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Geosciences 2017, 7(1), 14; doi:10.3390/geosciences7010014

Ophiolitic Remnants from the Upper and Intermediate Structural Unit of the Attic-Cycladic Crystalline Belt (Aegean, Greece): Fingerprinting Geochemical Affinities of Magmatic Precursors

1
Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Panepistimiopolis, Ano Ilissia, 15784 Athens, Greece
2
Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, 1205 Genève, GE, Switzerland
*
Author to whom correspondence should be addressed.
Academic Editors: Basilios Tsikouras, Antonio Acosta-Vigil and Jesus Martinez-Frias
Received: 21 November 2016 / Revised: 3 March 2017 / Accepted: 7 March 2017 / Published: 21 March 2017
(This article belongs to the Special Issue Petrogenesis of Ophiolites)
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Abstract

The ophiolitic rocks of the Attic-Cycladic crystalline belt are considered of key importance for understanding the Mesozoic tectonic evolution of the Aegean region. Unresolved questions concern their tectono-stratigraphic relationships across the region. The mode of occurrence of the Cycladic ophiolites varies, as they appear as: (a) dismembered blocks (olistoliths) within the supra-detachment units of Paros and Naxos; (b) mélange formations in the upper structural unit of western Samos and Skyros; and (c) meta-ophiolitic mélange in the Cycladic Blueschist Unit (CBU) from central Samos. The trace element geochemistry and Pb-Sr-Nd isotopes of the mafic ophiolitic rocks indicate four geochemical groups: (a) the upper unit metabasites from Paros and western Samos (Kallithea) display an evolved basaltic composition (Mg# 40.2–59.6), with low Zr/Nb values (5–16) and high Ce/Y values (1.3 to 2.6) compared to MORB, indicating island-arc tholeiite affinities; (b) Naxos upper unit metabasalts show spider diagrams patterns indicating ocean island basalt (OIB-type) affinities; (c) Central Samos metagabbros (CBU) are primitive rocks with Back-Arc Basin basalt affinities; (d) the Skyros metadolerites and Tinos (Mt Tsiknias) and S. Evia (CBU) metagabbros, cluster as a separate geochemical group; they exhibit high MgO values (>10 wt %), very low TiO2 values (0.1–0.2 wt %), Y and Yb, and depleted trace element N-MORB normalized patterns, similar to volcanic rocks formed in modern oceanic fore-arc settings, such as boninites. A combination of the Pb- and Sr-isotopic compositions of Cycladic metabasites indicate that the Pb and Sr incorporated in the Cycladic ophiolites correspond to mixtures of magmatic fluids with seawater (206Pb/204Pb = 18.51–18.80; 207Pb/204Pb = 15.59–15.7; 208Pb/204Pb = 39.03–39.80 and initial 87Sr/86Sr80 = 0.705–0.707). Furthermore, peridotite relicts from Samos, Paros, and Naxos—irrespective of the structural unit—display chemical affinities of ocean floor peridotites formed in a supra-subduction zone. The characteristics of harzburgite relicts in Cycladic serpentinites and Skyros indicate a highly residual nature of the mantle source. Geochemical data from this study shed further light on the complex structure of the oceanic lithosphere from which the Cycladic ophiolites originated. View Full-Text
Keywords: Aegean ophiolites; Sr-Nd-Pb isotopes; MORB, BABB; supra-subduction zone Aegean ophiolites; Sr-Nd-Pb isotopes; MORB, BABB; supra-subduction zone
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Stouraiti, C.; Pantziris, I.; Vasilatos, C.; Kanellopoulos, C.; Mitropoulos, P.; Pomonis, P.; Moritz, R.; Chiaradia, M. Ophiolitic Remnants from the Upper and Intermediate Structural Unit of the Attic-Cycladic Crystalline Belt (Aegean, Greece): Fingerprinting Geochemical Affinities of Magmatic Precursors. Geosciences 2017, 7, 14.

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