Abstract
Multiple episodes of deformation during the tectonic evolution of orogenic belts and ancient subduction-accretion complexes cause obfuscation of primary block-in-matrix fabric of mélanges, and thereby making the recognition of their tectonic, sedimentary or diapiric origin difficult. Here we present a comprehensive overview and synthesis of a diverse set of field-based stratigraphic and structural criteria, which are at the base of geological mapping rules, to differentiate between various mélange types, developed by disparate geological processes and mechanisms. We first define the current concepts of mélange and mélange nomenclature, and describe the most diagnostic features of tectonic, sedimentary and diapiric mélanges at different scales. We discuss some of the main issues complicating the application of these diagnostic criteria, such as: (i) similarities between the block-in-matrix fabric of different mélange types formed in partially lithified sediments at shallow structural levels, (ii) transformation of fabric elements with increased depth due to tectonic reworking and recrystallization processes, (iii) significance of “exotic” versus “native” blocks in mélange matrix, and (iv) age relationships between blocks and matrix in a mélange. We introduce two additional criteria in approaching these complexities and in recognizing different processes of polygenetic mélanges formation in the field when primary diagnostic fabrics were reworked by multiple deformational events. These new criteria are based on (i) the coherence between lithological compositions of mélange components (blocks and matrix) and characteristics and tectonic evolution of the geodynamic setting of their formation (“tectonic environment criterion”), and (ii) specificity and kinematic coherence in the distribution of deformation between blocks and the matrix (“deformation criterion”). The discussed diagnostic criteria can be applied to all field-based investigations of mélanges and broken formations in orogenic belts and exhumed subduction-accretion complexes around the world, regardless of their location, age, and tectonic history.
Original language | English |
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Pages (from-to) | 7-30 |
Number of pages | 24 |
Journal | Gondwana Research |
Volume | 74 |
DOIs | |
Publication status | Published - 1 Jan 2019 |
Funding
Our studies in mélanges in modern and ancient subduction-accretion complexes around the world have been supported by research grants from the Università di Torino (Ricerca Locale “ex 60%” 2014–2018) to AF; from the Italian Ministry of Education, University and Research (“Finanziamento annuale individuale delle attività base di ricerca” 2017) to AF and (PRIN 2010/2011 “GEOPROB” – Geodynamic Processes of Oceanic Basins, n. 2010AZR98L_002 ) to AF and GAP, the Università di Trieste (FRA 2013) to GAP, from the Spanish Government (grant CGL2012-34475 ) to AF and GAP, and from the NSF , Ocean Drilling Program (ODP) and NATO grants to YD. We extend our sincere thanks to the two anonymous reviewers for their constructive and thorough reviews, from which we have benefited greatly in revising our manuscript, and to the Editor-in-Chief Santosh for his careful editorial handling. Insightful discussions on various aspects of the mélange concept and mélange terminology with J.L., Alonso, P. Ballance, E. Barbero, G. Balestro, J. Bradshaw, A. Camerlenghi, G. Codegone, M. Cloos, D.S. Cowan, F. Dela Pierre, L.P. Fernandez, K.-H. Hisada, C.C. Lucente, C. Mantey, A. Marcos, M. Marroni, I. Milushi, S. Mittempergher, G.F. Moore, E. Mutti, Y. Ogawa, L. Pandolfi, J. Pettinga, A. Rassios, L.A. Raymond, F. Remitti, E. Sarifakioglu, M. Shallo, M.I. Spalla, B. Sporly, A. Suarez, P. Tartarotti, J. Wakabayashi, S. Wassmann and Y. Yamamoto were most helpful for the formulation of our ideas and interpretations presented in the paper. Our studies in mélanges in modern and ancient subduction-accretion complexes around the world have been supported by research grants from the Università di Torino (Ricerca Locale “ex 60%” 2014–2018) to AF; from the Italian Ministry of Education, University and Research (“Finanziamento annuale individuale delle attività base di ricerca” 2017) to AF and (PRIN 2010/2011 “GEOPROB” – Geodynamic Processes of Oceanic Basins, n. 2010AZR98L_002) to AF and GAP, the Università di Trieste (FRA 2013) to GAP, from the Spanish Government (grant CGL2012-34475) to AF and GAP, and from the NSF, Ocean Drilling Program (ODP) and NATO grants to YD. We extend our sincere thanks to the two anonymous reviewers for their constructive and thorough reviews, from which we have benefited greatly in revising our manuscript, and to the Editor-in-Chief Santosh for his careful editorial handling. Insightful discussions on various aspects of the mélange concept and mélange terminology with J.L., Alonso, P. Ballance, E. Barbero, G. Balestro, J. Bradshaw, A. Camerlenghi, G. Codegone, M. Cloos, D.S. Cowan, F. Dela Pierre, L.P. Fernandez, K.-H. Hisada, C.C. Lucente, C. Mantey, A. Marcos, M. Marroni, I. Milushi, S. Mittempergher, G.F. Moore, E. Mutti, Y. Ogawa, L. Pandolfi, J. Pettinga, A. Rassios, L.A. Raymond, F. Remitti, E. Sarifakioglu, M. Shallo, M.I. Spalla, B. Sporly, A. Suarez, P. Tartarotti, J. Wakabayashi, S. Wassmann and Y. Yamamoto were most helpful for the formulation of our ideas and interpretations presented in the paper.
Funders | Funder number |
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Spanish Government | CGL2012-34475 |
Università di Torino | |
Università di Trieste | FRA 2013 |
National Science Foundation | |
North Atlantic Treaty Organization | |
Ministero dell’Istruzione, dell’Università e della Ricerca | 2010AZR98L_002 |
National Science Foundation |
Keywords
- Diagnostic Criteria
- Mélanges
- Orogenic belts
- Polygenetic mélanges
- Subduction plate interface