Shoji Arai

Shoji Arai
Kanazawa University | Kindai · Department of Earth Science

PhD

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564
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Publications

Publications (564)
Article
The Korab Kansi and Abu Ghalaga Neoproterozoic mafic-ultramafic intrusions in the South Eastern Desert (SED) of Egypt host economic Fe–Ti–V oxide deposits, ∼41 million tons for Abu Ghalaga ores. The Korab Kansi deposits are composed of titanomagnetite with subordinate ilmenite layers in dunites, gabbros and troctolites. The Abu Ghalaga ores consist...
Article
The Paleozoic Jandaq ophiolite is situated in the western part of the Central-East Iranian microcontinent and is a remnant of the Paleo-Tethys oceanic crust. This ophiolite consists of mantle peridotites and serpentinized mantle peridotites, metagabbro, basic and ultrabasic metamorphosed dykes and lavas, metapyroxenite, amphibolite, rodingite and l...
Article
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Korab Kansi and Abu Dahr Neoproterozoic ophiolitic peridotites in the Southern Eastern Desert (SED) of Egypt, are parts of the largest ophiolitic nappes in the Arabian-Nubian Shield. They mainly comprise refractory harzburgites with minor dunites that are commonly altered to serpentinites and talc carbonates. Olivine relics in serpentinized peridot...
Article
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The geochemical compositions of minerals from the Moho transition zone of ophiolites potentially can help to understand the magmatic evolution of the ophiolites, and subsequent mantle-melt interactions. The Jurassic-Late Cretaceous Makran ophiolite of south Iran comprises one of the most extensive tracts of oceanic crust which were scraped off and...
Article
Hydrothermal circulation beneath the spreading axis plays a significant role in the exchange of energy and mass between the solid Earth and the oceans. Deep‐seated hydrothermal circulation down to the crust/mantle boundary in the fast‐spreading axis has been introduced by a number of studies regarding geological investigations and numerical models....
Article
Plagioclase-impregnated mantle harzburgites from Setogawa area in the Circum-Izu Massif Serpentine Belt (of Miocene in age), central Japan, contain chromian spinel (chromite) grains that have minute globular inclusions composed of micas, amphiboles and pyroxenes. They are similar in texture and chemistry to those in chromitites as well as in some p...
Article
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No genetic link between the two main types of chromitite, stratiform and podiform chromitites, has ever been discussed. These two types of chromitite have very different geological contexts; the stratiform one is a member of layered intrusions, representing fossil magma chambers, in the crust, and the podiform one forms pod-like bodies, representin...
Article
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The bulk of Sibuyan island in the Romblon Island Group, Philippines is underlain by remarkably fresh spinel lherzolites, harzburgites and dunites collectively called as the Sibuyan Ultramafics. Based on petrographic and geochemical characteristics, the Sibuyan Ultramafics can be classified into: (1) Group I peridotites composed of spinel lherzolite...
Article
Behavior and amount of hydrogen or water in olivine and other nominally anhydrous minerals in the mantle have been a matter of debate because of their significant influence on various mantle processes. Hydrogen very quickly diffuses in them so that its behavior is difficult to examine in geologic samples. Here we report traces of its presence in ma...
Article
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Nickel (Ni) enrichment (>0.40 wt%) in olivine was previously recognized in mantle xenoliths and volcanic rocks. Though this enrichment is often attributed to subarc metasomatic processes, the occurrence of Ni rich olivines in mantle peridotites remains to be established. We found peridotites that randomly contain unusually high-Ni olivines (up to N...
Article
The Lycian ophiolite in SW Turkey is mainly exposed in the Marmaris-Köyceğiz (Muğla) and Yeşilova (Burdur) regions. Its mantle section is widely exposed around Marmaris (=Marmaris peridotite) and is primarily composed of harzburgite of abyssal affinity with sparse lenses of dunites. Unusual chromitites indicating complicated mantle processes for ch...
Article
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Rare nickel hydroxide-hydroxyl carbonate, theophrastite (Ni(OH)2)-zaratite (Ni3(CO3)(OH)4·4H2O) aggregates were found from a partially serpentinized dunite from Fujiwara, the Sanbagawa metamorphic belt of high-pressure intermediate type, Japan. The dunite was regionally metamorphosed within the Sanbagawa subduction complex of Cretaceous age. The th...
Article
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Microdiamonds in metamorphic rocks are a signature of ultrahigh-pressure (UHP) metamorphism that occurs mostly at continental collision zones. Most UHP minerals, except coesite and microdiamond, have been partially or completely retrogressed during exhumation; therefore, the discovery of coesite and microdiamond is crucial to identify UHP metamorph...
Article
Highly carbonated mantle xenoliths have been found in rift-related alkaline basalts at the Wadi Natash area in the southern part of the Eastern Desert of Egypt. Although all olivine and most orthopyroxene was replaced by carbonate and/or quartz, textural and mineral chemical features show that they are plagioclase-free spinel peridotites (lherzolit...
Article
The interaction between migrating melts and the upper mantle largely affects the composition of the ascending melt and residual peridotites. In island arcs, melt-rock interactions and products which involved highly depleted mantle peridotites are still largely undocumented despite their petrological importance. In this contribution, the petrographi...
Article
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The role of water-rich solutions in the formation of chromitites has been the matter of controversy. We found small chromite concentrations (chromitites) in diopsidites, precipitated from high-temperature hydrothermal fluids, in the mantle to the crust of the Oman ophiolite. Here, we present petrologic characteristics of the hydrothermal chromitite...
Article
The concentrically zoned Dahanib Alaskan-type complex in the Southern Eastern Desert (SED) of Egypt contains cumulate dunites associated with banded chromitites in the core, through harzburgites, wehrlites, and gabbroic rocks to the rim. Primary mineral inclusions hosted in chromian spinels of the banded chromitites are usually pargasite, orthopyro...
Article
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The Neoproterozoic Korab Kansi mafic-ultramafic intrusion is one of the largest (100 km²) intrusions in the Southern Eastern Desert of Egypt. The intrusion consists of Fe-Ti-bearing dunite layers, amphibole peridotites, pyroxenites, troctolites, olivine gabbros, gabbronorites, pyroxene gabbros and pyroxene-hornblende gabbros, and also hosts signifi...
Article
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We present geochemical and 40Ar∕39Ar age data for a peridotite xenolith-bearing basalt dredged from the Seifu Seamount (SSM basalt) in the northeast Tsushima Basin, southwest Sea of Japan. An 40Ar∕39Ar plateau age of 8.33±0.15 Ma (2σ) was obtained for the SSM basalt, indicating that it erupted shortly after the termination of back-arc spreading in...
Article
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We examined the importance of tremolites as reservoirs of LILE (large–ion lithophile elements) in the mantle wedge. The Ochiai–Hokubo complex in the Suo metamorphic rocks of greenschist to blueschist facies, Japan, is mainly composed of depleted lherzolites, which commonly contain tremolite. The complex is concentrically zoned in terms of degree of...
Article
We present paleostress analyses of dike swarms intruded during the subduction initiation in the northern Oman Ophiolite to understand the tectonomagmatic environment. Five swarms of subparallel dikes extending WNW-ESE are 1−5 km in width and are spaced every 5 km N-S. Each swarm has a core of 100% sheeted dikes 1−2 km in width, which emanated from...
Article
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Mantle melts provide a window on processes related to global plate tectonics. The composition of chromian spinel (Cr-spinel) from mafic-ultramafic rocks has been widely used for tracing the geotectonic environments, the degree of mantle melting and the rate of mid-ocean ridge spreading. The assumption is that Cr-spinel's core composition (Cr# = Cr/...
Article
A stratiform chromite ore body crops out in the lower part of the dunitic mantle-crust transition zone (DTZ) that developed at the top of a mantle diapir in the Maqsad area in the Oman ophiolite. It is made of layers ranging in thickness from a few mm to a maximum of 3 m, and in modal composition from massive to antinodular and disseminated ore. Th...
Article
The formation of a petit-spot volcano involves the ascent of an asthenospheric melt to the outboard part of a plate subduction zone where flexure of the plate has taken place in the outer trench swell. On the Pacific Plate, the only previously known examples of such volcanoes were in the vicinity of the Japan Trench. We describe here a newly discov...
Article
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We report geochemical characteristics and Ar-Ar dating of a basalt dredged from the Seifu Seamount (SSM-basalt), located at northeast of the Tsushima Basin in the southwest Japan Sea, which is one of the western Pacific back-arc basin swarm. A plateau age of 8.33 ± 0.15 Ma (2σ) was obtained by the ⁴⁰Ar-³⁹Ar age spectrum of SSM-basalt. The SSM-basal...
Article
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A Paleogene accretionary complex, the Mineoka–Setogawa belt is distributed adjacent to the northern portion of the collision zone between Honshu and Izu–Bonin–Mariana (IBM) arcs in central Japan, comprising a mélange of ophiolitic fragments of various sizes. The Eocene-Oligocene plutonic rocks in this belt (gabbro, diorite, and tonalite) have been...
Article
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We applied apatite fission-track (AFT) thermochronometry to the Cretaceous-Paleogene granitic rocks across the southern part of the Northeast (NE) Japan Arc in order to elucidate the denudation history. As the results, AFT ages were estimated at 79.5–66.0 Ma on the fore-arc side, 29.8–5.5 Ma in the Ou Backbone range (OBR) and 19.1–4.6 Ma on the bac...
Article
To discuss the nature of the compositional heterogeneity of the peridotite massifs of the Polar Urals (Russia), the geochemical study by LA-ICP-MS of pyroxenes and amphiboles from these mantle formations was performed. The trace element compositions in clinopyroxenes indicate the existence of the mantle protolith of two types. The first protolith t...
Article
Multiple generations of amphibole may form in the lower crust due to magmatism and metamorphism during the development of oceanic core complexes. We investigated the occurrence and chemical compositions of amphibole in gabbro mylonites from the medial area of the Godzilla Megamullion along the Parece Vela Rift in the Philippine Sea. The samples con...
Article
Some arc magmas reside in the uppermost mantle and the lower crust. Their deep-seated behavior determines the composition of magmas that erupt at the surface. Mafic-ultramafic xenoliths newly found in Sabtang island, Batanes group of islands of the Luzon arc record subarc processes. The xenolith suite is comprised mainly of dunites, orthopyroxenite...
Conference Paper
Full-text available
Melt-impregnated plagioclase lherzolites from Nain mélange, Iran, contain pyroxenes which are enriched and chemically zoned in Sr. The pyroxenes from the lherzolite as well as from clinopyroxenite seams, which have been precipitated from the impregnating melt, show similar trace element chemical characteristics including a similar positive Sr anoma...
Article
The Lower Oligocene Kal-e-kafi (East of Anarak, Central Iran) lamprophyres occur as stocks and dikes, which cross-cut the Eocene volcanic and Cretaceous sedimentary rocks. The predominant minerals of these lamprophyres are hornblende (magnesiohastingsite) and clinopyroxene (diopside) phenocrysts set in a fine- to medium-grained matrix of the same m...
Article
The Ashin ophiolite is situated in the western part of Central Iran and presents two stages of Jurassic and Cretaceous spreading. The Ashin ophiolite represents fragments of the Neo-Tethys oceanic lithosphere. Plagiogranite intrusions of this ophiolite have good exposures. Plagiogranites of Cretaceous are more fresh than the metamorphosed samples o...
Article
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Lithology and petrologic nature of the forearc mantle have been left unclear due to the very limited sampling to date. Here, we present petrological data on a forearc peridotite suite obtained as xenoliths in an alkali basalt dike (7.5 Ma) from the Bankawa area in the Southwest Japan arc for our better understanding of the forearc mantle. The host...
Article
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Ultrahigh-pressure (UHP) chromitites containing UHP minerals such as coesite and diamond have been reported from some ophiolites in Tibet and the Polar Urals. Their nature, i.e., origin, P-T path and abundance, however, are still controversial and left unclear. Here we describe chromitites in the Higashi-akaishi (HA) ultramafic complex in the Creta...
Article
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A suite of peridotite xenoliths were collected from lahar flow deposits located close to the summit of Mt. Pinatubo. Spinel harzburgite is the most dominant lithology among dunites, pyroxenites and websterites. A rare spinel lherzolite xenolith (P12-7) is also present in this suite. The spinel lherzolite has well-preserved protogranular texture wit...
Article
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The Mersin ophiolite, Turkey, is of typical arc type based on geochemistry of crustal rocks without any signs of mid-ocean ridge (MOR) affinity. We examined its ultramafic rocks to reveal sub-arc mantle processes. Mantle peridotites, poor in clinopyroxene (<1.0 vol.%), show high Fo content of olivine (90–92) and Cr# [=Cr/(Cr + Al) atomic ratio] (=0...
Article
The mantle wedge is an important locus for material recycling, magma generation, and fluid transportation from the slab, and should therefore be thoroughly examined to better understand these processes. Peridotite xenoliths transported to the surface by arc magmas, or by other magmas, may be representative of the upper part (lithosphere) of the man...
Article
We describe mineralogy of magnetite deposits concentrated within a nonconformity surface between Aniba serpentinites and overlying limestones in the Southern Oman ophiolite and discuss their origin to understand iron mobility during serpentinization, with special reference to factors controlling the magnetite-orebody sizes. The Aniba magnetite depo...
Article
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Igneous activity in the rear-arc of the Paleogene Urumieh-Dokhtar Magmatic Belt of Iran is poorly known. An example of such activity is studied here: the Late Eocene potassic mafic to intermediate rocks in the Lahrud area of NW Iran. These lavas include olivine-bearing clinopyroxene-phyric basalts, analcime-bearing leucite-clinopyroxene-phyric basa...
Article
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The Nain ophiolites crop out along the western border of the central East Iran Microcontinent (CEIM) and consist of an ophiolitic mélange in which pargasite-bearing spinel and plagioclase mantle lherzolites are largely represented. Whole-rock and mineral chemistry data suggest that these rocks record the complex history of the asthenospheric and li...
Article
This work presents the results of geochemical (LA-ICP-MS) study of minerals of peridotites from ophiolite complexes of the Polar Urals to clarify the nature of these formations. The distribution of trace and rare earth elements in clinopyroxenes testifies that there were three types of the mantle substratum, which formed in different geodynamic set...
Article
Detrital materials supplied from mantle-derived rocks have peculiar mechanical and chemical characteristics that make them excellent sedimentological and tectonic markers. Chromian spinels are well known and favored petrogenetic indicators because they contain several important cations, including Mg²⁺, Fe²⁺, Cr³⁺, Al³⁺, and Fe³⁺, as their main comp...
Article
Magnetite bodies of the Late Cretaceous Nain ophiolite mélange (Central Iran) are hosted by a small volume of a serpentinized peridotite nappe. These ore bodies and their host peridotites have been studied in detail with respect to their mode of occurrence, petrography and mineral chemistry. The investigated ore deposits consist of m-scale lenses a...
Article
The lithology of the lower crust beneath arcs is more variable than that of the oceanic lithosphere due to variable pressure and temperature conditions during arc development. Mafic–ultramafic xenoliths in Cenozoic alkali basalts are documented near Kurose in southwest Japan, and are interpreted to have formed within the back-arc region of the Sout...
Article
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Platinum-group elements (PGEs) are one of the key tracers to reveal early differentiation processes of the Earth due to their preferential distribution into the metallic core. Meanwhile, informative evidence for early differentiation has been greatly disturbed through metasomatic PGE disturbance, which has been demonstrated through a number of PGE...
Article
Mantle xenoliths entrained in subduction-zone magmas often record metasomatic signature of the mantle wedge. Such xenoliths occur in magmas from Iraya and Pinatubo volcanoes, located at the volcanic front of the Luzon arc in the Philippines. In this study, we present the major element compositions of the main minerals, trace element abundances in p...
Chapter
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Possible secular changes in the way chromitite (accumulations of chromite) have been formed across Earth’s history are reexamined based on our understanding of the origin of podiform chromitites in the mantle. In the Phanerozoic moderately depleted harzburgites have been dominant in the upper mantle and provided optimum conditions for precipitation...
Article
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The Neoproterozoic peridotite-chromitite complexes in the Central Eastern Desert of Egypt, being a part of the Arabian-Nubian Shield, are outcropped along the E–W trend from Wadi Sayfayn, Wadi Bardah, and Jabal Al-Faliq to Wadi Al-Barramiyah, from east to west. Their peridotites are completely serpentinized, and the abundance of bastite after ortho...
Article
Boninites are widely distributed along the western margin of the Pacific Plate extruded during the incipient stage of the subduction zone development in the early Paleogene period. This paper discusses the genetic relationships of boninite and antecedent protoarc basalt magmas and demonstrates their recycled ancient slab origin based on the T–P con...
Article
We found clinopyroxenite dykes in a banded harzburgite block within the Sumeini area in the uppermost part of the metamorphic sole of the northern part of the Oman ophiolite. The dykes clearly cut the deformational structure of the harzburgite and contain its fragments, indicating dyke formation during obduction of the ophiolite. The Mg# [= Mg / (M...