scholarly journals Shona and Discovery Aseismic Ridge Systems, South Atlantic: Trace Element Evidence for Enriched Mantle Sources

2010 ◽  
Vol 51 (10) ◽  
pp. 2089-2120 ◽  
Author(s):  
A. le Roex ◽  
C. Class ◽  
J. O'Connor ◽  
W. Jokat
Keyword(s):  
Trace Element ◽  
South Atlantic ◽  
Enriched Mantle ◽  
Mantle Sources

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 Sub-arc mantle enrichment in the Sunda rear-arc inferred from HFSE systematics in high-K lavas from Java

2021 ◽  
Vol 177 (1) ◽  
Author(s):  
M. Kirchenbaur ◽  
S. Schuth ◽  
A. R. Barth ◽  
A. Luguet ◽  
S. König ◽  
...  
Keyword(s):  
Trace Element ◽  
Geochemical Data ◽  
Arc Volcanism ◽  
Enriched Mantle ◽  
Arc Melting ◽  
Sunda Arc ◽  
High K ◽  
Mantle Sources ◽  
Slab Tear ◽  
Arc Volcano

AbstractMany terrestrial silicate reservoirs display a characteristic depletion in Nb, which has been explained in some studies by the presence of reservoirs on Earth with superchondritic Nb/Ta. As one classical example, K-rich lavas from the Sunda rear-arc, Indonesia, have been invoked to tap such a high-Nb/Ta reservoir. To elucidate the petrogenetic processes active beneath the Java rear-arc and the causes for the superchondritic Nb/Ta in some of these lavas, we studied samples from the somewhat enigmatic Javanese rear-arc volcano Muria, which allow conclusions regarding the across-arc variations in volcanic output, source mineralogy and subduction components. We additionally report some data for an along-arc sequence of lavas from the Indonesian part of the Sunda arc, extending from Krakatoa in the west to the islands of Bali and Lombok in the east. We present major and trace element concentrations, Sr–Nd–Hf–Pb isotope compositions, and high-field-strength element (HFSE: Nb, Ta, Zr, Hf, W) concentrations obtained via isotope dilution and MC-ICP-MS analyses. The geochemical data are complemented by melting models covering different source compositions with slab melts formed at variable P–T conditions. The radiogenic isotope compositions of the frontal arc lavas in combination with their trace element systematics confirm previously established regional variations of subduction components along the arc. Melting models show a clear contribution of a sediment-derived component to the HFSE budget of the frontal arc lavas, particularly affecting Zr–Hf and W. In contrast, the K-rich rear-arc lavas tap more hybrid and enriched mantle sources. The HFSE budget of the rear-arc lavas is in particular characterized by superchondritic Nb/Ta (up to 25) that are attributed to deep melting involving overprint by slab melts formed from an enriched garnet–rutile-bearing eclogitic residue. Sub-arc slab melting was potentially triggered along a slab tear beneath the Sunda arc, which is the result of the forced subduction of an oceanic basement relief ~ 8 Myr ago as confirmed by geophysical studies. The purported age of the slab tear coincides with a paucity in arc volcanism, widespread thrusting of the Javanese basement crust as well as the short-lived nature of the K-rich rear-arc volcanism at that time.

A geochemical and Sr-Nd-O isotopic study of the Proterozoic Eriksfjord Basalts, Gardar Province, South Greenland: Reconstruction of an OIB signature in crustally contaminated rift-related basalts

2003 ◽  
Vol 67 (5) ◽  
pp. 831-853 ◽  
Author(s):  
R. Halama ◽  
T. Wenzel ◽  
B. G. J. Upton ◽  
W. Siebel ◽  
G. Markl
Keyword(s):  
Trace Element ◽  
Granulite Facies ◽  
Alkaline Basalt ◽  
Isotopic Study ◽  
Nd Isotope ◽  
Crustal Component ◽  
Isotope Data ◽  
Enriched Mantle ◽  
Mantle Sources ◽  
Lower Crustal

AbstractBasalts from the volcano-sedimentary Eriksfjord Formation (Gardar Province, South Greenland) were erupted at around 1.2 Ga into rift-related graben structures. The basalts have compositions transitional between tholeiite and alkaline basalt with MgO contents <7 wt.% and they display LREE-enrichment relative to a chondritic source. Most of the trace element and REE characteristics are similar to those of basalts derived from OIB-like mantle sources. Initial 87Sr/86Sr ratios of clinopyroxene separates range from 0.70278 to 0.70383 and initial ϵNd values vary from –3.2 to +2.1. The most unradiogenic samples overlap with the field defined by carbonatites of similar age and can be explained by mixing of isotopically depleted and enriched mantle components. Using AFC modelling equations, the Sr-Nd isotope data of the more radiogenic basalts can successfully be modelled by addition of <5% lower crustal granulite-facies gneisses as contaminants. δ18Ov-smow values of separated clinopyroxene range from +5.2 to +6.0% and fall within the range of typical mantle-derived rocks. However, up to 10% mixing with an average lower crustal component are permitted by the data.

Geochemistry of Ferrar Dolerite sills and dykes at Terra Cotta Mountain, south Victoria Land, Antarctica

1995 ◽  
Vol 7 (1) ◽  
pp. 73-85 ◽  
Author(s):  
A.D. Morrison ◽  
A. Reay
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Source Region ◽  
Crustal Component ◽  
Enriched Mantle ◽  
Victoria Land ◽  
Trace Element Signature ◽  
Geochemical Variation ◽  
Element Enrichment ◽  
Taylor Glacier

At Terra Cotta Mountain, in the Taylor Glacier region of south Victoria Land, a 237 m thick Ferrar Dolerite sill is intruded along the unconformity between basement granitoids and overlying Beacon Supergroup sedimentary rocks. Numerous Ferrar Dolerite dykes intrude the Beacon Supergroup and represent later phases of intrusion. Major and trace element data indicate variation both within and between the separate intrusions. Crystal fractionation accounts for much of the geochemical variation between the intrusive events. However, poor correlations between many trace elements require the additional involvement of open system processes. Chromium is decoupled from highly incompatible elements consistent with behaviour predicted for a periodically replenished, tapped and fractionating magma chamber. Large ion lithophile element-enrichment and depletion in Nb, Sr, P and Ti suggests the addition of a crustal component or an enriched mantle source. The trace element characteristics of the Dolerites from Terra Cotta Mountain are similar to those of other Ferrar Group rocks from the central Transantarctic Mountains and north Victoria Land, as well as with the Tasmanian Dolerites. This supports current ideas that the trace element signature of the Ferrar Group is inherited from a uniformly enriched mantle source region.

scholarly journals Trace-Element and Pb Isotope Evidence on Extracting Sulfides from Potassic Melts beneath Longmenshan and Molabushan Volcanoes, Wudalianchi, Northeast China

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 319 ◽  
Author(s):  
Sergei Rasskazov ◽  
Yi-Min Sun ◽  
Irina Chuvashova ◽  
Tatyana Yasnygina ◽  
Chen Yang ◽  
...  
Keyword(s):  
Trace Element ◽  
Volcanic Rocks ◽  
Volcanic Field ◽  
Lava Flows ◽  
Pb Isotope ◽  
Linear Pattern ◽  
Wide Range ◽  
Mantle Sources ◽  
Isotope Evidence ◽  
Isotope Study

In the Wudalianchi volcanic field, eruptions started with low-Mg potassic lava flows 2.5–2.0 Ma ago and later changed to both low- and moderate-Mg potassic compositions. Volcanic rocks from the Molabushan and Longmenshan volcanoes record an unusually wide range of Pb abundances (from 3.7 ppm to 21 ppm relative to predominant range of 10–15 ppm). To determine the cause of these, we performed a comparative trace-element and Pb isotope study of rocks from these volcanoes and older lava flows. On a uranogenic lead diagram, older low-Mg lavas from lithospheric mantle sources plot on a secondary isochron with a slope corresponding to an age of 1.88 Ga. This contrasts with moderate-Mg volcanic rocks from the Molabushan cone, interpreted to have been derived from a recent convective mantle source, which define a flat linear pattern. Low-Mg rocks from the Molabushan flow have lead isotopic compositions that indicate mixed Gelaqiu and Molabu sources. Relative to rocks from the Molabushan cone, moderate-Mg lavas and slags from the East Longmenshan volcano have modified compositions characterized by Pb, S, and Ni abundances, Ni/Co, Ni/MgO ratios as well as 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, Ce/Pb, Th/Pb, and U/Pb ratios. We infer that the older Wudalianchi magmas were likely derived from a Paleoproterozoic lithospheric fragment, related to the evolved primordial mantle, and that later magmas were generated in the convecting mantle. These were influenced by segregation of small amounts of sulfides.

A preliminary assessment of the application of Sr, Nd, Pb, He and N isotope analysis to fluid inclusions in kimberlite olivine: A new approach to trace deep-mantle sources

2020 ◽  
Author(s):  
Andrea Giuliani ◽  
Janne M. Koornneef ◽  
Peter Barry ◽  
Patrizia Will ◽  
Henner Busemann ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Trace Element ◽  
Mass Spectrometer ◽  
Fluid Inclusions ◽  
Noble Gas ◽  
Isotope Analysis ◽  
Helium Isotope ◽  
New Approach ◽  
Deep Mantle ◽  
Mantle Sources

&lt;p&gt;Kimberlites are the deepest melts that reach Earth&amp;#8217;s surface and, therefore, can provide unique insights into the composition and evolution of the convective mantle through time. Application of isotope geochemistry to trace the composition of kimberlite sources has thus far been hindered by the ubiquitous alteration and incorporation of xenocrystic material in kimberlite rocks. Bulk-kimberlite analyses are typically considered reliable for Nd and Hf isotopes due to their overwhelmingly higher concentrations in kimberlite melts compared to common mantle and crustal contaminants. Conversely, Sr and Pb isotope compositions of bulk kimberlite samples are seldom considered representative of their parental melts thus requiring analysis of robust magmatic phases, primarily perovskite. Addressing the primary (i.e. magmatic) isotopic composition of volatile elements, such as N and noble gases, requires analyses of volatile-rich phases, and fluid inclusions in olivine represent a typical primary target in mantle-derived magmas. However, fluid inclusions in kimberlitic olivine are dominantly secondary in origin. Secondary inclusions can form at any time after crystallisation of their mineral host, which requires assessment of the origin of trapped fluids (i.e. pristine magmatic fluids, crustal fluids of external derivation, or combination thereof) before their isotopic composition can be used to make inferences about kimberlite mantle sources.&lt;/p&gt;&lt;p&gt;Here we present trace-element and Sr-Nd-Pb-He-N isotopic compositions of multiple olivine aliquots representing two different magmatic units of the ~88 Ma Wesselton kimberlite (Kimberley, South Africa). The Sr and Nd isotopic composition of olivine analysed by isotope-dilution (ID) TIMS are within the narrow range of perovskite &lt;sup&gt;87&lt;/sup&gt;Sr/&lt;sup&gt;86&lt;/sup&gt;Sr (0.7043-0.7046) and whole-rock &lt;sup&gt;143&lt;/sup&gt;Nd/&lt;sup&gt;144&lt;/sup&gt;Nd (eNd&lt;sub&gt;i&lt;/sub&gt; = 0.4&amp;#8211;2.2) for the Kimberley kimberlites. These results indicate that the secondary fluid inclusions, which dominate the incompatible trace-element budget of olivine separates, have a pristine magmatic origin devoid of crustal contribution.&lt;/p&gt;&lt;p&gt;Helium isotope compositions were measured by laser heating of 1.6 to 9.8 mg of olivine using an ultrahigh-sensitivity compressor-source noble gas mass spectrometer. &lt;sup&gt;3&lt;/sup&gt;He/&lt;sup&gt;4&lt;/sup&gt;He ratios are between 1.6 R&lt;sub&gt;A&lt;/sub&gt; and 3.7 R&lt;sub&gt;A&lt;/sub&gt; (where R&lt;sub&gt;A&lt;/sub&gt; indicates the atmospheric &lt;sup&gt;3&lt;/sup&gt;He/&lt;sup&gt;4&lt;/sup&gt;He ratio), values more radiogenic than MORBs but comparable to HIMU OIBs. These results indicate a high time-integrated (U+Th)/He ratio in the source of the Kimberley kimberlites, which is consistent with the moderately high (i.e. HIMU-like) time-integrated U/Pb ratio implied by elevated initial &lt;sup&gt;206&lt;/sup&gt;Pb/&lt;sup&gt;204&lt;/sup&gt;Pb in Wesselton olivine (19.1-19.5), Kimberley kimberlites (up to 19.9) and megacrysts in southern African Cretaceous kimberlites (up to 20.5). The combination of low &lt;sup&gt;3&lt;/sup&gt;He/&lt;sup&gt;4&lt;/sup&gt;He, moderately radiogenic &lt;sup&gt;87&lt;/sup&gt;Sr/&lt;sup&gt;86&lt;/sup&gt;Sr, and negative d&lt;sup&gt;34&lt;/sup&gt;S values (-2.6&amp;#8240; to -5.7&amp;#8240;) require a contribution from subducted recycled material in the source of the Kimberley kimberlites. Conversely, a preliminary N isotope analysis of Wesselton olivine by in-vacuo crushing using a noble gas mass spectrometer returned a mantle-like d&lt;sup&gt;15&lt;/sup&gt;N of -2.9&amp;#8240;, which might suggest limited recycling of surface N (d&lt;sup&gt;15&lt;/sup&gt;N &gt;0&amp;#8240;) in the source of these kimberlites. We conclude that the combination of Sr-Nd-Pb and He-N isotope tracing of fluid inclusions in olivine can provide a robust new approach to address the composition of kimberlite sources and, therefore, the evolution of the deep mantle through time.&lt;/p&gt;

Experimental study in the Na2O–CaO–MgO–Al2O3–SiO2–CO2 system at 3 GPa: the effect of sodium on mantle melting to carbonate-rich liquids and implications for the petrogenesis of silicocarbonatites

2012 ◽  
Vol 76 (2) ◽  
pp. 285-309 ◽  
Author(s):  
K. R. Moore
Keyword(s):  
Sodium Content ◽  
Silicate Melts ◽  
Monovalent Cations ◽  
Silicate System ◽  
Free System ◽  
Enriched Mantle ◽  
Mantle Sources ◽  
Analogue System ◽  
Carbonated Liquids ◽  
Metasomatized Mantle

AbstractMelt compositions in equilibrium with peridotite assemblages were determined in the analogue system Na2O–CaO–MgO–Al2O3–SiO2–CO2 at 3 GPa with Ca/Ca + Mg = 0.56–0.43 and up to 6 wt.% Na2O. There is a greater compositional range generated isobarically over a larger temperature interval than in a sodium-absent system: increasing sodium content drives liquids to compositions with lower CaO and higher SiO2 concentrations. A positive correlation between silica and Na2O content of liquids produced at constant temperature is due to the depolymerization of silicate tetrahedra in the presence of monovalent cations, as in the volatile-free system. Liquids with Na2O >6 wt.% occur in association with wehrlites as the composition of diopsidic pyroxene expands towards enstatite with addition of Na2O, decreasing the orthopyroxene content of peridotite. The orthopyroxene-out curve intersects an enriched mantle solidus at 3 GPa where near-solidus liquids have Na2O = 7 1.5 wt.%. Sodium partitioning between a metaluminous liquid and clinopyroxene follows the jadeite partitioning models calculated for the dry silicate system but sodium partitions into peralkaline carbonated liquids as both the pyroxene and the carbonate molecules. The peralkaline liquids generated are essentially carbonated silicate melts that are analogous to silica-bearing carbonatites and silicocarbonatites from a range of possible metasomatized mantle sources.

Possible crustal contamination of Midcontinent Rift igneous rocks: examples from the Mineral Lake intrusions, Wisconsin

1992 ◽  
Vol 29 (6) ◽  
pp. 1140-1153 ◽  
Author(s):  
Karl E. Seifert ◽  
Zell E. Peterman ◽  
Scott E. Thieben
Keyword(s):  
Fractional Crystallization ◽  
Crustal Contamination ◽  
Flood Basalt ◽  
Igneous Rocks ◽  
Midcontinent Rift ◽  
Mafic Intrusions ◽  
Enriched Mantle ◽  
Mantle Sources ◽  
Geochemical Variations ◽  
Compositional Pattern

Interlayered mafic–telsic intrusions from the Mineral Lake intrusive complex in northwest Wisconsin reflect the typical bimodal basalt–rhyolite compositional pattern of the Midcontinent Rift flood basalt province in the Lake Superior region. The later felsic intrusions were emplaced between the mafic intrusions and overlying basalt flows, and postemplacement fractional crystallization produced gradational mineralogical and geochemical variations. Isotopic and trace-element data for the Mineral Lake intrusions are consistent with mantle sources for both mafic and felsic intrusions, with compositional differences explained by the extent of fractional crystallization and crustal contamination or mantle source characteristics.εNd–εSr plots of analyzed Midcontinent Rift igneous rocks define three largely separate isotopic fields that suggest separate sources. However, the spread in isotopic data and a spider diagram plot of mafic samples from the εNd = εSr = 0 field suggest a crustal component and derivation from depleted rather than chondritic mantle. Evolved felsic rocks plotting in two negative εNd – positive εSr fields can be explained by derivation from separate enriched mantle sources or crustal contamination or both.

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