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The timing of high-temperature conditions an d ductile shearing in the footwall of the Naxos metamorphic core complex, Aegean Sea, Greece
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
(English)In: Article in journal (Refereed) Submitted
Abstract [en]

We present eight Rb-Sr multi-mineral isochron ages showing that high-temperature metamorphic conditions and partial melting during top-to-the-NNE extensional shearing in the footwall of the Naxos metamorphic core complex lasted until about 14-12 Ma. One migmatite sample yielded an age of 14.34 ± 0.20 Ma (2σ uncertainties) for crystallization of migmatization related melt pockets. Four pegmatite samples, which are in part associated with partial melting of their host rocks, provided overlapping ages ranging from 13.81 to 12.23 Ma (age range includes 2σ uncertainties). Additional three samples of amphibolite-facies schist supplied Rb-Sr ages of around 14 Ma. Samples showing fluid- and/or deformation-assisted white mica and biotite reworking gave Rb-Sr mineral apparent ages of 11.1 ± 2.7, 10.16 ± 0.24, 9.7 ± 0.7 and 9.6 ± 0.15 Ma. These ages are interpreted to be associated with late stages of extensional shearing under greenschist-facies metamorphic conditions. Together with published U-Pb zircon ages of migmatite, and S- and I-type granite crystallization, the data indicate that presence of melt in the Naxos migmatite dome lasted for at least 7 Ma (from ~18 to ~11 Ma). This demonstrates that the thermal anomaly resulting from and aiding extensional deformation was a long-lived and not a transient event. We conclude that melt-assisted deformation facilitated large-scale displacement on the Naxos extensional fault system by drastically weakening the extending crust for long periods of time.

National Category
Earth and Related Environmental Sciences
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-155216OAI: oai:DiVA.org:su-155216DiVA, id: diva2:1197772
Available from: 2018-04-13 Created: 2018-04-13 Last updated: 2018-04-16Bibliographically approved
In thesis
1. The metamorphic history of Naxos (central Cyclades, Greece): Deciphering the Oligocene and Miocene exhumation events
Open this publication in new window or tab >>The metamorphic history of Naxos (central Cyclades, Greece): Deciphering the Oligocene and Miocene exhumation events
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High pressure, low temperature (HP-LT) rocks observed at the surface of the Earth are evidence ofpast subduction zones. Understanding the tectonics processes that control the exhumation of HP-LT metamorphic rocks in these subduction zones requires full comprehension of the pressure-temperature-time (P–T–t) cycle that the rocks experienced. In the Cyclades, Greece, the Cycladic Blueschist Unit (CBU) hosts eclogite and blueschist facies rocks. However, the processes that exhumed them are debated. The overall aim of this thesis is to understand how the Eocene HP-LT rocks were exhumed in the central Cyclades based on a study of the metamorphic history of Naxos Island and nearby Syros Island. In this thesis, I carried out a systematic geothermobarometric and geochronological investigation on Naxos to better constrain the P–T–t paths that are recorded by the rocks. The data indicate that high-P metamorphism on Naxos occurred in the Eocene at c. 40 Ma and the HP-LT rocks were exhumed by two tectonic events. The first exhumation event occurred in the Oligocene. The HP-LT rocks were exhumed in a convergent setting by an extrusion wedge. The top of the sequence reached greenschist facies conditions at c.32 Ma, whereas the bottom of the sequence remained at greater depth (equating to pressures of 8–12 kbar). Additionally rocks from southeastern Syros recorded a similar Eocene/Oligocene P–T–t history to that recorded by the top of the sequence on Naxos, suggesting a common Eocene/Oligocene metamorphic history for the central Cyclades. The second exhumation event occurred in the Miocene. The rocks were further exhumed in an extensional setting from c. 20 to 8 Ma. The top of the sequence on Naxos was already in the brittle crust at that time and therefore did not record this Miocene metamorphism. The bottom of the sequence was first isothermally exhumed at high-T conditions and thereafter cooled rapidly.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2018. p. 54
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper ; 371
Keywords
Cycladic Blueschist Unit, exhumation, fluid flow, geothermobarometry, Hellenide orogen, Rb-Sr dating, subduction-zone metamorphism, Heat flow, Lower crust, extensional domain, Metamorphic core complex
National Category
Earth and Related Environmental Sciences
Research subject
Geology
Identifiers
urn:nbn:se:su:diva-155218 (URN)978-91-7797-240-2 (ISBN)978-91-7797-241-9 (ISBN)
Public defence
2018-06-04, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper 4: Manuscript.

Available from: 2018-05-08 Created: 2018-04-13 Last updated: 2018-06-21Bibliographically approved

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