Ophiolites, blueschists and mélanges in convergent margin tectonics (co-organized)
Co-Conveners: Manuel Pubellier , Philippe Agard , Gian Andrea Pini 
Oral Programme
 / Mon, 03 May, 08:30–12:00  / Room 32
Poster Programme
 / Attendance Tue, 04 May, 17:30–19:00  / Hall A

This session derives from the merging of two previous sessions whose topics are historically linked: (1) “Ophiolites, blueschists and convergent margin tectonics” and (2) “Mélanges and broken formations: Processes vs. geodynamic settings of their formation”.

(1) Most ophiolites appear to have formed in suprasubduction zone tectonic settings and to have emplaced through collisions of continental margins with intra-oceanic arc-trench rollback systems. Blueschist assemblages, which are spatially associated with ophiolitic thrust sheets in orogenic belts, record high-P/low-T metamorphic conditions of subducted lithospheric material and their exhumation through a combination of specific thermal regimes and kinematic conditions along subduction channels in convergent zones. Ophiolite emplacement and blueschist exhumation are critical components of accretionary tectonics in continental margin evolution. Better understanding of the crustal and mantle processes involved in these events provides significant insights for inter-plate mechanical coupling in subduction factories. In this session, we will explore through process-oriented interdisciplinary approach different mechanisms of ophiolite emplacement and blueschist formation/exhumation in ancient and modern convergent margin settings to explore the spatial and temporal relations between global plate tectonic events, convergent margin tectonics and subduction zone processes. Contributions based on field-oriented structural and petrological studies, thermomechanical and analog modeling, and geophysical methods are welcome.

(2) Chaotic and mixed rock units forming mélanges may develop in diverse geodynamic environments, characterized by extensional, strike-slip or contractional tectonics. In the latter, mélanges represent a significant component of accretionary wedges and collisional mountain belts (from the circum-Mediterranean and Alpine-Himalayan belt to the circum-Pacific regions). Contributions on mélanges in this session will present case studies, discussing three main problems: (1) whether or not genetic relationships exist between mélange types and geodynamic setting of their formation; (2) the role of sedimentary (mass-transport) vs. contractional tectonic processes at the onset and during the evolution of different mélange types; and, (3) the nature of spatial relations between broken formations and true tectonic mélanges and their significance for mélange-forming processes. Interdisciplinary and field-based studies of mélanges and covering various tectonic settings in which mélanges may have formed are welcome.

Public information: The related "Poster Summaries and Discussion" session (PSD 83) will be held on Tuesday, 04 May, at room 35, from 9:00 to 9:45. Two solicited short oral presentations of selected posters are planned: 09:00-9:10 Ogata et al. (poster A537); 9:10-9:20 Utsunomiya et al. (poster A520). An open discussion on ophiolite and mélange topics will follow (9:20-9:45).
An informal, open discussion of the posters is expected during the poster attendance time, on Tuesday, 04 May 17:30–19:00.
Related event: PSD83 – TS6.5/GD5.10/GMPV55
Tue, 04 May, 09:00–09:45  / Room 35