scholarly journals Geochemical and isotopic evidence for Carboniferous rifting: mafic dykes in the central Sanandaj-Sirjan zone (Dorud-Azna, West Iran)

2017 ◽  
Vol 68 (3) ◽  
pp. 229-247 ◽  
Author(s):  
Farzaneh Shakerardakani ◽  
Franz Neubauer ◽  
Manfred Bernroider ◽  
Albrecht Von Quadt ◽  
Irena Peytcheva ◽  
...  
Keyword(s):  
Mantle Source ◽  
Crustal Contamination ◽  
Early Carboniferous ◽  
Main Trend ◽  
Geodynamic Setting ◽  
Mafic Dyke ◽  
Mafic Dykes ◽  
Enriched Mantle ◽  
Depleted Mantle ◽  
Sanandaj Sirjan Zone

Abstract In this paper, we present detailed field observations, chronological, geochemical and Sr–Nd isotopic data and discuss the petrogenetic aspects of two types of mafic dykes, of alkaline to subalkaline nature. The alkaline mafic dykes exhibit a cumulate to foliated texture and strike NW–SE, parallel to the main trend of the region. The 40Ar/39Ar amphibole age of 321.32 ± 0.55 Ma from an alkaline mafic dyke is interpreted as an indication of Carboniferous cooling through ca. 550 °C after intrusion of the dyke into the granitic Galeh-Doz orthogneiss and Amphibolite-Metagabbro units, the latter with Early Carboniferous amphibolite facies grade metamorphism and containing the Dare-Hedavand metagabbro with a similar Carboniferous age. The alkaline and subalkaline mafic dykes can be geochemically categorized into those with light REE-enriched patterns [(La/Yb)N = 8.32–9.28] and others with a rather flat REE pattern [(La/Yb)N = 1.16] and with a negative Nb anomaly. Together, the mafic dykes show oceanic island basalt to MORB geochemical signature, respectively. This is consistent, as well, with the (Tb/Yb)PM ratios. The alkaline mafic dykes were formed within an enriched mantle source at depths of ˃ 90 km, generating a suite of alkaline basalts. In comparison, the subalkaline mafic dykes were formed within more depleted mantle source at depths of ˂ 90 km. The subalkaline mafic dyke is characterized by 87Sr/86Sr ratio of 0.706 and positive ɛNd(t) value of + 0.77, whereas 87Sr/86Sr ratio of 0.708 and ɛNd(t) value of + 1.65 of the alkaline mafic dyke, consistent with the derivation from an enriched mantle source. There is no evidence that the mafic dykes were affected by significant crustal contamination during emplacement. Because of the similar age, the generation of magmas of alkaline mafic dykes and of the Dare-Hedavand metagabbro are assumed to reflect the same process of lithospheric or asthenospheric melting. Carboniferous back-arc rifting is the likely geodynamic setting of mafic dyke generation and emplacement. In contrast, the subalkaline mafic sill is likely related to the emplacement of the Jurassic Darijune gabbro.

Geochemical and isotopic (Nd–Sr–Hf–Pb) evidence for a lithospheric mantle source in the formation of the alkaline Monteregian Province (Quebec)

2013 ◽  
Vol 50 (6) ◽  
pp. 650-666 ◽  
Author(s):  
Emilie Roulleau ◽  
Ross Stevenson
Keyword(s):  
Mantle Source ◽  
Lithospheric Mantle ◽  
North Atlantic Ocean ◽  
Crustal Contamination ◽  
Ocean Island Basalts ◽  
The North ◽  
Enriched Mantle ◽  
Lithospheric Extension ◽  
Depleted Mantle ◽  
Lithospheric Mantle Source

We present new major element and isotopic (Nd–Sr–Hf–Pb) data and modelling from alkaline rocks of the Monteregian Igneous Province of southern Quebec (Canada) that constrain the mantle source and the magmatic origin of these rocks. The whole-rock chemical composition of the intrusions is consistent with fractional crystallization of an assemblage of olivine ± clinopyroxene (± plagioclase) derived from ocean island basalts (OIB)-like magmas, and variations in the Sr and Nd isotope compositions suggest as much as 20% crustal contamination. The bulk of the Nd–Sr–Hf and Pb isotopic data form a tight cluster between a depleted mantle end-member (HIMU, high-U/Pb mantle) and an enriched mantle (EMI) end-member and are thought to reflect a sub-continental lithospheric mantle that was metasomatized by a convecting asthenospheric plume. Variations in these isotopic compositions along the west–east axis of the Monteregian Province (from the Oka carbonatite to the Mount Shefford intrusion) may reflect various degrees of mixing between HIMU and EMI enriched mantle reservoirs. Anomalously low 207Pb/204Pb and 208Pb/204Pb isotopic ratios from some of the intrusions likely indicate incorporation of an Archean component within the lithospheric mantle. We propose a model in which Monteregian magmatism formed from melting of a predominantly Proterozoic metasomatized lithospheric mantle in response to lithospheric extension during the opening of the North Atlantic Ocean at ca. 124 Ma.

scholarly journals Ore and Geochemical Specialization and Substance Sources of the Ural and Timan Carbonatite Complexes (Russia): Insights from Trace Element, Rb–Sr, and Sm–Nd Isotope Data

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 711
Author(s):  
Irina Nedosekova ◽  
Nikolay Vladykin ◽  
Oksana Udoratina ◽  
Boris Belyatsky
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Crustal Evolution ◽  
Trace Element Data ◽  
The Urals ◽  
Nd Isotope ◽  
Enriched Mantle ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
Geochemical Specialization

The Ilmeno–Vishnevogorsk (IVC), Buldym, and Chetlassky carbonatite complexes are localized in the folded regions of the Urals and Timan. These complexes differ in geochemical signatures and ore specialization: Nb-deposits of pyrochlore carbonatites are associated with the IVC, while Nb–REE-deposits with the Buldym complex and REE-deposits of bastnäsite carbonatites with the Chetlassky complex. A comparative study of these carbonatite complexes has been conducted in order to establish the reasons for their ore specialization and their sources. The IVC is characterized by low 87Sr/86Sri (0.70336–0.70399) and εNd (+2 to +6), suggesting a single moderately depleted mantle source for rocks and pyrochlore mineralization. The Buldym complex has a higher 87Sr/86Sri (0.70440–0.70513) with negative εNd (−0.2 to −3), which corresponds to enriched mantle source EMI-type. The REE carbonatites of the Chetlassky сomplex show low 87Sr/86Sri (0.70336–0.70369) and a high εNd (+5–+6), which is close to the DM mantle source with ~5% marine sedimentary component. Based on Sr–Nd isotope signatures, major, and trace element data, we assume that the different ore specialization of Urals and Timan carbonatites may be caused not only by crustal evolution of alkaline-carbonatite magmas, but also by the heterogeneity of their mantle sources associated with different degrees of enrichment in recycled components.

scholarly journals Geochemistry and petrology of mafic Proterozoic and Permian dykes on Bornholm, Denmark: Four Episodes of magmatism on the margin of the Baltic Shield

2010 ◽  
Vol 58 ◽  
pp. 35-65
Author(s):  
Paul Martin Holm ◽  
L.E. Pedersen, ◽  
B Højsteen
Keyword(s):  
Mantle Plume ◽  
Mantle Source ◽  
Small Degree ◽  
Spinel Peridotite ◽  
Alkali Basalts ◽  
Enriched Mantle ◽  
Depleted Mantle ◽  
Proterozoic Basement ◽  
The Baltic ◽  
Back Arc

More than 250 dykes cut the mid Proterozoic basement gneisses and granites of Bornholm. Most trend between NNW and NNE, whereas a few trend NE and NW. Field, geochemical and petrological evidence suggest that the dyke intrusions occurred as four distinct events at around 1326 Ma (Kelseaa dyke), 1220 Ma (narrow dykes), 950 Ma (Kaas and Listed dykes), and 300 Ma (NW-trending dykes), respectively. The largest dyke at Kelseaa (60 m wide) and some related dykes are primitive olivine tholeiites, one of which has N-type MORB geochemical features; all are crustally contaminated. The Kelseaa type magmas were derived at shallow depth from a fluid-enriched, relatively depleted, mantle source,but some have a component derived from mantle with residual garnet. They are suggested to have formed in a back-arc environment. The more than 200 narrow dykes are olivine tholeiites (some picritic), alkali basalts, trachybasalts, basanites and a few phonotephrites. The magmas evolved by olivine and olivine + clinopyroxene fractionation. They have trace element characteristics which can be described mainly by mixing of two components: one is a typical OIB-magma (La/Nb < 1, Zr/Nb = 4, Sr/Nd = 16) and rather shallowly derived from spinel peridotite; the other is enriched in Sr and has La/Nb = 1.0 - 1.5, Zr/Nb = 9, Sr/Nd = 30 and was derived at greater depth, probably from a pyroxenitic source. Both sources were probably recycled material in a mantle plume. A few of these dykes are much more enriched in incompatible elements and were derived from garnet peridotite by a small degree of partial melting. The Kaas and Listed dykes (20-40 m) and related dykes are evolved trachybasalts to basaltic trachyandesites. They are most likely related to the Blekinge Dalarne Dolerite Group. The few NW-trending dykes are quartz tholeiites, which were generated by large degrees of rather shallow melting of an enriched mantle source more enriched than the source of the older Bornholm dykes. The source of the NW-trending dykes was probably a very hot mantle plume.

The age of the Ritscherflya Supergroup and Borgmassivet Intrusions, Dronning Maud Land, Antarctica

1995 ◽  
Vol 7 (1) ◽  
pp. 87-97 ◽  
Author(s):  
A.B. Moyes ◽  
J.R. Krynauw ◽  
J.M. Barton
Keyword(s):  
Mantle Source ◽  
Crustal Contamination ◽  
Unconsolidated Sediments ◽  
Rock Types ◽  
Geological Age ◽  
Depleted Mantle ◽  
Wide Range ◽  
Dronning Maud Land ◽  
Depositional Age ◽  
Nd Model Age

The Ahlmannryggen-Borgmassivet area of western Dronning Maud Land comprises a relatively undeformed, unmetamorphosed sequence of sedimentary-volcanogenic rocks, the Ritscherflya Supergroup, intruded by a suite of continental tholeiites, the Borgmassivet Intrusions. New Rb-Sr and Sm-Nd whole rock data from the Högfonna Formation at Grunehogna indicate a depositional age of ≈1080 Ma, the first reported direct dating of any member of the Ritscherflya Supergroup. These rocks are interpreted as a molasse-type deposit following the Kibaran orogeny at 1200–1100 Ma, and correlation is made with the Umkondo and Koras groups of southern Africa. The Ritscherflya Supergroup is intruded by the Grunehogna and Kullen sills; the ≈1000 Ma Grunehogna sill intruded unconsolidated sediments, causing partial melting of the sediments. Rb-Sr data from the Kullen sill yield an age of 1429 Ma, clearly inconsistent with these data. Combined Sr and Nd data are compatible with crustal contamination of this sill, producing a Rb-Sr pseudo-isochron with no geological age significance. By comparison with other outcrops of the Borgmassivet Intrusions at Robertskollen and Annandagstoppane, it is concluded that contamination and pseudo-isochrons may be responsible for the wide range in reported ages older than 1000 Ma. Thus the intrusive age of the Borgmassivet Intrusions is concluded to be ≈1000 Ma old. Nd model age data indicate that all rock types were ultimately derived from material separated from a depleted mantle source at ≈2200 Ma.

The Silurian(?) Passamaquoddy Bay mafic dyke swarm, New Brunswick: petrogenesis and tectonic implications

2001 ◽  
Vol 38 (11) ◽  
pp. 1565-1578 ◽  
Author(s):  
Nancy A Van Wagoner ◽  
Matthew I Leybourne ◽  
Kelsie A Dadd ◽  
Miranda LA Huskins
Keyword(s):  
New Brunswick ◽  
Incompatible Element ◽  
Tectonic Setting ◽  
Crustal Contamination ◽  
Dyke Swarm ◽  
Mafic Dyke ◽  
Mafic Dykes ◽  
The North ◽  
Passamaquoddy Bay ◽  
Mafic Dyke Swarm

The volcanic and sedimentary rocks of the Passamaquoddy Bay (PB) area of southeastern New Brunswick are part of the Silurian–Devonian Coastal Volcanic Belt (CVB), an extensive belt of bimodal volcanic rocks. The PB sequence is 4 km thick, has four cycles of mafic and felsic volcanism, and is intruded by mafic dykes at all levels. There are two ages of dykes, those related to the Late Silurian PB volcanism (PB dykes) and Mesozoic dykes (the Minister Island Dyke) related to the opening of the North Atlantic. The PB mafic dykes are subalkalic basalt to basaltic andesite, within-plate tholeiites. The dykes are moderately to highly evolved (Mg# = 66.6 to 26.6), with trends of major and trace elements typical of the fractionation of olivine, pyroxene, plagioclase, and ilmenite. The PB mafic dyke swarm comprises over 155 dykes which represent a greater range of compositions than the associated flows, suggesting that they give a more complete representation of the Late Silurian PB mafic magmas. They exhibit incompatible element characteristics best accounted for by crustal contamination. The dykes plot on a linear array away from mantle mixing lines between depleted and enriched mantle sources and toward the composition of the PB felsic units, suggesting that these felsic units are representative of partial melts and fractionates of the source contaminate. The variable TiO2 contents (1.2–4.3 wt.%) and incompatible element ratio trends plotted against a fractionation index suggest that mantle metasomatism, either fluid or melt derived, may also have influenced the mantle source of the dykes. The dykes dip steeply and have a relatively consistent strike to the north. Most dykes range in thickness from 0.5 to 2 m, but range up to 9 m. The single orientation of the dykes, along with their chemical characteristics and volume, and association with a bimodal intraplate volcanic sequence, are consistent with an extensional tectonic setting. Constraints of the regional geology suggest that this extension was associated with convergence, perhaps in a back-arc setting.

Aphebian mafic–ultramafic magmatism in the Labrador Trough (New Quebec): its age and the nature of its mantle source

1993 ◽  
Vol 30 (8) ◽  
pp. 1582-1593 ◽  
Author(s):  
M. -L. Rohon ◽  
Y. Vialette ◽  
T. Clark ◽  
G. Roger ◽  
D. Ohnenstetter ◽  
...  
Keyword(s):  
Mantle Source ◽  
Upper Mantle ◽  
Crustal Contamination ◽  
Magma Source ◽  
Mantle Heterogeneity ◽  
The South ◽  
Zircon Age ◽  
South Central ◽  
Depleted Mantle ◽  
Intrusive Rocks

The magmatic events occurring within the two main cycles in the south-central part of the Labrador Trough (New Quebec) have been dated. In cycle 1, a granophyre dike related to the Cramolet Lake gabbro sill, which intrudes the Seward subgroup, has a U–Pb zircon age of 2169 ± 2 Ma. In cycle 2, the tholeiitic basalts of the Willbob (Hellancourt) Formation and the related mafic–ultramafic sills are dated at ca. 1900 Ma by the Pb–Pb method. These data confirm the existence of at least two main magmatic cycles separated by about 270 Ma. The magma source was depleted upper mantle, and the magma did not experience any significant crustal contamination, as indicated by the μ1 ratio (7.9) and [Formula: see text] (+4) for the tholeiitic basalts. The μ1 value for the intrusive rocks (8.03) and the average [Formula: see text] value for the gabbroic rocks of cycle 2 (+2.8) and for the granophyre of cycle 1 (+1.05) could be the result of slight crustal contamination or of mantle heterogeneity. Whatever the cause of these values, the data indicate the prolonged presence of a depleted mantle source.

scholarly journals Unravelling the relationship between mafic magmatism and Sb mineralization through dolerite geochemistry (Central Iberian Zone, Spain)

2021 ◽  
Author(s):  
Héctor Ricardo Campos Rodríguez ◽  
Eric Gloaguen ◽  
Anthony Pochon ◽  
Pablo Higueras ◽  
Saturnino Lorenzo ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Crustal Contamination ◽  
Primitive Mantle ◽  
Variscan Belt ◽  
Mafic Magmatism ◽  
Mafic Dykes ◽  
Central Iberian Zone ◽  
Mafic Intrusions ◽  
Enriched Mantle ◽  
La Mancha

&lt;p&gt;This work presents the preliminary results of geochemistry of mafic intrusions (diabase dykes) and their relationship with antimony mineralization in the Central-Iberian Zone (Variscan Belt). Two different areas were studied, the Almad&amp;#233;n (Al) and the San Antonio (SA) areas.&lt;/p&gt;&lt;p&gt;Both macroscopic and microscopic observations show that mafic dykes are mainly composed by clinopyroxene, plagioclase, Fe-Ti oxides and to a lesser extent of calcite and sulphides (pyrite, chalcopyrite and pyrrhotite). These samples are altered presenting chlorite and epidote as alteration minerals. Pyroxene is sometimes altered to amphibole.&lt;/p&gt;&lt;p&gt;Whole rock geochemistry analyses from 20 samples show a difference between SA and Al dolerites. The first fall into the classical basalt field whereas the second fall into the alkali basalt field according to the Zr/TiO2 vs Nb/Y diagram. The tectonic setting for the SA samples coincides with the volcanic arc setting whereas the samples from Al fall into the within plate magmatism.&amp;#160;&lt;/p&gt;&lt;p&gt;Primitive mantle normalized diagrams display high negative anomalies in Rb, K, with small negative anomalies in Nb and Ta for both SA and Al. High positive anomalies for both areas in Cs, Pb (especially for SA) and Li accompanied by small positive anomalies in P and Ti can be observed. Dolerites from Al are more enriched in Ba, Th, U, Nb, Ba, La, Ce, Sr, P, Nd, Sn, Zr, Hf than SA. All samples are depleted in HREE and enriched in LREE. Anomalies in Rb, Nb, Ta and Li may be related with crustal contamination. Pb anomalies could be associated with assimilation of country rocks, especially marine sediments, this anomaly is also related to subduction processes. Positive P and Ti anomalies of some samples is due to the apatite and ilmenite enrichment respectively. Negative anomalies in K could be associated with presence of phlogopite in the source. Rare Earth Elements contents are compatible with the presence of garnet in the source and low degree of partial melting, this is consistent with the correlation between La/Sm vs Gd/Yb and La/Sm vs Rb. Trace element ratios such as Th/La (0,10 for SA) and (0,09 for Al) suggest an enriched mantle source.&lt;/p&gt;&lt;p&gt;Some of these mafic intrusions were collected near antimony mineralization whereas the other are located at distance but in the same swarm of mafic dykes. A spatial and genetic link between Sb mineralization and mafic magmatism has been proposed in other parts of the Variscan Belt, especially in the Armorican Massif.&lt;/p&gt;&lt;p&gt;The source of these Sb mineralization could be related to an enriched mantle with crustal contamination. The geochemical link between mafic magmatism and Sb mineralization and their source in the Central Iberian Zone is still a matter of study.&lt;/p&gt;&lt;p&gt;Acknowledgments&lt;/p&gt;&lt;p&gt;This work was funded by the ANR (ANR-19-MIN2-0002-01), the AEI (MICIU/AEI/REF.: PCI2019-103779) and author&amp;#8217;s institutions in the framework of the ERA-MIN2 AUREOLE project, as well as by Project SBPLY/17/180501/000273, Consejer&amp;#237;a de Educaci&amp;#243;n, Regional Government of Castilla-La Mancha, Spain.&lt;/p&gt;

The youngest Neoproterozoic mafic dyke suite in the Arabian Shield: mildly alkaline dolerites from South Jordan – their geochemistry and petrogenesis

2001 ◽  
Vol 138 (3) ◽  
pp. 309-323 ◽  
Author(s):  
G. JARRAR
Keyword(s):  
Tectonic Setting ◽  
Crustal Contamination ◽  
Spinel Lherzolite ◽  
Mafic Dyke ◽  
East African ◽  
Elemental Ratios ◽  
Mafic Dykes ◽  
Nubian Shield ◽  
Igneous Activity ◽  
Arabian Nubian Shield

The Arabian–Nubian Shield evolved through a sequence of tectonomagmatic cycles, which took place during Neoproterozoic time (1000–540 Ma). Dyke emplacement constitutes one of the conspicuous features of the Arabian–Nubian Shield, with mafic dykes being the most abundant. The investigated dykes represent the youngest Neoproterozoic mafic dykes and have been dated in Jordan at 545 ± 13 Ma. Geochemically the studied dykes are mildly alkaline, are enriched in large ion lithophile elements (LILE) and high field strength cations (HFSC), show moderate enrichment of REE, and lack Nb anomaly. These features are consistent with a predominantly extensional continental tectonic setting. Crystallization temperatures of the suite fall between 1050 and 800 °C to as low as 650 °C as deduced from pyroxene thermometry. The investigated dykes were derived from a metasomatized lithospheric mantle by 5 % modal batch partial melting of phlogopite-bearing spinel lherzolite, according to geochemical modelling. The intra-suite geochemical features are explicable by 64 % fractional crystallization of olivine, pyroxene, plagioclase and titanomagnetite and possibly other accessories like apatite at a later stage. The cumulate produced from this fractionation of the investigated dyke suite contributed to the formation of the mafic lower crust of the Arabian–Nubian Shield. Elemental ratios and petrographic evidence indicate possible minor crustal contamination of the suite. The youngest mafic dykes show striking geochemical similarities to the same generation of dolerite dykes in the adjacent countries, to transitional young basalt suites of the Main East African Rift, and to Quaternary Jordanian basalts. The youngest mafic dyke suite, the rhyolites of the Aheimir suite, and St Katherina rhyolites of Sinai represent the last igneous activity in the Arabian–Nubian Shield before the onset of the Cambrian at about 545 Ma ago.

scholarly journals Origin of the High-K Tertiary magmatism in Northern Greece: Implications for mantle geochemistry and geotectonic setting.

2013 ◽  
Vol 47 (1) ◽  
pp. 416
Author(s):  
K. Pipera ◽  
A. Koroneos ◽  
T. Soldatos ◽  
G. Poli ◽  
G. Christofides
Keyword(s):  
Mantle Source ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Calc Alkaline ◽  
Northern Greece ◽  
Mafic Rocks ◽  
High K ◽  
Depleted Mantle ◽  
Subducted Oceanic Crust ◽  
Compositional Variations

Tertiary plutonic and volcanic rocks cropping out in the Rhodope Massif (N. Greece) are studied using existing and new geochemical and isotopic data. Most of these rocks belong to the post-collisional magmatism formed as part of the prolonged extensional tectonics of the Rhodope region in Late Cretaceous– Paleogene time. This magmatism is considered to be of mantle origin; however, the character of the mantle source is controversial. Rock bulk chemistry and compositional variations show magmas with calc-alkaline to high-K calc-alkaline and shoshonitic features associated with magmatism at convergent margins. Initial 87Sr/86Sr, 143Nd/144Nd ratios, Pb isotopes and REE composition of the mafic rocks indicate mainly an enriched mantle source, even if some rocks indicate a depleted mantle source. Low- and High-K mafic members of these rocks coexist indicating a strongly heterogeneous mantle source. The High-K character of some of the mafic rocks is primarily strongly related to mantle enrichment by subduction-related components, rather than crustal contamination. The geochemical characteristics of the studied rocks (e.g Ba/Th,Th/Yb,Ba/La, U/Th, Ce/Pb) indicate that primarily sediments and/or sediment melts, rather than fluid released by the subducted oceanic crust controlled the source enrichment under the Rhodope Massif.

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