The origin of amphibolites from metamorphic soles beneath the ultramafic ophiolites in Evia and Lesvos (Greece) and their geotectonic implication

Gartzos, E; Dietrich, VJ; Migiros, G; Serelis, K; Lymperopoulou, Th

dc.contributor.author	Gartzos, E	en
dc.contributor.author	Dietrich, VJ	en
dc.contributor.author	Migiros, G	en
dc.contributor.author	Serelis, K	en
dc.contributor.author	Lymperopoulou, Th	en
dc.date.accessioned	2014-03-01T01:32:11Z
dc.date.available	2014-03-01T01:32:11Z
dc.date.issued	2009	en
dc.identifier.issn	0024-4937	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/20062
dc.subject	Greek ophiolites	en
dc.subject	Ophiolite emplacement	en
dc.subject	Ophiolites Evia island	en
dc.subject	Ophiolites Lesvos island	en
dc.subject	Petrography and geochemistry of amphibolite soles	en
dc.subject	Pindos and Vardar oceanic basins	en
dc.subject.classification	Geochemistry & Geophysics	en
dc.subject.classification	Mineralogy	en
dc.subject.other	amphibolite	en
dc.subject.other	continental crust	en
dc.subject.other	emplacement	en
dc.subject.other	flysch	en
dc.subject.other	gabbro	en
dc.subject.other	Jurassic	en
dc.subject.other	mid-ocean ridge basalt	en
dc.subject.other	obduction	en
dc.subject.other	oceanic crust	en
dc.subject.other	ophiolite	en
dc.subject.other	petrography	en
dc.subject.other	protolith	en
dc.subject.other	seafloor spreading	en
dc.subject.other	subduction zone	en
dc.subject.other	tectonic evolution	en
dc.subject.other	transform fault	en
dc.subject.other	Central Greece	en
dc.subject.other	Euboea	en
dc.subject.other	Eurasia	en
dc.subject.other	Europe	en
dc.subject.other	Greece	en
dc.subject.other	Hellenides	en
dc.subject.other	Lesbos	en
dc.subject.other	Northern Aegean	en
dc.subject.other	Pontides	en
dc.subject.other	Southern Europe	en
dc.subject.other	Turkey	en
dc.subject.other	Soleidae	en
dc.title	The origin of amphibolites from metamorphic soles beneath the ultramafic ophiolites in Evia and Lesvos (Greece) and their geotectonic implication	en
heal.type	journalArticle	en
heal.identifier.primary	10.1016/j.lithos.2008.09.013	en
heal.identifier.secondary	http://dx.doi.org/10.1016/j.lithos.2008.09.013	en
heal.language	English	en
heal.publicationDate	2009	en
heal.abstract	The dismembered Jurassic ophiolitic complexes of the two Greek islands, Evia and Lesvos show significant similarities concerning their general structural, petrographic and geochemical characteristics. However, their geotectonic position is quite different, the Evia ophiolites belonging to the ""Western Ophiolite Belt"" of the internal Hellenides, whereas the Lesvos ophiolites seem to be part of the ""Eastern Ophiolite Belt"", representing a possible link to the Pontides. Both ophiolites consist of large ultramafic masses, which are emplaced onto continental crust. The overthrust zones comprise flysch and ophiolitic mélange as well as amphibolitic metamorphic soles beneath the ultramafics. The identification of the protolithic character of the amphibolites as well as their metamorphic and deformation history allows a clarification of their complex emplacement processes from their original extensional oceanic ridge environment within the Pindos and Vardar marginal basins into a compressional supra-subduction zone, island arc and continental environment. On the basis of relict magmatic minerals and textures as well as on major and trace element bulk chemical composition, the medium to coarse grained Evia amphibolites are interpreted as former gabbroic and cumulate rocks similar to equivalent amphibolites dredged from numerous fracture zones in the Atlantic oceanic crust. Horizontal and vertical displacements which are able to produce such foliated and mylonitized gabbroic rocks suggest the existence of major deep reaching transform faults, which may be considered as one of the most important locations for the breakup of oceanic crust and lithosphere and subsequent incipient subduction. The Evia amphibolites could have been formed by a two-stage process: first, as gabbros that formed part of the gabbroic oceanic crust and secondly representing as small gabbroic and cumulate bodies within the ultramafic mantle. Either of these were transformed into low-grade epidote amphibolites under oceanic metamorphic facies conditions and deformed by transform fault displacement mechanism. Subsequently, within the Pindos intra-oceanic basin, these transform faults also facilitated obduction of slices of oceanic mantle and crust onto an accretionary wedge. In this respect, the Evia ophiolite complex shows a very similar emplacement process to that of the Othris, Vourinos and Pindos ophiolites, which can be interpreted using a combination of an intra-oceanic transform fault thrust and an obduction model. In this respect, the ""Evia transform fault-overthrust model"" sheds new light onto the discussion of the age of formation of oceanic crust, as well as on the timing of subduction and obduction. The so called ""sole amphibolites"", especially those of only low-grade epidote-amphibolite facies may have already been formed during mid-ocean floor spreading and transform fault movements and not later during the ophiolite emplacement processes. Therefore all of the ages of oceanic crust and amphibolites, both from sedimentary and paleontological evidence as well as from radiometric data indicate a specific time window between the generation of the older parts of oceanic crust around 170 Ma (Bajocian) and their emplacement processes at approximately 155 to 150 Ma. This leads to the conclusion that the Pindos marginal oceanic basin could have at least an age spread of 15 to 20 Ma. In contrast, the Lesvos amphibolites are fine to medium grained with granoblastic and nematoblastc textures with relics of clinopyroxene and plagioclase. Cataclastic fabrics are also present as well as retrograde mineral assemblages from greenschist to prehnite facies metamorphic overprinting. According to bulk chemical analyses, these amphibolites are identified as MORB-type oceanic basalts as well as SSZ (supra-subduction zone/IAT -island arc tholeiite) basalts and olivine gabbros. The Lesvos amphibolites are seen as basaltic and gabbroic slices, which were incorporated into a supra-subduction, gabbro bearing island arc environment, overridden by larger slices of depleted lherzolite and harzburgite mantle. Since the amphibolites show in many cases highly deformed fabrics and a rather high-grade metamorphism as well as MORB basaltic compositions, an intra-oceanic thrusting cannot be excluded. Their origin can rather be placed in the Vardar oceanic basin than in the Pindos basin. © 2008 Elsevier B.V. All rights reserved.	en
heal.publisher	ELSEVIER SCIENCE BV	en
heal.journalName	Lithos	en
dc.identifier.doi	10.1016/j.lithos.2008.09.013	en
dc.identifier.isi	ISI:000264332400012	en
dc.identifier.volume	108	en
dc.identifier.issue	1-4	en
dc.identifier.spage	224	en
dc.identifier.epage	242	en