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This study provides a comprehensive literature review of the distribution, the platinum- group elements (PGE) composition, and mineral chemistry of chromitites associated with Mesozoic Tethyan ophiolites in the Mediterranean Basin. These suites outcrop in the northern Italian Apennines, the Balkans, Turkey, and Cyprus. Most chromitites occur in depleted mantle tectonites, with fewer found in the mantle-transition zone (MTZ) and supra-Moho cumulates. Based on their Cr# = (Cr/(Cr + Al)) values, chromitites are primarily classified as high-Cr, with a subordinate presence of high-Al chromitites. Occasionally, high-Al and high-Cr chromitites co-exist within the same ophiolite complex. High-Cr chromitites are formed in supra-subduction zone (SSZ) environments, where depleted mantle interacts with high-Mg boninitic melts. Conversely, high-Al chromitites are typically associated with extensional tectonic regimes and more fertile peridotites. The co-existence of high-Al and high-Cr chromitites within the same ophiolite is attributed to tectonic movements and separate magma intrusions from variably depleted mantle sources, such as mid-ocean ridge basalts (MORB) and back-arc basin basalts. These chromitites formed in different geodynamic settings during the transition of the oceanic lithosphere from a mid-ocean ridge (MOR) to a supra-subduction zone (SSZ) regime or, alternatively, within an SSZ during the differentiation of a single boninitic magma batch. Distinct bimodal distribution and vertical zoning were observed: high-Cr chromitites formed in the deep mantle, while Al-rich counterparts formed at shallower depths near the MTZ. Only a few of the aforementioned chromitites, particularly the high-Cr ones, are enriched in the refractory IPGE (iridium-group PGE: Os, Ir, Ru) relative to PPGE (palladium-group PGE: Rh, Pt, Pd), with an average PPGE/IPGE ratio of 0.66, resulting in well-defined negative slopes in PGE patterns. The IPGE enrichment is attributed to their compatible geochemical behavior during significant degrees of partial melting (up to 30%) of the host mantle. It is suggested that the boninitic melt, which crystallized the high-Cr chromitites, was enriched in IPGE during melt-rock reactions with the mantle source, thus enriching the chromitites in IPGE as well. High-Al chromitites generally exhibit high PPGE/IPGE ratios, up to 3.14, and strongly fractionated chondrite-normalized PGE patterns with positive slopes and significant enrichments in Pt and Pd. The PPGE enrichment in high-Al chromitites is attributed to the lower degree of partial melting of their mantle source and crystallization from a MOR-type melt, which contains fewer IPGE than the boninitic melt above. High-Al chromitites forming at higher stratigraphic levels in the host ophiolite likely derive from progressively evolving parental magma. Thus, the PPGE enrichment in high-Al chromitites is attributed to crystal fractionation processes that consumed part of the IPGE during the early precipitation of co-existing high-Cr chromitites in the deep mantle. Only a few high-Al chromitites show PPGE enrichment due to local sulfur saturation and the potential formation of an immiscible sulfide liquid, which could concentrate the remaining PPGE in the ore-forming system. [ABSTRACT FROM AUTHOR]

The late Neoproterozoic Frog Lake pluton, in the Avalon terrane of the Cobequirj Highlands, Nova Scotia, consists predominantly of hornblende gabbro. It shows petrographic similarities to water-rich mafic intrusions known as appinites that are present in some collisional orogens. This study aims to further understanding of the origin of appinitic intrusions. In the field, the main hornblende gabbro was intruded between screens of meiasedimentary country rock that is of upper greenschist metamorphic grade. The contacts appear to have been pathways for magma of gabbroic, tonalitic-- granodioritic, and granitic composition that carried enclaves of gabbroic lithologies. Some of these magmas had a high volatile content, resulting in abundance of hydrous mineral phases, pegmatites, and diffuse felsic segregations. These varied rocks in the contact zones experienced progressive shear resulting in syn-magmatie deformation. Low-Ti hornblende gabbros have trace-element abundances similar to subduction-related low-K mafic rocks, including some enrichment in large-ion liihophile elements and marked relative depletion in Nb and Y. High-Ti hornblende gabbros and pyroxene-mica gabbro show more alkaline characteristics, with higher amounts of Nb, Y, [P.sub.2][O.sub.5], and high- field-strength elements. Tonalite and granite veins are geochemically similar to volcanic-arc granite. Comparison with appinites in the literature suggests that the Frog Lake pluton represents a deeper structural level than most appinites. The Frog Lake appinites were part of the feeder system to back-arc volcanic rocks of the Jeffers Group. Comparison with other appinites also leads to the conclusion that there is not a single type of 'appinitic magma': different appinitic plutons range in composition from low-K calc-alkaline to shoshonilic. The essential characteristic is a water-rich mafic magma. Appinites occur in settings undergoing crustal-scale strike-slip shear, where the faults allow rapid rise of mafic magma to shallow crustal levels. Le pluton de Frog Lake (Neoproterozoique tardif) dans le terrane Avalon des terres hautes de Cobequid, en Nouvelle-Ecosse, est principalement forme de gabbro a hornblende. Il montre des similarites petrographiques aux intrusions mafiques riches en eau, connues en tant qu'appinites, qui sont presenles dans quelques orogenes de collision. La presente etude vise a mieux comprendre l'origine des intrusions appinitiques. Sur le terrain, le principal gabbro a hornblende a ete introduit entre des ecrans de roche encaissante metasedimentaire au grade metamorphique de sous-facies superieur des schistes verts. Les contacts semblent avoir constitue des chemins pour des magmas de composition gabbroique, tonalitique--granodioritique et granitique qui charriaient des enclaves de lithologie gabbroique. Quelques-uns de ces magmas avaient un contenu hautement volatil, ce qui a conduit a une abondance de phases minerales hydratees. de pegmatites et de segregations felsiques diffuses. Ces roches variees dans les zones de contact out subi un cisaillement progressif produisant une deformation syn-magmatique. Des gabbros a faible teneur en hornblende Ti ont des abondances d'elements traces semblables aux roches mafiques reliees a la subduction et a faible teneur en K, incluant un certain enrichissement en elements liihophiles a grand rayon ionique et un appauvrissement relatif marque en Nb et Y. Des gabbros a haute teneur en Ti et un gabbro a pyroxene et mica montent plus de caracteristiques alcalines, avec de plus grandes quantites de Nb, d'Y, de [P.sub.2][O.sub.5] et d'elements a forte liaison atomique. Les filons de tonalite et de granite ont une composition geochimique semblable a celle d'un granite d'arc volcanique. Une comparaison avec les appinites dans la litterature suggere que le pluton de Frog Lake represente un niveau structural plus profond que la plupart des appinites. Les appinites de Frog Lake faisaient partie du systeme d'alimentation des roches volcaniques d'arriere-arc du Groupe de Jeffers. Une comparaison avec d'autres appinites mene aussi a la conclusion qu'il y a plus d'un type de << magma appinitique >> : la conrposition de differents plutons appinitiques varie de calco-alcaline a faible teneur en K a shoshonitique. La caracteristique essentielle est un magma mafique riche en eau. Les appinites se trouvent dans des environnements qui subissent un cisaillement de coulissage a l'echelle de la croute et dans lesquels des failles permettent au magma de s'elever rapidement a des niveaux pen profonds de la croute. [Traduit par la Redaction], Introduction Appinites were originally defined by Bailey and Maufe (1916) as the plutonic equivalents of various hornblenderich lamprophyres. The presence of large crystals of hornblende is a characteristic petrographic feature, [...]

The Miocene igneous rocks in the Basal Unit of the Lavrion area form part of the granitoid province of the central Aegean. Undeformed, subvertical dykes of quartz-syenite to granodiorite and granite porphyries, and a little deformed but variably altered granodiorite stock intrude metamorphic rocks of the Basal Unit. A 9.4 [+ or -] 0.3 Ma K-Ar age on feldspar for a dyke rock provides a minimum age for the igneous activity in the Basal Unit. East-west orientation of porphyry dykes is indicative of a regional extensional stress field with roughly north-south direction. Substantial extension in the Basal Unit after granodiorite emplacement is evident from widespread quartz veining associated with hydrothermal alteration of the granodiorite and the occurrence of mineralized tension gashes cutting the hydrothermally altered hornfelses. Final emplacement of the Blueschist Unit over the Basal Unit by extensional detachment post-dates contact metamorphism of the rocks surrounding the granodiorite. Geochemical diagrams show a continuous range of compositions from the dykes to the granodiorite. Radiogenic isotope compositions are compatible with a common magmatic source for the two lithologies. Elemental variations, as well as the considerable geochemical similarity of the dyke rocks to the Hercynian paragneiss of the central Cyclades, indicate that crustal melts were significant components during the evolution of the igneous rocks with fractional crystallization as an important process during later stages of evolution. The granodiorite displays geochemical signatures indicative of a significant mafic mantle-derived magma component. Keywords: granodiorite, dykes, Miocene, extensional tectonics, Lavrion, Greece.

Whole-rock geochemical and Sm/Nd isotope data are presented for a representative suite of crustal rocks from the Pindos Ophiolite in order to resolve the origin of the geochemical signature of the boninites. Comparison is made with Triassic MORB from the Avdella melange and with other ophiolitic rocks of northwestern Greece. Hydrothermal alteration results in large scatter in Sr and K and some variability in Ba, Th and U. The Pindos boninites contain high Zr and Hf with respect to REE, characteristic of many boninites. Pb, La/Sm and Nb decrease with decreasing Ti[O.sub.2] from MORB to IAT, but then increase in the boninites. Nd isotopic values expressed as [[epsilon].sub.Nd] decrease systematically with decreasing Ti[O.sub.2], from 7-8 in IAT to 0.6 3.0 in boninites. As mantle wedge harzburgite became increasingly depleted, another magma source contributed significant amounts of Pb, REE and probably Nb. The Pb and other large-ion lithophile elements may have been transported in aqueous solutions from the subducting slab, but the REE and Nb imply an ocean-island basalt (OIB)-type source within the mantle wedge. This OIB source is a consequence of mantle plume activity during late Triassic rifting. Keywords: Nd isotopes, basalt, Jurassic, geochemistry, ocean-island basalt.