ZIP Starter 2 (WP4.2): Fieldwork along and across the Alpine fossil subduction interface / 2 weeks.
Coordination: T. John (Berlin University)
Contributors: P. Agard (Paris University), M. Scambelluri (Genova University), S. Angiboust (GFZ Potsdam).
Training has been focussed on field observation of fossil plate interface from depth of 10 to nearly 100 km – with upscaling from the mineral (and analytical) scale to the scale of the whole plate interface. The fieldtrip provided an opportunity to study and walk down the fossil subduction interface, investigating remnants preserved from 10-15 km (Apennines) to 30-50 km (Dent Blanche) and finally 80 km depths (Monviso, Voltri).
Aim: disclose the nature and complexity of the subduction interface and show the key proxies of this geological environment. Training took place through critical observations in petrology and structures (with focus on fluid and rheology) and scale transfer from the field to the subduction interface. The fieldtrip provided a unique training in terms of field expertise and upscaling of geochemical tracers and petrological tools. In addition to field work, 2 days of indoor lecture provided general overviews of HP/UHP rocks, promoting discussion on field observations.
Through this field trip the ESRs and ERs developed real skills in tectonics and petrology, field measurements, acquisition of relevant data and ability to envision scale transfer. These are crucial prerequisites for understanding the combination of processes operating within the subduction interface at various space and time scales.
ZIP Starter 2 — Walking along the plate interface of the Alpine subduction zone
Day 1-3 (july 8-10): arrival of participants and transfer to Modena. Observation of accretionary wedge sediments, their tectonic transport to 5-10 km down the subduction zone. Discussion of rocks, field sketches and current theories gave the students understanding of the genesis of sediments at the surface and their subsequent accumulation and transport to greater depth.
Thanks to our field leaders Paola Vannucchi and Francesca Remitti for introducing us to the “accretionary world”.
Days 4-5 (July 11-12): 30-40 km down! Dent Blanche and Ophiolite units of the Western Alps (Valpelline, Aosta Valley) showing subduction accretion of continental and ophiolitic slices to 30-40 depths during blueschist-facies metamorphism. Migration of the plate interface during progressive accretion of continental and oceanic rocks has been thoroughly discussed in a (cold) field environment.
Day 5 (july 12, Saturday). The fieldtrip to Valpelline has been followed by one day of indoor lectures at Pontboset. Presentations by Onno Onken, Harold Tobin, Ylona van Dinther and Jason Phipps Morgan on the behaviour of plate interface domains, on the geophysical monitoring of the seismogenic zone and on numerical modelling plate interface settings, on plate serpentinization in bend-faults environments and the implications on plate interface domains.
Days 6-8 (July 13-15): 70-80 km down! Cold and rainy rise up the to Monviso. View of exposures of high- pressure eclogite facies ophiolitic rocks detached from accreted the plate interface. Hands-on rocks and on tectonic structures and explanation by Philippe Agard and Samuel Angiboust. Overnight stay in Rifugio SellaOn day 7, we analysed unique eclogite breccias, revealing fluid overpressure and possibly seismogenic tremors, giving way to the development of plate-interface mylonitic shear zones. Overnight stay in Rifugio SellaOn day 7, we analysed unique eclogite breccias, revealing fluid overpressure and possibly seismogenic tremors, giving way to the development of plate-interface mylonitic shear zones.
Transfer at hotel Torinetto and presentations/lectures/discussions during day 8 on major aspects related to the downward transition from the seismogenic zone into intermediate-depths. Indoor presentations by Thomas Pettke, Philippe Agard, Marco Scambelluri, Timm John and Peter van Keken on the structure, petrology, fluid flow and geophysical modelling of deep plate interface domains.
Day 9 (July 16): 70-80 km down and into the mantle. Early morning transfer from Hotel Torinetto in Sampeyre to the Ligurian Alps, inland Genova. Jump into subduction-zone serpentinites, their high-pressure history of eclogite facies dehydration with formation of vein systems that drain and transport the subduction-zone fluids. Discussion lead by Marco Scambelluri and Timm John. Hands on rocks and discussions on progressive dehydration of serpentinized mantle peridotite in subduction environments.
Overnight stay in Genova and end of the field trip.
Day 10 (july 17, Thursday): departure
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