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.

Mineral ages and zircon Hf isotopic composition of the Andong ultramafic complex: implications for the evolution of Mesozoic subduction system and subcontinental lithospheric mantle beneath SE Korea

2013 ◽  
Vol 151 (5) ◽  
pp. 765-776 ◽  
Author(s):  
GI YOUNG JEONG ◽  
CHANG-SIK CHEONG ◽  
KEEWOOK YI ◽  
JEONGMIN KIM ◽  
NAMHOON KIM ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Tectonic Setting ◽  
Eastern China ◽  
Mantle Xenoliths ◽  
Late Triassic ◽  
Magmatic Differentiation ◽  
Suprasubduction Zone ◽  
Ultramafic Complex ◽  
Yeongnam Massif ◽  
Subduction System

AbstractThe Phanerozoic subduction system of the Korean peninsula is considered to have been activated by at least Middle Permian time. The geochemically arc-like Andong ultramafic complex (AUC) occurring along the border between the Precambrian Yeongnam massif and the Cretaceous Gyeongsang back-arc basin provides a rare opportunity for direct study of the pre-Cretaceous mantle wedge lying above the subduction zone. The tightly constrained SHRIMP U–Pb age of zircons extracted from orthopyroxenite specimens (222.1±1.0 Ma) is indistinguishable from the Ar/Ar age of coexisting phlogopite (220±6 Ma). These ages represent the timing of suprasubduction zone magmatism likely in response to the sinking of cold and dense oceanic lithosphere and the resultant extensional strain regime in a nascent arc environment. The nearly coeval occurrence of a syenite-gabbro-monzonite suite in the SW Yeongnam massif also suggests an extensional tectonic setting along the continental margin side during Late Triassic time. The relatively enriched ɛHf range of dated zircons (+6.2 to −0.6 at 222 Ma) is in contrast to previously reported primitive Sr–Nd–Hf isotopic features of Cenozoic mantle xenoliths from Korea and eastern China. This enrichment is not ascribed to contamination by the hypothetical Palaeozoic crust beneath SE Korea, but is instead attributable to metasomatism of the lithospheric mantle during the earlier subduction of the palaeo-Pacific plate. Most AUC zircons show a restricted core-to-rim spread of ɛHf values, but some grains testify to the operation of open-system processes during magmatic differentiation.

Granitoids of the Central Asian Orogenic Belt and continental growth in the Phanerozoic

2000 ◽  
Vol 91 (1-2) ◽  
pp. 181-193 ◽  
Author(s):  
Bor-ming Jahn ◽  
Fuyuan Wu ◽  
Bin Chen
Keyword(s):  
Central Asia ◽  
Basaltic Magma ◽  
Orogenic Belt ◽  
Source Rocks ◽  
Central Asian Orogenic Belt ◽  
Central Asian ◽  
Wide Range ◽  
Mantle Component ◽  
T Values ◽  
Lower Crustal

The Central Asian Orogenic Belt (CAOB), also known as the Altaid Tectonic Collage, is characterised by a vast distribution of Paleozoic and Mesozoic granitic intrusions. The granitoids have a wide range of compositions and roughly show a temporal evolution from calcalkaline to alkaline to peralkaline series. The emplacement times for most granitic plutons fall between 500 Ma and 100 Ma, but only a small proportion of plutons have been precisely dated. The Nd-Sr isotopic compositions of these granitoids suggest their juvenile characteristics, hence implying a massive addition of new continental crust in the Phanerozoic. In this paper we document the available isotopic data to support this conclusion.Most Phanerozoic granitoids of Central Asia are characterised by low initial Sr isotopic ratios, positive εNd(T) values and young Sm—Nd model ages (TDM) of 300-1200 Ma. This is in strong contrast with the coeval granitoids emplaced in the European Caledonides and Hercynides. The isotope data indicate their ‘juvenile’ character and suggest their derivation from source rocks or magmas separated shortly before from the upper mantle. Granitoids with negative εNd(T) values also exist, but they occur in the environs of Precambrian microcontinental blocks and their isotope compositions may reflect contamination by the older crust in the magma generation processes.The evolution of the CAOB is probably related to accretion of young arc complexes and old terranes (microcontinents). However, the emplacement of large volumes of post-tectonic granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, intercalation of basaltic magma with lower crustal granulites, partial melting of the mixed lithologic assemblages leading to generation of granitic liquids, followed by extensive fractional crystallisation. The proportions of the juvenile or mantle component for most granitoids of Central Asia are estimated to vary from 70% to 100%.

Grenvillean evolution of the Beishan Orogen, NW China: Implications for development of an active Rodinian margin

2019 ◽  
Vol 132 (7-8) ◽  
pp. 1657-1680
Author(s):  
Jérémie Soldner ◽  
Chao Yuan ◽  
Karel Schulmann ◽  
Pavla Štípská ◽  
Yingde Jiang ◽  
...  
Keyword(s):  
Basaltic Magma ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Metamorphic Event ◽  
Garnet Growth ◽  
Geodynamic Setting ◽  
Element Analysis ◽  
Nw China ◽  
Central Asian ◽  
Back Arc

Abstract New geochemical and geochronological data are used to characterize the geodynamic setting of metasediments, felsic orthogneisses, and eclogite and amphibolite lenses forming the Beishan complex, NW China, at the southern part of the Central Asian Orogenic Belt. The metasediments correspond compositionally to immature greywackes receiving detritus from a heterogeneous source involving a magmatic arc and a Precambrian continental crust. Metagranitoids, represented by felsic orthogneisses, show both composition of greywacke-derived granitic melt with incompatible trace element patterns similar to the host metasediments. The eclogite lenses are characterized by high Nb contents (5.34–27.3 ppm), high (Nb/La)N (&gt;1), and low Zr/Nb ratios (&lt;4.5), which together with variable and negative whole-rock εNd(t) (–4.3 to –10.3) and zircon εHf(t) (–5.0 to + 2.3) values indicate an origin of enriched mantle source as commonly manifested by back-arc basalts at stretched continental margins. Combined with monazite rare earth element analysis, the in situ monazite U-Pb dating of metagraywacke (880.7 ± 7.9) suggests garnet growth during a high-temperature (HT) metamorphic event. Together with U-Pb dating of zircon metamorphic rims in amphibolite (910.9 ± 3.0 Ma), this indicates that the whole crustal edifice underwent a Grenvillian-age metamorphic event. The protolith ages of the eclogite (889.3 ± 4.8 Ma) and orthogneiss (867.5 ± 1.9 Ma) suggest that basalt underplating and sediment melting were nearly coeval with this HT metamorphism. Altogether, the new data allow placing the Beishan Orogen into a Grenvillean geodynamic scenario where: (1) The late Mesoproterozoic to early Neoproterozoic was marked by deposition of the greywacke sequence coeval with formation of an early arc. (2) Subsequently, an asthenospheric upwelling generated basaltic magma underneath the thinned subcontinental mantle lithosphere that was responsible for HT metamorphism, melting of the back-arc basin greywackes and intrusion of granitic magmas. These events correspond to a Peri-Rodinian supra-subduction system that differs substantially from the Neoproterozoic ophiolite sequences described in the Mongolian part of the Central Asian Orogenic Belt, thus indicating important lateral variability of supra-subduction processes along the Rodinian margin.

scholarly journals Petrology and geochemistry of high-Al chromitites from the MedellÍn Metaharzburgitic Unit (MMU), Colombia

2020 ◽  
Vol 72 (3) ◽  
pp. A120620
Author(s):  
Juan S. Hernández-González ◽  
Lídia Butjosa ◽  
Núria Pujol-Solà ◽  
Thomas Aiglsperger ◽  
Marion Weber ◽  
...  
Keyword(s):  
Thermal Evolution ◽  
Atomic Ratio ◽  
Ore Deposits ◽  
Chromian Spinel ◽  
Tholeiitic Magma ◽  
Fine Grained ◽  
San Pedro ◽  
Petrology And Geochemistry ◽  
Compositional Variations ◽  
Back Arc

The Medellin Metaharzburgitic Unit (MMU), emplaced onto the western continental margin of Pangea during Triassic time, is located in the Central Cordillera of Colombia and consists of metaharzburgites, minor metadunites and chromitite bodies (Patio Bonito and San Pedro ore deposits). The ultramafic rocks contain relicts of mantle-derived olivine, chromian spinel and minor orthopyroxene, and a later metamorphic mineral assemblage composed by tremolite, chlorite, talc, fine-grained recrystallized olivine, serpentine-group minerals, magnetite, and secondary chromian spinel, formed during the thermal evolution of the unit. The Cr# [Cr/(Cr+Al) atomic ratio] of the accessory primary chromian spinel in the metaperidotites ranges from 0.58 to 0.62 and overlaps those of supra-subduction peridotites from ophiolites. According to textural and compositional variations, the accessory chromian spinel in the metaperidotites can be classified into three groups: i) partially altered chromian spinel with an Al-rich core, ii) porous, Cr-Fe2+-enriched and Al-Mg-depleted chromian spinel, and iii) homogeneous Fe3+-rich chromian spinel. These variations can be related to superimposed medium-T metamorphism that reached amphibolite facies (ca. 600 ºC). Chromitite bodies associated with the metaperidotites have massive and semi-massive textures, and mainly consist of chromian spinel crystals, which show large unaltered cores surrounded by thin alteration rims of ferrian chromian spinel and chlorite. Chromitites are Al-rich (#Cr <0.6) and strongly depleted in platinum group elements (ΣPGE <41 ppb). The primary petrological and geochemical characteristics preserved in the metaperidotites and chromitites indicate that the MMU formed at shallow levels of a suboceanic lithospheric mantle related to a supra-subduction zone (back-arc basin/incipient arc scenario), and that the chromitites crystallized from a tholeiitic magma (back-arc basin basalt type).

Corundum-rich dykes constraining Triassic alkaline magmatism in the Ivrea-Verbano Zone (Southern Alps): a zircon approach

2021 ◽  
Author(s):  
Mattia Bonazzi ◽  
Antonio Langone ◽  
Simone Tumiati ◽  
Edoardo Dellarole ◽  
Maurizio Mazzucchelli ◽  
...  
Keyword(s):  
High Pressures ◽  
Crustal Contamination ◽  
Weighted Average ◽  
Western Alps ◽  
Southern Alps ◽  
Accessory Mineral ◽  
Alkaline Magmatism ◽  
Mafic Complex ◽  
High Concentrations ◽  
Parental Melts

&lt;p&gt;Zircon is a common accessory mineral in evolved magmatic rocks and its investigation can provide unevaluable geochronological and geochemical information. The lower continental crust forming the Ivrea-Verbano Zone (IVZ, Southern Alps) locally shows the discordant intrusion of swarms of felsic dykes, which petrology was poorly constrained. Corundum-rich (Crn up to 55 vol.%) felsic dykes were sampled in two different outcrops along the Sabbiola valley (central IVZ). Besides corundum, they consist mainly of sodic plagioclase (An=5-10 %), biotite-siderophyllite, &amp;#177;K-feldspar and &amp;#177;hercynite. These dykes intrude granulites and Permian mafic intrusives, showing either pegmatite-like or porphyroclastic textures and contain abundant zircon. Trace elements concentration, as well as the isotopic U-Pb and Lu-Hf compositions of zircons have been determined by LA-ICP-(MC)MS to unravel emplacement ages and nature of parental melts. U-Pb weighted average ages point to Norian emplacement (ca. 224 Ma). Zircons are characterized by very high concentrations in REE, Th, U, Nb and Ta. REE patterns show marked negative Eu anomaly. These data, in association with the enrichments of Na in plagioclases and of Fe in micas and oxides, suggest that the parent melts were extremely evolved differentiates. Porphyroclastic texture developed in the frame of magmatic processes due to volatiles overpressure. Strongly positive Hf&lt;sub&gt;(&lt;/sub&gt;&lt;sub&gt;t)&lt;/sub&gt; values (+13 on average) suggest a derivation of the parental melts from depleted to mildly enriched mantle sources. This observation and the corundum saturation (evidence for low silica activity) point to limited crustal contamination, which was favored by the high eutectic temperature of the host rocks. It is proposed that studied dykes segregated from peraluminous melts produced by exsolution processes affecting volatile-rich differentiates during alkaline magmatism (Bonazzi et al., 2020).&lt;/p&gt;&lt;p&gt;Triassic magmatic activity is largely documented throughout the Southern Alps, being related to different tectono-magmatic cycles. Nevertheless, before this study, the evidence of Triassic magmatism in IVZ was restricted only in its northernmost tip (Finero area, e.g. Zanetti et al., 2013; Schaltegger et al., 2015). This work provides robust constraints about the transition of the geochemical affinity of Southern Alps magmatism from orogenic-like to anorogenic during Norian, linked to a regional uprising of the asthenosphere and changes of tectonic regime.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Bonazzi, M.; Langone, A.; Tumiati, S.; Dellarole, E.; Mazzucchelli, M.; Giovanardi, T.; Zanetti, A. Mantle-Derived Corundum-Bearing Felsic Dykes May Survive Only within the Lower (Refractory/Inert) Crust: Evidence from Zircon Geochemistry and Geochronology (Ivrea&amp;#8211;Verbano Zone, Southern Alps, Italy). Geosciences 2020, 10, 281.&lt;/p&gt;&lt;p&gt;Schaltegger, U.; Ulianov, A.; Muntener, O.; Ovtcharova, M.; Peytcheva, I.; Vonlanthen, P.; Vennemann, T.; Antognini, M.; Girlanda, F. Megacrystic zircon with planar fractures in miaskite-type nepheline pegmatites formed at high pressures in the lower crust (Ivrea Zone, southern Alps, Switzerland). Am. Miner. 2014, 100, 83&amp;#8211;94.&lt;/p&gt;&lt;p&gt;Zanetti, A.; Mazzucchelli, M.; Sinigoi, S.; Giovanardi, T.; Peressini, G.; Fanning, C.M. SHRIMP U-Pb Zircon Triassic Intrusion Age of the Finero Mafic Complex (Ivrea-Verbano Zone, Western Alps) and its Geodynamic Implications. J. Pet. 2013, 54, 2235&amp;#8211;2265.&lt;/p&gt;

The chemistry and mineralogy of the olivine nodules of Calton Hill, Derbyshire

1963 ◽  
Vol 33 (261) ◽  
pp. 483-497 ◽  
Author(s):  
S. el D. Hamad
Keyword(s):  
Host Rock ◽  
Chromium Content ◽  
Basaltic Magma ◽  
Optical Data ◽  
Chromian Spinel ◽  
Chemical Analyses ◽  
High Chromium ◽  
Cell Parameters ◽  
Tie Line

SummaryChemical analyses, optical data, and cell parameters are given for olivine (Fo90·3 and Fo91·4), orthopyroxene (Ca1·5Mg89·0Fe9·5 and Ca9·8Mg88·6Fe10·6), clinopyroxene (Ca39·6Mg55·8Fe4·6), and chromian spinel from olivine nodules from the Carboniferous basalt of Calton Hill, Derbyshire. Chemical and modal analyses of the nodules and of their host rock are also presented. The distribution of Mg and Fe in the coexisting pyroxenes is fairly similar to that observed by Ross, Foster, and Myers (1954) but differs slightly in that the extension of the pyroxene tie-line intersects the Ca-Mg side of the Ca-Mg-Fe triangle. The clinopyroxene is a normal augite rather than the hydrous augite previously reported (Tomkeieff, 1928). The high chromium content of the spinel and clinopyroxene contrasts with the low value for this element in the host rock, suggesting that these minerals are not differentiates of the basaltic magma: the nodules are considered to represent fragments from a deep-seated peridotite.

Oxide minerals in the Turnagain ultramafic complex, northwestern British Columbia

1978 ◽  
Vol 15 (12) ◽  
pp. 1893-1903 ◽  
Author(s):  
Thomas Clark
Keyword(s):  
British Columbia ◽  
Oxygen Fugacity ◽  
Upper Triassic ◽  
Turbidity Currents ◽  
Chrome Spinel ◽  
Magmatic Differentiation ◽  
Cooling Process ◽  
Ultramafic Complex ◽  
Wide Range ◽  
Oxide Minerals

The oxide minerals in the Turnagain ultramafic complex, an Alaskan-type intrusion of possible Upper Triassic age in northwestern British Columbia, offer some important clues concerning the composition of magmas from which they separated and the chemical changes that they underwent during the cooling process. Chromite occurs as disseminations and vein-like concentrations in dunite, and as disseminations in wehrlite and olivine clinopyroxenite. Ilmenite is found in hornblendite. A small amount of primary magnetite is associated with intercumulus sulfide. Chrome spinel exhibits a very wide range of compositions. The ratio 100 Mg/(Mg + Fe2+) ranges from 69.7–3.6, and this is paralleled by a decrease in Cr2O3 (60.1–9.3%), and by increases in Fe2O3, TiO2, and MnO. Chromite rims are poorer in Cr and richer in Fe3+ than chromite cores. Magmatic differentiation was responsible for most of these variations. Subsolidus re-equilibration caused Mg/Fe2+ zoning in coexisting chromite and olivine, the ratio decreasing in chromite rims and increasing in rims of contacting olivine grains. Subsolidus re-equilibration was probably responsible for the enrichment in Mg of the minerals in a chromite-rich layer relative to those in the adjacent dunite. Disseminated chromite originated by cotectic crystallization; chromite-rich layers may have been deposited by magmatic turbidity currents. Several mineralogical and chemical features suggest that oxygen fugacity in the magmas was relatively low.

The ophiolites of southern Quebec: oceanic crust of Betts Cove type

1977 ◽  
Vol 14 (7) ◽  
pp. 1668-1673 ◽  
Author(s):  
W. R. Church
Keyword(s):  
Oceanic Crust ◽  
Basaltic Rocks ◽  
Internal Zone ◽  
External Domain ◽  
Ultramafic Cumulate ◽  
Ultramafic Cumulates ◽  
Orogenic Belts ◽  
Internal Domain

The Thetford and Asbestos ophiolites of the Eastern Townships of Quebec (Internal Domain) resemble the Betts Cove ophiolite of Newfoundland in three significant respects: (1) ultramafic cumulate sequences of the ophiolites include units with cumulus orthopyroxene; (2) the 'gabbro' unit is composed of a relatively thin yet compositionally and structurally complex clinopyroxenite–gabbro member which unconformably overlies the ultramafic cumulate sequence; and (3) basaltic rocks associated with the ophiolites have extremely low Ti contents. In contrast, in the Bay of Islands region of western Newfoundland (External Domain) basaltic rocks of the ophiolites of the Humber Arm Allochthon have Ti contents typical of normal oceanic crust; the cumulate sequences rarely contain cumulus orthopyroxene; and the 'gabbro' unit includes a major sequence of cumulus plagioclase-bearing rocks which appear to conformably follow the ultramafic cumulates. The Baie Verte ophiolite of Newfoundland is intermediate in character and location between the Betts Cove and Bay of Islands complexes. All of the ophiolites of the Internal Domain are overlain by sequences having conglomerate, olistostrome, and greywacke units containing abundant clastic material derived from ophiolitic rocks.The homologous nature of the Betts Cove and Thetford ophiolites lends some support to the view that the Fleur de Lys and Caldwell - Chain Lakes orthotectonic zones of the Appalachian system are laterally correlative, and that all ophiolites of the Internal Zone of the Appalachians are allochthonous rather than collapsed in situ small ocean basins. The variation exhibited by the ophiolites of the Appalachian system, even within the Internal Zone, cautions however against a too simplistic view of the role of ophiolites in plate tectonic models of orogenic belts of Appalachian type.

CHROMIAN SPINEL AS A PETROGENETIC INDICATOR: PART 2. PETROLOGIC APPLICATIONS

1967 ◽  
Vol 4 (1) ◽  
pp. 71-103 ◽  
Author(s):  
T. N. Irvine
Keyword(s):  
Oxygen Fugacity ◽  
Peritectic Reaction ◽  
High Pressures ◽  
Volcanic Rocks ◽  
Distribution Coefficients ◽  
Chromian Spinel ◽  
Low Oxygen ◽  
Petrogenetic Indicator

The crystallization of chromium-bearing spinel from silicate magmas is first examined, and then an attempt is made to apply the theory developed in Irvine (1965) to the principal occurrences of the mineral for which data are available. It is concluded that the chromium-rich varieties commonly known as chromite have generally formed simultaneously with olivine, and that their crystallization has in many occurrences been terminated by a peritectic (reaction) relation leading to formation of a pyroxene. The origin of the aluminium-rich varieties is more problematical and perhaps more varied; however, they evidently occur only in alpine-type peridotite bodies and peridotite "nodules" in basaltic volcanic rocks, and their formation may generally have involved high pressures. It is found that there is a rough correlation between the Mg/Fe++ ratios of chromian spinels, olivines, and pyroxenes occurring in the same rock bodies, and there is some evidence that the Mg–Fe++ distribution coefficients of spinel–silicate pairs may significantly be sensitive to temperature. The chromites of stratiform intrusions reflect an appreciable range of oxygen fugacities, whereas the spinels of alpine- type peridotite bodies seem generally to have formed at about the same relatively low oxygen fugacity. Chromites from ultra mafic bodies of the type common to southeastern Alaska have exceptionally high Fe+++/Cr + Al + Fe+++ ratios, probably because the bodies crystallized from magma that was extremely poor in silica.

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