scholarly journals Hydrous mineral inclusions in chromian spinel from the Yanomine ultramafic complex of the Sangun zone, Southwest Japan.

1995 ◽  
Vol 90 (9) ◽  
pp. 333-338 ◽  
Author(s):  
Ichiro MATSUMOTO ◽  
Shoji ARAI ◽  
Takeshi HARADA
Keyword(s):  
Chromian Spinel ◽  
Southwest Japan ◽  
Hydrous Mineral ◽  
Mineral Inclusions ◽  
Ultramafic Complex

scholarly journals Abyssal Peridotite as a Component of Forearc Mantle: Inference from a New Mantle Xenolith Suite of Bankawa in the Southwest Japan Arc

Minerals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 540 ◽  
Author(s):  
Shoji Arai ◽  
Akihiro Tamura ◽  
Makoto Miura ◽  
Kazuma Seike
Keyword(s):  
Alkali Basalt ◽  
Mantle Peridotite ◽  
Chromian Spinel ◽  
Abyssal Peridotite ◽  
Southwest Japan ◽  
Limited Sampling ◽  
Basalt Dike ◽  
Light Rare Earth Elements ◽  
Arc Magma ◽  
Forearc Mantle

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.

scholarly journals Petrological Features of the Burlakski and Nizhne-Derbinsk Mafic-Ultramafic Plutons (East Sayan Mountains, Siberia, Russia)

Minerals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 119
Author(s):  
Tamara Yakich ◽  
Matthew Brzozowski ◽  
Alexey Chernishov ◽  
Giovanni Grieco ◽  
Olesya Savinova ◽  
...  
Keyword(s):  
High Pressures ◽  
Basaltic Magma ◽  
Atomic Ratio ◽  
Chromian Spinel ◽  
Magmatic Differentiation ◽  
Central Asian ◽  
Ultramafic Complex ◽  
Ultramafic Cumulate ◽  
Ultramafic Cumulates ◽  
Parental Melts

The Nizhne-Derbinsk mafic-ultramafic complex is located between the Central Asian Orogenic Belt and the Siberian Craton and, is associated with the Ballyk fault. The largest, spatially related to each other, plutons in the central part of the complex are the Burlakski and Nizhne-Derbinsk. Rocks in the main units of these plutons are divided into three groups: peridotites (ultramafic), pyroxenites (sub-ultramafic), and gabbroic rocks (mafic). The ultramafic and sub-ultramafic cumulate series are devoid of plagioclase and contain <3 vol. % chromian spinel. The Fo content of olivine in the sub-ultramafic cumulates from both plutons ranges from Fo79 to Fo86. The En content [= Mg/(Mg + Fe + Ca) × 100 atomic ratio] of clinopyroxenes and orthopyroxenes varies from 46–56, and 63–80, respectively. Plagioclase corresponds to labradorite with An contents between 55 and 57. Hornblende is compositionally similar to pargasite. The sequence of change of rock units corresponds to the paragenesis: olivine − olivine + clinopyroxene (orthopyroxene) − clinopyroxene + orthopyroxene – clinopyroxene + orthopyroxene + plagioclase – orthopyroxene. Petrographic, mineralogical, and mineral chemical features of the Burlakski and Nizhne-Derbinsk plutons suggest that the diversity of the material composition of these plutons is due to the processes of magmatic differentiation in deep-seated conditions. Estimates of crystallization pressures and temperatures of the Burlakski and Nizhne-Derbinsk plutons suggest that they crystallized at high pressures ≥ 10kb and temperatures ranging from 1000–1400 °C. Mineralogical and petrological features suggest that the mafic-ultramafic cumulates were derived from a high-Mg basaltic magma. The presence of magmatic hornblende and hydrous mineral assemblages within the ultramafic cumulates indicates that the parental melts had been enriched in dissolved volatile constituents. Taking into account the age of the gabbronorites of the Burlakski pluton (~490 ± 11.8 Ma), the magmatism likely occurred during the Ordovician collision stage of the evolution of the Central Asian Fold Belt.

scholarly journals Synchrotron FTIR imaging of OH in quartz mylonites

2017 ◽  
Author(s):  
Andreas K. Kronenberg ◽  
Hasnor F. B. Hasnan ◽  
Caleb W. Holyoke III ◽  
Richard D. Law ◽  
Zhenxian Liu ◽  
...  
Keyword(s):  
Fluid Inclusions ◽  
Light Sources ◽  
Main Central Thrust ◽  
Absorption Bands ◽  
Hydrous Mineral ◽  
Ir Radiation ◽  
Mineral Inclusions ◽  
Measurement Resolution ◽  
Quartz Grains ◽  
Water Contents

Abstract. Methods of measuring OH absorption bands of fluid inclusions and hydrogen defects in deformed quartz rocks at high spatial resolution are described, using synchrotron infrared IR radiation coupled with a Fourier transform infrared FTIR microscope, and applied to imaging OH in mylonites of the Moine Thrust (from the Stack of Glencoul, NW Scotland Caledonides) and the Main Central Thrust (from the Himalayan front, Sutlej Valley, NW India). Previous measurements of water in deformed quartzites using conventional FTIR instruments, through apertures of 50–100 μm for specimens ~ 100 μm in thickness have shown that water contents of larger grains vary from one grain to another. However, the non-equilibrium variations in water content between neighboring grains and within quartz grains cannot be interrogated further without greater measurement resolution, nor can water contents be measured in finely recrystallized grains without including absorption bands due to fluid inclusions, films, and secondary minerals at grain boundaries. Synchrotron IR radiation is brighter and more collimated than offered by conventional FTIR globar light sources, and we have been able to distinguish and measure OH bands due to fluid inclusions, hydrogen point defects, and secondary hydrous mineral inclusions through an aperture of 10 μm for specimens > 40 μm thick. Doubly polished IR plates can be prepared with thicknesses down to 4–8 μm, but measurement of small OH bands is currently limited by strong interference fringes for samples

scholarly journals Zones of PGE–Chromite Mineralization in Relation to Crystallization of the Pados-Tundra Ultramafic Complex, Serpentinite Belt, Kola Peninsula, Russia

Minerals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 68
Author(s):  
Andrei Y. Barkov ◽  
Andrey A. Nikiforov ◽  
Larisa P. Barkova ◽  
Vladimir N. Korolyuk ◽  
Robert F. Martin
Keyword(s):  
Ferric Iron ◽  
Chromian Spinel ◽  
High Field Strength ◽  
Ultramafic Complex ◽  
Key Characteristics ◽  
Layered Complex ◽  
Outer Contact ◽  
Moving Front ◽  
Single Batch ◽  
Sulfide Species

The lopolithic Pados-Tundra layered complex, the largest member of the Serpentinite belt–Tulppio belt (SB–TB) megastructure in the Fennoscandian Shield, is characterized by (1) highly magnesian compositions of comagmatic dunite–harzburgite–orthopyroxenite, with primitive levels of high-field-strength elements; (2) maximum values of Mg# in olivine (Ol, 93.3) and chromian spinel (Chr, 57.0) in the Dunite block (DB), which exceed those in Ol (91.7) and Chr (42.5) in the sills at Chapesvara, and (3) the presence of major contact-style chromite–IPGE-enriched zones hosted by the DB. A single batch of primitive, Al-undepleted komatiitic magma crystallized normally as dunite close to the outer contact, then toward the center. A similar magma gave rise to Chapesvara and other suites of the SB–TB megastructure. Crystallization proceeded from the early Ol + Chr cumulates to the later Ol–Opx and Opx cumulates with accessory Chr in the Orthopyroxenite zone. The accumulation of Chr resulted from efficient cooling along boundaries of the Dunite block. The inferred front of crystallization advanced along a path traced by vectors of Ol and Chr compositions. Grains and aggregates of Chr were mainly deposited early after the massive crystallization of olivine. Chromium, Al, Zn and H2O, all incompatible in Ol, accumulated to produce podiform segregations or veins of chromitites. This occurred episodically along the moving front of crystallization. Crystallization occurred rapidly owing to heat loss at the contact and to a shallow level of emplacement. The Chr layers are not continuous but rather heterogeneously distributed pods or veins of Chr–Ol–clinochlore segregations. Isolated portions of melt enriched in H2O and ore constituents accumulated during crystallization of Ol. Levels of fO2 in the melt and, consequently, the content of ferric iron in Chr, increased progressively, as in other intrusions of the SB–TB megastructure. The komatiitic magma vesiculated intensely, which led to a progressive loss of H2 and buildup in fO2. In turn, this led to the appearance of anomalous Chr–Ilm parageneses. Diffuse rims of Chr grains, abundant in the DB, contain elevated levels of Fe3+ and enrichments in Ni and Mn. In contrast, Zn is preferentially partitioned into the core, leading to a decoupling of Zn from Mn, also known at Chapesvara. The sulfide species display a pronounced Ni-(Co) enrichment in assemblages of cobaltiferous pentlandite, millerite (and heazlewoodite at Khanlauta), deposited at ≤630 °C. The oxidizing conditions have promoted the formation of sulfoselenide phases of Ru in the chromitites. The attainment of high degrees of oxidation during crystallization of a primitive parental komatiitic magma accounts for the key characteristics of Pados-Tundra and related suites of the SB–TB megastructure.

Podiform and stratiform chromitite with PGE in Paleoproterozoic (2.1 Ga) Pados-Tundra ultramafic (ophiolite) complex (N-E part of the Fennoscandian Shield, Arctic region)

2020 ◽  
Author(s):  
Tamara Bayanova ◽  
Serov Pavel ◽  
Kunakkuzin Evgeniy ◽  
Steshenko Ekaterina ◽  
Borisenko Elena
Keyword(s):  
Arctic Region ◽  
Fennoscandian Shield ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Ophiolite Complex ◽  
Enriched Mantle ◽  
Ultramafic Complex ◽  
Magma Sources ◽  
Podiform Chromitites ◽  
Research Contract

&lt;p&gt;Pados-Tundra ultramafic complex belong to Serpentinite belt in the northern Fennoscandian Shield and composed of dunite-harzburgite-orthopyroxenite with 7 rhythms and 4 Cr layers. The associated massif named as Malyi Pados are considered as a satellite intrusion (Mamontov, Dokuchaeva, 2005) or dislocated block detached according by (Barkov et al., 2016). Nevertheless the complex includes of Dunite Zone with podiform and stratiform chromitite with Ir subgroup PGE (Ru, Os, Ir &amp;#8211; IPGE) and associated with chromian spinel in ophiolite (Joban, 2006). Fiestly unusual microtextures and mineralogical features with clinochlore, laurite and native Ru was found (Barkov et al., 2017).&lt;/p&gt;&lt;p&gt;Isotope U-Pb data on baddeleyite in core of zircon from mafic gabbronorite rocks of the Malyi Pados gave 2083&amp;#177;7 Ma and are coeval to ages of Cu-Ni Pechenga (1980 Ma) and PGE Bushveld deposits. Notably are measured new U-Pb ages with 2087&amp;#177;3 Ma for baddeleyite and metamorphic rutile with 1804&amp;#177;10 Ma from hornblendite dyke which are cutted ultramafic rocks of the Pados-Tundra complex.&lt;/p&gt;&lt;p&gt;New Sm-Nd mapping data for the main rocks of the complex are reflected model T&lt;sub&gt;DM&lt;/sub&gt; ages of primary protolith from 2.78 Ga to 2.36 Ga and 3.13 Ga for host rock with positive &amp;#949;Nd values from +2.7 to +2.1. New Sm-Nd investigations to podiform chromitites of the Pados-Tundra complex are similar to Sopcheozerskoe Cr-deposit (Dunite Block) of the Monchegorsk ore region with positive &amp;#949;Nd and young protolith ages about 2.7 Ga for primary magma sources instead of Paleoproterozoic Co-Cu-Ni and PGE layered intrusions of the Fennoscandian Shield with 2.4 Ga to 2.5 Ga for origin and 3.2 - 3.5 Ga of the protolith EM-1 enriched mantle plume reservoir (Bayanova et al., 2009, 2014, 2018). All new U-Pb on baddeleyite and Sm-Nd studies to whole rocks of the Pados-Tundra complex infer about ophiolite (spreading or oceanization of the crust) and presence diamond in podiform chromitites according to new highlights of (Ballhause et al., 2017).&lt;/p&gt;&lt;p&gt;All investigations are supported by RFBR 18-05-70082 (Arctic resources), 18-35-00152, 18-35-00246, Scientific Research Contract N0.0226-2019-0053 and Program of Presidium RAS 8.48.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document