Fluid-rock interaction in mud volcanoes and fault zones at the Hellenic Subduction Zone

This PhD project focusses on flu­id-rock in­ter­ac­tion in serpentine- and clay-be­a­ring de­po­sits from sub­duc­tion zone-re­la­ted mud volcanoes and fault zo­nes. Se­di­ment co­res and pore wa­ter sam­ples are ex­ami­ned re­gar­ding their mi­ne­ra­lo­gy, che­mi­cal and iso­to­pic si­gna­tu­re as well as their phy­si­cal pro­per­ties. Material expelled by mud volcanoes and fault zones provide the opportunity to investigate processes like fluid-rock interactions which take place in greater depth. In case of the main working area, the Mediterranean Ridge (MedRidge) Accretionary Complex in the Mediterranean Sea, the pore fluids show signatures, which point to mobilization depths as deep as the décollement (5-7.5 km) (Camerlenghi et al., 1995; Schulz et al, 1997).

The MedRidge Accretionary Complex is the fastest growing accretionary complex on earth, hosts many mud volcanoes (> 150) and is caused by the Hellenic Subduction Zone. Although the subduction zone setting shows the highest seismic activity in Europe, larger earthquakes with magnitudes > 6.5 are rare. The composition of the subducted material, fluid-rock interaction and hence mobilized fluids might play a major role in earthquake triggering. A connection between the eruption of mud volcanoes through overpressured fluids and earthquakes has already been suggested (Zhong et al., 2019; Bonini, 2019). Through the investigation of expelled mud breccia and pore water samples of mud volcanoes and fault zones, deep seated water-rock interactions will be elucidated.

Pore-water freshening has been observed in different intensity within many mud volcanoes at the MedRidge. Some pore waters of mud volcanoes in the Olimpi Mud Volcanic Field (south of Crete) show reaction temperatures of ~200°C to 280°C, which are calculated by the Mg-Li geothermometer (Kharaka and Mariner, 1989). Those temperatures are much higher than the temperature range in which clay mineral dehydration like Illitization takes place (60-160°C) and point to a deep source of the expelled pore fluids. Mobile elements like B and Li and their isotopes are unique tracers which are used to reveal information about fluid migration and to model water-rock interaction (Kopf et al., 2003; Deyhle and Kopf, 2005).

Mud breccia material and pore waters are decoupled within the MedRidge mud volcanoes and therefore mud breccia will be examined by further methods including petrographic and mineralogical investigations (e.g. X-ray diffractometry and analysis of clay mineral fraction (< 2 µm).  Geotechnical experiments on mud breccia material expelled by the thrust- and backthrust faults between the MedRidge Accretionary Complex and the Cretan Margin are conducted to explain the absence of greater earthquakes in this region.  Torsional Ring Shear test will be conducted to determine the residual shear strength of mud breccia material to characterize frictional properties and other parameters to unravel geodynamic processes.

The investigated material occurs from Poseidon expedition P410 in 2011 and is supplemented with material from Sonne expedition SO278, which took place in October/November 2020. During SO278 expedition, mud volcanoes at different positions relative to the subduction zone have been sampled. This enables the possibility to compare the pore water signatures and illuminate differences of the ongoing reactions in consideration of the relative position to the subduction zone.

Duration: 01.07.2019-30.06.2022

Contacts: Nele Behrendt, Achim Kopf

References

• Bonini, M., Rudolph, M. L., Manga, M. (2016) Long- and short-term triggering and modulation of mud volcano eruptions by earthquakes. Tectonophysics 672-673: 190-211.
• Bonini, M. (2019) Seismic loading of fault-controlled fluid seepage systems by great subduction earthquakes. Scientific Reports
• Camerlenghi, A., Cita, M. B., Della Vendova, B., Fusi, N., Mirabile, L., Pellis, G. (1995) Geophysical Evidence of Mud Diapirism on the Mediterranean Ridge Accretionary Complex. Marine Geophysical Researches 17: 115-141.
• Deyhle, A., Kopf, A. J. (2005) The use and usefulness of boron isotopes in natural silicate-water systems. Physics and Chemistry of the Earth 30: 1038-1046.
• Kharaka, Y. K., Mariner, R. H. (1989) Chemical Geothermometers and Their Application to Formation Waters from Sedimentary Basins. Thermal History of Sedimentary Basins pp.: 99-117.
• Kopf, A., Mascle, J., Klaeschen, D. (2003) The Mediterranean Ridge: A mass balance across the fastest growing accretionary complex on Earth. Journal of Geophysical Research 108.
• Schulz, H. M., Emeis, K. C., Volkmann, N. (1997) Organic carbon provenance and maturity in the mud breccia from the Napoli mud volcano: Indicators of origin and burial depth. Earth and Planetary Science Letters 147: 141-151.
• Zhong, S., Wan, Z., Duan, B., Liu, D., Luo, B. (2019) Do earthquakes trigger mud volcanoes? A case study from the southern margin of the Junggar Basin, NW China. Geological Journal 54: 1223-1237.