserved.

can be produced from monomineral rocks (e.g. from marble) as a result of insolation (Eppes and Griffing, 2010; Siegesmund et al., 2000), the dominant thought since the work of Blackwelder (1933) was that the origin of metres-thick grus from granite was mainly caused by alteration of primary biotite and feldspars in granite (e.g. Blank, 1951; Clayton et al., 1979; Eggler et al., 1969; Isherwood and Street, 1976; Larsen, 1948; Ollier, 1965; Wahrhaftig, 1965). However, chemical alteration in grus is not profound as demonstrated by values of numerical indices applied to weathering. The values of Chemical Index of Alteration (Nesbitt and Young, 1989) for gruses range from 60 to 70, while the values for unweathered granitic rock are around 50. The Chemical Weathering Index (Sueoka, 1988) shows values from 15 to 20% for gruses and from 13 to 15% for unaltered granites. Changes in mineralogical composition are negligible too. Main differences between fresh granite and grus reside in the alteration of biotite connected with expansion of mica crystals (Dixon and Young, 1981; Eggler et al., 1969; Isherwood and Street, 1976; Pye, 1985; Wahrhaftig, 1965) and with neoformation of secondary iron oxides (Eggler et al., 1969; Evans and Bothner, 1993; Isherwood and Street, 1976; Pye, 1985; Wahrhaftig, 1965). Alteration, mainly sericitization, of core parts of plagioclase is also common (Clayton et al., 1979; Dixon and Young, 1981; Evans and Bothner, 1993; Isherwood and Street, 1976; Marchand, 1974; Wahrhaftig, 1965). K-feldspar is usually less altered and only slight signs of sericitization have been described (Clayton et al., 1979; Evans and Bothner, 1993; Isherwood and Street, 1976).

B. Kajdas et al. / Catena 150 (2017) 230–245

Abbreviations Outcrop symbols GL Głębock KS Kowary Średnie MI Miłów SP Szklarska Poręba Mineral abbreviations Ab albite An anorthite Ap fluorapatite Bt biotite Cer cerianite-(Ce) Chl chlorite Feox hematite or other unidentified Fe oxides FeTiox unidentified Fe-Ti oxides Flo florencite-(Ce) Kfs K-feldspar Ms. muscovite Mnz monazite-(Ce) Or orthoclase Pl plagioclase Qz quartz Rha rhabdophane-(Ce) Ser sericite Sme smectite Tiox unidentified Ti oxides Ttn titanite Vrm vermiculite Zrn zircon

Quartz does not show any chemical alteration, but may be cut by intramineral microfractures, which can produce angular shards (Dixon and Young, 1981). Secondary minerals present in granitic gruses are mainly limited to clay minerals, among which sericite, vermiculite, smectite and/or kaolinite are most common (Clayton et al., 1979; Dixon and Young, 1981; Eggler et al., 1969; Isherwood and Street, 1976; Marchand, 1974; Migoń and August, 2000; Pye, 1985; Wahrhaftig, 1965), but there are also descriptions of microfractures filled by quartz and carbonates (Evans and Bothner, 1993; Marchand, 1974). Although the majority of researchers considered grus as product of weathering, the considerable depth and homogeneity of this type of rock alteration prompted Dixon and Young (1981) to invoke interactions with hydrothermal fluids as possible mechanisms of the development of granitic grus. A similar view was presented by Evans and Bothner (1993). Mineralogical evidence for hydrothermal changes in the rock include the presence of hydrothermally originated minerals, e.g. albite or sericite in feldspar, chlorite besides biotite, secondary quartz and carbonates (Barboni and Bussy, 2013; Dixon and Young, 1981). The paper by Dixon and Young (1981) generated discussion (Ollier, 1983; Young and Dixon, 1983), illustrating that unequivocal separation between hydrothermal versus weathering changes may not be straightforward. Thus, the issue of weathering versus hydrothermal origin of grus, or the role of hydrothermal preconditioning in the development of grus, is still open and this paper aims to add to this discussion by looking anew at granite-derived gruses in the Karkonosze-Izera granite pluton in the south-western part of Poland. In terms of general relief (rolling topography with tors and boulders) and characteristics of weathering mantles there are similarities between the Bega Basin in south-east Australia, where Dixon and Young (1981) and Ollier (1983) discussed the origin

231

of grus, and the least elevated part of the Karkonosze-Izera plution, the Jelenia Góra Basin. The widespread presence of a near-surface zone of grusification, from just a few meters to N10 m thick, has been known since the early geological mapping of region (Berg, 1941). Subsequent descriptions have focused on geomorphological significance of grus and its relation to the origin of granite boulders and tors (Dumanowski, 1968; Jahn, 1962; Migoń, 1997). Much later, the focus shifted to mineralogy of grus (Migoń and August, 2000, 2001) and various, although invariably small, quantities of clay minerals such as smectite, vermicultite and kaolinite were identified. It was also emphasized that grus exposures are not homogeneous. Some reports provide excellent examples of corestone development within the alteration mantle, others show vertical or horizontal contacts between only faintly altered, slightly disintegrated granite and completely disaggregated grus, whereas in certain exposures, clear sub-vertical zones of heavily altered material occur, and they are distinctive macroscopically by colour, compactness, and the amount of clay (Migoń and August, 2000). Variability of alteration patterns within these outcrops suggests that various mechanisms of grusification may have operated, side by side or superimposed, and hence an opportunity arises to investigate pathways of grus development. In order to do so comprehensively, a range of analytical methods should be employed and in this paper we use several complementary analyses to infer the origin of grus. Consequently, the aims of this paper are to examine mineralogy, as well as chemical and isotopic composition of grus from three representative outcrops, to discuss evidence for supergene versus hydrothermal alteration, and to propose a scheme of grusification. 2. Geological setting The Karkonosze-Izera granite pluton is situated in the South-West region of Poland and North region of Czechia, and builds a part of the mountainous terrain of West Sudetes. The granite body is elongated from west to east, is ca. 70 km long and up to 22 km wide in N–S direction (Fig. 1). The age of the pluton was long regarded as Carboniferous, the emplacement taking place in the waning stages of the Variscan orogeny (Mierzejewski and Oberc-Dziedzic, 1990). More recent isotopic dating of the porphyritic granite variant yielded ages of 329 ± 17 Ma (Rb-Sr method; Duthou et al., 1991) or 318.5 ± 3.7 Ma (SHRIMP on zircons; Machowiak et al., 2008), whereas the fine-grained granite is younger, dating to 310 ± 14 Ma (Rb-Sr method). Latest age determinations rejuvenate the age of the porphyritic granite to the range between 313 ± 3.0 Ma and 307.8 ± 3.4 Ma (SHRIMP U-Pb ages of monazites and zircons; Kusiak et al., 2014) and Kryza et al. (2014) obtained an age of ca. 312 Ma (CA-ID-TIMS zircon ages). Textural variability in the Karkonosze-Izera granite was noticed already in the 19th century. Borkowska (1966) distinguished three varieties of granitic rocks: a) ‘ridge granite’ – medium to fine grained, b) ‘central granite’ – coarse to medium grained, porphyritic locally with K-feldspars up to 10 cm long, c) granophyric facies. More recent petrographic analysis of the Karkonosze granite (Słaby and Martin, 2005, 2008) allow us to narrow the number of facies to two: a) an equigranular, variety (the ‘ridge’ granite of Borkowska (1966) or the ‘crestal’ and ‘Harrachov’ granite of Žák and Klomínský (2007) and b) a porphyritic variety, mainly correlating with the ‘central’ and ‘granophyric’ granites of Borkowska (1966) or the ‘Liberec’ and ‘Jizera’ granite of Žák and Klomínský (2007) (Fig. 1). All samples collected for this study represent the porphyritic variety of the Karkonosze granite. Porphyritic granite contains big (4–5 cm on average) phenocrysts of pink, automorphic K-feldspar (often with small rim of white plagioclase and zones enriched in small crystals of biotite inside). Medium-grained background contains pink K-feldspar, white plagioclase, gray quartz and black biotite. Plagioclase crystals differ in chemical composition exhibiting zoning with a more calcic core surrounded by progressively more sodic rims (usually from An25 in the centre to An0 in the rim; Słaby et al., 2007). Biotite (annite) in

232

B. Kajdas et al. / Catena 150 (2017) 230–245

Fig. 1. Simplified geological map of the Karkonosze Pluton and its metamorphic envelope (after Žák and Klomínský, 2007). The circles indicate approximate location of outcrops. SP – quarry in Szklarska Poręba – Huta, GL – gravel pit in Głębock, MI – roadcut in Miłków, KS – gravel pit in Kowary Średnie.

Karkonosze granite is usually partially chloritized (Słaby and Martin, 2008; Wilamowski, 2002). Zircon, apatite, epidote group minerals (epidote, allanite, and pistacite), titanite and iron oxides are the main accessory minerals in porphyritic granite. In some coarse granular variants, hornblende occurs as a mafic mineral. Typical for the porphyritic granite is the presence of MME (microgranular mafic enclaves) and biotitic schlieren from a few to several cm thick (Mierzejewski, 2005; Słaby and Martin, 2008; Žák and Klomínský, 2007). Granites are often accompanied by thin (few mm to a few cm) aplite veinlets. Inside the aplite zones, it is possible to find simple pegmatite nests consisting of quartz and feldspars (Borkowska, 1966). Less common, but also present, are mafic veins of lamprophyres (Awdankiewicz, 2007).

Sampling strategy was dictated by the variability of altered granites as recognized in the field. Four main types of altered rock were distinguished, according to their toughness (Table 1): • compact granites (group I) – without any visible signs of weathering or weakening of the fabric, • friable granites (group II) – with fabric weakened to the degree that it is possible to crumble fairly large pieces of rock in a hand, • granitic grus (group III) – the primary texture of the rock is retained but the material is disaggregated and it is not possible to take a sample as a one piece, • highly altered zones (HAZ) which include thin veins and bodies of clayey material (typically up to 1 cm thick), present within granites of all types named above.

3. Study sites Three large outcrops of granite disintegrated into grus were sampled for mineralogical and geochemical analysis. Two of them, Miłków and Głębock, are located in the floor of the Jelenia Góra Basin – a large intramontane depression in front of the Karkonosze Mountains. The third site, Kowary Średnie, occupies the northern footslope of the Karkonosze Mts. In the working quarry in Szklarska Poręba Huta, samples of unweathered granite were collected and analyzed as reference material. Altogether, 43 samples were analyzed.

Macroscopically visible evidence of hydrothermal alteration such as intense chloritization, albitization of feldspars, hematitization of rock or crystallization of quartz veins, was identified in every investigated outcrop and inside granites classified as type I and II, but not within type III. The Miłków site (50°48′42″N, 15°46′10″E, altitude 430–440 m above sea level (a.s.l.); Figs. 1 and 2a) is considered as the most representative among all grus outcrops in the region, revealing various styles and degree of grusification in various parts of the exposure (Migoń and August, 2001). It is located at the foot and in the lower slope of an

Table 1 Degrees of granites grusification. Degrees of grusification

Group I Compact granite

Group II Friable granite

Group III Granitic grus

Highly altered zones

Types of alterations Number of analyzed samples

No visible signs of weathering; no clear weakening of fabric SPa–2; MI–2; MIhb–6 KS–1

Rock is so weakened, that fairly large pieces can be broken and crumbled in the hands MI–1; KS–4; GL–8

primary texture of the rock is still present in the outcrop MI–5; KS–6; GL–5

no recognizable rock texture, high amount of clay fraction MI–1; KS–1; GL–1

a b

Granites from Szklarska Poręba Huta quarry [SP] were used as a reference rocks. Hydrothermally altered granites from Miłków.

B. Kajdas et al. / Catena 150 (2017) 230–245

233

Fig. 2. Outcrops in a) Miłków and b) Kowary Średnie.

isolated residual hill, typical for the relief of the Jelenia Góra Basin. The outcrop is nearly 200 m long and up to 10 m high, with grus being dominant in the northern section, while much more compact granite is present in the remaining section. A sub-vertical fault zone separates the two parts, evidenced also by narrow zones of highly hydrothermally altered material. However, grus itself does not occur as a homogeneous mantle either. It contains frequent cores of slightly weathered or even unweathered granite (corestones), from 0.5 to 2 m long. Exfoliation transformed the original cubic compartments into rounded boulders (Fig. 2a). A highly altered vein of vogezite, 1 m thick, cuts grus in the northern section of the outcrop and is causally related to the late-magmatic stage. Fifteen samples were collected: two fragments of cores representing compact granite, a sample of friable granite from a brittle marginal zone of a corestone, five samples of granitic grus and one sample of clayey veinlet, and six samples of heavily altered granites from the northern part of the outcrop (Table 1). Samples were taken in batches of about 5 kg per sample. The Głębock site (50°49′12″N, 15°44′56″E, altitude 410–420 m a.s.l.; Fig. 1), an old gravel pit, occurs in a similar morphological setting at the foot of an elongated, low residual hill which owes its presence to higher resistance of microgranite veins, making the backbone of the N–S trending elevation. The outcrop takes half of the height of the slope and the maximum thickness of grus is 12 m. Two veins of microgranite, 1–2 m thick, cut the exposure, but otherwise grus is relatively homogeneous and does not show any corestones, so abundant in Miłków. Fourteen samples were collected: eight from friable granites, five from granitic gruses and one sample of clayey grus. In Głębock, compact granites were absent. Samples were taken horizontally in batches of about 5 kg per sample from both levels of the gravel pit. Grus at the Kowary Średnie site (50°46′59″N, 15°50′45″E, altitude 515–530 m a.s.l.; Figs. 1 and 2b), also an abandoned gravel pit, occupies a lower slope setting, which is about 30 m above the valley floor. As in Głębock, grus appears rather homogeneous, except in localized zones of considerable alteration containing clayey material. Cores of unweathered granite do not occur. The thickness of grus in the pit is 6 m, but exposures within the adjacent valley side demonstrate that the nearsurface zone of grusification may be as thick as 15 m. In fact, another outcrop at Krzaczyna, 3.3 km to the west and in the lower slope of the Karkonosze Mountains also reveals this thickness of grus. Twelve samples were collected: one from compact granite (with macroscopically visible signs of hydrothermal alteration), four from friable granites, six

samples of granitic gruses and one sample of clayey veinlets. Samples from this gravel-pit were taken in a similar manner as in other two outcrops, horizontally, in batches of about 5 kg per sample. Reference samples were collected from the only working granite quarry in the Polish part of the Karkonosze-Izera pluton, at Szklarska Poręba Huta within the valley side of the Kamienna river (50°49′38″N, 15°29′39″E, altitude 770–800 m a.s.l.; Fig. 1). Porphyritic facies of granite is subject to exploitation and the quarry depth is nearly 30 m. No signs of grusification, except for the very top section of the exposure, are present. Two homogenous samples on unaltered porphyritic granite were collected from the quarry face. 4. Analytical methods Samples were examined using a petrographic microscope Nikon ECLIPSE E600 POL, field emission scanning electron microscopy (FESEM) using a HITACHI S-4700 microscope coupled with a NORAN Vantage energy dispersive spectrometer in the Laboratory of Field Emission Scanning Electron Microscopy and Microanalysis at the Institute of Geological Sciences of the Jagiellonian University, Kraków, Poland, and Jeol JXA-8530F HyperProbe at the Centre for Experimental Mineralogy, Petrology and Geochemistry, Uppsala University, Sweden. Identification of main mineral phases was accomplished with X-ray Diffraction methods (XRD) using a Philips X'Pert APD diffractometer (Cu-Kα radiation generated at 40 kV and 30 mA by generator PW 1870, and equipped with a vertical goniometer PW 3020) and BioRad FTIR-Spectrometer FTS 135 at the Institute of Geological Sciences, Jagiellonian University, Kraków, Poland. Because the XRD analyses were qualitative, the proportion of minerals in samples were estimated from proportions of the height of diffraction peaks. Identification of clay minerals in friable granites and granitic gruses was performed using the procedure of separation of the clay minerals according to Jackson (1974) before XRD analyses. Chemical analyses of the whole rock samples were performed with Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) at Acme Analytical Laboratories, Vancouver, Canada. Statistical analyses of chemical data were performed using Canoco 5.0 software in Department of Soil Science and Soil Protection at University of Agriculture in Kraków. Principal Component Analysis (PCA) were based on the log-transformed [y = lg(1 ∗ x + 1)] chemical data (SiO2, Al2O3, Fe2O3, MgO, CaO, K2O, Na2O, TiO2 and LOI value).

234

B. Kajdas et al. / Catena 150 (2017) 230–245

Stable isotope (hydrogen and oxygen) ratios of selected samples (for both whole rock and clay fraction) were obtained at the Stable Light Isotope Laboratory at the Department of Geological Sciences of University of Cape Town, RSA. Detailed description of the analytical procedure can be found in Harris and Vogeli (2010) and Fourie and Harris (2011).

5. Results 5.1. Microcrack analysis Petrographic microscope observations of thin sections revealed that granites in different stages of compactness (compact granites, friable granites and granitic gruses) contain different sets of microcracks. In reference granites from Szklarska Poręba, only the intramineral microcracks are present (Fig. 3a). They are short, thin and do not continue between mineral grains. They do not affect the conciseness of the granite. Compact granites (group I), which do not show weakening of rock fabric but are present in the same outcrop as the grusified granites (e.g. samples from Kowary Średnie and Miłków), reveal the presence of chaotic, transmineral microcracks with accordant pore surfaces (cf.

definition of Risse by Beckmann and Geyger, 1967) in every sample (Fig. 3b). In some rocks classified as friable granites (group II), as well as in granitic gruses (group III), transmineral microcracks with non-accordant pore surfaces are present. Microcracks are much wider and may be partially or completely filled with iron oxides or clay minerals (usually stained by iron oxides; Fig. 3c–f). These types of fractures, which are usually continuations of mica cleavage planes, show the cleavage planes of altered (vermiculized) biotite and, less often, other primary mafic minerals. In samples of friable granites, where primary biotite is replaced by white mica, this type of microcrack does not occur. 5.2. Mineral composition XRD diffraction of bulk samples confirmed that analyzed granites and gruses, especially samples from Miłków, but also most of the samples of granitic grus from Kowary Średnie and Głębock, have mineralogical compositions typical for porphyritic granites (K-feldspar, quartz, plagioclase and biotite). Petrographic microscope observations and SEM-EDS analysis show that quartz and K-feldspar do not reveal distinct alterations in comparison to the reference granite. More significant differences are visible

Fig. 3. Microcracks in investigated granites and granitic gruses: a) lack of transmineral microcracks in reference granite from Szklarska Poręba (PPL); b) set of transmineral microcrack of 1st generation (black arrows) in compact granite from Miłków (PPL); c) initial development of secondary, vermiculitization induced transmineral microcracks (white arrows), older microckracks (black arrows) still visible, in friable granites from Miłków (XPL); d) microcracks (white arrows) originating in vermiculized biotite in granitic grus from Kowary Średnie (XPL); e) vermiculitization induced microcracks (white arrows) in feldspar from granitic grus from Głębock (XPL); f) microcracks (white arrows) parallel to cleavage planes of feldspar and vermiculized biotite from granitic grus from Głębock (XPL). Mineral abbreviations: Bt – biotite, Chl – chlorite, Kfs – K-feldspar, Pl – plagioclase, Qz – quartz, Ser – sericite, Ttn – titanite, Vrm – vermiculite.

B. Kajdas et al. / Catena 150 (2017) 230–245

within biotite and plagioclases. XRD analyses of bulk samples show that the amounts of biotite and plagioclase decrease with the progress of grusification. At the same time, slight increases in the amount of other phyllosilicates (mainly vermiculite and smectite) are noted. XRD analysis coupled with SEM-EDS observations indicate that primary biotite may be partially or completely replaced by vermiculite (Fig. 4). Results of SEM-EDS chemical analysis of the crystals of biotite in granites show decreasing content of K2O (about 10 wt.% in biotite from reference granite and from 7 wt.% to 0 wt.% in biotite-like mineral from grusified granites; Fig. 4a). The decrease of K2O content in biotite is usually coupled with the appearance of Fe and Ti oxides (Fig. 4). In some samples, especially in friable granites form Kowary Średnie and Głębock, primary biotite is altered into pseudomorph of muscovite and iron oxyhydroxides (Fig. 5). Primary plagioclase shows less alteration than biotite, but in some samples feldspars are partially replaced by clay minerals. FT-IR spectroscopy analysis of secondary clay minerals coating cracks in feldspar and chemical microanalysis (EDS) indicate that plagioclases altered into smectite. Development of secondary smectite is mainly limited to cleavage planes and microcracks within the plagioclase crystals and rarely involves transformation of the whole crystal (Fig. 6). Clay minerals are formed mainly as the result of alteration of feldspars and neoformation in small veinlets inside the altered granite. Alteration of mafic minerals (e.g. biotite) resulted in partial or complete replacement of primary crystals by coarse crystalline vermiculite. Secondary vermiculite replacing biotite was identified mainly via EDS chemical composition. Main differences between biotite and vermiculite was related to K2O content (average 9.4wt.% in biotite and 2.6wt.% in vermiculite), TiO2 (average 4.7wt.% in biotite and 0.8wt.% in vermiculite) and CaO (lack in biotite and 0.6wt.% in vermiculite on average). Contents of Fe and Mg were similar in primary biotite and secondary vermiculite. 5.3. Geochemical analysis Differences in chemical composition between the reference granite from Szklarska Poręba and granites in different stages of grusification

235

from Głębock, Kowary Średnie and Miłków are small. Selected indices of chemical alteration (Table 2): LOI (loss on ignition; Sueoka et al., 1985), PIA (Plagioclase Index of Alteration; Fedo et al., 1995) and BoxPlot (Large et al., 2001) were used to determine the progress of chemical alteration of granites in different stages of grusification. Results of chemical analysis of major elements and LOI values are presented in Table 3 (Table 3) and calculations of the chemical alteration indices are marked on biplots (Fig. 7). Very high values of PIA are typical for intensely chloritized and albitized samples from Miłków (Fig. 7a). Samples with chloritized or muscovitized primary biotite from Kowary Średnie (Fig. 7c) and Głębock (Fig. 7e) have the highest values. In samples from Miłków, not showing this type of alterations, values of PIA increase with decreasing of compactness of sample (I b II b III b HAZ; Fig. 7a). In samples from Kowary Średnie (Fig. 7c) and Głębock (Fig. 7e), values of PIA for I and II are noticeably higher than values for granitic gruses III (III b I, II b HAZ; Fig. 7c, e), which mimic the behaviour of LOI values. The alteration box plot (Large et al., 2001; Table 2; Fig. 7b, d, f) was used to indicate chemical alteration of investigated samples caused by hydrothermal fluids. Two alteration indices are used in this plot: Alteration Ishikawa Index AI which indicates the development of secondary sericite from plagioclase and chlorite from white mica (Table 2; Ishikawa et al., 1976 after Large et al., 2001) and Chlorite-Carbonate-Pyrite Index CCPI, which indicates increasing FeO and MgO content during chemical alteration of albite, K feldspar and sericite into chlorite, crystallization of secondary Mg and Fe carbonates and the development of Fe sulfides and oxides (Large et al., 2001). The box in the middle of the BoxPlot (Large et al., 2001) shows unaltered or least altered rocks, while samples outside the box show features of hydrothermal alteration. The majority of data points from the reference granite from Szklarska Poręba and from samples collected at Głębock, Kowary Średnie and Miłków is plotted inside the box of least alteration, reflecting small differences in chemical composition (Fig. 7b, d and f), but some variations are noticeable. Samples of compact granites (I), friable granite (II) and gruses (III) from Miłków (Fig. 7b) almost all fit inside the box of least alteration,

Fig. 4. Vermiculitization of biotite: a) initial vermiculitization on the edge of biotite crystal in granitic grus from Miłków, in brackets amount of K2O in wt.% (EDS) in biotite and vermiculite; b) partially vermiculized biotite from granitic grus from GL; c) biotite completely altered into vermiculite from granitic grus from GL, crevasses parallel to cleavage planes of mica due to increasing of volume during alteration; d) vermiculized biotite in grus from KS with secondary Ti and Fe oxides; BSE images. Mineral abbreviations: Ab – albite, Ap – fluorapatite, Bt – biotite, Feox – unidentified Fe oxides, FeTiox – unidentified Fe-Ti oxides, Kfs – K-feldspar, Qz – quartz, Ttn – titanite, Vrm – vermiculite.

236

B. Kajdas et al. / Catena 150 (2017) 230–245

Fig. 5. Muscovitization of biotite in friable granites from Kowary Średnie and Głębock: a) petrographic microscope image (PPL) of primary biotite completely altered into muscovite and Fe oxides in sample from Głębock; b) BSE image of muscovitized biobite from Kowary Średnie; c) BSE image of close up of secondary Fe oxides in muscovitized biotite from Kowary Średnie; d) BSE image of primary biotite nearly completely replaced by secondary Fe oxides, small flakes of muscovite are present between iron oxide concretions. Mineral abbreviations: Ap – fluorapatite, Feox – unidentified Fe oxides, Kfs – K-feldspar, Ms. – muscovite, Qz – quartz, Tiox – unidentified Ti oxides.

but small increases of the CCPI according to the degree of grusification can be recognized. In contrast, heavily altered granites from the southern part of the outcrop in Miłków fit the path of “chloritization ± sericitization ± development of pyrite”, consistent with mineralogical composition of these rocks (Large et al., 2001). In samples from Kowary Średnie (Fig. 7d) and Głębock (Fig. 7f), alterations took different paths. The main direction of alterations in the samples can be connected with the “weak sericitization” path (Large et al., 2001), but the progress of this process is independent from the degree of grusification of granites. Granitic gruses (III) show chemical composition closest to the reference granite, and mainly fall inside the least alteration box, while group II in both cases reveals higher degrees of alteration. Highly altered zones (HAZ; diamonds on Fig. 7b, d, e) show higher degrees of chemical alteration than other samples of altered granite, but these differences are not as distinct as in case of LOI values or PIA (Fig. 7a, c, e). Principal Component Analysis (PCA) was possible to use, because our data were compositional and had 0.5 standard deviation units. The first and second principal components (PC1, PC2) embrace 43.53% and 30.36% of the total variability, respectively. The third and fourth principal

components (PC3, PC4) are much smaller than PC1 and PC2 and capture only 14.64% and 6.17% of total variability, respectively. The first four principal components embrace 94.70% of total variability, while the first two embrace 73.89%. PC1 displays positive correlation with the mafic components (Fe2O3, MgO and TiO2) and LOI, and negative correlation with felsic components (K2O, Na2O and SiO2) (Fig. 8). PC2 correlates positively with the K2O and LOI components and negatively with CaO and Na2O. Significant differences between the samples from Miłków and Kowary Średnie and Głębock are clearly visible (Fig. 8a). 5.4. Stable isotopes From selected samples of friable granites and granitic gruses (Table 4), stable isotope ratios of hydrogen (δD) and oxygen (δ18O) were obtained. Besides the analyses of bulk samples, clay fractions from gruses was also analyzed. Data are plotted on the biplots (Fig. 9). Samples of unaltered reference granite, compact granites and samples revealing advanced alteration (e.g. chloritization, muscovitization, albitization) show rather similar values of δD and δ18O. Stable isotopes ratios for granitic gruses and some friable granites are characterized

Fig. 6. BSE images of plagioclases altered into smectite along cleavage planes and cracks in feldspar crystals from a) Kowary Średnie and b) Głębock. Mineral abbreviations: Ab – albite, Ap – fluorapatite, Kfs – K-feldspar, Pl – plagioclase, Qz – quartz, Sme – smectite.

B. Kajdas et al. / Catena 150 (2017) 230–245

237

Table 2 Summary of weathering indices evaluated in this study. Index

Formula

LOI

PIA

Optimum fresh value

Optimum altered value

Ideal trend (increase of alteration)

Reference

H2O+ and other volatiles content (in weight) of specimen heated n.a. to 1000 °C

n.a.

Positive

(100)[(Al2O3 − K2O) / (Al2O3 + CaO* + Na2O − K2O)]

≤50

100

Positive

AI: 20–65 CCPI: 15–40 (for granitic rocks)

Depending on the processes

e.g. Goldich, 1938; Sueoka et al., 1985 Fedo et al., 1995 Large et al., 2001

BoxPlot AI = (100)[(K2O + MgO) / (K2O + MgO + Na2O + CaO)] CCPI = (100)[(MgO + FeO) / (MgO + FeO + Na2O + K2O)]

CaO* - for the alteration of silicate rocks, the CaO must be restricted to that derived from silicate minerals.

by significantly lower value of δD, even about 40‰ at Miłków (Fig. 9a). On the other hand, clay minerals (separated from granitic gruses and friable granites) show similar δD values to unaltered rocks, but higher values of δ18O (usually N10‰; Fig. 9). 6. Discussion 6.1. Indicators of hydrothermal alteration Minor hydrothermal alteration of rock-forming minerals (e.g. sericitization of feldspars, chloritization of biotite, albite rims on

plagioclase crystals) is present in both the reference granite from Szklarska Poręba and the granites and gruses from Miłków, Kowary Średnie and Głębock, and could be result of postmagmatic changes which do not influence the grusification process. In granites which were not influenced by hydrothermal fluids, primary biotite is fresh or, especially in granitic gruses, partially or completely altered to vermiculite. Albite is present only as a perthitic exolutions in K-feldspar or at the outer rims of plagioclase crystals, which is typical for postmagmatic alteration of the Karkonosze granite (Borkowska, 1966; Fig. 10). Also in the granitic gruses (group III), only the indicators of minor, postmagmatic hydrothermal alteration as described above are present.

Table 3 Chemical composition (main oxides) of samples divided into degrees of grusification. Degree of grusification

Sample

SiO2 wt.%

Al2O3

Fe2O3

MgO

CaO

Na2O

K2O

TiO2

P2O5

LOI

I Ia II II II II III III III III III III HAZ II II II II II II II IIa III III III III III HAZ I I Ia Ia Ia Ia Ia Ia II III III III III III HAZ

SP KS01 KS03 KS07 KS09 KS10 KS02 KS04 KS06 KS11 KS13 KS05 KS15 GL01 GL05 GL13 GL14 GL17 GL18 GL19 GL06 GL02 GL04 GL08 GL09 GL15 GL10 MI01 MI03 MI11 MI13 MI14 MI15 MI16 MI17 MI04 MI05 MI06 MI07 MI08 MI09 MI19

72.32 68.88 70.13 71.67 72.01 71.88 71.63 69.89 71.96 72.68 71.26 68.24 70.85 73.23 70.61 70.10 69.51 72.62 69.45 68.76 69.89 71.30 69.47 70.40 69.97 70.24 69.58 70.82 68.72 69.96 68.44 63.55 66.31 72.19 63.16 68.96 65.99 70.29 68.40 67.48 67.73 59.16

14.26 16.58 14.31 14.32 13.27 12.89 14.00 15.6 14.3 13.38 14.04 15.04 12.32 13.11 14.28 13.82 14.97 12.50 14.18 14.49 15.09 13.89 15.37 13.63 14.68 14.25 13.64 13.66 15.09 14.42 15.07 15.74 14.91 14.03 15.64 15.44 15.83 14.02 15.18 14.99 14.60 19.61

2.07 2.12 3.11 2.36 2.81 3.93 2.45 1.77 2.12 2.62 2.61 3.78 2.28 2.37 3.22 3.42 2.84 2.77 3.07 2.77 2.92 2.79 1.99 3.56 2.65 3.13 3.33 3.34 2.98 2.71 2.60 4.16 4.29 2.65 4.08 2.64 3.94 2.87 2.91 3.82 3.75 2.19

0.66 0.33 0.76 0.54 0.76 0.50 0.54 0.39 0.38 0.55 0.54 0.80 0.98 0.88 0.79 1.39 1.41 0.73 0.62 0.69 0.55 0.90 0.47 0.67 0.57 0.73 0.82 1.24 1.19 2.37 2.61 5.97 3.27 1.49 5.68 0.88 1.17 0.91 0.83 1.13 1.17 1.31

1.60 0.18 0.5 0.16 0.27 0.30 0.28 0.88 0.15 1.08 0.90 0.33 0.62 0.32 0.31 0.30 0.70 0.27 0.33 0.48 0.25 0.38 0.61 0.88 0.53 1.41 1.45 2.25 1.60 0.32 0.34 0.33 0.42 0.27 0.41 2.21 1.89 1.55 1.33 2.13 2.09 2.32

3.47 2.64 2.37 1.43 1.48 2.13 2.04 2.81 1.97 2.68 2.99 1.89 0.50 2.52 2.69 1.89 3.21 2.48 2.03 2.35 1.79 2.66 3.01 3.41 3.39 3.14 2.59 3.26 3.44 2.54 2.84 2.41 3.12 0.02 2.02 3.62 2.93 2.79 3.22 3.24 3.22 2.40

4.86 6.76 4.98 6.81 6.28 5.51 5.97 6.62 6.77 4.58 5.17 5.69 5.02 5.29 5.7 5.75 4.75 5.63 6.98 6.75 6.79 5.27 6.74 4.06 5.20 4.97 3.61 3.51 4.24 3.98 4.95 2.31 2.86 4.47 2.56 4.10 4.12 4.18 4.75 4.06 4.18 2.78

0.30 0.46 0.47 0.29 0.41 0.56 0.35 0.26 0.27 0.39 0.37 0.45 0.42 0.38 0.43 0.43 0.42 0.31 0.36 0.42 0.47 0.41 0.28 0.50 0.38 0.44 0.49 0.56 0.51 0.52 0.52 0.54 0.58 0.49 0.58 0.43 0.58 0.46 0.45 0.59 0.59 0.28

0.11 0.13 0.15 0.07 0.13 0.16 0.11 0.08 0.08 0.13 0.14 0.14 0.11 0.12 0.14 0.15 0.15 0.11 0.12 0.14 0.15 0.14 0.10 0.17 0.12 0.15 0.17 0.18 0.16 0.17 0.17 0.17 0.20 0.15 0.20 0.15 0.18 0.16 0.14 0.17 0.17 0.10

0.20 1.80 3.10 2.20 2.50 2.00 2.50 1.50 1.90 1.70 1.80 3.40 6.70 1.70 1.70 2.60 1.90 1.50 1.70 2.20 2.00 2.10 1.80 2.50 2.30 1.30 4.10 1.10 1.50 3.00 2.40 4.80 4.00 3.30 4.90 1.50 3.20 2.70 2.60 2.20 2.30 9.50

a

Samples with macro- or microscopically visible hydrothermal alteration.

238

B. Kajdas et al. / Catena 150 (2017) 230–245 100

100

MI

a

MI

b

90

90

80 70

80 CCPI

PIA

60 70

50 40

60

30 20

50

10 40

0 0.0

2.0

4.0 6.0 LOI [% wt.]

100

8.0

0

10.0 100

KS

c

10

30

40

50 AI

60

70

80

90

100

90

100

90

100

KS

d

90

90

20

80 70

80 CCPI

PIA

60 70

50 40

60

30 20

50

10 0

40 0.0

2.0

4.0 6.0 LOI [% wt.]

100

8.0

0

10.0 100

GL

e

10

30

40

50 AI

60

70

80

GL

f

90

90

20

80 70

80 CCPI

PIA

60 70

50 40

60

30 20

50

10 0

40 0.0

2.0

4.0 6.0 LOI [% wt.]

8.0

10.0

0

10

20

30

40

50 AI

60

70

80

Fig. 7. Alteration indices: (a), (c) and (e): LOI vs PIA (Fedo et al., 1995); (b), (d) and (f): Alteration Box Plot (Large et al., 2001) for samples from Miłków (upper row), Kowary Średnie (middle row) and Głębock (lower row); reference granite from Szklarska Poręba (dark gray square), compact granites (dark gray dots), friable granites (light gray dots) granitic gruses (white dots) and highly altered zones (diamonds); hydrothermally altered samples were marked with dashed rim on the points; rectangle on Alteration Box Plot shows field of least altered rhyolite (Large et al., 2001).

On the other hand, samples from the southern part of the outcrop in Miłków, compact and friable granites from Kowary Średnie and friable granites from Głębock show more advanced hydrothermal alteration, e.g. complete albitization of plagioclases (especially in the friable granites from Głębock and Kowary Średnie; Fig. 10), crystallization of secondary idiomorphic quartz (Fig. 11a), K-feldspar (adularia) and hematite (Fig. 11b), decomposition of primary LREE minerals (mainly monazites-(Ce) and allanites-(Ce); Fig. 11c) and neoformation of secondary hydrous LREE minerals (rhabdophane-(Ce) and florencite(Ce), Fig. 11c, d).

6.2. Origin of microcracks The presence of chaotic, transmineral microcracks with accordant pore surfaces present in compact granites (group I) usually coincides with minor postmagmatic hydrothermal alteration of primary minerals (e.g. sericitization of plagioclase or chloritization of biotite). However, the origin of this type of transmineral microcracks (Fig. 3b) is uncertain. Wahrhaftig (1965), Clayton et al. (1979), Isherwood and Street (1976) and Pye (1985) considered the development of microfractures in parent rocks as the first stage of the grusification process. This type of transmineral microcrack was described by Dixon and Young (1981) as

the result of hydrothermal fluids activity, but these could also be formed as a result of tectonic stress and mechanical unloading (Clayton et al., 1979) or cooling. The presence of this type of fractures only adjacent to grusified granites and its lack in the reference granites from Szklarska Poręba (where granitic grus is absent) indicates its role in the process of granite grusification. Pye (1985) mentions that during the initial stage of weathering, the widening of pre-existing microcracks is the main factor of disaggregation. Development of friability consequent to the alteration of biotite is the late stage phenomenon (Pye, 1985). It seems that transmineral microcracks worked as the channels for fluids necessary for further alteration of granite (Clayton et al., 1979; Dixon and Young, 1981). The mechanism of development of transmineral microcracks with non-accordant pore surfaces present in some friable granites and granitic gruses (Fig. 3c–f), in opposition to microcracks with accordant pore surface, is well described. Microcracks result from expansion of the primary biotite, as a consequence of biotite alteration into vermiculite (Eggler et al., 1969; Isherwood and Street, 1976; Wahrhaftig, 1965; Wright, 2007). Biotite is partially or completely replaced with vermiculite during the two stage reaction of oxidation (reaction 1) and cation exchange (reaction 2; Velde and Meunier, 2008): biotite þ H2 O→oxybiotite þ Fe þ Mg þ K

ðreaction 1Þ

B. Kajdas et al. / Catena 150 (2017) 230–245

239

Fig. 8. Results of PCA of log-transformed data for reference granite from Szkalrska Poręba (dark gray square), compact granites (dark gray dots), friable granites (light gray dots), granitic gruses (white dots) and highly altered zones (diamonds); hydrothermally altered samples were marked with dashed rim on the symbols. Scores for samples and loadings for oxides. (a) overall areas of samples from different localizations; (b) samples from Miłków; (c) samples from Kowary Średnie; (d) samples from Głębock.

oxybiotite þ Mþ exchangable →tri‐vermiculite þ Kþ

ðreaction 2Þ

During vermiculitization of biotite, the basal spacing grows from 10 Å (mica) to 14 Å (vermiculite), increasing volume parallel to the Z axis (Banfield and Eggleton, 1988; Fig. 4). The increase of vermiculitized Table 4 Isotopic data of bulk sample and clay fraction from selected samples. Bulk rock

Clay fraction

Outcrop

Sample

Group

δ18O

δD

δ18O

δD

Szklarska Poręba Miłków

SP00 MI01 MI05 MI07 MI13 MI14 GL05 GL10 GL13 GL15 KS01 KS03 KS05 KS11

I I III III I⁎ I⁎

8.96 8.57 10.60 10.21 10.23 9.72 11.17 10.53 10.59 10.27 9.64 10.73 10.94 10.12

−77.54 −72.47 −118.65 −106.53 −51.15 −53.80 −78.15 −104.66 −88.96 −100.84 −64.82 −100.24 −81.00 −103.25

– – 16.90 15.63 – – – 16.86 – 16.19 – – 14.50 –

– – −93.10 −82.58 – – – −64.81 – −74.49 – – −79.31 –

Głębock

Kowary Średnie

II HAZ II III I⁎ II III III

biotite can result in breaking the granite from inside, producing wider microcracks. The development of these microcracks is the reason of disintegration of granites, and production of granitic grus sensu stricto. This study confirms that transmineral microcracks are closely associated with the process of biotite vermiculitization. Moreover, these microcracks are absent in friable granites from Kowary Średnie and Głębock, where the primary biotite was replaced by “non-swelling” pseudomorphs of white mica and Fe and Ti oxides (Fig. 5). In this type of granite, only microcracks not related to alterations of biotite are present, which then are often filled with secondary minerals (e.g. mica). Although Singer and Stoffers (1987) described the development of vermiculite in hydrothermal conditions, field and laboratory evidence strongly suggests that most macroscopic vermiculite were formed after biotite in the supergene conditions (Banfield and Eggleton, 1988; Bassett, 1959, 1961; Boettcher, 1966; Hong et al., 2014). 6.3. Mineral composition The main components of clay fraction in samples from Miłków are vermiculite, mica and kaolinite. Association of vermiculite and kaolinite is commonly described as a product of grusification of granites (e.g. Aoudjit et al., 1995; Eggler et al., 1969; Isherwood and Street, 1976; Islam et al., 2002; Sequeira Braga et al., 2002). The presence of vermiculite can result from decomposition of primary K-feldspar and

240

B. Kajdas et al. / Catena 150 (2017) 230–245

muscovite (di-octahedral vermiculite) or biotite (trioctahedral vermiculite; Meunier, 2005). In Miłków both types of alteration occurred – feldspars altered into dioctahedral vermiculite, and biotite altered into trioctahedral vermiculite. Only the latter is present in Kowary Średnie and Głębock.

By contrast, granitic gruses from Kowary Średnie and Głębock contain smectite in the clay fraction, instead of vermiculite. Smectite, mica and kaolinite from these outcrops were formerly reported by Migoń and August (2000, 2001). Development of vermiculite in these outcrops is strictly limited to the vermiculite pseudomorphs after primary biotite and is absent in the clay fraction lower than 2 μm. The presence of mica + smectite ± kaolinite association in the clay fraction of altered granites does not provide unequivocal answers about the conditions of its origin. This mineral association was described as a typical product of an initial weathering of granites in temperate climates (Aoudjit et al., 1995; Sikora and Stoch, 1972; Velde, 2013), although Meunier (2005) demonstrated that crystallization of secondary smectite is unlikely in ‘normal’ weathering conditions because the activity of alkaline elements is too high and the activity of Si4+ is too low. Also, Clayton et al. (1979) suggested that the development of smectite in granitic gruses may be connected with hydrothermal alteration. The sets of clay minerals in samples from Miłków indicate different paths of alteration from the samples from Kowary Średnie and Głębock. Aoudjit et al. (1995) suggested that vermiculite is more typical for welldrained saprolites, while smectite occurs in wetter conditions. Considering the fact that samples from Kowary Średnie and Głębock show the presence of typical hydrothermal alteration (e.g. albitization of plagioclases, chloritization of biotite or hematitization of rock), the presence of a smectite - mica association in the clay fraction of granitic gruses is likely to be a product of alteration caused by warmer, hydrothermal fluids (Barboni and Bussy, 2013; Clayton et al., 1979; Dixon and Young, 1981). The presence of small amounts of kaolinite, usually coupled with the Fe oxide staining recognized in every sample, can be the result of post-grusification subaerial weathering (Dixon and Young, 1981). Argilitized highly altered zones (HAZ) are present in each examined outcrop of grusified granite (Miłków, Kowary Średnie, Głębock). They occur in the form of veins (few mm thick in Kowary Średnie and Miłków) or irregular bodies (Głębock). Smectite and white mica (sericite) are the main components of these zones. Composition of fractions smaller than 2 μm in HAZ from Kowary Średnie and Miłków distinctly differs from the clay fractions in grusified granites. The clayey veinlets contain smectite with small amounts of mica and without kaolinite. In Głębock, one sample of grusified granite (sample GL10) contained much more clay fraction than other samples of grus, with smectite as the only clay mineral present. Because of this, it was also classified as the HAZ, even if this material occurs as a broad zone, and not as a thin clayey veinlet. Differences in composition of clay minerals in HAZ and granitic gruses from Miłków, Kowary Średnie and Głebock are the result of a much higher degree of decomposition of primary minerals in HAZ. The main component of HAZ, independent from the composition of clay fraction of granitic grus, is smectite. White mica is present in HAZ from Kowary Średnie and Miłków, but is absent in samples from Głębock (which also contain the remains of primary minerals). This mica seems to be sericite developed during post-magmatic or hydrothermal alteration which remains after alteration of the rock. Elongated shapes (vein-like forms and vertical zones) and mineral compositions (smectite with mica or pure smectite) of HAZ suggest that these veins and zones were the spaces of the most intensive circulation of, and

Fig. 9. Isotopic ratios of analyzed samples from: a) Miłków, b) Kowary Średnie and c) Głębock. Reference granite from Szklarska Poręba (dark gray square), compact granites (dark gray dots), friable granites (light gray dots) granitic gruses (white dots) and highly altered zones (diamonds); clay fraction (triangles); hydrothermally altered samples were marked with dashed rim on the points. Background: Isotopic relationships between meteoric water and smectite (after Mix and Chamberlain, 2014, modified). GMWL: Global Meteoric Water Line (Craig, 1961); SMOW: Standard Mean Ocean Water; dashed Smectite Lines parallel to the GMWL at 60 °C, 30 °C and 0 °C (Mix and Chamberlain, 2014); dotted line refers to H/S line (Sheppard and Gilg, 1996). Dotted arrows indicate changes in mineral formation temperature and aridity (Mix and Chamberlain, 2014).

B. Kajdas et al. / Catena 150 (2017) 230–245

241

alteration by, hydrothermal fluids inside the granite. According to chemical indices of alteration (Fig. 7), hydrothermally altered granites and highly altered zones also show much more advanced chemical alteration than other samples. 6.4. Geochemical indices of alteration

Fig. 10. Ternary diagrams of plagioclase composition (EDS data) from Szklarska Poręba, Miłków, Kowary Średnie and Głębock. Compact granites (dark gray dots), friable granites (light gray dots), granitic gruses (white dots); hydrothermally altered samples were marked with dashed rim on the points. In Miłków composition of plagioclases is similar in samples from group I, II and III. In samples from KS and GL it is clearly visible, that in granitic gruses (group III) Ca-bearing plagioclases are present, while in samples from I and II group, similarly as in hydrothermally altered granites from MI, plagioclase shows albitic composition. Mineral abbreviations: Ab – albite, An – anorthite, Or – orthoclase.

Most chemical alteration indices are calculated on the basis of the oxides of the most abundant minerals in the rock, i.e. feldspars (Al2O3, CaO, Na2O, K2O). Based on this assumption, Nesbitt and Young (1982) proposed a Chemical Index of Alteration (CIA), which describes the decomposition of feldspars. Because of the various behaviour of potassium in rocks during alteration (potassium can be removed from rock with fluids or accumulated in the form of secondary K-bearing minerals), Harnois (1988) proposed a Chemical Index of Weathering (CIW), which ignores K2O. Further study (e.g. Fedo et al., 1995) showed that complete removal of K2O from the equation renders CIW unsuitable for samples with high content of potassium. Plagioclase Index of Alteration (PIA = 100*(Al2O3 − K2O) / (Al2O3 + CaO* + Na2O − K2O); Fedo et al., 1995) resolves these problematic issues with potassium, and that is why it was used for analyzing samples in this work (Table 2; Fig. 7a, c, e). Mineralogical observations confirm that the main chemical alteration process during grusification of granites is associated with the alteration of feldspars (mainly plagioclases) and mafic minerals (biotite; e.g. Blank, 1951; Clayton et al., 1979; Eggler et al., 1969; Isherwood and Street, 1976; Larsen, 1948; Migoń and Thomas, 2002; Ollier, 1965; Wahrhaftig, 1965). This is why most noticeable chemical alterations apply to the chemical components of those mineral species (Al2O3, CaO, Na2O, K2O, FeO and MgO; Fedo et al., 1995; Harnois, 1988; Nesbitt and Young, 1982). Furthermore, during alteration of granite induced by either weathering or hydrothermal fluids, water and CO2 are commonly incorporated into the neoformed minerals (e.g. phyllosilicates, carbonates). Therefore, the LOI value shows distinct differences between unaltered and altered granites (Sueoka et al., 1985).

Fig. 11. Evidence of hydrothermal activity in friable granites from Kowary Średnie and Głębock: a) petrography microscope image (XPL) of secondary, hydrothermal quartz crystal cluster in sericitized plagioclase (Kowary Średnie); b) SEM-BSE image of secondary radiating globules of hematite in sericitized plagioclase (Kowary Średnie); c) muscovite – rhabdophane-(Ce) – Fe oxides pseudomorph after primary REE mineral (probably monazite-(Ce); Głębock); d) secondary florencite-(Ce) in cleavage planes and along joints in sericitized plagioclase (Kowary Średnie). Mineral abbreviations: Feox – hematite or other unidentified Fe oxides, Flo – florencite-(Ce), Kfs – K-feldspar, Ms. – muscovite, Qz – quartz, Rha – rhabdophane-(Ce), Ser – sericite, Zrn – zircon.

242

B. Kajdas et al. / Catena 150 (2017) 230–245

Geochemical analyses reveal, consistent with mineralogical composition, that granites and granitic gruses from Miłków are distinctly different from altered granites from Kowary Średnie and Głębock. The directly proportional trend in the degree of grusification (I → II → III → HAZ) coupled with the increasing values of LOI and PIA in samples from Miłków indicates that weathering was the main process leading to grusification in this outcrop. On the other hand, the inversion of values of alteration indices in samples from Kowary Średnie and Głębock (I, III → II → HAZ) may indicate that these samples took two separate paths of alteration – one involving type I and II and another one involving type III. The similarity between the granitic grus (type III) from Kowary Średnie and Głębock and the granitic grus from Miłków (in terms of chemical composition) and to samples from Miłków and the reference granite (in terms of mineralogical composition) can indicate similar pathways of alteration, probably in response to weathering. By contrast, samples of disintegrated granite of type I and II from Kowary Średnie and Głębock show higher degrees of alteration (according to LOI values or PIA), likely the result of minor influence by hydrothermal fluids. This is consistent with the mineralogical composition of samples and results of plotting these samples' chemical data on the Alteration Box Plot. Positions of HAZ samples on the alteration box plot are derived from proportions of smectite and mica in the mineralogical composition of samples. In smectite-rich HAZ from Głębock (Fig. 7f) and Miłków (Fig. 7b), data points lie in the upper part of the least alteration box (beginning of the “chloritization ± sericitization ± development of pyrite path”), whereas in samples from Kowary Średnie, where the amount of mica in highly altered zones is higher, data points are located on the “sericitization” path. Statistical analysis of samples (Fig. 8) also clearly distinguishes different groups, which coincide with groups obtained during geochemical and mineralogical analyses. Values of PC1 are strongly dependent on the amount of K2O in samples, while values of PC2 can be connected to the amount of Ca-bearing plagioclases in rocks. Because the amount and stage of alteration of K-feldspars in all samples are similar, the positive values of PC1 indicates the presence of secondary, low-K (non-K) phyllosilicates such as vermiculite, smectite or kaolinite, or chlorite present in hydrothermally altered samples from Miłków, while negative PC1 values indicates primary (e.g. biotite) or secondary (e.g. muscovite or sericite) mica in analyzed samples. PC2 describes the composition of feldspars in investigated samples. Negative values of PC2 are characteristic for samples containing primary, non-altered, Ca-plagioclase, which are common in the reference granite as well as in samples from Miłków. In contrast, positive values of PC2 are shown for samples containing albite as the only plagioclase (e.g. granites of I and II group from Kowary Średnie (Figs. 8c and 10) and Głębock (Figs. 8d and 10), or hydrothermally altered samples from Miłków (Figs. 8b and 10). The negative values of PC1 and PC2 (3rd quarter) indicate mainly unaltered or slightly altered rocks with Ca-plagioclases, primary or partially altered biotite and scarce amounts of secondary phyllosilicates (reference granite from Szklarska Poręba, and nearly all samples from Miłków and gruses from Kowary Średnie and Głębock). Samples altered by high temperature hydrothermal fluids occur on the upper right side of the biplot (positive PC1 and positive PC2 values; 1st quarter; hydrothermally altered samples from Miłków and HAZ from Kowary Średnie). Samples altered in the presence of low-temperature weathering fluids are present in lower right part (positive PC1 and negative PC2 values; 4th quarter; group II and III samples from Kowary Średnie and Głębock). In the upper left side of the biplot (negative values for PC1 and positive for PC2; 2nd quarter) are clustered samples with high amounts of Kbearing phyllosilicates (white mica in form of sericite and pseudomorphs after primary biotite; HAZ from Miłków and Głębock and some hydrothermally altered samples from Miłków). Major elements, especially alkalis, are commonly mobilized within the rock under the influence of hydrothermal or weathering alteration, especially if hydrothermal fluids are rather low-temperature. As a result

of this influence, similar mineral assemblages in granitic gruses are formed (Dixon and Young, 1981; Evans and Bothner, 1993). Since the amount of secondary minerals is minor, it is difficult to establish which kind of fluids altered the investigated rocks. Some mineralogical evidence may indicate that hydrothermal rather than weathering process occurred, especially in an early stage of alteration of granitic rocks from Kowary Średnie or Głębock (e.g. alteration of primary plagioclases into albite (Hövelmann et al., 2010) or into smectite (Clayton et al., 1979; Sonntag et al., 2012), muscovitization of biotite (Peters, 1987) or complete decomposition of primary REE minerals, (e.g. monazite(Ce); Berger et al., 2008). 6.5. Stable isotopes Values of δD and δ18O for the reference samples from Szklarska Poręba are typical for primary, magmatic waters (Sheppard, 1986; Fig. 9). Similar ranges of δD and δ18 O are recognized in compact granite from Miłków and hydrothermally altered samples from Miłków (Fig. 9a) and Kowary Średnie (Fig. 9b). In samples of friable granites and granitic gruses the values of δD decrease with the increase of degree of grusification, while the values of δ18O for bulk samples increase only slightly. Stable isotopic ratios in clay minerals are significantly water dependent (Savin and Epstein, 1970; Sheppard, 1986). Sheppard and Gilg (1996) suggested that stable isotope values can be used to discriminate the type of geochemical environment in which clay minerals crystallized (in this case kaolinite). For kaolinite, Sheppard et al. (1969) noticed that ratios of stable isotopes adjust according to the temperature of crystallization, and proposed the supergene/hypogene line (S/H line; dotted line on the Fig. 9a–c) parallel to the Global Meteoric Water Line (GMWL) (Craig, 1961), which distinguishes minerals that originate in weathering environments (under 35 °C) from those that originate in hydrothermal (over 35 °C) conditions. For other minerals similar lines were also prepared (e.g. for smectites Clark and Fritz, 1997; Mix and Chamberlain, 2014; Fig. 9). While the values of δ18O for all bulk samples remain more or less uniform, and the only visible variation is associated with δD, stable isotope ratios in the clay fraction are more variable and differ from outcrop to outcrop (Fig. 9). Because the clay fraction contains mixtures of different clay minerals (smectite, mica, vermiculite and kaolinite in different proportions), it is not an ideal geothermometer. Some observations, however, can be made. Independent from the type of mineral, usually the isotopic trend of increasing temperature is similar – a higher temperature results in higher values of δD and δ18O in the neoforming clay minerals (Mix and Chamberlain, 2014; dotted arrow on Fig. 9). The clay fraction in samples from Miłków is dominated by vermiculite, mica and kaolinite and shows the lowest values of δD and δ18O. This means that the crystallization temperatures of clays were the lowest (clay minerals are plotted under the S/H line and near the 30 °C smectite line; Fig. 9a; Mix and Chamberlain, 2014). In samples from Kowary Średnie (Fig. 9b) and Głębock (Fig. 9c), the clay fraction appears to have been formed at higher temperatures (much closer to the 60 °C smectite line, almost overlapping the H/S line). This difference in ratios for the stable isotopes of hydrogen and oxygen at Miłków versus Kowary Średnie and Głębock seems to confirm our mineralogical and geochemical observations that more advanced hydrothermal alteration in samples from Kowary Średnie and Głębock was caused by higher temperature fluids. 7. Pathways of grusification Based on the results of our mineralogical, geochemical and isotopic analysis, two distinct paths of grusification of granites can be inferred. In Miłków, where grusification is strictly connected with the development of secondary vermiculite (both as a pseudomorphs after biotite and in the clay fraction), plagioclases have similar compositions to

B. Kajdas et al. / Catena 150 (2017) 230–245

those of the reference granite (Fig. 10) and hydrothermal alteration is mainly the result of postmagmatic processes. That is, grus is essentially of weathering origin. This conclusion is also supported by the geochemical analyses (the more grusified granite, the higher values of alteration indices) and the stable isotope geothermometer, which shows crystallization of clays at low temperatures. The same mineralogical and geochemical features typify gruses from Kowary Średnie and Głębock. Signs of hydrothermal alteration are present, e.g. complete albitization of plagioclases (Fig. 10), muscovitization of biotite (Fig. 5) and other mineralogical features (Fig. 11) in compact and friable granites from Kowary Średnie and in friable granites from Głębock. Additionally, geochemical indices (Fig. 7) and stable isotope geothermometer data appear to confirm hydrothermal alterations present in these samples.

243

Analytical data and their interpretations allows us to develop a scheme for the grusification of granitic rock (Fig. 12). In the reference granite (Fig. 12a), only typical postmagmatic alterations occur (e.g. sericitization of plagioclases (Borkowska, 1966) or partial chloritization of biotite; Borkowska, 1966; Wilamowski, 2002). Microcracks observed in non-grusified granite occur only inside the individual crystals of rockforming minerals. In compact and friable granites (group I and II; Fig. 12b), the occurrence of transmineral microcracks coincides with signs of hydrothermal alteration (e.g. intense alteration of plagioclases and biotite or decomposition of primary and crystallization of secondary REE minerals). We infer that whatever their origin, the transmineral microcracks presence facilitated circulation of fluids inside the rock, which results in the

LOW TEMPERATURE HYDROTHERMAL OR WEATHERING ALTERATIONS

HYDROTHERMAL ALTERATIONS

a

b

d

c

Fig. 12. Simplified scheme of the granite grusification: a) unaltered granite; b) development of transmineral microcracks coupled with initial hydrothermal alterations; c) grusification sensu stricto due to biotite vermiculitization and generation of vermiculitization induced microcracks; d) advanced hydrothermal alteration leading to the development of the friable granites. More complex information in body text of the paper. Mineral abbreviations: Ab – albite, Ap – fluorapatite, Bt – biotite, Cer – cerianite-(Ce), Chl – chlorite, Flo – florencite(Ce), Ms. – muscovite, Mnz – monazite-(Ce), Pl – plagioclase, Qz – quartz, Rha – rhabdophane-(Ce), Ser – sericite, Sme – smectite, Vrm – vermiculite.

244

B. Kajdas et al. / Catena 150 (2017) 230–245

vermiculitization of biotite. Alteration of primary biotite into secondary vermiculite is associated with increased volume of the micas. Expansion of phyllosilicates inside the granite causes widening of older, transmineral microcracks with accordant pore surfaces and their further development, usually parallel to the primary biotite cleavage planes (Fig. 12c). These types of microcracks are the main culprit of development of granitic gruses sensu stricto (group III; Eggler et al., 1969; Isherwood and Street, 1976; Wahrhaftig, 1965; Wright, 2007). The samples from Miłków (II and III group) and some samples from Kowary Średnie and Głębock (III group) show that the activity of low-temperature fluids inside the granitic rock leads to partial alteration of primary plagioclase into secondary clay minerals: into vermiculite under “normal” weathering conditions (Miłków) and into smectite, when the low-temperature hydrothermal fluids are present during alteration (Kowary Średnie and Głębock). If, after the first stage of hydrothermal alteration, hydrothermal fluids did not cool enough or another hydrothermal event occurred, much more intense hydrothermal alteration of primary minerals takes place (Fig. 12d). In the friable granites from Kowary Średnie and Głębock, primary biotite was transformed into muscovite and Fe and Ti oxides underwent pseudomorphosis. During this type of alteration, the volumes of primary biotite and secondary muscovite are similar; thus, the development of the 2nd type of crack does not occur and granitic grus sensu stricto is not formed. Friable granite is usually the result of 1st generation of microcracks and weakening of the rock along mica cleavage planes and crystal boundaries. Muscovitization of primary biotite, albitization of plagioclase and neoformation of secondary white mica in the form of authigenic crystals and microcrystal infillings of microcracks occur at the same time. This kind of hydrothermal alteration is more chemically advanced than low temperature vermiculitization and the development of granitic grus. Therefore, samples from Kowary Średnie and Głębock show higher alteration indices and are more similar to hydrothermally altered samples than to the compact and friable granites from Miłków. Decomposition of primary minerals into secondary smectite was strongest in the channels where fluid circulation developed highly altered zones (HAZ), which are present in all investigated locations. 8. Conclusions Because of their geographical location and geomorphology (e.g. moderate climate, typical for this part of Europe), the Karkonosze Mountains are a good site for studying granites in various stages of granular disintegration. Granitic gruses are usually considered as a typical product of deep weathering in temperate humid climates, linked temporally with the late Neogene and warmer intervals of the Quaternary (Migoń, 1997; Migoń and August, 2001). Recent investigations show that despite macroscopic similarities between granitic gruses, even within a small region such as the Karkonosze Mountains, pathways of granite alteration can be very different. The most important step in granite grusification appears to be the alteration of primary biotites into vermiculite pseudomorphs. This type of alteration causes expansion of mica crystals and leads to disintegration of granite into grus sensu stricto. On the other hand, all investigated grusified and friable granites show the presence of microcracks, which apparently serve as channels for alteration fluids, but the final alteration products seem to depend on the type of fluid. In the Miłków outcrop, where granitic grus coexists with granitic corestones, mineralogical and chemical analyses reveal the least amount of granite alteration, and stable isotope analysis indicates the lowest origin temperatures. In the Kowary Średnie and Głębock outcrops, there is much greater mineralogical and geochemical diversity between samples. Granitic gruses sensu stricto from Kowary Średnie and Głębock are similar in mineralogical and chemical composition to granitic gruses from Miłków, but friable granites from those outcrops show evident traces of hydrothermal alteration which are not present

in Miłków. Mineralogical, geochemical and isotopic analysis of the friable granites show that the influence of hydrothermal fluids resulted in the loss of compactness, but usually did not cause development of granitic grus sensu stricto. This is apparently because alteration of primary biotites into muscovite-Fe-oxides pseudomorphs does not change their volume during alteration. Also, the composition of stable isotopes in the clay fractions of minerals from Kowary Średnie and Głębock reveal a higher temperature of origin. Acknowledgements The authors are greatly indebted to anonymous reviewers for their constructive comments and helpful suggestions. This work was financially supported by the Polish National Science Centre [grant number N N307 426993]. We acknowledge Prof. Chris Harris from Department of Geological Science, Cape Town University, for helping with the δD and δ18O analyses and Dr. Jarosław Majka from Department of Earth Sciences, Uppsala University for microprobe analyses. Marek Michalik was financially supported by the Institute of Geological Sciences of the Jagiellonian University, Kraków, via statutory fund. Piotr Migoń was financially supported by the Institute of Geography and Regional Development, University of Wrocław, via statutory fund 1015/S/2015/IGRR. References Aoudjit, H., Robert, M., Elsass, F., Curmi, P., 1995. Detailed study of smectite genesis in granitic saprolites by analytical electron microscopy. Clay Miner. 30, 135–147. Awdankiewicz, M., 2007. Late palaeozoic lamprophyres and associated mafic subvolcanic rocks of the Sudetes (SW Poland): petrology, geochemistry and petrogenesis. Geol. Sudet. 39, 11–97. Banfield, J.F., Eggleton, R.A., 1988. Transmission electron microscope study of biotite weathering. Clay Clay Miner. 36 (1):47–60. http://dx.doi.org/10.1346/CCMN.1988. 0360107. Barboni, M., Bussy, F., 2013. Petrogenesis of magmatic albite granites associated to cogenetic A-type granites: Na-rich residual melt extraction from a partially crystallized A-type granite mush. Lithos 177:328–351. http://dx.doi.org/10.1016/j.lithos. 2013.07.005. Bassett, W.A., 1959. The origin of the vermiculite deposit at Libby, Montana. Am. Mineral. 44, 282–299. Bassett, W.A., 1961. The geology of vermiculite occurrences. Clay Clay Miner. 10 (1): 61–69. http://dx.doi.org/10.1346/CCMN.1961.0100106. Bates, R.L., Jackson, J.A., 1987. Glossary of Geology. 788. American Geological Institute, Alexandria, Virginia. Beckmann, W., Geyger, E.V., 1967. Entwurf einer Ordnung der natürlichen Hohlraum-, aggregat-und Strukturformen im Boden. Die Mikromorphometrische Bodenanalyse. In: Kubiena, W.L. (Ed.), Die mikromorphometrische Boden-analyse. Ferdinand Enke Verlag, Stuttgart, pp. 163–188. Berg, G., 1941. Geologische Karte des Deutschen Reiches 1:25,000. Erläuterungen zu Blatt Bad Warmbrunn (Berlin). Berger, A., Gnos, E., Janots, E., Fernandez, A., Giese, J., 2008. Formation and composition of rhabdophane, bastnäsite and hydrated thorium minerals during alteration: implications for geochronology and low-temperature processes. Chem. Geol. 254 (3–4): 238–248. http://dx.doi.org/10.1016/j.chemgeo.2008.03.006. Blackwelder, E., 1933. The insolation hyphothesis of rock weathering. Am. J. Sci. 26: 97–113 (Series 5). 10.2475/ajs.s5-26.152.97. Blank, H.R., 1951. “Rock doughnuts”, a product of granite weathering. Am. J. Sci. 249 (11): 822–829. http://dx.doi.org/10.2475/ajs.249.11.822. Boettcher, A.L., 1966. Vermiculite, hydrobiotite, and biotite in the Rainy Creek igneous complex near Libby, Montana. Clay Miner. 6 (4):283–296. http://dx.doi.org/10. 1180/claymin.1966.006.4.03. Borkowska, M., 1966. Petrografia granitu Karkonoszy. Geol. Sudet. 2 (1), 7–119. Clark, I.D., Fritz, P., 1997. Environmental Isotopes in Hydrogeology. CRC press. Clayton, J.L., Megahan, W.F., Hampton, D., 1979. Soil and Bedrock Properties: Weathering and Alteration Products and Process in the Idaho Batholith. USDA Forest Service, Ogden, Utah, USA (Research Paper INT-237). Craig, H., 1961. Isotopic variations in meteoric waters. Science 133 (3465):1702–1703 (New York, N.Y.). 10.1126/science.133.3465.1702. Dixon, J.C., Young, R.W., 1981. Character and origin of deep arenaceous weathering mantles on the bega batholith, southeastern Australia. Catena 8 (1):97–109. http://dx.doi. org/10.1016/S0341-8162(81)80007-0. Dumanowski, B., 1968. Influence of petrographical differentiation of granitoids on land forms. Geogr. Pol. 14, 93–98. Duthou, J.L., Couturie, J.P., Mierzejewski, M.P., Pin, C., 1991. Oznaczenia wieku granitu Karkonoszy metodą izochronową, rubidowo-strontową, na podstawie całych próbek

B. Kajdas et al. / Catena 150 (2017) 230–245 skalnych. [next dating of granite sample from the Karkonosze Mountains using Rb-Sr total rock isochrone method]. Prz. Geol. 36, 75–79. Eggler, D.H., Larson, E.E., Bradley, W.C., 1969. Granites, grusses, and the Sherman erosion surface, southern Laramie range, Colorado–Wyoming. Am. J. Sci. 267 (4):510–522. http://dx.doi.org/10.2475/ajs.267.4.510. Eppes, M.C., Griffing, D., 2010. Granular disintegration of marble in nature: a thermal-mechanical origin for a grus and corestone landscape. Geomorphology 117 (1–2): 170–180. http://dx.doi.org/10.1016/j.geomorph.2009.11.028. Evans, C.V., Bothner, W.A., 1993. Genesis of altered Conway granite (grus) in New Hampshire, USA. Geoderma 58 (3–4):201–218. http://dx.doi.org/10.1016/00167061(93)90042-J. Fedo, C.M., Nesbitt, H.W., Young, G.M., 1995. Unravelling the effects of potassium metasomatism in sedimentary rocks and paleosols, with implications for paleoweathering conditions and provenance. Geology http://dx.doi.org/10.1130/ 0091-7613(1995)023b0921:UTEOPMN2.3.CO. Fourie, D., Harris, C., 2011. O-isotope study of the Bushveld complex granites and granophyres: constraints on source composition, and assimilation. J. Petrol. 52 (11): 2221–2242. http://dx.doi.org/10.1093/petrology/egr045. Goldich, S.S., 1938. A study in rock-weathering. J. Geol. 46 (1):17–58. http://dx.doi.org/10. 2307/30079586. Goudie, A., Atkinson, B.W., Gregory, K.J. (Eds.), 1994. The Encyclopedic Dictionary of Physical Geography. Blackwell, Oxford. Harnois, L., 1988. The CIW index: a new chemical index of weathering. Sediment. Geol. 55 (3–4):319–322. http://dx.doi.org/10.1016/0037-0738(88)90137-6. Harris, C., Vogeli, J., 2010. Oxygen isotope composition of garnet in the peninsula granite, cape granite suite, South Africa: constraints on melting and emplacement mechanisms. S. Afr. J. Geol. 113 (4):401–412. http://dx.doi.org/10.2113/gssajg.113.4.401. Hong, H., Churchman, G.J., Yin, K., Li, R., Li, Z., 2014. Randomly interstratified illite-vermiculite from weathering of illite in red earth sediments in Xuancheng, southeastern China. Geoderma 214-215:42–49. http://dx.doi.org/10.1016/j.geoderma.2013.10.004. Hövelmann, J., Putnis, A., Geisler, T., Schmidt, B.C., Golla-Schindler, U., 2010. The replacement of plagioclase feldspars by albite: observations from hydrothermal experiments. Contrib. Mineral. Petrol. 159 (1):43–59. http://dx.doi.org/10.1007/s00410009-0415-4. Isherwood, D., Street, A., 1976. Biotite-induced grussification of the Boulder Creek Granodiorite, Boulder County, Colorado. Bull. Geol. Soc. Am. 87 (3):366–370. http://dx.doi. org/10.1130/0016-7606(1976)87b366:BGOTBCN2.0.CO;2. Ishikawa, Y., Sawaguchi, T., Iwaya, S., Horiuchi, M., 1976. Delineation of prospecting targets for Kuroko deposits based on modes of volcanism of underlying dacite and alteration halos. Min. Geol. 26, 105–117 (in Japanese with English abs.). Islam, M.R., Peuraniemi, V., Aario, R., Rojstaczer, S., 2002. Geochemistry and mineralogy of saprolite in Finnish Lapland. Appl. Geochem. 17 (7):885–902. http://dx.doi.org/10. 1016/S0883-2927(02)00016-1. Jackson, M.L., 1974. Soil chemical analysis: advanced course: a manual of methods useful for instruction and research in soil chemistry, physical chemistry of soils, soil fertility, and soil genesis. 2nd Edition. Dept. of Science, University of Wisconsin, Madison, Wis. Jahn, A., 1962. Geneza skałek granitowych. Czas. Geogr 33 (1), 19–44. Johannsen, A., 1934. A Descriptive Petrography Of The Igneous Rocks. Vol. II: The QuartzBearing Rocks. University of Chicago Press, p. 428. Kryza, R., Pin, C., Oberc-Dziedzic, T., Crowley, Q.G., Larionov, A., 2014. Deciphering the geochronology of a large granitoid pluton (Karkonosze granite, SW Poland): an assessment of U–Pb zircon SIMS and Rb–Sr whole-rock dates relative to U–Pb zircon CA-IDTIMS. Int. Geol. Rev. 56 (6):756–782. http://dx.doi.org/10.1080/00206814. 2014.886364. Kusiak, M.A., Williams, I.S., Dunkley, D.J., Konečny, P., Słaby, E., Martin, H., 2014. Monazite to the rescue: U-Th-Pb dating of the intrusive history of the composite Karkonosze pluton, Bohemian Massif. Chem. Geol. 364:76–92. http://dx.doi.org/10.1016/j. chemgeo.2013.11.016. Large, R.R., Gemmeli, J.B., Paulick, H., Huston, D.L., 2001. The alteration box plot: a simple approach to understanding the relationship between alteration mineralogy and lithogeochemistry associated with volcanic-hosted massive sulfide deposits. Econ. Geol. 96 (5):957–971. http://dx.doi.org/10.2113/96.5.957. Larsen, E.S., 1948. Batholith and associated rocks of Corona, Elsinore, and San Luis Rey quadrangles southern California. Geol. Soc. Am. Mem. 29, 1–185. Machowiak, K., Armstrong, R., Kryza, R., Muszyński, A., 2008. Late-orogenic magmatism in the central European Variscides: SHRIMP U-Pb zircon age constraints from the Żeleźniak intrusion, Kaczawa Mountains, west Sudetes. Geol. Sudet. 40, 1–18. Marchand, D.E., 1974. Chemical weathering, soil development, and geochemical fractionation in a part of the White Mountains, Mono and Inyo Counties, California. Geological Survey Professional Paper, p. 352-J. Meunier, A., 2005. Clays. Clays. 10.1007/b138672. Mierzejewski, M.P., 2005. Karkonosze – ewolucja masywu granitowego. In: Mierzejewski, M.P. (Ed.), Karkonosze. Przyroda nieożywiona i człowiek. Wydawnictwo Uniwersytetu Wrocławskiego, Wrocław, pp. 83–132. Mierzejewski, M.P., Oberc-Dziedzic, T., 1990. The Izera-Karkonosze block and its tectonic development (Sudetes, Poland). N. Jb. Geol. Paläont. (Abh.) 179 (2–3), 197–222. Migoń, P., 1997. Palaeoenvironmental significance of grus weathering profiles: a review with special reference to northern and central Europe. Proceedings of the Geologists' Association. 108:pp. 57–70. http://dx.doi.org/10.1016/S0016-7878(97)80006-5. Migoń, P., August, C., 2000. Zróżnicowanie pokryw gruzowych Karkonoszy i Kotliny Jeleniogórskiej i ich ewolucja w czwartorzędzie. In: Jahn, A., Chodak, T., Migoń, P., August, C. (Eds.), Studia Geograficzne LXXII: Utwory zwietrzelinowe Dolnego Śląska. Nowe stanowiska, wiek i znaczenie geomorfologiczne. Wydawnictwo Uniwersytetu Wrocławskiego, Wrocław, pp. 131–149. Migoń, P., August, C., 2001. Cechy litologiczne zwietrzelin ziarnistych masywu karkonosko-izerskiego. In: Kostrzewski, A. (Ed.), Geneza, litologia i stratygrafia

245

utworów czwartorzędowych. Tom III. Wydawnictwo Naukowe Uniwersytetu im. Adama Mickiewicza, Poznań, pp. 283–305. Migoń, P., Thomas, M.F., 2002. Grus weathering mantles - problems of interpretation. Catena 49 (1–2):5–24. http://dx.doi.org/10.1016/S0341-8162(02)00014-0. Mix, H.T., Chamberlain, C.P., 2014. Stable isotope records of hydrologic change and paleotemperature from smectite in Cenozoic western North America. Geochim. Cosmochim. Acta 141:532–546. http://dx.doi.org/10.1016/j.gca.2014.07.008. Nesbitt, H.W., Young, G.M., 1982. Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature 299:21. http://dx.doi.org/10.1038/ 299715a0. Nesbitt, H.W., Young, G.M., 1989. Formation and Diagenesis of weathering profiles. J. Geol. 97 (2):129–147. http://dx.doi.org/10.2307/30065535. Ollier, C.D., 1965. Some features of granite weathering in Australia. Z. Geomorphol. 9, 285–304. Ollier, C.D., 1983. Weathering and hydrothermal alteration. Catena 10:57–59. http://dx. doi.org/10.1016/S0341-8162(83)80004-6. Peters, T., 1987. Hydrothermal alteration of a variscian granite, magmatic autometasomatism and fault related vein metasomatism. Chemical Transport in Metasomatic Processes. Springer Netherlands:pp. 577–590 http://dx.doi.org/10. 1007/978–94–009-4013-0_21. Pye, K., 1985. Granular disintegration of gneiss and migmatites. Catena 12 (2–3): 191–199. http://dx.doi.org/10.1016/0341-8162(85)90010-4. Savin, S.M., Epstein, S., 1970. The oxygen and hydrogen isotope geochemistry of clay minerals. Geochim. Cosmochim. Acta 34 (1):25–42. http://dx.doi.org/10.1016/00167037(70)90149-3. Sequeira Braga, M.A., Paquet, H., Begonha, A., 2002. Weathering of granites in a temperate climate (NW Portugal): granitic saprolites and arenization. Catena 49 (1–2):41–56. http://dx.doi.org/10.1016/S0341-8162(02)00017-6. Sheppard, S.M.F., 1986. Characterization and isotopic variations in natural waters. Rev. Mineral. Geochem. 16, 165–183. Sheppard, S.M.F., Gilg, H.A., 1996. Stable isotope geochemistry of clay minerals. Clay Miner. 31 (1):1–24. http://dx.doi.org/10.1180/claymin.1996.031.1.01. Sheppard, S.S.M.F., Nielsen, R.L.R., Taylor, H., Taylor Jr., H.P., 1969. Oxygen and hydrogen isotope ratios of clay minerals from porphyry copper deposits. Econ. Geol. Bull. Soc. Econ. Geol. 64 (7):755–777. http://dx.doi.org/10.2113/gsecongeo.64.7.755. Siegesmund, S., Ullemeyer, K., Weiss, T., Tschegg, E.K., 2000. Physical weathering of marbles caused by anisotropic thermal expansion. Int. J. Earth Sci. 89 (1):170–182. http:// dx.doi.org/10.1007/s005310050324. Sikora, W., Stoch, L., 1972. Mineral forming processes in weathering crusts of acid magmatic and metamorphic rocks of lower Silesia. Mineral. Pol. 3, 39–52. Singer, A., Stoffers, P., 1987. Mineralogy of a hydrothermal sequence in a core from the Atlantis II deep, Red Sea. Clay Miner. 22:251–267. http://dx.doi.org/10.1180/claymin. 1987.022.3.01. Słaby, E., Martin, H., 2005. Mechanisms of differentiation of the Karkonosze granite. Polish Mineralogical Society, Special Papers. 26, pp. 264–267. Słaby, E., Martin, H., 2008. Mafic and felsic magma interaction in granites: the Hercynian Karkonosze pluton (Sudetes, Bohemian Massif). J. Petrol. 49 (2):353–391. http://dx. doi.org/10.1093/petrology/egm085. Słaby, E., Galbarczyk-Gąsiorowska, L., Seltmann, R., Muller, A., 2007. Alkali feldspar megacryst growth: geochemical modelling. Mineral. Petrol. 89:1–29. http://dx.doi. org/10.1007/s00710-006-0135-7. Sonntag, I., Laukamp, C., Hagemann, S.G., 2012. Low potassium hydrothermal alteration in low sulfidation epithermal systems as detected by IRS and XRD: an example from the Co-O mine, eastern Mindanao, Philippines. Ore Geol. Rev. 45:47–60. http://dx.doi. org/10.1016/j.oregeorev.2011.08.001. Sueoka, T., 1988. Identification and classification of granitic residual soils using chemical weathering index. Geomechanics in tropical soils. Proceedings of the Second International Conference on Geomechanics in Tropical Soils, Singapore, 1988, vol. 1. Balkema, Rotterdam, pp. 55–61. Sueoka, T., Lee, I.K., Muramatsu, M., Imamura, S., 1985. Geomechanical properties and engineering classification for decomposed granite soils in Kaduna district, Nigeria. Proceedings of the First International Conference on Geomechanics in Tropical Lateritic and Saprolitic Soils, Brasilia. 1, pp. 175–186. Origin and mineralogy of clays. In: Velde, B. (Ed.), Clays and the Environment. Springer, Berlin Heidelberg http://dx.doi.org/10.1007/978-3-662-12648-6. Velde, B., Meunier, A., 2008. The origin of clay minerals in soils and weathered rocks. The Origin of Clay Minerals in Soils and Weathered Rocks http://dx.doi.org/10.1007/9783-540-75634-7. Wahrhaftig, C., 1965. Stepped topography of the southern sierra Nevada, California. Geol. Soc. Am. Bull. 76:1165–1190. http://dx.doi.org/10.1130/0016-7606(1965)76[1165: STOTSS]2.0.CO;2. Wilamowski, A., 2002. Chloritization and polytypism of biotite in the Łomnica granite, Karkonosze massif, Sudetes, Poland: stable isotope evidence. Chem. Geol. 182 (2– 4):529–547. http://dx.doi.org/10.1016/S0009-2541(01)00344-8. Wright, J.S., 2007. An overview of the role of weathering in the production of quartz silt. Sediment. Geol. 202 (3):337–351. http://dx.doi.org/10.1016/j.sedgeo.2007.03.024. Young, R.W., Dixon, J.C., 1983. Weathering and hydrothermal alteration: critique of Ollier's argument. Catena 10 (1–2):439–440. http://dx.doi.org/10.1016/S03418162(83)80033-2. Žák, J., Klomínský, J., 2007. Magmatic structures in the Krkonoše-Jizera plutonic complex, bohemian massif: evidence for localized multiphase flow and small-scale thermalmechanical instabilities in a granitic magma chamber. J. Volcanol. Geotherm. Res. 164 (4):254–267. http://dx.doi.org/10.1016/j.jvolgeores.2007.05.006.