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Article

The Petrology of Tuffisite in a Trachytic Diatreme from the Kızılcaören Alkaline Silicate–Carbonatite Complex, NW Anatolia

by
Yalçın E. Ersoy
1,
Hikmet Yavuz
2,*,
İbrahim Uysal
3,
Martin R. Palmer
4 and
Dirk Müller
5
1
Department of Geological Engineering, Dokuz Eylül University, 35390 İzmir, Türkiye
2
The Graduate School of Natural and Applied Sciences, Dokuz Eylül University, 35390 İzmir, Türkiye
3
Department of Geological Engineering, Karadeniz Technical University, 61080 Trabzon, Türkiye
4
School of Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK
5
Department for Earth and Environmental Sciences, Ludwig-Maximilians-Universität München, 80333 Munich, Germany
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(8), 867; https://doi.org/10.3390/min15080867 (registering DOI)
Submission received: 14 July 2025 / Revised: 7 August 2025 / Accepted: 14 August 2025 / Published: 17 August 2025
(This article belongs to the Special Issue Critical Metal Minerals, 2nd Edition)
Browse Figures
Versions Notes

Abstract

The Kızılcaören alkaline silicate–carbonatite complex, located in the Sivrihisar (Eskişehir, NW Anatolia) region, includes phonolite, trachyte, carbonatite, pyroclastics, and REE mineralization (bastnäsite as a critical REE mineral). The emplacement and origin of this complex are poorly constrained, as previous studies mostly concentrated on the petrology of the alkaline rocks, carbonatite, and REE-mineralization, and little attention has been paid to the texture, composition, and origin of the pyroclastic rocks. The pyroclastic rocks in the region contain both rounded and angular-shaped cognate and wall-rock xenoliths derived from syenitic/trachytic hypabyssal rocks and carbonatites, as well as juvenile components such as carbonatite droplets and pelletal lapilli. The syenitic/trachytic hypabyssal rock fragments contain sanidine with high BaO (up to 3.3 wt.%) contents, amphibole (magnesio-fluoro-arfvedsonite), and apatite. Some clasts seem to have reacted with carbonatitic material, including high-SrO (up to 0.6 wt.%) calcite, dolomite, baryte, benstonite, fluorapatite. The carbonatite rock fragments are composed of calcite, baryte, fluorite, and bastnäsite. The carbonatite droplets have a spinifex-like texture and contain rhombohedral Mg-Fe-Ca carbonate admixtures, baryte, potassic-richterite, and parisite embedded in larger crystals of high-SrO (up to 0.7 wt.%) calcite. The spherical–elliptical pelletal lapilli (2–3 mm) contain a lithic center mantled by flow-aligned prismatic sanidine (with BaO up to 3.5 wt.%) microphenocrysts settled in a high-SrO (up to 0.7 wt.%) cryptocrystalline CaCO3 matrix. All these components are embedded in an ultra-fine-grained matrix. The EPMA results from the matrix reveal that, chemically, it consists largely of BaO-rich sanidine, with minor carbonate, baryte and Fe-Ti oxide. The presence of pelletal lapilli, which is one of the most common and characteristic features of diatreme fillings in alkaline silicate–carbonatite complexes, reveals that the pyroclastic rocks in the region represent a tuffisite formed by intrusive fragmentation and fluidization processes in the presence of excess volatile components consisting mainly of CO2 and F.

1. Introduction

Diatremes are defined as funnel-shaped concave volcanic pipes that are filled with brecciated material as a consequence of gaseous explosions (e.g., [1,2]). Although diatremes can form from any type of magma, the term is mostly used applied to kimberlite pipes [3,4,5,6]. In this context, kimberlite diatremes have typically been described as having an elliptical or circular “crater zone” at the surface which contains pyroclastic and epiclastic kimberlite. This zone is underlain by a 1–2 km long vertical pipe (the “diatreme zone”), which is filled by brecciated materials, i.e., tuffisitic kimberlite breccia. Below the diatreme zone lies a “root zone”, which is represented by hypabyssal dikes. However, this model has recently been revised and the terminology significantly changed, with the diatreme zone now described as volcaniclastic kimberlite, i.e., fragmental rocks (including pyroclastic kimberlite, resedimented volcaniclastic kimberlite, and massive volcaniclastic kimberlite), and the root zone now described as hypabyssal kimberlite, i.e., non-fragmental rocks [5,7,8].
The term “tuffisite” was introduced to distinguish the intrusive pyroclastics filling the pipe (diatreme zone) from the extrusive pyroclastics at the crater zone in the Swabian volcanic pipes, in southern Germany [9]. Tuffisite (tuff-penetrated breccias or tuffisitic breccia, [10,11]) contains pyroclastic material, ranging from large blocks to ash, which contains juvenile and xenolithic fragments (both cogenetic, i.e., cognate and wall-rock) [9,10]. Tuffisite-type material has been described in both kimberlites and alkaline silicate–carbonatite complexes (e.g., [12,13,14,15,16]). Despite the term tuffisite for the intrusive pyroclastics in the kimberlites having been revised to “Kimberley-type pyroclastic kimberlite” [17], it remains in wide use in studies of alkaline silicate–carbonatite complexes; hence, it is also favored here.
The distinctive characteristic of tuffisite material is the presence of “pelletal lapilli” [18]. These are spherical to elliptical juvenile clasts composed of a crystal or rock fragment in the center (a kernel) and a rim or mantle consisting of flow-aligned prismatic microphenocrysts embedded in primary igneous material (e.g., [12,18,19,20,21,22]). Revised terminology for kimberlites uses the term “melt-bearing pyroclast”, a type of magmaclast in kimberlites [23]. However, the term pelletal lapilli is still widely used for a wide range of rock types, including kimberlites, ultramafic lamprophyres and other types of alkaline rocks [24,25,26,27,28], and this terminology is used in this study.
Diatremes and their pipe fillings (pelletal lapilli-bearing tuffisite) have also been described from alkaline silicate–carbonatite complexes. Examples include the Dicker Willem Complex, SW Namibia [29], Ruri Volcano in western Kenya [15], West Eifel, Germany [30], Goias alkaline province, Brazil [31], Laetolil Beds, Tanzania [32], Mt. Vulture Volcano, southern Italy [12,24], and other Italian carbonatites [16,33].
The Kızılcaören alkali silicate–carbonatite complex in the Sivrihisar (Eskişehir, NW Anatolia) region, includes phonolitic and trachytic volcanics, carbonatites, and fluorite–barite–bastnäsite ore zones, as well as pyroclastic rocks emplaced in a small (~6–7 km2) area (34–40; Figure 1). Fluorite–barite–bastnäsite deposits were found by the Mining Exploration Institute of Turkey, and a reserve of 4.67 Mt of REE [34] is reported; hence, it represents a unique REE resource in Türkiye. Previous studies in this area have mostly concentrated on the petrology of the alkaline silicate rocks, mineralogy and origin of the fluorite–barite–bastnäsite deposits and carbonatites [34,35,36,37,38,39,40,41,42,43], with little attention paid to the texture, composition, and origin of the pyroclastic rocks. Hatzl [35] described lithic ash and lapilli tuffs or agglomerates, vent breccias, and glass tuffs or ignimbrites. Özgenç [38] mapped “trachytic tuffs” in small areas. Stumpfl and Kırıkoglu [40] and Hatzl [35] conducted whole-rock analyses from these rocks and proposed a trachytic composition. Genç [34] pointed out that the breccia-like rocks, previously described as conglomerate, should be described as explosion breccia, or vent breccia, because the thickness of the unit exceeds 800 m.
This study presents new field-based geological data and the first detailed petrographic examination of the pyroclastic rocks and their components in the Kızılcaören area. We present detailed electron probe micro analyzer (EPMA) results of the magmatic mineral components in the pyroclastic rocks. For the first time, we also describe pelletal lapilli in these rocks, which are a characteristic component of diatreme-filling intrusive pyroclastics, i.e., tuffisite. Furthermore, we show that the formation and emplacement of this alkaline silicate–carbonatite complex was controlled by NW-trending strike-slip faults.
The results of this study are helpful in understanding the tectonic settings of alkali silicate–carbonatite complexes and their relationships with strike-slip fault systems in detail. Furthermore, from an economic perspective, the outcome of this study may provide a key tool in exploring for similar rock types in the region.

2. Geological Setting

The Kızılcaören alkaline silicate–carbonatite complex is located in the Sivrihisar (Eskişehir, NW Anatolia) region (Figure 1). The NW Anatolian region is composed of two major continental blocks, the Rhodope–Pontides to the north and the Anatolide–Tauride Block to the south, which were amalgamated along the İzmir–Ankara Suture zone during the Late Cretaceous–Paleocene (Figure 1a) [44]. The Rhodope–Pontides in this region is composed of (a) metagreywacke and phyllites with blocks of metabasite and recrystallized pelagic limestones (the Karakaya Complex), and (b) the unconformably overlying Upper Jurassic–Lower Cretaceous neritic limestones (the Bilecik Limestone) [44,45]. These units are tectonically underlain by a thick ophiolite slab representing obducted oceanic fragments of the northern Neotethys, which form part of the İzmir–Ankara Suture. Radiometric ages from the metamorphic sole rocks of these slabs reveal a Late Cretaceous (~93–90 Ma) intra-oceanic subduction event [46]. The ophiolite slabs are underlain by Late Cretaceous high-pressure metamorphic rocks (blueschists-eclogite facies marbles and metasediments) of the Tavşanlı Zone [47], which represent the northward subducted edge of the Anatolide–Tauride Block (Figure 1a,b).
The pre-Eocene basement units in the Kızılcaören area are overlain by pyroclastic rocks covering an area of ~6–7 km2 (Figure 1c). Following emplacement of the pyroclastic rocks, trachytic to phonolitic domes and lava flows, as well as carbonatite veins and fluorite–bastnäsite–barite ore zones were emplaced (e.g., [37,38]). The emplacement of the alkaline volcanism, carbonatites, and associated fluorite–bastnäsite–barite mineralization in the region developed during the Late Oligocene, as evidenced by 25 Ma (Ar/Ar) and 24.8–24.1 Ma (K-Ar) ages from the phonolites, a 24.9 Ma (K-Ar) age from the carbonatites and a 25.7 Ma (K-Ar) age from the phlogopite–calcite–albite rock from the mineralization zone [37,42,48].

3. Materials and Methods

Seven representative pyroclastic rock samples were collected from the unit in the field. Following petrographic observations, 3 out of 23 thin sections were selected for electron probe micro analyzer (EPMA) measurements at the Department for Earth and Environmental Sciences, LMU Munich, Germany. Depending on the mineral investigated, adapted measurement conditions were applied in each case: The accelerating voltage was 15 kV for all analyses, and the current and beam diameter were chosen to be 10 nA and 10 µm, respectively, for feldspars, micas and carbonates, while a 40 nA current and a focused beam were used for amphiboles and oxides. The following standards were used: Si, Fe (Kα, Springwater olivine); Al (Kα, orthoclase); Ca (Kα, wollastonite); Mg (Kα, periclase); Na (Kα, albite); Mn (Kα, bustamite); Ti (Kα, rutile); P (Kα, Durango fluorapatite); Ba (Lα, BaSO4); Sr (Kα, SrSO4); Nb (Lα, met. Nb); Ta (Lα, met. Ta); Y (Lα, YPO4); Zr (Lα, cubic zirconia); La (Lα, LaPO4); Ce (Lα, CePO4); Pr (Lβ, PrPO4); Nd (Lα, NdPO4); Sm (Lβ, SmPO4); Eu (Lα, EuPO4); U (Mβ, UO2); Th (Mα, ThSiO4); Pb (Mα, vanadinite); F (Kα, LiF). The peak and background times were 10 and 5 s, respectively, except for Ce, La, Nd, Pr, Sm, Nb, Th (20 s/10 s) and Ta, U (20 s/20 s). Overlap corrections were carefully applied where required.

4. Results

4.1. Field Relations with Strike-Slip Faulting

Our geological observations and mapping studies reveal that the region was shaped by a set of NW–SE-trending right-lateral strike-slip faults which cut and offset the original thrust faults between the Karakaya Complex and the ophiolitic rocks (Figure 1c). Detailed field studies revealed that the sheared sandstones of the Karakaya Complex were juxtaposed with the brecciated serpentinites along a right-lateral strike slip fault which strikes N 58–63° W and dips 90° (Figure 2). The deformation can be traced along a ~10 m width. Notably, the field relations reveal the phonolitic domes were emplaced along this fault system. This zone is defined as the Kızılcaören shear zone in Figure 1b.

4.2. Petrography

The petrography, mineral chemistry, and petrology of the alkaline silicate rocks, carbonatites, and associated fluorite–bastnäsite–barite ore zones in the region have been extensively studied [34,35,37,38,40,41,42,43,48]. In contrast, the pyroclastic rocks remain poorly characterized.
The pyroclastic rocks appear dark grey to pale yellow or brownish in both field exposures and hand specimens (Figure 3a,b). They consist mainly of lapilli-like clasts (<2 cm), displaying both angular and subrounded morphologies (Figure 3c), with some clasts preserving chilled margins. Although the basement comprises the Karakaya Complex and the ophiolitic serpentinites, wall-rock xenoliths in the pyroclastic are solely derived from the Karakaya Complex (sandstone and limestone clasts), and no ophiolitic fragments were observed.
Petrographic analysis reveals that, in addition to the wall-rock xenoliths, the pyroclastic rocks contain abundant autholithic (or cognate xenolithic) rock and mineral fragments (fragments that are genetically related [cogenetic] to the unit itself), as well as juvenile components.
In the following section, we describe the petrographic features and chemical characteristics of each component within the pyroclastic rocks, using a coding system that references thin section numbers and designated areas. For example, a rock fragment determined in circle number 3 of section 82a is labelled as “fragment 82a-c3”.

4.2.1. Cognate Inclusions

Cognate inclusions in the pyroclastic rocks include a variety of magmatic (syenitic composition with hypabyssal origin) and metasomatic rocks (silicate–carbonate rocks), displaying diverse mineralogies and textures (Figure 3). The magmatic rocks are uniformly fine-grained (<0.2 mm) and show holocrystalline textures, consistent with a hypabyssal origin. The most prevalent type of these rock fragments consists almost entirely of sanidine (>97 vol.%; Figure 4a–d). Some fragments show trachytic textures defined by oriented euhedral (tabular) sanidine crystals less than ~100 µm in size (fragment 82a-c8; Figure 4a). In some rock fragments, the orientation is less pronounced or absent (fragments 51a-c4 and 82b-c6; Figure 4b,c, respectively). Furthermore, some fragments contain larger sanidine crystals (up to 300 µm) with subhedral to anhedral forms (fragment 51a-c6; Figure 4d). In this particular type of rock, sanidine is associated with carbonate minerals containing Mg and Ca admixtures (Figure 4c).
Some samples show sanidine-rich rock fragments partially replaced by carbonate + baryte along diffusive contacts (fragment 82b-c7; Figure 4e,f). Other magmatic rock fragments exhibit syenitic compositions, including assemblages of sanidine + albite + phlogopite + apatite (Figure 4g), and sanidine + amphibole (magnesio-fluoro-arfvedsonite) + apatite (fragment 82a-c7; Figure 4h). These minerals are frequently euhedral and measure less than 1 mm.
Another type of cognate inclusion comprises carbonatite and carbonate–silicate rock fragments. The carbonatite clasts consist of calcite, Fe-Mg carbonates, baryte, fluorite, and radial bastnäsite (fragments 82a-c2 and 82b-c8; Figure 5a–d), sharing mineralogical and textural similarities with surface carbonatites [34,35,36,37,38,40,43]. The carbonate–silicate rock fragments include an “albite–calcite rock” (fragment 82a-c4; Figure 5e,f), an analogue of the phlogopite–calcite–albite rocks reported by [37].
The pyroclastic rocks also contain abundant mineral fragments, dominated by euhedral sanidine, baryte, calcite, and phlogopite, most likely derived from the fragmentation of the cognate materials described above. It is noteworthy that the majority of sanidine and phlogopite crystals exhibit euhedral morphologies.

4.2.2. Juvenile Components

Juvenile components in the pyroclastic rocks are represented by carbonatite droplets and spherical to ellipsoidal pelletal lapilli. Unlike the angular carbonatite rock fragments, the carbonatite droplets have smooth, ellipsoidal margins and flow-oriented crystals (droplet 82b-c4; Figure 6a). These droplets display distinct textures and mineralogies compared to both the carbonatite rock fragments and surface carbonatite veins. In detail, these occurrences are characterized by needle-shaped brownish carbonates showing spinifex-like textures, indicative of rapid cooling [15] (Figure 6b) and amphiboles (potassic-richterite; Figure 6c) arranged in spinifex-like textures with randomly oriented laths. EPMA studies also identified euhedral baryte and radial parisite (Figure 6d). Some carbonate droplets contain brownish rhombohedral carbonate crystals embedded in large calcite grains (droplet 82a-c5; Figure 6e,f), with chemical compositions corresponding to Fe-Mg-Ca carbonate admixtures (see below).
The primary component of the pyroclastic rocks is composed of spherical to ellipsoidal lapilli which are smaller than 5 mm. These features typically consist of a kernel, composed of microcrystal or lithic fragments, mantled by a cryptocrystalline matrix. Flow-aligned euhedral sanidine microphenocrysts (less than 500 µm) are embedded within this matrix (Figure 7a–f). The kernels can reach sizes of up to 2 mm. EPMA studies reveal that the mantling matrix is predominantly composed of calcium carbonate (see below).

4.3. Mineral Chemistry

4.3.1. Feldspar

Our EPMA investigations of cognate magmatic fragments (51a-c4, Figure 4b; 82b-c6, Figure 4c; 51a-c6, Figure 4d; 82a-c7, Figure 4h) consistently identify sanidine as the dominant feldspar phase (columns 1–8 in Table A1). The sole exception occurs in fragment 82a-c7 (Figure 4h), where feldspars display perthitic textures with fine-scale anorthoclase to albite exsolutions (Figure 8d). All analyzed feldspars share key characteristics: strictly alkaline compositions (Ca-free) with considerably elevated BaO contents. We represent these compositions on a ternary KAlSi3O8 (sanidine, Sa)—NaAlSi3O8 (albite, Ab)—BaAlSi2O8 (celsian, Cls) diagram (Figure 8). Pure sanidine fragments (51a-c4, Figure 4b; 82b-c6, Figure 4c; 51a-c6, Figure 4d) contain up to 2.68 wt.% BaO (Table A1), plotting within the compositional range Sa44–99–Ab1–56–Cls0–5 (Figure 8a–d). Pyroclastic-hosted feldspar fragments mirror these compositions (columns 9–10 in Table A1; Figure 8e), varying in the range Sa70–99–Ab2–26–Cls0–6. In contrast, the carbonate–silicate rock fragment (fragment 82a-c4, Figure 5e) contains nearly pure Ba-free albite (Sa3–28–Ab72–97–Cls0; columns 11 and 12 in Table A1; Figure 8f). Flow-aligned feldspar microphenocrysts surrounding lapilli show extreme K2O (up to 16.4 wt.%) and BaO (3.54 wt.%) enrichment (columns 13 and 14 in Table A1). Their compositions are expressed as Sa71–99–Ab1–25–Cls0–7 (Figure 8g).

4.3.2. Amphibole

Amphibole, observed in the cognate magmatic rock fragment 82a-c7 (Figure 4h), exhibits Na2O, K2O, and CaO concentrations in the ranges 9.4–11.0 wt.%, 1.4–2.2 wt.%, and 0.3–0.9 wt.%, respectively, (columns 1 to 7 in Table A2). Florine contents vary in the range 3.0–4.1 wt.% (F apfu > 1). The Si (apfu) and Mg# (=Mg/Mg+Fe2+) contents are 8.0–8.1 and 0.8–0.9, respectively. Because both the amphibole and associated rocks are alkaline in composition, and the maximum ferric iron calculation [49] has been applied. Estimated Al(VI) and Fe3+ (apfu) values fall within the ranges of 0–0.2 and 0.3–0.8, respectively. Based on these parameters and the classification scheme of [49], the amphiboles are classified as sodic amphiboles, specifically magnesio-fluoro-arfvedsonite (Figure 9a).
Amphibole from the carbonatite droplet (82b-c4; Figure 6c) shows Na2O, K2O, and CaO contents of 4.3–5.6, 2.9–4.0, and 6.3–8.5 wt.%, respectively, (columns 8 to 14 in Table A2). These amphiboles have low F (1.2–1.8 wt.%) and display high Mg# values in the range 0.96–0.98. Applying the maximum ferric iron calculation, these amphiboles are classified as sodic-calcic amphibole, specifically potassic-richterite (Figure 9b).

4.3.3. Mica

Cognate mica fragments in the pyroclastic rocks exhibit high Mg# (>0.89) and elevated F contents (>4 wt.%; Table A3). Mineral composition calculations, based on [50], indicate all mica fragments are classified as phlogopite on a IVAl/(IVAl+IVSi) vs. Mg# plot (Figure 10).

4.3.4. Carbonates and Fluorocarbonates

In addition to the limestone clasts and calcite fragments in the pyroclastic rocks, carbonate minerals are documented in (1) the cognate magmatic fragments, which are partially replaced by carbonatitic material (e.g., fragment 82b-c7; Figure 4e,f), (2) in the cognate carbonatite clasts (fragments 82a-c2 and 82b-c8; Figure 5a–d) and silicate–carbonate clasts (fragment 82a-c4; Figure 5e,f), (3) in the juvenile carbonatite droplets (droplets 82b-c4 and 82a-c5; Figure 6), and (4) as cryptocrystalline material among the sanidines in the mantle of the juvenile lapilli (Figure 7).
Carbonatitic materials replacing sanidine-rich rocks consist of larger calcite crystals (Figure 4f) with MgO + FeO totals below 3 wt.% (columns 1 and 2 in Table A4), as well as smaller, euhedral ankerite and dolomite crystals (columns 3 and 4 in Table A4; Figure 11a). It is noteworthy that these carbonates contain up to 0.6 wt.% SrO. In addition, BaO-, FeO-, and MgO-rich carbonate minerals were observed during the EPMA studies (column 5 in Table A4). Carbonates among the sanidine-rich fragments (82b-c6; Figure 4c) have dolomite compositions (column 6 in Table A4).
Large carbonates in the carbonatite clasts (Figure 5c) are generally calcite, with MgO reaching 4.6 wt.% (columns 7 and 8 in Table A4). Smaller, brownish carbonates of similar nature exhibit slightly higher MgO or FeO contents. Additionally, BaO-rich carbonates display compositions between barytocalcite (BaCa[CO3]2) and calcite (CaCO3), as depicted in Figure 11b (columns 9 and 10 in Table A4). There are REE (Rare Earth Elements)-bearing fluorocarbonates, with high amounts of light REE (La, Ce, Pr, and Nd), in the range 66.2–68.5 wt.% (columns 11 and 12 in Table A4). On the CaCO3–BaCO3–REEFCO3 ternary diagram, they form a solid solution between parisite and bastnäsite (Figure 11b). These minerals also contain ThO2 at concentrations between 4.33 and 5.09 wt.%.
Carbonate droplets in the pyroclastic rocks (Figure 6) are composed mostly of large calcite crystals (columns 13 and 14 in Table A4) and smaller rhombohedral carbonates with elevated MgO and FeO contents (columns 15 and 16 in Table A4; Figure 11a). SrO contents in these droplets reach up to 0.24 wt.%. Some droplets also host REE-fluorocarbonates (columns 17 and 18 in Table A4), which tend to plot closer to parisite compositions on the CaCO3–BaCO3–REEFCO3 ternary plot (Figure 11b).
Carbonate material in the lapilli, surrounding the sanidine microphenocrysts, is composed mostly of calcium carbonate with MgO < 1.5 and FeO < 0.2 wt.% (columns 19 and 20 in Table A4; Figure 11a), although two measurements yielded elevated FeO values (2.53 and 22.90 wt.%). These carbonate phases contain SrO between 0.24 and 0.65 wt.% and Ce2O3 from 0.02 to 0.17 wt.%. The compositionally similar matrix of the lapilli mantle and the carbonatite droplets indicates a common magmatic origin (Figure 11a).

4.3.5. Matrix Composition

Whole-rock analyses by Hatzl [35] and Stumpfl and Kırıkoglu [40] show that the pyroclastic matrix exhibits a broad compositional spectrum, with SiO2 (10.8–76.0 wt.%), MgO (0.1–17.5 wt.%), Fe2O3 (0.5–19.7 wt.%), and K2O (0.1–14.6 wt.%). These results are illustrated on a TAS (total alkali–silica) diagram (Figure 12), where they display considerable scatter. This compositional diversity is apparently related to the hybrid nature of the pyroclastic rocks, because they contain abundant wall-rock xenoliths (sandstone, limestone, etc.), i.e., xenolith contamination. Notably, most compositions cluster around the trachyte and phonolite fields. To refine this assessment, we performed EPMA analyses on 29 points within the fine-grained matrix, with 23 analyses yielding consistent results indicative of a trachytic to potassic-trachyte/phonolite composition with SiO2 of 62.8–66.5, K2O of 10.8–15.8, Na2O of 0.1–1.8, Al2O3 of 18.3–20.2, and BaO up to 2.92 (wt.%; Table A5, Figure 12). The remaining six points yielded mixed mineral compositions, including K-feldspar, baryte, carbonates, and Fe-Ti oxides.

5. Discussion

5.1. Implications for a Diatreme Structure

Petrographic examination of the Kızılcaören pyroclastic rocks reveals spherical and ellipsoidal lapilli-sized clasts, composed of a kernel of rock or mineral fragments enveloped by a carbonate mantle in which euhedral, prismatic sanidine microphenocrysts are flow-aligned (Figure 7). These discrete components are comparable to pelletal lapilli [16] described in kimberlites, carbonatites, and other types of alkaline rocks such as kamafugites, melilitites, and orangeites [12,18,51,52]. These clasts are also known as tuffisitic lapilli [51], spherical lapilli [53], spinning droplets [54,55,56], cored lapilli [52,57], and concentrically shelled lapilli [58]. The recent literature, especially that dealing with kimberlites, has used the term melt-bearing pyroclast as a magmaclast [23].
These clasts appear to be very similar to the accretionary lapilli, or armoured (or mantle) lapilli, which formed via interaction between magma and meteoric water, an indicator for phreatomagmatic eruptions [59,60]. For the pelletal lapilli, two main models have been proposed for their formation: (a) The spherical shapes of these occurrences are formed during spinning of magma clots around a solid kernel in a fluidized system [19,61]. (b) Melt droplets and microphenocrysts stick to the solid kernel due to surface tension in a gas jet, and these clasts rotate during transport, resulting in a flow-arrangement [12,20,21,22]. Hence, the particles in the accretionary lapilli, or armoured (or mantle) lapilli, are thought to form by interaction with water, whilst the pelletal lapilli represent accretions from juvenile melts [62].
For example, pelletal lapilli in kamafugitic diatreme in the Goiás alkaline province (Brazil) are composed of a core including both cognate (pyroxene and olivine cumulates and leucite mafurite), and xenolithic fragments of granite, feldspar, and sandstone. The rim of these clasts includes melilite, kalsilite, diopside, phlogopite, apatite, calcite, etc., in a devitrified glassy or glass or cryptocrystalline groundmass [31]. In addition, pelletal lapilli from the melilitite–carbonatite from Mt. Vulture (Southern Italy) have wherlitic xenolith cores and rims with xenocrystic olivine, clinopyroxene, and subhedral to euhedral microcrystic haüyne and melilite laths [24].
In the Kızılcaören example, the pelletal lapilli contains mostly xenolithic or cognate cores (sandstone, sanidine fragments) mantled by an ultra-fine-grained, cryptocrystalline carbonate-rich matrix in which euhedral high-BaO sanidine laths are flow-oriented. Therefore, regardless of their precise genesis, it is clear that the pyroclastic rocks in the Kızılcaören area include pelletal lapilli, and this component is a characteristic feature of the tuffisite, i.e., tuff-penetrated breccias in kimberlite or alkaline silicate–carbonatite diatremes [9,10,12]. Drilling studies carried out by MTA have found that the thickness of the unit exceeds 800 m in the central parts of its exposures [34], indicating that the pelletal lapilli-bearing pyroclastic rocks in the Kızılcaören area likely represent the intrusive pyroclastic material in the “diatreme zone”, which filled the pipe with brecciated materials, i.e., tuffisite. These implications are summarized in Figure 13.
It is noted that the pelletal lapilli are often found with magma clots and fragments of fine-grained, cogenetic hypabyssal igneous rocks (cognate inclusions or cognate xenoliths) [12]. These components are crucial in understanding the origin and evolution of these magmatic complexes. The cognate inclusions in the tuffisite in the Kızılcaören area predominantly comprise fine-grained (<0.2 mm) magmatic fragments with high-BaO sanidine, sodic alkali amphiboles, and mineral fragments of high-BaO sanidine and phlogopite. On the surface, the alkali silicate rocks are represented by (a) foid-bearing phonolite with high-BaO sanidine, aegirine-augite, altered foids (haüyne and nepheline), and garnet; and (b) trachyte with sanidine, diopside, sphene, and quartz, according to [35,37,48] and our unpublished data. Their hypabyssal nature suggests an origin from the “root zone” of the diatreme, likely representing intrusive dikes and sills in the subsurface environment (Figure 13).
Notably, the tuffisite in the Kızılcaören area also contains bastnäsite-bearing carbonatite and albite–calcite rock fragments. These lithologies have also been recorded in the surface [37,38] and throughout the drilling cores [34] as alternating veins in the tuffisite (e.g., [37]), revealing that they formed after emplacement of the tuffisite. Therefore, the presence of these fragments in the tuffisite as xenoliths further suggests that similar carbothermal/metasomatic events forming the REE-bearing carbonatites [38] also occurred before emplacement of the pyroclastic rocks, i.e., a multi-stage generation of carbonatite, and alkaline silicate rocks, as well as REE-mineralization.
Furthermore, the presence of carbonatite droplets (as magmaclasts) with calcite, dolomite, and richteritic amphibole in the Kızılcaören tuffisite indicates the presence of immiscible carbonatite melt (e.g., [12]) in the genesis of this complex.

5.2. Regional Implications

While regional magmatism in NW Anatolia mainly includes Eocene to Late Miocene post-collisional units (Figure 1a; see [63] for a detailed review), the Kızılcaören alkali silicate–carbonatite complex stands out due to its association with evolved, silica-undersaturated (phonolitic), Na-alkaline rocks, including phonolites, carbonatites and REE deposits, features not common in the surrounding magmatic provinces. This indicates a distinct genetic mechanism for this complex, independent from the regional magmatism.
Tectonic structures are crucial for understanding how this magmatic complex was formed. Historically, the main tectonic contact between ophiolites and the Karakaya Complex (Figure 1c) was mapped as a thrust [35,37,40,64], with interpretations ranging from high-angle to normal faulting [34,38]. Some authors [39,65] placed the Kızılcaören alkaline silicate–carbonatite complex within the North Anatolian shear zone, which is interpreted as having developed in an accretionary zone along the İzmir–Ankara suture. However, as shown in Figure 1, the North Anatolian Fault Zone lies more than 100 km north of the study area.
Our field studies revealed that the region was shaped by NW–SE-trending right-lateral strike-slip faults (Figure 1c and Figure 2). The tectonic contact between the ophiolites and the Karakaya Complex can be observed along a road section to the west of the study area, located ~3.5 km east of Halilbağı village, where an 8–10 m wide shear zone juxtaposes these units. More importantly, the phonolitic domes emplaced along this fault have not undergone deformation. Considering the ~25–24 Ma age of the phonolites [37,42,48], these observations reveal that the NW–SE-trending right-lateral strike-slip faulting in the region most likely occurred during the late Oligocene. The trachytic domes and volcanics also appear to be aligned in a similar direction; however, no fault was identified during field studies in those areas. Nonetheless, the data strongly indicate that the formation of the Kızılcaören alkali silicate–carbonatite complex was controlled by a NW–SE-trending right-lateral strike-slip fault system (Figure 1c).
On a regional scale, it is proposed that, following the late Cretaceous amalgamation of a micro-continent along the Rhodopes, NW–SE-trending right-lateral faulting (the Maritza Shear Zone; MSZ) occurred in response to the N–S compression [66]. During the early Eocene, this fault zone likely migrated further southeast, giving rise to the formation of the right-lateral Kapıdağ Shear Zone (KSZ) to the south of the Marmara Sea [67,68,69]. This deformation propagated further to the SE during Oligocene times, leading to the development of the Uludağ shear zone (USZ) [70,71], potentially driven by ongoing N–S contraction. Therefore, the NW–SE-trending right-lateral faulting observed at ~25 Ma in the Kızılcaören area, identified here, appears to be related to this regional deformation that migrated from the MSZ (~80 Ma), through the KSZ (~50 Ma), and eventually to the USZ (~27 Ma). Subsequently, during the Miocene, this zone was cut and offset by the right-lateral North Anatolian Fault Zone (Figure 1, inset).
These observations provide important clues concerning the origin of the Kızılcaören alkali silicate–carbonatite complex, suggesting that it formed through lithosphere-scale strike-slip motion. The radiogenic and stable isotopic compositions (Sr-Nd and B, respectively) of the alkaline silicates and carbonatites in the area confirm a mantle origin for these rocks [41,58]. However, the highly evolved nature of phonolites and trachytes indicates they are not direct mantle-derived melts, but rather products of extensive differentiation and fractional crystallization of mantle melts. Overall, this small and regionally unique alkali complex is interpreted to have originated from very low-degree partial melting of the mantle, triggered within a lithosphere deformed by strike-slip faulting at a regional scale. Low-degree decompressional melting of the lithospheric mantle may have developed in response to local extensional domains along transtensional deformation (e.g., [72]). The presence of carbonatites, in addition to the silica-undersaturated silicate rocks, as well as their diatreme-like structure, requires a carbonated magmatic precursor. This process can be explained by contamination of the low-degree alkali melts by assimilation of marbles from the Tavşanlı Zone, which represent the buried northern edge of the Anatolide–Tauride carbonate platform. The assimilation of these marbles likely produced CO2-rich, undersaturated melts that, upon ascending through the crust, explosively decompressed, forming the Kızılcaören diatreme filled with a tuffisitic material, i.e., intrusive pyroclastics.

6. Conclusions

The geological and petrological evidence for a diatreme structure within the Kızılcaören alkali silicate–carbonatite complex is summarized in Figure 13. The data suggest that the phonolitic diatreme in this region formed within the Karakaya Complex, accounting for the absence of ophiolite xenoliths in the pyroclastic rocks. The presence of the pelletal lapilli in the pyroclastic rocks clearly reveals formation in a fluidized eruption environment driven by volatile (CO2 and F)-rich magmatism, with these structures representing the filling material (known as tuffisite) of the diatreme. The abundant hypabyssal alkali rock fragments in the pyroclastic rocks likely indicate the presence of a root zone (dikes and sills), which served as a magmatic feeder system. However, the extent and internal architecture of the diatreme’s crater zone remain poorly constrained, suggesting the need for further volcanological investigations, such as facies analyses, and detailed geophysical studies, to fully delineate the structure of the Kızılcaören phonolitic diatreme. The geological record also reveals that the Kızılcaören alkali silicate–carbonatite complex was emplaced along a strike-slip fault zone. Thus, this zone may serve as an exploration target for similar potential occurrences.

Author Contributions

Conceptualization, Y.E.E., H.Y. and M.R.P.; methodology, Y.E.E., İ.U. and D.M.; software, D.M., İ.U. and Y.E.E.; validation: Y.E.E., D.M., M.R.P. and H.Y.; formal analysis, İ.U. and D.M.; investigation, Y.E.E., H.Y. and D.M.; resources, Y.E.E. and H.Y.; data curation, İ.U. and D.M.; writing—original draft preparation, Y.E.E. and H.Y.; writing—review and editing, Y.E.E., H.Y., İ.U. and M.R.P.; visualization, Y.E.E. and H.Y.; supervision, project administration, and funding acquisition, Y.E.E. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Turkish Academy of Sciences, grant number TÜBA-GEBİP/2018.

Data Availability Statement

Data will be made available on request.

Acknowledgments

This study is a part of Hikmet Yavuz’s Ph.D. thesis. We want to express our gratitude to Osman Candan and Fatma Özaydın for their contributions during preparation of the thin sections. Three anonymous referees are acknowledged for their positive and constructive comments. Pei Ni is acknowledged for editorial handling.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
EPMAElectron probe microanalyzer

Appendix A

Table A1. Representative compositions of feldspar from the pyroclastic rocks. -: below detection limit. 1–8: cognate magmatic rock fragments; 9–10: mineral fragments 11–12: carbonate–silicate rock fragments; 13–14: lapilli.
Table A1. Representative compositions of feldspar from the pyroclastic rocks. -: below detection limit. 1–8: cognate magmatic rock fragments; 9–10: mineral fragments 11–12: carbonate–silicate rock fragments; 13–14: lapilli.
1234567891011121314
Sample51a-c451a-c482b-c682b-c651a-c951a-c982a-c782a-c751a-c551a-c582a-c482a-c451a-c751a-c7
SiO263.7265.6063.3266.2262.4363.9565.0962.5361.5863.5668.3067.5862.4762.25
Al2O319.8819.5219.0019.5719.0219.0318.3018.0619.3819.4620.8620.5119.3918.46
FeO0.250.011.730.810.180.210.120.500.280.42-1.180.570.52
CaO0.070.04-0.04-0.080.020.010.030.060.17-0.060.04
Na2O0.380.380.835.931.471.390.760.831.761.9811.0610.491.821.73
K2O14.6215.4513.206.9614.0313.7215.1314.2212.5912.400.500.7612.7013.06
BaO2.681.150.040.030.961.900.381.743.273.140.030.023.192.74
Total101.69102.1499.1199.5898.21100.5899.9299.7399.16101.21100.96100.78100.4999.12
Si2.942.972.942.982.952.963.012.942.922.942.962.952.922.95
Al1.081.041.041.041.061.041.001.001.081.061.061.051.071.03
Fe2+0.010.000.070.030.010.010.000.020.010.02-0.040.020.02
Ca0.000.00-0.00-0.000.000.000.000.000.01-0.000.00
Na0.030.030.070.520.130.120.070.080.160.180.930.890.160.16
K0.860.890.780.400.850.810.890.850.760.730.030.040.760.79
Ba0.050.020.000.000.020.030.010.030.060.060.000.000.060.05
Total4.974.974.954.965.014.994.985.025.004.984.994.995.005.01
End-member compositions (%)
KAl2Si3O891.394.491.243.684.783.692.288.877.475.72.94.577.279.0
NaAlSi3O83.63.58.756.413.512.87.17.916.418.497.195.416.815.9
BaAl2Si2O85.12.20.10.11.83.60.73.36.25.90.10.06.05.1
Table A2. Representative compositions of amphibole from the cognate magmatic rock fragments in the pyroclastic rocks. 1–6: fragment 82a-c7, 7–12: fragment 82b-c4.
Table A2. Representative compositions of amphibole from the cognate magmatic rock fragments in the pyroclastic rocks. 1–6: fragment 82a-c7, 7–12: fragment 82b-c4.
12345678910111213
SiO2 57.2556.2555.8256.3056.3056.4757.6357.0356.1957.3856.8356.1956.75
TiO2 0.541.370.290.810.801.620.230.280.310.260.160.220.18
Al2O3 0.390.610.410.360.280.330.060.050.070.020.060.070.03
FeO 9.659.7710.369.399.167.891.451.451.631.391.601.921.64
MnO 1.932.031.141.620.811.020.190.290.280.330.250.310.29
MgO 16.4515.6416.2116.8016.5917.1524.6524.5224.1924.2324.1323.7423.78
CaO 0.900.600.610.740.350.326.447.046.857.176.716.936.38
Na2O 9.439.509.659.549.7610.035.395.144.304.815.405.295.26
K2O 1.911.931.931.851.941.503.333.613.933.472.942.933.43
F3.023.123.703.783.633.761.731.291.201.251.591.381.49
--O=F1.271.311.561.591.531.580.730.540.510.530.670.580.63
Total 100.2999.5498.6799.6798.2498.62100.36100.1698.4699.7999.0098.4098.61
Si8.068.028.037.998.108.067.897.837.857.897.887.867.91
Ti0.060.150.030.090.090.170.020.030.030.030.020.020.02
Al (IV)0.000.000.000.010.000.000.010.010.010.000.010.010.01
Al (VI)0.070.100.070.050.050.060.000.000.000.000.000.000.00
Fe2+0.640.760.710.530.750.630.170.170.190.160.190.220.19
Fe3+0.500.400.540.580.350.310.000.000.000.000.000.000.00
Mn0.000.000.000.000.000.000.020.030.030.040.030.040.03
Mg3.453.323.483.553.563.655.035.025.044.974.994.954.94
Ca0.140.090.090.110.050.050.941.041.021.061.001.040.95
Na2.572.632.692.632.722.771.431.371.161.281.451.441.42
K0.340.350.350.340.360.270.580.630.700.610.520.520.61
F1.361.421.701.721.671.710.750.560.530.540.700.610.66
OH0.640.580.300.280.330.291.251.441.471.461.301.391.34
Total15.8215.8216.0015.8816.0315.9716.0916.1316.0416.0316.0816.0916.08
Mg#0.840.810.830.870.830.850.970.970.960.970.960.960.96
Table A3. Representative compositions of mica fragments in the pyroclastic rocks.
Table A3. Representative compositions of mica fragments in the pyroclastic rocks.
123456789
SiO242.8844.0344.0444.0043.4543.5843.9642.6644.46
TiO20.720.850.921.021.090.800.770.820.55
Al2O310.379.709.399.409.209.679.9010.359.45
FeO6.615.575.626.056.095.325.245.819.48
MnO0.650.600.720.670.670.640.600.760.50
MgO21.7322.1122.1821.8321.9021.3022.6222.3519.37
BaO0.090.140.030.100.070.180.110.070.06
CaO0.040.030.040.050.020.040.080.060.11
Na2O0.360.420.440.410.470.370.360.340.33
K2O10.0310.0510.199.9910.1710.2610.1710.228.48
F4.304.924.964.914.724.984.934.563.71
SrO---------
Total97.8398.4398.5498.4697.8697.1598.7398.0196.50
T.Si3.133.203.213.213.193.213.193.123.24
T.Al0.760.690.690.680.690.690.730.800.56
T.Fe3+0.110.100.100.110.120.100.090.080.20
sumTet4.004.004.004.004.004.004.004.004.00
M.Al0.130.140.120.130.110.150.120.090.25
M.Mg2.362.402.412.372.402.342.442.432.07
M.Fe2+0.280.240.250.270.270.290.240.270.30
M.Fe3+0.01------0.010.08
M.Ti0.050.060.070.070.080.070.060.060.05
M.Mn0.040.040.040.040.040.040.040.050.03
Sumoct2.892.882.902.882.892.892.892.902.78
Oct.Vac.0.110.120.100.120.110.110.110.100.22
A.K0.950.940.960.940.960.980.950.970.83
A.Na0.050.060.060.060.070.050.050.050.05
A.Ba0.000.000.000.000.000.010.000.000.00
A.Ca0.000.000.000.000.000.000.010.000.01
Suminter1.001.011.021.011.031.041.011.020.88
InterVac.--------0.12
W.F0.981.121.131.121.091.151.111.040.81
W.OH0.770.600.580.580.620.600.620.710.81
W.O2-0.250.270.290.300.300.250.270.250.39
Fe3+/Fetot0.300.300.290.290.310.260.270.250.48
Mg#0.890.910.900.900.900.890.910.900.87
Table A4. Representative compositions of carbonate and fluorocarbonates in the carbonatite clasts and carbonatite droplets in the pyroclastic rocks. CO2 is calculated stoichiometrically. n.a.: not analyzed. 1–6: Carbonatite replacing the sanidine-rich rocks [1–6: fragment 82b-c7, 6: fragment 82b-c6]; 7–12: carbonatite clasts [7–8: fragment 82b-c8, 9–10: 82a-c, 11–12: 82b-c8]; 13–18: carbonatite droplet; 19–20 [droplet 82b-c49]: lapilli mantle [51a-c7].
Table A4. Representative compositions of carbonate and fluorocarbonates in the carbonatite clasts and carbonatite droplets in the pyroclastic rocks. CO2 is calculated stoichiometrically. n.a.: not analyzed. 1–6: Carbonatite replacing the sanidine-rich rocks [1–6: fragment 82b-c7, 6: fragment 82b-c6]; 7–12: carbonatite clasts [7–8: fragment 82b-c8, 9–10: 82a-c, 11–12: 82b-c8]; 13–18: carbonatite droplet; 19–20 [droplet 82b-c49]: lapilli mantle [51a-c7].
1234567891011121314151617181920
FeO0.01 0.04 23.10 0.54 15.66 0.73 0.00 0.64 1.29 1.12 0.00 0.00 0.16 0.02 13.35 15.07 0.52 0.00 0.150.12
MnO0.00 0.01 0.22 0.04 0.16 0.09 0.08 0.02 0.19 1.27 0.00 0.00 0.03 0.00 0.06 0.03 0.00 0.00 0.130.03
MgO2.62 2.20 2.47 10.39 10.77 18.39 1.71 4.57 0.72 0.74 0.03 0.03 1.13 2.50 3.55 1.06 0.37 0.08 0.850.36
CaO53.47 54.17 29.93 39.39 14.47 33.69 52.06 48.80 15.37 14.76 4.82 4.35 55.24 58.62 39.20 39.68 7.63 8.57 55.9754.59
BaO0.00 0.00 0.11 0.10 8.09 0.00 0.10 0.00 30.79 27.47 0.15 0.11 0.04 0.00 0.00 0.06 0.20 0.30 0.000.03
SrO0.34 0.38 0.05 0.10 0.05 0.11 0.02 0.06 0.06 0.00 2.67 2.44 0.02 0.24 0.04 0.02 2.61 2.42 0.340.45
La2O3n.a.n.a.n.a.n.a.n.a.n.a.0.06 n.a.n.a.n.a.24.14 23.72 n.a.n.a.n.a.n.a.22.85 22.17 n.a.n.a.
Ce2O30.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 2.31 1.76 31.48 32.10 0.00 0.00 0.00 0.00 27.28 29.75 0.100.08
Pr2O3n.a.n.a.n.a.n.a.n.a.n.a.0.24 n.a.n.a.n.a.2.85 2.91 n.a.n.a.n.a.n.a.2.57 2.61 n.a.n.a.
Nd2O3n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.8.40 8.89 n.a.n.a.n.a.n.a.7.40 8.21 n.a.n.a.
Sm2O3n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.0.57 0.72 n.a.n.a.n.a.n.a.0.61 0.81 n.a.n.a.
ThO2n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.4.33 4.45 n.a.n.a.n.a.n.a.5.60 5.73 n.a.n.a.
F n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.4.05 4.12 n.a.n.a.n.a.n.a.5.70 3.99 n.a.n.a.
--O=F 1.70 1.73 2.40 1.68
CO244.97 45.10 40.53 42.67 35.15 47.08 42.81 43.72 23.23 22.22 22.91 22.63 44.72 48.85 42.88 41.58 23.98 24.74 45.1943.55
Total101.40 101.92 97.51 93.66 84.58 100.25 96.90 97.82 74.14 69.56 100.44 100.34 101.36 110.27 99.18 97.56 98.81 101.25 102.8799.41
CaCO393.31 94.25 57.96 72.43 32.31 56.17 95.44 87.60 51.91 52.12 16.51 15.10 96.94 94.17 71.75 74.89 24.96 27.17 97.2098.36
End-member compositions (%)
MgCO36.37 5.31 6.66 26.58 33.45 42.67 4.36 11.42 3.37 3.64 0.14 0.13 2.76 5.59 9.04 2.79 1.66 0.37 2.040.91
FeCO30.01 0.06 34.92 0.77 27.29 0.95 0.00 0.89 3.39 3.10 0.00 0.00 0.22 0.02 19.08 22.21 1.33 0.00 0.200.17
MnCO30.00 0.01 0.34 0.05 0.28 0.12 0.11 0.03 0.50 3.53 0.00 0.00 0.04 0.00 0.09 0.05 0.00 0.00 0.170.05
SrCO30.32 0.36 0.05 0.10 0.06 0.10 0.02 0.06 0.11 0.00 4.95 4.58 0.02 0.21 0.04 0.03 4.63 4.16 0.320.44
BaCO30.00 0.00 0.08 0.07 6.61 0.00 0.07 0.00 38.05 35.48 0.19 0.13 0.02 0.00 0.00 0.04 0.24 0.35 0.000.02
LaCO3n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.28.46 28.31 n.a.n.a.n.a.n.a.25.74 24.21 n.a.n.a.
CeCO3n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.2.67 2.13 36.84 38.04 n.a.n.a.n.a.n.a.30.51 32.24 0.060.05
PrCO3n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.3.32 3.43 n.a.n.a.n.a.n.a.2.87 2.81 n.a.n.a.
NdCO3n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.n.a.9.58 10.28 n.a.n.a.n.a.n.a.8.07 8.68 n.a.n.a.
Table A5. Representative compositions of matrix of the pyroclastic rocks. -: below detection limit.
Table A5. Representative compositions of matrix of the pyroclastic rocks. -: below detection limit.
123456789101112131415
SiO263.4962.7662.8363.8262.8063.6763.8663.5966.0664.6764.5565.1365.2865.5364.53
TiO20.030.030.030.030.030.050.040.040.030.010.020.040.040.010.05
Al2O318.9118.3318.9118.6819.1419.0119.4219.1819.4319.8218.8319.4519.1020.1619.63
FeO0.490.630.570.560.540.520.500.500.380.260.920.510.440.520.56
MnO-0.030.010.040.00-0.010.03---0.01---
MgO-0.530.000.01-0.000.020.000.230.02---0.00-
CaO0.121.290.071.910.180.050.100.040.060.630.190.080.070.080.08
Na2O1.250.681.831.301.481.601.671.590.120.151.411.551.601.491.59
K2O12.8214.2212.8111.1712.9612.7512.4213.1314.3414.6013.8812.2013.7210.8312.74
P2O50.010.01--0.010.01--0.000.260.02----
BaO2.391.272.652.482.922.492.662.620.410.751.622.401.242.822.52
Ce2O30.130.120.200.160.120.190.140.180.030.170.030.150.040.150.08
Total99.6499.9099.90100.16100.19100.35100.85100.91101.09101.42101.46101.52101.54101.57101.78

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Figure 1. (a) Geological map of NW Anatolia (simplified from 1:500,000 scale Geological map of Türkiye). (b) A–B geological cross section showing the general tectonic structure of the region. (c) Detailed geological map of the Kızılcaören alkaline silicate–carbonatite complex. MSZ: Maritza Shear Zone (~80 Ma), KSZ: Kapıdağ Shear Zone (~50 Ma), USZ: Uludağ Shear Zone (~27 Ma), Sample locations are indicated by asterisks. C–D refers to the geological cross-section given below.
Figure 1. (a) Geological map of NW Anatolia (simplified from 1:500,000 scale Geological map of Türkiye). (b) A–B geological cross section showing the general tectonic structure of the region. (c) Detailed geological map of the Kızılcaören alkaline silicate–carbonatite complex. MSZ: Maritza Shear Zone (~80 Ma), KSZ: Kapıdağ Shear Zone (~50 Ma), USZ: Uludağ Shear Zone (~27 Ma), Sample locations are indicated by asterisks. C–D refers to the geological cross-section given below.
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Figure 2. (a) Field view of the N 58–63° W/90° fault zone juxtaposing the sheared sandstones of the Karakaya Complex against the brecciated serpentinites (location: 39°36.511′ N–31°18.235′ E). (b) close-up view of the brecciated serpentinites.
Figure 2. (a) Field view of the N 58–63° W/90° fault zone juxtaposing the sheared sandstones of the Karakaya Complex against the brecciated serpentinites (location: 39°36.511′ N–31°18.235′ E). (b) close-up view of the brecciated serpentinites.
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Figure 3. Field photos (a,b) and a polished slab of a hand specimen (c) from the pyroclastic rocks. The arrows indicate the wall-rock clasts (mostly sandstone) with chilled margins.
Figure 3. Field photos (a,b) and a polished slab of a hand specimen (c) from the pyroclastic rocks. The arrows indicate the wall-rock clasts (mostly sandstone) with chilled margins.
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Figure 4. Microscope views from the cognate magmatic rock fragments with variable mineralogy and textures in the pyroclastic rocks in the Kızılcaören area. The fragments are (a) 82a-c8, (b) 51a-c4, (c) 82b-c6, (d) 51a-c6, (e,f) 82b-c8, (g) 52a-c4, (h) 82a-c7. Ab—albite, Ap—apatite, Cal—calcite, Fe-Mg-carb—Fe- and Mg-bearing carbonate admixtures, Mfarf—Magnesio-fluoro-arfvedsonite, Phl—phlogopite, Sa—sanidine. +N: crossed Nichols,//N: parallel Nichols. See text for detailed explanations.
Figure 4. Microscope views from the cognate magmatic rock fragments with variable mineralogy and textures in the pyroclastic rocks in the Kızılcaören area. The fragments are (a) 82a-c8, (b) 51a-c4, (c) 82b-c6, (d) 51a-c6, (e,f) 82b-c8, (g) 52a-c4, (h) 82a-c7. Ab—albite, Ap—apatite, Cal—calcite, Fe-Mg-carb—Fe- and Mg-bearing carbonate admixtures, Mfarf—Magnesio-fluoro-arfvedsonite, Phl—phlogopite, Sa—sanidine. +N: crossed Nichols,//N: parallel Nichols. See text for detailed explanations.
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Figure 5. Microscope and back-scattered image (BSE) views from the carbonatite and carbonate–silicate rocks in the pyroclastic rocks. The fragments are (a,b) 82a-c2, (c,d) 82b-c8, and (e,f) 82a-c4. Ab—albite, Brt—baryte, Bsn—bastnaesite, Cal—calcite, Fe-Mg-Cal—Fe-Mg-bearing calcite (admixture of Fe-, Mg- and Ca-rich carbonates), Flr—fluorite. +N: crossed Nichols,//N: parallel Nichols. See text for detailed explanations.
Figure 5. Microscope and back-scattered image (BSE) views from the carbonatite and carbonate–silicate rocks in the pyroclastic rocks. The fragments are (a,b) 82a-c2, (c,d) 82b-c8, and (e,f) 82a-c4. Ab—albite, Brt—baryte, Bsn—bastnaesite, Cal—calcite, Fe-Mg-Cal—Fe-Mg-bearing calcite (admixture of Fe-, Mg- and Ca-rich carbonates), Flr—fluorite. +N: crossed Nichols,//N: parallel Nichols. See text for detailed explanations.
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Figure 6. Microscope and back-scattered image (BSE) views of the carbonatite droplets in the pyroclastic rocks. The droplets are (a–d) 82b-c4 and (e,f) 82a-c5. Brt—baryte, Cal—calcite, Fe-Mg-Ca—admixtures of calcite, dolomite and ankerite, Prct—potassic-richterite, Pst—parisite. N: crossed Nichols,//N: parallel Nichols. See text for detailed explanation.
Figure 6. Microscope and back-scattered image (BSE) views of the carbonatite droplets in the pyroclastic rocks. The droplets are (a–d) 82b-c4 and (e,f) 82a-c5. Brt—baryte, Cal—calcite, Fe-Mg-Ca—admixtures of calcite, dolomite and ankerite, Prct—potassic-richterite, Pst—parisite. N: crossed Nichols,//N: parallel Nichols. See text for detailed explanation.
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Figure 7. Microscope views from the pelletal lapilli in the pyroclastic rocks (a–f). N: crossed Nichols,//N: parallel Nichols. See text for detailed explanation.
Figure 7. Microscope views from the pelletal lapilli in the pyroclastic rocks (a–f). N: crossed Nichols,//N: parallel Nichols. See text for detailed explanation.
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Figure 8. Feldspar ternary plots with KAlSi3O8 (sanidine, Sa), NaAlSi3O8 (albite, Ab), and BaAlSi2O8 (celsian, Cls) end-members. (a–d) Cognate rock fragments of 51a-c4, 82b-c6, 51a-c6, and 82a-c7, (e) mineral fragments, (f) carbonate–silicate rock fragment 82a-c4, (g) sanidine microphenocrysts in lapilli.
Figure 8. Feldspar ternary plots with KAlSi3O8 (sanidine, Sa), NaAlSi3O8 (albite, Ab), and BaAlSi2O8 (celsian, Cls) end-members. (a–d) Cognate rock fragments of 51a-c4, 82b-c6, 51a-c6, and 82a-c7, (e) mineral fragments, (f) carbonate–silicate rock fragment 82a-c4, (g) sanidine microphenocrysts in lapilli.
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Figure 9. Si (apfu, atoms per formula unit) vs. Mg# (Mg/Mg+Fe2+) classification plots for (a) sodic amphiboles with NaB ≥ 1.50, (Mg+Fe2++Mn2+) > 2.5, (AlVI or Fe3+) > Mn3+, Li < 0.5; (Mg or Fe2+) > Mn2+, and (Na + K)A ≥ 0.50; and (b) sodic-calcic amphiboles with (Na + K)A ≥ 0.50, (Ca + NaB) ≥ 1.00, and 0.50 < NaB < 1.50 [49]. (a) Amphiboles in the cognate magmatic rock fragment 82a-c7 (Figure 4h), and (b) amphiboles in the carbonatite droplet 82b-c4 (Figure 5c).
Figure 9. Si (apfu, atoms per formula unit) vs. Mg# (Mg/Mg+Fe2+) classification plots for (a) sodic amphiboles with NaB ≥ 1.50, (Mg+Fe2++Mn2+) > 2.5, (AlVI or Fe3+) > Mn3+, Li < 0.5; (Mg or Fe2+) > Mn2+, and (Na + K)A ≥ 0.50; and (b) sodic-calcic amphiboles with (Na + K)A ≥ 0.50, (Ca + NaB) ≥ 1.00, and 0.50 < NaB < 1.50 [49]. (a) Amphiboles in the cognate magmatic rock fragment 82a-c7 (Figure 4h), and (b) amphiboles in the carbonatite droplet 82b-c4 (Figure 5c).
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Figure 10. Mg# (Mg/Mg+Fe2+) vs. IVAl/(IVAl+IVSi) vs. classification plot for cognate mica fragments in the pyroclastic rocks.
Figure 10. Mg# (Mg/Mg+Fe2+) vs. IVAl/(IVAl+IVSi) vs. classification plot for cognate mica fragments in the pyroclastic rocks.
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Minerals 15 00867 g011
Figure 11. CaCO3–MgCO3–FeCO3 (a), and CaCO3–BaCO3–REEFCO3 (b) ternary plots for the carbonates and fluorocarbonates in the studied samples.
Figure 11. CaCO3–MgCO3–FeCO3 (a), and CaCO3–BaCO3–REEFCO3 (b) ternary plots for the carbonates and fluorocarbonates in the studied samples.
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Minerals 15 00867 g012
Figure 12. Total alkali (Na2O+K2O wt.%) vs. Silica (SiO2 wt.%) plot for the whole-rock [35,40] and EPMA (this study) analyses from the pyroclastic rocks.
Figure 12. Total alkali (Na2O+K2O wt.%) vs. Silica (SiO2 wt.%) plot for the whole-rock [35,40] and EPMA (this study) analyses from the pyroclastic rocks.
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Minerals 15 00867 g013
Figure 13. Schematized A–B geological cross section (see Figure 1c for location) showing the structure of the Kızılcaören alkali silicate–carbonatite complex and the diatreme.
Figure 13. Schematized A–B geological cross section (see Figure 1c for location) showing the structure of the Kızılcaören alkali silicate–carbonatite complex and the diatreme.
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MDPI and ACS Style

Ersoy, Y.E.; Yavuz, H.; Uysal, İ.; Palmer, M.R.; Müller, D. The Petrology of Tuffisite in a Trachytic Diatreme from the Kızılcaören Alkaline Silicate–Carbonatite Complex, NW Anatolia. Minerals 2025, 15, 867. https://doi.org/10.3390/min15080867

AMA Style

Ersoy YE, Yavuz H, Uysal İ, Palmer MR, Müller D. The Petrology of Tuffisite in a Trachytic Diatreme from the Kızılcaören Alkaline Silicate–Carbonatite Complex, NW Anatolia. Minerals. 2025; 15(8):867. https://doi.org/10.3390/min15080867

Chicago/Turabian Style

Ersoy, Yalçın E., Hikmet Yavuz, İbrahim Uysal, Martin R. Palmer, and Dirk Müller. 2025. "The Petrology of Tuffisite in a Trachytic Diatreme from the Kızılcaören Alkaline Silicate–Carbonatite Complex, NW Anatolia" Minerals 15, no. 8: 867. https://doi.org/10.3390/min15080867

APA Style

Ersoy, Y. E., Yavuz, H., Uysal, İ., Palmer, M. R., & Müller, D. (2025). The Petrology of Tuffisite in a Trachytic Diatreme from the Kızılcaören Alkaline Silicate–Carbonatite Complex, NW Anatolia. Minerals, 15(8), 867. https://doi.org/10.3390/min15080867

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