Formation of chaotic rock units during primary accretion processes: Examples from the Miura–Boso accretionary complex, central Japan

Abstract

Chaotic rock units exposed in the upper part of the accretionary complex preserve detailed tectonic information related to the periods before, during, and immediately after accretion. Based on the detailed survey in the upper Miocene Miura-Boso accretionary complex, central Japan, three types of chaotic rock units were identified on the basis of the grain sizes and characteristics of blocks and surrounding matrices. The chaotic rock units composed of silt matrices and sandy to pebbly blocks (Type 3) formed by gravitydriven slumping upon the seafloor. The slumping occurred contemporaneously with deposition of the Misaki and Nishizaki Formations within the Izu-Bonin forearc. Vertical variations in the direction of slump vergence represent successive changes from an initially flat seabed to tilting to the northwest and finally to the southeast. Slumping with a northwest vergence indicates landward tilting of the seafloor immediately prior to accretion, whereas vergence to the southeast reflects oceanward tectonic tilting that occurred once the sediments had crossed the deformation front. Other chaotic rock units that have matrices abundant in sand and pebbles (Types 1, 2) formed as a result of subsurface liquefaction and injection associated with large earthquakes that occurred during and after accretion of the sediments. These chaotic rock units are useful in examining surface/ subsurface changes such as tectonic tilting of the seafloor and earthquake events during the initial accretion process.

Formation of Taconic mélanges and broken formations in the Hamburg Klippe, Central Appalachian Orogenic Belt, Eastern Pennsylvania

“…Liquefaction-related deformation of un-cemented sandy layers as a result of earthquake shaking represents the most prominent mechanism related to this in situ deformation. Similar chaotic deposits are described by Yamamoto et al (2009) in the Miura-Boso accretionary complex onshore Central Japan.…”

“…This is the case of different orogenic belts and accretionary complexes around the world where mélanges and olistostromes occur, for example in the Alpine-Himalayan belt (e.g. Ring et al, 1990;Trommsdorff, 1990;Liu and Einsele, 1996;Federico et al, 2007), circum-Mediterranean orogens (e.g., Elter and Trevisan, 1973;Dilek et al, 1999Dilek et al, , 2007Pini, 1999;Okay, 2000;Robertson et al, 2009;Camerlenghi and Pini, 2009;Ghikas et al, 2010;Festa et al, 2010b), Appalachians (e.g., Lash, 1987a;Rast and Horton, 1989;Cousineau and St-Julien, 1992;Tremblay et al, 1995;Ganis and Wise, 2008), circum-Pacific regions (e.g., Hsü, 1968;Matsuda and Ogawa, 1993;Cowan, 1985;Cloos, 1982;Wakabayashi, 1992;Kimura et al, 1996;Kusky and Bradley, 1999;Ikesawa et al, 2005;Yamamoto et al, 2009;Wakabaysahi et al, 2010) and many others.…”

The Šariš Transitional Zone, revealing interactions between Pieniny Klippen Belt, Outer Carpathians and European platform

“…Chaotic sedimentation and mélange-forming processes in similar geotectonic settings as well as the appearance of submarine landslides along the subduction margin at the front of accretionary prisms were described by Alonso et al (2006), Yamamoto et al (2009), Yamada et al (2010 and Festa et al (2010Festa et al ( , 2012Festa et al ( , 2016, among others. Concurrent tectonic and gravitational motions leading to the formation of polygenetic olistostromes are common in a large part of the Western Alps at the top of the Alpine foreland basin succession (Perotti et al 2012) and in the Northern Apennines (Pini 1999;Codegone et al 2012;Ogata et al 2012).…”

Small-scale polygenetic mélanges in the Ligurian accretionary complex, Northern Apennines, Italy, and the role of shale diapirism in superposed mélange evolution in orogenic belts

“…The well-preserved on-land examples of ancient accretionary complexes are, therefore, highly important to conduct three-dimensional studies of chaotic bodies of mixed rocks and mélanges at various scales, and to better document different processes and their superposition during progressive evolution of accretionary complexes (Hsü, 1968;Aalto , 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 4 al., 2007;Festa et al, 2010aFesta et al, , 2010bFesta, 2011). This is particularly the case for "polygenetic mélanges" whose evolution may have transcended several different tectonic settings with complex spatial and temporal interrelationships and superposition (e.g., Raymond, 1984;Orange, 1990;Pini, 1999;Cowan and Pini, 2001;Bettelli et al, 2002;Dilek et al, 2005;Dela Pierre et al, 2007;Camerlenghi and Pini, 2009;Yamamoto et al, 2009;Festa et al, 2010aFesta et al, , 2010bFesta, 2011).…”