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- Peillod, Alexandre, 1988-
(author)
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The metamorphic history of Naxos (central Cyclades, Greece) : Deciphering the Oligocene and Miocene exhumation events
- 2018
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 2. |
- Zhang, Xiaojing, 1984-
(author)
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Provenance of late Paleozoic and Mesozoic clastic sediments of Taimyr and their significance for understanding Arctic tectonics
- 2013
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Licentiate thesis (other academic/artistic)abstract
- The Taimyr Peninsula is a key element in the circum-Arctic region and represents the northern margin of the Siberian Craton. The Taimyr Peninsula preserves late Paleozoic through Mesozoic clasitic sedimentary successions in its Mesozoic fold belt, providing an ideal location to investigate the Mesozoic tectonic evolution associated with the opening of Amerasia Basin within a circum-Arctic framework. This thesis aims to establish the tectonic setting in which the late Paleozoic through Mesozoic sediments of Taimyr were deposited, in order to correlate Taimyr with other Arctic terranes utilizing provenance investigations. Multiple methods are adopted, including petrography, heavy mineral analysis and detrital zircon U-Pb geochronology. The preliminary results of this work indicate that the late Paleozoic sediments of southern Taimyr were deposited in a foreland basin of the Uralian orogen during Uralian orogeny. The final collision between Baltica and Siberia in the last stage of Uralian orogenesis occurred between Early and Late Permian. Early Cretaceous sediments in northern Taimyr were mainly derived from Siberian Trap-related magmatism in Taimyr. Cretaceous sediment deposition is unrelated to Jurassic to Cretaceous rifting associated with the Verkhoyansk fold belt and instead relates to a rifting or post-rifting passive margin setting.
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