 A combined diagram of the Aegean and Anatolian plates. The southern margin of the Hellenic arc is shown, which is the trend line of the faults separating the arc and the Hellenic Trench. The body of the arc is the chain called the outerHellenides, which includes west Peloponnesus, Crete, Rhodes, southwestern Turkey, and all the islands between. | |
  middle arc Hellas and the Aegean Sea Show map of Mediterranean middle arc middle arc (Greece) Show map of Greece | |
| Etymology | Hellenic Republic (Greece) |
|---|---|
| Geography | |
| Location | The center of Crete is at about center of the arc |
| Coordinates | 35°12′50″N24°58′01″E / 35.21389°N 24.96694°E /35.21389; 24.96694 |
| Archipelago | southern outer Hellenides |
| Adjacent to | Aegean Sea, Ionian Sea, Mediterranean Sea |
| Administration | |
Greece | |
TheHellenic arc orAegean arc is anarcuate mountain chain of the southernAegean Sea located on the southern margin of theAegean Sea plate. Geologically it results from thesubduction of theAfrican plate under it along theHellenic subduction zone. TheHellenic Trench trends parallel to its southern side. The Aegean Sea plate, a microplate, is often considered part of theEurasian plate from which it is in the process of diverging. The arc itself is mainly marine, the mountaintops appearing as islands in the Ionian Sea, Crete and its environs, or in theDodecanese group. It encroaches on mainland terrain in the Peloponnesus, on Crete, on Rhodes, and on the southern coast of Anatolia, thus being encompassed by both Greece and Turkey.
The direction of subduction is northward. Locations on the arc or near it on the north side are therefore called "outer" as they are at the outer margin of the plate. Locations further north are "inner." Generally the motion of subduction is from outer to inner. It so happens that, due to back-arc extension, the Hellenic Arc and Trench are moving in the reverse direction, from inner to outer, accounting for the severe arcuate form. There are in essence two layers at the subduction zone, a bottom one moving from outer to inner, and a top one moving from inner to outer.
The extension of the top layer required for this excursion of the arc and the trench comes from thinning of the back-arc ("in back of the arc"), weakening the crust there. There was already a mountain chain north of the arc, a legacy from theAlpine Orogeny, called the "inner arc." Its tops are theCyclades. In addition, a chain of volcanos has appeared across it, due to magma breaking through the weakened crust; hence, this "inner arc" is termed theSouth Aegean Volcanic Arc. The two arcs are considered distinct, being from differentorogenies. The term "Hellenic Arc" most often refers to the marginal, or "non-volcanic" arc, also called the Aegean forearc in the direction from outer to inner, which is consonant with the Hellenic Trench being the foredeep.
The Hellenic arc extends from theIonian Islands in the west to just east of the island ofRhodes in the east, where it links to theCyprus arc.
The current geometry of the Hellenic arc is a result of the southwards migration of the subduction zone.[1] This has led to extension both along the line of the arc as it bulged out and extension perpendicular to the arc, which is the current tectonic state.
The Hellenic arc is one of the most active seismic zones in western Eurasia.[2] It has regularly been the source formagnitude 7 earthquakes in the last hundred years of instrumental recording and the location for at least two historical events that were probably of about magnitude 8 or more, the365 Crete earthquake and the1303 Crete earthquake.[3]
Media related toHellenic arc at Wikimedia Commons