419 results on '"Shoji Arai"'
Search Results
2. Formation of lower fast-spread oceanic crust: a structural and geochemical study of troctolites in the Hess Deep Rift (East Pacific Rise)
- Author
-
Norikatsu Akizawa, Marguerite Godard, Benoît Ildefonse, and Shoji Arai
- Subjects
IODP expedition 345 ,Lower oceanic crust ,Fractional crystallization ,Mid-ocean ridge basalt ,Porous melt migration ,Melt-mantle interaction ,Geography. Anthropology. Recreation ,Geology ,QE1-996.5 - Abstract
Abstract Troctolites were recovered during Integrated Ocean Drilling Program Expedition 345 at the Hess Deep Rift, next to fast-spreading East Pacific Rise. These troctolites are divided into three groups based on textural differences: coarse-grained (1–10 mm in length) troctolite, fine-grained (~ 2 mm in length) troctolite, and skeletal olivine-bearing troctolite. All troctolites exhibit a magmatic fabric. The major-element compositions of olivine, plagioclase, and clinopyroxene in the troctolites are intermediate between those of Hess Deep gabbros and harzburgites. The trace-element compositions of olivine, plagioclase, and clinopyroxene in the troctolites overlap with those of troctolites from slow-spread crust, but they record no petrographic evidence indicating assimilation of mantle peridotite. Thermodynamic calculation for mineral chemistry showed that fractional crystallization of melt is the dominant process responsible for the formation of the troctolites. The fine-grained troctolite was crystallized with high crystallization rate resulting from hot melt injection into colder wall gabbro. In contrast, interactions between the unsolidified troctolite containing interstitial melt and newly injected melt resulted in the formation of the skeletal olivine-bearing troctolite. While our results demonstrate that the troctolites exhibit multiple melt injections and partial dissolution of a troctolite precursor, fractional crystallization is the dominant process for the creation of the lower crust in the Hess Deep Rift.
- Published
- 2023
- Full Text
- View/download PDF
3. Cr-spinel records metasomatism not petrogenesis of mantle rocks
- Author
-
Hamed Gamal El Dien, Shoji Arai, Luc-Serge Doucet, Zheng-Xiang Li, Youngwoo Kil, Denis Fougerouse, Steven M. Reddy, David W. Saxey, and Mohamed Hamdy
- Subjects
Science - Abstract
Chromian-spinel from mafic-ultramafic rocks is used as a reliable geotectonic and mantle melting indicator. Here, the authors argue that this only works partially – it can be used to assess information on mantle metasomatic processes but not petrogenesis.
- Published
- 2019
- Full Text
- View/download PDF
4. Remarkably fresh abyssal peridotites from Sibuyan island, Romblon Island Group, Philippines: Markers of young arc-continent collision
- Author
-
Betchaida D. Payot, Satoko Ishimaru, Akihiro Tamura, Carla B. Dimalanta, Graciano P. Yumul, Jr., and Shoji Arai
- Subjects
Ultramafics ,Peridotites ,Abyssal ,Arc-continent collision ,Sibuyan ,Philippines ,Geology ,QE1-996.5 - Abstract
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 lherzolites and harzburgites with spinel Cr# < 0.35, (2) Group II harzburgites and dunites with intermediate spinel Cr# = 0.40–0.65, and (3) Group III dunites with very high spinel Cr# (>0.75). Increase in spinel Cr# is accompanied by decreasing Al2O3 contents and increasing Mg# in the pyroxenes from the Group I to Group II and Group III peridotites. Chondrite-normalized clinopyroxene data revealed various trace-element patterns for the three groups suggestive of different processes (e.g. anhydrous and hydrous melting, mantle-melt interaction) involved in their formation. The Sibuyan Ultramafics is closely associated with the similarly fresh Calaton Hill metamorphic/plutonic complex in Tablas island which is thought to be representative of the lower crust of the Philippine island arc. At a more regional context, the Sibuyan Ultramafics and the Calaton Hill metamorphic/plutonic complex can be used as markers for the young arc-continent collision in western Philippines. Rapid uplift and emplacement due to the collision of the Philippine Mobile Belt and the Palawan Microcontinental Block during the Miocene or even later may have led to the remarkably fresh state of these lithologies. This occurrence is similar to the Horoman peridotite complex in the Hidaka metamorphic belt in Northern Japan. The Sibuyan Ultramafics and the Calaton Hill metamorphic/plutonic complex therefore provide a rare and fresh glimpse into the upper mantle and lower crust in the Philippines due to their young ages of emplacement.
- Published
- 2021
- Full Text
- View/download PDF
5. Petrogenesis of heterogeneous mantle peridotites with Ni-rich olivine from the Pujada Ophiolite, Philippines
- Author
-
Valerie Shayne V. Olfindo, Betchaida D. Payot, Gabriel Theophilus V. Valera, and Shoji Arai
- Subjects
Pujada ophiolite ,Peridotites ,Ni-rich olivine ,Philippines ,Geology ,QE1-996.5 - Abstract
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 Ni = 0.53 wt%) from the mantle section of the Pujada Ophiolite, Philippines. The Pujada mantle peridotites can be classified into three groups based on their occurrence and spinel Cr#: Group I - massive lherzolites and harzburgites with Cr# = 0.10–0.40, Group II - lherzolite-dunite and harzburgite-dunite interlayers with Cr# = 0.10–0.40, and Group III - interlayered harzburgites and dunites with Cr# >0.40. Rare earth element composition of clinopyroxenes shows general light rare earth element (LREE) depletion and relatively flat heavy rare earth element (HREE) with minor LREE enrichment. The high-Ni olivines are associated to the occurrence of secondary orthopyroxenes, high modal abundance of orthopyroxenes (>30%) and LREE enrichment. The Ni enrichment in olivine is the result of the diffusion of Ni from a pyroxenitic melt. The crystallization of a hybridized melt formed by the combination of pyroxenite melt, primitive MORB melt and siliceous slab-derived melt, shows the same case of formation for the high Ni-olivine phenocrysts in alkali basalts from Hawaii, Kamchatka and the Mexican Volcanic Belt.
- Published
- 2020
- Full Text
- View/download PDF
6. Thermal fluid activities along the Mozumi-Sukenobu fault, central Japan, identified via zircon fission-track thermochronometry
- Author
-
Shigeru Sueoka, Zuitetsu Ikuho, Noriko Hasebe, Masaki Murakami, Ryuji Yamada, Akihiro Tamura, Shoji Arai, and Takahiro Tagami
- Subjects
Geology ,QE1-996.5 - Abstract
This study uses zircon fission-track (ZFT) thermochronometry to investigate thermal anomalies along the Mozumi-Sukenobu fault, central Japan, and assesses the most plausible mechanisms by which reheating events occurred. In total, 14 samples were collected from Mesozoic sedimentary rocks along a research tunnel excavated across the fault. The mean ZFT ages range from 110.3 to 73.3 Ma, whereas the mean ZFT lengths are 7.1–9.0 μm. Thermal histories estimated by inverse modeling based on the ZFT data indicate two reheating episodes at ∼60 Ma and ∼30–15 Ma. The reheating episode at ∼60 Ma was detected from two samples collected from between the two major fracture zones. This episode can be attributed to thermal fluids sourced from the Kamioka Mine region in the south on the basis of the timing of the event and the presence of minerals produced via hydrothermal alteration. Reheating at ∼30–15 Ma is indicated in majority of the samples. This is thought to be related to magmatism associated with the opening of the Sea of Japan, but the source and mechanism of reheating cannot be clearly determined. Reheating is not attributable to simple thermal diffusion from volcanic products deposited at the surface. The spatial pattern of the thermal anomalies can be explained by the dextral slip along the two major fracture zones since the late Quaternary. Although the identified thermal episodes are background events potentially related to fluid activities, they are important for quantifying thermal history along the fault zone including the frictional heating. Keywords: Fission-track thermochronometry, Zircon, Mozumi-Sukenobu fault (Atotsugawa Fault Zone), Thermal history, Thermal fluid
- Published
- 2019
- Full Text
- View/download PDF
7. Thermal history analysis of granitic rocks in an arc-trench system based on apatite fission-track thermochronology: A case study of the Northeast Japan Arc
- Author
-
Shoma Fukuda, Shigeru Sueoka, Noriko Hasebe, Akihiro Tamura, Shoji Arai, and Takahiro Tagami
- Subjects
Geology ,QE1-996.5 - Abstract
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 back-arc side. Thermal inverse modeling with HeFTy offered high-resolution thermal histories, which were converted into denudation rates under the assumption of appropriate geothermal gradients. On the fore-arc side, stable and slow denudation setting (denudation rates
- Published
- 2019
- Full Text
- View/download PDF
8. Genetic Link between Podiform Chromitites in the Mantle and Stratiform Chromitites in the Crust: A Hypothesis
- Author
-
Shoji Arai
- Subjects
chromite-hosted inclusions ,peridotite–melt reaction ,stratiform chromitite ,podiform chromitite ,genetic link ,Mineralogy ,QE351-399.2 - Abstract
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, representing fossil magma conduits, in the upper mantle. Chromite grains contain peculiar polymineralic inclusions derived from Na-bearing hydrous melts, whose features are so similar between the two types that they may form in a similar fashion. The origin of the chromite-hosted inclusions in chromitites has been controversial but left unclear. The chromite-hosted inclusions also characterize the products of the peridotite–melt reaction or melt-assisted partial melting, such as dunites, troctolites and even mantle harzburgites. I propose a common origin for the inclusion-bearing chromites, i.e., a reaction between the mantle peridotite and magma. Some of the chromite grains in the stratiform chromitite originally formed in the mantle through the peridotite–magma reaction, possibly as loose-packed young podiform chromitites, and were subsequently disintegrated and transported to a crustal magma chamber as suspended grains. It is noted, however, that the podiform chromitites left in the mantle beneath the layered intrusions are different from most of the podiform chromitites now exposed in the ophiolites.
- Published
- 2021
- Full Text
- View/download PDF
9. DISCOVERY OF FERROPICRITES AND HIGH-MAGNESIAN ANDESITES FROM THE ERDENETSOGT FORMATION, CENTRAL MONGOLIA
- Author
-
Ganbat Erdenesaikhan, Akira Ishiwatari, Demberel Orolmaa, Shoji Arai, and Akihiro Tamura
- Subjects
Uyanga area in Hangay-Hentey belt, Erdenetsogt Formation in Tsetserleg terrane, oceanic plateau, ferropicrite and ferrobasalt, high-Mg andesite (HMA) ,Science ,Social Sciences - Abstract
New geochemical and petrological results are presented for greenstones from the Erdenetsogt Formation hosted by the Tsetserleg accretionary terrane in the Hangay region, with particular emphasis on newly found picritic and andesitic rocks. These rocks occur mostly in the lower portion of the Erdenetsogt Formation as massive lavas, sills, and dykes closely associated with varicolored bedded ribbon cherts and siltstones. The protoliths of the studied greenstones comprise (1) plume-derived tholeiitic greenstones with oceanic plateau basalt affinity, (2) arc-derived, calc-alkaline andesites. The plume-derived rocks are characterized by chemical signatures such as slight LREE enrichment similar to that of tholeiitic OIB and the existence of ferropicrite with high FeO* (>14 wt%) and MgO (12–22 wt%), which is characteristic of large igneous provinces (LIPs), including oceanic plateaus. Therefore, their tholeiitic composition and high-Fe and -Ti contents require melting of the source mantle peridotite with addition of some recycled Fe- and Ti-rich basaltic material. The andesites are characterized by glassy texture, high MgO content (up to 7 wt%), and significant LREE enrichment with depletion in Nb and resemble sanukite type of high-magnesian andesite (HMAs). We infer that the Hangay tholeiitic greenstones probably represent an accreted upper section of an oceanic plateau that developed in the deep-water region of the Hangay-Henteypaleo-ocean in the Upper Silurian-Lower Devonian. The Hangay HMAs may have been produced by subduction of young oceanic plate after an oceanward back-stepping of the subduction zone that was a result of the collision during the Carboniferous of the oceanic plateau and the active continental margin of the Central Mongolian Massif.
- Published
- 2016
- Full Text
- View/download PDF
10. Post-Serpentinization Formation of Theophrastite-Zaratite by Heazlewoodite Desulfurization: An Implication for Shallow Behavior of Sulfur in a Subduction Complex
- Author
-
Shoji Arai, Satoko Ishimaru, Makoto Miura, Norikatsu Akizawa, and Tomoyuki Mizukami
- Subjects
theophrastite ,zaratite ,serpentinization ,heazlewoodite ,millerite ,desulfurization ,Mineralogy ,QE351-399.2 - Abstract
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 theophrastite-zaratite aggregate from Fujiwara most typically occurs in association with nickel sulfides, which form a composite grain with awaruite and magnetite within an antigorite-rich part of the rock. The theophraste-zaratite formed possibly together with millerite (NiS) from heazlewoodite (Ni3S2). This represents a partial desulfurization of heazlewoodite, which contains or interlocks with laths of antigorite, suggesting their cogenesis. The desulfurization occurred at an early stage of, or during, exhumation of the subduction complex toward the surface, where sulfur was oxidized and removed as sulfate ions. Serpentinization of olivine has not been associated with the formation of theophrastite-zaratite, and an oxidized condition has been kept at this post-serpentinization stage. The sulfate ions liberated in part precipitated anhydrite where calcium was available in the surrounding rocks. This shows one of the shallow migration pathways of sulfur in the subduction zone, especially to the forearc area.
- Published
- 2020
- Full Text
- View/download PDF
11. Hydrothermal Chromitites from the Oman Ophiolite: The Role of Water in Chromitite Genesis
- Author
-
Shoji Arai, Makoto Miura, Akihiro Tamura, Norikatsu Akizawa, and Akira Ishikawa
- Subjects
hydrothermal chromitites ,ca-al silicates ,seawater ,oman ophiolite ,slab-derived fluids ,platinum-group elements ,Mineralogy ,QE351-399.2 - Abstract
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 chromitites to understand their genesis. In the chromitites, the chromite is associated with uvarovite in the crust and diopside + grossular in the mantle. They are discriminated from the magmatic podiform chromitite by dominance of the Ca-Al silicates in the matrix. The fluids responsible for chromite precipitation are possibly saline, being derived from the seawater circulated into the mantle through the crust. The saline fluids precipitate chromite to form chromite upon decompression and cooling, and transport platinum-group elements (especially Pt and Pd). The fluids obtain Ca and Al from the crustal rocks and Cr from the mantle rocks during circulation. Saline fluids are also supplied from the slab to the mantle wedge, and can metasomatically precipitate chromite and pyroxenes within peridotites. They re-distribute Cr and chromite in peridotites along with circulation of saline fluids in the mantle wedge.
- Published
- 2020
- Full Text
- View/download PDF
12. Structural Analysis of Crystalline R(+)-α-Lipoic Acid-α-cyclodextrin Complex Based on Microscopic and Spectroscopic Studies
- Author
-
Naoko Ikuta, Takatsugu Endo, Shota Hosomi, Keita Setou, Shiori Tanaka, Noriko Ogawa, Hiromitsu Yamamoto, Tomoyuki Mizukami, Shoji Arai, Masayuki Okuno, Kenji Takahashi, Keiji Terao, and Seiichi Matsugo
- Subjects
cyclodextrin ,lipoic acid ,ATR/FT-IR ,microscopic Raman ,solid-state NMR ,Biology (General) ,QH301-705.5 ,Chemistry ,QD1-999 - Abstract
R(+)-α-lipoic acid (RALA) is a naturally-occurring substance, and its protein-bound form plays significant role in the energy metabolism in the mitochondria. RALA is vulnerable to a variety of physical stimuli, including heat and UV light, which prompted us to study the stability of its complexes with cyclodextrins (CDs). In this study, we have prepared and purified a crystalline RALA-αCD complex and evaluated its properties in the solid state. The results of 1H NMR and PXRD analyses indicated that the crystalline RALA-αCD complex is a channel type complex with a molar ratio of 2:3 (RALA:α-CD). Attenuated total reflection/Fourier transform infrared analysis of the complex showed the shift of the C=O stretching vibration of RALA due to the formation of the RALA-αCD complex. Raman spectroscopic analysis revealed the significant weakness of the S–S and C–S stretching vibrations of RALA in the RALA-αCD complex implying that the dithiolane ring of RALA is almost enclosed in glucose ring of α-CD. Extent of this effect was dependent on the direction of the excitation laser to the hexagonal morphology of the crystal. Solid-state NMR analysis allowed for the chemical shift of the C=O peak to be precisely determined. These results suggested that RALA was positioned in the α-CD cavity with its 1,2-dithiolane ring orientated perpendicular to the plane of the α-CD ring.
- Published
- 2015
- Full Text
- View/download PDF
13. Spectroscopic Studies of R(+)-α-Lipoic Acid—Cyclodextrin Complexes
- Author
-
Naoko Ikuta, Akira Tanaka, Ayako Otsubo, Noriko Ogawa, Hiromitsu Yamamoto, Tomoyuki Mizukami, Shoji Arai, Masayuki Okuno, Keiji Terao, and Seiichi Matsugo
- Subjects
cyclodextrin ,lipoic acid ,microscopic FT-IR ,microscopic Raman ,raman spectroscopic mapping ,Biology (General) ,QH301-705.5 ,Chemistry ,QD1-999 - Abstract
α-Lipoic acid (ALA) has a chiral center at the C6 position, and exists as two enantiomers, R(+)-ALA (RALA) and S(−)-ALA (SALA). RALA is naturally occurring, and is a cofactor for mitochondrial enzymes, therefore playing a major role in energy metabolism. However, RALA cannot be used for pharmaceuticals or nutraceuticals because it readily polymerizes via a 1,2-dithiolane ring-opening when exposed to light or heat. So, it is highly desired to find out the method to stabilize RALA. The purpose of this study is to provide the spectroscopic information of stabilized RALA and SALA through complexation with cyclodextrins (CDs), α-CD, β-CD and γ-CD and to examine the physical characteristics of the resultant complexes in the solid state. The RALA-CD structures were elucidated based on the micro fourier transform infrared (FT-IR) and Raman analyses. The FT-IR results showed that the C=O stretching vibration of RALA appeared at 1717 cm−1 and then shifted on formation of the RALA-CD complexes. The Raman spectra showed that the S–S and C–S stretching vibrations for RALA at 511 cm−1 (S–S), 631 cm−1 (C–S) and 675 cm−1 (C–S) drastically weakened and almost disappeared upon complexation with CDs. Several peaks indicative of O–H vibrations also shifted or changed in intensity. These results indicate that RALA and CDs form host-guest complexes by interacting with one another.
- Published
- 2014
- Full Text
- View/download PDF
14. Editorial for Special Issue 'Petrology, Geochemistry and Mineralogy of the Mantle as Tools to Read Messages from the Earth’s Interior'
- Author
-
Shoji Arai
- Subjects
n/a ,Mineralogy ,QE351-399.2 - Abstract
n/a
- Published
- 2019
- Full Text
- View/download PDF
15. Abyssal Peridotite as a Component of Forearc Mantle: Inference from a New Mantle Xenolith Suite of Bankawa in the Southwest Japan Arc
- Author
-
Shoji Arai, Akihiro Tamura, Makoto Miura, and Kazuma Seike
- Subjects
forearc mantle ,lherzolite xenoliths ,abyssal peridotite ,alkali basalt ,Bankawa ,Southwest Japan arc ,Mineralogy ,QE351-399.2 - Abstract
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 alkali basalt is of asthenosphere origin, and passed through a slab window with slight chemical modification by the slab-derived component. The Bankawa peridotite suite is comprised of lherzolites, which contain various amounts of secondary phlogopite and were metasomatized to various degrees. The least metasomatized lherzolite exhibits Fo91 of olivine, Cr/(Cr + Al) = 0.3 of chromian spinel, and depletion of middle to light rare-earth elements in clinopyroxene, and is overall similar to an abyssal lherzolite. It had originally formed at the proto-Pacific Ocean and then was trapped at a eastern margin of Eurasian continent by initiation of subduction. The forearc mantle peridotite formed as a residue of proto-arc magma formation is depleted harzburgite as represented by the peridotites obtained from the forearc seafloor, but can be less depleted abyssal peridotite if being devoid of partial melting or reaction with magmas after entrapment.
- Published
- 2018
- Full Text
- View/download PDF
16. Petrology of Chromitites in the Higashi-Akaishi Ultrahigh-Pressure (UHP) Peridotite Complex, Japan: Toward Understanding of General Features of the UHP Chromitites
- Author
-
Makoto Miura, Shoji Arai, Tomoyuki Mizukami, Vladimir R. Shmelev, and Satoko Ishimaru
- Subjects
chromitite ,ultrahigh-pressure metamorphism ,the Higashi-akaishi peridotite complex ,diopside lamella ,arc-related magmatism ,subduction ,Mineralogy ,QE351-399.2 - Abstract
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 Cretaceous Sanbagawa metamorphic belt, Japan, which experienced UHP condition (up to 3.8 GPa) at the peak metamorphism via subduction, in order to understand the nature of UHP chromitites. The HA peridotites typically contain garnets and are associated with eclogites, and their associated chromitites are expected to have experienced the UHP metamorphism. The Higashi-akaishi (HA) chromitites show banded to massive structures and are concordant to foliation of the surrounding peridotite. Chromian spinels in the chromitite and surrounding peridotites were sometimes fractured by deformation, and contain various inclusions, i.e., blade- and needle-like diopside lamellae, and minute inclusions of pyroxenes, olivine, and pargasite. The peculiar UHP minerals, such as coesite and diamond, have not been found under the microscope and the Raman spectrometer. Spinels in the HA chromitites show high Cr#s (0.7 to 0.85), and low Ti contents (
- Published
- 2018
- Full Text
- View/download PDF
17. Mantle Evolution from Ocean to Arc: The Record in Spinel Peridotite Xenoliths in Mt. Pinatubo, Philippines
- Author
-
Betchaida D. Payot, Shoji Arai, Masako Yoshikawa, Akihiro Tamura, Mitsuru Okuno, and Danikko John V. Rivera
- Subjects
xenoliths ,Mt. Pinatubo ,Philippines ,mantle wedge ,abyssal lherzolite ,arc harzburgite ,Mineralogy ,QE351-399.2 - Abstract
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 with very minimal presence of secondary amphibole, low Cr# in the chromian spinel, and depleted and hump shaped patterns of chondrite-normalized rare earth element (REE) patterns for the clinopyroxenes. In contrast, the spinel harzburgites contain abundant secondary amphiboles and orthopyroxenes, higher Cr# in the spinel, and slightly elevated patterns for the chondrite-normalized REE patterns for the amphiboles. The spinel lherzolite also exhibits higher olivine Fo content for a given spinel Cr# compared to the spinel harzburgites. The spinel lherzolite is interpreted as a typical residue from partial melting of abyssal peridotites whereas the spinel harzburgites may have formed via partial melting with subsequent modification during the influx of fluids in the mantle wedge. Our results suggest that fragments of MOR-derived lithosphere exist in the mantle wedge beneath the Philippine island arc. This work provides evidence for the conversion of abyssal to arc peridotites in the mantle wedge.
- Published
- 2018
- Full Text
- View/download PDF
18. Decoding of Mantle Processes in the Mersin Ophiolite, Turkey, of End-Member Arc Type: Location of the Boninite Magma Generation
- Author
-
Satoko Ishimaru, Yuji Saikawa, Makoto Miura, Osman Parlak, and Shoji Arai
- Subjects
arc-type ophiolite ,mantle wedge ,partial melting ,metasomatism ,peridotite-melt reaction ,boninite ,Mersin ,Turkey ,Mineralogy ,QE351-399.2 - Abstract
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 km) in Mersin than in MOR-related ophiolite (mostly < 500 m), and this is one of the features of arc-type ophiolite.
- Published
- 2018
- Full Text
- View/download PDF
19. Crystallisation of Ca-bearing nepheline in basanites from Kajishiyama of Tsuyama Basin, Southwest Japan
- Author
-
Keiya Yoneoka, Maki Hamada, and Shoji Arai
- Subjects
Geochemistry and Petrology - Published
- 2023
20. AMPHIBOLE IN ULTRA-DEPLETED PERIDOTITES FROM THE HOROKANAI OPHIOLITE, HOKKAIDO, JAPAN: BONINITE MELT TRAPPED IN THE MANTLE WEDGE.
- Author
-
Akihiro Tamura, Ikuya Nishio, Yuya Iwata, Shoji Arai, and Tomoaki Morishita
- Subjects
PERIDOTITE ,AMPHIBOLES ,METASOMATISM ,ORTHOPYROXENE ,MELTING ,DUNITE - Abstract
Ultra-depleted peridotites have been reported from the mantle sections of a number of ophiolitic complexes (e.g., Papua New Guinea and New Caledonia). Such rocks are residues derived from boninitic melts in supra-subduction zones, particularly in forearcs. In the mantle wedge, slab-derived fluid-melt containing H
2 O increases the degree of melting and metasomatizes the peridotites. However, the relationship between high-degree melting under hydrous conditions and metasomatism is not well understood. In this paper, we report petrological features of amphibole-bearing ultra-depleted peridotites from the Horokanai ophiolite, Hokkaido, Japan. The peridotite complex in the Horokanai ophiolite consists of clinopyroxene-free harzburgite, orthopyroxene-poor harzburgite, and dunite. The harzburgites contain high-Cr# spinel (0.70-0.85) and orthopyroxene with very low abundances of incompatible elements (e.g., Y < 0.01 μg/g; Ti ~ 2 μg/g). Pargasitic-edenitic amphibole occurs as spinel-hosted inclusions and as an interstitial phase to olivine and orthopyroxene. The harzburgite is a residue formed by the high-degree melting caused by fluid flux. The hydrous conditions cause incongruent melting of orthopyroxene, producing a depleted Si-rich melt (i.e., a boninitic melt). Because such Si-rich melt can coexist with Cr-rich spinel under these conditions, amphibole is ultimately crystallized in the harzburgite. Such amphibole formation is important in producing secondary sodic amphibole during alteration of ultra-depleted peridotites. [ABSTRACT FROM AUTHOR]- Published
- 2024
- Full Text
- View/download PDF
21. Petrogenesis of Gerf Neoproterozoic carbonatized peridotites (Egypt): Evidence of convergent margin metasomatism of depleted sub-arc mantle
- Author
-
Mohamed Zaki Khedr, Ahmed A. Al Desouky, Samir Kamh, Christoph Hauzenberger, Shoji Arai, Akihiro Tamura, Scott A. Whattam, Tomoaki Morishita, El Saeed R. Lasheen, and Amr El-Awady
- Subjects
Geochemistry and Petrology ,Geology - Published
- 2023
22. Relating words and image segments on multiple layers for effective browsing and retrieval.
- Author
-
Andrea Kutics, Akihiko Nakagawa, Shoji Arai, Hiroyuki Tanaka, and Sakuichi Ohtsuka
- Published
- 2004
- Full Text
- View/download PDF
23. Mapping image segments to words for image retrieval.
- Author
-
Akihiko Nakagawa, Shoji Arai, Andrea Kutics, and Hiroyuki Tanaka
- Published
- 2004
- Full Text
- View/download PDF
24. Microdiamond in a low-grade metapelite from a Cretaceous subduction complex, western Kyushu, Japan
- Author
-
Kazuki Harada, Yousuke Moribe, Ukyo Nishi, Yasushi Mori, Miki Shigeno, Shoji Arai, Kouhei Unoki, Akira Yoshiasa, Kousuke Fukuba, Hiroaki Ohfuji, Masami Terauchi, Satoko Ishimaru, and Tadao Nishiyama
- Subjects
Solid Earth sciences ,Multidisciplinary ,010504 meteorology & atmospheric sciences ,Subduction ,Continental collision ,Metamorphic rock ,lcsh:R ,Geochemistry ,Metamorphism ,lcsh:Medicine ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Article ,Cretaceous ,Tectonics ,Coesite ,Planetary science ,engineering ,lcsh:Q ,lcsh:Science ,Geology ,0105 earth and related environmental sciences - Abstract
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 metamorphism and to understand the tectonic history of metamorphic rocks. Microdiamonds typically occur as inclusions in minerals such as garnet. Here we report the discovery of microdiamond aggregates in the matrix of a metapelite from the Nishisonogi unit, Nagasaki Metamorphic Complex, western Kyushu, Japan. The Nishisonogi unit represents a Cretaceous subduction complex which has been considered as an epidote–blueschist subfacies metamorphic unit, and the metapelite is a member of a serpentinite mélange in the Nishisonogi unit. The temperature condition for the Nishisonogi unit is 450 °C, based on the Raman micro-spectroscopy of graphite. The coexistence of microdiamond and Mg-carbonates suggests the precipitation of microdiamond from C–O–H fluid under pressures higher than 2.8 GPa. This is the first report of metamorphic microdiamond from Japan, which reveals the hidden UHP history of the Nishisonogi unit. The tectonic evolution of Kyushu in the Japanese Archipelago should be reconsidered based on this finding.
- Published
- 2020
25. Petrogenesis of the ~740 Korab Kansi mafic-ultramafic intrusion, South Eastern Desert of Egypt: Evidence of Ti-rich ferropicritic magmatism
- Author
-
Tomoaki Morishita, Mohamed Zaki Khedr, Shoji Arai, Amr El-Awady, Akihiro Tamura, Christoph Hauzenberger, and Robert J. Stern
- Subjects
Fractional crystallization (geology) ,Olivine ,010504 meteorology & atmospheric sciences ,biology ,Geochemistry ,Geology ,Pyroxene ,Forsterite ,engineering.material ,010502 geochemistry & geophysics ,biology.organism_classification ,01 natural sciences ,Ultramafic rock ,engineering ,Mafic ,Lile ,Amphibole ,0105 earth and related environmental sciences - Abstract
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 significant Fe-Ti deposits, mainly as titanomagnetite-ilmenite. These lithologies show rhythmic layers and intrusive contacts against the surrounding granites and ophiolitic-island arc assemblages. The wide ranges of olivine forsterite contents (Fo67.9-85.7), clinopyroxene Mg# (0.57–0.95), amphibole Mg# (0.47–0.88), and plagioclase compositions (An85.8-40.9) indicate the role of fractional crystallization in the evolution from ultramafic to mafic rock types. Clinopyroxene (Cpx) has high REE contents (2–30 times chondrite) with depleted LREE relative to HREE, like those crystallized from ferropicritic melts generated in an island-arc setting. Melts in equilibrium with Cpx also resemble ferropicrites crystallized from olivine-rich mantle melts. Cpx chemistry and its host rock compositions have affinities to tholeiitic and calc-alkaline magma types. Compositions of mafic-ultramafic rocks are depleted in HFSE (e.g. Nb, Ta, Zr, Th and U) relative to LILE (e.g. Li, Rb, Ba, Pb and Sr) due to the addition of subduction-related hydrous fluids (rich in LILE) to the mantle source, suggesting an island-arc setting. Fine-grained olivine gabbros may represent quenched melts approximating the primary magma compositions because they are typically similar in assemblage and chemistry as well as in whole-rock chemistry to ferropicrites. We suggest that the Korab Kansi intrusion crystallized at temperatures ranging from ~700 to 1100 °C from ferropicritic magma derived from melting of metasomatized mantle at
- Published
- 2020
26. Melt-rock interaction in the subarc mantle: records from the plagioclase peridotites of the southern Palawan Ophiolite, Philippines
- Author
-
Florence Annette C. Labis, Gabriel Theophilus V. Valera, Shoji Arai, Jesley Mei A. Dycoco, Tomoaki Morishita, Betchaida D. Payot, Julius A. Pasco, and Akihiro Tamura
- Subjects
020209 energy ,Geochemistry ,Geology ,02 engineering and technology ,engineering.material ,010502 geochemistry & geophysics ,Ophiolite ,01 natural sciences ,Mantle (geology) ,0202 electrical engineering, electronic engineering, information engineering ,engineering ,Plagioclase ,Island arc ,0105 earth and related environmental sciences - Abstract
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 petrographic and geochemical signatures of refractory and refertilized peridotites comprising the mantle section of the southern Palawan Ophiolite, Philippines are investigated. The peridotites are dominantly comprised of residual spinel harzburgites with minor dunite and plagioclase peridotites. Spinel harzburgites are similar to other highly depleted residual mantle materials of other suprasubduction zone ophiolites. Plagioclase peridotites, which are cut by gabbroic intrusions, preserve distinct petrological characteristics indicating melt-rock interaction. The melts preserved as gabbroic dikes have signatures transitional between mid-ocean ridge and island arc, and are comparable to back-arc basin lavas. We therefore propose that the plagioclase peridotites were formed due to the reaction between highly depleted mantle peridotites beneath an intraoceanic arc and migrating BABB-like magmas possibly during the incipient stages of back-arc rifting.
- Published
- 2020
27. Geochemical variability among stratiform chromitites and ultramafic rocks from Western Makran, South Iran
- Author
-
Hadi Shafaii Moghadam, Shoji Arai, William L. Griffin, Mohamed Z. Khedr, Emilio Saccani, Hadrien Henry, Suzanne Y. O'Reilly, and Ghasem Ghorbani
- Subjects
Geochemistry and Petrology ,Makran ,Geochemical variations ,Stratiform chromitites ,Ambientale ,Ultramafic rocks ,Geology ,Iran - Published
- 2022
28. Petrogenesis of Gerf Neoproterozoic Carbonatized Peridotites (Egypt): Evidence of Convergent Margin Metasomatism of Depleted Sub-Arc Mantle
- Author
-
Mohamed Zaki Khedr, Ahmed A. Al Desouky, Samir Kamh, Christoph Hauzenberger, Shoji Arai, Akihiro Tamura, Scott A. Whattam, and Amr Amr El-Awady
- Published
- 2022
29. The conversion tectonics from spreading to subduction: Paleostress analysis of dike swarms during the subduction initiation in the Oman Ophiolite
- Author
-
Yuki Kusano, Shoji Arai, Susumu Umino, Akihiro Tamura, Takahiro Fudai, and Atsushi Yamaji
- Subjects
Dike ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Subduction ,Geochemistry ,Geology ,010502 geochemistry & geophysics ,Ophiolite ,01 natural sciences ,Paleostress ,Tectonics ,0105 earth and related environmental sciences - Abstract
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 the dunite-wherlite-clinopyroxenite-gabbronorite-diorite-tonalite complexes below and intruded through V1 and into V2 extrusive rocks. Individual dike strikes are varied but generally subparallel to the overall trend of the swarm. Paleostress analyses indicate subvertical σ1, ∼σ2, and subhorizontal σ3 with high magma pressures, resulted in the mutually intrusive, extensional shear dikes and abrupt changes in dike strike at high angles. These occurrences suggest intrusions under a more compressive environment compared to the extensional stress field that formed the N-S–striking sheeted dikes of V1 spreading stage. Most E-W–striking dikes possess both boninitic and tholeiitic geochemistry. The latter resemble the V1 flows and dikes with affinities of mid-ocean ridge basalt. Some tholeiitic dikes strike N-S, which are mutually intrusive to E-W–striking dikes. Tholeiitic dikes are more intensely altered than boninite, suggesting their older ages. Conversion of the stress field from a N-S–running spreading axis to inextensional E-W–running rift zones associated with the change in magma geochemistry agree with the relatively compressive V2 arc above a forced subduction zone, which originated from intraoceanic thrusting caused by the clockwise rotation of a microplate including the future northern ophiolite.
- Published
- 2019
30. Melt–fluid infiltration along detachment shear zones in oceanic core complexes: Insights from amphiboles in gabbro mylonites from the Godzilla Megamullion, Parece Vela Basin, the Philippine Sea
- Author
-
Akihiro Tamura, Shoji Arai, Katsuyoshi Michibayashi, Tomoaki Morishita, Hiroyuki Yamashita, Yumiko Harigane, Yasuhiko Ohara, Jonathan E. Snow, and Atsushi Okamoto
- Subjects
010504 meteorology & atmospheric sciences ,Gabbro ,Metamorphic rock ,Geochemistry ,Metamorphism ,Geology ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Detachment fault ,Oceanic core complex ,Geochemistry and Petrology ,engineering ,Plagioclase ,Amphibole ,0105 earth and related environmental sciences ,Mylonite - Abstract
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 contain brown and green amphiboles with a variety of different textures that may have different origins. The brown amphibole occurs mainly as blebs in clinopyroxene porphyroclasts (Bleb amphibole), the rims around clinopyroxene porphyroclasts (Coronitic amphibole), and as porphyroclasts and fine-grained amphibole within the matrix (Matrix amphibole). The trace element and Cl contents of the bleb and green amphiboles indicate magmatic and metamoprhic origins, respectively. The bleb amphibole is interpreted to have crystallized from a hydrous silicate melt derived from an oxide gabbro-forming melt prior to retrograde metamorphism. In contrast, the compositions of the coronitic amphibole and matrix amphibole vary between those of typical magmatic and metamorphic amphiboles, suggesting that the amphibole-forming reactions were continuously retrogressive. Retrograde metamorphism is generally interpreted to have involved seawater-derived fluids, but the trace element contents of the coronitic and matrix amphiboles do not differ significantly from those of the original minerals (i.e., clinopyroxene and plagioclase). One sample of gabbro mylonite (KH07–02-D18–1) contains amphiboles with high concentrations of light rare earth elements, indicating a large influx of externally derived LREE-enriched fluids. These fluids are interpreted to have formed from an interaction between hydrous silicate melt with LREE-enriched composition and seawater-derived fluid. Our results suggest that multiple phases of melt–fluid infiltration occurred during the development of the detachment fault at the Godzilla Megamullion.
- Published
- 2019
31. Styles of Fe–Ti–V ore deposits in the Neoproterozoic layered mafic-ultramafic intrusions, south Eastern Desert of Egypt: Evidence for fractional crystallization of V-rich melts
- Author
-
Mohamed Zaki Khedr, Eiichi Takazawa, Shoji Arai, Robert J. Stern, Tomoaki Morishita, and Amr El-Awady
- Subjects
Geology ,Earth-Surface Processes - Published
- 2022
32. Magma mixing model for the genesis of middle crust in the Izu–Bonin–Mariana arc: evidence from plutonic rocks in the Mineoka-Setogawa ophiolitic mélange, central Japan
- Author
-
Akihiro Tamura, Hisatoshi Ito, Yuji Ichiyama, and Shoji Arai
- Subjects
020209 energy ,Continental crust ,Pluton ,Geochemistry ,Geology ,Crust ,02 engineering and technology ,010502 geochemistry & geophysics ,Collision zone ,01 natural sciences ,Accretionary complex ,Arc (geometry) ,0202 electrical engineering, electronic engineering, information engineering ,Igneous differentiation ,Paleogene ,0105 earth and related environmental sciences - Abstract
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, c...
- Published
- 2019
33. Heterogeneity of Mantle Peridotites from the Polar Urals (Russia): Evidence from New LA-ICP-MS Data
- Author
-
Akihiro Tamura, Shoji Arai, and Vladimir R. Shmelev
- Subjects
Peridotite ,020209 energy ,Pargasite ,Partial melting ,Geochemistry ,Metamorphism ,02 engineering and technology ,Pyroxene ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle (geology) ,0202 electrical engineering, electronic engineering, information engineering ,General Earth and Planetary Sciences ,Protolith ,Amphibole ,Geology ,0105 earth and related environmental sciences - Abstract
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 type, represented by lherzolites and diopside harzburgites, was originated from the partial melting (5%–10%) under the spinel fades conditions, while the second one, represented by diopside harzburgites, was formed under the polybaric partial melting (17%–19%) under garnet and spinel fades conditions. Subsequently, the mantle peridotite protolith was subject to fluid-induced partial melting in the suprasubduction setting that was resulted in the formation of harzburgites. Being affected by penetrating melts and fluids peridotites experienced the refertilization (LREE enrichment of clinopyroxenes) and high-temperature hydratation with subsequent development of pargasite and Mg amphibole. The high-T fluid-induced metamorphism at the subduction zone was accompanied by the formation of metaperidotites with clinochlore and REE-depleted tremolite.
- Published
- 2019
34. Petrologic nature of the active subarc crust-mantle boundary: Mixed magmatic-metasomatic processes recorded in xenoliths from Sabtang island, Luzon arc
- Author
-
Shoji Arai, Akihiro Tamura, Satoko Ishimaru, Miyuki Takeuchi, Betchaida D. Payot, and Gabriel Theophilus V. Valera
- Subjects
Basalt ,Olivine ,010504 meteorology & atmospheric sciences ,Andesite ,Geochemistry ,Crust ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle (geology) ,Geophysics ,Geochemistry and Petrology ,engineering ,Xenolith ,Metasomatism ,Geology ,Amphibole ,0105 earth and related environmental sciences - Abstract
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, orthopyroxenites, clinopyroxenites, hornblendites, and gabbros, all hosted in basaltic to andesitic lavas. Petrographic characteristics suggest the metasomatic formation of orthopyroxenites and hornblendites from dunites and clinopyroxenites, respectively. The apparently primary minerals are homogeneous in composition. Olivine is relatively magnesian (Fo82–90) and chromian spinel is rich in Cr# (=Cr/[Cr + Al], around 0.7) in dunites. Clinopyroxene is relatively magnesian (Mg# = Mg/[Mg + Fe2+] = 0.73–0.93) in clinopyroxenites and gabbros, and plagioclase is highly anorthitic (An89–98) in the gabbros. The primary mineral assemblage reflects crystallization of olivine and spinel followed by clinopyroxene all occurring in the uppermost mantle and lower crust of the Luzon arc. The orthopyroxenes and amphiboles were metasomatically produced at the expense of olivine and clinopyroxene, respectively. Clinopyroxene in the xenoliths is in equilibrium with the magmas that formed the Sabtang volcanics. They have relatively elevated contents of large-ion lithophile elements and light-rare-earth elements, which suggest derivation from an enriched mantle. The Sabtang xenoliths evidence the very active modification of the subarc mantle-crust boundary zone by mantle-derived magmas and slab-derived melts/fluids so that the mineral assemblage of the resultant rocks is similar to that of the predominant recent magma.
- Published
- 2019
35. Compositional heterogeneity of a websterite xenolith from Kurose, southwest Japan: insights into the evolution of lower crust beneath the Japan Arc
- Author
-
Akihiro Tamura, Tahmineh Pirnia, Makoto Miura, Shoji Arai, and Miyuki Takeuchi
- Subjects
Arc (geometry) ,Geochemistry and Petrology ,Websterite ,Geochemistry ,Island arc ,Crust ,Xenolith ,Geology - Published
- 2019
36. Na–bearing tremolites as reservoirs of fluid–mobile elements in the mantle wedge: inference from the Ochiai–Hokubo complex (Southwest Japan) in high–P schists
- Author
-
Hidehiko Inoue, Shoji Arai, Miki Shirasaka, and Yoshito Ishida
- Subjects
Geophysics ,Bearing (mechanical) ,Mantle wedge ,law ,Mantle metasomatism ,Schist ,Inference ,Geology ,Petrology ,law.invention - Published
- 2019
37. Crustal anorthosite formation by deep‐seated hydrothermal circulation beneath fast‐spreading axis: Constraints from chronological approach, Sr isotope, and fluid–chromite inclusion investigation
- Author
-
Jiwon Eom, Shoji Arai, Shigeyuki Wakaki, Hisashi Asanuma, Akira Tsuchiyama, Akira Miyake, Norikatsu Akizawa, Takahiro Aze, Hodaka Kawahata, Tsuyoshi Ishikawa, Tetsu Kogiso, Yohei Igami, and Yusuke Yokoyama
- Subjects
Anorthosite ,Isotope ,Geochemistry ,Geology ,Chromite ,Inclusion (mineral) ,Hydrothermal circulation - Published
- 2021
38. Metasomatized peridotite xenoliths from the cretaceous rift-related Natash volcanics and their bearing on the nature of the lithospheric mantle beneath the southern part of the Eastern Desert of Egypt
- Author
-
Ahmed A. Madani, Shoji Arai, Natsue Abe, and Adel A. Surour
- Subjects
Basalt ,Peridotite ,Diopside ,Olivine ,010504 meteorology & atmospheric sciences ,Geochemistry ,Geology ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Mantle (geology) ,Geochemistry and Petrology ,visual_art ,engineering ,visual_art.visual_art_medium ,Phlogopite ,Xenolith ,Metasomatism ,0105 earth and related environmental sciences - Abstract
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 (lherzolite to harzburgite). Cr and Mg numbers (Cr#, Mg#) of Cr-spinel vary from 0.06 to 0.45 and 0.73 to 0.81, respectively. The correlation between Cr# and Mg# of the Cr-spinel in the studied xenoliths is weakly negative and its TiO2 content is slightly higher than in abyssal peridotite that was not affected by melt injection. The chemistry of ortho- and clinopyroxene suggests enstatite and chromian diopside compositions, respectively, with distinct signatures of a sub-continental mantle source. In particular, the Na2O contents (>1.0 wt%) and AlVI/AlIV ratios (1.2–2.6) of chromian diopside suggest such an origin. Two-pyroxene geothermometry indicates a temperature of about 900 °C, which is slightly lower than that of ordinary spinel peridotite xenoliths from other rift zones. It is evident that the studied peridotite xenoliths had experienced mantle processes (e.g. decompression melting, magma upwelling and metasomatism) at higher pressure than abyssal peridotites. The trace-element chemistry of clinopyroxene, e.g. high LREE/HREE ratios {(Ce/Yb)n = 7}, high LREE contents (>3.6 ppm and up to 30.0 ppm Ce) and high Sr between >85.6 ppm and 466 ppm, indicates metasomatic alteration of the peridotite. Clinopyroxene in one sample has very low Ti/Eu and high LREE/HREE ratios. Clinopyroxene with (Ce/Yb)n higher than 3–4 and Ti/Eu ratio lower than 1500 may have experienced carbonatite or carbonate-rich melt metasomatism prior to their incorporation into the host basalt. The basalt itself is almost devoid of any carbonatization and hence the studied mantle peridotites were carbonatized before the generation of the basaltic magma but following an earlier event of K-metasomatism as indicated by the presence of phlogopite. The studied peridotites from the Wadi Natash area were altered by a carbonate-rich melt during a rifting stage. The results of the present paper indicate that the Natash basalts with their peridotite xenoliths extruded along transversal fractures of the NW-trending Nuqra-Kom Ombo-Kharit continental rift on its western shoulder in the south Eastern Desert of Egypt.
- Published
- 2021
39. Petrogenesis of arc-related serpentinized peridotites (Egypt): Insights into Neoproterozoic mantle evolution beneath the Arabian-Nubian Shield
- Author
-
Mohamed Zaki Khedr, Eiichi Takazawa, Christoph Hauzenberger, Akihiro Tamura, Shoji Arai, Robert James Stern, Tomoaki Morishita, and Amr El-Awady
- Subjects
Geology ,Earth-Surface Processes - Published
- 2022
40. Post-Serpentinization Formation of Theophrastite-Zaratite by Heazlewoodite Desulfurization: An Implication for Shallow Behavior of Sulfur in a Subduction Complex
- Author
-
Tomoyuki Mizukami, Norikatsu Akizawa, Shoji Arai, Satoko Ishimaru, and Makoto Miura
- Subjects
lcsh:QE351-399.2 ,010504 meteorology & atmospheric sciences ,Metamorphic rock ,Geochemistry ,serpentinization ,engineering.material ,010502 geochemistry & geophysics ,Sanbagawa metamorphic belt ,01 natural sciences ,chemistry.chemical_compound ,Japan ,theophrastite ,zaratite ,Sulfate ,0105 earth and related environmental sciences ,Awaruite ,Anhydrite ,Olivine ,lcsh:Mineralogy ,Geology ,desulfurization ,Heazlewoodite ,millerite ,Geotechnical Engineering and Engineering Geology ,heazlewoodite ,chemistry ,engineering ,exhumation ,Carbonate ,subduction ,Millerite - Abstract
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 theophrastite-zaratite aggregate from Fujiwara most typically occurs in association with nickel sulfides, which form a composite grain with awaruite and magnetite within an antigorite-rich part of the rock. The theophraste-zaratite formed possibly together with millerite (NiS) from heazlewoodite (Ni3S2). This represents a partial desulfurization of heazlewoodite, which contains or interlocks with laths of antigorite, suggesting their cogenesis. The desulfurization occurred at an early stage of, or during, exhumation of the subduction complex toward the surface, where sulfur was oxidized and removed as sulfate ions. Serpentinization of olivine has not been associated with the formation of theophrastite-zaratite, and an oxidized condition has been kept at this post-serpentinization stage. The sulfate ions liberated in part precipitated anhydrite where calcium was available in the surrounding rocks. This shows one of the shallow migration pathways of sulfur in the subduction zone, especially to the forearc area.
- Published
- 2020
41. Origin of spinel-hosted mineral inclusions in mantle peridotite from Setogawa in the Circum-Izu Massif Serpentine Belt, central Japan: Implications for the chromitite genesis
- Author
-
Akihiro Tamura, Tomoaki Morishita, Shoji Arai, and Makoto Miura
- Subjects
Peridotite ,Spinel ,Geochemistry ,Geology ,Magma chamber ,engineering.material ,Geochemistry and Petrology ,Transition zone ,Magma ,engineering ,Chromitite ,Economic Geology ,Chromite ,Melt inclusions - Abstract
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 plutonic rocks, such as dunites and troctolites, form the Moho transition zone (MTZ). The Setogawa harzburgite host is similar in petrography and geochemistry to the MTZ harzburgite from the Oman ophiolite, and is possibly a low-pressure restite after melt-assisted partial melting or reaction with a percolating magma. The orthopyroxene-melt reaction, which is essentially responsible for producing those rocks from the peridotite (harzburgite), can precipitate chromian spinel as well as generate chemically heterogeneous melts along decomposing orthopyroxenes. The spinel-hosted melt inclusions in podiform chromitites are most frequently trapped at the reaction front between the spinel-oversaturated, spinel-loaden magma and mantle orthopyroxene (=harzburgite). The spinel-loaden magma had been produced via the same reaction at lower levels and moved upward. The spinel quickly overgrows to include chemically heterogenous melt drops, some of which are high in Cr/Al ratio and precipitate high-Cr spinel via reaction with the wall spinel. The chemical character (Cr/Al ratio) of podiform chromitites would be determined by the accumulative contribution from the melt derived from orthopyroxene decomposition during the passage of the melt through the upper mantle. We can speculate that the chromian spinel grains containing similar melt inclusions from the stratiform chromitite are transported as xenocrysts of mantle origin. The parental magma for layered intrusions possibly reacted with the peridotite when it passed through the mantle before arriving at a crustal magma chamber, showing a possible genetic linkage between the podiform and stratiform chromitites.
- Published
- 2022
42. Composite origin of magnetite deposits hosted in Oman peridotites: Evidence for iron mobility during serpentinization
- Author
-
Shoji Arai and Mohamed Zaki Khedr
- Subjects
Calcite ,Olivine ,010504 meteorology & atmospheric sciences ,Spinel ,Partial melting ,Geochemistry ,Geology ,engineering.material ,010502 geochemistry & geophysics ,Ophiolite ,01 natural sciences ,chemistry.chemical_compound ,chemistry ,Geochemistry and Petrology ,engineering ,Economic Geology ,Chemical composition ,Chlorite ,0105 earth and related environmental sciences ,Magnetite - Abstract
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 deposits occur in several forms such as fibrous crystals, oval or rounded grains, strings and cluster shapes, in fine-grained iron-rich chlorite and calcite matrices. The chromian spinel (Cr# = 0.38–0.56) within the magnetite deposits is similar in texture, mode of occurrence and chemical composition to that in the underlying serpentinized harzburgites (chromian spinel Cr# = 0.37–0.50), and plots in the space of abyssal peridotites. The mineral chemistry of chromian spinel, olivine and clinopyroxene (Cpx) suggested that the Aniba harzburgites are refractory residue after high-degree (15–25%) partial melting and are similar to abyssal harzburgites from a normal ridge segment. This is confirmed by a Cpx trace-element character with high depletion in light rare earth elements (LREE), Ta and Zr relative to heavy REE. The iron of our magnetite deposits was possibly derived from two sources: one is an essentially internal source of iron from the breakdown of Fe-rich serpentines after olivine during low-T serpentinization (
- Published
- 2018
43. Multi-scale development of a stratiform chromite ore body at the base of the dunitic mantle-crust transition zone (Maqsad diapir, Oman ophiolite): The role of repeated melt and fluid influxes
- Author
-
Nicolas Granier, Anastassia Y. Borisova, Shoji Arai, Mathieu Rospabé, Georges Ceuleneer, Géosciences Environnement Toulouse (GET), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Department of Earth Science [Kanazawa], Kanazawa University (KU), Lomonosov Moscow State University (MSU), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Brest (UBO), Dynamique terrestre et planétaire (DTP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Geology Department, Moscow State University, Moscow 119992, and Université Fédérale Toulouse Midi-Pyrénées-Centre National d'Études Spatiales [Toulouse] (CNES)
- Subjects
010504 meteorology & atmospheric sciences ,[SDU.STU.PE]Sciences of the Universe [physics]/Earth Sciences/Petrography ,Geochemistry ,[SDU.STU]Sciences of the Universe [physics]/Earth Sciences ,engineering.material ,010502 geochemistry & geophysics ,Ophiolite ,Oman ophiolite ,01 natural sciences ,chemistry.chemical_compound ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,Geochemistry and Petrology ,Transition zone ,ComputingMilieux_MISCELLANEOUS ,Dunitic mantle-crust transition zone ,0105 earth and related environmental sciences ,Olivine ,Fractional crystallization (geology) ,Melt hybridization ,Chromite ,Stratiform chromitite ,Geology ,Diapir ,Silicate ,chemistry ,[SDU]Sciences of the Universe [physics] ,engineering ,Chromitite ,[SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy - Abstract
International audience; 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. The ore body is about 50 m thick and its lateral extent does not exceed several hundred meters. The layering dips gently to the southeast, parallel to that of the overlying gabbroic cumulates. The chromite composition is typical of a MORB kindred - moderate XCr (100 x Cr/(Cr + Al) atomic ratio), ranging from 48 to 60, and relatively high TiO2 content, ranging from about 0.3 to 0.5 wt% -, a characteristic shared by most lithologies issued from the igneous activity of the Maqsad diapir. The silicate matrix is essentially made of slightly serpentinized olivine with minor clinopyroxene and rare pargasitic amphibole, orthopyroxene and garnet. This strongly contrasts with the nature of the mineral inclusions mostly made of the assemblage amphibole-orthopyroxene-mica, enclosed in the chromite grains and represented in abundance all along the ore body whatever the ore grade. The inclusions demonstrate the involvement of a silica- and water-rich melt and/or fluid, in addition to MORB, in the early stages of chromite crystallization. The chemical composition of chromite, silicate matrix, together with the one of silicate inclusions display well-defined evolutions vertically along the stratiform chromitite. At the scale of the ore body, the compositional trends are independent of the ore concentration but the major kinks in these trends are well-correlated with levels of magmatic breccias. This shows that abrupt chemical changes can be attributed to sudden melt ± fluids injection events followed mainly by melt-fluid-rock interaction and in a lesser extent by quieter evolution by fractional crystallization. At the thin section scale, second order chemical variations, essentially in the Mg# (100 Mg/(Mg þ Fe2þ) atomic ratio) of chromite and Fo of olivine, are clearly attributable to re-equilibration between these two solid phases, possibly in the presence of an interstitial melt/fluid.
- Published
- 2019
44. Petrologic characteristics of the upper mantle beneath island arcs
- Author
-
Shoji Arai and Satoko Ishimaru
- Subjects
010504 meteorology & atmospheric sciences ,General Engineering ,Geochemistry ,General Earth and Planetary Sciences ,Island arc ,010502 geochemistry & geophysics ,01 natural sciences ,Geology ,0105 earth and related environmental sciences ,General Environmental Science - Published
- 2018
45. Cr-spinel records metasomatism not petrogenesis of mantle rocks
- Author
-
Luc Serge Doucet, Shoji Arai, Youngwoo Kil, Steven M. Reddy, David W. Saxey, Zheng-Xiang Li, Mohamed Hamdy, Hamed Gamal El Dien, and Denis Fougerouse
- Subjects
010504 meteorology & atmospheric sciences ,Science ,General Physics and Astronomy ,Mid-Atlantic Ridge ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,Mantle (geology) ,Metasomatism ,lcsh:Science ,Petrology ,0105 earth and related environmental sciences ,Petrogenesis ,Multidisciplinary ,Subduction ,Spinel ,General Chemistry ,Mineralogy ,Plate tectonics ,Geochemistry ,engineering ,lcsh:Q ,Geology - Abstract
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/(Cr + Al)) is homogenous, insensitive to post-formation modification and therefore a robust petrogenetic indicator. However, we demonstrate that the composition of Cr-spinel can be modified by fluid/melt-rock interactions in both sub-arc and sub-mid oceanic mantle. Metasomatism can produce Al-Cr heterogeneity in Cr-spinel that lowers the Cr/Al ratio, and therefore modifies the Cr#, making Cr# ineffective as a geotectonic and mantle melting indicator. Our analysis also demonstrates that Cr-spinel is a potential sink for fluid-mobile elements, especially in subduction zone environments. The heterogeneity of Cr# in Cr-spinel can, therefore, be used as an excellent tracer for metasomatic processes., Chromian-spinel from mafic-ultramafic rocks is used as a reliable geotectonic and mantle melting indicator. Here, the authors argue that this only works partially – it can be used to assess information on mantle metasomatic processes but not petrogenesis.
- Published
- 2019
46. Diversity and evolution of suboceanic mantle: Constraints from Neotethyan ophiolites at the eastern margin of the Indian plate
- Author
-
Soumi Chattopadhaya, Akihiro Tamura, Sarmishtha Mukhopadhyay, Shoji Arai, Thungyani N. Ovung, Tomoaki Morishita, Debaditya Bandyopadhyay, and Biswajit Ghosh
- Subjects
geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Trace element ,Geochemistry ,Geology ,Mid-ocean ridge ,010502 geochemistry & geophysics ,Ophiolite ,01 natural sciences ,Mantle (geology) ,Abyssal zone ,Forearc ,0105 earth and related environmental sciences ,Earth-Surface Processes - Abstract
The mantle sections of four Neotethyan ophiolite bodies viz. Nagaland, Manipur, Andaman island and Rutland island lie along the eastern margin of the Indian plate. Among the at least two existing ophiolite belts in this region, all of these four ophiolite bodies belong to the western ophiolite belt. The major and trace element signatures of the constituent minerals of mantle peridotites of these ophiolites suggest that the samples from Nagaland, Manipur bear unequivocal signatures of abyssal peridotites. The compositional spectrum observed in them is within the limit of anhydrous melting of a MORB mantle source under reasonable melting condition. The Andaman ophiolite although overall characterizes the same, however, some mantle peridotites from this ophiolite might have experienced a hydrous melting event. The Rutland samples are distinct, showing signatures attesting to their forearc origin. The compositional spectrum observed in Nagaland, Manipur and a group of Andaman samples are grossly similar with samples recovered from Philippine Sea basins. Accordingly, interpretation regarding the geotectonic setting for the origin of these ophiolites straddles between mid-ocean ridge (MOR) and back-arc. If they truly represent their origin at MOR setting then the plagiogranites in these places showing arc affinity likely represent a later arc-related event, without having much connotation to the age of these ophiolites. Alternatively this study establishes a back-arc origin of these ophiolites.
- Published
- 2018
47. Roll-Back, Extension and Mantle Upwelling Triggered Eocene Potassic Magmatism in NW Iran
- Author
-
Hadi Shafaii Moghadam, Ghasem Ghorbani, Jun-Ichi Kimura, Mohamed Zakie Khedr, Maria Kirchenbaur, Dieter Garbe-Schönberg, William L. Griffin, Shoji Arai, Suzanne Y. O'Reilly, Reza Maghdour-Mashhour, Robert J. Stern, and R. C. Murphy
- Subjects
Geophysics ,010504 meteorology & atmospheric sciences ,Subduction ,Geochemistry and Petrology ,Magmatism ,Geochemistry ,Upwelling ,010502 geochemistry & geophysics ,01 natural sciences ,Geology ,Mantle (geology) ,0105 earth and related environmental sciences - Published
- 2018
48. Metallogeny of the peridotite-hosted magnetite ores of the Nain ophiolite, Central Iran: Implications for Fe concentration processes during multi-episodic serpentinization
- Author
-
Shoji Arai, Mohammad Ali Mackizadeh, Makoto Miura, and Alireza Eslami
- Subjects
Peridotite ,010504 meteorology & atmospheric sciences ,Geochemistry ,Geology ,010502 geochemistry & geophysics ,Ophiolite ,01 natural sciences ,Silicate ,Metallogeny ,Petrography ,chemistry.chemical_compound ,chemistry ,Geochemistry and Petrology ,Economic Geology ,Shear zone ,Chlorite ,0105 earth and related environmental sciences ,Magnetite - Abstract
Magnetite bodies of the Late Cretaceous Nain ophiolite melange (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 and pods of massive magnetite rocks exposed along a semi-brittle shear zone between pervasively serpentinized harzburgites, upper one with higher-Cr# [=Cr/(Cr + Al), 0.6–0.7] spinel and lower one with lower Cr# (0.5). Silicate mesostasis of the ore bodies is composed of stringy serpentine and chlorite. Cr-spinel grains are occasionally found dispersed within the magnetite rocks. Serpentines of the host serpentinized harzburgites show mesh and bastite textures, and were in part replaced by fibrous serpentine showing an interpenetrating texture. The Cr-spinels show a wide range of Cr# (0.5–0.7) and Mg# [=Mg/(Mg + Fe2+), 0.5–0.7], low TiO2 contents (
- Published
- 2018
49. Analysis of detritus from mantle-derived rocks
- Author
-
Shoji Arai
- Subjects
010504 meteorology & atmospheric sciences ,General Engineering ,Geochemistry ,General Earth and Planetary Sciences ,01 natural sciences ,Mantle (geology) ,Geology ,0105 earth and related environmental sciences ,General Environmental Science - Published
- 2018
50. Chromian spinels and olivines in a contact-metamorphosed peridotite-sediment system from Nagasawa, SW Japan: Implications for mobility of elements in a hydrothermal condition system
- Author
-
Makoto Miura, Shoji Arai, and Ichiro Matsumoto
- Subjects
Peridotite ,Mineral ,010504 meteorology & atmospheric sciences ,Pentlandite ,Metamorphic rock ,Spinel ,Geochemistry ,Geology ,engineering.material ,010502 geochemistry & geophysics ,01 natural sciences ,Hydrothermal circulation ,chemistry.chemical_compound ,chemistry ,Geochemistry and Petrology ,engineering ,Economic Geology ,Pyrrhotite ,0105 earth and related environmental sciences ,Magnetite - Abstract
We describe some unusual metaperidotites that form a mega-block in thermally metamorphosed sediments adjacent to a granitic intrusion in the Nagasawa area, SW Japan, to investigate mobility of elements in a peridotite-sediment-fluid system. The critical mineral assemblage of the metaperidotite is olivine + talc + antigorite, indicating a univariant reaction at ∼500 °C. The metaperidotites contain chromian spinels as well as up to 5% of sulfides (pyrrhotite and pentlandite with limited solid solutions) that form composite grains with magnetite. The host sediments contain detrital chromian spinels. The olivines in the metaperidotites have low contents of NiO (0.1–0.2 wt%), almost irrespective of variable Fo contents (85–92). The chromian spinels in the metaperidotites have high values of Cr# (0.9–1.0) [Cr# = Cr/(Cr + Al)], and low values of Mg# (∼0.2) [Mg# = Mg/(Mg + Fe 2+ )] and Y Fe ( Fe = Fe 3+ /(Fe 3+ + Cr + Al)]. They contain appreciable amounts of ZnO (∼1 wt%) and low contents of CoO and NiO. The detrital chromian spinels in the metasediments have intermediate values of Cr# (0.4–0.8) and low values of Mg# (∼0) and Y Fe (∼0), but they have high contents of ZnO (up to 10 wt%). The olivines in the peridotites contain inclusions of high-Cr# chromian spinel rather than magnetite. The peculiar characteristics of the Nagasawa metaperidotites and hornfelses resulted from a contact metamorphic event at ∼500 °C that was accompanied by interactions between peridotite and sediment that were facilitated by circulating hydrothermal fluids. The mobile zinc in these fluids was possibly derived from the sediments.
- Published
- 2017
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.