Abstract
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 Al 2 O 3 , CaO and Na 2 O 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 207 Pb over 206 Pb and high time-integrated 232 Th/ 238 U. 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.
Highlights
Lamproites are rare and exotic ultrapotassic igneous rocks (K2O . 3 wt.%, with K2O/Na2O . 2; Foley et al 1987) showing peculiar geochemical and isotopic compositions
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, Balkan Peninsula (Serbia–Macedonia) and Western Anatolia (Turkey), and their associated shoshonitic and calc-alkaline rocks
Orogenic lamproites represent exotic and rare mantle-derived magmas believed to originate in highly metasomatized lithospheric mantle domains (Peccerillo et al 1988; Conticelli et al 1992, 2002, 2007, 2015; Prelević et al 2005, 2008, 2010; Prelević and Foley 2007)
Summary
Lamproites are rare and exotic ultrapotassic igneous rocks (K2O . 3 wt.%, with K2O/Na2O . 2; Foley et al 1987) showing peculiar geochemical and isotopic compositions. Pb isotopes composition of the Mediterranean lamproites (Fig. 5b, c) show high 207Pb/204Pb over 206Pb/204Pb with respect to the Northern Hemisphere Reference Line (NHRL, Hart 1984), confirming the ubiquitous, variable, contribution of crustal components recycled in their mantle source.
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