Chaos and geodynamics: Mélanges, mélange-forming processes and their significance in the geological record

Dilek, Yıldırım; Festa, Andrea; Ogawa, Yujiro; Pini, Gian Andrea

doi:10.1016/j.tecto.2012.08.002

Cited by 36 publications

(21 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…MTDs therefore represent fundamental markers of most of the tectonic events, and the documentation and understanding of their overall architecture, internal fabric, composition, and mechanisms of their downslope deformation and emplacement are relevant for better understanding the characteristics of depositional basins and the evolution of orogenic belts. However, in most orogenic belts and exhumed subduction-accretion complexes, a strong similitude of fabric exists between MTDs with a block-in-matrix fabric (i.e., olistostrome sensu Flores, 1955; sedimentary mélanges, e.g., see Raymond, 1984) and tectonic mélanges (e.g., Hsü, 1974;Raymond, 1984;Cowan, 1985;Bettelli and Panini, 1989;Pini, 1999;Festa et al, 2010Festa et al, , 2013Dilek et al, 2012;Alonso et al, 2015;Balestro et al, 2015b;Platt, 2015;Wakabayashi, 2015). This similitude is the basis of a longlasting debate on the processes of formation of chaotic rock units (i.e., tectonic versus gravitational), and is strongly amplified in metamorphic belts, where polyphase deformation and metamorphic recrystallization to eclogitic conditions commonly rework and obscure the primary internal structure of chaotic rock units.…”

Section: Introductionmentioning

confidence: 99%

Record of Jurassic mass transport processes through the orogenic cycle: Understanding chaotic rock units in the high-pressure Zermatt-Saas ophiolite (Western Alps)

et al. 2017

Self Cite

View full text Add to dashboard Cite

The eclogite facies Zermatt-Saas ophiolite in the Western Alps includes a composite chaotic unit exposed in the Lake Miserin area, in the southern Aosta Valley region. The chaotic unit is characterized by a block-in-matrix texture consisting of ultramafic clasts and blocks embedded within a carbonate matrix. This unit overlies massive serpentinite and ophicarbonate rocks and is unconformably overlain by layered calcschist. Despite the effects of subduction and collision-related deformation and metamorphism, the internal stratigraphy and architecture of the chaotic unit are recognizable and are attributed to different types of mass transport processes in the Jurassic Ligurian-Piedmont Ocean. This finding represents an exceptional record of the preorogenic history of the Alpine ophiolites, marked by different pulses of extensional tectonics responsible for the rough seafloor topography characterized by structural highs exposed to submarine erosion. The Jurassic tectonostratigraphic setting envisioned is comparable to that observed in present-day magma-poor slow-and ultraslow-spreading ridges, characterized by mantle exposure along fault scarps that trigger mass transport deposits and turbiditic sedimentation. Our preorogenic reconstruction is significant in an eclogitized collisional orogenic belt in which chaotic rock units may be confused with the exclusive product of subduction-related tectonics, thus obscuring the record of an important preorogenic history. LITHOSPHERE

show abstract

Section: Introductionmentioning

confidence: 99%

Record of Jurassic mass transport processes through the orogenic cycle: Understanding chaotic rock units in the high-pressure Zermatt-Saas ophiolite (Western Alps)

et al. 2017

Self Cite

View full text Add to dashboard Cite

show abstract

“…Silver and Beutner 1980;Raymond 1984;Cowan 1985;Suzuki 1986;Kusky and Bradley 1999;Pini 1999;Alonso et al 2006;Festa et al 2010a;Wakabayashi and Dilek 2011;Dilek et al 2012;. They may commonly form at different tectonic settings and structural levels during the evolution of convergent plate margins, reflecting a close relationship between the active processes (tectonic, sedimentary, and diapiric), the physical and mechanical conditions (e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, systematic and process-oriented, inter-disciplinary studies of chaotic rock units with block-in-matrix structure may provide much-needed information about convergent plate margin evolution (e.g. Dilek et al 2012).…”

Section: Introductionmentioning

confidence: 99%

“…This is the case for different types of mélange and BIM occurrence worldwide (e.g. see localities and references in Festa et al (2010a), Wakabayashi and Dilek (2011), and Dilek et al (2012)), where an interesting and prolonged debate has focused on the relative contribution of sedimentary, diapiric, and tectonic processes in their formation. On the contrary, in the Western Alps a forthright debate on mélanges and mélange-forming processes is still awaited probably because the severe tectonic shearing, folding, transposition, and strong metamorphic recrystallization under highpressure (HP) to ultra-high-pressure (UHP) conditions prevent the acquisition of useful information on the nature of sedimentary or diapiric origin.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Tectonic significance of different block-in-matrix structures in exhumed convergent plate margins: examples from oceanic and continental HP rocks in Inner Western Alps (northwest Italy)

Balestro

Festa

Tartarotti

2014

International Geology Review

Self Cite

View full text Add to dashboard Cite

In the Inner Western Alps, three different types of block-in-matrix structures (BIMs) formed sequentially through time at a convergent plate margin. These show the superposition of progressive deformation from (i) subduction to eclogite-facies depths, (ii) collision, accretion, and exhumation of oceanic crust, represented by the Monviso Meta-ophiolite Complex, to (iii) collision, accretion, and exhumation of the continental Dora Maira units. The Type 1 occurs in the metasedimentary cover of the Dora Maira Unit and consists of a map-scale broken formation with boudinaged 'native' blocks of marble (Early Jurassic) in a calcschist matrix. It results from the tectonic overprinting of exhumation-related folding (D2-stage) on an earlier subduction-related dismembered succession (D1-stage). Type 1 also includes 'non-mappable' BIMs with 'exotic' blocks, resulting from the gravitational collapse of the Triassic carbonate platform of European Continental Margin, triggered by the Early Jurassic rifting. In the Monviso Meta-ophiolite Complex, Types 2 and 3 represent tectonically induced broken and dismembered formations, respectively. They differ from each other in the degree of stratal disruption of primary interbedded horizons of mafic metabreccia (Type 3) and mafic metasandstone (Types 2 and 3) sourced by the Late Jurassic-Early Cretaceous denudation of an oceanic core complex. Dismembered interbeds (Type 2) and isolated blocks were mixed together (Type 3) by the overlap of D2 tectonics and late-to post-exhumation extensional shearing (D3-stage). Development of these types of BIMs may be common in many exhumed convergent plate margins, where severe tectonics and metamorphic recrystallization under high-pressure conditions normally prevent the reconstruction of BIMs or mélange-forming processes. Our findings show that documenting the mode and time of the processes forming BIMs is highly relevant in order to reconstruct the oceanic seafloor morphology and composition of associated stratigraphic successions, and their control in the evolution of those convergent plate margins.

show abstract

“…The evolution of this spectacular structure is still poorly understood. Importance of sedimentary processes at the surface versus tectonic processes at depth, or both in combination, remains a matter of debate (Dilek et al, 2012). In any case, BIM structures imply contrasts in mechanical properties -the blocks undergoing no notable permanent deformation while the matrix must deform at very high strain rate, despite identical conditions in terms of temperature and stress.…”

Section: W Friederich Et Al: Seismic Visibility Of a Deep Subductiomentioning

confidence: 99%

Seismic visibility of a deep subduction channel – insights from numerical simulation of high-frequency seismic waves emitted from intermediate depth earthquakes

et al. 2014

View full text Add to dashboard Cite

Abstract. Return flow in a deep subduction channel (DSC) has been proposed to explain rapid exhumation of high pressure-low temperature metamorphic rocks, entirely based on the fossil rock record. Supported by thermo-mechanical models, the DSC is envisioned as a thin layer on top of the subducted plate reaching down to minimum depths of about 150 km. We perform numerical simulations of highfrequency seismic wave propagation (1-5 Hz) to explore potential seismological evidence for the in situ existence of a DSC. Motivated by field observations, for modeling purposes we assume a simple block-in-matrix (BIM) structure with eclogitic blocks floating in a serpentinite matrix. Homogenization calculations for BIM structures demonstrate that effective seismic velocities in such composites are lower than in the surrounding oceanic crust and mantle, with nearly constant values along the entire length of the DSC. Synthetic seismograms for receivers at the surface computed for intermediate depth earthquakes in the subducted oceanic crust for models with and without DSC turn out to be markedly influenced by its presence or absence.While for both models P and S waveforms are dominated by delayed high-amplitude guided waves, models with DSC exhibit a very different pattern of seismic arrivals compared to models without DSC. The main reason for the difference is the greater length and width of the low-velocity channel when a DSC is present. Seismic velocity heterogeneity within the DSC or oceanic crust is of minor importance. The characteristic patterns allow for definition of typical signatures by which models with and without DSC may be discriminated.The signatures stably recur in slightly modified form for earthquakes at different depths inside subducted oceanic crust. Available seismological data from intermediate depth earthquakes recorded in the forearc of the Hellenic subduction zone exhibit similar multi-arrival waveforms as observed in the synthetic seismograms for models with DSC. According to our results, observation of intermediate depth earthquakes along a profile across the forearc may allow to test the hypothesis of a DSC and to identify situations where such processes could be active today.

show abstract

Chaos and geodynamics: Mélanges, mélange-forming processes and their significance in the geological record

Cited by 36 publications

References 45 publications

Record of Jurassic mass transport processes through the orogenic cycle: Understanding chaotic rock units in the high-pressure Zermatt-Saas ophiolite (Western Alps)

Record of Jurassic mass transport processes through the orogenic cycle: Understanding chaotic rock units in the high-pressure Zermatt-Saas ophiolite (Western Alps)

Tectonic significance of different block-in-matrix structures in exhumed convergent plate margins: examples from oceanic and continental HP rocks in Inner Western Alps (northwest Italy)

Seismic visibility of a deep subduction channel – insights from numerical simulation of high-frequency seismic waves emitted from intermediate depth earthquakes

Contact Info

Product

Resources

About