Radiolarian biostratigraphy and geochemistry of the Koziakas massif ophiolites (Greece)

Abstract

The Koziakas massif, located at the western boundary of the Thessaly plain, consists of a nappe pile, which includes from bottom to top: 1– the Paleocene-Eocene Pindos Flysch; 2– the Western Thessaly Units (WTU); 3– the Ophiolitic Nappe, which consists of four minor tectonic units: a) the ophiolite-bearing Koziakas Mélange; b) the Fourka Unit; c) a thin discontinuous level of amphibolites (Metamorphic sole); d) a “Peridotite Unit”. This work focuses on the study of both the radiolarian assemblages of cherts situated at the top of basalts and the geochemistry of the latter. Our data show that in the Fourka Unit the cherts overlying the various basalts have diverse ages: a) latest Anisian (associated to WPB-OIB), almost coeval to the trachyandesites effused onto the continental rifts to the west; b) Early Carnian-Middle Norian and Late Carnian-Early Norian (associated to WPB-OIB); c) Early Norian (associated to E-MORB). In the Koziakas Mélange the age is Early-Middle Bathonian (associated to WPB-OIB). These data confirm the geodynamic evolution hypothesized for all the other ophiolitic massifs of the southern portions of the Dinaric-Hellenic belt, which can be synthesized as follows: a) birth of the Vardar-“Maliac” ocean in the Middle Triassic, coeval to continental basins to the west (Pindos basin, etc.); b) ocean spreading until Late Jurassic with intraoceanic subduction at the beginning of Middle Jurassic, followed by intraoceanic obduction; c) closure of the ocean (latest Jurassic-earliest Cretaceous) and thrusting of the Ophiolitic Nappe onto the eastern continental margin of Adria (the Pelagonian); d) westward displacement of the Ophiolitic Nappe testified by the presence of ophiolitic detritus first in the WTU (latest Jurassic to Late Cretaceous) and then, to the west, in the Pindos Flysch (Paleocene-Eocene).

Middle Jurassic age of basalts and the post-obduction sedimentary sequence in the Guevgueli Ophiolite Complex (Republic of Macedonia)

“…The Jurassic supra-subduction ophiolites of the Western Vardar Ophiolitic Unit are therefore mostly older but partly also contemporaneous with the Jurassic ophiolites of the Eastern Vardar Unit. A thick Upper Bajocian to Oxfordian ophiolitic mélange is further characteristic of the Mirdita Zone and other Western Vardar ophiolite zones (Chiari et al 2004(Chiari et al , 2012Gawlick et al 2008). This mélange unit has no equivalent in the Eastern Vardar ophiolites.…”

Late Norian (Late Triassic) Radiolarian assemblages from chert pebbles of the Pentalofos Formation (Mesohellenic basin, Greece). Palaeogeographic implications

“…Mélange sequences that lie structurally underneath the Vourinos ophiolite, located directly to the east of the Mesohellenic basin, yield also blocks of Mesozoic radiolarian cherts [Ghikas et al, 2010]. A number of Triassic radiolarian chert samples were dated recently by Chiari et al [2012Chiari et al [ , 2013 from the Koziakas ophiolite. The obtained ages range from Middle/Late Carnian to Early/Middle Norian.…”

“…More particularly, Triassic Radiolaria have the potential to decipher the early stages of geodynamic and palaeogeographic evolution of the Neotethys ocean [i.e. Al Riyami et al, 2002;Bragin and Krylov, 1996;Bragin and Tekin, 1996;Bragin et al, 2011;Chiari et al, 2012Chiari et al, , 2013Danelian et al, 2012;Gawlick et al, 2012;Gorian et al, 2005;Ozsvárt et al, 2012;Ozsvárt and Kovács 2012;Tekin et al, 2002].…”

“…In Central Greece, Middle and Late Triassic Radiolaria are reported from the Lower Tertiary ophiolite-bearing mélange of the Pindos flysch [Bortolotti et al, 2009]. Recently, Chiari et al [2012] reported on Middle and Upper Triassic radiolarites associated with lavas of the Koziakas ophiolite. Late Triassic radiolarian assemblages point to Carnian -early /middle Norian ages.…”

Erosion of a Jurassic ophiolitic nappe-stack as indicated by exotic components in the Lower Cretaceous Rossfeld Formation of the Northern Calcareous Alps (Austria)

“…Slightly older and age equivalent ?Early/Middle Jurassic (late Early Jurassic to Bajocian according to Babić et al 2002 and Bajocian to Callovian according to Halamić et al 1998Halamić et al , 1999 ophioliticradiolaritic mélanges occur in Croatia (e.g. Halamić et al 1999;Babić et al 2002), Bosnia and Herzegovina (Hrvatović 2006), Serbia (Dimitrijević et al 2003;Gawlick et al 2009a,b;Kovács et al 2011), Albania (Bortolotti et al 2005) and Greece (Jones & Robertson 1991;Jones et al 1992;Stampfli et al 2003;Bortolotti et al 2004;Chiari et al 2012;Ozsvárt et al 2012;Robertson 2012). Enhanced pressure and temperature together with fluid-flow within the accreted ophiolite nappes and the mélanges led to recrystallization and partial loss of colour of different radiolarites.…”