The University of Tokyo · Earth and Planetary Sciences
Professor Simon Wallis's research focuses on high-pressure and ultrahigh-pressure metamorphism, with an emphasis on the tectonic processes that transport deep-earth materials to the surface. His work explores the geodynamic evolution of convergent margins, particularly in regions like the Sulu and Sanbagawa terranes, where metamorphic belts preserve critical records of subduction and exhumation. He integrates petrology, geochronology, and thermobarometry to reconstruct P–T paths and understand the role of partial melting and fluid activity in metamorphic systems. His studies also examine the structural and chemical evolution of eclogite and granitoid rocks under extreme conditions, contributing to broader models of continental collision and orogenic belt formation.
Figures are computed from collected data and may differ slightly.
Strongly deformed potassium feldspar-rich dikes are widely distributed in the northern part of the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. The fact that the crystallization ages of these dikes overlap with the age of peak UHP metamorphic conditions implies the presence of melt during metamorphism. Sr isotopic ratios of the dikes are compatible with their origin as partial melts of the dominant felsic Sulu gneiss. Partial melting may be the key to solving several unusual
Abstract Prograde P–T paths and thermal modelling suggest metamorphism in the Sanbagawa belt represents unusually warm conditions for subduction‐type metamorphic belts, and these likely reflect conditions of a convergent margin a few million years before the arrival of an active spreading ridge. Radiometric age data and kinematic indicators of ductile deformation suggest the Sanbagawa belt formed in a Cretaceous convergent margin associated with a plate movement vector that had a large sinistral
Research Article| September 01, 2003 Cenozoic and Mesozoic metamorphism in the Longmenshan orogen: Implications for geodynamic models of eastern Tibet Simon Wallis; Simon Wallis 1Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8602, Japan Search for other works by this author on: GSW Google Scholar Tatsuki Tsujimori; Tatsuki Tsujimori 2Research Institute of Natural Sciences, Okayama University of Science, Okayama 700-0005, Japan
Tectonic processes that have been proposed to explain the transport to the surface of regional metamorphic belts can be broadly divided into two types. (i) Corner‐flow within a convergent margin bounded by two essentially rigid plates associated with extension at shallow levels. This type of model assumes deformation is distributed throughout the margin and that any discontinuities are of secondary importance. (ii) Expulsion or extrusion of coherent metamorphic nappes. In this second idea, tecto
Coesite eclogite is associated with metagranitoid in a 50×100 m 2 outcrop within the regionally developed amphibolite-facies Su-Lu orthogneiss. Primary intrusive relationships between the metagranitoid and basic rocks and bulk-chemistry analyses show that together they represent a composite igneous body that has subsequently been strongly deformed and metamorphosed. The presence of rutile, sodie pyroxene, corona garnet, and possible pseudomorphs after coesite all suggest very high pressures of m
Known eclogite occurrences in the Sanbagawa metamorphic belt of SW Japan are dominantly in metagabbro bodies which have complex polyphase metamorphic histories. These bodies are generally described as tectonic blocks and their relationship to the Sanbagawa metamorphism is unclear. New findings of foliated eclogite in the Seba and Kotsu areas show that eclogite facies metamorphism is much more widespread than generally thought. Evidence that the foliated eclogite units originated as lavas or sedi
Abstract The Precambrian and lower Paleozoic units of the Japanese basement such as the Hida Oki and South Kitakami terranes have geological affinities with the eastern Asia continent and particularly strong correlation with units of the South China block. There are also indications from units such as the Hitachi metamorphics of the Abukuma terrane and blocks in the Maizuru terrane that some material may have been derived from the North China block. In addition to magmatism, the Japanese region
Abstract Deformation in the Sanbagawa Belt is characterized by ductile flow in an east‐west direction sub‐parallel to its length. The east‐west flow (D 1 ) caused large‐scale recumbent folding of the metamorphic sequence in central Shikoku, which can explain the inverted thermal structure of this region. Chemical zoning of metamorphic minerals associated with D 1 microstructures also suggest that the east‐west flow developed under retrograde conditions. D 1 is therefore related to exhumation rat
Petrological and isotopic evidence suggests that the protolith of the Sulu ultrahigh-pressure (UHP) terrane was Precambrian continental crust consisting of granite, granodiorite, gabbro, marble, and basic dikes, with local granulite-facies assemblages. Around 220 Ma this unit of continental rocks was buried to depths up of ∼120 km within the mantle. Structures formed during exhumation suggest highly mobile behavior of acidic rocks, even under conditions of very low water activity. Petrological s
It has been 25 years since publication of the most recent English language summary of the geology of Japan. This book offers an up-to-date comprehensive guide for those interested both in the geology of the Japanese islands and geological processes of island arcs in general. It contains contributions from over 70 different eminent researchers in their fields and is divided into 12 main chapters: Geological Evolution of Japan: an Overview;Regional Tectonostratigraphy (consisting of seven separate
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