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.

The chromian spinels of the Lyavaraka ultrabasic complex, Serpentinite Belt, Kola Peninsula, Russia: Patterns of zoning, hypermagnesian compositions, and early oxidation

2021 ◽  
Vol 59 (6) ◽  
pp. 1693-1709
Author(s):  
Andrei Y. Barkov ◽  
Andrey A. Nikiforov ◽  
Vladimir N. Korolyuk ◽  
Larisa P. Barkova ◽  
Robert F. Martin
Keyword(s):  
Kola Peninsula ◽  
First Generation ◽  
Ferric Iron ◽  
Chromian Spinel ◽  
Maximum Value ◽  
Two Generations ◽  
High Level ◽  
A Minor ◽  
Compositional Series ◽  
Minor Quantity

ABSTRACT The maximum value of Mg# [= 100Mg/(Mg + Fe2+ + Mn)] in chromium-bearing spinel-group minerals (Chr) in the Ultrabasic Core Zone (UCZ) of the Lyavaraka orthopyroxenite – harzburgite – dunite complex of the Serpentinite Belt in the Kola Peninsula is 54.5–67.5. Such highly magnesian compositions of spinel are associated with notable enrichments of ferric iron (Fe3+# 58–63). There are two generations of accessory Chr in the UCZ unit. The first generation occurs as inclusions in olivine that is not unusually magnesian (Mg# 90.3), and the second is closely associated with serpentine. The compositional series of Chr at Lyavaraka attains more aluminous compositions than was observed in nearby intrusive bodies. The anomalously high level of Mg in Chr, also manifest in ilmenite, is mainly a result of the high intrinsic fugacity of oxygen attained locally in the melt. A progressive buildup in H2O and increase in fO2 likely resulted from efficient vesiculation and selective loss of H2 from the Al-undepleted komatiitic magma crystallizing in a shallow setting. The chromian spinel forming in such a modified magma is virtually unzoned in Mn, and a minor quantity of Mn is also present in olivine and orthopyroxene. In contrast, zinc is strongly partitioned in the core of Chr, as it is relatively incompatible in the coexisting olivine and orthopyroxene at that stage. Zinc efficiently partitioned into the H2O-enriched melt, which crystallized as the pegmatitic orthopyroxenite near the contacts at Lyavaraka. A high potential of oxidation appears to be characteristic of all orthopyroxenite – harzburgite – dunite suites of the Serpentinite Belt formed from a primitive melt of komatiitic composition.

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.

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;

Petrogenesis and tectonic setting of the Bondla mafic-ultramafic complex, western India: Inferences from chromian spinel chemistry

2016 ◽  
Vol 130 ◽  
pp. 192-205 ◽  
Author(s):  
C. Ishwar-Kumar ◽  
V.J. Rajesh ◽  
B.F. Windley ◽  
T. Razakamanana ◽  
T. Itaya ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Chromian Spinel ◽  
Western India ◽  
Ultramafic Complex

Learning Motivation of Adults Involved in AAC Intervention

2011 ◽  
Vol 20 (2) ◽  
pp. 69-74 ◽  
Author(s):  
Amber Thiessen ◽  
Christy Horn ◽  
David Beukelman ◽  
Sarah E. Wallace
Keyword(s):  
Adult Learners ◽  
Augmentative And Alternative Communication ◽  
Learning Motivation ◽  
Alternative Communication ◽  
Key Characteristics

Abstract The augmentative and alternative communication (AAC) personnel framework identifies the various types of people involved in successful AAC interventions. The purposes of this article are to summarize information in the AAC intervention literature that documents the role and impact of various AAC personnel, describe key characteristics of adult learners, and review research that focuses on learning motivations and preferences of adults within the AAC framework.

Combining SPARSE fMRI Designs with SENSE at High Field Strength

2006 ◽  
Vol 178 (01) ◽  
Author(s):  
L Scheef ◽  
M Daamen ◽  
U Fehse ◽  
MW Landsberg ◽  
DO Granath ◽  
...  
Keyword(s):  
Field Strength ◽  
High Field ◽  
High Field Strength

APPLYING THE ISF TECHNOLOGY TO PRODUCE THE CAR PART MODELS

2010 ◽  
Vol 13 (4) ◽  
pp. 91-98
Author(s):  
Tuan Dinh Phan ◽  
Binh Thien Nguyen ◽  
Dien Khanh Le ◽  
Phuong Hoang Pham
Keyword(s):  
Rapid Prototyping ◽  
Incremental Sheet Forming ◽  
Cad Model ◽  
Post Processing ◽  
Technological Parameters ◽  
Batch Production ◽  
Complex Products ◽  
3D Cad ◽  
Real Size ◽  
Single Batch

The paper presents an application the research results previously done by group on the influence of technological parameters to the deformation angle and finish surface quality in order to choose technology parameters for the incremental sheet forming (ISF) process to produce products for the purpose of rapid prototyping or single-batch production, including all steps from design and process 3D CAD model, calculate and select the technological parameters, setting up manufacturing and the stage of post-processing. The samples formed successfully showed high applicability of this technology to practical work, the complex products with the real size can be produced in industries: automotive, motorcycle, civil...

Mechanisms of Global Governance: Economic Analysis

2013 ◽  
pp. 4-28 ◽  
Author(s):  
L. Grigoryev ◽  
A. Kurdin
Keyword(s):  
Property Rights ◽  
Economic Analysis ◽  
Global Governance ◽  
International Organizations ◽  
Economic Activity ◽  
Global Level ◽  
Narrow Sense ◽  
Key Characteristics ◽  
Global Problems

The coordination of economic activity at the global level is carried out through different mechanisms, which regulate activities of companies, states, international organizations. In spite of wide diversity of entrenched mechanisms of governance in different areas, they can be classified on the basis of key characteristics, including distribution of property rights, mechanisms of governance (in the narrow sense according to O. Williamson), mechanisms of expansion. This approach can contribute not only to classifying existing institutions but also to designing new ones. The modern aggravation of global problems may require rethinking mechanisms of global governance. The authors offer the universal framework for considering this problem and its possible solutions.

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