Anastasakis, George (1981) Sedimentation and shallow structure of the south Cretan-Karpathos sector of the Hellenic trench system. Doctoral thesis, Keele University.

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Abstract

The Central Hellenic Trench System is part of a well-developed convergent plate boundary, the Hellenic Trench and Arc, associated with the continental collisions of the Aegean and African Plates,and divided Into the Gavdos, Gortys, PHny and Strabo sectors.
The present study evaluates the principal structural, stratigraphic and sedimentological factors Involved in the evolut1on~of this tectonically active region. The study utilised bathymetric, seismic reflection and other geophysical data, and involved examination of gravity and piston cores, and petrological and mineralogical analyses of carbonate and non-carbonate components.
This study has demonstrated that the West Pliny portion of the Central Hellenic Trench has been an active sector of the System since the Upper Miocene and displays a morphology typical of a fully mature active subduction system, while the Gavdos-Gortys sectors are marked by features indicative of an early stage of development of the subduction complex. Between the eastern tip of Crete and Kasos the morphostructural features are attributed to a lateral modification of the mature subduction complex by a new stress regime, probably initiated by suturing in the region south of Kasos. The Strabo Trench is connected with major strike- slip movement and 1s separated from the PHny by an area which, to the east is characterised by strong uplift induced by convergence of the strike slipe system, while to the west, the inter-trench area is dominated by pull-apart basins associated with diverging strike-slip faults.
Seismic facies analysis of the Central Hellenic Trench region demonstrates that the major tectonic events of the Upper Miocene, Middle Pliocene and Lower Quaternary known from the S. Aegean Sea islands can be recognised in this offshore area, south of Crete-Rhodes, and that the major water input during the Pliocene regression was from the west.
Central Hellenic Trench lithofacies analysis shows a close correlation between the general depositional province and the nature of the sedimentary assemblage. The cores reveal a general cyclic stratigraphy broadly corresponding to that established in less tectonically active areas of the Eastern Mediterranean. The Late Quaternary sedimentation rates calculated for cores from the topographic highs and isolated basins are consistent with rates deduced from seismic profiles but there is a conspicuous difference between these two parameters in sediments from the trenches. This difference is attributed to active underthrusting of the trench-fill beneath the trench floor.
Most sands from the Trench region belong compositionally to the
Collision Orogen Provenance field and heavy mineral analyses indicate an
extension of the Alpine nappes, known from the islands of the S. Aegean
Sea, into the Mediterranean Ridge and emphasise the importance of internal
sediment-sources. Most Mg-rich calcite in the pelagic carbonates is
inorganically precipitated below the water-sediment interface. Ba2+ ions
2+
influence the precipitation of Mg in the secondary minerals while the 2+
amount of Sr controls the degree of initial calcite alteration. A new method for quantitative determination of amorphous material (composed of SI, Al, Fe and Mg) reveals a general increase with depth of this constituent through alteration of an amorphous volcanic component to material characterised as opal A.
Lateral variations 1n the clay minerals are attributed to relative proximity to different sources, while vertical variations are larger and related to the depositional background of each layer, together with post- deposltional transformation of the smectite and vermiculite to chlorite and mite.
The genesis of sapropelic layers is briefly examined and the sedimentary associations of the Central Hellenic Trench are correlated with possible ancient counterparts. The Hellenic Trench appears to be significantly more complex, in terms of structural and sedimentary history than any other trench to which it has been previously compared.

Item Type: Thesis (Doctoral)
Subjects: Q Science > QE Geology
Divisions: Faculty of Natural Sciences > School of Geography, Geology and the Environment
Depositing User: Lisa Bailey
Date Deposited: 19 May 2020 15:11
Last Modified: 19 May 2020 15:11
URI: https://eprints.keele.ac.uk/id/eprint/8010

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