An integrated zircon geochronological and geochemical investigation into the Miocene plutonic evolution of the Cyclades, Aegean Sea, Greece: Part 1: Geochronology |
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| Authors: | Robert Bolhar Uwe Ring Charlotte M Allen |
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| Institution: | (1) School of Earth Sciences, University of Queensland, Brisbane, 4072, Australia;(2) Department of Geological Sciences, University of Canterbury, Christchurch, 8140, New Zealand;(3) Research School of Earth Sciences, Australian National University, Canberra, 2006, Australia |
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| Abstract: | We use 369 individual U–Pb zircon ages from 14 granitoid samples collected on five islands in the Cyclades in the Aegean Sea,
Greece, for constraining the crystallisation history of I- and S-type plutons above the retreating Hellenic subduction zone.
Miocene magmatism in the Cyclades extended over a time span from 17 to 11 Ma. The ages for S-type granites are systematically
~2 million years older than those for I-type granites. Considering plutons individually, the zircon data define age spectra
ranging from simple and unimodal to complex and multimodal. Seven of the 14 investigated samples yield more than one distinct
zircon crystallisation age, with one I-type granodiorite sample from Mykonos Island representing the most complex case with
three resolvable age peaks. Two samples from S-type granites on Ikaria appear to have crystallised zircon over 2–3 million
years, whereas for the majority of individual samples with multiple zircon age populations the calculated ages deviate by
1–1.5 million years. We interpret our age data to reflect a protracted history involving initial partial melting at deeper
lithospheric levels, followed by crystallisation and cooling at shallower crustal levels. Our study corroborates published
research arguing that pluton construction is due to incremental emplacement of multiple magma pulses over a few million years.
Assuming that multiple age peaks of our 14 samples can indeed serve to quantify time spans for magmatic emplacement, our data
suggest that Aegean plutons were constructed over a few million years. Our tectonic interpretation of the U–Pb ages is that
the S-type granites resulted from partial melting and migmatisation of the lower crust, possibly starting at ~23 Ma. The I-type
granites and associated mafic melts are interpreted to reflect the magmatic arc stage in the Cyclades starting at ~15 Ma. |
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