Diagenetic Albitization in the Tera Group, Cameros Basin (NE Spain) Recorded by Trace Elements and Spectral Cathodoluminescence

Chemical Geology 312–313 (2012) 148–162

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Research paper Diagenetic albitization in the Tera Group, Cameros Basin (NE Spain) recorded by trace elements and spectral cathodoluminescence

Laura González-Acebrón a,⁎, Jens Götze b, Donatella Barca c, José Arribas d, Ramón Mas e, Carlos Pérez-Garrido f a Dpto. Estratigrafía, Facultad de Ciencias Geológicas (UCM), C/ Jose Antonio Novais 2, 28040 Madrid, Spain b Institut für Mineralogie, Freiberg, Brennhausgasse 14, 09599, Germany c Università degli Studi della Calabria, Campus di Arcavacata, Vía P. Bucci, 87036, Arcavacata di Rende, Cosenza, Italy d Dpto. Petrología y Geoquímica, Facultad de Ciencias Geológicas (UCM) — Instituto de Geociencias (IGEO, CSIC-UCM), C/ Jose Antonio Novais 2, 28040 Madrid, Spain e Dpto. Estratigrafía, Facultad de Ciencias Geológicas (UCM) — Instituto de Geociencias (IGEO, CSIC-UCM), C/ Jose Antonio Novais 2, 28040 Madrid, Spain f Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), Paseo de Atapuerca s/n, 09002 Burgos, Spain article info abstract

Article history: This paper deals with the diagenetic albitization of both plagioclases and K-feldspars in the Tithonian fluvial sand- Received 26 September 2011 stones of a rift basin (Cameros Basin). The sandstones in the lower part of the rift record have not suffered this Received in revised form 13 April 2012 albitization process. A clear relationship is observed between sodium contents, as the main element of some feld- Accepted 16 April 2012 spars and their cathodoluminescence (CL) color (the higher the sodium content, the lower is their CL intensity). In Available online 26 April 2012 conclusion, albitization processes are detectable by decreased CL intensities and changes in the CL spectra. Editor: J.D. Blum In addition, very different trace element compositions are obtained by laser ablation when comparing trace elements of non-albitized feldspars in sandstones of the lower part of the rift record with those of albitized feldspars Keywords: in sandstones of the infill top. Non-albitized K-feldspars show Rb, Sr, Ba and Pb contents of up to 1000 ppm. In Albitization contrast, very flat profiles of trace element contents (b250 ppm) are recorded in albitized feldspars (both K- Feldspar feldspars and plagioclases). Thus, albitization implies feldspars impoverished in trace elements, including REE, Plagioclase which suggests that albitization is a dissolution and reprecipitation process. Further, albitized plagioclases Cathodoluminescence show higher REE contents than albitized K-feldspars. We report here that REE patterns partly depend on the ini- Laser ablation ICP-MS tial composition of the feldspar (K-feldspar or plagioclase) as a useful geochemical criterion for distinguishing Trace elements albitized detrital plagioclases from albitized detrital K-feldspars. CL spectra from non-albitized and albitized K-feldspars and plagioclases revealed marked differences. Non-albitized K-feldspars present blue (main emission band at 460 nm) and brownish CL colors (590 nm), sometimes in the same grain. Brownish colors are related to weathering processes. The primary blue emission is related to Al–O−–Al centers, enhanced probably by Al incorporation due to the coupled substitution of Ba2+ + Al3+ ↔M++Si4+. Weathered K-feldspars present 4.8 times lower Ba content than fresh blue luminescent ones. The brownish colors are related to the external border or fractured grain zones, altered by weathering processes. Therefore, the observed 590 nm emission is assumed to be caused by structural defects resulting from weathering and alteration. Albitized K-feldspars are usually weak luminescent with a typical CL emission band at 620 nm. Sometimes, relicts of the original blue luminescence (460 nm band) are still present. The leaching of probably both Al and Ba can be responsible for the decrease in the blue band. The characteristic 620 nm band is also dominant in albitized weak luminescent plagioclases. Two additional emission bands at 440 nm (Al–O−–Al center) and 565 nm (Mn2+) occur, when albitized plagioclases preserved their original CL characteristics (green CL color). Another spectral peak at ca. 720 nm can be explained by Fe3+ activation due to Fe3+–Al3+ substitution. The spectral CL measure- ments indicate that changes in luminescence due to albitization (620 nm emission) seem to be more related to structural defects than to trace element activation or quenching. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.

1. Introduction

⁎ Corresponding author. Tel.: +34 913944785; fax: +34 91394485. Feldspars are particularly common minerals in siliciclastic sedi- E-mail addresses: [email protected] (L. González-Acebrón), ments. The albitization of detrital K-feldspar and plagioclase is one [email protected] (J. Götze), [email protected] (D. Barca), [email protected] (J. Arribas), [email protected] (R. Mas), of the most important diagenetic changes that occur in feldspathic [email protected] (C. Pérez-Garrido). sandstones (McBride, 1985; Milliken, 2005). The albite grains that

0009-2541/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.chemgeo.2012.04.012 L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162 149 replace the original detrital K-feldspar or plagioclase are highly pseu- character of the feldspars, as well as the luminescence relicts, has be- domorphic and can hinder provenance interpretations. come an additional criterion to recognize albitization processes. In this The cathodoluminescence (CL) of feldspars is a useful tool for paper, we demonstrate that also weathering processes can produce a interpreting the genetic conditions of rock formation and alteration decrease on the luminescence of K-feldspars, and we have been able (Owen, 1991; Götze et al., 1999; Slaby et al., 2008). Feldspars formed to characterize both processes in terms of CL spectroscopy. under varying conditions can show different luminescence properties The blue emission of feldspars has been related to structural defects depending on the crystallization environment and trace element up- as Al–O−–Al centers (Marfunin and Bershov, 1970; Marfunin, 1979; take during growth or recrystallization (Götze et al., 1999; Kayama et Finch and Klein, 1999; Götze et al., 2000; Slaby et al., 2008)orTicenters al., 2010). Although feldspars exhibit substantial CL color variation (Mariano et al., 1973; Lee et al., 2007). In contrast, Mn2+ causes the yel- (Owen, 1991; Finch and Klein, 1999), CL in feldspars has yet to be low emissions of feldspars (Geake et al., 1971, 1973; Lee et al., 2007)and thoroughly exploited in sedimentary petrology. Fe3+ red or infrared emissions (Finch and Klein, 1999; Krbetschek et al., Plagioclase is often yellow-green but may show a variety of emission 2002). The luminescent color produced by Fe3+ activation is red alone colors. Variations in plagioclase colors as a function of plagioclase com- but in many cases other activators compete with Fe3+ and the feldspar position were described by Mora and Ramseyer (1992). Thus, calcic pla- may exhibit blue, green or yellow CL (Mariano, 1988). Other elements gioclase (An87–97) is distinguished by its yellow color, and intermediate that have been cited as potential activators of CL in feldspars are Tl, Pb, plagioclase (An39–65)appearsgreentoyellow.Microclineandorthoclase Cu, Cr and rare earth elements (REE) (Mariano et al., 1973; Marshall, exhibit usually blue CL (Owen, 1991). In sandstones, authigenic feldspar 1988; Götze et al., 1999). Among the REE, Eu has been reported to acti- is generally nonluminescent (Kastner, 1971; Kastner and Siever, 1979). vate CL in plagioclases (Mariano and Ring, 1975). According to Marshall In addition, authigenic feldspar, which is assumed to form at low tem- (1988), however, REE rarely occur in sufﬁcient amounts in natural feld- perature, seems to have low concentrations of trace elements (Escobar spars to be CL activators and REE contents are usually higher in plagio- and Mariano, 1976). clases than in K-feldspars (Götze et al., 1999). Several petrographic studies have described albitized K-feldspars or In the present study conducted on feldspathic sandstones from the plagioclases as nonluminescent (Kastner, 1971; Saigal et al., 1988; Cameros Basin (NE Spain), we try to gain new insight into the possible Ramseyer et al., 1992). The grains become totally nonluminescent or trace elements or defects of importance in feldspar luminescence and present weak remains of their original luminescence color in case of their variation through feldspar alteration processes. For this, we com- partial albitization (Boles, 1982; Ramseyer et al., 1992; Ochoa, 2006; pared CL spectra of feldspars to trace element amounts in an effort to Caja et al., 2008). Nonluminescent areas are common in the fractured elucidate whether trace element activation is possible or structural de- grains and on cleavage traces, generating nonluminescent lines in fects can better explain the differences of luminescence among fresh, the feldspars (González-Acebrón et al., 2010a). The nonluminescent weathered and albitized feldspars.

Fig. 1. Geological map of the Cameros Basin. The positions of the stratigraphic sections of the Tera Group are also marked. Sections in the western basin area have been studied by Arribas et al. (2003). Modiﬁed from Mas et al. (2002). Sample coordinates: SAN: 2° 0′ 58″ W, 41° 56′ 23″ N (San Felices); VUR: 1° 54′ 7″ W, 41° 58′ 20″ N (Valdegutur); ESP: 2° 12′ 2″, 41° 50′ 44″ (El Espino); BLA: 1° 58′ 20″ W, 41° 51′ 10″ N (San Blas). MOV: 2° 44′ 58″ W, 42°5′ 22″ N (Montenegro de Cameros). 150 L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162

In addition, the mobility of trace elements, particularly REE, dur- of up to 6000 m of sediments at the depocenter. The sedimentary infill ing different diagenetic and metamorphic processes has long been a has been divided into eight depositional sequences (Mas et al., 2002, subject of debate (Baker, 1985; Götze, 1998). In effect, discrimination 2003) and consists mainly of continental sediments corresponding to between different provenances, magma types and/or their tectonic alluvial and lacustrine systems with scarce marine incursions (Mas et settings is often based on the assumed immobility of certain trace el- al., 1993; Gómez Fernández and Meléndez, 1994). ements or REE (e.g. Taylor and McLennan, 1985; McLennan, 1989; Depositional Sequences 1 and 2 (DS 1 and DS 2) represent the first Blundy and Wood, 1991; Singer et al., 1995). rifting stages (Tera Group, Tithonian–Berriasian). In the eastern area In this paper, we unveil a leaching process of trace elements in feld- of the basin, the Tera Group is made up of alluvial-fan deposits, spars that is associated with the diagenetic albitization of the Tera meandering fluvial sediments and lacustrine–palustrine limestones Group sandstones in the Cameros Basin. Our observations indicate the (Mas et al., 1993; Gómez Fernández and Meléndez, 1994; Mas et al., different behaviors of REE due to their more immobile nature, yet we 2002; González-Acebrón, 2009). demonstrate how the albitization leaching process also involves a Petrofacies of the Tera Group sandstones indicate erosion of the general impoverishment in the REE composition of the feldspars. pre-rift sedimentary substratum (quartzolithic petrofacies) as rifting commenced, and erosion of crystalline/metamorphic basement in 2. Geological setting later stages to generate quartzofeldspathic petrofacies (González- Acebrón et al., 2007, 2010a) in a provenance cycle (Arribas et al., TheCamerosBasininthenorthernIberianRange(Fig. 1)formspartof 2007). A diagenetic albitization process of both plagioclases and K- the Mesozoic Iberian Rift System (Mas et al., 1993; Guimerà et al., 1995; feldspars has been described for DS 2 sandstones (González- Salas et al., 2001; Mas et al., 2002). Intraplate rifting was a consequence Acebrón et al., 2010b). Main lines of evidence for diagenetic of a generalized extensional regime that separated Iberia from Europe. albitization are: 1. absence of K-feldspar grains. 2. All types of feldspar

The Cameros Basin formed during the second rift event of the Iberian present very similar composition very rich in Na (Ab94.0 An4.5 Or1.5). Rift, from the Tithonian to the early Albian. The basin-ﬁll succession of 3. Chemically pure albite is relatively common (Ab> 99%). 4. The lack the Cameros Basin embodies a large cycle or megasequence composed of CL of most feldspar grains and evidence of partial albitization

Fig. 2. Photomicrographs of the different types of feldspars in the Tera Group: A. K-feldspars (type 1) stained with sodium cobaltinitrite (Chayes, 1952). DS 1. Parallel nichols. B. Albitized K-feldspar (type 1). DS 2. Crossed nichols. C. Albitized detrital albite (type 2). DS 2. Crossed nichols. D. Albitized polysynthetic plagioclase grain showing well developed overgrowths (type 2). Cement twinning shows optical continuity with grain twinning. DS 2. Crossed nichols. L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162 151

Fig. 3. Photomicrographs of the different types of feldspars in the Tera Group (all scale bars are 0.25 mm except F which is 0.05 mm): A and B: crossed nichols and cathodoluminescence. Type 1 K-feldspars. Fresh grains show intense blue luminescence (1) whereas altered grains (2 and 3) show brownish colors in the marginal parts. Yellow luminescent grains are apatites. DS 1. C and D: crossed nichols and cathodoluminescence. (1) Type 1 albitized K-feldspars still show blue CL. (2) Type 1 albitized K-feldspar with relicts of the original blue CL following exfoliation lines. (3) Type 2 albitized feldspar is almost non-luminescent. The carbonate replacement and cement show orange luminescence. DS 2. E: Cathodoluminescence image of albitized type 1 K-feldspars (analyses 1, 2, 3, 5) and albitized type 2 feldspar (albitized plagioclase, analysis 4). DS 2. F. Back scattered electron image of an albitized feldspar grain showing relicts of the original feldspar composition. The tables in E and F show the chemical composition expressed by percentages of albite, anorthite and orthoclase in mol% (Ab, An, Or). shown by CL. 5. Relicts of the original K-feldspar or plagioclase com- Three possible Na sources have been invoked: (1) the percolation position (González-Acebrón et al., 2010a). of moderate to high salinity residual brines from related alkaline lakes The possibility that albitization took place in the source rock has developed at top of DS 2; (2) clay mineral reactions (sodium smectite been discarded because no albitized units or sodium-rich feldspar to illite and chlorite) indicated by mudstone composition in the inter- units have been described in these areas. Although a sodium-rich layered mudstones, and (3) the replacement of detrital sodium pla- unit could have existed and have been eroded, feldspars present sev- gioclases by carbonate (González-Acebrón et al., 2010b). In addition, eral different source areas for DS 2 (González-Acebrón et al., 2010b): albitization also depends on K-sink (Aagaard et al., 1990) and Ca- in D1 K-feldspars come from metamorphic source areas. In DS 2, sink, which in our case is probably related to illitization of kaolin these areas still keep eroding but polysynthetic plagioclases from plu- pore fillings and epimatrixes in the case of the K-sink, and non- tonic source areas also appear. Feldspar grains with similar aspect and ferroan calcite cements associated to albitization in the case of the textures appear in DS 2 in comparison to DS 1, but in DS 2 are Ca-sink (González-Acebrón, 2009; González-Acebrón et al., 2010a). albitized. The mechanism of albitization of DS 2 K-feldspar and plagioclases has been interpreted as dissolution–reprecipitation process 3. Materials and methods which, in combination with fracturing, is responsible for the fluid in- filtration and the mineral-replacement process (González-Acebrón et Samples (n=256) of medium-grained sandstones (125–250 μm) al., 2010a) as have been proposed by other authors (e.g. Boles, 1982; were collected from 15 representative stratigraphic sections of the Saigal et al., 1988; Ramseyer et al., 1992; Engvik et al., 2008). Tera Group (see Fig. 1 for locations). Doubly polished thin sections 152 L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162

Fig. 4. Distribution sketch of the two feldspar types in both DS 1 and DS 2. Feldspars in DS 1 are not albitized and present fresh blue luminescent (BL) type 1 K-feldspars (A) and altered type 1 K-feldspars (B: weak BL usually with nonluminescent (NL) boundaries). Feldspars in DS 2 are albitized and present similar type 1 K-feldspars very rich in Na content that are usually NL or preserve relicts of BL (C). In addition, feldspars of type 2 are present, which can be polysynthetic or untwinned plagioclases (D); they are usually NL, but also can be green luminescent or contain green relicts.

(30 μm) of the samples were used for a petrographic provenance under standardized conditions (wavelength calibration by Hg- analysis (González-Acebrón et al., 2007; González-Acebrón, 2009; halogen lamp, spot width 30 μm, measuring time 2 s). González-Acebrón et al., 2010a), characterizing the whole framework Deconvolution of selected characteristic spectra of each feldspar by the integrated Gazzi–Zuffa point counting method (Gazzi, 1966; Zuffa, type of both DS has been done using eXPFit software, designed by 1985). Forty selected samples were studied by cathodoluminescence Dr. R. Nix of the University of London. CL spectra in energy units (CL), using a cold cathodoluminescence instrument (Citl MK4 equip- were deconvoluted into Gaussian component corresponding ob- ment, 300–500 μA, 11–16 kV, 0.1–0.2 Torr). served peaks and characteristic emission center peaks based on the A second series of seven selected sections 300 μm-thick represen- literature, peaked at 430, 460, 480, 500, 590, 615, 680, 718, and tative of both DS was prepared for a study conducted at the Depart- 865 nm (Götze et al., 2000; Correcher and García-Guinea, 2001, and ment of Earth Sciences of the Università della Calabria (Italy) references in both). involving simultaneous laser ablation (LA) and inductively coupled Microanalytical tests were performed on 23 sections (thin and plasma mass spectrometry (ICP-MS) using an Elan DRCe instrument thick) using a Jeol JXA-8900 M probe with four detectors under the (Perkin Elmer/SCIEX) linked to a New Wave UP213 solid-state Nd- working conditions: 15 kV, 20 nA and 5 μm of diameter of the elec- YAG laser probe (213 nm). Samples in a cell were ablated by a laser tron beam (measuring time of 10 s on peak and 5 s in each back- beam and the ablated material was then ﬂushed in a continuous ground). Measured oxide and their mean detection limits in ppm

ﬂow of argon and helium mixture to the ICP, where it was atomized were SiO2 (400), Al2O3 (170), CaO (150), Na2O (170), K2O (140), and ionized for quantiﬁcation in the mass spectrometer. The diameter FeO (260), MnO (285), MgO (120), TiO2 (260), Cr2O3 (320), using al- of the ablation spot was 50 μm, the laser repetition rate was 10 Hz, bite (for SiO2 and Na2O), sillimanite (Al2O3), microcline (K2O), and the standards were NIST612 and BCR2. This set up allows the de- kaersutite (CaO, MgO, TiO2), almandine (MnO, FeO) and Cr metal tection of ppm levels of REE and trace elements; the detection limit (Cr2O3) as standards (Jarosewich et al., 1980; McGuire et al., 1992). was 0.01 ppm. Microprobe determinations of several major elements Microprobe analyses were also conducted on the feldspar grains

(as SiO2 and CaO) were used to calibrate these readings. whose trace element compositions had been determined by LA-ICP- Carbon-coated, polished thin sections were also investigated using MS. One section was chosen for selective mapping of Ba, Al, K and Si a “hot cathode” CL microscope HC1-LM (cf., Neuser et al., 1995). The in K-feldspar grains of known luminescence. system was operated at 14 kV accelerating voltage and a current den- REE abundances for the feldspars grains were plotted on sity of about 10 μA/mm2. Luminescence images were captured by a chondrite-normalized diagrams (composition of chondrite by Peltier cooled digital video-camera (KAPPA 961‐1138 CF 20 DXC). Nakamura, 1974). The term “feldspar” is used here in its broadest CL spectra in the wavelength range of 380 to 900 nm were recorded sense to include non-albitized K-feldspar, albitized detrital K- with an Acton Research SP-2356 digital triple-grating spectrograph feldspar and albitized detrital plagioclase. with a Princeton Spec-10 CCD detector that was attached to the CL microscope by a silica-glass ﬁber guide. CL spectra were measured 4. Results

Table 1 4.1. Conventional petrography and CL Mean chemical compositions of the different feldspar types in each DS. Ab, An and Or represent albite, anorthite and orthoclase proportions in mol % (taken from González- Two types of feldspars were distinguished in the Tera Group of the Acebrón et al., 2010a). eastern Cameros Basin: (1) untwinned, turbid feldspars present in DS DS Type of feldspars Mean 1 as K-feldspars and in DS 2 as plagioclases (Fig. 2.A and B). They usu- composition ally present bigger size in DS 1 (0.2–0.6 mm) than in DS 2 (0.1– DS 2 Type 2: untwinned or polysynthetic twinned plagioclases. Ab94.0 An4.5 Or1.5 0.4 mm). (2) Untwinned or polysynthetically twinned rectangular Type 1: Untwinned turbid feldspars. Ab96 1 An3.1 Or0.8 0.1–0.4 mm plagioclases, which are almost exclusively present in DS DS 1 Type 1: Untwinned turbid feldspars. Or 98 2(Fig. 2.C and D). L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162 153

Fig. 5. Type 1 K-feldspars (DS 1) spectral analysis. Black dots illustrate some areas chosen for the spectral analysis of altered K-feldspars, whereas the blue dots are on fresh areas of K-feldspars. For the sketch see Fig. 4A and B.

Type 1 feldspars occurring in DS 2 as well as type 2 are very rich in band but shifted to 590 nm and generally quite symmetrical (n=8, Na (mostly albites) due to the albitization process. Type 2 feldspars Fig. 5), with intensities three to ten times lower than the blue zones. have been interpreted as albitized plagioclases (González-Acebrón Albitized K-feldspars (type 1 feldspar in DS 2) present two emis- et al., 2010a). sion bands in their dark zones or grains, one main band at ca. The two morphological types of feldspars were examined. In DS 1, 620 nm and a second one, usually less intense and asymmetric, cen- type 1 K-feldspar mainly shows blue luminescence. Around 40% of tered at 710–720 nm (spectra 4 in Figs. 6, 7). When these types of this type 1 K-feldspars appear totally dark or present dark external feldspars show relicts of the blue luminescent original color, a shoul- boundaries in transmitted light. These dark grains or dark rims and der around 440–450 nm is observed (spectra 3.1 and 3.2 in Figs. 6, 7). ﬁssures are anisotropic and highly porous, and appear non- Maximum intensities are up to four times higher than in dark zones, luminescent or present weak blue luminescence (Figs. 3.A,B and 4). but twice or three times lower than blue luminescent non-albitized Under CL it can be observed that the dark rims penetrate into the K-feldspars of DS 1 (Fig. 8). grain through ﬁssures. Albitized plagioclases (type 2, DS 2) with almost no visible CL pre- In DS 2, independent of their morphological appearance or twin- sent a typical emission band around 620 nm (spectra 5 in Fig. 6); in ning, the two types of feldspar are very similar in composition and areas with green luminescence they exhibit an additional shoulder very rich in sodium due to the albitization. Type 1 feldspar of an albit- around 440–450 nm. In primary green plagioclases another CL emis- ic composition is usually nonluminescent or presents very weak re- sion around 565 nm (Mn2+ activation) occurs instead the 620 nm mains of blue luminescence on fractured grains and on cleavage band (spectra 6.1 and 6.2 in Fig. 6). traces. Feldspars of type 2 are often nonluminescent, although they can also show green luminescence (Figs. 3C, D, E and 4). In both cases, relicts from former K-feldspar or plagioclase have been recog- 4.3. Chemical composition of feldspars nized in back scattered electron and CL images (e.g.: Fig. 3E and F). All types of feldspars together with their mean compositions in each Major element compositions reveal a clear relation between the DS are compiled in Table 1. Na contents and the luminescence intensity of feldspars. The higher the Na content in feldspar, the more reduced is its luminescence 4.2. CL spectroscopy (González-Acebrón et al., 2010b). The non-albitized blue K-feldspars of DS 1 show high contents of Non-albitized K-feldspar (type 1 feldspar in DS 1) presents differ- the trace elements Rb, Sr, Ba and Pb (Fig. 9A, the major and trace el- ent CL spectra in the blue zones compared to dark zones or totally ement contents of the feldspars are provided in Tables 3, 4 and 5) dark grains (Fig. 5; spectra 1 and 2 in Fig. 6, Table 2). Blue zones compared to non-albitized dark K-feldspars of the same DS. This im- show generally one emission band around 460 nm with a clear asym- poverishment is in particular evident for Ba. The mean Ba content of metric shape (n=6, Fig. 5). Dark zones present only one emission blue luminescent K-feldspars is 1875 ppm, whereas this content is 154 L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162

Fig. 6. Selected spectra for deconvolution. Types of feldspars: 1. BL K-feldspar DS 1; 2. NL K-feldspar DS 1. 3.1. and 3.2. Albitized BL K-feldspar DS 2; 4. Albitized NL K-feldspar DS 2. 5. Albitized NL plagioclase DS 2; 6.1 and 6.2. Albitized GL plagioclase DS 2. See Table 2 for deconvolution parameters.

393 ppm in dark ones (Fig. 11A). This result has been confirmed by luminescent plagioclases are richer in some transition metals (Ni, comparing CL images with Ba-distribution maps (Fig. 11). Al, K, and Zn, Cr, V), as well as in Rb, Ce and Th. Si distribution maps were also obtained for the same grains, but there is no correlation with the luminescence color. 5. Discussion In contrast to non-albitized K-feldspars (DS 1), a very flat REE pro- file was observed for the albitized feldspars of DS 2 (both detrital K- 5.1. K-feldspar weathering in DS 1 feldspars and plagioclases, Fig. 10B). Normalized REE patterns of albitized feldspars with respect to non-albitized feldspars (Fig. 12) Secondary K-feldspar overgrowths usually present dark CL confirmed that the albitized K-feldspars generally show lower trace (Kastner, 1971; Kastner and Siever, 1979). However, in our case the element levels, including most REE. This impoverishment was more dark CL rims and areas in DS 1 K-feldspars cannot be interpreted as evident for the more incompatible elements (left side of Fig. 12). Un- authigenic overgrowths. They do not exclusively develop along the fortunately, this comparison was not possible for the albitized plagio- grain boundaries but also penetrate into the grains, producing both clases, because of a lack of data for non-albitized plagioclases due to partially and totally dark grains. their scarcity in DS 1. Petrographic evidence in K-feldspars from DS 1 for alteration The chondrite-normalized REE patterns of K-feldspars of DS 1 (dark rims and fissures under transmitted light with lower blue CL in- (Fig. 13) show a decline from light REE (LREE) to heavy REE tensities or dark luminescence, Figs. 3 A, B; 4A, B) and the associated (HREE). A positive Eu-anomaly is visible in non-albitized K- impoverishment in trace elements (in particular Rb, Sr, Ba and Pb, feldspars in DS 1, which was more distinct for the blue luminescent Figs. 5, 10A, 11), suggest near surface meteoric alteration, either dur- K-feldspars. The albitized feldspars of DS 2 present an equivalent pat- ing weathering or telodiagenesis (exhumation), because all type 1 K- tern featuring high LREE, low HREE and a distinct positive Eu anoma- feldspars present similar provenance areas (González-Acebrón et al., ly. Albitized detrital plagioclases display higher values than albitized 2011). Assuming that the telodiagenetic processes would be respon- detrital K-feldspars. Eu2+ is one of the elements accepted in the feld- sible for CL variations, probably most of the grains should exhibit al- spar structure because of its similar ionic size and charge to Ca2+ teration features. Since this is not the case, the results point to (Götze et al., 1999). Feldspars usually exhibit positive anomalies of weathering processes as cause for the observed CL features. Similar Eu, due to the incorporation of Eu2+ to replace Ca2+ or Sr2+. meteoric rims have been observed in feldspars of other geological oc- Green luminescent plagioclases have higher Mn, Sr, Nd and Pb currences, even in K feldspars of metamorphic rocks (González- contents than plagioclases with dark CL (Table 5). In contrast, weak Acebrón and Götze, in press). L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162 155

The trace element Ba is common in K-feldspars because it usually re- places K (Guo and Green, 1989; Deer et al., 1992; Icenhower and % London, 1996) and may substitute Ca (Mahood and Stimac, 1990;

.2 RMS 57.3 Blundy and Wood, 1991). In our study non-albitized BL type 1 K-feldspars are Ba rich (mean of 1875 ppm). Ba maximum values correlate with the blue luminescent zones, whereas minimum values are related to dark CL zones or grains (Fig. 11). The correlation between Ba Height FWHM Area content and blue luminescence has already been shown by Slaby et al. (2008). These authors pinpointed that Ba itself is not a CL-

% activator but acts through the formation of structural Al defects. High and variable Ba contents should affect the Al incorporation required for charge balance. They observed magmatic CL zoning in relationship with Ba contents. In our case, the variation in Ba content between fresh and altered grains is not an original feature. It more Height FWHM Area likely derives from weathering, which probably provokes an impoverishment in Ba and with that also a decrease in the number of Al de-

% fects in the feldspar structure, because alkalis and alkali earth elements can be easily removed due to their position in interstitial places in the feldspar structure. In this sense, it is well known that Ba incorporation causes local structural distortions due to coupled KSi–BaAl exchange (Viswanathan and Brandt, 1980; Viswanathan Height FWHM Area and Kielhorn, 1983). Even though feldspar weathering has been extensively studied,

% the mechanism and surface chemistry of this process are still poorly e intensity of the peaks or height in counts, and relative integrated area (%). Feldspar understood and are a matter of controversy (Blum and Stillings, 1995 and references therein, Brantley and Stillings, 1996; Brantley and Stillings, 1997; Walther, 1997). Dissolution models postulate that feldspars dissolve via two separate, pH dependent mechanisms: Height FWHM Area 1) nonstoichiometric dissolution (preferential element release) and near-surface alteration at acid to neutral pH, and 2) stoichiometric

% dissolution and absence of near-surface alteration at basic pH (e.g., Chou and Wollast, 1985; Holdren and Speyer, 1985; Nesbitt and Muir, 1988; Casey et al., 1989a,b; Hellmann, 1995; Schweda et al., 1997). The observed weathered rims imply near-surface alteration. Therefore, our case is probably better explained by nonstoichiometric

Height FWHM Area dissolution at acid to neutral pH. In addition, alteration layers on natural and artiﬁcial weathered feldspars have been studied by using different high resolution techniques % (e.g.: Nesbitt and Muir, 1988; Muir et al., 1990, Schweda, 1990; Hellmann, 1994, 1995; Hellmann et al., 2003). These layers are usually depleted in interstitial cations (Ca, Na, K, depending on feldspar composition) and Al, whereas are enriched in H, O and Si (e.g. Nesbitt and Skinner, 2001; Hellmann et al., 2003). This process has been explained Height FWHM Area by preferential leaching (Nesbitt and Skinner, 2001) or alternatively as a result of interfacial dissolution–reprecipitation (Hellmann et al.,

% 2003). To assess whether the leaching of trace elements (especially Ba) and/or structural changes are responsible for the change in CL properties, and to clarify the nature of this leaching process, further studies at atomic level with electron paramagnetic resonance (EPR) would be

Feld. type: 2 RMS 52.4Height FWHM Feld. type: 3.1. Area RMS 53.3 Feld. type: 3.2. RMS 53.6 Feld. type: 4 RMS 17.5 Feld. type: 5 RMS 38.0 Feld. type: 6.1 RMS 43.3 Feld. type: 6 required. Unfortunately, this method does not allow spatially re- solved analyses of separate grain parts. Our results show that the position of the blue peak in blue type 1 % K-feldspars (460 nm, Fig. 5) ﬁts well with the emission of Al–O−–Al centers (450–480 nm, Marfunin, 1979). Thus, the blue emission (Fig. 5) is probably caused by Al–O−–Al defects although the K, Si and Al distribution maps do not show correlation with the luminescence images of the K-feldspars. This may be explained with the Feld. type: 1 RMS 227.0 much higher concentration of these elements compared to Ba. gure caption 6.

ﬁ Other activators, which are assumed for the blue emission in K- feldspar are Ti3+ (460±10 nm, Geake et al., 1973; Walker, 1985; Lee et al., 2007)orEu2+ (420 nm, Mariano and Ring, 1975). Eu is more abundant in BL type 1 K-feldspars than in NL (Fig. 12) but its amount is almost negligible in both types (b2 ppm, Table 4) and in these quantities is ineffective as a luminescence activator. The Ti con- 123 4304 4605 480 2.8906 500 2.695 46407 555 2.583 7620 0.6608 590 2.480 0.800 1963.49 615 2.254 8280 0 3908.2 79010 680 2.102 3660 0.820 0.800 700 718 2.010 0.580 1330 0.600 865 4352.9 1.823 0.560 2340 0.740 1407.9 293.8 890 1.722 0.0 2520 0.620 1.434 251.3 631.0 0.740 90 780 0 280 0.800 2110 930.1 90 0.860 0.800 0.600 422.2 1530 0.600 1292.5 0 0.800 0.900 250 0.620 0.600 400.1 1082.2 107.7 49.6 0 0.700 0.0 51.9 608.2 810 1320 0.800 0 0 4310 0 0.0 680 112.2 0.740 0.560 0.800 0.740 0.664 0.600 180 720 0.800 384.3 0.0 473.9 1834.8 0.800 0.240 1600 348.8 1730 72 0.0 0.0 0.0 0.800 369.3 0.620 0 0 730 27.7 0.800 610 0 820.6 0.600 0 0.820 687.7 0.520 0.800 260 36.9 800 0.600 0 0.800 383.8 690 203.4 0.800 0.600 0.0 100 0.0 0.620 5820 0.840 133.4 0.0 0.0 318.0 0.440 0.820 5030 214.4 4510 0 0 0.0 0 1641.8 0.580 710 0.800 0.740 52.6 0 0.800 650 307.7 0.800 0.600 846.3 490 0.800 0 5020 4560 0.520 0.0 0.780 0.600 0.0 364.2 0.574 0.786 0.0 216.7 1000 0.0 409.7 1847.4 0 0 2297.9 860 0.820 470 0.0 4730 0 0 0.900 0.500 0.740 0.720 0 525.7 0.780 0.600 0.880 0 233.4 0.580 2365.3 217.0 0.0 880 0.0 0.600 0.0 750 0.0 0.500 0 0.0 1200 0 0.900 0.0 0 282.1 0.780 0.880 0.600 0.600 630 432.8 0 677.0 0.480 0.0 0.0 0.600 0.0 193.9 0 0.0 0 0.600 0.600 0 0.600 0.0 0.0 0 0.0 0.600 0 0.600 0.0 0.0 Peaks Position Energy Height FWHM Area Table 2 Deconvolution parameters of characteristic CL emission bands of different feldspar types of both DS: position in nm, energy in eV, FWHM in nm, relativ types are explained in tent is higher (maximum individual value of 218 ppm) but does not 156 L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162

Fig. 7. Albitized type 1 K-feldspars (DS 2) spectral analysis. Black dots illustrate dark CL areas chosen for the spectral analysis, whereas the blue dots are on the relictic BL areas. For the sketch see Fig. 4C.

Fig. 8. CL spectra of albitized type 1 K-feldspars (DS 2) vs non-albitized BL K-feldspars (DS 1). Purple dots illustrate BL areas in albitized type 1 K-feldspars. For the sketch see Fig. 4A and C. L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162 157

Fig. 9. CL spectra of albitized type 2 feldspars (albitized plagioclases, DS 2). Black dots illustrate dark CL areas chosen for the spectral analysis, whereas the green dots are on relictic green luminescent (GL) areas or GL plagioclases. For the sketch see Fig. 4D.

seem to have a correlation with the presence of blue luminescence appears in most albitized type 1 feldspars (Fig. 7) and has not been (Tables 4 and 5). Thus, an emission center different from the Al– observed in non-albitized type 1 feldspars (Fig. 8). Thus, the Fe3+ O−–Al defects has not been determined. contents might be higher after the albitization process. Unfortunately, The structural change in the K-feldspar after weathering is we cannot make a correlation between the intensity of this emission manifested by the presence of a new defect center causing a CL emission with Fe3+ content, because by using electron microprobe there is no at ca. 590 nm in the spectra of weathered grains. The nature of this de- discrimination between Fe3+ (usually on T-site of feldspars) and Fe2+ fect is still unknown and has to be investigated in further studies. (usually on M-site). In addition, we cannot exclude the presence of minor microphases of iron oxides or iron-bearing inclusions. Further 5.2. Albitization of DS 2 studies on Raman microprobe or EPR are required in this sense. Fe3+ red activation occurs due to Fe3+–Al3+ substitution, which can Red luminescence emission around 720 nm is usually related to rearrange the distribution of Al tetrahedral sites (Slaby et al., 2008). Fe3+ (exact position depends on feldspar composition: e.g., Sippel If the albitization process has increased the Fe3+ contents, this would and Spencer, 1970; Geake et al., 1973; Borosnovskaya et al., 1982; probably imply a change in the feldspar structure by Fe3+–Al3+ substi- Mora and Ramseyer, 1992; Krbetschek et al., 2002). In our study it tution or oxidation of Fe2+ to Fe3+.

Fig. 10. Concentration diagrams. A. Mean values obtained for K-feldspars in DS 1 (type 1 feldspars) in sections BLA and VUR (Fig. 1). NL: non- or weak luminescent (n=10). BL: blue luminescent (n=7). B. Mean values obtained for albitized feldspars in DS 2 (type 1 and 2 feldspars, n=40) sections SAN, MOV and ESP (Fig. 1): San Felices, Montenegro and El Espino sections. Elements ordered as follows: Sc, Ti, V, Cr, Co, Ni, Zn, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Th, U. 158 L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162

Fig. 11. Microprobe Ba concentration maps. Sample of DS 1 (BLA section, Fig. 1) showing fresh and altered type 1 non-albitized K-feldspars. Notice that K-feldspars with higher luminescence intensities are those richer in Ba, whereas altered weak luminescent feldspars are Ba-poor (see number 1). The variations in luminescence are also reﬂected in the spectral analysis of these grains. In this case BL K-feldspars show asymmetrical peaks around 440, 580 nm and 680 nm. Dark zones have only one emission band centered at ca. 590 nm and generally quite symmetrical.

The diminished amounts of trace elements observed in albitized and cleavage lines (Figs. 5, 7, 8). Although in both cases the Ba con- feldspars compared to non-albitized feldspars (Figs. 10 and 12) can tent is lowered (fresh grains compared with weathered grains or be due to the leaching of a portion of the original trace elements non-albitized compared with albitized grains, Figs. 10 and 12), the that formed part of the initial feldspar structure. The impoverishment decrease in CL intensity is probably a result of different structural of Ba is more important in the case of albitization than in the case of changes, because spectral analysis reveals differences in the position weathering (Fig. 10). Both processes, weathering and albitization, re- of the main peak (590 nm in weathered K-feldspars and 620 nm in duce the initial luminescence, but generate different petrographic and albitized feldspars, Figs. 6 and 7, respectively). spectral analytical results: weathered grains show dark luminescence The yellow emission around 565 nm (Fig. 9) in green luminescent mainly in their outer boundaries which penetrates into the grain, albitized plagioclases is probably related to Mn2+ (Sippel and whereas albitization preferentially occurs along fractures, twinning Spencer, 1970; Mariano et al., 1973; Mora and Ramseyer, 1992), because Mn2+ is more abundant in green plagioclases than in weakly

Fig. 12. Diagram of mean trace-element contents recorded in the albitized K-feldspars (DS 2) normalized to the mean values obtained for the non-albitized K-feldspars (DS 1, Fig. 13. Chondrite-normalized mean REE distribution patterns of non-albitized K-feldspars n=17). Albitized K-feldspars can be either dark (NL, n=18) or blue luminescent (BL, grains of DS 1 (normalization according to data of Nakamura, 1974). NL: weak- and non- n=5). luminescent (n=13). BL: blue luminescent (n=14). Table 3 Contents of major elements in feldspars (in weight-%) determined by electron microprobe. Ab, An, Or in mol-%. The color of cathodoluminescence is indicated as: NL: nonluminescent, BL: blue luminescent, GL: green luminescent, (low): low visible intensity. A hyphen marks when values are below the detection limit.

Non-albitized K-feldspars nonluminescent (NL)

Element BLA-A2 BLA-A3 BLA-C1 BLA-C2 BLA-F4 BLA-F5 BLA-F6 VUR-B1 VUR-H1 VUR-H2 MEAN DESVEST

SiO2 63.55 59.94 59.57 45.47 70.21 43.75 60.53 62.37 63.00 63.80 59.22 8.27 Al2O3 18.53 21.39 22.55 28.97 7.25 33.66 20.75 19.10 17.13 17.98 20.73 7.06 FeO 0.02 0.15 0.01 3.29 – 0.03 0.03 – 0.04 0.07 0.46 1.15 MnO 0.03 0.03 – 0.01 0.07 – 0.04 0.03 0.02 0.03 0.03 0.02 MgO ––0.02 2.09 0.03 – 0.03 0.02 0.03 0.03 0.32 0.78 CaO 0.01 0.06 0.08 1.87 0.04 0.05 0.06 0.01 0.20 0.07 0.24 0.57 Na2O 0.22 0.39 0.18 0.09 0.10 0.13 0.23 0.27 0.62 0.48 0.27 0.18 K2O 16.69 15.81 15.62 2.05 1.35 9.74 16.05 16.08 16.08 16.08 12.55 6.06 TiO2 – 0.04 0.04 0.05 0.02 0.03 0.03 –– 0.01 0.03 0.01 Cr2O3 –––––––– 0.03 0.07 0.05 0.03 Total 99.04 97.81 98.06 83.85 79.06 87.39 97.74 99.29 99.29 99.29 94.08 7.63

Ab (%) 0.83 1.50 0.70 1.45 4.18 0.82 0.88 1.04 2.32 1.84 1.56 1.06 312 Geology Chemical / al. et González-Acebrón L. An (%) 0.06 0.29 0.40 42.75 2.16 0.40 0.31 0.05 0.99 0.38 4.78 13.36 Or (%) 99.10 98.21 98.89 55.80 93.65 98.78 98.82 98.92 96.69 97.78 93.67 13.41 CL NL NL NL NL NL NL NL NL NL NL

Non-albitized K-feldspars blue luminescent (BL)

Element BLA-C3 BLA-C4 BLA-C5 BLA-D1 BLA-D2 BLA-F1&2 BLA-F3 VUR-A1 VUR-A2 VUR-C1 VUR-C2 VUR-D2 VUR-E3 VUR-F1 Mean DESVEST

SiO2 51.87 47.31 56.29 46.23 63.64 59.77 53.90 61.76 63.81 63.09 63.60 57.45 62.95 62.72 58.17 6.18 Al2O3 27.96 27.94 24.96 35.28 18.70 20.52 20.21 17.63 18.17 18.03 17.65 21.89 18.25 17.57 21.77 5.36 FeO 0.04 0.03 0.10 0.02 0.04 – 0.06 0.06 0.01 0.02 0.14 0.07 0.03 0.07 0.05 0.04 MnO ––0.04 0.05 –– –––0.01 0.01 ––0.05 0.03 0.02 MgO –––––– –0.02 0.01 0.04 0.00 0.03 0.02 0.03 0.02 0.01 CaO 0.06 0.04 0.03 0.06 0.14 0.02 0.05 0.07 0.02 0.06 – 0.11 0.02 0.05 0.06 0.04 Na2O 0.30 0.25 0.17 0.27 0.27 0.37 0.25 0.19 0.17 0.37 0.23 0.36 0.26 0.28 0.27 0.07 K2O 13.90 11.43 14.83 11.35 16.37 15.37 13.33 16.08 16.08 16.08 16.08 16.08 16.08 16.08 14.94 1.76 TiO2 ––0.00 – 0.04 – 0.03 ––––0.02 0.08 0.01 0.03 0.03

Cr O –––––– –0.02 0.04 –––0.01 0.04 0.03 0.01 –

2 3 148 (2012) 313 Total 94.13 87.00 96.42 93.26 99.20 96.05 87.82 99.29 99.29 99.29 99.29 99.29 99.29 99.29 96.35 4.33 Ab (%) 1.31 1.32 0.73 1.43 1.03 1.46 1.14 0.73 0.65 1.41 0.89 1.37 1.00 1.06 1.11 0.28 An (%) 0.38 0.30 0.16 0.44 0.71 0.10 0.29 0.34 0.12 0.30 0.00 0.56 0.12 0.24 0.29 0.19 Or (%) 98.31 98.38 99.12 98.12 98.27 98.44 98.57 98.93 99.22 98.29 99.11 98.07 98.88 98.69 98.60 0.39 CL BL (low) BL (low) BL (low) BL (low) BL (low) BL (low) BL (low) BL BL BL BL BL BL BL – 162 Albitized K-feldspars nonluminescent (NL)

Element MOV- MOV- MOV- SAN- SAN- SAN- SAN- SAN- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- Mean DESVEST A1 A2 L1 A1 A3 D3 G2 G4 A1 A2 A3 C2 C3 E1 E2 F2 H1 H2 C1 F1

SiO2 0.07 67.54 67.06 67.91 66.10 65.17 67.43 67.03 66.58 67.85 67.33 66.60 68.98 67.95 68.21 67.10 68.33 68.53 68.54 65.18 63.97 15.08 Al2O3 19.76 19.69 20.69 19.75 18.36 18.84 18.96 18.01 18.82 19.50 19.36 20.98 19.48 19.20 19.38 17.86 18.84 19.71 18.91 21.02 19.35 0.86 FeO 0.04 0.08 0.03 ––0.04 – 0.03 0.04 0.04 0.03 0.01 0.01 0.00 0.01 0.00 0.00 0.00 0.01 0.06 0.02 0.02 MnO 0.05 0.04 0.01 0.01 ––––0.01 0.00 0.04 0.03 0.00 0.00 0.02 0.01 0.00 0.00 0.03 0.00 0.02 0.02 MgO 0.03 0.03 0.03 – 0.05 0.15 0.02 0.12 0.04 0.04 0.00 0.01 0.00 0.01 0.00 0.18 0.01 0.00 0.02 0.02 0.04 0.05 CaO 0.71 0.43 0.42 0.21 0.08 0.34 0.06 0.16 0.09 0.05 0.00 0.06 0.03 0.02 0.01 0.28 0.07 0.04 0.01 0.08 0.16 0.19 Na2O 11.31 11.40 11.60 11.60 11.60 11.60 11.60 11.60 11.45 11.35 11.46 11.15 11.69 11.71 11.81 11.06 11.36 11.61 11.63 11.34 11.50 0.19 K2O 0.10 0.11 0.51 0.06 0.07 0.12 0.09 0.09 0.05 0.04 0.07 0.04 0.07 0.04 0.02 0.06 0.04 0.03 0.01 0.05 0.08 0.10 TiO2 0.02 0.00 – 0.02 0.00 0.08 0.01 0.01 0.02 0.03 0.03 0.01 0.00 0.00 0.00 0.05 0.00 0.00 0.00 0.05 0.02 0.02 Cr2O3 –––0.05 0.04 –––0.02 0.02 0.05 0.00 0.00 0.00 0.01 0.00 0.04 0.00 0.00 0.03 0.02 0.02 Total 99.29 99.29 99.29 99.29 99.29 99.29 99.29 99.29 97.13 98.94 98.45 98.93 100.32 98.92 99.51 96.59 98.77 99.93 99.26 97.91 98.95 0.87 Ab (%) 91.06 93.73 89.40 96.86 98.10 94.69 98.03 97.00 98.35 98.88 99.03 98.69 98.73 99.23 99.68 95.87 98.71 99.10 99.68 98.43 97.16 2.87 An (%) 7.68 4.78 4.38 2.34 0.91 3.73 0.71 1.80 1.01 0.63 0.03 0.71 0.35 0.23 0.08 3.26 0.80 0.44 0.13 0.89 1.74 2.03 Or (%) 1.26 1.49 6.22 0.80 0.99 1.58 1.26 1.20 0.63 0.49 0.94 0.59 0.92 0.54 0.24 0.87 0.49 0.46 0.19 0.68 1.09 1.27 159 (continued on next page) Table 3 (continued) Albitized K-feldspars nonluminescent (NL) 160 Element MOV- MOV- MOV- SAN- SAN- SAN- SAN- SAN- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- ESP- Mean DESVEST Table 3 (continuedA1 ) A2 L1 A1 A3 D3 G2 G4 A1 A2 A3 C2 C3 E1 E2 F2 H1 H2 C1 F1 CL NL NL NL NL NL NL NL NL NL NL NL NL NL NL NL NL NL NL NL NL Albitized K-feldspars blue luminescent (BL)

SAN-E4 ESP-H4 ESP-H5 Mean DESVEST

SiO2 64.68 67.51 66.25 66.15 1.41 Al2O3 19.42 19.97 21.06 20.15 0.84 FeO – 0.00 0.01 0.00 0.00 MnO 0.03 0.00 0.04 0.02 0.02 MgO 0.01 0.01 0.00 0.01 0.01 CaO 0.89 0.59 1.32 0.93 0.37 Na2O 11.60 11.19 11.09 11.29 0.27 K2O 0.15 0.13 0.10 0.13 0.02 TiO2 – 0.04 0.00 0.02 0.03 Cr2O3 0.06 0.00 0.02 0.03 0.03 Total 99.29 99.54 100.32 99.71 0.54 Ab (%) 89.07 91.82 85.11 88.67 3.37 .Gnáe-cbó ta./Ceia elg 312 Geology Chemical / al. et González-Acebrón L. An (%) 9.13 6.49 13.61 9.74 3.60 Or (%) 1.79 1.69 1.28 1.59 0.27 CL BL (low) BL BL

Albitized plagioclases green luminescent (GL)

MOV-C3 MOV-G1 MOV-K1 MOV-L2 ESP-B1 ESP-B2 ESP-G1 ESP-G3 SAN-G1 ESP-G2 Mean DESVEST

SiO2 65.22 66.70 65.11 67.69 65.95 64.99 66.96 66.22 67.59 65.22 66.16 1.03 Al2O3 21.09 19.79 20.73 19.39 20.66 20.96 20.99 20.61 18.48 21.72 20.44 0.95 FeO 0.07 0.02 0.08 0.10 0.00 0.08 0.08 0.00 0.04 0.01 0.05 0.04 MnO 0.04 0.01 0.03 0.02 0.00 0.00 0.04 0.05 – 0.04 0.03 0.02 MgO 0.04 0.02 0.05 0.07 0.01 0.01 0.03 0.00 0.09 0.01 0.03 0.03 CaO 1.47 0.32 0.69 0.15 1.34 1.63 0.75 1.27 0.16 0.42 0.82 0.56 Na2O 10.32 11.60 11.60 11.60 10.94 10.56 10.42 10.82 11.60 10.42 10.99 0.56 K2O 0.56 0.17 0.48 0.29 0.14 0.08 0.52 0.12 0.07 1.21 0.36 0.35 TiO2 0.04 0.06 0.00 0.02 0.02 0.00 0.05 0.04 0.00 0.03 0.03 0.02

Cr2O3 ––––0.00 0.00 0.04 0.01 – 0.00 0.01 0.02 – 1 21)148 (2012) 313 Total 99.29 99.29 99.29 99.29 99.40 98.72 100.04 99.38 99.29 99.26 99.32 0.32 Ab (%) 78.28 94.24 87.30 94.62 84.44 82.00 85.01 85.10 97.21 80.69 86.89 6.41 An (%) 14.94 3.50 6.95 1.65 13.85 17.01 8.17 13.45 1.81 4.38 8.57 5.80 Or (%) 6.78 2.25 5.75 3.74 1.72 0.99 6.82 1.46 0.98 14.93 4.54 4.32 CL GL (low) GL GL (low) GL GL (low) GL (low) GL (low) GL (low) BL/GL (low) GL (low) – 162 Albitized plagioclases nonluminescent (NL)

MOV-C2 SAN-B1 SAN-D1 SAN-E1 ESP-D1 ESP-D2 ESP-D3 ESP-F3 ESP-H3 MEAN DESVEST

SiO2 67.59 67.05 64.15 67.88 64.62 67.79 62.86 64.36 69.13 66.16 2.17 Al2O3 19.61 18.91 20.62 19.50 22.07 17.55 22.65 22.43 19.61 20.33 1.75 FeO – 0.04 0.08 – 0.01 0.07 0.46 0.79 0.06 0.21 0.30 MnO –––0.02 0.00 0.05 0.01 0.00 0.00 0.01 0.02 MgO 0.02 0.04 0.08 0.03 0.20 0.22 0.27 0.10 0.01 0.11 0.10 CaO 0.45 0.10 0.48 0.03 0.30 0.35 0.07 0.72 0.01 0.28 0.24 Na2O 11.57 11.60 11.60 11.60 10.19 10.81 9.40 9.40 11.72 10.88 0.97 K2O 0.08 0.43 0.32 0.05 0.10 0.09 1.89 0.83 0.04 0.43 0.61 TiO2 – 0.01 ––0.03 0.01 0.01 0.03 0.00 0.01 0.01 Cr2O3 – 0.03 – 0.01 0.01 0.00 0.02 0.00 0.04 0.01 0.01 Total 99.29 99.29 99.29 99.29 97.65 96.97 97.73 98.74 100.62 98.76 1.12 Ab (%) 94.04 93.36 91.00 98.93 94.83 94.63 75.07 80.39 99.32 91.29 8.22 An (%) 4.94 1.10 5.00 0.34 3.71 4.08 0.75 8.26 0.08 3.14 2.77 Or (%) 1.03 5.53 4.00 0.72 1.46 1.29 24.18 11.34 0.60 5.57 7.80 CL NL NL NL NL NL NL NL NL NL L. González-Acebrón et al. / Chemical Geology 312–313 (2012) 148–162 161 luminescent ones (0.026>0.014 wt.%, Table 3). The combination of References this yellow emission with the blue emission (450 nm, Fig. 9) gener- ates the green luminescence of these plagioclases. Albitized green Aagaard, P., Egeberg, P.K., Saigal, G.C., Morad, S., Bjorlykke, K., 1990. Diagenetic 2+ albitization of detrital K-feldspar in Jurassic, Lower Cretaceous and Tertiary clastic plagioclases with higher Mn are less Na rich than albitized dark reservoir rocks from offshore Norway. II. Formation of water chemistry and kinetic 2+ 2+ plagioclases with lower Mn , confirming that Mn probably sub- considerations. Journal of Sedimentary Petrology 60, 575–581. stitutes in Ca2+ sites. Arribas, J., Alonso, A., Mas, R., Tortosa, A., Rodas, M., Barrenechea, J.F., Alonso-Azcárate, J., Artigas, R., 2003. Sandstone petrography of continental depositional sequences Albitized plagioclases show higher REE contents than albitized K- of an intraplate rift basin: Western Cameros Basin (North Spain). Journal of Sedi- feldspars, since the REE preferentially substitute for Ca in the struc- mentary Research 73 (2), 309–327. tural M-site of plagioclases (Gorobets et al., 1989), whereas the sub- Arribas, J., Ochoa, M., Mas, R., Arribas, M.E., González-Acebrón, L., 2007. Sandstone pet- stitution for K is not so common due to its monovalent valence and rofacies in the northwestern sector of the Iberian Basin. Journal of Iberian Geology 33 (2), 191–206. larger ionic radius. This is probably the reason for the higher REE con- Baker, J.H., 1985. Rare earth and other trace element mobility accompanying centrations in albitized detrital plagioclases compared to albitized de- albitization in a Proterozoic granite, W. Bergslagen, Sweden. Mineralogical Maga- – trital K-feldspars (Tables 4 and 5). Higher REE levels in plagioclases zine 49, 107 115. Blum, A.E., Stillings, L.L., 1995. Feldspar dissolution kinetics. In: White, A.F., Brantley, than K-feldspars in non-albitized feldspars have been reported by S.L. (Eds.), Chemical weathering rates of silicate minerals: Reviews in Mineralogy, other authors (e.g. Götze et al., 1999). Thus, the REE composition of 31, pp. 291–351. albitized feldspars seems to be partly conditioned by their original Blundy, J.D., Wood, B.J., 1991. Crystal-chemical controls on the partitioning of Sr and Ba between plagioclase feldspar, silicate melts, and hydrothermal solutions. Geo- composition (K-feldspar or plagioclase). chimica et Cosmochimica Acta 55, 193–209. The impoverishment in trace elements during albitization was Boles, J.R., 1982. Active albitization of plagioclase. Gulf Coast Tertiary. American Journal more evident in nonluminescent albitized K-feldspars for the more of Science 282, 165–180. Borosnovskaya, N.N., Lesnov, F.P., Scherbakova, M.Ya., 1982. On the X-ray lumines- incompatible elements with the exception of the relatively immobile cence of Fe3+ in calcic plagioclase (in Russian). Geokhimiya 9, 129–131. Th, Nb and Ta (Fig. 11, first two lined areas). Finally, our results sup- Brantley, S.L., Stillings, L.L., 1996. Feldspar dissolution at 25 °C and low pH. American port albitization as a dissolution–reprecipitation process, based on Journal of Science 296, 101–127. Brantley, S.L., Stillings, L.L., 1997. Reply to comment: feldspar dissolution at 25 °C and petrographic evidence (grains that show albitized areas in weak low pH. American Journal of Science 297, 1021–1032. zones such as cleavage and fracture planes) and structural changes Caja, M.A., Marfil, R., Salas, R., Permanyer, A., Lago, M., Garcia, D., 2008. Petrology and possibly related to Fe3+–Al3+ substitution (indicated by CL provenance as a key to interpret albitization: a case study from syn-rift Lower Cre- – spectroscopy). taceous sandstones, Maestrat Basin, Iberian Range. Geotemas 10, 1385 1388. Casey, W.H., Westrich, H.R., Arnold, G.W., Banfield, J.F., 1989a. The surface chemistry of dissolving labradorite feldspar. Geochimica et Cosmochimica Acta 53, 821–832. Casey, W.H., Westrich, H.R., Massis, T., Banfield, J.F., Arnold, G.W., 1989b. The surface of – 6. Conclusions labradorite feldspar after acid hydrolysis. Chemical Geology 78, 205 218. Chayes, F., 1952. Notes of the staining of potash feldspar with sodium cobaltinitrite in thin section. American Mineralogist 37, 337–340. Geochemical and cathodoluminescence studies of non-albitized Chou, L., Wollast, R., 1985. 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On the origin of Colombian emeralds. 2nd Biannual – −– Meeting of the Mineralogical Society of America, Tucson, Abstract. gests Al O Al centers as CL activators. Finch, A., Klein, J., 1999. The causes and petrological significance of cat- 2. The Ba content in K-feldspars significantly decreases during hodoluminescence emission from alkali feldspars. Contributions to Mineralogy weathering. The release of probably both Ba and Al can be respon- and Petrology 135, 234–243. fl sible for the decrease in the blue CL emission band. Gazzi, P., 1966. Le arenarie del ysch sopracretaceo dell'Appenino modenese; correlazioni con il flysch di Monghidoro. Mineralogica et Petrographica Acta 12, 69–97. 3. Both albitized feldspars and weathered feldspars can be dark under Geake, J.E., Walker, G., Mills, A.A., Garlick, G.F.J., 1971. Luminescence of Apolo lunar CL or can exhibit weakly luminescent areas, but with different pet- samples. Proc. Second Lunar Sci. Conf., Geochim. Cosmochim. 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CL spectra of albitized K-feldspars are different from those of Cameros: ambientes sedimentarios, procedencia y evolución diagenética. The Tera group in the Eastern Sector of the Cameros Basin: sedimentary environments, albitized plagioclases indicating structural differences. provenance and diagenetic evolution. European PhD Thesis. 422 pp. 5. The higher REE contents of albitized detrital plagioclases compared González-Acebrón, L., Götze, J. (in press): Cathodoluminescence of feldspars and car- to albitized detrital K-feldspars are partly conditioned by their bonates in sedimentary Rocks. In: Quantitative Mineralogy and Microanalysis of Sediments and Sedimentary Rocks (P. Sylvester, ed.). Mineralogical Association original compositions (K-feldspar or plagioclase). We propose the of Canada Short Course Series, 42. use of this distinguishing feature as a geochemical criterion to dis- González-Acebrón, L., Arribas, J., Mas, R., 2007. 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