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Geosciences
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Geology of Mélanges
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Geology of Mélanges

A special issue of Geosciences (ISSN 2076-3263).

Deadline for manuscript submissions: closed (31 August 2019) | Viewed by 23866

Special Issue Editor

Dr. Kei Ogata

E-Mail Website
Guest Editor
Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse (DiSTAR), Università degli Studi di Napoli "Federico II”, Complesso Universitario Monte S.Angelo - Edificio L, Via Vicinale Cupa Cintia 21, 80126 Napoli, Italy
Interests: structural geology; stratigraphy; shallow crustal deformation; sedimentary geology

Special Issue Information

Dear Colleagues,

In the shallow parts of accretionary complexes, mélanges may directly originate from sedimentary mass-transport processes (sedimentary mélanges), and/or mud-diapiric processes (diapiric mélanges), being subsequently tectonically deformed at progressively deeper crustal levels (tectonic mélanges). This continuous interplay of overlapping processes leads to the development of polygenetic mélanges, widely represented in exhumed orogenic belts. Nonetheless their widespread occurrence, poor communication still lingers among specialists dealing with mass transport deposit, subsurface remobilization and studies on mélange-forming processes in the shallow subsurface. In this framework, multidisciplinary and comparative studies of “fossil” and “modern” mass transport deposits and mud diapirs identified in mountain chains and contemporary sedimentary basins, respectively, provide hard facts on long debated arguments, like what influences preservation of primary (e.g. sedimentary) features in mélanges during the subsequent tectonic/mud-diapiric deformations, and, at larger scales, what control the distribution and types of “fossil” mass transport deposits in light of the increasing recognition and (re)interpretation of sedimentary mélanges in subduction and collisional settings.

The aim of this Special Issue is to outline the current and further ways of research on polyphased “chaotic” units, focusing on the earlier and shallower phases of deformation, at the various scales.

Dr. Kei Ogata
Guest Editor

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Keywords

  • Sedimentary-diapiric mélanges
  • mass transport deposits
  • subsurface sediment remobilization
  • olistostromes

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Published Papers (4 papers)

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Research

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23 pages, 5639 KiB  
Article
Distinguishing the Mélange-Forming Processes in Subduction-Accretion Complexes: Constraints from the Anisotropy of Magnetic Susceptibility (AMS)
by Claudio Robustelli Test, Andrea Festa, Elena Zanella, Giulia Codegone and Emanuele Scaramuzzo
Geosciences 2019, 9(9), 381; https://doi.org/10.3390/geosciences9090381 - 31 Aug 2019
Cited by 7 | Viewed by 3674
Abstract
The strong morphological similitude of the block-in-matrix fabric of chaotic rock units (mélanges and broken formations) makes problematic the recognition of their primary forming-processes. We present results of the comparison between magnetic fabric and mesoscale structural investigations of non-metamorphic tectonic, sedimentary, and polygenetic [...] Read more.
The strong morphological similitude of the block-in-matrix fabric of chaotic rock units (mélanges and broken formations) makes problematic the recognition of their primary forming-processes. We present results of the comparison between magnetic fabric and mesoscale structural investigations of non-metamorphic tectonic, sedimentary, and polygenetic mélanges in the exhumed Late Cretaceous to early Eocene Ligurian accretionary complex and overlying wedge-top basin succession in the Northern Apennines (northwest Italy). Our findings show that the magnetic fabric reveals diagnostic configurations of principal anisotropy of magnetic susceptibility (AMS) axes orientation that are well comparable with the mesoscale block-in-matrix fabric of mélanges formed by different processes. Broken formations and tectonic mélanges show prolate and neutral-to-oblate ellipsoids, respectively, with magnetic fabric elements being consistent with those of the mesoscale anisotropic “structurally ordered” block-in-matrix fabric. Sedimentary mélanges show an oblate ellipsoid with a clear sedimentary magnetic fabric related to downslope gravitational emplacement. Polygenetic mélanges show the occurrence of a cumulative depositional and tectonic magnetic fabric. The comparison of field and laboratory investigations validate the analysis of magnetic features as a diagnostic tool suitable to analytically distinguish the contribution of different mélange forming-processes and their mutual superposition, and to better understand the geodynamic evolution of subduction-accretion complexes. Full article
(This article belongs to the Special Issue Geology of Mélanges)
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0 pages, 18659 KiB  
Article
Superposed Sedimentary and Tectonic Block-In-Matrix Fabrics in a Subducted Serpentinite Mélange (High-Pressure Zermatt Saas Ophiolite, Western Alps)
by Paola Tartarotti, Sara Sibil Giuseppina Guerini, Francesca Rotondo, Andrea Festa, Gianni Balestro, Gray E. Bebout, Enrico Cannaò, Gabe S. Epstein and Marco Scambelluri
Geosciences 2019, 9(8), 358; https://doi.org/10.3390/geosciences9080358 - 16 Aug 2019
Cited by 20 | Viewed by 5994
Abstract
The primary stratigraphic fabric of a chaotic rock unit in the Zermatt Saas ophiolite of the Western Alps was reworked by a polyphase Alpine tectonic deformation. Multiscalar structural criteria demonstrate that this unit was deformed by two ductile subduction-related phases followed by brittle-ductile [...] Read more.
The primary stratigraphic fabric of a chaotic rock unit in the Zermatt Saas ophiolite of the Western Alps was reworked by a polyphase Alpine tectonic deformation. Multiscalar structural criteria demonstrate that this unit was deformed by two ductile subduction-related phases followed by brittle-ductile then brittle deformation. Deformation partitioning operated at various scales, leaving relatively unstrained rock domains preserving internal texture, organization, and composition. During subduction, ductile deformation involved stretching, boudinage, and simultaneous folding of the primary stratigraphic succession. This deformation is particularly well-documented in alternating layers showing contrasting deformation style, such as carbonate-rich rocks and turbiditic serpentinite metasandstones. During collision and exhumation, deformation enhanced the boudinaged horizons and blocks, giving rise to spherical to lozenge-shaped blocks embedded in a carbonate-rich matrix. Structural criteria allow the recognition of two main domains within the chaotic rock unit, one attributable to original broken formations reflecting turbiditic sedimentation, the other ascribable to an original sedimentary mélange. The envisaged geodynamic setting for the formation of the protoliths is the Jurassic Ligurian-Piedmont ocean basin floored by mostly serpentinized peridotites, intensely tectonized by extensional faults that triggered mass transport processes and turbiditic sedimentation. Full article
(This article belongs to the Special Issue Geology of Mélanges)
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17 pages, 5120 KiB  
Article
A Geophysical-Geochemical Approach to the Study of the Paleogene Julian—Slovenian Basin “Megabeds” (Southern Alps—Northwestern Dinarides, Italy/Slovenia)
by Kei Ogata, Željko Pogačnik, Giorgio Tunis, Gian Andrea Pini, Andrea Festa and Kim Senger
Geosciences 2019, 9(4), 155; https://doi.org/10.3390/geosciences9040155 - 3 Apr 2019
Cited by 7 | Viewed by 3930
Abstract
The Paleogene “megabeds” of the Julian-Slovenian Basin are regional, basin-wide deposits, produced by catastrophic carbonate platform collapses. They record the emplacement of a bipartite slide mass behaving as a cohesive blocky/debris flow in the lower part, and as a grain to turbulent flow [...] Read more.
The Paleogene “megabeds” of the Julian-Slovenian Basin are regional, basin-wide deposits, produced by catastrophic carbonate platform collapses. They record the emplacement of a bipartite slide mass behaving as a cohesive blocky/debris flow in the lower part, and as a grain to turbulent flow in the upper part. Several types of primary (sedimentary) soft sediment deformation structures testify fluid overpressure conditions during emplacement. Such structures are identified within a brecciated, fine grained matrix that encloses and intrudes slide blocks and clasts, characterized by NE-, NW- and SW-directed paleo-transport directions, indicating a depositional setting close to the basin margins. Here we present an updated review of some representative megabeds, exposed in the open-pit quarry outcrops of Anhovo (SW Slovenia). In particular, we here discuss new interpretations based on X-ray fluorescence spectrometry (XRF), thermo-gravimetry (TG) and electric resistivity tomography (ERT). Our results indicate that basal marly clasts of the megabeds are markedly different from the uppermost draping marls, suggesting two different coeval sources. The relationships with the underlying successions are strongly erosive, with deep localized scouring of the substrate and amalgamations between different megabeds, and the depositional units inside individual megabeds, supporting the geochemical differences. Full article
(This article belongs to the Special Issue Geology of Mélanges)
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Review

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31 pages, 8272 KiB  
Review
Origin of Mélanges of the Franciscan Complex, Diablo Range and Northern California: An Analysis and Review
by Loren A. Raymond
Geosciences 2019, 9(8), 338; https://doi.org/10.3390/geosciences9080338 - 1 Aug 2019
Cited by 9 | Viewed by 10265
Abstract
The Franciscan Complex of California is characterized in part by the presence of mélanges. In general, mélange origins are attributed to sedimentary, tectonic, or diapiric processes—or a combination of these. Published reviews list the main features of mélanges characteristic of each type of [...] Read more.
The Franciscan Complex of California is characterized in part by the presence of mélanges. In general, mélange origins are attributed to sedimentary, tectonic, or diapiric processes—or a combination of these. Published reviews list the main features of mélanges characteristic of each type of origin. In this review, particular diagnostic features typical of sedimentary, tectonic, and diapiric mélanges are used to assess 15 specific mélanges, which in some cases have been interpreted in contrasting ways in the literature. The data do not support the view that most Franciscan mélanges were formed by sedimentary processes, but rather that both tectonic and sedimentary processes are important. There is little evidence that diapirism contributed significantly to Franciscan mélange genesis. Tectonic features present in most mélanges of subduction accretionary complexes create challenges in assessing mélange-forming processes. Notably, although tectonic overprints commonly mask the primary diagnostic fabric of sedimentary mélanges, some diagnostic features—such as depositional contacts, fossils in mélange matrix, and interlayering of mélange and non-mélange units—are critical to recognition of mélanges of sedimentary origin. Full article
(This article belongs to the Special Issue Geology of Mélanges)
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