The Mamonia Complex (SW Cyprus) revisited: remnant of Late Triassic intra-oceanic volcanism along the Tethyan southwestern passive margin

Abstract

International audienceUpper Triassic volcanic and sedimentary rocks of the Mamonia Complex in southwestern Cyprus are exposed in erosional windows through the post-Cretaceous cover, where the Mamonia Complex is tectonically imbricated with the Troodos and Akamas ophiolitic suites. Most of these Upper Triassic volcanic rocks have been considered to represent remnants of Triassic oceanic crust and its associated seamounts. New Nd and Pb isotopic data show that the whole Mamonia volcanic suite exhibits features of oceanic island basalts (OIB). Four rock types have been distinguished on the basis of the petrology and chemistry of the rocks. Volcanism began with the eruption of depleted olivine tholeiites (Type 1) and oceanic island tholeiites (Type 2) associated with deep basin siliceous and/or calcareous sediments. The tholeiites were followed by highly phyric alkali basalts (Type 3) interbedded with pelagic Halobia-bearing limestones or white reefal limestones. Strongly LREE-enriched trachytes (Type 4) were emplaced during the final stage of volcanic activity. Nd and Pb isotopic ratios suggest that tholeiites and mildly alkali basalts derived from partial melting of heterogeneous enriched mantle sources. Fractional crystallization alone cannot account for the derivation of trachytes from alkaline basalts. The trachytes could have been derived from the partial melting at depth of mafic material which shares with the alkali basalts similar trace element and isotopic compositions. This is corroborated by the rather similar isotopic compositions of the alkali basalts and trachytes. The correlations observed between incompatible elements (Nb, Th) and {varepsilon}Nd and Pb isotopic initial ratios suggest that the Mamonia suite was derived from the mixing of a depleted mantle (DMM) and an enriched component of High µ (µ = 238U/204Pb, HIMU) type. Models using both Nd and Pb isotopic initial ratios suggest that the depleted tholeiites (Type 1) derived from a DMM source contaminated by an Enriched Mantle Type 2 component (EM2), and that the oceanic tholeiites (Type 2), alkali basalts (Type 3) and trachytes (Type 4) were derived from the mixing of the enriched mantle source of the depleted tholeiites with a HIMU component. None of the Mamonia volcanic rocks show evidence of crustal contamination. The Upper Triassic within-plate volcanism likely erupted in a small southerly Neotethyan basin, located north of the Eratosthenes seamount and likely floored by oceanic crust

The alkaline intraplate volcanism of the Antalya nappes (Turkey): a Late Triassic remnant of the Neotethys

“…The isotope geochemistry of the studied intraplate volcanics can therefore be accounted for by their derivation from mantle components ( with a local contribution of pelagic sediments for AY02-20), and there is no need to envision the contribution of continental crust to their genesis. Similar conclusions have been reached by Lapierre et al [2007] for the Late Triassic Mamonia Complex in SW Cyprus, which differs mostly from the Antalya sequence by the additional occurrence of alkali basalt-related trachytes, and of tholeiites deriving from larger degrees of partial melting of OIB-type mantle.…”

“…Therefore, the emplacement of these lavas may have occurred in an intra-oceanic (plume-related) setting, such as in the neighbouring island of Cyprus [Lapierre et al, 2007].…”

“…The absence of any continental crustal component in the genesis of the Antalya basalts, unlike in those from younger rift-related environments [Chazot and Bertrand, 1993;Baker et al, 1996] or from some of the Middle Permian basins in which the Hawasina Nappes materials were deposited [Lapierre et al, 2004], combined with the pelagic and carbonate-platform types of sedimentation associated with the Antalya basalts, allow to envision their emplacement in an intra-oceanic (plume-related) setting. This OIB volcanism was widespread during the Upper Triassic all along the southern Tethyan margin, from the Himalayas [Bassoullet et al, 1980a, b;Corfield et al, 1999] to Oman [Béchennec et al, 1989[Béchennec et al, , 1991Pillevuit et al, 1997] and the Eastern Mediterranean, in Cyprus [Malpas et al, 1993;Lapierre et al, 2007], the Baër-Bassit in Syria [Delaune-Mayère, 1984;Al-Riyami and Robertson, 2002] and Antalya.…”

“…In the eastern Mediterranean, the latter are stratigraphically associated with pelagic and/or carbonate-platform limestones dated to the Upper Triassic [Marcoux, 1970;Dumont et al, 1972;Robertson and Waldron, 1990]. The Carnian age of the opening of the Izmir-Ankara branch of the Neotethys according to radiolarian faunas [Tekin et al, 2002] sets the problem of the geodynamic setting of the Late Triassic submarine volcanism in the eastern Mediterranean, which might be rift-related, ridge-related or finally oceanic island-type as recently shown for the Mamonia Complex in Cyprus [Lapierre et al, 2007]. In this paper, we present a new set of petrologic and geochemical data on the Antalya nappes (southwestern Turkey) submarine volcanic rocks.…”

Ophiolite Tectonics, Rock Magnetism and Palaeomagnetism, Cyprus

“…2,3). These were variably metamorphosed and emplaced in Later Cretaceous (early Maastrichtian) times, together with oceanic-island volcanic rocks of Triassic age (Bailey et al 2000;Henson et al 1949;Ealy and Knox 1975;LaPierre et al 2007). The subterranean extent of the terrane may be considerable considering the depressed Bouguer Fig.…”