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The role of ductile flow of the lower crust in controlling heat advection in the footwall of the Naxos extensional fault system (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.
Stockholm University, Faculty of Science, Department of Geological Sciences.
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(English)In: Article in journal (Refereed) Submitted
Abstract [en]

Geothermobarometric and structural work indicates that metamorphism in the footwall of the migmatitic Naxos core complex is strongly coupled to heat advection in the lower crust. Using the average pressure-temperature (P-T) method of THERMOCALC for geothermobarometric calculations coupled with detailed textural work, we constructed P-T paths for nine samples that have different spatial relationships to the Naxos extensional fault system and a migmatite dome in the center of the Naxos core complex. All nine samples show early near isothermal decompression. The late, cooling segment of the P-T paths shows systematic spatial differences in temperature gradients relative to the distance of the samples below the Naxos extensional detachment (representing the top of the Naxos extensional fault system). The differences in late thermal gradients correlate with finite strain, a proxy for the intensity of ductile flow. High finite strain correlates with high thermal gradients that do not change with distance below the Naxos detachment, whereas low finite strain correlates with downward decreasing thermal gradients. The difference in late thermal gradients and finite strain define a thermal asymmetry controlled by ductile flow, which we interpret to show that ductile flow controlled advection of heat and thus high-grade metamorphism on Naxos. We conclude that advective heating is an important driver of metamorphism in extensional settings.

Keywords [en]
Heat flow, Geothermobarometric, Lower crust, Extensional domain, Metamorphic core complex, Aegean Sea, Naxos
National Category
Earth and Related Environmental Sciences
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-155214OAI: oai:DiVA.org:su-155214DiVA, id: diva2:1197771
Available from: 2018-04-13 Created: 2018-04-13 Last updated: 2018-06-26Bibliographically 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)
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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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