# Petrogenesis and Geochemistry of Upper Paleozoic Komatiites (Mashhad, NE Iran)

Mohsen Mobasheri, Nicholas Arndt, Carole Cordier, Alexander Sobolev, Habibollah Ghasemi, Claudio Marchesi, Mossaieb Sabzehei, Carlos Garrido

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Mohsen Mobasheri, Nicholas Arndt, Carole Cordier, Alexander Sobolev, Habibollah Ghasemi, et al. Petrogenesis and Geochemistry of Upper Paleozoic Komatiites (Mashhad, NE Iran). Journal of Petrology, 2025, 66 (1), 10.1093/petrology/egae131. hal-04933005

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# Petrogenesis and Geochemistry of Upper Paleozoic Komatiites (Mashhad, NE Iran)

MOHSEN MOBASHERI ID <fnref n="1" />,<fnref n="2" />,*, NICHOLAS ARNDT<fnref n="3" />, CAROLE CORDIER<fnref n="3" />, ALEXANDER SOBOLEV<fnref n="3" />, HABIBOLLAH GHASEMI<fnref n="1" />,<fnref n="2" />,

CLAUDIO MARCHESI<fnref n="4" />, MOSSAIEB SABZEHEI<fnref n="5" /> and CARLOS J. GARRIDO<fnref n="6" />

Upper Paleozoic, probably Permian, komatiites have been found in the Paleo-Tethys suture zone in NE Iran. These rocks are divided into three groups: (i) differentiated and undifferentiated komatiite lava flows, (ii) komatiitic basalts, and (iii) ultramafic-mafic pillow lavas. The rocks have a wide range of textures including random olivine spinifex, layered olivine spinifex, random and string-beef pyroxene spinifex, micrographic intergrowths of plagioclase and clinopyroxene, and cumulate textures. MgO contents range from 7.1 wt % in basalts and gabbros in differentiated flows to 38.0 wt % in cumulates, flow margins and samples with olivine spinifex textures. The MgO content of the parental melt is estimated using the Fo content of olivine (89–91) to be between 20 and 25 wt %, and the higher MgO content in spinifex samples (30 to 36 wt %) is attributed to accumulation of olivine. The rocks have low Al₂O₃/TiO₂ and are relatively depleted in heavy rare earth elements. They, therefore, are classified as Al-depleted komatiite, the first report of this magma type in a Phanerozoic locality. These characteristics are attributed to the presence of garnet in the source during mantle melting and melt extraction. The rocks also have relatively low contents of the more incompatible trace elements indicating derivation from a depleted source. Our study indicates that the parental magma formed by 10% to (about) 20% partial melting in a mantle plume at pressures of about 4 to 5 GPa (depths of 120–150 km). Ascent of the plume into the Late Paleozoic subduction zone at the margin of the Paleo-Tethys Ocean is a possible petrogenetic model for the generation of these komatiites.

**Key words:** Hydrous peridotite; Komatiite; Mantle melting; Spinifex; Upper paleozoic

## INTRODUCTION

Komatiites are volcanic ultramafic rocks observed in many Archean greenstone belts, such as Barberton and Commondale in South Africa (Viljoen & Viljoen, 1969; Wilson, 2019), Belingwe in Zimbabwe (Nisbet et al., 1987), Banasandra in India (Maya et al., 2017), Rio das Velhas in Brazil (Zucchetti et al., 2000; Verma et al., 2017) and Abitibi in Canada (Sproule et al., 2002). The Archean mantle is thought to have been hotter than the modern mantle (Nisbet et al., 1993; Herzberg et al., 2010), leading to the formation of ultramafic magmas during high degrees of partial melting.

Komatiites are rare in the Phanerozoic, the sole well-documented example being the Cretaceous komatiites on Gorgona Island, Colombia (Echeverria, 1980; Aitken & Echeverria, 1984). In recent years, ultramafic lavas have been reported in different parts of Asia, such as in the Permian–Triassic Song Da region in NW Vietnam (Hanski et al., 2004; Balykin et al., 2010), the Late Paleozoic of Yunnan (SW of China) (Fang & Niu, 2003) and the Permian Chhongtash Formation in Karakoram Tethys basin of India (Rao & Rai, 2007). However, spinifex texture, which is considered emblematic of komatiite (Nesbitt, 1971; Arndt et al., 2008), has not been reported at these localities.

In this paper, we describe newly discovered outcrops of high-magnesium volcanic rocks in a late Paleozoic sedimentary-magmatic sequence near the city of Mashhad in NE Iran (Fig. 1). These units were previously interpreted as ophiolitic relicts of Paleo-Tethys oceanic crust (e.g. Stöcklin, 1968; Berberian & King, 1981; Diefenbach et al., 1986; Alavi, 1991; Eftekharnezhad & Behroozi, 1991; Ruttner, 1993; Mirnejad et al., 2013) (Fig. 1). Majidi (1981) reported volcanic ultramafic rocks near Mashhad and the town of Fariman, and proposed that they are komatiites. This interpretation did not receive much attention, and in following decades divergent views were expressed on the genesis of these rocks. Moghadam et al. (2015) considered the assemblage of ultramafic-mafic rocks and associated sediments in the Mashhad region to be fragments of an ophiolite and accretionary complex. They interpreted the ultramafic rocks as mantle harzburgites, and they reported the existence of ultramafic pillow lavas in only a few places. Li et al. (2018) classified the ultramafic-mafic rocks near Mashhad as komatiitic and picro-basaltic lavas. Topuz et al. (2018) accepted the volcanic nature of ultramafic-mafic outcrops around Fariman town, but they did not accept their komatiitic character; instead, they proposed that these rocks are parts of basaltic lava flows.

<footnote n="1">¹Department of Petrology and Economic Geology, Faculty of Earth sciences, Shahrood University of Technology, Haft-e-Tir Sq., Shahrood 3619995161, Iran</footnote>

<footnote n="2">²Section of Earth Science, Zargan Natural Resources and Mineral Industries Research and Consulting Group, Paradise Blvd., Kerman 7614655140, Iran</footnote>

<footnote n="3">³Institut des Sciences de la Terre (ISTerre), Université Grenoble Alpes, 1381 rue de la Piscine, Saint-Martin- d'Hères, 38058 Grenoble Cedex 9, France</footnote>

<footnote n="4">⁴Departamento de Mineralogía y Petrología, Universidad de Granada, Av. Fuentenueva sn, 18002 Granada, Spain</footnote>

<footnote n="5">⁵No.16, Lane No 113, Eram Blvd, Mehrshahr, Karaj 1433894168, Iran</footnote>

<footnote n="6">⁶Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC, Av. De las Palmeras 4, Armilla, 18100 Granada, Spain</footnote>

<footnote>*Corresponding author. Telephone: +98 936 222 6110, E-mail: mobasheri.mohsen@yahoo.com</footnote>

<footnote>†Handling Editor: Prof. Marlina Elburg</footnote>
<figure><img src="image_2.png" /><figcaption>**Fig. 1.** Modified and simplified geological map of the Mashhad and Fariman complexes (from Eftekharnezhad & Behroozi, 1991).</figcaption></figure>

In our study, we report detailed field observations, geological maps at different scales, petrographic descriptions, and mineral and whole rock chemical compositions of the ultramafic rocks of NE Iran, to clarify their nature and origin.

## RESEARCH METHODOLOGY

Field studies of the Mashhad and Fariman Complexes were carried out across more than 35 cross-sections to document the field relations, internal stratigraphy and petrography of the lavas. Analyses of Si, Al, Fe, Mg, Ca, Mn, P and Cr on selected minerals in thin section were performed using a Cameca SX100 Electron Microprobe with wavelength-dispersive spectrometers at the Centro de Instrumentación Científica (CIC), Universidad de Granada (Spain) using a beam size of 5 µm, an accelerating voltage of 15 kV, a beam current of 20 nA, and a counting time of 20 s on peaks for each element. Additional analyses were conducted using a JEOL JXA-iHP200F electron microprobe at the ISTerre, University Grenoble Alps in France. The acceleration voltage was 25 or 20 kV with a probe current of 500 and 900 nA and a probe diameter of 1 to 2 µm using the high-precision analytical procedure from Batanova et al. (2015, 2018). The ZAF matrix correction was applied to all measurements.

The major and minor element concentrations of 48 whole-rock samples were determined at the Instituto Andaluz de Ciencias de la Tierra (IACT, Granada, Spain). A jaw crusher and an agate ring mill were used to powder the samples. Major elements and the trace elements Cr, Zr and Ni were determined

by conventional X-ray fluorescence analysis using a PHILIPS PW-2440 instrument. Other trace elements were analyzed using a Triple Quadrupole Agilent 8800 Inductively Coupled Plasma Mass Spectrometer. Dissolution of ultramafic rocks was performed following the HF-HClO₄ digestion procedure on hotplate described by Ionov et al. (1992). Element concentrations were determined by external calibration. The compositions of the reference samples UB-N, PM-S, BIR-1 and WS-E, analysed as unknowns during the analytical runs, are in agreement with published values of these standards (Godard et al., 2008; Marchesi et al., 2009; Jochum et al., 2016). Eight additional samples were analyzed at the Service d'Analyse des Roches et des Minéraux of the Centre de Recherches Pétrographiques et Géochimiques using procedures described at CRPG (2024).

## GEOLOGICAL CONTEXT AND FIELD CHARACTERISTICS

Two NW-SE trending mountain ranges dominate the geomorphology of northeastern Iran. The mountains in the NE of the Paleo-Tethys suture zone are known as the Kopet-Dagh Zone and belong to the Eurasian or Turan plate (Fig. 1). The second range, called the Binalud Zone, is the SE continuation of the Alborz Mountains and is part of the Gondwana plate (Lammerer et al., 1984; Eftekharnezhad & Behroozi, 1991; Alavi, 1992; Wilmsen et al., 2009). Based on geodynamic models, various authors (e.g. Stöcklin, 1968; Stöcklin, 1977; Berberian & King, 1981; Diefenbach et al., 1986; Boulin, 1988) proposed that in the Late Paleozoic and Early
<figure><img src="image_3.png" /><figcaption>**Fig. 2.** Stratigraphic column and field examples of komatiites from Sefid Sang section in Fariman town. (a) The upper contact of komatiite lavas. This contact is mainly tectonic, and shows no signs of metamorphism. (b) Contact metamorphism has produced a garnet-epidote skarn in the lower contact of komatiitic lava flows. (c, d) The mingling of lava and Upper Paleozoic sediments and formation of peperite at the lower contact of komatiitic lava flows.</figcaption></figure>

Mesozoic, a branch of the Paleo-Tethys Ocean existed in what is now NE Iran, between the Turan plate in the north and the Iranian Cimmerian microcontinent (Lut block) to the south. Alavi (1991), Ruttner (1993) and Sheikholeslami & Kouhpeyma (2012) proposed that the ultramafic-mafic rocks in the Mashhad region were parts of ophiolite sequences associated with this ocean.

The new geological surveys conducted in this project do not confirm this hypothesis. Instead, the presence of turbidites, andesitic and basaltic lavas, siliciclastics, volcaniclastic sandstones and slates (Alavi, 1991; Zanchetta et al., 2013) indicates an active margin. In addition, ophiolitic slices in the Aghdarband erosion window, 50 km northeast of Fariman, have characteristics typical of a supra-subduction-zone (Mobasheri et al., 2022) and were interpreted by Eftekharnezhad & Behroozi (1991) as obducted slabs from the upper mantle.

The nature of the ultramafic and mafic rocks is distinctly different from those in typical ophiolites. A major difference is found in the contacts between the ultramafic-mafic units and the adjacent sediments. Understanding these contacts can be challenging due to Quaternary cover and tectonic deformation, but examples located E-SE of Sefid Sang village and W-SW Mashhad city provide evidence that ultramafic lava erupted onto poorly consolidated sediments (Mobasheri et al., 2024) (Fig. 2c, d). At these localities, we find convincing geological evidence of a volcanic origin such as contact metamorphism, skarn formation (Fig. 2b), and or magma-sediment mingling (peperite) (Fig. 2c, d) at lower contacts. No reaction traces have been observed in sediments above the upper

contacts of the ultramafic units (Fig. 2a), and the ultramafic units have normal contacts with the sedimentary units. The above observations, and especially the presence of random olivine spinifex texture (i.e. spinifex textures in which the olivine crystals are randomly oriented; Fig. 5a–f), provides convincing evidence of an extrusive, komatiitic nature of these rocks (Mobasheri et al., 2024).

## Mashhad complex

This complex, an assemblage of metasedimentary and komatiitic rocks (Figs 1 and 3b), extends for 32 km from west of Mashhad city to Shandiz town. Its maximum thickness is 5 km (Fig. 1). The rocks in the complex experienced varying degrees of hydrothermal alteration during regional and contact metamorphism (Majidi, 1978; Alavi, 1991). The komatiites are typically metamorphosed in the lower to upper greenschist facies, or to hornblende hornfels facies along the contacts with Triassic Mashhad granitoids.

The work carried out in this study shows that the complex contains about 20 individual units: differentiated and undifferentiated komatiitic lava flows, komatiite-basaltic lavas and ultramafic pillowed units (Mobasheri et al., 2019; Mobasheri et al., 2024) ranging in thickness from less than 10 m to more than 100 m. The maximum thickness of individual komatiite flows is about 150 m.

Available biostratigraphic evidence indicates that the Mashhad complex formed in the Upper Paleozoic. Majidi (1981) proposed a Devonian-Carboniferous age by comparing this rock suite with the
<figure><img src="image_4.png" /><figcaption>**Fig. 3.** Field views of the Mashhad komatiites. Photograph (a, b) Field photograph of (a) differentiated komatiites in the Fariman complex and (b) the Mashhad complex. (c) komatiitic basalt lavas and (d) ultramafic pillow lavas in Fariman complex.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Fig. 4.** (a) Chilled upper margin of a komatiite lava flow. Several large olivine phenocrysts in a matrix containing abundant small olivine crystals. (b) Matrix of an olivine cumulate with hornblende (hbl) and phlogopite (phl). (c, d) Olivine cumulate in plane polarized light and under crossed polars.</figcaption></figure>

rocks in the Hindu Kush and South of Tian Shan regions. Specifically, recrystallized limestones in this rock suite contain fossil assemblages, including *Stafella* sp., *Parafusulina* sp., *Schubertella* sp. and *Tentularia* sp., as reported by Taheri & Ghaemi (1996). This fossil evidence indicates that the rock suite dates to the Late Permian. Additionally, radiolarian cherts in meta-carbonates contain *Entactinia* sp., suggesting a Devonian to Permian age, as noted by Sheikholeslami & Kouhpeyma (2012). In addition, Ghazi

et al. (2001) reports a mid-Permian Ar-Ar isotopic age of 281 to 277 Ma for two amphibole-bearing gabbros.

## Fariman complex

The Fariman Complex extends approximately 50 km from the N-NE of Fariman town to the SE of Sefidsang village (Fig. 1) and contains more than 15 distinct komatiitic flows. These flows range in thickness from less than 10 m to a maximum of around
<figure><img src="image_6.png" /><figcaption>**Fig. 5.** (a–d) Photographs of random olivine spinifex textures observed in the upper portion of differentiated komatiites, both in outcrop and hand samples. (e, f) Photomicrographs of random olivine spinifex completely serpentinized. The matrix is made up of skeletal pyroxene and devitrified glass. Figures a and f represent FC-5 sample.</figcaption></figure>

100 m (Fig. 2). According to Zanchetta *et al.* (2013), a lower unit of metapelites, metabasites, marbles and serpentinites is overlain by an upper layer of massive Permian carbonates, basaltic-andesitic lava flows, volcanoclastic sandstones and slates (Fig. 2). These authors propose that the sediments were deposited in a marine basin close to an active volcanic arc. The volcanic sequence includes differentiated and undifferentiated komatiite lavas (Fig. 3a), komatiite-basaltic lavas (Fig. 3c), ultramafic-mafic pillow lavas (Fig. 3d) (Mobasheri *et al.*, 2019; Mobasheri *et al.*, 2024) and high-Mg basalts. In general, komatiites in the Fariman Complex are less affected by metamorphism than those in the Mashhad Complex, and relatively fresh komatiitic flows can be observed. Based on pelagic conodonts in a chert near Sefid Sang village, Kozur & Mostler (1991) proposed an Early Permian age. Topuz *et al.* (2018) obtained a $^{40}$Ar/$^{39}$Ar age of 276±4 Ma for magmatic amphiboles in a komatiite flow.

## MINERALOGICAL AND TEXTURAL FEATURES

### Mineralogy

The ultramafic rocks consist of olivine with various morphologies set in a matrix of clinopyroxene and accessory chromian

spinel, magmatic amphibole and plagioclase. The more mafic rocks contain mainly clinopyroxene and plagioclase. In most samples, olivine is partly or completely replaced by secondary serpentine or chlorite, clinopyroxene and chromian spinel are largely unaltered, and plagioclase is totally replaced by fine-grained secondary minerals.

Olivine has two principal morphologies. It occurs as solid polyhedral grains with long dimensions ranging from less than 50 µm in chilled margins (Fig. 4a) to a maximum of about 3 mm in cumulates (averaging 0.25 to 0.7 mm; Fig. 4c, d). In spinifex-textured rocks and in some cumulates, olivine occurs as stubby elongate grains with length-width ratios from about 4:1 to 10:1 (Fig. 5e, f). Some grains are skeletal, as shown in Fig. 7a, b, but most are largely solid. Highly skeletal to dendritic grains, and fine, highly elongate grains, which are common in Archean komatiites, are absent in the Mashhad komatiites. In addition, the dimensions of the olivine grains are smaller than in typical Archean komatiites where the grain size in cumulates is 0.7 to 1 mm (Pyke *et al.*, 1973).

Chromian spinel is an accessory phase in most of the ultramafic rocks (Table 2). We distinguish two types: 1) Delicate acicular, dendritic and cruciform skeletal grains in spinifex zone and skeletal cumulate zone; and 2) Small euhedral crystals in the cumulate
<figure><img src="image_7.png" /><figcaption>**Fig. 6.** (a) Branching morphology of acicular pyroxenes. (b) String beef pyroxene spinifex textures in an exposure of komatiitic basalt. (c–d) Alternating layers of olivine cumulate (c) or gabbro (d) and spinifex textures in differentiated komatiites.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 7.** (a) Photomicrographs of skeletal cumulate zone of Mashhad komatiites, this view shows skeletal olivine phenocrysts and intersertal skeletal clinopyroxenes (sample of SFS-1). (b) Back-scattered electron (BSE) image of skeletal cumulate zone of Mashhad komatiites.</figcaption></figure>

and skeletal cumulate zones. In some cases, euhedral spinel crystals are enclosed in olivine crystals.

Clinopyroxene occurs as relatively large subhedral grains with dimensions only slightly smaller than the olivine grains, in both spinifex-textured and cumulate samples. It also occurs as large, fine plates or needles in pyroxene spinifex samples, and as smaller, elongate, moderately to highly skeletal grains interstitial to olivine in other ultramafic rocks (Fig. 7a, b). In gabbros, it has a morphology typical of slowly-cooled mafic rocks; i.e. it accompanies plagioclase and is subhedral to anhedral.

In ultramafic rocks, plagioclase is a minor phase, usually totally altered to secondary minerals. It occurs as small elongate tabular grains, in some cases with a moderately skeletal morphology, interstitial to olivine and pyroxene.

Amphibole occurs as small tabular to acicular grains in the matrix of spinifex and cumulate samples. Its brown colour and pleochroism distinguish it from secondary amphibole which partially replaces some clinopyroxene and hornblende grains. Phlogopite, a very minor phase, occurs as small plates, usually associated with hornblende (Fig. 4b).

## Lithologies and flow architecture

The three main lithofacies observed in Archean typical komatiites—chilled margins, spinifex-textured rocks and cumulates (Arndt et al., 2008) – are also identified in Mashhad komatiites. However, there are notable differences in the subdivisions of each group. The key features of each lithofacies in the Mashhad komatiites are presented below, and more detailed descriptions are given in Supplementary Data Electronic Appendix File EA1.

### Chilled margins

Fine-grained chilled margins are observed in both the upper and lower portions of the flows. The 0.5- to 2-m-thick upper marginal layer consists of hard, fine-grained green to brown rock (Fig. 3a). This layer is often characterized by polyhedral joints or fractures, with some portions being brecciated. The rock typically contains sparse, relatively large (1–2 mm) olivine phenocrysts embedded in a finer-grained matrix of olivine, clinopyroxene, chromite, and patches of glass (Fig. 4a). Pyroxene remains largely unaltered, and olivine is preserved only as relics.
<figure><img src="image_9.png" /><figcaption>**Fig. 8.** Internal architectures of the flow units in the Mashhad komatiites.</figcaption></figure>

Olivine porphyry. A 1- to 2.5-m-thick layer of olivine porphyry intervenes between the upper chilled margin and the spinifex layer (Fig. 3a). In a flow from the Virani locality, this layer reaches 5 m in thickness and is cut by columnar joints. The size of olivine phenocryst increases from 0.4 to 0.5 mm to about 1 mm from top to base of the layer where the porphyry grades into spinifex-textured lava.

## Spinifex-textured rocks

In their form and disposition within the lava flows, the spinifex textures in the Mashhad komatiites differ from those in Archean komatiites, as described in the following paragraphs. However, they consist of distinctive, elongate, in some cases skeletal, olivine crystals that are readily visible in the field and in hand samples. As such, it is legitimate to refer to these textures as spinifex. Both olivine and pyroxene spinifex textures are present (Figs 5a-f and 6a-d).

Random olivine spinifex-textured layer. This is the most distinctive and noteworthy texture in the Mahhad komatiites. Layers exhibiting this texture range in thickness from 40 cm to about 4 m (Fig. 3a). In most cases, the crystals are small, no more than 10 mm long and 1 mm wide (Fig. 5a, b and d), but in samples such as the one shown in Fig. 5c, they may reach 2 cm. Thin sections reveal a rather stubby morphology (Fig. 5e and f). The olivine grains lie in a matrix of relatively large subhedral grains

of clinopyroxene, abundant small equant grains of chromian spinel, fine prismatic grains of plagioclase, and sparse altered glass (Fig. 5e and f). Clinopyroxene and chromite are little altered, olivine is partially to completely altered to serpentine or chlorite, and plagioclase is totally replaced by secondary minerals.

Pyroxene spinifex. The textures in this layer are similar to those in many Archean and Proterozoic komatiitic basalts (Nesbitt, 1971; Arndt & Fleet, 1979; Lowrey et al., 2017). These rocks are composed of acicular, hollow, and elongate clinopyroxene phenocrysts arranged in large sheaths, 5 to 15 cm in length and oriented almost parallel to one another, or as randomly oriented crystals, ranging in length from 1.5 mm to 5 cm. Locally in this layer, pyroxene needles, reaching lengths of up to 5 cm, cluster and branch out from a central core (Fig. 6a), with some arranged in a radial formation. In the upper part of a basaltic komatiite lava in Fariman, a spectacular texture is made up of coarse parallel pyroxene needles (Fig. 6b). This texture superficially resembles 'string-beef' texture in Archean komatiitic basalts (Arndt et al., 1977). Perhaps because of incomplete exposures, transitions from olivine to pyroxene spinifex have not been observed. Pyroxene spinifex texture occurs within layers varying in thickness from 0.5 to 3 m. In most cases the pyroxene is entirely altered to secondary amphibole and chlorite, but in some samples, a central zone is mantled by augite resembling the zoned pigeonite-augite crystals in Archean komatiitic basalts. These textures resemble those in
<table><caption>**Table 1:** Representative olivine compositions from Mashhad komatiites</caption><thead><tr><th>Sample Data Point</th><th>SFS241-A2-OL3-C2</th><th>SFS1-A8-OL3-C1</th><th>SFS1-A8-OL4-R1</th><th>SFS1-A8-OL4-C1</th><th>SFS1-A1-OL1-C1</th><th>SFS1-A1-OL1-R1</th><th>PUN38 Area5-OL1-C1</th><th>PUN38 Area5-OL1-C2</th><th>PUN38 Area5-OL2-C1</th><th>PUN38 Area5-OL10-C1</th><th>PUN38-A4-OL6-R1</th></tr></thead><tbody><tr><td>SiO<sub>2</sub></td><td>39.59</td><td>40.29</td><td>40.16</td><td>40.26</td><td>40.18</td><td>40.15</td><td>39.26</td><td>39.24</td><td>39.30</td><td>38.25</td><td>39.85</td></tr><tr><td>TiO<sub>2</sub></td><td>0.00</td><td>0.00</td><td>0.00</td><td>0.01</td><td>0.01</td><td>0.00</td><td>0.03</td><td>0.03</td><td>0.03</td><td>0.03</td><td>0.03</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>0.03</td><td>0.03</td><td>0.05</td><td>0.03</td><td>0.03</td><td>0.03</td><td>0.01</td><td>0.02</td><td>0.03</td><td>0.03</td><td>0.08</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.07</td><td>0.08</td><td>0.10</td><td>0.08</td><td>0.05</td><td>0.08</td><td>0.01</td><td>0.04</td><td>0.04</td><td>0.03</td><td>0.03</td></tr><tr><td>FeO</td><td>13.15</td><td>10.59</td><td>10.74</td><td>10.67</td><td>10.71</td><td>10.30</td><td>13.98</td><td>13.78</td><td>13.57</td><td>11.22</td><td>10.14</td></tr><tr><td>MnO</td><td>0.21</td><td>0.16</td><td>0.14</td><td>0.19</td><td>0.15</td><td>0.17</td><td>0.20</td><td>0.22</td><td>0.23</td><td>0.53</td><td>0.60</td></tr><tr><td>MgO</td><td>46.47</td><td>48.15</td><td>48.05</td><td>48.16</td><td>48.38</td><td>48.43</td><td>45.50</td><td>45.59</td><td>45.65</td><td>49.29</td><td>48.10</td></tr><tr><td>NiO</td><td>0.33</td><td>0.37</td><td>0.35</td><td>0.35</td><td>0.35</td><td>0.37</td><td>0.35</td><td>0.39</td><td>0.39</td><td>0.35</td><td>0.36</td></tr><tr><td>CaO</td><td>0.30</td><td>0.29</td><td>0.31</td><td>0.29</td><td>0.31</td><td>0.30</td><td>0.11</td><td>0.12</td><td>0.12</td><td>0.13</td><td>0.03</td></tr><tr><td>Total</td><td>100.26</td><td>100.09</td><td>100.00</td><td>100.16</td><td>100.29</td><td>99.94</td><td>99.61</td><td>99.60</td><td>99.50</td><td>99.96</td><td>99.34</td></tr><tr><td>Cr</td><td>0.001</td><td>0.002</td><td>0.002</td><td>0.002</td><td>0.001</td><td>0.002</td><td>0.000</td><td>0.001</td><td>0.001</td><td>0.001</td><td>0.001</td></tr><tr><td>Fe(ii)</td><td>0.275</td><td>0.219</td><td>0.222</td><td>0.221</td><td>0.221</td><td>0.213</td><td>0.295</td><td>0.291</td><td>0.286</td><td>0.221</td><td>0.211</td></tr><tr><td>Mn</td><td>0.004</td><td>0.003</td><td>0.003</td><td>0.004</td><td>0.003</td><td>0.004</td><td>0.004</td><td>0.005</td><td>0.005</td><td>0.003</td><td>0.013</td></tr><tr><td>Mg</td><td>1.732</td><td>1.775</td><td>1.774</td><td>1.774</td><td>1.781</td><td>1.786</td><td>1.711</td><td>1.714</td><td>1.716</td><td>1.781</td><td>1.782</td></tr><tr><td>Ni</td><td>0.007</td><td>0.007</td><td>0.007</td><td>0.007</td><td>0.007</td><td>0.007</td><td>0.007</td><td>0.008</td><td>0.008</td><td>0.007</td><td>0.007</td></tr><tr><td>Ca</td><td>0.008</td><td>0.008</td><td>0.008</td><td>0.008</td><td>0.008</td><td>0.008</td><td>0.003</td><td>0.003</td><td>0.003</td><td>0.008</td><td>0.001</td></tr><tr><td>Mg#</td><td>86.1</td><td>88.9</td><td>88.7</td><td>88.8</td><td>88.8</td><td>89.2</td><td>85.1</td><td>85.3</td><td>85.5</td><td>88.2</td><td>88.9</td></tr></tbody></table>

<table><caption>**Table 2:** Representative chromian spinel compositions from Mashhad komatiites</caption><thead><tr><th>Sample Data Point</th><th>SFS241 A4-cr6</th><th>SFS241 A7-cr1</th><th>SFS1 A8-cr1</th><th>SFS1 A8-cr1</th><th>SFS1 A8-cr2</th><th>SFS1 A8-cr3</th><th>SFS10 A6-cr1</th></tr></thead><tbody><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>37.59</td><td>39.39</td><td>43.77</td><td>43.28</td><td>42.00</td><td>43.29</td><td>43.63</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>19.55</td><td>18.54</td><td>17.42</td><td>17.84</td><td>18.79</td><td>17.97</td><td>17.46</td></tr><tr><td>TiO<sub>2</sub></td><td>1.44</td><td>1.66</td><td>0.76</td><td>0.84</td><td>0.77</td><td>0.74</td><td>0.75</td></tr><tr><td>FeO</td><td>16.36</td><td>15.75</td><td>14.10</td><td>12.96</td><td>12.98</td><td>13.05</td><td>15.05</td></tr><tr><td>Fe<sub>2</sub>O<sub>3</sub></td><td>10.28</td><td>9.37</td><td>8.48</td><td>8.94</td><td>9.15</td><td>8.84</td><td>8.72</td></tr><tr><td>MgO</td><td>12.61</td><td>12.98</td><td>13.47</td><td>14.36</td><td>14.39</td><td>14.24</td><td>13.00</td></tr><tr><td>MnO</td><td>0.16</td><td>0.16</td><td>0.14</td><td>0.15</td><td>0.12</td><td>0.12</td><td>0.14</td></tr><tr><td>NiO</td><td>0.23</td><td>0.25</td><td>0.22</td><td>0.21</td><td>0.22</td><td>0.23</td><td>0.19</td></tr><tr><td>SiO<sub>2</sub></td><td>0.07</td><td>0.10</td><td>0.11</td><td>0.10</td><td>0.12</td><td>0.11</td><td>0.11</td></tr><tr><td>V<sub>2</sub>O<sub>3</sub></td><td>0.23</td><td>0.28</td><td>0.17</td><td>0.19</td><td>0.18</td><td>0.15</td><td>0.17</td></tr><tr><td>ZnO</td><td>0.07</td><td>0.05</td><td>0.06</td><td>0.09</td><td>0.04</td><td>0.08</td><td>0.02</td></tr><tr><td>CoO</td><td>0.06</td><td>0.05</td><td>0.07</td><td>0.07</td><td>0.08</td><td>0.07</td><td>0.08</td></tr><tr><td>Total</td><td>98.7</td><td>98.6</td><td>98.8</td><td>99.0</td><td>98.8</td><td>98.9</td><td>99.3</td></tr></tbody></table>

Archean komatiitic basalts (Arndt & Fleet, 1979; Lowrey et al., 2017), but there are some significant differences. Most notably, in Archean rocks, the pyroxene occurs as clusters or sheaths of closely packed needles, whereas in the Mashhad lavas the needles are widely dispersed in a more abundant matrix. The length of individual crystals is also greater—up to 15 cm in the Mashhad samples—compared with a maximum length of about 5 cm in Archean samples.

**Foliated skeletal olivine.** According to Pyke et al. (1973), the B1 layer in Archean komatiite flows contains elongate hopper olivine phenocrysts with lengths of 1 to 3 mm, orientated parallel to the flow margin. In the Mashhad komatiites, this texture has been observed only in one differentiated flow at the Fariman locality where a layer containing foliated skeletal olivine textures with a thickness of about 5 to 10 cm intervenes between the olivine spinifex layer and the gabbro layer. The olivine crystals in this subzone are oriented parallel to the contact of the flow.

## Cumulates

**Olivine cumulate layer.** The lower portion of most flows consists of a thick olivine cumulate containing clinopyroxene oikocrysts

(Fig. 4b–c). This layer of hard greenish-gray rock is massive, 10 to >70 meters thick, and constitutes more than 70% of the field outcrops. The pyroxene oikocrysts resisted weathering and stand out as nodule-like knobs.

**Rhythmically layered olivine spinifex and cumulate.** Rhythmic fine-scale layering, similar to that described by Wilson (2019) in Paleoarchean komatiites from South Africa, is a notable feature of the olivine cumulate and gabbro layers in thick komatiite units. In these structures, centimeter-scale olivine cumulate layers (1–5 cm) alternate with thinner spinifex-textured layers (0.1–2 cm) (Fig. 6c), typically aligned parallel to flow contacts. In the ~150 m thick Sarhang Ali lava flow near Mashhad, such rhythmic layering occurs 13 to 15 m below the transition layer in the upper olivine cumulate section. Commonly, 50 to over 100 alternating layers of near-constant thickness are observed. For example, in one section with over 100 layers, the spacing is ~2 cm, with spinifex layers measuring 1 to 2 mm. Thicker separations (up to 5 cm) are associated with thinner spinifex layers (0.5–2 cm). In gabbroic segments, 3- to 40-cm-thick spinifex layers alternate with 2- to 15-cm-thick gabbroic layers (Fig. 6d).
<table><caption>**Table 3:** Representative compositions of clinopyroxene from Mashhad komatiites</caption><thead><tr><th>Sample<br>Data Point</th><th>SFS1<br>px4</th><th>SFS1<br>px4-1</th><th>SFS33<br>A3-px1</th><th>SFS33<br>A3-px2</th><th>SFS33<br>A3-px3</th><th>SFS33<br>A2-px1</th><th>PUN-38<br>A3-px1-c</th><th>PUN-38<br>A1-px1-c</th><th>NDH-23<br>A2-px1-r</th><th>NDH-23<br>A2-px1-c</th></tr></thead><tbody><tr><td>SiO<sub>2</sub></td><td>45.33</td><td>45.95</td><td>50.45</td><td>49.14</td><td>49.10</td><td>49.44</td><td>51.84</td><td>51.71</td><td>50.18</td><td>52.13</td></tr><tr><td>TiO<sub>2</sub></td><td>1.59</td><td>1.07</td><td>0.70</td><td>1.15</td><td>0.95</td><td>1.07</td><td>0.42</td><td>0.37</td><td>0.4</td><td>0.52</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>8.76</td><td>8.43</td><td>3.13</td><td>4.32</td><td>2.37</td><td>4.01</td><td>3.08</td><td>3</td><td>3.76</td><td>2.54</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.18</td><td>0.12</td><td>1.13</td><td>0.14</td><td>0.00</td><td>0.09</td><td>1</td><td>1.21</td><td>1.13</td><td>0.62</td></tr><tr><td>Fe<sub>2</sub>O<sub>3</sub></td><td>3.62</td><td>3.43</td><td>1.90</td><td>2.79</td><td>3.32</td><td>2.65</td><td>0.41</td><td>1.09</td><td>2.89</td><td>1.09</td></tr><tr><td>FeO</td><td>4.90</td><td>6.06</td><td>3.18</td><td>3.88</td><td>10.14</td><td>4.27</td><td>3.61</td><td>2.89</td><td>1.8</td><td>4.4</td></tr><tr><td>MnO</td><td>0.16</td><td>0.23</td><td>0.13</td><td>0.16</td><td>0.40</td><td>0.19</td><td>0.08</td><td>0.12</td><td>0.1</td><td>0.13</td></tr><tr><td>MgO</td><td>12.18</td><td>11.97</td><td>16.47</td><td>15.13</td><td>13.28</td><td>15.31</td><td>17.07</td><td>17.18</td><td>16.6</td><td>17.09</td></tr><tr><td>CaO</td><td>21.57</td><td>20.91</td><td>21.17</td><td>21.63</td><td>18.74</td><td>21.31</td><td>21.27</td><td>21.47</td><td>21.76</td><td>20.87</td></tr><tr><td>Na<sub>2</sub>O</td><td>0.26</td><td>0.31</td><td>0.23</td><td>0.22</td><td>0.28</td><td>0.21</td><td>0.19</td><td>0.2</td><td>0.19</td><td>0.22</td></tr><tr><td>NiO</td><td>0.01</td><td>0.00</td><td>0.05</td><td>0.03</td><td>0.00</td><td>0.01</td><td>0.06</td><td>0.06</td><td>0.07</td><td>0.04</td></tr><tr><td>Total</td><td>98.7</td><td>98.6</td><td>98.7</td><td>98.7</td><td>98.7</td><td>98.7</td><td>99.18</td><td>99.42</td><td>99.01</td><td>99.77</td></tr><tr><td>Si</td><td>1.73</td><td>1.76</td><td>1.89</td><td>1.85</td><td>1.90</td><td>1.86</td><td>1.91</td><td>1.9</td><td>1.87</td><td>1.92</td></tr><tr><td>Al<sup>IV</sup></td><td>0.27</td><td>0.24</td><td>0.11</td><td>0.15</td><td>0.10</td><td>0.14</td><td>0.09</td><td>0.1</td><td>0.13</td><td>0.08</td></tr><tr><td>Al<sup>VI</sup></td><td>0.12</td><td>0.14</td><td>0.02</td><td>0.04</td><td>0.00</td><td>0.04</td><td>0.04</td><td>0.03</td><td>0.03</td><td>0.03</td></tr><tr><td>Fe*</td><td>0.26</td><td>0.29</td><td>0.15</td><td>0.20</td><td>0.42</td><td>0.21</td><td>0.12</td><td>0.12</td><td>0.14</td><td>0.17</td></tr><tr><td>Fe<sup>iii</sup></td><td>0.10</td><td>0.10</td><td>0.05</td><td>0.08</td><td>0.10</td><td>0.07</td><td>0.01</td><td>0.03</td><td>0.08</td><td>0.03</td></tr><tr><td>Fe<sup>ii</sup></td><td>0.15</td><td>0.19</td><td>0.10</td><td>0.12</td><td>0.33</td><td>0.13</td><td>0.11</td><td>0.09</td><td>0.06</td><td>0.14</td></tr><tr><td>Cr</td><td>0.01</td><td>0.00</td><td>0.03</td><td>0.00</td><td>0.00</td><td>0.00</td><td>0.029</td><td>0.035</td><td>0.033</td><td>0.018</td></tr><tr><td>Ti</td><td>0.05</td><td>0.03</td><td>0.02</td><td>0.03</td><td>0.03</td><td>0.03</td><td>0.012</td><td>0.010</td><td>0.011</td><td>0.014</td></tr><tr><td>Mg</td><td>0.69</td><td>0.68</td><td>0.92</td><td>0.85</td><td>0.77</td><td>0.86</td><td>0.94</td><td>0.94</td><td>0.92</td><td>0.94</td></tr><tr><td>Ca</td><td>0.88</td><td>0.86</td><td>0.85</td><td>0.87</td><td>0.78</td><td>0.86</td><td>0.84</td><td>0.85</td><td>0.87</td><td>0.82</td></tr><tr><td>Na</td><td>0.02</td><td>0.02</td><td>0.02</td><td>0.02</td><td>0.02</td><td>0.02</td><td>0.01</td><td>0.01</td><td>0.01</td><td>0.02</td></tr><tr><td>Total</td><td>4</td><td>4</td><td>4</td><td>4</td><td>4</td><td>4</td><td>4</td><td>4</td><td>4</td><td>4</td></tr><tr><td>Wo</td><td>47.99</td><td>46.65</td><td>44.10</td><td>45.29</td><td>39.28</td><td>44.47</td><td>44.14</td><td>44.29</td><td>45.02</td><td>42.65</td></tr><tr><td>En</td><td>37.70</td><td>37.15</td><td>47.76</td><td>44.07</td><td>38.74</td><td>44.46</td><td>49.29</td><td>49.29</td><td>47.76</td><td>48.58</td></tr><tr><td>Fs</td><td>14.32</td><td>16.20</td><td>8.14</td><td>10.64</td><td>21.98</td><td>11.07</td><td>6.57</td><td>6.42</td><td>7.22</td><td>8.78</td></tr></tbody></table>

**Skeletal olivine cumulate.** A layer containing skeletal olivine crystals (Fig. 7a and b) is found in the upper portion of the cumulate layer of some flows. These textures resemble olivine harrisite in Archean komatiite flows in Australia (Lesher, 1989; Hill et al., 1995).

**Clinopyroxene cumulate (Transitional layer).** This layer forms a 1 to >10 m thick transition between the ultramafic and mafic portions of differentiated flows. Typically, a zone of plagioclase-bearing pyroxenite overlies a zone of olivine pyroxenite in which large clinopyroxene oikocrysts enclose smaller rounded olivine crystals. In thicker flows, the transition zone has a layered structure defined by 0.1 to 10 cm wide dark and whitish bands. Petrographic investigations indicate that the dark bands resulted from the segregation of pyroxene crystals and whitish bands are saussuritized plagioclase (Majidi, 1981).

**Gabbro.** A layer of gabbro underlies the chilled margin and olivine porphyry or spinifex layers in the upper parts of most komatiitic basalts and many komatiite flows. The thickness of this gabbroic layer varies from 2 m in smaller flows to around 40 m in thicker flows, with thicknesses below 10 m being most common. In some instances, the uppermost portion of the komatiitic basalt layer contains a sub-zone characterized by the presence of skeletal and branching clinopyroxene crystals set within a matrix of devitrified glass. This sub-zone is typically 1 to 2 m thick.

## Internal architectures of the flows

Four different flow types were identified on the basis of their structural, textural, and volcanological features (Fig. 8). All are distinguished by olivine cumulates in the lower sections and mafic to ultramafic compositions in the upper sections. What distinguishes them is the type of layering in the upper parts. For example, in Type 3 flows, an upper chilled margin is underlain by olivine spinifex that grades downwards into pyroxene spinifex,

as in typical Archean komatiites (Pyke et al., 1973). Type 3 flows show a progression from chilled margin, olivine porphyry, olivine and pyroxene spinifex to gabbro, as in Archean thick layered komatiitic basalt flows (Arndt, 1977). Types 1 and 2 flows show a more complex alternation of layers with different textures and lithologies.

Undifferentiated units are also present. Some ultramafic units are composed entirely of massive olivine cumulates or olivine porphyries; others are pillowed (Fig. 3d). Mafic lithologies represented by pillowed or massive lava flows and the gabbroic parts of flows or intrusions. Further information is given in Supplementary Data Electronic Appendix File EA2.

## MINERAL CHEMISTRY
### Olivine

The compositions of the magmatic minerals the Mashhad komatiites resemble those in other komatiites, but with some notable differences. The forsterite content of olivine grains, primarily in cores, ranges from Fo84 to Fo91 (Fo = 100*MgO/(MgO + Fe²⁺O)). NiO contents range from 0.31% to 0.39%, and the maximum Cr₂O₃ content is 0.1%. Both values are slightly lower than in olivine in Archean spinifex samples. (Table 1, more detailed EPMA analyses of olivine and other minerals are given in Supplementary Data Electronic Appendix File EA3).

### Chromian spinel

Chromian spinel has various morphologies—skeletal, dendritic, euhedral cubic—and is present in the groundmass and as inclusions in olivines. Typically, the larger grains are zoned with rims richer in Ti and Fe but lower in Cr than the cores. Like other komatiites, they have high Cr# [100 × Cr/(Cr + Al)] values ranging
<table><caption>**Table 4:** Representative compositions of amphibole from Mashhad komatiites</caption><thead><tr><th>Sample</th><th>KHR37</th><th>KHR37</th><th>KHR37</th><th>KHR37</th><th>KHR37</th><th>KHR59</th><th>KHR59</th><th>KHR59</th></tr></thead><tbody><tr><td>Data Point</td><td>A<sub>1</sub>-am<sub>3</sub></td><td>A<sub>2</sub>-am<sub>1</sub></td><td>A<sub>2</sub>-am<sub>11</sub></td><td>A<sub>2</sub>-am<sub>3</sub></td><td>A<sub>2</sub>-am<sub>5</sub></td><td>A<sub>6</sub>-am<sub>2</sub></td><td>A<sub>2</sub>-am<sub>1</sub></td><td>A<sub>1</sub>-am<sub>1</sub></td></tr><tr><td>SiO<sub>2</sub></td><td>45.61</td><td>42.85</td><td>45.13</td><td>42.68</td><td>42.70</td><td>52.36</td><td>44.64</td><td>43.24</td></tr><tr><td>TiO<sub>2</sub></td><td>3.90</td><td>4.78</td><td>0.83</td><td>4.63</td><td>4.53</td><td>0.18</td><td>0.48</td><td>0.52</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>7.87</td><td>10.60</td><td>10.46</td><td>10.45</td><td>10.38</td><td>3.42</td><td>11.42</td><td>12.67</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>1.22</td><td>1.25</td><td>1.23</td><td>1.48</td><td>1.54</td><td>0.01</td><td>0.04</td><td>0.36</td></tr><tr><td>Fe<sub>2</sub>O<sub>3</sub></td><td>5.44</td><td>0.99</td><td>6.53</td><td>7.03</td><td>3.76</td><td>2.29</td><td>2.39</td><td>2.48</td></tr><tr><td>FeO</td><td>1.28</td><td>5.47</td><td>0.00</td><td>0.00</td><td>2.78</td><td>8.38</td><td>10.89</td><td>11.03</td></tr><tr><td>MnO</td><td>0.09</td><td>0.10</td><td>0.08</td><td>0.11</td><td>0.09</td><td>0.28</td><td>0.25</td><td>0.24</td></tr><tr><td>MgO</td><td>17.86</td><td>16.10</td><td>18.27</td><td>17.10</td><td>16.82</td><td>16.39</td><td>12.33</td><td>11.68</td></tr><tr><td>CaO</td><td>10.49</td><td>11.18</td><td>11.55</td><td>10.77</td><td>11.08</td><td>12.24</td><td>12.05</td><td>11.91</td></tr><tr><td>Na<sub>2</sub>O</td><td>2.62</td><td>2.88</td><td>2.33</td><td>2.18</td><td>2.70</td><td>0.61</td><td>1.96</td><td>2.26</td></tr><tr><td>K<sub>2</sub>O</td><td>0.37</td><td>0.61</td><td>0.43</td><td>0.58</td><td>0.61</td><td>0.16</td><td>0.37</td><td>0.37</td></tr><tr><td>NiO</td><td>0.10</td><td>0.11</td><td>0.12</td><td>0.15</td><td>0.08</td><td>0.02</td><td>0.00</td><td>0.03</td></tr><tr><td>F</td><td>0.08</td><td>0.13</td><td>0.11</td><td>0.08</td><td>0.10</td><td>0.19</td><td>0.13</td><td>0.13</td></tr><tr><td>Cl</td><td>0.08</td><td>0.14</td><td>0.16</td><td>0.15</td><td>0.13</td><td>0.09</td><td>0.02</td><td>0.01</td></tr><tr><td>Total</td><td>97.02</td><td>97.19</td><td>97.24</td><td>97.39</td><td>97.31</td><td>96.61</td><td>96.97</td><td>96.92</td></tr><tr><td>Si</td><td>6.54</td><td>6.24</td><td>6.43</td><td>6.13</td><td>6.18</td><td>7.57</td><td>6.59</td><td>6.42</td></tr><tr><td>Ti</td><td>0.42</td><td>0.52</td><td>0.09</td><td>0.50</td><td>0.49</td><td>0.02</td><td>0.05</td><td>0.06</td></tr><tr><td>Al</td><td>1.33</td><td>1.82</td><td>1.76</td><td>1.77</td><td>1.77</td><td>0.58</td><td>1.99</td><td>2.22</td></tr><tr><td>Cr</td><td>0.14</td><td>0.14</td><td>0.14</td><td>0.17</td><td>0.18</td><td>0.00</td><td>0.00</td><td>0.04</td></tr><tr><td>Fe<sup>(iii)</sup></td><td>0.59</td><td>0.11</td><td>0.70</td><td>0.76</td><td>0.41</td><td>0.25</td><td>0.27</td><td>0.28</td></tr><tr><td>Fe<sup>(ii)</sup></td><td>0.15</td><td>0.67</td><td>0.00</td><td>0.00</td><td>0.34</td><td>1.01</td><td>1.35</td><td>1.37</td></tr><tr><td>Mg</td><td>3.82</td><td>3.49</td><td>3.88</td><td>3.66</td><td>3.63</td><td>3.53</td><td>2.72</td><td>2.59</td></tr><tr><td>K</td><td>0.07</td><td>0.11</td><td>0.08</td><td>0.11</td><td>0.11</td><td>0.03</td><td>0.07</td><td>0.07</td></tr><tr><td>Ca</td><td>1.61</td><td>1.74</td><td>1.76</td><td>1.66</td><td>1.72</td><td>1.90</td><td>1.91</td><td>1.89</td></tr><tr><td>Na</td><td>0.39</td><td>0.26</td><td>0.24</td><td>0.34</td><td>0.28</td><td>0.10</td><td>0.09</td><td>0.11</td></tr><tr><td>Al<sup>(iv)</sup></td><td>1.33</td><td>1.76</td><td>1.57</td><td>1.77</td><td>1.77</td><td>0.43</td><td>1.41</td><td>1.58</td></tr><tr><td>Al<sup>(v)</sup></td><td>0.00</td><td>0.05</td><td>0.18</td><td>0.00</td><td>0.00</td><td>0.15</td><td>0.58</td><td>0.64</td></tr></tbody></table>

from 56 to 71, moderate Mg# [100 × Mg/(Mg + Fe)] values between 35 and 67, and varying amounts of Cr₂O₃ (37 to 50 wt %) and Al₂O₃ from 15 to 19 wt % (Table 2).

### Clinopyroxene

Clinopyroxenes are uniform and unzoned. Their compositions are WO₃~48, En₃₂~53, Fs₆~23, corresponding to endiopside–augite–salite. These compositions are almost identical to those of pyroxenes in Archean and Proterozoic komatiites (Arndt & Fleet, 1979; Waterton et al., 2020). Their CaO contents range from 20 to 22 wt % (with one exception) and are higher than in Archean komatiites (Table 3).

### Amphibole

Both primary and secondary amphiboles are present (Table 4). The primary magmatic amphiboles include kaersutites, magnesio-hastingsite and tschermakite to magnesio-hornblende. They are distinguished by their high Mg# >80, and TiO₂ contents of 0.88 to 4.88 wt % (with an average of 3.92 wt %).

The secondary amphiboles are magnesio-hornblende, actinolite, pargasite and edenite, characterized by Mg# between 60.67 and 75.79 and TiO₂ contents ranging from 0.28 to 0.56 wt % with an average of 0.26 wt %. The magmatic amphiboles are also enriched in Cr₂O₃, NiO, Al₂O₃, Na₂O and K₂O compared to the secondary amphiboles.

### Plagioclase

No fresh plagioclase is present in the samples and its composition cannot be determined.

### WHOLE ROCK GEOCHEMISTRY

A total of 48 samples of Mashhad komatiites and associated rocks were analyzed for major, minor, and trace elements (Table 5 and Supplementary Data Electronic Appendix File EA4). All major element contents have been normalized to 100% on a volatile-free basis.

In the ultramafic portions of differentiated komatiite flows, the MgO content varies from 38 wt % in the olivine cumulates to 30 wt % in the most evolved samples (Fig. 10). The olivine spinifex textured samples have unusually high MgO contents, from 30 to 35 wt %. In pyroxene spinifex-textured samples, pyroxene cumulates and gabbros, MgO contents are lower, from 7 to 11 wt %, similar to those in the basalts. Figure 9 shows that the concentrations of relatively immobile elements like Al, Ti, Ca and Nd in the komatiite flows plot mainly on linear arrays that project to the composition of olivine with the composition Fo90–91. This indicates that the compositions of these rocks are controlled by the accumulation or fractionation of olivine with this composition. In the MgO vs Cr₂O₃ diagram (Fig. 9g), the chrome content is seen to decrease with decreasing MgO indicating that chrome spinel fractionated or accumulated together with olivine. The concentrations of elements, such as Ti, Zr or Nd, in several samples of olivine cumulate plot above or below the trends defined by the olivine spinifex samples. These samples also have distinctly different trace element patterns (discussed later) and probably derive from another magma type. The concentrations of mobile elements, such as Rb and Sr (not shown), scatter widely, as is typical of altered ultramafic–mafic rocks. In the mafic samples,
<figure><img src="image_10.png" /><figcaption>**Fig. 9.** Variation diagrams illustrating showing the compositions of ultramafic Mashhad komatiites and mafic rocks, those of olivine within chilled margin and olivine. The regression lines (dotted) pass through spinifex samples. Variation within the rock compositions of is controlled by the ultramafic lavas and intersect accumulation of olivine with the olivine compositions at about Fo91composition Fo89–90.</figcaption></figure>

the concentrations of most elements are widely dispersed, probably due to a combination of fractionation of pyroxene, plagioclase and iron oxides, and element mobility during alteration.

The variations of major and minor elements in individual layered flows are illustrated in Fig. 10. These patterns resemble those reported in layered komatiitic flows in other regions (Arndt, 1977; Francis & Hynes, 1979; Wilson, 2019) and are explained by fractional crystallization, which produced the pyroxene spinifex and gabbroic layers, and the segregation of pyroxene and olivine in the cumulate layers.

## Trace element signatures

The trace-element patterns are best illustrated by mantle-normalized trace element diagrams. In Fig. 11, the compositions of representative samples are plotted according to the lava type, shown in Fig. 8. The patterns for most of

the ultramafic samples have a pronounced hump shape because both the highly incompatible elements, such as the light REE (LREE), and the more compatible elements, such as the heavy REE (HREE), have low normalized concentrations compared to elements with intermediate compatibilities. In samples of gabbro and in a second group of ultramafic lavas, the mantle-normalized concentrations are higher and the more incompatible elements (e.g. LREE, Th, Nb) are relatively enriched.

In Fig. 12, the relative depletion of the more compatible elements such as the HREE, as measured by the (Gd/Yb)$_{N}$ ratio (where the subscript indicates that the values are normalized using the primitive mantle values of Hofmann, 1988), is plotted against the Al$_{2}$O$_{3}$/TiO$_{2}$ ratio. This diagram shows that the Mashhad komatiites have low Al$_{2}$O$_{3}$/TiO$_{2}$ and depleted HREE, and plot in the field of Al-depleted komatiite (ADK) as defined by Nesbitt & Sun (1976) and Jahn *et al.* (1982).
<figure><img src="image_11.png" /><figcaption>**Fig. 10.** Variations of major and minor elements in (a) differentiated komatiite flow and (b) komatiitic basalt flow.</figcaption></figure>

In Fig. 13, (Gd/Yb)$_{N}$ is plotted against (La/Sm)$_{N}$, which is a measure of the relative depletion of the more incompatible elements. In this figure, two types of Mashhad komatiites are clearly distinguished. Those with hump-shaped patterns resemble those of komatiites in localities, such as Ruth Well in Australia (Nisbet & Chinner, 1981) or Jeesiörova in Finland (Hanski et al., 2001), whereas the other patterns, which are more strongly enriched in incompatible elements, resemble alkali picrites, such as the Gudchikhinsky lavas in the Siberian plateau (Wooden et al., 1993).

Examination of the trace element characteristics of the Mashhad komatiites reveals the presence of four separate magma types, as shown in Fig. 14. The term 'D1' (where D denotes 'depleted') refers to magmas with a hump-shaped mantle-normalized trace-element pattern and relatively low concentrations of these elements; 'D2' magmas have similar patterns but higher concentrations of trace elements; 'E' magmas (where E denotes 'enriched') have a very different pattern distinguished by relative enrichment of the more incompatible elements; and 'U' magmas have a distinctive U-shaped pattern.

U-type magmas are restricted to rocks with mafic compositions, either discrete basaltic lava flows or the gabbroic portions of differentiated units. The other three types occur in both ultramafic and mafic lithologies. Ultramafic rocks from chilled upper margins and with olivine spinifex textures fall in the category D1,

but olivine cumulates include types D1, D2 and E. And, as shown in Fig. 15, types D2 and U are found in the gabbroic portions of a differentiated flow, and types E and D1 are found in the olivine cumulate of another flow.

The trace-element patterns of D1 and D2 are similar—both have the distinctive hump-shape. The higher concentrations in type D2 might be explained by a more advanced extent of fractional crystallization of olivine, which would increase concentrations while preserving the form of the patterns or the accumulation of olivine in D1 samples. However, in the MgO vs TiO₂ diagram (Fig. 9c), the D2 samples plot above the trend defined by the other samples indicating that either the olivine that crystallized in these rocks had a higher Fo content, or, more likely, the parental magma had a higher TiO₂ content. Reference to Fig. 16 shows that, at a given MgO content, the TiO₂ contents of the D1 magmas are similar to those in typical Al-depleted komatiites, such as those from the Barberton Greenstone Belt in South Africa, whereas the D2 magma have much higher TiO₂ contents. This would normally be taken as evidence for the derivation of the two magma types from different parental magmas. The same is true for the E and U magma types for which the contrasting patterns and pronounced enrichment of incompatible elements would normally imply very different mantle sources or very different partial melting conditions.
<figure><img src="image_12.png" /><figcaption>**Fig. 11.** Mantle-normalized trace element patterns of Mashhad komatiites: (a, b) Differentiated komatiites (Type 1), (c) Differentiated komatiites (Type 2), (d, e) Komatiitic basalts Type 1 (d) and Type 2 (e), (f) basalts. Normalizing values after Sun & McDonough (1989).</figcaption></figure>

# DISCUSSION

## Magma types

The presence in individual volcanic suites of magmas with contrasting compositions and different origins is not unusual. For example, many continental large igneous provinces (LIP) contain populations of basalts with contrasting, low or high, TiO₂ contents (e.g. Marsh, 1987; Pik et al., 1998). In the Siberian LIP, the compositions of rocks in sub-volcanic intrusions and in the overlying lava sequence show considerable variation and provide evidence for near-contemporaneous intrusion and eruption of several different magma types (Lightfoot et al., 1990; Wooden et al., 1993).

A complicating factor comes from the location of the samples within the differentiated lava flows in the Mashhad region. As described in the previous section and illustrated in Fig. 15, the two contrasting magma types were sampled in the gabbro zone of a single lava flow. There are two alternative interpretations of this observation; 1) either the trace element patterns were affected by alteration and do not reflect those of the original magma, or 2) magmas with contrasting compositions and origins were injected into a single flow. Observations in support of both interpretations can be found in the literature. For example, Blais et al. (1987) and Arndt et al. (1989) reported contrasting trace element patterns in the upper spinifex and lower cumulate zones of individual layered komatiite lava flows; the upper portions display depletion

of the more incompatible elements, whereas the lower portions are enriched in these elements. Blais et al. (1987) interpreted these patterns to indicate the injection of two different magma types into the lava flows, whereas Arndt et al. (1989) proposed that the trace element concentrations in the cumulates had been affected by element mobility during metamorphism or near-surface alteration.

In the Mashhad komatiites, it is difficult for the following reasons to support the interpretation that alteration changed the compositions of the rocks. 1) There is no obvious correlation between the extent or type of alteration in the samples and their trace element patterns; and 2) the distinctive and contrasting patterns, such as D1 and E, occur in spinifex-textured as well as cumulate ultramafic rocks and in mafic gabbros. If the latter were derived by fractional crystallization from parental magmas with compositions similar to those of the ultramafic rocks, the incompatible elements would be preferentially enriched in the more evolved magmas. This is not the case for the samples shown in Fig. 15 where ratios of incompatible to compatible elements are similar in both ultramafic and mafic samples, but vary within individual lithological units.

On the basis of these arguments, we conclude that several different magma types, each produced under different conditions in the mantle, or with contrasting fractionation/contamination
<figure><img src="image_13.png" /><figcaption>**Fig. 12.** Al₂O₃/TiO₂ against (Gd/Yb)N for Mashhad komatiites and representative komatiites from other localities. ADK, Al-depleted komatiite; AUK, Al-undepleted komatiite; data sources: Komati ADK and Weltevreden (Puchtel et al., 2013); Ruth Well-Regal, Komati AUK, Belingwe, Munro, Yilgarn (Sossi et al., 2016), Winnipegosis (Waterton et al., 2017), Kambalda (Lesher & Arndt, 1995), Kostomuksha (Puchtel et al., 1998), Gorgona komatiites and picrites (Révillon et al., 2000), Commondale (Wilson, 2019), Jeesiörova (Hanski et al., 2001), Boston Creek (Puchtel et al., 2018).</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>**Fig. 13.** (Gd/Yb)N vs (La/Sm)N for Mashhad komatiites and representative komatiites from other localities. Data sources as in Fig. 12.</figcaption></figure>

paths during their ascent to the surface, were parental to the komatiites and related mafic rocks on the Mashhad region. The presence in individual flows of samples with contrasting compositions then indicates that magmas with different origins were injected into individual lava flows. The origins of these magmas are discussed in a following section.

## Composition of the parental magma and the origin of spinifex textures

A feature that distinguishes the Mashhad lavas from all other komatiites is the usually high MgO contents of the olivine spinifex-textured rocks. In the analyzed samples, the MgO content ranges from about 30% to 36%, far higher than in spinifex-textured samples from almost all Archean flows (e.g. Arndt et al., 2008). Similarly elevated MgO contents are found in samples from upper and lower chilled margins and in the olivine cumulates of the Mashhad lavas. The high MgO contents in the olivine spinifex

<figure><img src="image_15.png" /><figcaption>**Fig. 14.** Representative analyses of Mashhad komatiitic lavas illustrating the four main magma types. Normalizing values after Hofmann (1988).</figcaption></figure>

lavas poses a problem because such rocks are commonly thought to have crystallized rapidly under conditions that precluded the accumulation of olivine (Viljoen & Viljoen, 1969; Nesbitt, 1971; Arndt et al., 2008); as such, their compositions should be similar to that of the erupted melt. In the Mashhad komatiite suite, there is strong evidence that the erupted melts had far lower MgO contents.

The compositions of the parental melt of komatiites are usually estimated using several complementary approaches. One method is based on the compositions of rapidly cooled samples, such as chilled upper margins or fine random spinifex-textured rocks, as mentioned above. Other approaches depend on the composition of olivine, either as measured using the electron microprobe or inferred from whole-rock compositions.

Microprobe analysis of olivine in the Mashhad lavas reveals a relatively restricted range of forsterite contents, from about Fo84 to a maximum of Fo91. Similar compositions can be inferred from the variation diagrams reported in Fig. 9. In these diagrams, the linear arrays defined by the contents of immobile elements like Al₂O₃ and TiO₂ intersect the compositions of olivine at the composition Fo90-91. The same is seen in the MgO vs FeO(tot) diagram (Fig. 9e), even though the result is less precise due to some scatter of the FeO(tot) data and uncertainties about the Fe²⁺/Fe³⁺ ratio in the magmas. The MgO content of the melt in equilibrium with the most magnesian olivine (Fo91) can then be estimated using an Mg-Fe distribution coefficient of 0.33, as is appropriate from ultramafic melts (Ford et al., 1983). We also assumed that the melt contained 10.5 wt % FeO, the latter being the average value in the komatiites. This approach gives an MgO content of 20 ± 2 wt %. The error is large because it takes into account the uncertainties on the partition coefficient and in the estimation of the Fe²⁺/Fe³⁺ ratio of the melt. Using the highest (13 wt %) and lowest (10.5 wt %) FeO contents of the spinifex-textured samples gives MgO contents of 22 and 18 wt %, respectively. All these values are far lower than the 30 to 36 wt % MgO in analyses of the olivine spinifex-textured lavas.

Another approach to determining the MgO content and eruption temperature of komatiite melt is based on geothermometry. As shown in Fig. 17, we estimate a temperature of 1460°C using the compositions of olivine (Fo90.2) and coexisting spinel and following the method of Wan et al. (2008). For the dry parental melt with composition of sample FC-5, this temperature corresponds to olivine with a higher forsterite content, Fo92, which would have crystallized from anhydrous melt containing ~22 wt %
<figure><img src="image_16.png" /><figcaption>**Fig. 15.** Diagrams illustrating the internal architecture of two flow and the presence of different geochemical types within single lithological units—types U and D2 in the gabbroic portions of one flow, and types E and D1 in the olivine cumulate of another flow.</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>**Fig. 16.** The concentrations of Al₂O₃ and TiO₂ in D1 and D2 type Mashhad komatiites, normalized to 25 wt % MgO using the procedure described by Waterton & Arndt (2024). The data for types E and U cannot be represented because they do not plot on coherent trends on MgO variation diagrams.</figcaption></figure>

‰ MgO (Fig. 17a). The presence of magmatic amphibole in the groundmass, however, suggests that the parental melt contained some water. If it contained 0.5 wt % water, as reported in other komatiites (Sobolev et al., 2019), the initial olivine would have a composition of Fo94 and the MgO content in the equilibrium melt would be ~25 wt % (Fig. 17b). The discrepancy between the measured and predicted forsterite contents may indicate that olivine is partially re-equilibrated with melt at a lower temperature.

We considered several possible explanations for the difference between the extremely high MgO contents of spinifex-textured samples (30–35 wt %) and the estimated MgO contents of the parental melts (20–25 wt %). The first is addition of MgO to the

samples during alteration associated with the metamorphism. To test this hypothesis, we conducted electron microprobe analysis and chemical mapping of several spinifex-textured samples. Interpretation of the results shown in Fig. 18 and evaluated in the Supplementary Data Electronic Appendix File EA5 leads to the following conclusions. 1) The only MgO-rich phase is magmatic olivine; the secondary serpentine that replaces olivine has a lower MgO content, as do the primary and secondary phases in the matrix. 2) The bulk MgO in the sample, as estimated by combining the proportions of minerals in the image and their compositions, is similar within error to the MgO content in the chemical analysis of the rock. On the basis of these interpretations, we conclude that no MgO was added by secondary processes and that the MgO contents reported in Table 4 are those of the original spinifex-textured lavas.

The alternative explanation is that olivine accumulated in the rock during its emplacement or solidification. In random olivine spinifex-textured samples, be they from Archean localities or from Gorgona Island, the olivine crystals have a delicate, skeletal or dendritic morphology and random orientation (Nesbitt, 1971; Echeverria, 1980), a configuration that would seem to preclude accumulation of olivine during the solidification of the lava. In samples of platy olivine spinifex, in contrast, the crystals are oriented perpendicular to the flow top, and in such samples, mineralogical, geochemical and theoretical observations suggest that olivine accumulated during constrained growth within the crust of the flow (Lesher et al., 1981; Bickle, 1982; Huppert et al., 1984; Faure et al., 2006). In the Mashhad spinifex lavas, such a process seems improbable, because, as illustrated in Fig. 5, the crystals are randomly oriented.

A possible explanation stems from the unusual morphology of olivine crystals in Mashhad spinifex lavas and from characteristics of samples from the chilled upper margin. As shown in Fig. 4a, these the latter rocks contain sparse, moderately large phenocrysts (50–100 µm) in a matrix composed of abundant smaller (10–20 µm) crystals. Both types of crystal have solid, polyhedral habits and it is possible that they represent a crystal cargo that was entrained in the lava as it erupted. The dimensions
<figure><img src="image_18.png" /><figcaption>**Fig. 17.** The olivine-spinel Al partition temperature (Wan et al., 2008) and a model of olivine fractional crystallization from the least MgO-rich random spinifex sample of Mashhad komatiite. (a) Fo content of olivine and crystallization temperatures for different amounts of H₂O in parental melt after Danyushevsky & Plechov (2011). The olivine-spinel temperature for Mashhad komatiites is from this study, fields of olivine-spinel temperatures for Abitibi and Belingwe komatiites are from Sobolev et al. (2016) and Asafov et al. (2018). (b) MgO content and equilibrium temperature for the same model as on a. MgO<sup>equilibrium melt</sup> field represent estimates of MgO content of equilibrium melt at the olivine-spinel temperature of Mashhad komatiites.</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>**Fig. 18.** A back-scattered electron (BSE) image and electron microprobe elemental mapping of a sample with spinifex texture.</figcaption></figure>
<table><caption>**Table 5:** Selected geochemical analyses of Mashhad komatiites (oxides are in wt % and trace elements in ppm)</caption><thead><tr><th rowspan="3">Rock type:</th><th colspan="8">Differentiated komatiites</th></tr><tr><th colspan="8">Mashhad Complex</th></tr><tr><th>cumulate layer</th><th>cumulate layer</th><th>cumulate layer</th><th>cumulate layer</th><th>cumulate layer</th><th>cumulate layer</th><th>cumulate layer</th><th>cumulate layer</th></tr></thead><tbody><tr><td>Sample</td><td>PUN-1</td><td>PUN-3</td><td>PUN-38</td><td>PUN-40</td><td>NAM-9</td><td>NAM-19</td><td>NAM-16</td><td>NAM-196</td></tr><tr><td>SiO<sub>2</sub></td><td>43.65</td><td>42.89</td><td>42.44</td><td>42.47</td><td>43.73</td><td>44.15</td><td>43.52</td><td>44.26</td></tr><tr><td>TiO<sub>2</sub></td><td>0.50</td><td>0.32</td><td>0.35</td><td>0.34</td><td>0.46</td><td>0.47</td><td>0.47</td><td>0.42</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>5.40</td><td>3.98</td><td>3.82</td><td>3.56</td><td>4.82</td><td>5.79</td><td>4.92</td><td>5.84</td></tr><tr><td>FeO*</td><td>11.86</td><td>11.27</td><td>11.40</td><td>11.43</td><td>11.10</td><td>12.30</td><td>11.56</td><td>12.20</td></tr><tr><td>CaO</td><td>6.34</td><td>3.33</td><td>4.02</td><td>2.89</td><td>4.25</td><td>5.13</td><td>4.93</td><td>5.04</td></tr><tr><td>MgO</td><td>31.07</td><td>36.94</td><td>36.70</td><td>37.98</td><td>34.43</td><td>30.94</td><td>33.40</td><td>31.03</td></tr><tr><td>MnO</td><td>0.20</td><td>0.17</td><td>0.18</td><td>0.18</td><td>0.19</td><td>0.20</td><td>0.19</td><td>0.20</td></tr><tr><td>Na<sub>2</sub>O</td><td>0.13</td><td>0.04</td><td>0.04</td><td>0.05</td><td>0.04</td><td>0.13</td><td>0.04</td><td>0.15</td></tr><tr><td>K<sub>2</sub>O</td><td>0.01</td><td>0.01</td><td>0.01</td><td>0.01</td><td>0.01</td><td>0.01</td><td>0.01</td><td>0.01</td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>0.04</td><td>0.02</td><td>0.04</td><td>0.03</td><td>0.04</td><td>0.04</td><td>0.04</td><td>0.04</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.56</td><td>0.70</td><td>0.70</td><td>0.76</td><td>0.66</td><td>0.59</td><td>0.67</td><td>0.56</td></tr><tr><td>NiO</td><td>0.24</td><td>0.31</td><td>0.31</td><td>0.31</td><td>0.27</td><td>0.24</td><td>0.25</td><td>0.24</td></tr><tr><td>LOI</td><td>8.36</td><td>9.71</td><td>9.51</td><td>9.95</td><td>9.54</td><td>9.40</td><td>8.27</td><td>8.51</td></tr><tr><td>(Total)</td><td>99.05</td><td>99.35</td><td>99.29</td><td>98.90</td><td>98.97</td><td>99.12</td><td>98.80</td><td>99.36</td></tr><tr><td>Cs (ppm)</td><td>1.01</td><td>0.21</td><td>0.30</td><td>0.23</td><td>0.71</td><td>0.79</td><td>0.40</td><td>0.41</td></tr><tr><td>Rb</td><td>1.41</td><td>0.91</td><td>1.03</td><td>0.78</td><td>1.16</td><td>1.25</td><td>1.29</td><td>1.23</td></tr><tr><td>Ba</td><td>5.35</td><td>7.45</td><td>2.28</td><td>1.14</td><td>5.35</td><td>6.31</td><td>109</td><td>141</td></tr><tr><td>Th</td><td>0.12</td><td>0.33</td><td>0.30</td><td>0.27</td><td>0.25</td><td>0.40</td><td>0.56</td><td>0.56</td></tr><tr><td>U</td><td>2.38</td><td>0.02</td><td>0.01</td><td>0.01</td><td>0.05</td><td>0.06</td><td>0.09</td><td>0.09</td></tr><tr><td>Nb</td><td>1.15</td><td>1.02</td><td>1.10</td><td>0.87</td><td>1.22</td><td>1.55</td><td>1.52</td><td>1.60</td></tr><tr><td>Ta</td><td>0.08</td><td>0.08</td><td>0.08</td><td>0.06</td><td>0.09</td><td>0.12</td><td>0.11</td><td>0.13</td></tr><tr><td>La</td><td>1.03</td><td>1.14</td><td>1.20</td><td>0.95</td><td>1.23</td><td>1.64</td><td>1.90</td><td>1.85</td></tr><tr><td>Ce</td><td>3.28</td><td>3.03</td><td>3.31</td><td>2.70</td><td>3.45</td><td>4.31</td><td>5.27</td><td>5.09</td></tr><tr><td>Pb</td><td>1.68</td><td>1.49</td><td>0.65</td><td>0.44</td><td>1.03</td><td>0.74</td><td>0.44</td><td>0.40</td></tr><tr><td>Pr</td><td>0.51</td><td>0.40</td><td>0.47</td><td>0.38</td><td>0.50</td><td>0.59</td><td>0.67</td><td>0.70</td></tr><tr><td>Sr</td><td>48.17</td><td>17.22</td><td>17.50</td><td>13.43</td><td>15.66</td><td>23.89</td><td>35.60</td><td>42.23</td></tr><tr><td>Nd</td><td>2.76</td><td>2.00</td><td>2.23</td><td>1.88</td><td>2.43</td><td>2.87</td><td>3.38</td><td>3.28</td></tr><tr><td>Zr</td><td>19.73</td><td>21.07</td><td>23.27</td><td>19.88</td><td>12.51</td><td>14.94</td><td>26.95</td><td>26.46</td></tr><tr><td>Hf</td><td>0.58</td><td>0.51</td><td>0.55</td><td>0.47</td><td>0.40</td><td>0.50</td><td>0.70</td><td>0.71</td></tr><tr><td>Sm</td><td>0.92</td><td>0.63</td><td>0.70</td><td>0.59</td><td>0.81</td><td>0.91</td><td>1.01</td><td>1.03</td></tr><tr><td>Eu</td><td>0.35</td><td>0.20</td><td>0.25</td><td>0.21</td><td>0.27</td><td>0.33</td><td>0.37</td><td>0.37</td></tr><tr><td>Ti</td><td>2998</td><td>1918</td><td>2098</td><td>2038</td><td>2758</td><td>2818</td><td>2790</td><td>2522</td></tr><tr><td>Gd</td><td>1.34</td><td>0.87</td><td>1.00</td><td>0.85</td><td>1.08</td><td>1.30</td><td>1.40</td><td>1.40</td></tr><tr><td>Tb</td><td>0.22</td><td>0.14</td><td>0.16</td><td>0.13</td><td>0.18</td><td>0.20</td><td>0.22</td><td>0.23</td></tr><tr><td>Dy</td><td>1.40</td><td>0.89</td><td>1.02</td><td>0.85</td><td>1.18</td><td>1.30</td><td>1.45</td><td>1.45</td></tr><tr><td>Y</td><td>6.61</td><td>4.37</td><td>5.00</td><td>4.14</td><td>5.56</td><td>6.34</td><td>7.18</td><td>7.46</td></tr><tr><td>Ho</td><td>0.29</td><td>0.18</td><td>0.21</td><td>0.17</td><td>0.23</td><td>0.26</td><td>0.29</td><td>0.30</td></tr><tr><td>Er</td><td>0.79</td><td>0.50</td><td>0.60</td><td>0.52</td><td>0.65</td><td>0.72</td><td>0.83</td><td>0.86</td></tr><tr><td>Tm</td><td>0.11</td><td>0.07</td><td>0.08</td><td>0.07</td><td>0.10</td><td>0.09</td><td>0.11</td><td>0.12</td></tr><tr><td>Yb</td><td>0.68</td><td>0.46</td><td>0.51</td><td>0.45</td><td>0.60</td><td>0.64</td><td>0.75</td><td>0.72</td></tr><tr><td>Lu</td><td>0.10</td><td>0.07</td><td>0.08</td><td>0.07</td><td>0.09</td><td>0.10</td><td>0.11</td><td>0.11</td></tr></tbody></table>

of the stubby elongate crystals in olivine spinifex lavas are slightly greater than those of the small crystals in the chilled margin, which suggests that the larger crystals could have nucleated and grown on the smaller crystals. The proportion of small phenocrysts in the chilled margins is 30 to 50 vol % and if they formed the nuclei of the crystals in the spinifex lavas, their presence would have increased the MgO content from the 22 wt % in the melt to the 30 to 35 wt % in the spinifex-textured rocks (Supplementary Data Electronic Appendix File EA5).

## Origin of the magmas

Two of the four magma types illustrated in Fig. 14 (D1 and D2) have similar REE element patterns and the two others have contrasting patterns. We exclude the possibility that these differences

could have been due, in part or entirely, to contamination with material from the continental crust by referring to the mantle-normalized trace element diagrams (Fig. 11). Most rocks in the continental crust are relatively depleted in Nb compared with other incompatible trace elements (Rudnick & Gao, 2014) and the assimilation of continental material should produce a negative Nb anomaly. Such anomalies are absent from the Mashhad komatiites.

We also considered whether the magmas could have been related by fractional crystallization or accumulation of olivine. The presence of up to 50% excess olivine was present in the spinifex-textured or chilled margin samples could explain the lower concentrations in the D1 samples. The departures in e.g. TiO₂ and FeO contents from the olivine control lines in Fig. 9, if
<table><caption>**Table 5:** Continued</caption><thead><tr><th rowspan="3">Sample</th><th colspan="8">Rock type:</th></tr><tr><th colspan="8">Differentiated komatiites</th></tr><tr><th colspan="8">Mashhad Complex</th></tr><tr><th></th><th>transition layer</th><th>transition layer</th><th>transition layer</th><th>transition layer</th><th>transition layer</th><th>gabbro</th><th>gabbro</th><th>gabbro</th></tr></thead><tbody><tr><td>SiO<sub>2</sub></td><td>44.90</td><td>45.12</td><td>44.92</td><td>45.16</td><td>45.15</td><td>50.37</td><td>51.74</td><td>50.21</td></tr><tr><td>TiO<sub>2</sub></td><td>0.57</td><td>0.57</td><td>0.51</td><td>0.57</td><td>0.56</td><td>0.70</td><td>0.82</td><td>0.59</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>8.08</td><td>8.07</td><td>6.53</td><td>8.13</td><td>7.99</td><td>16.91</td><td>11.84</td><td>15.44</td></tr><tr><td>FeO</td><td>11.61</td><td>11.44</td><td>11.57</td><td>11.43</td><td>11.52</td><td>5.67</td><td>9.41</td><td>7.80</td></tr><tr><td>CaO</td><td>8.09</td><td>8.19</td><td>5.88</td><td>8.24</td><td>8.28</td><td>14.00</td><td>12.15</td><td>13.17</td></tr><tr><td>MgO</td><td>25.66</td><td>25.50</td><td>29.50</td><td>25.38</td><td>25.43</td><td>8.72</td><td>11.31</td><td>10.47</td></tr><tr><td>MnO</td><td>0.17</td><td>0.17</td><td>0.20</td><td>0.17</td><td>0.17</td><td>0.11</td><td>0.19</td><td>0.18</td></tr><tr><td>Na<sub>2</sub>O</td><td>0.22</td><td>0.24</td><td>0.11</td><td>0.22</td><td>0.21</td><td>3.25</td><td>1.87</td><td>1.83</td></tr><tr><td>K<sub>2</sub>O</td><td>0.01</td><td>0.01</td><td>0.01</td><td>0.02</td><td>0.01</td><td>0.06</td><td>0.41</td><td>0.19</td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>0.05</td><td>0.05</td><td>0.04</td><td>0.04</td><td>0.04</td><td>0.06</td><td>0.07</td><td>0.05</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.44</td><td>0.44</td><td>0.50</td><td>0.43</td><td>0.44</td><td>0.11</td><td>0.16</td><td>0.05</td></tr><tr><td>NiO</td><td>0.19</td><td>0.19</td><td>0.22</td><td>0.19</td><td>0.19</td><td>0.03</td><td>0.03</td><td>0.03</td></tr><tr><td>LOI</td><td>5.98</td><td>5.79</td><td>7.32</td><td>5.89</td><td>5.86</td><td>1.50</td><td>1.86</td><td>2.54</td></tr><tr><td>(Total)</td><td>99.04</td><td>98.96</td><td>99.37</td><td>98.91</td><td>99.08</td><td>98.14</td><td>98.96</td><td>99.16</td></tr><tr><td>Cs (ppm)</td><td>0.31</td><td>0.32</td><td>0.34</td><td>0.32</td><td>0.33</td><td>0.032</td><td>0.73</td><td>0.68</td></tr><tr><td>Rb</td><td>0.87</td><td>0.98</td><td>0.88</td><td>0.90</td><td>1.02</td><td>0.40</td><td>9.67</td><td>5.58</td></tr><tr><td>Ba</td><td>4.02</td><td>4.07</td><td>4.99</td><td>4.16</td><td>3.26</td><td>15.00</td><td>123</td><td>47.58</td></tr><tr><td>Th</td><td>0.22</td><td>0.21</td><td>0.26</td><td>0.20</td><td>0.22</td><td>1.30</td><td>1.37</td><td>1.04</td></tr><tr><td>U</td><td>0.05</td><td>0.05</td><td>0.04</td><td>0.05</td><td>0.05</td><td>0.20</td><td>0.24</td><td>0.18</td></tr><tr><td>Nb</td><td>1.29</td><td>1.23</td><td>1.13</td><td>1.32</td><td>1.30</td><td>3.60</td><td>6.77</td><td>4.19</td></tr><tr><td>Ta</td><td>0.11</td><td>0.11</td><td>0.09</td><td>0.11</td><td>0.11</td><td>0.26</td><td>n.d.</td><td>n.d.</td></tr><tr><td>La</td><td>1.28</td><td>1.32</td><td>1.17</td><td>1.26</td><td>1.31</td><td>4.39</td><td>5.67</td><td>3.84</td></tr><tr><td>Ce</td><td>3.91</td><td>3.88</td><td>3.50</td><td>3.84</td><td>3.95</td><td>11.32</td><td>14.06</td><td>9.66</td></tr><tr><td>Pb</td><td>0.54</td><td>0.58</td><td>0.53</td><td>0.62</td><td>0.54</td><td>3.86</td><td>6.84</td><td>5.38</td></tr><tr><td>Pr</td><td>0.62</td><td>0.61</td><td>0.51</td><td>0.62</td><td>0.62</td><td>1.34</td><td>1.71</td><td>1.20</td></tr><tr><td>Sr</td><td>48.03</td><td>43.78</td><td>67.10</td><td>53.85</td><td>38.63</td><td>257</td><td>184</td><td>342</td></tr><tr><td>Nd</td><td>3.24</td><td>3.33</td><td>2.70</td><td>3.25</td><td>3.39</td><td>5.83</td><td>7.70</td><td>5.67</td></tr><tr><td>Zr</td><td>21.65</td><td>21.00</td><td>20.44</td><td>21.30</td><td>20.63</td><td>38.44</td><td>35.82</td><td>44.76</td></tr><tr><td>Hf</td><td>0.76</td><td>0.77</td><td>0.70</td><td>0.79</td><td>0.74</td><td>1.19</td><td>1.19</td><td>1.19</td></tr><tr><td>Sm</td><td>1.09</td><td>1.14</td><td>0.93</td><td>1.12</td><td>1.16</td><td>1.69</td><td>2.21</td><td>1.58</td></tr><tr><td>Eu</td><td>0.40</td><td>0.42</td><td>0.34</td><td>0.40</td><td>0.41</td><td>0.60</td><td>0.77</td><td>0.56</td></tr><tr><td>Ti</td><td>3417</td><td>3417</td><td>3057</td><td>3417</td><td>3366</td><td>4197</td><td>4916</td><td>3537</td></tr><tr><td>Gd</td><td>1.59</td><td>1.55</td><td>1.26</td><td>1.52</td><td>1.57</td><td>1.98</td><td>3.11</td><td>2.06</td></tr><tr><td>Tb</td><td>0.27</td><td>0.27</td><td>0.22</td><td>0.26</td><td>0.28</td><td>0.34</td><td>0.51</td><td>0.35</td></tr><tr><td>Dy</td><td>1.75</td><td>1.71</td><td>1.48</td><td>1.73</td><td>1.78</td><td>2.23</td><td>3.29</td><td>2.13</td></tr><tr><td>Y</td><td>9.52</td><td>9.32</td><td>7.46</td><td>9.18</td><td>9.46</td><td>12.35</td><td>17.57</td><td>11.69</td></tr><tr><td>Ho</td><td>0.35</td><td>0.34</td><td>0.29</td><td>0.34</td><td>0.35</td><td>0.43</td><td>0.66</td><td>0.43</td></tr><tr><td>Er</td><td>0.96</td><td>0.94</td><td>0.82</td><td>0.93</td><td>1.00</td><td>1.21</td><td>1.93</td><td>1.23</td></tr><tr><td>Tm</td><td>0.14</td><td>0.13</td><td>0.12</td><td>0.14</td><td>0.14</td><td>0.18</td><td>0.26</td><td>0.17</td></tr><tr><td>Yb</td><td>0.88</td><td>0.87</td><td>0.74</td><td>0.86</td><td>0.90</td><td>1.16</td><td>1.66</td><td>1.05</td></tr><tr><td>Lu</td><td>0.12</td><td>0.13</td><td>0.11</td><td>0.12</td><td>0.13</td><td>0.17</td><td>0.25</td><td>0.16</td></tr></tbody></table>

not due to element mobility, suggest derivation from different parental magmas. We considered whether fractional crystallization of phases such as amphibole or clinopyroxene could have produced the changes in pattern, or relative enrichment of the LREE in E and U-type magma, but ruled this out because the levels of REE in these samples are no higher than in the D2 samples. If amphibole or clinopyroxene had fractionated in large enough quantities to radically change the REE patterns, the concentrations of moderately incompatible elements like Sm or Gd would have increased markedly, to levels far higher than in the D2 samples. As seen in Fig. 17, the concentrations of these elements are lower.

To explore how and where in the mantle the parental magmas were produced, we use an approach similar to that adopted by

Waterton & Arndt (2024). We preferred not to use a numerical approach to estimate the pressure and temperature at the melting site, such as the one suggested by Lee & Chin (2014) because this procedure does not properly account for the specific melting processes that operate during the formation of komatiite, nor for the influence of a small amount of water in the source.

Instead, we apply the following constraints: (1) the MgO contents of the parental magmas are between 20 and 22 wt%; lower than in Archean komatiites but higher than in most Phanerozoic lavas. Reference to the phase diagram plotted as Fig. 19 indicates that a melt with 20 to 22 wt% MgO could have formed either near the dry solidus at a depth around 100 to 150 km (pressure = 4–5 GPa) or by a higher degree of partial melting at shallower depth. (2) The Al-depleted character and relative depletion of the
<table><caption>**Table 5: Continued**</caption><thead><tr><th rowspan="3">Sample</th><th colspan="4">Rock type:</th><th colspan="4">Differentiated komatiites</th></tr><tr><th colspan="4">Mashhad Complex</th><th colspan="4">Fariman Complex</th></tr><tr><th>KHR-49</th><th>SAV-265</th><th>SAV-266</th><th>SAV-26</th><th>FC-1</th><th>FC-8</th><th>FC-3</th><th>FC-5</th></tr></thead><tbody><tr><td>SiO<sub>2</sub></td><td>48.24</td><td>49.78</td><td>48.71</td><td>48.67</td><td>43.38</td><td>43.98</td><td>43.53</td><td>44.42</td></tr><tr><td>TiO<sub>2</sub></td><td>0.73</td><td>0.51</td><td>0.36</td><td>0.37</td><td>0.39</td><td>0.44</td><td>0.41</td><td>0.54</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>15.22</td><td>16.12</td><td>20.09</td><td>21.09</td><td>4.37</td><td>5.37</td><td>4.84</td><td>6.33</td></tr><tr><td>FeO</td><td>8.19</td><td>6.10</td><td>4.57</td><td>4.33</td><td>10.55</td><td>10.81</td><td>10.74</td><td>11.01</td></tr><tr><td>CaO</td><td>16.02</td><td>15.93</td><td>16.80</td><td>16.55</td><td>4.37</td><td>5.29</td><td>4.68</td><td>7.13</td></tr><tr><td>MgO</td><td>9.71</td><td>9.56</td><td>7.06</td><td>6.45</td><td>35.91</td><td>33.05</td><td>34.77</td><td>29.76</td></tr><tr><td>MnO</td><td>0.17</td><td>0.14</td><td>0.11</td><td>0.10</td><td>0.16</td><td>0.16</td><td>0.17</td><td>0.18</td></tr><tr><td>Na<sub>2</sub>O</td><td>1.42</td><td>1.56</td><td>2.01</td><td>2.17</td><td>0.04</td><td>0.17</td><td>0.06</td><td>0.09</td></tr><tr><td>K<sub>2</sub>O</td><td>0.18</td><td>0.24</td><td>0.22</td><td>0.21</td><td>0.00</td><td>0.00</td><td>0.00</td><td>0.00</td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>0.05</td><td>0.03</td><td>0.02</td><td>0.03</td><td>0.00</td><td>0.00</td><td>0.00</td><td>0.00</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.06</td><td>0.01</td><td>0.03</td><td>0.02</td><td>0.58</td><td>0.50</td><td>0.55</td><td>0.35</td></tr><tr><td>NiO</td><td>0.02</td><td>0.02</td><td>0.01</td><td>0.01</td><td>0.25</td><td>0.23</td><td>0.24</td><td>0.20</td></tr><tr><td>LOI</td><td>1.57</td><td>1.62</td><td>2.11</td><td>2.25</td><td>11.10</td><td>8.90</td><td>10.50</td><td>8.01</td></tr><tr><td>(Total)</td><td>99.33</td><td>99.11</td><td>99.03</td><td>98.99</td><td>100.03</td><td>99.76</td><td>100.13</td><td>99.83</td></tr><tr><td>Cs (ppm)</td><td>0.45</td><td>1.72</td><td>1.52</td><td>1.47</td><td>0.47</td><td>0.78</td><td>0.80</td><td>1.63</td></tr><tr><td>Rb</td><td>4.50</td><td>9.97</td><td>10.07</td><td>9.60</td><td>1.17</td><td>2.10</td><td>1.62</td><td>3.17</td></tr><tr><td>Ba</td><td>61.87</td><td>78.47</td><td>123</td><td>122</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>9.50</td></tr><tr><td>Th</td><td>0.11</td><td>0.16</td><td>0.20</td><td>0.19</td><td>0.06</td><td>0.06</td><td>0.06</td><td>0.08</td></tr><tr><td>U</td><td>0.03</td><td>0.04</td><td>0.04</td><td>0.03</td><td>0.02</td><td>0.02</td><td>0.02</td><td>0.02</td></tr><tr><td>Nb</td><td>1.14</td><td>0.82</td><td>0.62</td><td>0.62</td><td>0.59</td><td>0.63</td><td>0.61</td><td>0.85</td></tr><tr><td>Ta</td><td>0.09</td><td>0.06</td><td>0.05</td><td>0.05</td><td>0.05</td><td>0.05</td><td>0.05</td><td>0.07</td></tr><tr><td>La</td><td>1.46</td><td>1.06</td><td>0.97</td><td>0.95</td><td>0.70</td><td>0.91</td><td>0.85</td><td>1.09</td></tr><tr><td>Ce</td><td>4.29</td><td>3.24</td><td>2.81</td><td>2.70</td><td>2.20</td><td>2.72</td><td>2.53</td><td>3.39</td></tr><tr><td>Pb</td><td>1.71</td><td>0.45</td><td>0.79</td><td>0.89</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td></tr><tr><td>Pr</td><td>0.75</td><td>0.51</td><td>0.41</td><td>0.39</td><td>0.35</td><td>0.43</td><td>0.40</td><td>0.54</td></tr><tr><td>Sr</td><td>122</td><td>328</td><td>347</td><td>390</td><td>13.24</td><td>23.04</td><td>15.16</td><td>56.52</td></tr><tr><td>Nd</td><td>4.08</td><td>2.81</td><td>2.35</td><td>2.07</td><td>1.98</td><td>2.30</td><td>2.20</td><td>2.92</td></tr><tr><td>Zr</td><td>31.09</td><td>20.55</td><td>14.56</td><td>13.54</td><td>16.76</td><td>18.55</td><td>17.03</td><td>23.53</td></tr><tr><td>Hf</td><td>1.06</td><td>0.68</td><td>0.49</td><td>0.46</td><td>0.47</td><td>0.53</td><td>0.50</td><td>0.67</td></tr><tr><td>Sm</td><td>1.51</td><td>1.04</td><td>0.81</td><td>0.75</td><td>0.70</td><td>0.82</td><td>0.78</td><td>1.01</td></tr><tr><td>Eu</td><td>0.57</td><td>0.49</td><td>0.38</td><td>0.37</td><td>0.27</td><td>0.33</td><td>0.31</td><td>0.40</td></tr><tr><td>Ti</td><td>4390</td><td>3057</td><td>2158</td><td>2218</td><td>2361</td><td>2619</td><td>2458</td><td>3234</td></tr><tr><td>Gd</td><td>2.08</td><td>1.50</td><td>1.04</td><td>1.01</td><td>0.88</td><td>1.00</td><td>0.93</td><td>1.25</td></tr><tr><td>Tb</td><td>0.35</td><td>0.24</td><td>0.19</td><td>0.18</td><td>0.15</td><td>0.18</td><td>0.16</td><td>0.23</td></tr><tr><td>Dy</td><td>2.27</td><td>1.63</td><td>1.22</td><td>1.14</td><td>1.02</td><td>1.20</td><td>1.04</td><td>1.49</td></tr><tr><td>Y</td><td>12.14</td><td>8.92</td><td>6.62</td><td>6.10</td><td>5.17</td><td>6.22</td><td>5.38</td><td>7.57</td></tr><tr><td>Ho</td><td>0.46</td><td>0.32</td><td>0.24</td><td>0.22</td><td>0.21</td><td>0.25</td><td>0.22</td><td>0.31</td></tr><tr><td>Er</td><td>1.21</td><td>0.84</td><td>0.63</td><td>0.59</td><td>0.56</td><td>0.65</td><td>0.59</td><td>0.80</td></tr><tr><td>Tm</td><td>0.17</td><td>0.13</td><td>0.09</td><td>0.08</td><td>0.08</td><td>0.10</td><td>0.09</td><td>0.12</td></tr><tr><td>Yb</td><td>1.14</td><td>0.74</td><td>0.54</td><td>0.51</td><td>0.51</td><td>0.59</td><td>0.53</td><td>0.73</td></tr><tr><td>Lu</td><td>0.15</td><td>0.10</td><td>0.07</td><td>0.07</td><td>0.08</td><td>0.09</td><td>0.08</td><td>0.11</td></tr></tbody></table>

heavy rare earth elements indicate that the magma formed in the presence of garnet. (3) If Ti is assumed to be incompatible during partial melting, its concentration in the Mashhad lavas can be used to estimate the degree of melting. Assuming 0.13 wt % in a depleted mantle source (Salters & Stracke, 2004), we estimate that a D1 type of magma containing 0.6 wt % TiO₂ at 20% MgO could have been produced by 20% partial melting and that a D2 magma containing 1.0 wt % TiO₂ could have been produced by 13% partial melting. Reference to the experimental results of Walter (1998); Fig. 19) indicates that melt with 20 to 22 wt % MgO could have formed by 10–15% melting in the garnet stability field at a pressure of 4 to 5 GPa, or a depth of about 120 to 150 km.

The E and B types of lavas were produced under different conditions or from a more enriched source. Ongoing analyses of the Nd and Hf isotopic compositions of the komatiites should help distinguish between these possibilities.

## GEODYNAMIC SETTING

During the Late Paleozoic, southern Asia and the Central Asian Orogenic Belt experienced considerable tectonic instability. These areas comprised a mosaic of microcontinents derived from Gondwana, which re-assembled during the Paleozoic and Mesozoic within southern Eurasia. A major consequence of these tectonic disruptions was extensive magmatism associated with
<table><caption>**Table 5:** Continued</caption><thead><tr><th rowspan="3">Rock type:</th><th colspan="3">Differentiated Kom.</th><th colspan="3">Undifferentiated komatiites</th><th colspan="3">Komatiitic-basalt flows</th></tr><tr><th rowspan="2">random<br>olivine<br>spinifex</th><th rowspan="2">random<br>olivine<br>spinifex</th><th colspan="3">Fariman Complex</th><th rowspan="2">olivine<br>cumulate<br>layer</th><th rowspan="2">olivine<br>cumulate<br>layer</th><th rowspan="2">olivine<br>cumulate<br>layer</th></tr><tr><th>skeletal<br>olivine<br>cumulate</th><th>skeletal<br>olivine<br>cumulate</th><th>skeletal<br>olivine<br>cumulate</th></tr><tr><th>Sample</th><th>FC-24</th><th>FC-25</th><th>SFS1</th><th>SFS112</th><th>SFS10</th><th>SFS-6</th><th>SFS29</th><th>SFS24</th></tr></thead><tbody><tr><td>SiO<sub>2</sub></td><td>44.23</td><td>44.20</td><td>43.70</td><td>43.64</td><td>43.75</td><td>43.68</td><td>43.28</td><td>44.77</td></tr><tr><td>TiO<sub>2</sub></td><td>0.53</td><td>0.51</td><td>0.50</td><td>0.50</td><td>0.52</td><td>0.67</td><td>0.47</td><td>0.93</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>6.37</td><td>6.02</td><td>5.58</td><td>5.52</td><td>5.53</td><td>5.29</td><td>4.99</td><td>6.29</td></tr><tr><td>FeO</td><td>11.00</td><td>10.85</td><td>11.31</td><td>11.30</td><td>11.25</td><td>11.91</td><td>10.93</td><td>11.93</td></tr><tr><td>CaO</td><td>7.26</td><td>6.30</td><td>5.14</td><td>5.15</td><td>5.27</td><td>5.66</td><td>5.12</td><td>6.10</td></tr><tr><td>MgO</td><td>29.72</td><td>31.16</td><td>32.39</td><td>32.49</td><td>32.41</td><td>31.55</td><td>34.11</td><td>28.62</td></tr><tr><td>MnO</td><td>0.18</td><td>0.17</td><td>0.19</td><td>0.18</td><td>0.18</td><td>0.20</td><td>0.18</td><td>0.18</td></tr><tr><td>Na<sub>2</sub>O</td><td>0.08</td><td>0.08</td><td>0.17</td><td>0.17</td><td>0.11</td><td>0.15</td><td>0.06</td><td>0.42</td></tr><tr><td>K<sub>2</sub>O</td><td>0.04</td><td>0.04</td><td>0.11</td><td>0.13</td><td>0.11</td><td>0.08</td><td>0.01</td><td>0.05</td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>0.00</td><td>0.00</td><td>0.04</td><td>0.04</td><td>0.05</td><td>0.07</td><td>0.04</td><td>0.09</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.39</td><td>0.46</td><td>0.63</td><td>0.63</td><td>0.58</td><td>0.49</td><td>0.55</td><td>0.41</td></tr><tr><td>NiO</td><td>0.20</td><td>0.20</td><td>0.24</td><td>0.24</td><td>0.23</td><td>0.25</td><td>0.27</td><td>0.22</td></tr><tr><td>LOI</td><td>8.58</td><td>8.62</td><td>7.14</td><td>7.07</td><td>7.65</td><td>7.69</td><td>7.83</td><td>6.02</td></tr><tr><td>(Total)</td><td>99.82</td><td>99.79</td><td>99.15</td><td>99.33</td><td>99.13</td><td>99.00</td><td>99.04</td><td>99.17</td></tr><tr><td>Cs (ppm)</td><td>2.56</td><td>2.22</td><td>0.32</td><td>n.d.</td><td>0.03</td><td>0.75</td><td>2.31</td><td>1.68</td></tr><tr><td>Rb</td><td>3.64</td><td>3.11</td><td>3.80</td><td>n.d.</td><td>2.81</td><td>4.61</td><td>1.85</td><td>4.62</td></tr><tr><td>Ba</td><td>6.16</td><td>n.d.</td><td>7.84</td><td>n.d.</td><td>4.55</td><td>14.28</td><td>3.34</td><td>11.00</td></tr><tr><td>Th</td><td>0.07</td><td>0.07</td><td>0.07</td><td>n.d.</td><td>0.07</td><td>0.20</td><td>0.08</td><td>0.36</td></tr><tr><td>U</td><td>0.03</td><td>0.02</td><td>0.02</td><td>n.d.</td><td>0.02</td><td>0.05</td><td>0.02</td><td>0.09</td></tr><tr><td>Nb</td><td>0.80</td><td>0.80</td><td>1.14</td><td>n.d.</td><td>1.14</td><td>2.15</td><td>0.80</td><td>3.43</td></tr><tr><td>Ta</td><td>0.07</td><td>0.06</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>0.14</td><td>0.06</td><td>0.25</td></tr><tr><td>La</td><td>1.13</td><td>1.01</td><td>0.97</td><td>n.d.</td><td>1.01</td><td>1.86</td><td>0.93</td><td>3.23</td></tr><tr><td>Ce</td><td>3.42</td><td>3.10</td><td>2.95</td><td>n.d.</td><td>2.92</td><td>5.20</td><td>2.74</td><td>8.55</td></tr><tr><td>Pb</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>0.24</td><td>0.10</td><td>0.33</td></tr><tr><td>Pr</td><td>0.52</td><td>0.49</td><td>0.48</td><td>n.d.</td><td>0.48</td><td>0.81</td><td>0.46</td><td>1.30</td></tr><tr><td>Sr</td><td>32.79</td><td>27.05</td><td>27.72</td><td>n.d.</td><td>36.57</td><td>50.14</td><td>13.42</td><td>70.69</td></tr><tr><td>Nd</td><td>2.80</td><td>2.71</td><td>2.73</td><td>n.d.</td><td>2.74</td><td>4.08</td><td>2.48</td><td>6.46</td></tr><tr><td>Zr</td><td>22.21</td><td>21.40</td><td>22.06</td><td>n.d.</td><td>22.14</td><td>48.74</td><td>28.98</td><td>73.22</td></tr><tr><td>Hf</td><td>0.64</td><td>0.62</td><td>0.66</td><td>n.d.</td><td>0.67</td><td>1.09</td><td>0.70</td><td>1.65</td></tr><tr><td>Sm</td><td>0.99</td><td>0.96</td><td>0.95</td><td>n.d.</td><td>0.92</td><td>1.30</td><td>0.89</td><td>1.98</td></tr><tr><td>Eu</td><td>0.38</td><td>0.36</td><td>0.34</td><td>n.d.</td><td>0.35</td><td>0.50</td><td>0.33</td><td>0.70</td></tr><tr><td>Ti</td><td>3200</td><td>3055</td><td>2998</td><td>n.d.</td><td>3117</td><td>4028</td><td>2837</td><td>5575</td></tr><tr><td>Gd</td><td>1.22</td><td>1.17</td><td>1.23</td><td>n.d.</td><td>1.23</td><td>1.70</td><td>1.26</td><td>2.55</td></tr><tr><td>Tb</td><td>0.22</td><td>0.21</td><td>0.20</td><td>n.d.</td><td>0.20</td><td>0.27</td><td>0.21</td><td>0.39</td></tr><tr><td>Dy</td><td>1.41</td><td>1.37</td><td>1.30</td><td>n.d.</td><td>1.28</td><td>1.64</td><td>1.32</td><td>2.27</td></tr><tr><td>Y</td><td>7.26</td><td>7.08</td><td>7.26</td><td>n.d.</td><td>7.07</td><td>7.91</td><td>6.79</td><td>10.70</td></tr><tr><td>Ho</td><td>0.30</td><td>0.28</td><td>0.25</td><td>n.d.</td><td>0.25</td><td>0.31</td><td>0.27</td><td>0.43</td></tr><tr><td>Er</td><td>0.79</td><td>0.77</td><td>0.69</td><td>n.d.</td><td>0.73</td><td>0.84</td><td>0.73</td><td>1.18</td></tr><tr><td>Tm</td><td>0.12</td><td>0.11</td><td>0.10</td><td>n.d.</td><td>0.10</td><td>0.11</td><td>0.11</td><td>0.15</td></tr><tr><td>Yb</td><td>0.71</td><td>0.68</td><td>0.60</td><td>n.d.</td><td>0.61</td><td>0.69</td><td>0.68</td><td>0.94</td></tr><tr><td>Lu</td><td>0.11</td><td>0.11</td><td>0.09</td><td>n.d.</td><td>0.09</td><td>0.10</td><td>0.10</td><td>0.14</td></tr></tbody></table>

subduction zones across the region. The numerous occurrences of mafic and ultramafic rocks linked to mantle plumes—such as in the Emeishan in southwest China (Fang & Niu, 2003; Yigang et al., 2007), the Song Da suture zone in Vietnam (Hanski et al., 2004), the Chhongtash Formation in the Karakoram region of India (Rao & Rai, 2007), and the Alborz Mountains in northern Iran (Derakhshi et al., 2022)—underscore the significance of magmatic events in the geodynamic evolution of the region.

The Mashhad komatiites are intercalated with metasediments in the suture zone of the Paleo-Tethys Ocean. As discussed in the previous section, the high-MgO parental magma of

these komatiites formed by partial melting of the mantle at high pressures within the stability field of garnet. This requires a high-temperature source such as a mantle plume. We propose that this plume ascended into an upper Paleozoic subduction zone along the active margin of the Paleo-Tethys Ocean. It is likely that intense thermal disturbances at the core-mantle boundary during the Late Paleozoic led to the formation of multiple mantle plumes. These plumes interacted with the lithosphere of the Central Asian Orogenic Belt and southern Asia, resulting in the eruption of picritic and komatiitic ultramafic lavas, further shaping the region's geodynamic history.
<table><caption>**Table 5: Continued**</caption><thead><tr><th rowspan="3">Rock type:</th><th colspan="9">Komatiitic-basalt flows</th></tr><tr><th colspan="3">Fariman Complex</th><th colspan="3">Mashhad Complex</th><th colspan="4">Fariman Complex</th></tr><tr><th>olivine cumulate</th><th>randomly orient. px.</th><th>randomly orient. px.</th><th>olivine cumulate</th><th>olivine cumulate</th><th>olivine cumulate</th><th>olivine cumulate</th><th>gabbro</th><th></th></tr><tr><th>Sample</th><th>SFS40</th><th>NAM-28</th><th>NAM-208</th><th>FC20</th><th>SFS14</th><th>SFS21</th><th>FC16</th><th>SFS-13</th><th></th></tr></thead><tbody><tr><td>SiO<sub>2</sub></td><td>43.47</td><td>50.14</td><td>49.82</td><td>44.60</td><td>43.88</td><td>43.33</td><td>43.74</td><td>49.97</td><td></td></tr><tr><td>TiO<sub>2</sub></td><td>0.16</td><td>1.34</td><td>1.32</td><td>0.67</td><td>0.73</td><td>0.49</td><td>0.82</td><td>1.33</td><td></td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>5.98</td><td>14.23</td><td>14.53</td><td>5.90</td><td>5.11</td><td>5.11</td><td>5.38</td><td>13.90</td><td></td></tr><tr><td>FeO</td><td>10.52</td><td>11.38</td><td>11.44</td><td>11.97</td><td>10.75</td><td>10.99</td><td>13.20</td><td>12.83</td><td></td></tr><tr><td>CaO</td><td>4.86</td><td>10.71</td><td>10.59</td><td>5.81</td><td>4.89</td><td>5.54</td><td>5.26</td><td>9.42</td><td></td></tr><tr><td>MgO</td><td>33.76</td><td>8.14</td><td>8.23</td><td>30.06</td><td>33.48</td><td>33.38</td><td>30.40</td><td>8.36</td><td></td></tr><tr><td>MnO</td><td>0.18</td><td>0.18</td><td>0.18</td><td>0.19</td><td>0.17</td><td>0.18</td><td>0.19</td><td>0.19</td><td></td></tr><tr><td>Na<sub>2</sub>O</td><td>0.06</td><td>3.72</td><td>3.73</td><td>0.24</td><td>0.10</td><td>0.06</td><td>0.27</td><td>3.72</td><td></td></tr><tr><td>K<sub>2</sub>O</td><td>0.01</td><td>0.06</td><td>0.04</td><td>0.00</td><td>0.06</td><td>0.01</td><td>0.08</td><td>0.16</td><td></td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>0.02</td><td>0.09</td><td>0.09</td><td>0.00</td><td>0.06</td><td>0.04</td><td>0.00</td><td>0.10</td><td></td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.71</td><td>0.02</td><td>0.02</td><td>0.37</td><td>0.50</td><td>0.59</td><td>0.46</td><td>0.01</td><td></td></tr><tr><td>NiO</td><td>0.27</td><td>0.02</td><td>0.02</td><td>0.19</td><td>0.29</td><td>0.28</td><td>0.19</td><td>0.01</td><td></td></tr><tr><td>LOI</td><td>9.69</td><td>7.69</td><td>8.13</td><td>8.03</td><td>9.03</td><td>8.84</td><td>8.06</td><td>3.21</td><td></td></tr><tr><td>(Total)</td><td>98.97</td><td>98.63</td><td>99.17</td><td>98.68</td><td>99.04</td><td>99.00</td><td>99.61</td><td>99.06</td><td></td></tr><tr><td>Cs (ppm)</td><td>3.11</td><td>0.03</td><td>0.02</td><td>1.19</td><td>n.d.</td><td>0.57</td><td>1.91</td><td>0.36</td><td></td></tr><tr><td>Rb</td><td>1.65</td><td>0.30</td><td>0.28</td><td>4.51</td><td>n.d.</td><td>1.84</td><td>6.84</td><td>2.82</td><td></td></tr><tr><td>Ba</td><td>5.21</td><td>12.67</td><td>11.57</td><td>17.54</td><td>n.d.</td><td>2.34</td><td>26.04</td><td>30.36</td><td></td></tr><tr><td>Th</td><td>0.10</td><td>0.23</td><td>0.22</td><td>0.14</td><td>n.d.</td><td>0.09</td><td>0.26</td><td>0.90</td><td></td></tr><tr><td>U</td><td>0.01</td><td>0.07</td><td>0.07</td><td>0.04</td><td>n.d.</td><td>0.03</td><td>0.07</td><td>0.26</td><td></td></tr><tr><td>Nb</td><td>0.40</td><td>3.18</td><td>3.16</td><td>1.56</td><td>n.d.</td><td>0.93</td><td>2.46</td><td>12.50</td><td></td></tr><tr><td>Ta</td><td>0.03</td><td>n.d.</td><td>n.d.</td><td>0.12</td><td>n.d.</td><td>0.07</td><td>0.19</td><td>n.d.</td><td></td></tr><tr><td>La</td><td>0.40</td><td>2.64</td><td>2.64</td><td>1.68</td><td>n.d.</td><td>1.13</td><td>2.98</td><td>8.38</td><td></td></tr><tr><td>Ce</td><td>0.93</td><td>7.80</td><td>7.72</td><td>4.87</td><td>n.d.</td><td>3.13</td><td>7.89</td><td>21.79</td><td></td></tr><tr><td>Pb</td><td>1.40</td><td>1.94</td><td>1.89</td><td>n.d.</td><td>n.d.</td><td>0.34</td><td>0.86</td><td>0.15</td><td></td></tr><tr><td>Pr</td><td>0.12</td><td>1.33</td><td>1.34</td><td>0.74</td><td>n.d.</td><td>0.50</td><td>1.10</td><td>3.35</td><td></td></tr><tr><td>Sr</td><td>11.93</td><td>136</td><td>138</td><td>38.57</td><td>n.d.</td><td>9.49</td><td>22.52</td><td>162</td><td></td></tr><tr><td>Nd</td><td>0.55</td><td>7.41</td><td>7.12</td><td>3.82</td><td>n.d.</td><td>2.76</td><td>5.44</td><td>16.74</td><td></td></tr><tr><td>Zr</td><td>6.78</td><td>64.14</td><td>58.94</td><td>29.38</td><td>n.d.</td><td>29.54</td><td>39.17</td><td>143.0</td><td></td></tr><tr><td>Hf</td><td>0.17</td><td>1.76</td><td>1.64</td><td>0.83</td><td>n.d.</td><td>0.73</td><td>1.07</td><td>3.70</td><td></td></tr><tr><td>Sm</td><td>0.23</td><td>2.53</td><td>2.54</td><td>1.26</td><td>n.d.</td><td>0.91</td><td>1.60</td><td>4.77</td><td></td></tr><tr><td>Eu</td><td>0.10</td><td>1.02</td><td>1.02</td><td>0.47</td><td>n.d.</td><td>0.38</td><td>0.60</td><td>1.63</td><td></td></tr><tr><td>Ti</td><td>959</td><td>8033</td><td>7933</td><td>4038</td><td>n.d.</td><td>2938</td><td>4938</td><td>7992</td><td></td></tr><tr><td>Gd</td><td>0.42</td><td>3.44</td><td>3.45</td><td>1.44</td><td>n.d.</td><td>1.26</td><td>1.66</td><td>5.80</td><td></td></tr><tr><td>Tb</td><td>0.09</td><td>0.57</td><td>0.57</td><td>0.24</td><td>n.d.</td><td>0.21</td><td>0.27</td><td>0.88</td><td></td></tr><tr><td>Dy</td><td>0.69</td><td>3.65</td><td>3.67</td><td>1.55</td><td>n.d.</td><td>1.32</td><td>1.61</td><td>5.20</td><td></td></tr><tr><td>Y</td><td>4.13</td><td>19.27</td><td>19.11</td><td>7.36</td><td>n.d.</td><td>6.55</td><td>7.74</td><td>26.48</td><td></td></tr><tr><td>Ho</td><td>0.16</td><td>0.70</td><td>0.70</td><td>0.31</td><td>n.d.</td><td>0.26</td><td>0.31</td><td>0.92</td><td></td></tr><tr><td>Er</td><td>0.51</td><td>1.98</td><td>1.98</td><td>0.76</td><td>n.d.</td><td>0.76</td><td>0.77</td><td>2.52</td><td></td></tr><tr><td>Tm</td><td>0.07</td><td>0.27</td><td>0.27</td><td>0.11</td><td>n.d.</td><td>0.10</td><td>0.11</td><td>0.33</td><td></td></tr><tr><td>Yb</td><td>0.55</td><td>1.61</td><td>1.69</td><td>0.64</td><td>n.d.</td><td>0.65</td><td>0.63</td><td>2.06</td><td></td></tr><tr><td>Lu</td><td>0.09</td><td>0.25</td><td>0.25</td><td>0.10</td><td>n.d.</td><td>0.10</td><td>0.09</td><td>0.30</td><td></td></tr></tbody></table>

## CONCLUSIONS

* Ultramafic lavas with spinifex textures occur in the Paleotethys suture zone in NE Iran. Their age is estimated to be Permian and, together with Cretaceous lavas from Gorgona Island, they represent the sole examples of Phanerozoic komatiites.

* Most of the lavas were differentiated following their eruption into layered flows with spinifex-textured, olivine porphyritic or gabbroic upper layers, and olivine ± pyroxene cumulate lower layers.

* The lavas erupted into poorly consolidated clastic sediments, probably in an active margin setting.

* One suite of lavas has high MgO contents, low Al₂O₃/TiO₂ and relatively depleted heavy rare earth elements indicating that, unlike the ultramafic lavas on Gorgona Island, which are the only other well-documented example of Phanerozoic komatiite, they belong to the Al-depleted komatiite type. The more incompatible trace elements are relatively depleted in these samples. Other suites are relatively enriched in incompatible trace elements.

* The MgO of the parental magma is estimated to have been between 20 and 25 wt %. Samples with random olivine spinifex texture, which would normally be assumed to have crystallized directly from the komatiite melt, have far higher MgO contents, between 30 and 35 wt %. The difference in MgO
<table><caption>**Table 5:** Continued</caption><thead><tr><th rowspan="3">Rock type:</th><th colspan="6">Komatiitic-basalt flows</th><th colspan="3">Basalts</th></tr><tr><th colspan="6">Fariman Complex</th><th rowspan="2">basalt</th><th rowspan="2">basalt</th><th rowspan="2">basalt</th></tr><tr><th>gabbro</th><th>gabbro</th><th>gabbro</th><th>gabbro</th><th>gabbro</th><th>SFS18</th><th>SFS7</th><th>SFS17</th></tr></thead><tbody><tr><td>Sample</td><td>SFS-26</td><td>SFS-38</td><td>SFS-27</td><td>SFS-33</td><td>SFS-25</td><td>SFS18</td><td>SFS7</td><td>SFS17</td><td>SFS17</td></tr><tr><td>SiO<sub>2</sub></td><td>48.51</td><td>48.99</td><td>49.64</td><td>52.38</td><td>50.06</td><td>49.86</td><td>48.29</td><td>48.58</td><td>48.58</td></tr><tr><td>TiO<sub>2</sub></td><td>1.00</td><td>1.33</td><td>1.22</td><td>2.08</td><td>0.56</td><td>0.51</td><td>0.88</td><td>0.51</td><td>0.51</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>14.70</td><td>15.17</td><td>14.12</td><td>15.37</td><td>14.36</td><td>14.61</td><td>14.39</td><td>14.95</td><td>14.95</td></tr><tr><td>FeO</td><td>10.00</td><td>12.61</td><td>12.24</td><td>10.74</td><td>9.86</td><td>9.88</td><td>8.73</td><td>10.30</td><td>10.30</td></tr><tr><td>CaO</td><td>13.29</td><td>10.00</td><td>10.89</td><td>6.47</td><td>11.68</td><td>10.95</td><td>14.67</td><td>15.29</td><td>15.29</td></tr><tr><td>MgO</td><td>9.59</td><td>7.54</td><td>8.18</td><td>7.05</td><td>10.14</td><td>10.61</td><td>10.44</td><td>8.29</td><td>8.29</td></tr><tr><td>MnO</td><td>0.19</td><td>0.17</td><td>0.18</td><td>0.16</td><td>0.18</td><td>0.19</td><td>0.20</td><td>0.16</td><td>0.16</td></tr><tr><td>Na<sub>2</sub>O</td><td>2.59</td><td>4.04</td><td>3.28</td><td>5.37</td><td>2.92</td><td>2.86</td><td>2.22</td><td>1.73</td><td>1.73</td></tr><tr><td>K<sub>2</sub>O</td><td>0.01</td><td>0.03</td><td>0.14</td><td>0.18</td><td>0.01</td><td>0.32</td><td>0.01</td><td>0.01</td><td>0.01</td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>0.06</td><td>0.10</td><td>0.08</td><td>0.19</td><td>0.12</td><td>0.11</td><td>0.06</td><td>0.11</td><td>0.11</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.04</td><td>0.01</td><td>0.02</td><td>0.01</td><td>0.09</td><td>0.08</td><td>0.09</td><td>0.07</td><td>0.07</td></tr><tr><td>NiO</td><td>0.02</td><td>0.01</td><td>0.02</td><td>0.01</td><td>0.03</td><td>0.03</td><td>0.02</td><td>0.02</td><td>0.02</td></tr><tr><td>LOI</td><td>3.86</td><td>3.71</td><td>2.87</td><td>3.25</td><td>3.73</td><td>3.77</td><td>4.05</td><td>4.25</td><td>4.25</td></tr><tr><td>(Total)</td><td>99.20</td><td>99.26</td><td>99.51</td><td>98.85</td><td>99.17</td><td>99.37</td><td>99.02</td><td>99.50</td><td>99.50</td></tr><tr><td>Cs (ppm)</td><td>0.37</td><td>0.98</td><td>0.99</td><td>1.33</td><td>0.10</td><td>0.49</td><td>0.26</td><td>0.02</td><td>0.02</td></tr><tr><td>Rb</td><td>0.34</td><td>1.06</td><td>2.80</td><td>1.57</td><td>0.30</td><td>4.54</td><td>0.25</td><td>0.12</td><td>0.12</td></tr><tr><td>Ba</td><td>37.64</td><td>12.72</td><td>49.09</td><td>76.56</td><td>30.29</td><td>63.72</td><td>38.71</td><td>28.47</td><td>28.47</td></tr><tr><td>Th</td><td>0.15</td><td>0.20</td><td>0.19</td><td>0.21</td><td>1.47</td><td>1.37</td><td>0.13</td><td>1.42</td><td>1.42</td></tr><tr><td>U</td><td>0.04</td><td>0.07</td><td>0.06</td><td>0.06</td><td>0.27</td><td>0.26</td><td>0.04</td><td>0.27</td><td>0.27</td></tr><tr><td>Nb</td><td>2.16</td><td>3.49</td><td>3.20</td><td>3.44</td><td>14.60</td><td>12.84</td><td>1.83</td><td>13.24</td><td>13.24</td></tr><tr><td>Ta</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td></tr><tr><td>La</td><td>2.01</td><td>2.83</td><td>2.72</td><td>2.89</td><td>8.82</td><td>7.64</td><td>1.68</td><td>8.33</td><td>8.33</td></tr><tr><td>Ce</td><td>5.85</td><td>8.48</td><td>7.62</td><td>8.53</td><td>15.97</td><td>14.11</td><td>5.08</td><td>14.71</td><td>14.71</td></tr><tr><td>Pb</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>n.d.</td><td>1.03</td><td>0.71</td><td>n.d.</td><td>1.08</td><td>1.08</td></tr><tr><td>Pr</td><td>0.99</td><td>1.45</td><td>1.28</td><td>1.44</td><td>1.76</td><td>1.57</td><td>0.84</td><td>1.60</td><td>1.60</td></tr><tr><td>Sr</td><td>103</td><td>68.24</td><td>154</td><td>152</td><td>57.87</td><td>93.75</td><td>117</td><td>29.61</td><td>29.61</td></tr><tr><td>Nd</td><td>5.42</td><td>7.72</td><td>6.87</td><td>7.98</td><td>6.70</td><td>5.81</td><td>4.73</td><td>6.10</td><td>6.10</td></tr><tr><td>Zr</td><td>42.99</td><td>63.55</td><td>55.85</td><td>66.75</td><td>43.14</td><td>38.59</td><td>38.92</td><td>38.72</td><td>38.72</td></tr><tr><td>Hf</td><td>1.33</td><td>1.80</td><td>1.70</td><td>1.88</td><td>1.03</td><td>0.89</td><td>1.15</td><td>0.95</td><td>0.95</td></tr><tr><td>Sm</td><td>1.81</td><td>2.44</td><td>2.27</td><td>2.70</td><td>1.44</td><td>1.28</td><td>1.72</td><td>1.35</td><td>1.35</td></tr><tr><td>Eu</td><td>0.74</td><td>0.90</td><td>0.87</td><td>0.96</td><td>0.51</td><td>0.47</td><td>0.71</td><td>0.47</td><td>0.47</td></tr><tr><td>Ti</td><td>5995</td><td>7973</td><td>7314</td><td>12470</td><td>3357</td><td>3057</td><td>5276</td><td>3057</td><td>3057</td></tr><tr><td>Gd</td><td>2.62</td><td>3.11</td><td>3.10</td><td>3.49</td><td>1.91</td><td>1.76</td><td>2.34</td><td>1.85</td><td>1.85</td></tr><tr><td>Tb</td><td>0.44</td><td>0.53</td><td>0.52</td><td>0.58</td><td>0.33</td><td>0.31</td><td>0.39</td><td>0.32</td><td>0.32</td></tr><tr><td>Dy</td><td>2.85</td><td>3.34</td><td>3.32</td><td>3.61</td><td>2.32</td><td>2.20</td><td>2.52</td><td>2.26</td><td>2.26</td></tr><tr><td>Y</td><td>15.14</td><td>18.70</td><td>17.65</td><td>19.53</td><td>14.42</td><td>13.75</td><td>13.31</td><td>14.66</td><td>14.66</td></tr><tr><td>Ho</td><td>0.55</td><td>0.67</td><td>0.64</td><td>0.70</td><td>0.51</td><td>0.48</td><td>0.49</td><td>0.51</td><td>0.51</td></tr><tr><td>Er</td><td>1.61</td><td>1.86</td><td>1.86</td><td>2.03</td><td>1.63</td><td>1.57</td><td>1.40</td><td>1.67</td><td>1.67</td></tr><tr><td>Tm</td><td>0.21</td><td>0.27</td><td>0.25</td><td>0.27</td><td>0.25</td><td>0.23</td><td>0.19</td><td>0.25</td><td>0.25</td></tr><tr><td>Yb</td><td>1.31</td><td>1.63</td><td>1.59</td><td>1.66</td><td>1.70</td><td>1.60</td><td>1.19</td><td>1.69</td><td>1.69</td></tr><tr><td>Lu</td><td>0.19</td><td>0.24</td><td>0.24</td><td>0.26</td><td>0.29</td><td>0.25</td><td>0.18</td><td>0.27</td><td>0.27</td></tr></tbody></table>

content is attributed to the accumulation of entrained olivine phenocrysts which provided nuclei for the crystallization of spinifex olivine.

* The Al-depleted komatiites are estimated to have formed through about 20% partial melting of depleted slightly hydrous peridotite source at a depth between 120 and 150 km. The enriched samples formed by a lower degree of melting of a similar, or more enriched, source.

## SUPPLEMENTARY DATA

Supplementary data are available at *Journal of Petrology* online.

## ACKNOWLEDGEMENTS

This project received funding from the European Research Council under the European Union's Horizon 2020 program (grant agreement 856555). We thank Steve Barnes, Euan Nisbet, and Allan Wilson for helpful discussions and acknowledge constructive reviews from Mike Lesher and Pedro Waterton. This paper is respectfully dedicated by the first author to Dr. Mossaieb Sabzehei, a pioneering Iranian Geologist at the Geological Survey of Iran and one of the co-authors, who recently passed away (1942–2024). He graduated from the Université Grenoble Alpes and, along with B. Majidi, was one of the first to point out the possible komatiitic nature of these rocks in the 1970s.

<footnote>* Notes: major elements are normalized to 100% on an anhydrous basis; trace elements are not normalized; * total iron reported as Fe<sup>2+</sup>O; LOI - loss on ignition; Total - sum of major element oxides including LOI</footnote>
<figure><img src="image_20.png" /><figcaption>**Fig. 19.** Phase diagram, from Walter (1998), for mantle peridotite illustrating the conditions in which the Mashhad komatiites might have formed. The numbers in circles represent MgO contents of melts produced by about 15% partial melting. Melts with 20–22% MgO are produced at this degree of melting in the garnet stability field at pressures between 4 and 5 GPa.</figcaption></figure>

## DATA AVAILABILITY STATEMENT

The entire dataset utilized in this research can be accessed in two ways: as data tables or via the online Supplementary Appendix. Furthermore, Analytical data for this study is available in the EarthChem.org database at the following links: (https://doi.org/10.60520/IEDA/113454) and (https://doi.org/10.60520/IEDA/113455).

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