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 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.

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 the Little Dal basalts: continental tholeiites from the Mackenzie Mountains, Northwest Territories, Canada

1997 ◽  
Vol 34 (1) ◽  
pp. 50-58 ◽  
Author(s):  
Francis Ö. Dudás ◽  
Rigel L. Lustwerk
Keyword(s):  
Northwest Territories ◽  
Fractional Crystallization ◽  
Source Region ◽  
Sedimentary Rocks ◽  
Crustal Component ◽  
Lava Sequence ◽  
Original Magma ◽  
Geochemical Variation ◽  
Mackenzie Mountains ◽  
Nd Isotopic Composition

Analyses of the Little Dal lavas and the 779 Ma Tsezotene sills, both of the Mackenzie Mountains Supergroup, Northwest Territories, Canada, show them to be continental tholeiites that are geochemically related. The plagioclase- and clinopyroxene-phyric lavas are geochemically evolved and enriched in iron (up to 20.2 wt.% as Fe2O3). Two magmatic lineages are identifiable and may represent different degrees of partial melting in the same source region, but cannot be related by fractional crystallization. Within each lineage, geochemical variation can be explained by fractional crystallization involving up to 60% crystallization of the original magma. The most evolved lavas occur at the base of the pile; less fractionated lavas occur toward the top of the sequence. The Nd isotopic composition of the Little Dal lavas averages ε = 1.4 at 780 Ma. Trace element and isotopic compositions are permissive of contamination by continental crust, but do not require a crustal component. The preserved volume of the Little Dal basalts is anomalously low (−100 km3) compared with other Proterozoic continental tholeiites. There is considerable basaltic detritus in the sedimentary rocks of the overlying Coates Lake and Rapitan groups, and much of the original lava sequence may have been eroded. The Little Dal magmatic event is interpreted to be an early manifestation of rifting of North America from Australia.

Sm-Nd and Lu-Hf isotope and trace-element systematics of Mesoarchaean amphibolites, inner Ameralik fjord, southern West Greenland

2015 ◽  
Vol 79 (4) ◽  
pp. 857-876 ◽  
Author(s):  
Kristoffer Szilas ◽  
J. Elis Hoffmann ◽  
Christina Hansmeier ◽  
Julie A. Hollis ◽  
Carsten Münker ◽  
...  
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Source Region ◽  
Hf Isotope ◽  
Apparent Paradox ◽  
West Greenland ◽  
The North ◽  
Mantle Sources ◽  
Sample Set ◽  
North Atlantic Craton

AbstractFragmented supracrustal rocks are typical components of Archaean high-grade gneiss terranes, such as those in the North Atlantic Craton. Here we present the first major, trace element and Nd-Hf isotope data for amphibolites collected in the yet poorly studied southern inner Ameralik fjord region of southern West Greenland. In addition, new U-Pb zircon ages were obtained from the surrounding TTG gneisses.Based on their trace-element patterns, two different groups of amphibolites can be distinguished. Following screening for post-magmatic alteration and outlying ε values, a reduced sample set defines a147Sm/143Nd regression age of 3038 Ma ±310 Ma (MSWD = 9.2) and a176Lu/176Hf regression age of 2867 ±160 Ma (MSWD = 5.5). Initial εNd2970Mavalues of the least-altered amphibolites range from 0.0 to +5.7 and initial εHf2970Ma range from +0.7 to +10.4, indicating significant isotopic heterogeneity of their mantle sources with involvement of depleted domains as well as crustal sources.Surprisingly, the amphibolites which are apparently most evolved and incompatible element-rich have the most depleted Hf-isotope compositions. This apparent paradox may be explained by the sampling of a local mantle source region with ancient previous melt depletion, which was re-enriched by a fluid component during subduction zone volcanism or alternatively by preferential melting of an ancient pyroxenite component in the mantle source of the enriched rocks.

Minettes from Schirmacher Oasis, East Antarctica — indicators of an enriched mantle source

1998 ◽  
Vol 10 (4) ◽  
pp. 476-486 ◽  
Author(s):  
Marion Hoch ◽  
Heinz J. Tobschall
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Incompatible Element ◽  
East Antarctica ◽  
Magma Ascent ◽  
Element Abundances ◽  
Enriched Mantle ◽  
Schirmacher Oasis ◽  
Compatible Elements ◽  
Ree Patterns

Minette dykes intersect the Precambrian crystalline basement of Schirmacher Oasis, East Antarctica. The rocks have intermediate to basic compositions, showing shoshonitic to ultrapotassic character. The samples show enhanced concentrations of compatible elements and high mg# combined with extreme enrichments in LILE (especially Ba) and LREE. Mantle-normalized trace element patterns are characterized by coupled relative depletions of Nb and Ti and strong fractionations between LILE and HFSE. The minettes display fractionated chondrite-normalized REE patterns with high and varying LREE concentrations in contrast to relative low and nearly constant HREE contents. High magma-ascent and cooling rates of lamprophyric magmas argue against a fundamental change of the primary geochemical signatures in minette magmas by interactions with the continental crust during ascent. The major and trace element abundances of the studied minettes point to varying degrees of partial melting of a mantle source, which was enriched in LILE and LREE during or before the melting event. Incompatible element signatures argue for the involvement of subducted pelagic sediments.

Trace-element and Nd isotopic variations in Early Proterozoic dyke swarms emplaced in the vicinity of the Kapuskasing structural zone: enriched mantle or assimilation and fractional crystallization (AFC) process?

1991 ◽  
Vol 28 (1) ◽  
pp. 26-36 ◽  
Author(s):  
M. Boily ◽  
J. N. Ludden
Keyword(s):  
Trace Element ◽  
Fractional Crystallization ◽  
Lower Crust ◽  
Crustal Material ◽  
Early Proterozoic ◽  
Crustal Rocks ◽  
Asthenospheric Mantle ◽  
Enriched Mantle ◽  
Element Enrichment ◽  
Dyke Swarms

Several Early Proterozoic Hearst–Matachewan (2.454 Ga), Kapuskasing (2.14 Ga), and Preissac (2.04 Ga) dykes were emplaced within the Archean crust surrounding the Kapuskasing structural zone (KSZ). The dykes are composed of moderately to highly fractionated tholeiitic basalts (Mg number = 24–55) that exhibit trace-element characteristics similar to those of intraplate basaltic magmas or ocean–island basalts (e.g., Zr/Nb = 6–21, Zr/Y = 2–5, high TiO2 = 0.9–3.2 wt.%, and (Fe2O3)t = 12.4–18.7 wt.%). Their initial Nd isotopic compositions display a range of depleted [Formula: see text] to enriched [Formula: see text] values that are negatively correlated with the degree of light rare-earth element enrichment. We evaluate two models for the origin of these dykes: (i) The basaltic parental magmas were derived from two distinct sources, an isotopically depleted asthenospheric mantle (εNd = +4 and La/Sm = 2.7) and an isotopically enriched lithospheric(?) mantle (εNd = −4 to−8 and La/Sm = 5.1). The magmas subsequently underwent mixing and fractionation during ascent in the mantle or the lower crust. (ii) The parental magmas originated from a homogeneous Nd isotopically depleted asthenospheric mantle but later assimilated a substantial amount of Archean crustal material upon fractionation and ascent in the lower crust. Results derived for the latter model preclude any participation of the exposed crustal rocks in the KSZ, and the assimilation and fractional crystallization (AFC) model remains a viable hypothesis only if the parental magmas assimilated an older and perhaps more isotopically enriched crust than that represented in the KSZ.

Geochemistry of a Tertiary continental basalt suite, Red Sea coastal plain, Egypt: petrogenesis and characteristics of the mantle source region

2003 ◽  
Vol 140 (1) ◽  
pp. 11-24 ◽  
Author(s):  
ABDEL-KADER M. MOGHAZI
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Red Sea ◽  
Fractional Crystallization ◽  
Coastal Plain ◽  
Mantle Source ◽  
Source Region ◽  
Rift System ◽  
Mantle Source Region ◽  
Continental Basalt

Major and trace element data on Tertiary continental basalt flows from the Shalatein area, Red Sea coastal plain of Egypt, have been presented and used to obtain more information about their source region and the processes involved in their generation. The rocks are mainly alkali olivine basalt with MgO and Mg no. in the range of 9.8–5 wt % and 65–46, respectively. They display wide variations in incompatible element concentrations, particularly LREE, Zr, Nb, K, Y, Ba and Sr. There is no evidence of significant crustal contamination or a lithospheric mantle signature in these rocks. Normalized trace element patterns and diagnostic elemental ratios are very similar to those of modern ocean-island basalts (OIB) a feature which suggests that the mantle source region was the asthenosphere. Comparison with the different types of OIB indicates that the basalts may be derived from a high U/Pb (HIMU) source with slightly elevated K and Ba contents. The basalts show general trends of increasing incompatible elements (K2O, Nb, Y, Sr and Yb), and decreasing contents of compatible elements (Cr, Ni, Sc and Ca) with decreasing Mg no. Furthermore, TiO2, P2O5, LREE and Th define maxima at about Mg no.=56, suggesting late fractionation of Fe–Ti oxides and apatite. Although these variations are consistent with fractional crystallization processes, the wide variations in LREE contents and the incompatible trace element ratios Ce/Y (1.2–3.8), Zr/Nb (2.3–7.1) and Nb/Y (0.6–4) in the least fractionated samples (Mg no. > 56) suggest that fractional crystallization involving the observed phenocryst assemblage (olivine and clinopyroxene) cannot fully explain such compositional variations. Modelling of the mafic rocks (Mg no. > 56) using REE suggests varying degrees of partial melting of an enriched mantle source region in the garnet stability field. Partial melting is attributed to plume-related mantle upwelling beneath the Red Sea rift system.

Th–Sr–Nd–Pb isotope and trace element evidence for the origin of the São Miguel, Azores, enriched mantle source

1997 ◽  
Vol 140 (1-2) ◽  
pp. 49-68 ◽  
Author(s):  
E Widom ◽  
R.W Carlson ◽  
J.B Gill ◽  
H.-U Schmincke
Keyword(s):  
Trace Element ◽  
Mantle Source ◽  
Pb Isotope ◽  
Enriched Mantle

scholarly journals Geochemistry of basic magmatism of Western Antarctic Rift: implications for volatiles storage and recycling in the mantle

2020 ◽  
Author(s):  
Pier Paolo Giacomoni ◽  
Carmelo Ferlito ◽  
Costanza Bonadiman ◽  
Federico Casetta ◽  
Luisa Ottolini ◽  
...  
Keyword(s):  
Mantle Source ◽  
Melt Inclusions ◽  
Secondary Ion Mass Spectrometry ◽  
Alkaline Magmatism ◽  
Spinel Lherzolite ◽  
Enriched Mantle ◽  
Global Comparison ◽  
Victoria Land ◽  
Basic Magmatism ◽  
Petrologic Study

&lt;p&gt;The petrologic study of olivine-hosted melt inclusions (MIs) from alkaline primary Cenozoic basalts of Northern Victoria Land (Antarctica) provide new insights on the role of volatiles in the onset of rift-related magmatism. The concentration of volatile species (H&lt;sub&gt;2&lt;/sub&gt;O, CO&lt;sub&gt;2&lt;/sub&gt;, F, Cl) have been determined by Secondary Ion Mass Spectrometry (SIMS) on a selection of MIs which have been previously re-homogenized at high pressure and temperature conditions in order to avoid any heterogeneity and reducing the H diffusion. The least differentiated MIs vary in composition from basanitic to alkaline basalts, analogously to what is found in McMurdo volcanics, while their volatile concentrations reach up to 2.64 wt% H&lt;sub&gt;2&lt;/sub&gt;O, 3900 ppm CO&lt;sub&gt;2&lt;/sub&gt;, 1377 ppm F and 1336 Cl. Taking into account the most undegassed MIs a H&lt;sub&gt;2&lt;/sub&gt;O/(H&lt;sub&gt;2&lt;/sub&gt;O+CO&lt;sub&gt;2&lt;/sub&gt;) ratio equal to 0.88 was determined, which in turn brings the CO&lt;sub&gt;2&lt;/sub&gt; content in the basanitic melt with the highest water content up to 8800 ppm.&lt;/p&gt;&lt;p&gt;Major and trace element melting modelling indicate that basanite and alkali basalt composition can be reproduced by 3 and 7% of partial melting of an amphibole-bearing spinel lherzolite respectively. Assuming a perfect incompatible behavior for H&lt;sub&gt;2&lt;/sub&gt;O and CO&lt;sub&gt;2&lt;/sub&gt; these melting proportions allow to constrain the water and CO&lt;sub&gt;2&lt;/sub&gt; contents in the mantle source in the range 780-840 and 264-273 ppm respectively. The resulting CO&lt;sub&gt;2&lt;/sub&gt;/Nb, CO&lt;sub&gt;2&lt;/sub&gt;/Ba and H&lt;sub&gt;2&lt;/sub&gt;O/Ce ratio are lower than those estimated for Depleted MORB Mantle (DMM), suggesting that the NVL Cenozoic alkaline magmatism could be originated by an enriched mantle source composed by a range from 70% to 60% of Enriched Mantle (EM) and from 30% to 40% of Depleted Morb Mantle (DMM).&lt;/p&gt;&lt;p&gt;A global comparison of fluid-related, highly incompatible and immobile/low incompatible elements such as Li, K, Cl, Ba, Nb, Dy and Yb allow to put forward that the prolonged (~500 to 100 Ma) Ross subduction event played a fundamental role in &amp;#160;providing the volatile budget into the lithospheric mantle before the onset of the Cenozoic continental rifting.&lt;/p&gt;

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