Timing and nature of formation of the Ios metamorphic core complex, southern Cyclades, Greece
Published:January 01, 2009
Stuart N. Thomson, Uwe Ring, Stephanie Brichau, Johannes Glodny, Thomas M. Will, 2009. "Timing and nature of formation of the Ios metamorphic core complex, southern Cyclades, Greece", Extending a Continent: Architecture, Rheology and Heat Budget, U. Ring, B. Wernicke
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We apply low-temperature thermochronology, Rb/Sr geochronology, petrological data, and structural mapping to constrain the timing and kinematics of the Ios metamorphic core complex. Top-to-north extension in the lower plate Headland Shear Zone was active at 18–19 Ma under metamorphic conditions of 475–610 °C and 0.65–1.1 GPa. The South Cyclades Shear Zone/Ios Detachment Fault (SCSZ/IDF) system shows top-to-south extensional shear active at c. 19 Ma at 380–550 °C, with local top-to-north bands. Extensional shear above the SCSZ/IDF is dominantly top-to-south to top-to-SW. PT estimates from an eclogite boudin constrain Eocene high-pressure metamorphism to 430–560 °C and 1.21±0.42 GPa to 0.66±0.37 GPa. Similar low-temperature thermochronometric ages across Ios demonstrate that ductile extensional movement ceased by c. 15 Ma. Exhumation to shallow crustal levels took place between c. 15 and 9 Ma at cooling rates of up to 120 °C Ma−1 with a slow down to <20 °C Ma−1 between 12 and 9 Ma, most likely accommodated by extensional slip at rates of c. 3 km Ma−1 along the top-to-SW Coastal Fault System. We propose a model of bivergent extension for exhumation of the Ios core complex between 19 and 9 Ma, with Ios forming a secondary antithetic top-to-south to top-to-SW extensional fault system to a more dominant top-to-north Naxos/Paros detachment system.
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Extending a Continent: Architecture, Rheology and Heat Budget
Over the last three decades, there has been a growing appreciation of the role of extensional tectonics in convergent orogens. The opening contribution to this book, by Brian Wernicke, provides a flavour of how this ‘detachment era’ has changed our views on tectonometamorphic relationships in mountain belts. This introduction provides a historical account on how our views on large-scale tectonic contacts in mountain belts have changed over the years. Wernicke concludes that controversy still persists over the existence and mechanics of slip on shallowly dipping extensional detachments, although incontrovertible field evidence indicates that slip on shallowly dipping extensional faults occurs in nature. Other papers in the volume provide a mix of new, innovative and controversial ideas that may help to solve the mechanical paradox on slip on shallowly dipping extensional detachments and quantitative case studies from New Zealand, the Aegean extensional province, the Alps and Finland.