Extension and Exhumation of the Hellenic Forearc Ridge in Kythera

Abstract

Detailed mapping and new structural observations on Kythera demonstrate that there is a major detachment fault, here termed the Potamos detachment fault (PDF), exposed on the northern part of the island and bordering the domed structure of a metamorphic core complex. The detachment forms the contact of contrasting metamorphic and nonmetamorphic units, and both ductile and brittle structures are found, related to its extensional development. The earliest Potamos mylonites, as well as some other early ductile structures near the mapped detachment fault, indicate initiation of the PDF under NE-trending extension, in mid-to late Miocene time. Later ductile, ductile-brittle, and some brittle structures in the metamorphic unit near the detachment indicate (in contrast) a significant NW-SE extension along the forearc ridge. The younger brittle structures indicate return to NE-SW extension. Late Miocene-Pliocene strata cover the detachment unconformably and are affected only by the late faults. Trench rollback and slab retreat of the subducting African lithosphere in the late Miocene requires expansion and increased curvature of the Hellenic (Crete-Peloponnese) forearc ridge. Differential movement between and vertical axis rotation of segments of the forearc ridge may have localized along-arc stretching. Cross-ridge strike-slip faults may be linked to the later parts of this process. Evidence of young E-W dextral faulting is seen in northern Kythera outcrops, related to a significant submarine fault of this type located between Kythera and the Peloponnese.

An application of GIS analysis on structural data from metamorphic rocks in Santorini Island.

“…(Figure 6). This is a range of approximately 60 o degrees, compared to some 90 o degrees of variation shown in the Kythera lineation data (Marsellos & Kidd, 2008;Marsellos et al, 2010). A lineation histogram (Figure 4) .…”

“…The Aegean Sea is an excellent example of episodic extension and exposes a wide range of regional detachment faults (e.g. Fassoulas et al, 1994;Thomson et al, 1999;Brix et al, 2002;Jolivet et al, 2003;Marsellos & Kidd, 2008;Ring et al, 2010;Skourtsos & Lekkas, 2010) and localized multi-detachments with more than one extension direction as observed in Kythera and Peloponnese (Marsellos et al, 2010). Correlation between structural data and thermochronological data has been shown to be useful in deconstructing multi-extensional complex tectono-low-thermal histories of HP-rocks associated with arc-normal or/and arc-parallel extensional detachments…”

“…The importance of those rocks is that they show two different post-metamorphic cooling ages and associated exhumation paths in Eocene and Miocene times, respectively (Marsellos et al, 2012). Other Aegean detachment faults such as the Potamos detachment fault in Kythera (Marsellos & Kidd, 2008) or the southeastern Peloponnese detachment (Marsellos et al, 2010) exhibit metamorphic rocks of similar age, but very different structural-oriented data such as lineations of perpendicular relationship. Very distinctive lineations of approximately 90 o degrees azimuth variation allow easier study of their distribution.…”

Exhumation of the Hellenic Accretionary Prism – Evidence From Fission-Track Thermochronology

“…4, 5). Ductile structures are also present in the PQU associated with the exhumation of those HP-rocks (Xypolias & Koukouvelas, 2001;Xypolias & Kokkalas, 2001;Xypolias et al, 2008;Marsellos, 2006;Marsellos & Kidd, 2008;Xypolias et al, 2008;Marsellos et al, 2010) but are missing from the upper plate. The cooling event (9-13 Ma) associated with the detachment activity has been recorded in the fully reset zircons in the Kythera PQU while rocks in the upper plate did not cross the ZPAZ.…”

“…The pre-Neogene thrust nappes exposed in the Hellenic forearc ridge overlie the young metamorphosed basement of HP rocks. The forearc ridge became emergent in connection with rapid exhumation and uplift of the underlying HP-rocks beginning in Early Miocene in Crete (Fassoulas et al, 1994;Jolivet et al, 1996;Thomson et al, 1999, Brix et al, 2002, in central Peloponnese (Marsellos et al, 2010), and since Middle-Late Miocene in Kythera (Marsellos & Kidd, 2008, Marsellos et al, 2010.…”