Origin of mud breccia from the Mediterranean Ridge accretionary complex based on evidence of the maturity of organic matter and related petrographic and regional tectonic evidence
✍ Scribed by A. Kopf; A.H.F. Robertson; N. Volkmann
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 988 KB
- Volume
- 166
- Category
- Article
- ISSN
- 0025-3227
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✦ Synopsis
Drilling the Milano mud dome situated in the Olimpi field on the northern flank of the Mediterranean Ridge accretionary complex has documented episodic eruptive activity over the last 1 to Ͼ1.5 million years. Mud extrusion is related to backthrust faulting due to subduction of the Africa Plate beneath a relatively rigid backstop of Cretan continental crust. The mud dome is mainly composed of mud breccia with up to 65% of polymictic clasts embedded in a clayey matrix.
Previously published results from petrography and new maturity data of both clasts and mud matrix presented here allow us to distinguish between two different areas of provenance: (1) A northern province, characterised by a trimodal maturity distribution of organic material, was found for the majority of the mud breccia matrix samples studied. Similarly, some of the clasts studied show the three vitrinite-reflectance populations. These are carbonate and sandstone clasts, inferred to have been eroded from the upper nappes of the Cretan thrust stack after exhumation in the late Miocene, as well as mudstone clasts. Clay mineralogy of these clasts coincides with earlier results on seafloor samples of a northern provenance, recovered in the Hellenic Trench. (2) A southern provenance is proposed for a second group of clasts with a bimodal maturity distribution, not showing the second population (0.64-0.82% Rm). These clasts are litharenites, calcilutites and calciturbidites of a proposed southern provenance, i.e. North Africa.
The presence of huminite in all clast and matrix samples studied (0.26-0.45% Rm) is indicative of a shallow burial history. Estimates regarding the depth of mobilisation of the mud using the regional thermal gradient indicate burial not deeper than 2 km below the seafloor. Organoclastic matrix components mirror the northern clast provenance so that, prior to subduction and subsequent extrusion, deposition of the mud in the Northeastern Mediterranean can be inferred. We propose a model in which sediment from the north was trapped within the forerunner of the Pliny trench; this sediment was deposited above the backstop of the subduction complex, which was later overridden by the accretionary prism as a result of incipient collision; density inversion forces then favoured uprise and extrusion of underconsolidated sediments as mud volcanoes. The mud matrix was probably largely derived from a Messinian succession, although alternatives remain possible.