Petrogenesis of Mediterranean lamproites and associated rocks: The role of overprinted metasomatic events in the post-collisional lithospheric upper mantle

Abstract High-MgO lamproite and lamproite-like (i.e. lamprophyric) ultrapotassic rocks are recurrent in the Mediterranean and surrounding regions. They are associated in space and time with ultrapotassic shoshonites and high-K calc-alkaline rocks. This magmatism is linked with the geodynamic evolution of the westernmost sector of the Alpine–Himalayan collisional margin, which followed the closure of the Tethys Ocean. Subduction-related lamproites, lamprophyres, shoshonites and high-K calc-alkaline suites were emplaced in the Mediterranean region in the form of shallow level intrusions (e.g. plugs, dykes and laccoliths) and small volume lava flows, with very subordinate pyroclastic rocks, starting from the Oligocene, in the Western Alps (northern Italy), through the Late Miocene in Corsica (southern France) and in Murcia-Almeria (southeastern Spain), to the Plio-Pleistocene in Southern Tuscany and Northern Latium (central Italy), in the Balkan peninsula (Serbia and Macedonia) and in the Western Anatolia (Turkey). The ultrapotassic rocks are mostly lamprophyric, but olivine latitic lavas with a clear lamproitic affinity are also found, as well as dacitic to trachytic differentiated products. Lamproite-like rocks range from slightly silica under-saturated to silica over-saturated composition, have relatively low Al2O3, CaO and Na2O contents, resulting in plagioclase-free parageneses, and consist of abundant K-feldspar, phlogopite, diopsidic clinopyroxene and highly forsteritic olivine. Leucite is generally absent, and it is rarely found only in the groundmasses of Spanish lamproites. Mediterranean lamproites and associated rocks share an extreme enrichment in many incompatible trace elements and depletion in High Field Strength Elements and high, and positively correlated Th/La and Sm/La ratios. They have radiogenic Sr and unradiogenic Nd isotope compositions, high 207Pb over 206Pb and high time-integrated 232Th/238U. Their composition requires an originally depleted lithospheric mantle source metasomatized by at least two different agents: (1) a high Th/La and Sm/La (i.e. SALATHO) component deriving from lawsonite-bearing, ancient crustal domains likely hosted in mélanges formed during the diachronous collision of the northward drifting continental slivers from Gondwana; (2) a K-rich component derived from a recent subduction and recycling of siliciclastic sediments. These metasomatic melts produced a lithospheric mantle source characterized by network of felsic and phlogopite-rich veins, respectively. Geothermal readjustment during post-collisional events induced progressive melting of the different types of veins and the surrounding peridotite generating the entire compositional spectrum of the observed magmas. In this complex scenario, orogenic Mediterranean lamproites represent rocks that characterize areas that were affected by multiple Wilson cycles, as observed in the Alpine–Himalayan Realm.

The extreme enrichment in K 2 O and incompatible trace elements of lamproites was shown to be not dependent upon crustal contamination during magma ascent to surface, which was instead demonstrated to be negligible (Conticelli 1998;Murphy et al. 2002;Prelevićet al. 2004). Hence, it is thought that such an enrichment is a primary feature of their mantle source (Peccerillo et al. 1988;Conticelli and Peccerillo 1992;Conticelli et al. 2002Conticelli et al. , 2009Conticelli et al. , 2015Davies et al. 2006;Peccerillo and Martinotti 2006;Duggen et al. 2008;Prelevićet al. 2008;Avanzinelli et al. 2009;Krmícěk et al. 2016Krmícěk et al. , 2020. Occurrences of lamproites are described in both anorogenic (i.e. within-plate) and orogenic, postcollisional tectonic settings, rarely within ancient cratons, more often in areas of thickened crust at cratonal margins, which experienced one or several episodes of compression or post-collisional collapse (Mitchell and Bergman 1991;Mitchell 2020).
To our knowledge, recent (,30 Ma) orogenic lamproites are mainly concentrated in Europe and in the Tibet region, along the Alpine-Himalayan belt. Lamproitic magmatism is relatively common in the Mediterranean area ( Fig. 1) and it is considered to be the consequence of the post-collisional events, which took place in the orogenic belt originated from the Mesozoic and Paleogene convergence between Africa and Eurasia ). In such a post-collisional setting lamproites are frequently intimately associated with calc-alkaline lamprophyric, shoshonitic and high-K calc-alkaline rocks (Conticelli et al. , 2013(Conticelli et al. , 2015Prelevićet al. 2004Prelevićet al. , 2005Prelevićet al. , 2012Prelevićet al. , 2015Peccerillo and Martinotti 2006;Owen 2008;Avanzinelli et al. 2009).
In this paper we describe the geochemical and isotopic data available on the orogenic group of Mediterranean lamproites (Fig. 1), including the occurrences from Murcia (SW Spain), Western Alps (NW Italy), Corsica (France), Tuscany (central Italy), Balkan Peninsula (Serbia-Macedonia) and Western Anatolia (Turkey), and their associated shoshonitic and calc-alkaline rocks. The discussion will be framed on the origin of the subduction-related signature of their mantle source and on the nature of the metasomatic agents and recycled crustal materials. The geochemical and isotopic data are supplemented with chemical data on rock-forming minerals, as well as data on mantle xenoliths possibly representing proxies for the sources of such peculiar magmas. All together the genesis of lamproitic magmas is discussed in the frame of the geodynamic evolution of the region.
Lamproites are Mg-rich alkaline ultrapotassic volcanic to hypo-abyssal rocks (Foley and Venturelli 1989;Mitchell 2020). They are characterized by relatively low Al 2 O 3 , FeO Tot , CaO and Na 2 O counterbalanced by extremely high MgO, and extremely variable silica contents, the latter ranging from basic to intermediate compositions. Lamproites are generally silica-saturated, plagioclase-free rocks, consisting of highly forsteritic olivine, chromian spinel, Al-poor clinopyroxene, K-richterite, sanidine, picroilmenite and apatite. Leucite is rarely found in minor silica-undersaturated lamproites.
Lamprophyre is an important category of hypabyssal rocks (Rock 1987), whose name is based on mineralogical criteria, such as the type of occurring feldspar and possible amphibole; minette, spessartite and kersantite are the rock names according to the mineralogical classification. They are potassic to ultrapotassic with higher alumina and lime with respect to lamproites, but in some cases they are chemically very similar to lamproitic to ultrapotassic shoshonitic rocks (Foley et al. 1987).
Shoshonite is a group of igneous rocks ranging from mildly enriched in potassium to ultrapotassic, with variable silica saturation. The rock types range from potassic trachybasalt (shoshonitic basalt) to trachyte, passing through shoshonite sensu stricto and latite. These rocks have variable enrichment in K 2 O in the most primitive terms.
High-K calc-alkaline and calc-alkaline rocks are defined on the basis of K 2 O contents with respect to silica (Wheller et al. 1987). They match the chemical and mineralogical parameters provided by Arculus (2003). They are sub-alkaline with terms ranging from basalts to rhyolites, passing through basaltic andesite, andesite and dacite. The prefix high-K is added when needed.

Geodynamic framework of the Mediterranean region
The Circum-Mediterranean region experienced a long-term evolution including oceanic subduction and continental collision processes related to the convergence between Africa-Arabia and Eurasia plates (McKenzie 1970;Dewey et al. 1989;Faccenna et al. 2004). Multiple convergences and collisions among Africa-Arabia and Eurasia plates caused the diachronous closure of the Paleo-Tethys and Neo-Tethys oceans, and the progressive accretion of peri-Gondwana blocks to the southern margin of the Eurasian plate (Sengör 1979;Allen and Armstrong 2008;Zanchetta et al. 2013). Subduction and collisional processes caused the formation of different orogenic belts, including the Late Triassic-early Jurassic Cimmerian Orogeny in Turkey and Iran (Stocklin 1974;Zanchi et al. 2009), and the almost continuous Alpine orogenic belt that extends from the Gibraltar Arc, which is the westernmost segment of the Alpine-Mediterranean Belt, to western Anatolia in Turkey (Fig. 1). Interestingly, within the whole Alpine-Mediterranean Belt, vestiges of older (Paleozoic) orogenic cycles are well represented and testify the polycyclic geodynamic evolution of the area (Von Raumer et al. 2002).
During this long-lasting process, the tectonic evolution of the convergent margins was mainly controlled by the geometry and nature of the convergent plates, which were characterized by the presence of continental promontories, such as the Arabian plate and the Adriatic promontory of Africa which underwent an early collisional stage, interleaved with areas where subduction of the oceanic lithosphere is still going on (e.g. Calabrian, Aegean and Ciprus arcs). This heterogeneity in the subduction system was responsible for the complex evolution of the upper plate system, which was characterized by the presence of arcuate orogenic systems, back-arc basins (Alboran, Liguro-Provençal, Tyrrhenian, Aegean Sea basins) and kinematically independent crustal blocks (e.g. Corsica-Sardinia, Anatolia), which developed as a consequence of roll-back in the subducting slab and lateral extrusion of pieces of continental lithosphere (McKenzie 1970;Horvath and Berckheimer 1982;Dewey et al. 1989). This complexity is also responsible for the large variability in metasomatic processes and magmatism occurred in the Mediterranean region.

Western Mediterranean
The western Mediterranean area was exposed to multiple orogenic episodes that left inheritance in the subsequent, more recent geodynamic evolution (Ribeiro et al. 2007). A large number of palaeotectonic reconstructions proposed that during the Oligocene (about 30 Ma) the boundary between Africa and Eurasian plates in the western Mediterranean area was characterized by the presence of a convergent margin with almost continuous northward subduction of the African plate from Gibraltar to the Apennine chain (Faccenna et al. 2004) (Fig. 1). The subduction of the African plate evolved with a backward motion of the subduction trench, enhanced by the fragmentation of the subducting slab which brought about the progressive formation of the Calabrian Arc and Gibraltar. The former is associated with the opening of the Liguro-Provençal (30-16 Ma) and Tyrrhenian (12-1 Ma) back arc basins, the latter is associated to the opening of the Alboran back arc basin (Lower Miocene) ( Fig. 1) (Lonergan and White 1997;Faccenna et al. 2004Faccenna et al. , 2014Mattei et al. 2006;Cifelli et al. 2008). During the Late Miocene, the Gibraltar region experienced drastic modification of the tectonic regime, then the whole Betic-Rif and the Alboran Sea Basin underwent a complex pattern of compressional and strike-slip tectonics which, in some cases, inverted previous extensional structures (Watts et al. 1993;Comas et al. 1999). Volcanism accompanied and post-dated Neogene extension, with arc-tholeiitic, calc-alkaline, shoshonitic and ultrapotassic volcanism scattered across the eastern sector of Alboran Sea and Betic-Rif chain (Venturelli et al. 1984a;Duggen et al. 2005Duggen et al. , 2008Mattei et al. 2014).
The Miocene-to-Present formation of the Apennine chain was coeval with the fast opening of the Liguro-Provençal (first) and the Tyrrhenian back arc (later) basins following the southeastward retreat of a NW-west dipping Ionian/Adriatic slab (Malinverno and Ryan 1986;Royden et al. 1987;Faccenna et al. 2004;Cifelli et al. 2007). Linked to this geodynamic evolution are the lamproite and associated volcanic rocks of Corsica and the northern Tyrrhenian Sea, which migrated regularly with time, from Miocene to Pleistocene following the Adriatic slab roll back, to Tuscany, on the Italian Peninsula (Faccenna et al. 2014).

Western Alps
The western Alps are a continuation of the same convergent system but with an opposite polarity of the subducted plate, the direction of which reversed in the Ligurian area (Pfiffner 2021). They also originated from Africa and Eurasia convergence, from the late Cretaceous onward, causing the closure of the Ligurian-Piedmont and Valais oceans and the subsequent collision between the Adriatic promontory and the Eurasian plate (Dercourt et al. 1986;Stampfli et al. 2001). Collision was accommodated by crustal stacking and subduction of continental material as attested by the presence of ultra-high pressure rocks in the Dora Maira massif (Chopin 1984;Schreyer et al. 1987). Rare hypabyssal bodies and volcanic rocks were emplaced shortly after the climax of the Alpine orogenesis (Dal Piaz et al. 1979;Venturelli et al. 1984b;Callegari et al. 2004). It appears clear that this 'alpine' geodynamic phase was influenced by pre-alpine lineaments that left their inheritance on palaeogeographic domains (Festa et al. 2020).

Dinarides
The Dinarides orogenic system represents the northern part of a continuous belt extending from the eastern Alps to southern Greece, including the Albanides and Hellenides orogens (Fig. 1). The Dinaride geodynamic evolution records a long-lasting history of orogenic deformation at least from the Paleozoic (Ilic et al. 2005), which continued during the Early-Middle Jurassic and is still going on. The geodynamics of the internal Dinarides was controlled by the presence of oceanic basins (including the Alpine Tethys and Neo-Tethys) opened during the break-up of Pangea (Stampfli et al. 2001) with episodes of intra-oceanic subduction represented in local ophiolites (Bortolotti et al. 2013). The Neo-Tethys opened during Triassic and Early to Mid-Jurassic times, whilst the Alpine Tethys started to open during the Mid-Jurassic and was contemporaneous with partial closure of the western Neo-Tethys and the obduction of the Eastern and Western Vardar Ophiolitic Units on top of the Adriatic passive margin (Schmid et al. 2004). The external part of the Dinarides is formed by shallow marine and basinal sedimentary units deriving from the deformation of the Adriatic passive margin, which was progressively involved in the Dinaride orogenic system as a consequence of the eastward subduction of the Adriatic margin. This orogenic deformation is still active along the coastal sector of the Dinaride and Albanide orogenic systems, as testified by the strong seismicity of the area.

Western Anatolia
Western Anatolia consists of different continental units, derived from Laurentia and Gondwana margins, originally separated by the Paleo-Tethys and Neo-Tethys oceans and eventually amalgamated during the Alpine Orogeny (Robertson et al. 2012). The Pontide units, which outcrop in the northern sector of the Anatolia region, show a Laurasian affinity and were deformed by the Variscan and Cimmerian orogenies, showing analogies with the pre-Alpine geological history of many European zones (Okay et al. 2006). The Paleo-Tethys and Neo-Tethys sutures separate the Pontides units from the the Anatolide-Tauride realms, showing Gondwana affinities and lacking evidence of Variscan and Cimmerian orogenesis (Okay 2008). The closure of these Mesozoic oceans was followed by the progressive subduction, along the southern margin of Anatolia, of the Ionian lithosphere. As a consequence, the entire Western Anatolia region today is located in the upper plate of the Aegean subduction system, where the Ionian oceanic lithosphere is subducting northeastward underneath the southern margin of the Eurasian plate. This active subducting slab is limited to the NE by the Kefalonia fault, which separates the Adriatic continental lithosphere, to the north, from the oceanic Ionian lithosphere to the south. Slab roll-back during the last 30-35 Ma has been responsible for extensional back-arc opening in the Aegean Sea and of the progressive curvature of the Aegean Arc (Kissel and Laj 1988), which caused the exhumation of high pressure/low temperature metamorphic cores (Jolivet and Brun 2010).

Occurrence and petrologic, geochemical and isotopic characteristics of Mediterranean lamproites
Mediterranean lamproites occur in a narrow belt ( Fig. 1) composed of small-volume hypo-abyssal (e.g. plugs, laccoliths, lopoliths and dykes) and lava flows from the Murcia-Almeria region (southeastern Spain), through the Italian and French Alpine chain (Western Alps and Corsica, respectively), and the northern edge of the Apennine chain (Tuscany), to the Dinarides (Serbia-Macedonia) and Taurides (Western Anatolia). The Mediterranean region represents the westernmost segment of the major collisional system that led to the formation of the Alpine-Himalayan Orogeny. Overall, the entire set of Alpine-Himalayan lamproites were referred to as Tethyan Realm Lamproites (i.e. Tommasini et al. 2011).
Murcia-Almeria is the westernmost and largest magmatic province among those including Tethyan Realm Lamproites (Fig. 1). Lamproite-like ultrapotassic rocks (Murcia) are associated to shoshonitic to high-K calc-alkaline magmatism (Cabo de Gata, Mazàron). Two-pyroxene calc-alkaline rocks, found exclusively at Capo de Gata (Almeria), high-K calc-alkaline and shoshonites, found along the Murcia-Almeria coast (Mazàron) are among the oldest volcanic products of the region (13.4-6.8 Ma), whilst Murcia lamproites were emplaced during the last phases of the volcanic activity (8.1-6.4 Ma) (Turner et al. 1999;Duggen et al. 2005;Kuiper et al. 2006;Pérez-Valera et al. 2013;Mattei et al. 2014). Murcia lamproites show the largest compositional variability of any region of lamproites in the whole Mediterranean (Fig. 2). Among the associated volcanic rocks shoshonites are rare, most of them straddling the boundary between shoshonitic and high-K calc-alkaline fields in the K 2 O v. SiO 2 diagram (Fig. 2). However, some shoshonites plot along a trend at very high K 2 O contents, connecting with lamproites. Intermediate to strongly differentiated calc-alkaline rocks are abundantly found in Cabo de Gata volcanic field (Mattei et al. 2014).
The Western Alps post-collisional lamproite and related shoshonitic to high-K calc-alkaline igneous rocks are found within a restricted area in the internal zone of the northwestern Alps (Venturelli et al. 1984b;Peccerillo and Martinotti 2006;Owen 2008;Conticelli et al. 2009;Casalini 2018). The age of this magmatism was found to be within the range 34-30 Ma (Krummenacher and Evernden 1960;Carraro and Ferrara 1978;Hunziker 1974), which is coeval with the peak of post-collisional magmatism of the entire Alps (Von Blanckenburg et al. 1998). Lamproitic-like plagioclase-free rocks were classified by Owen (2008) as minette due to their micaceous appearance; groundmasses have intersertal textures with phlogopite, clinopyroxene and K-feldspar, accompanied by minor altered olivine and riebeckite-arfvedsonite amphibole. Shoshonitic to high-K calc-alkaline plagioclase-bearing rocks (kersantite to spessartite) are found associated in space and time with ultrapotassic rocks. Strictly speaking, these rocks should be classified as lamprophyres on a mineralogical basis (Owen 2008), but we prefer to use the term lamproite on the basis of the chemical classification suggested by Foley et al. (1987). In the SiO 2 -K 2 O diagram, Western Alp lamproites plot close to the lamproitic samples from Corsica and Murcia-Almeria ( Fig. 2) overlapping at the low-silica end those from Corsica (Fig. 2).
Miocene lamproitic, shoshonitic and high-K calc-alkaline igneous rocks association is found along the eastern margin of the Sardinia-Corsica micro-plate (Fig. 1). Lamproites are restricted to the northeastern portion of the Corsica Island, in the form of a sill intruded into the Alpine terranes belonging to the 'Schistes Lustrés' (Wagner and Velde 1986;Peccerillo et al. 1988;Conticelli et al. 2009); shoshonitic to high-K calc-alkaline subvolcanic to volcanic rocks are found a few kilometres offshore from Sardinia and Corsica in the locality of Sisco, at Sarcya seamount (Cornacya) and Capraia Island, respectively (Mascle et al. 2001;Chelazzi et al. 2006;Conticelli et al. 2007;Gasparon et al. 2009;Avanzinelli et al. 2009). The Sisco lamproites have an age of 14.6 Ma (Civetta et al. 1978), whilst the shoshonitic samples from Cornacya were erupted at 12.6 Ma (Mascle et al. 2001). The Capraia high-K calc-alkaline rocks were erupted between 7.8 and 7.2 Ma, with a small cinder cone at Punta dello Zenobito erupted at 4.8 Ma (Gasparon et al. 2009). The Sisco lamproite is a leucite-and plagioclase-free ultrapotassic rock with intersertal texture and a parageneses made of phlogopite, clinopyroxene, olivine, sanidine and K-richterite associated to subordinate abundance of chromian spinel, ilmenite, pseudobrookite and priderite (Wagner and Velde 1986). Shoshonitic (Cornacya) and high-K calc-alkaline rocks (Capraia) range from shoshonites, to olivine latites, trachytes, high-K andesites, trachy-dacites and rhyolites and they are characterized by the occurrence of modal plagioclase, with sanidine and hornblende restricted to the most differentiated rocks (Mascle et al. 2001;Gagnevin et al. 2007;Conticelli et al. 2015). The Sisco lamproites show a peralkaline index .1, and the highest K 2 O and the lowest Al 2 O 3 , respectively, among the whole Central Mediterranean lamproites (Prelevićet al. 2008;Conticelli et al. 2009).
In western Anatolia Tertiary lamproitic rocks were produced along the Hellenic and Cyprus arc (Fig. 1), at the eastern end of the Aegean volcanic arc, resulting from the northward subduction of the African Plate beneath the Aegean (Doglioni et al. 2002;Innocenti et al. 2005). Here, volcanism started with calc-alkaline products in the Eocene, partially coeval with Aegean volcanism, and continued during the Miocene with shoshonitic to lamproitic products (e.g. Prelevićet al. , 2012. Another occurrence of ultrapotassic volcanics is located slightly to the south in the north-south trending Kýrka-Afyon-Isparta volcanic province (Francalanci et al. 2000;Akal 2008). This province was emplaced in three steps that exhibit southward younging from Kýrka (21-17 Ma) to Afyon (14-8 Ma) and Isparta (4.7-4.0 Ma). These rocks have ultrapotassic to potassic character (i.e. shoshonitic; Fig. 2). Among lamproites, the ultrapotassic terms, Kýrka and Afyon show a clear orogenic signature whilst Isparta displays a withinplate signature (Francalanci et al. 2000;Akal 2008).

Trace element distribution
Mediterranean lamproites usually have high contents of compatible trace elements (e.g. Ni . 200 ppm and Cr . 500 ppm) coupled with significant enrichments in incompatible elements and rare earth elements (REEs), with some large ion lithophile element (LILE, e.g. Rb, Cs) concentrations up to four orders of magnitude higher than those of the Primitive Mantle (Fig. 3). In addition, they display a notable depletion in high field strength elements (HFSEs, e.g. Nb, Ta), resulting in high LILE/HFSE ratios, which, along with Pb peaks, are clearly indicative of a subduction-related signature.
Despite their general crustal-like patterns, K and highly incompatible elements (e.g. Rb, Ba, Th and U) in orogenic lamproites have on average different distributions with respect to the present-day upper crust (Rudnick and Gao 2003) and Global Subducting Sediment (GLOSS, Plank and Langmuir 1998). Indeed, a distinctive signature of Mediterranean and, more in general, of Tethyan Realm Lamproites is their relative depletion in Ba and Sr with respect to Rb and Th . Ratios between the aforementioned elements ( Fig. 4) also help in distinguishing orogenic from anorogenic lamproites. Indeed, orogenic lamproites show higher Rb/Sr coupled with lower Ba/Rb than anorogenic ones (Fig. 4a), suggesting an important role for bulk melting of phlogopite and amphibole, respectively, in their mantle sources.
The extreme enrichment of Th (up to .200 ppm) in all the orogenic, Tethyian Realm Lamproites results in high Th/U, well beyond the Th/U ratio of c. 4 of the crust and most mantle-derived igneous rocks (Fig. 4b) (Plank and Langmuir 1998;Rudnick and Gao 2003). The high Th content entails one of the most striking features of these rocks, that is the positive correlation between Th/La and Sm/La (Fig. 4d). These key ratios are instead not correlated with K 2 O (e.g. Fig. 4c).
This characteristic is due, beside the extreme Th content, also to the slightly downward convex light (L) REE patterns (Conticelli et al. , 2015. The positive correlation between Th/ La and Sm/La observed by Tommasini et al. (2011), actually represents a sort of paradox when compared to subduction-related magmas worldwide. Indeed, Plank (2005) showed that typical volcanic arc magmas exhibit a negative correlation on Th/ La v. Sm/La, arguing for mixing between depleted mantle (at low Th/La and high Sm/La) and subduction-related components (i.e. end-members), the latter derived from melts of recycled sediments characterized by relatively high Th/La (c. 0.5-0.7) and low Sm/La (c. 0.1). The composition of Tethyan Realm Lamproites fall along the trend between the recycled sediment end-member (Plank 2005) and another one at high Th/La and Sm/La (up to 2.2 and 0.4, respectively, see also Fig. 4d), termed SAL-ATHO (high Sm, La and Th; Tommasini et al. 2011), which is difficult to explain in terms of notional mantle and crustal reservoirs.
Pb isotopes composition of the Mediterranean lamproites (Fig. 5b, c) show high 207 Pb/ 204 Pb over 206 Pb/ 204 Pb with respect to the Northern Hemisphere Reference Line (NHRL, Hart 1984), confirming the ubiquitous, although variable, contribution of crustal components recycled in their mantle source.
The data broadly align along a trend starting from the composition of the GLOSS (Plank and Langmuir 1998) towards higher 207 Pb/ 204 Pb values. The same general array is observed in Figure 5c ( 208 Pb/ 206 Pb  (Sun and McDonough 1989) incompatible trace element patterns of orogenic lamproites and associated shoshonitic and high-K calc-alkaline rocks (a-f ). Data source as in Figure 2 (Table S1).
v. 206 Pb/ 204 Pb) where the investigated rocks display again a general array that departs from the GLOSS and deviates from the NHRL towards higher 208 Pb/ 206 Pb at low 206 Pb/ 204 Pb (Fig. 5c). Overall, the Pb isotope composition of Mediterranean lamproites is well distinct from that of anorogenic ones, which plot at significantly less radiogenic values of 206 Pb/ 204 Pb (Murphy et al. 2002;Mirnejad and Bell 2006;Jaques and Foley 2018).
High 87 Sr/ 86 Sr and low 143 Nd/ 144 Nd isotopic values of mantle-derived basaltic rocks are classically interpreted as due to shallow level crustal contamination. In the case of orogenic lamproites, however, a major role for crustal contamination is excluded by several evidences (Conticelli 1998;Murphy et al. 2002;Prelevićet al. 2004Prelevićet al. , 2005Conticelli et al. 2007Conticelli et al. , 2015, such as: (1) high MgO and compatible elements contents, such as Co, Ni and Cr, which are not derived from olivine cumulation; (2)  (Miller et al. 1999;Gao et al. 2007). Anorogenic lamproites are shown with a unique symbol and include ultrapotassic rocks from Australia (McCulloch et al. 1983;Jaques et al. 1986;Nelson et al. 1986;Fraser et al. 1985;Jaques and Foley 2018), Antarctica (Murphy et al. 2002), USA (Vollmer et al. 1984;Fraser et al. 1985;Lambert et al. 1995;Mirnejad and Bell 2006;Badal et al. 2014) and Russia (Davies et al. 2006). the presence of mafic mineral phases (e.g. high Fo-olivine and clinopyroxene) in equilibrium with their bulk compositions (Conticelli et al. , 2015Ammannati et al. 2016), excluding both cumulus and crustal contamination processes; (3) incompatible trace element contents significantly higher than continental crust composition (e.g. Rudnick and Gao 2003 and references therein). Therefore, the exotic isotopic and geochemical characteristics of Mediterranean lamproites must be related to processes directly affecting their mantle sources.
Combining mineral chemistry data with bulk rock major and trace elements and Sr-Nd-Pb isotopes previous studies have identified at least three different mantle components (Prelevićet al. 2005;Conticelli et al. 2009;Tommasini et al. 2011).
An original ultra-depleted mantle source, with unradiogenic Pb and Sr isotopes and high 143 Nd/ 144 Nd, is indicated by the low CaO and Al 2 O 3 contents of all Mediterranean Lamproites and by the presence of high Fo-olivine with Cr-rich spinel inclusions (e.g. Arai 1994;Conticelli et al. 2015 and references therein).
A K-rich component re-fertilizing the depleted mantle source is required to impart the extreme incompatible trace element enrichment along with the crust-like Sr and Nd isotope signature. This metasomatic component is believed to derive from subduction-related sediment melts that permeated and reacted with the depleted peridotitic mantle, producing a orthopyroxene/phlogopite-rich (Fig. 4a) vein network (Foley 1992;Conticelli et al. 2015;Ammannati et al. 2016).
The high Th/La and Sm/La values of many Mediterranean lamproites require the further involvement of the above-mentioned SALATHO component   (Fig. 4d). This particular characteristic is not correlated with the Kenrichment (Fig. 4c) and thus not reconcilable with typical subduction-related processes such as the sediment recycling described above.
The evidence for the SALATHO component is not unique to Mediterranean lamproites but represents a specific characteristic of all the orogenic Tethyan Realm Lamproites, recurring also more than 10 000 km to the East in Tibet ). Among Mediterranean lamproites, those from Spain and Italy display a more marked SALATHO signature, whilst those from other localities such as Corsica, Serbia and Western Anatolia show lower evidence of this component (Fig. 4d), which is likely overprinted by a larger contribution from the more 'typical' sediment melt (Prelevicé

Possible origins for the SALATHO component
As seen above, the SALATHO component represents a specific characteristic of all Tethyan Realm Lamproites which is difficult to explain with the processes typically characterizing subduction-related magmatism . The budget of incompatible trace elements in subduction zones and in the related magmatism is largely controlled by the solubility of accessory phases during sediment melting, which also depends on the subducted lithology, that are able to concentrate and selectively release specific elements (Klimm et al. 2008;Hermann and Rubatto 2009;Skora and Blundy 2010;Martindale et al. 2013;Skora et al. 2015;Avanzinelli et al. 2009Avanzinelli et al. , 2012Avanzinelli et al. , 2018Casalini et al. 2019).
In particular, Th and REEs are likely controlled by the possible presence of residual apatite, allanite or monazite (Klimm et al. 2008;Avanzinelli et al. 2009Avanzinelli et al. , 2012Hermann and Rubatto 2009;Skora and Blundy 2010;Martindale et al. 2013) during partial melting of subducted sediments, whilst Nb and other HFSEs seems to be controlled by the solubility of rutile (e.g. Klimm et al. 2008 The presence/absence of such accessory phases during sediment melting exerts a strong control on the composition of sediment-dominated, subductionrelated magmas, in particular dictating their variable Th/U (Avanzinelli et al. 2009(Avanzinelli et al. , 2012 and determining their ubiquitous depletion in Nb and Ta (Klimm et al. 2008;Avanzinelli et al. 2009Avanzinelli et al. , 2012. In this context, the role of possible accessory phases can be considered also to explain the exotic SALATHO component. Recently, Soder and Romer (2018) working on Variscan lamprophyres from southwestern Germany and eastern France, which share similar Th/La and Sm/La to Mediterranean lamproites, attributed the  (Table S1). The boxes include the median value and are delimited by the 25th and the 75th percentiles of each population; the whiskers show the tenth and the 90th percentiles, whilst the dots represent the outliers at the fifth and 95th percentiles. genesis of the SALATHO component to residual allanite during partial melting of subducted sediments metasomatizing the sub-continental lithospheric mantle, and subsequent melting of the metasomatized mantle domains during post-collisional lithospheric extension. We have tried to model this hypothesis using the partition coefficients of allanite (Klimm et al. 2008), the composition of GLOSS (Plank and Langmuir 1998) and assuming different percentages of residual allanite (1, 0.1 and 0.01%) along with different degrees of partial melting (F = 1-30%) (Fig. 7). The results clearly show that residual allanite, owing to its D La . D Th ≥ D Sm , is liable to create a metasomatizing melt with roughly twice Th/La and Sm/La of the starting GLOSS source, but the values remain well below those observed in lamproites (Fig. 7). Also, in our model we have assumed that the budget of Th, La and Sm is controlled only by allanite, and this cannot be the case given that melts from subducted sediments show a general slight increase in Th/La and decrease in Sm/La with respect to their sources (Johnson and Plank 1999;Hermann and Rubatto 2009;Skora and Blundy 2010;Wang et al. 2017). In any case, allanitesaturated sediment melts are expected to have low Th/U, which is the opposite of what is observed in orogenic lamproites that are always characterized by extremely high Th/U (Fig. 4b).
The alternative model, originally postulated by Tommasini et al. (2011) and successively confirmed by other studies (Lustrino et al. 2016;Wang et al. 2017Wang et al. , 2019Wang and Foley 2020), involves the participation of lawsonite-bearing low-grade metamorphic rocks in controlling this peculiar feature of orogenic lamproites. Indeed, lawsonite is a major repository for Sr, Pb, U, Th and LREEs (Spandler et al. 2003;Usui et al. 2006;Martin et al. 2014), and a number of Th, La, Sm compositions of lawsonite Vitale Brovarone et al. 2014;Wang et al. 2017) are reported in Figure 7. These lawsonites clearly have high Th/La and Sm/La, the latter even higher than that recorded in Mediterranean lamproites, and upon melting  or dehydration (Lustrino et al. 2016) are capable of imparting to lamproite magmas their unique trace element signature (see below). In the case of melting, in order to produce the high Th/ La and Sm/La, lawsonite must have been totally consumed. The recent experimental work of Wang and Foley (2020), specifically designed to investigate the role of blue schists stored in the shallow lithosphere (2GPa), showed that upon melting lawsonite is completely removed from the residue at 800°C, producing melts enriched in Th/La with respect to their lawsonite-rich crustal protoliths. Tommasini et al. (2011) suggested that the SAL-ATHO signature can be ascribed to the stabilization and long-term (c. 300-500 Myr, see fig. 8   crust (basalt and sediments) at relatively low grade of metamorphism. This is indicated by the high 208 Pb/ 206 Pb values over 206 Pb/ 204 Pb (Fig. 5b) of orogenic lamproites, requiring high time-integrated ( 232 Th/ 238 U) and relatively low time-integrated ( 238 U/ 204 Pb). These mélange domains experienced different storage times in each sector of the Tethyan Realm orogenic belts, in agreement with the diachronous collision of the northward drifting continental slivers from Gondwana (e.g. Hun Terrane, Variscan and Cimmerian terranes ;Stampfli 2000;Stampfli and Borel 2002;Gaetani et al. 2003;Scotese 2004). Incidentally, the occurrence of the SALATHO component has been observed in the so-called lampyrites outcropping in the Variscan Bohemian Massif (Krmícěk et al. 2020), and provides further support for a long storage time of these mélange domains within the subcontinental lithospheric mantle.

The lithospheric mantle source of Mediterranean Lamproites
It is widely accepted that a normal four-phase peridotitic mantle cannot represent the source of lamproitic magmas, which requires the presence of an additional K-rich hydrous mineral, generally identified as phlogopite (Mitchell and Bergman 1991;Foley 1992Foley , 1993. Accordingly, previous studies interpreted lamproitic magmas as the products of partial melting of metasomatized sub-continental refractory lithospheric mantle (e.g. Foley et al. 1987;Foley and Venturelli 1989;Conticelli 1998;. Since the pioneering work of Foley (1992), it was suggested that large volumes of metasomatic components, required to generate the peculiar geochemical and isotopic characteristics of the mantle source of lamproite magmas, are accommodated within a vein network in the sub-continental lithospheric mantle (Foley 1992;Conticelli et al. 2002Conticelli et al. , 2007Conticelli et al. , 2009Prelevicé t al. 2008;Avanzinelli et al. 2009Avanzinelli et al. , 2020Ammannati et al. 2016;Dallai et al. 2019). It was experimentally demonstrated that K-rich metasomatizing agents may react with the depleted peridotitic mantle producing phlogopite-rich veins (Sekine and Wyllie 1982;Foley 1990Foley , 1992Conceição and Green 2004). Other studies, mainly based on the high Ni content of high-Fo olivine crystals, have indicated that subduction-derived silica-rich melts would react with the peridotitic mantle producing orthopyroxene at the expense of olivine (Straub et al. 2008;Foley et al. 2013). Within a pyroxenitic assemblage without olivine (high D Ni ), Ni will be mostly hosted in pyroxene (lower D Ni ), resulting, after partial melting, in magmas with higher Ni contents, hence later crystallizing high-Ni olivine phenocrysts (Straub et al. 2008;Foley et al. 2013). The recent study of Ammannati et al. (2016) showed extremely high Ni in high-Fo olivine in Italian orogenic lamproites, confirming the key role of orthopyroxene-rich domains (i.e. veins) in the mantle source of these magmas. Therefore, the presence of phlogopiteorthopyroxene domains in the lithospheric mantle seems to be required to generate lamproite-like magmas. Natural evidence of subduction-related, orthopyroxene-generating metasomatic agents, sometimes associated with the presence of phlogopite, have been observed in ultramafic xenoliths from several localities affected by orogenic metasomatism (Brandon et al. 1999;Grégoire et al. 2001;Franz et al. 2002), also in the Mediterranean area and surroundings (Cvetkovićet al. 2004b;Kovács et al. 2007), as well as in the Finero peridotite massif (Zanetti et al. 1999).
Among this large xenolith variability, the Tallante magmas also exhumed rare composite xenoliths where peridotite is locally crosscut by felsic veins containing plagioclase and orthopyroxene + quartz + phlogopite + amphibole (Arai et al. 2003;Beccaluva et al. 2004;Shimizu et al. 2005;Bianchini et al. 2011;Dallai et al. 2019;Avanzinelli et al. 2020). These mineralogical associations are again consistent with the postulated lithospheric mantle source of lamproitic magmas, characterized by the reaction of the depleted mantle with crustalderived, hydrous, silica-oversaturated melts rich in alkalis. Within the composite xenoliths of Tallante, Avanzinelli et al. (2020) also documented the presence of a millimetric veinlet hosting accessory minerals such as apatite, thorite/huttonite, rutile and graphite, hence producing isolated domains particularly enriched in incompatible trace elements. Overall, the compositional variability of mantle xenoliths erupted at Tallante testifies the presence, in a region where lamproites were produced, of an extremely heterogeneous mantle, characterized by a number of metasomatic events producing different domains, which upon melting may be capable of generating lamproites, hence providing an extraordinary window on the possible mantle sources of these extremely peculiar magmas.
The detailed study by Avanzinelli et al. (2020) on veined mantle xenoliths from Tallante, reported some key features that may confirm the link between these xenoliths and lamproites, especially regarding the occurrence of the SALATHO component within the metasomatized lithospheric mantle. Their data showed that the effect of metasomatism is not confined to the mineral phases of the felsic vein and the orthopyroxene-rich reaction zone (i.e. in plagioclase and orthopyroxene), but it permeated also the surrounding peridotitic mantle, as also observed in peridotite Massifs (Woodland et al. 1996). Indeed, the clinopyroxene (and orthopyroxene) of the peridotitic portion of the Tallante veined xenolith, which had not experienced any mineralogical modification, preserve geochemical and isotopic evidence of the metasomatic enrichment. They show anomalous incompatible trace element and 'm-shaped' REE pattern (Avanzinelli et al. 2020), being extremely enriched in middle (M)REE and Th, but depleted in LREE. The origin of such a peculiar composition has to be related to the geochemical characteristic of the metasomatic melts (see previous section) and/or in the competing role of the other phases equilibrating in the same portion of the mantle (Avanzinelli et al. 2020). In any case, upon partial melting such anomalous pyroxene would produce melts enriched with Th and Sm over La, hence imparting the characteristic SALATHO flavour common to all Tethyan Realm Lamproites.
In order to better define the origin of SALATHO, we calculated the hypothetic incompatible trace element composition (Fig. 8) of partial melts in equilibrium with clinopyroxene, orthopyroxene and plagioclase hosted in the various portions of the veined xenoliths (i.e. surrounding mantle, vein envelope, vein) reported in Avanzinelli et al. (2020) using a selected set of partition coefficients (Green et al. 2000;Foley and Jenner 2004;Aigner-Torres et al. 2007;Fig. 8). It is worth emphasizing that using different sets of partition coefficients the results shown in Figure 8 do not change significantly. Figure 8 shows that melts in equilibrium with clino-and orthopyroxenes have invariably high Th/La and Sm/La reaching values (up to 10.4 and 3.6, respectively, in clinopyroxene Fig. 8a), as well as extreme enrichment in Th (up to almost 300 ppm, Fig. 8b). Melts in equilibrium with plagioclase show lower Th content and Th/La ratios, and variable but still relatively high Sm/La (up to 0.87). A bulk composition of the partial melts deriving from such a veined mantle is extremely difficult to model. This would require assumptions on the exact knowledge of the relative proportions between the vein, the reaction zone and the surrounding peridotite involved in the melting process. In addition, lamproitic magmas are likely made up by the sum of several different melts deriving various portions of the metasomatized mantle (see previous section). For example, a significant contribution to the composition of Mediterranean lamproites must derive from melting of phlogopite-rich mantle domains (see previous discussion; Conticelli et al. 2015;Ammannati et al. 2016). The modelled melts in equilibrium with each single mineral (clinopyroxene, orthopyroxene and plagioclase; Fig. 8), however, clearly show that even a small amount of such melts may impart the characteristic high Th/La and Sm/La to the erupted lamproites. In such, the described mantle xenoliths likely represent the portion of the lithospheric mantle hosting the SALATHO component required by orogenic lamproites.
Further considerations can be done on the basis of isotopic composition. The Pb isotope composition of the aforementioned xenoliths is similar to that of Spanish lamproites, with high 208 Pb/ 206 Pb over 206 Pb/ 204 Pb (see Fig. 5b). The comparison for Sr and Nd isotope ratios is not as good, although they could be dominated by melts deriving from phlogopite-rich domains with higher 87 Sr/ 86 Sr and lower 143 Nd/ 144 Nd. The high 208 Pb/ 206 Pb is also consistent with a high time integrated (c. 300-500 Myr) Th/U of the metasomatic melts . This long-term storage, however, seems to be related to the crustal component from which the melts were generated rather than to the age of the metasomatic processes, which instead appears to be rather recent. Dallai et al. (2019) measured oxygen isotopes in the same veined samples described above, reporting continuously decreasing δ 18 O values, from the vein, which had typically crustal values (up to 10.5), to typical mantle values in the surrounding peridotite. The authors calculated that, in order to preserve such a difference from diffusion-assisted re-equilibration, the metasomatic process (i.e. the vein formation) must have occurred ,5 Myr before their entrapment in the Tallante magmas. The same is supported by the large variability in Sr isotope in the same sample, from the vein (0.7124) to the peridotite (0.7060) (Avanzinelli et al. 2020).

Petrogenesis of Mediterranean lamproites and geodynamic relationships
Based on the available evidence described above we suggest that Mediterranean lamproites were generated during the late stage of plate convergence characterized by continental collision and interlayering of mantle and continental slivers including low solidus crustal lithologies of different origins (Fig. 9). Similar crust-mantle mélanges are observed in massifs such as Ronda and Beni Bousera, where the exhumed fossil crust mantle boundary is characterized by mylonites and mélanges (Tubía et al. 2004;Platt et al. 2003Platt et al. , 2013Bartoli et al. 2015). Similar cases of interlayered crust-mantle associations are common throughout and nearby the Mediterranean region, such as in the fossil deep crust-mantle sections of the Ivrea-Verbano (Quick et al. 1995), the Ulten Zone (Braga and Massonne 2012) and central Calabria (Rizzo et al. 2001).
Lawsonite-rich crustal domains at high Th/La and Th/U hosted within the mélanges should have formed during an old events related to the diachronous collision of the northward drifting continental slivers from Gondwana in order to develop their high 208 Pb/ 206 Pb ). The most recent subduction events (e.g. the Neo-Tethys and Alpine Tethys oceanic basin) and continental collision (Alpine, Apennine, Himalayan Orogeny), brought to depth further crustal material, which underwent partial melting and metasomatized the depleted lithospheric mantle domains of the previously accreted chaotic mélange. These melts imparted the K-rich flavour and subduction signature to the lithospheric mantle, likely as phlogopiteorthopyroxene vein network (Fig. 9;Foley 1992;Melzer and Foley 2000;Ammannati et al. 2016).
Successively, lithosphere extension, thermal relaxation and associated mantle uplift produced during back-arc extension (Platt et al. 2003(Platt et al. , 2013, determined melting of the older lawsonite-rich crustal domains, completely exhausting lawsonite at relatively low temperature (i.e. 800°C; Wang and Foley 2020). These highly reactive SALATHOlike crustal melts segregated from their sources and reacted with the surrounding mantle domains, forming the felsic-veined mantle domains observed in the Tallante xenoliths (Dallai et al. 2019;Avanzinelli et al. 2020). Indeed, as indicated by oxygen isotopes, the formation of the felsic veins must have occurred relatively recently to prevent diffusion-assisted re-equilibration.
Proceeding with lithosphere extension and thermal relaxation, partial melting of such a heterogeneous and variable metasomatized mantle occurred, first affecting the different metasomatic veins (i.e. both phlogopite-rich and SALATHO-like), characterized by low solidus temperatures and continued progressively involving also the surrounding ambient peridotite. In this context, the geochemical and Fig. 9. Suggested schematic scenario for the genesis of Mediterranean orogenic lamproites. Subducted crustal material of different ages is represented with different colours (light yellow, lawsonite-bearing crust from old subduction event; orange, K-rich crust from recent subduction event). Round insets show the development of the two sets of metasomatic veins (i.e. SALATHO-like and phlogopite bearing) responsible for the key geochemical and isotopic features of the studied magmas. The bottom squares provide cartoons of the metasomatic reactions and mineralogy of the modified mantle. The image of the felsic SALATHO-like vein reproduces the petrography of the Tallante composite mantle xenoliths (Avanzinelli et al. 2020), whilst that of the phlogopite-rich veins is based on the study of Ammannati et al. (2016). isotopic variability of Mediteranean lamproites (and Tethyan lamproites in general) (Figs 4,5 & 6) can be interpreted as the result of mixing of different batches of melt deriving from the various mantle domains. This process may also account for progressive dilution of the 'lamproitic' character in the less potassic members (Figs 2 & 3) (Avanzinelli et al. 2009;Conticelli et al. 2009;Mattei et al. 2014), along the lines of the vein-plus-wall rock melting mechanism (Foley 1992). Since the geochemical and isotopic crustal signature is not limited to the veins but permeates also the surrounding peridotite, melts deriving from different proportion of the various veins and surrounding peridotite will inherit variable levels of trace element and isotopic enrichment. Yet, some general common characteristics (e.g. high LILE/HFSE, high Th/La and Sm/La) are preserved also in higher degree melts producing the shoshonitic and calc-alkaline products.
In the proposed scenario the origin of Mediterranean lamproites occurs at rather shallow depths, likely within the spinel stability field. The mantle xenoliths erupted at Tallante, here suggested as representative of possible sources for the SALATHO component, are equilibrated at pressure (0.7-0.9 GPa; Rampone et al. 2010;Bianchini et al. 2011 and references therein) straddling the transition between plagioclase and spinel. Tuscan lamproites (Torre Alfina) erupted mantle xenoliths confined within the spinel stability field (1.5-2.2 GPa: Conticelli and Peccerillo 1990), suggesting slightly higher depths, yet never crossing the spinel garnet transition. Similar pressure ranges (0.7-2 GPa) are indicated by thermobarometric constraints based on phlogopite composition of Mediterranean lamproites (Fritschle et al. 2013). This is also consistent with the high silica contents of these magmas, despite their primitive composition.
The inferred shallow origin of orogenic Mediterranean lamproites represents a further distinctive characteristic that differentiate them from lamproites erupted in anorogenic settings. Anorogenic lamproites are indeed interpreted as originated at high depth (.4 GPa;Foley 1993, Edgar and Mitchell 1997, Mirnejad and Bell 2006Jaques and Foley 2018) as also indicated by the occasional presence of diamond (McCulloch et al. 1983;Jaques et al. 1990;Lambert et al. 1995;Davies et al. 2006).
We conclude that orogenic lamproites, such as those of the Mediterranean and the Tethyan Realm in general, are rocks that characterize areas that were affected by multiple Wilson cycles, as observed in the Alpine-Himalayan Realm. They are originated at relatively shallow depth in a peridotite lithospheric mantle crosscut by several vein networks with different age and composition, but similar subductionrelated origin. Late partial melting events mix variable contributions from the veins and the host peridotite, generating the observed spectrum of orogenic magmas that appears typical of the specific geodynamic framework. Data availability All data generated or analysed during this study are included in this published article (and its supplementary information files).