Tecronophysics, 223 (1993) 237-272 Elsevier Science Publishers B.V., Amsterdam 237 The geochemistry and petrogenesis of volcanics and sheeted dikes from the Hatay (Kizildag) Ophiolite, southern Turkey: possible formation with the Troodos Ophiolite, Cyprus, along fore-arc spreading centers J.N. Lytwyn and J.F. Casey Department of’Geosciences, University of Houston, University Park, Houston, TX 77204-5503, USA (Received May 28,Wl; revised version accepted December 7, 1992) ABSTRACT Geochemical and petrological investigations of the Hatay Wizildag) Ophiolite, southern Turkey, indicate that the volcanics and sheeted dikes com~sitionally range from island-arc tholeiites and basaltic andesites to transitional boninitic- type Iavas formed within a supra-subduction zone environment. Geochemical modeling indicates that the com~sitional trends within both the sheeted dike and pillow basalt sections of Hatay cannot be related through fractional crystallization alone but require multiple parental magmas of differing compositions within each unit. The more refractory liquids (higher MgO, Ni and Cr coupled with lower concentrations of Ti, Zr, Y and REE) formed at lower pressures (shallower depths) through greater degrees of partial melting of a more depleted mantle source relative to less-refractory magmas which formed at higher pressures and possibly lower degrees of melring. The Hatay volcanics and dikes span the compositional range of Lower Pillow Lavas (LPLs) and Upper Pillow Lavas (UPLs) from the Troodos Complex, Cyprus, suggesting, along with other evidence, that the two ophiolites may be petrogeneti~lly and tectonically reiated. Formation of the Hatay and Troodos ophiolites was possibly associated with extension within a fore-arc environment following compression and detachment along an intra-oceanic ridge system and development of a subduction zone. The range of parental liquid compositions for volcanics and dikes may reflect variable mixing of geochemically diverse melt increments generated within a polybaric melting column in the mantle wedge. The melting column may have additionally received contributions of LREE-enriched melts from deeper, more juvenile (fertile) sources. Formation of parental liquids through variable mixing of melt increments appears to be common to both the Hatay and Troodos ophiolites. Introduction Ophiolites are ultramafic-mafic rock se- quences found along major erogenic belts and are generally interpreted as remnants of oceanic crust and mantle. A typical ophiolite is several kilome- ters thick and composed of a basal mantle unit of tectonized peridotite and dunite, an intermediate plutonic sequence consisting of ultramafic and mafic cumulates associated with layered and isotropic gabbros, and upper units of sheeted dikes, massive flows and pillowed lavas some- times intercalated with sediments. Ophiolites can form in a variety of tectonic en~ro~ents which include mid-ocean ridges, island arcs, leaky trans- form faults, marginal basins, aseismic ridges and possibly ocean islands (Miyashiro, 1973, 1975; Boudier and Coleman, 1981; Moores, 1982; Casey and Dewey, 1984; Pearce et al., 1984; Boudier and Nicolas, 1985; Boudier et al., 1988). Various models have been proposed to explain the em- placement of oceanic crust and mantle onto con- tinental margins (e.g. Dewey, 1976; Moores, 1982; Casey and Dewey, 1984; Boudier et al., 1988; Edelman, 1988; Hacker, 1990; Sengiir, 1990). Ophiolites along the Eastern Mediterranean extend from Greece, through Turkey and into northwest Syria and include the Troodos Com- plex, Cyprus. Eastern Mediterranean ophiolites are relicts of two extinct oceanic realms which comprised the Tethyan region. The earlier Palaeo-Tethys existed during the Permian but closed by Middle Jurassic time (Seng6r and Yil- maz, 1981). The Palaeo-Tethyan suture occurs HO-1951/93/$~.~ 0 1993 - Elsevier Science Publishers B.V. All rights reserved