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The Age, Origin, and Emplacement of the Tsiknias Ophiolite, Tinos, Greece
Author(s) -
Lamont Thomas N.,
Roberts Nick M.W.,
Searle Michael P.,
Gopon Phillip,
Waters David J.,
Millar Ian
Publication year - 2020
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/2019tc005677
Subject(s) - ophiolite , geology , geochemistry , zircon , protolith , massif , partial melting , ultramafic rock , metamorphic rock , oceanic crust , metamorphic facies , greenschist , petrology , subduction , basalt , paleontology , facies , tectonics , structural basin
The Tsiknias Ophiolite, exposed at the highest structural levels of Tinos, Greece, represents a thrust sheet of Tethyan oceanic crust and upper mantle emplaced onto the Attic‐Cycladic Massif. We present new field observations and a new geological map of Tinos, integrated with petrology, THERMOCALC phase diagram modeling, U–Pb geochronology and whole rock geochemistry, resulting in a tectonothermal model that describes the formation and emplacement of the Tsiknias Ophiolite and newly identified underlying metamorphic sole. The ophiolite comprises a succession of partially dismembered and structurally repeated ultramafic and gabbroic rocks that represent the Moho Transition Zone. A plagiogranite dated by U‐Pb zircon at 161.9 ± 2.8 Ma, reveals that the Tsiknias Ophiolite formed in a suprasubduction zone setting, comparable to the “East‐Vardar Ophiolites,” and was intruded by gabbros at 144.4 ± 5.6 Ma. Strongly sheared metamorphic sole rocks show a condensed and inverted metamorphic gradient, from partially anatectic amphibolites at P‐T conditions of ~8.5 kbar 850–600 °C, downstructural section to greenschist‐facies oceanic metasediments over ~250 m. Leucosomes generated by partial melting of the uppermost sole amphibolite, yielded a U‐Pb zircon protolith age of ~190 Ma and a high‐grade metamorphic‐anatectic age of 74.0 ± 3.5 Ma associated with ophiolite emplacement. The Tsiknias Ophiolite was therefore obducted ~90 Myr after it formed during initiation of a NE dipping intraoceanic subduction zone to the northeast of the Cyclades that coincides with Africa's plate motion changing from transcurrent to convergent. Continued subduction resulted in high‐pressure metamorphism of the Cycladic continental margin ~25 Myr later.