Carbonatites and lamprophyres of the Gardar Province – a ‘window’ to the sub-Gardar mantle?

2003 ◽  
Vol 67 (5) ◽  
pp. 855-872 ◽  
Author(s):  
I. M. Coulson ◽  
K. M. Goodenough ◽  
N. J. G. Pearce ◽  
M. J. Leng
Keyword(s):  
Lithospheric Mantle ◽  
Nepheline Syenite ◽  
Crustal Contamination ◽  
Small Degree ◽  
Isotopic Signatures ◽  
Asthenospheric Mantle ◽  
Isotope Data ◽  
Mantle Sources ◽  
O Isotope ◽  
Parental Melts

AbstractCarbonatite magmas are considered to be ultimately derived from mantle sources, which may include lithospheric and asthenospheric reservoirs. Isotopic studies of carbonatite magmatism around the globe have typically suggested that more than one source needs to be invoked for generation of the parental melts to carbonatites, often involving the interaction of asthenosphere and lithosphere.In the rift-related, Proterozoic Gardar Igneous Province of SW Greenland, carbonatite occurs as dykes within the Igaliko Nepheline Syenite Complex, as eruptive rocks and diatremes at Qassiarsuk, as a late plug associated with nepheline syenite at Grønnedal-Íka, and as small bodies associated with ultramafic lamprophyre dykes. The well-known cryolite deposit at Ivittuut was also rich in magmatic carbonate. The carbonatites are derived from the mantle with relatively little crustal contamination, and therefore should provide important information about the mantle sources of Gardar magmas. In particular, they are found intruded both into Archaean and Proterozoic crust, and hence provide a test for the involvement of lithospheric mantle.A synthesis of new and previously published major and trace element, Sr, Nd, C and O isotope data for carbonatites and associated lamprophyres from the Gardar Province is presented. The majority of Gardar carbonatites and lamprophyres have consistent geochemical and isotopic signatures that are similar to those typically found in ocean island basalts. The geochemical characteristics of the two suites of magmas are similar enough to suggest that they were derived from the same mantle source. C and O isotope data are also consistent with a mantle derivation for the carbonatite magmas, and support the theory of a cogenetic origin for the carbonatites and the lamprophyres. The differences between the carbonatites and lamprophyres are considered to represent differing degrees of partial melting of a similar source.We suggest that the ultimate source of these magmas is the asthenospheric mantle, since there is no geochemical or isotopic evidence for their having been derived directly from ancient, enriched sub-continental lithospheric mantle. However, it is likely that the magmas actually formed through a two-stage process, with small-degree volatile-rich partial melts rising from the asthenospheric mantle and being ‘frozen in’ as metasomites, which were then rapidly remobilized during Gardar rifting.

Geochemical evolution of Devonian-Carboniferous igneous rocks of the Magdalen basin, Eastern Canada: Pb- and Nd-isotope evidence for mantle and lower crustal sources

1998 ◽  
Vol 35 (3) ◽  
pp. 201-221 ◽  
Author(s):  
Georgia Pe-Piper ◽  
David JW Piper
Keyword(s):  
Lithospheric Mantle ◽  
Crustal Contamination ◽  
Mafic Magma ◽  
Igneous Rocks ◽  
Geochemical Evolution ◽  
Eastern Canada ◽  
Nd Isotope ◽  
Isotopic Compositions ◽  
Mantle Sources ◽  
Lower Crustal

Magmatism associated with the extensional Magdalen basin includes voluminous tholeiitic gabbro and basalt and local granite and rhyolite. Pb- and (or) Nd-isotope determinations have been made on 70 igneous rocks from throughout the basin, and a further 15 samples of Avalonian basement from the southern margin of the basin, to characterize the contribution of lower crustal blocks and mantle sources to the magmatism and to constrain tectonic models for the basin. Five phases of magmatic evolution are distinguished in the Magdalen basin. (1) Middle to Late Devonian partial melting of lithospheric mantle, producing principally tholeiites and minor alkalic basalt. Tholeiites have Pb isotopic compositions similar to that of younger Triassic tholeiites generated from the same mantle, but experienced less crustal contamination. Regional variations in trace element composition of the mantle can be recognized. (2) The mafic magma triggered anhydrous base-of-crust melting, principally along the transpressive Cobequid and Rockland Brook faults, producing A-type granites in which radiogenic Pb increases northeastward. (3) In the latest Devonian, a large base-of-crust fractionating magma chamber evolved. It contained immiscible mafic and minor felsic magma, with uniform Nd isotopes, and high Ti in the mafic magma. (4) Although late Tournaisian dykes are not strongly fractionated, their evolution involved more crustal assimilation than earlier mafic rocks. (5) Local Viséan-Westphalian alkalic magmas, which ascended along crustal-scale faults, have Pb and Nd isotopic compositions resembling mantle plumes or their mixtures with lithospheric mantle sources. Only these youngest rocks show any isotopic evidence for input from an asthenospheric plume source, suggesting that regional extension was responsible for most of the magmatism.

Sub-lithospheric mantle sources for overlapping southern African Large Igneous Provinces

2021 ◽  
Author(s):  
L.D. Ashwal
Keyword(s):  
Lithospheric Mantle ◽  
Isotopic Data ◽  
Isotopic Signatures ◽  
Large Igneous Provinces ◽  
Igneous Provinces ◽  
Depleted Mantle ◽  
Heating Event ◽  
Mantle Sources ◽  
Short Time ◽  
Melt Composition

Abstract At least four spatially overlapping Large Igneous Provinces, each of which generated ∼1 x 106 km3 or more of basaltic magmas over short time intervals (<5 m.y.), were emplaced onto and into the Kaapvaal Craton between 2.7 and 0.18 Ga: Ventersdorp (2 720 Ma, ∼0.7 x 106 km3), Bushveld (2 056 Ma, ∼1.5 x 106 km3), Umkondo (1 105 Ma, ∼2 x 106 km3) and Karoo (182 Ma, ∼3 x 106 km3). Each of these has been suggested to have been derived from melting of sub-continental lithospheric mantle (SCLM) sources, but this is precluded because: (1) each widespread heating event sufficient to generate 1 to 2 x 106 km3 of basalt from the Kaapvaal SCLM (volume = 122 to 152 x 106 km3) would increase residual Mg# by 0.5 to 2 units, depending on degree of melting, and source and melt composition, causing significant depletion in already-depleted mantle, (2) repeated refertilization of the Kaapvaal SCLM would necessarily increase its bulk density, compromising its long-term buoyancy and stability, and (3) raising SCLM temperatures to the peridotite solidus would also have repeatedly destroyed lithospheric diamonds by heating and oxidation, which clearly did not happen. It is far more likely, therefore, that the Kaapvaal LIPs were generated from sub-lithospheric sources, and that their diverse geochemical and isotopic signatures represent variable assimilation of continental crustal components. Combined Sr and Nd isotopic data (n = 641) for the vast volumetric majority of Karoo low-Ti tholeiitic magmatic products can be successfully modelled as an AFC mixing array between a plume-derived parental basalt, with <10% of a granitic component derived from 1.1 Ga Namaqua-Natal crust. Archaean crustal materials are far too evolved (εNd ∼ -35) to represent viable contaminants. However, a very minor volume of geographically-restricted (and over-analysed) Karoo magmas, including picrites, nephelinites, meimechites and other unusual rocks may represent low-degree melting products of small, ancient, enriched domains in the Kaapvaal SCLM, generated locally during the ascent of large-volume, plume-derived melts. The SCLM-derived rocks comprise the well-known high-Ti (>2 to 3 wt.% TiO2) magma group, have εNd, 182 values between +10.5 and -20.9, and are characteristically enriched in Sr (up to 1 500 ppm), suggesting a possible connection to kimberlite, lamproite and carbonatite magmatism. These arguments may apply to continental LIPs in general, although at present, there are insufficient combined Sr + Nd isotopic data with which to robustly assess the genesis of other southern African LIPs, including Ventersdorp (n = 0), Bushveld (n = 55) and Umkondo (n = 18).

scholarly journals Petrogenesis and Geodynamic Implications of a Newly Discovered Basanite Dike in Zaolin, Jingdezhen City, South China

Lithosphere ◽  
2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Xiaofei Pan ◽  
Yufeng Ren ◽  
Zengqian Hou ◽  
Yongpeng Ouyang ◽  
Xuejing Gong ◽  
...  
Keyword(s):  
South China ◽  
Lithospheric Mantle ◽  
Eastern China ◽  
Crustal Contamination ◽  
Alkaline Basalt ◽  
Southeastern China ◽  
Ocean Island Basalts ◽  
Asthenospheric Mantle ◽  
The Matrix ◽  
Geochemical Analyses

Abstract A recently discovered basanite dike in the Zaolin area of Jingdezhen, South China, contains mantle xenocrysts such as kink-banded olivines, olivines + orthopyroxenes assemblage, and chromites. In addition, polymorphic carbonates of the MgCO3–FeCO3 series occur as augens, either independently or interspersed with diopside and spinel in the matrix. The rock is characterized by high Cr and Ni contents, high whole-rock Mg# values (0.66–0.72), and high Ca/Al (0.72–1.03) and TFeO/MgO (1.1–1.3) ratios and is alkali-rich with Na2O > K2O. The trace-element partition patterns are similar to those of other basanites in eastern China as well as ocean island basalts. Whole-rock geochemical analyses show depleted Sr and Nd isotopic compositions (86Sr/87Sr=0.70358–0.703853, εNd=2.52–6.73). These data indicate that the rock has experienced negligible crustal contamination, should be derived from asthenospheric mantle, or mixed by the MORB with EMI/EMII mantle and have been carbonated. The calculated T–P conditions of the melt in equilibrium with xeno-olivine are 1160–1320°C at the mantle depth. The high Cr# values of the spinel xenocrysts indicate that the lithospheric mantle under the Jingdezhen area was probably relict Proterozoic mantle. The Ar–Ar plateau age and the isochron and inverse isochron ages for the matrix of the basanite are all 44 Ma. The basanite, as well as other alkaline basalt or lamprophyre dikes in southeastern China, formed in a rifting regime during the Eocene.

Geochemistry of bimodal amphibolitic—felsic gneiss complexes from eastern Massif Central, France

1995 ◽  
Vol 132 (3) ◽  
pp. 321-337 ◽  
Author(s):  
Bernard Briand ◽  
Jean-Luc Bouchardon ◽  
Houssa Ouali ◽  
Michel Piboule ◽  
Paul Capiez
Keyword(s):  
Crustal Contamination ◽  
Igneous Rocks ◽  
Chemical Characteristics ◽  
Continental Margins ◽  
High Grade ◽  
Transitional Stage ◽  
Crust Formation ◽  
Massif Central ◽  
Mantle Sources ◽  
Two Populations

AbstractHigh-grade basic and acidic meta-igneous rocks are widespread in the bimodal amphibolitic—felsic gneiss complexes, which are characteristic formations of the ‘Middle Allochthonous Unit’ from eastern and southern French Massif Central. The metabasites from the Lyonnais and Doux complexes are chemically diverse and range from N-MORB type tholeiitic to transitional types. The two populations are not related by fractional crystallization or crustal contamination processes and their chemical characteristics reflect differences in their mantle sources. An ensialic setting is supported by the crustally-derived character of some of the associated felsic rocks, but the presence of N-MORB-type metabasites argues for an extensional environment. This bimodal association compares well with the magmatism of rifted continental margins and may reflect a transitional stage between continental rifting and oceanic crust formation during the Cambro-Ordovician spreading event.

Variable modes of formation for tonalite-trondhjemite-granodiorite-diorite (TTG)-related porphyry-type Cu ± Au deposits in the Neoarchean southern Abitibi subprovince (Canada): Evidence from petrochronology and oxybarometry

2021 ◽  
Author(s):  
Xuyang Meng ◽  
Jeremy P Richards ◽  
Daniel J Kontak ◽  
Adam C Simon ◽  
Jackie M Kleinsasser ◽  
...  
Keyword(s):  
Crustal Contamination ◽  
Edge Structure ◽  
Isotopic Signatures ◽  
Porphyry Cu ◽  
Abitibi Subprovince ◽  
Local Restriction ◽  
Fractionation Trend ◽  
Magma Crystallization ◽  
X Ray Absorption

Abstract Most known porphyry Cu ± Au deposits are associated with moderately oxidized and sulfur-rich, calc-alkaline to mildly alkalic arc-related magmas in the Phanerozoic. In contrast, sodium-enriched tonalite-trondhjemite-granodiorite-diorite (TTG) magmas predominant in the Archean are hypothesized to be unoxidized and sulfur-poor, which together preclude porphyry Cu deposit formation. Here, we test this hypothesis by interrogating the causative magmas for the ~2.7 Ga TTG-related Côté Gold, St-Jude, and Clifford porphyry-type Cu ± Au deposit settings in the Neoarchean southern Abitibi subprovince. New and previously published geochronological results constrain the age of emplacement of the causative magmas at ~2.74 Ga, ~2.70 Ga, and ~2.69 Ga, respectively. The dioritic and trondhjemitic magmas associated with Côté Gold and St-Jude evolved along a plagioclase-dominated fractionation trend, in contrast to amphibole-dominated fractionation for tonalitic magma at Clifford. Analyses of zircon grains from the Côté Gold, St-Jude, and Clifford igneous rocks yielded εHf(t) ± SD values of 4.5 ± 0.3, 4.2 ± 0.6, and 4.3 ± 0.4, and δ18O ± SD values of 5.40 ± 0.11 ‰, 3.91 ± 0.13 ‰, and 4.83 ± 0.12 ‰, respectively. These isotopic signatures indicate that although these magmas are mantle-sourced with minimal crustal contamination, for the St-Jude and Clifford settings the magmas or their sources may have undergone variable alteration by heated seawater or meteoric fluids. Primary barometric minerals (i.e., zircon, amphibole, apatite, and magnetite-ilmenite) that survived variable alteration and metamorphism (up to greenschist facies) were used for estimating fO2 of the causative magmas. Estimation of magmatic fO2 values, reported relative to the fayalite-magnetite-quartz buffer as ΔFMQ, using zircon geochemistry indicate that the fO2 values of the St-Jude, Côté Gold, and Clifford magmas increase from ΔFMQ -0.3 ± 0.6, ΔFMQ +0.8 ± 0.4, to ΔFMQ +1.2 ± 0.4, respectively. In contrast, amphibole chemistry yielded systematically higher fO2 values of ΔFMQ +1.6 ± 0.3 and ΔFMQ +2.6 ± 0.1 for Côté Gold and Clifford, respectively, which are consistent with previous studies that indicate amphibole may overestimate the fO2 of intrusive rocks by up to one log unit. Micro X-ray absorption near edge structure (μ-XANES) spectrometric determination of sulfur (i.e., S6+/ΣS) in primary apatite yielded ≥ΔFMQ -0.3 and ΔFMQ +1.4–1.8 for the St-Jude and Clifford, respectively. The magnetite-ilmenite mineral pairs from the Clifford tonalite yielded ΔFMQ +3.3 ± 1.3 at equilibrium temperatures of 634 ± 21 °C, recording the redox state of the late stage of magma crystallization. Electron probe microanalyses revealed that apatite grains from Clifford are enriched in S (up to 0.1 wt. %) relative to those of Côté Gold and St-Jude (below the detection limit), which is attributed to either relatively oxidized or sulfur-rich features of the Clifford tonalite. We interpret these results to indicate the deposits at Côté Gold and Clifford formed from mildly (~ΔFMQ +0.8 ± 0.4) to moderately (~ΔFMQ +1.5) oxidized magmas where voluminous early sulfide saturation was probably limited, whereas the St-Jude deposit represents a rare case whereby the ingress of externally derived hydrothermal fluids facilitated metal fertility in a relatively reduced magma chamber (~ΔFMQ +0). Furthermore, we conclude that variable modes of formation for these deposits and, in addition, the apparent rarity of porphyry-type Cu-Au deposits in the Archean may be attributed to either local restriction of favorable metallogenic conditions, and/or preservation, or an exploration bias.

scholarly journals Deep Crustal Contamination of the Lithospheric Mantle Source to Variscan Ultrapotassic Magmas – Geochemical and Geodynamic Consequences

2020 ◽  
Author(s):  
Vojtěch Janoušek ◽  
John Milan Hora ◽  
Yulia Erban Kochergina ◽  
Simon Couzinié ◽  
Tomáš Magna ◽  
...  
Keyword(s):  
Mantle Source ◽  
Lithospheric Mantle ◽  
Crustal Contamination ◽  
Lithospheric Mantle Source

scholarly journals Adakites, High-Nb Basalts and Copper–Gold Deposits in Magmatic Arcs and Collisional Orogens: An Overview

Geosciences ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 29
Author(s):  
Pavel Kepezhinskas ◽  
Nikolai Berdnikov ◽  
Nikita Kepezhinskas ◽  
Natalia Konovalova
Keyword(s):  
Subduction Zones ◽  
Far East ◽  
Gold Deposits ◽  
Type I ◽  
Isotopic Signatures ◽  
Epithermal Mineralization ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
East Russia ◽  
Collisional Orogens

Adakites are Y- and Yb-depleted, SiO2- and Sr-enriched rocks with elevated Sr/Y and La/Yb ratios originally thought to represent partial melts of subducted metabasalt, based on their association with the subduction of young (<25 Ma) and hot oceanic crust. Later, adakites were found in arc segments associated with oblique, slow and flat subduction, arc–transform intersections, collision zones and post-collisional extensional environments. New models of adakite petrogenesis include the melting of thickened and delaminated mafic lower crust, basalt underplating of the continental crust and high-pressure fractionation (amphibole ± garnet) of mantle-derived, hydrous mafic melts. In some cases, adakites are associated with Nb-enriched (10 ppm < Nb < 20 ppm) and high-Nb (Nb > 20 ppm) arc basalts in ancient and modern subduction zones (HNBs). Two types of HNBs are recognized on the basis of their geochemistry. Type I HNBs (Kamchatka, Honduras) share N-MORB-like isotopic and OIB-like trace element characteristics and most probably originate from adakite-contaminated mantle sources. Type II HNBs (Sulu arc, Jamaica) display high-field strength element enrichments in respect to island-arc basalts coupled with enriched, OIB-like isotopic signatures, suggesting derivation from asthenospheric mantle sources in arcs. Adakites and, to a lesser extent, HNBs are associated with Cu–Au porphyry and epithermal deposits in Cenozoic magmatic arcs (Kamchatka, Phlippines, Indonesia, Andean margin) and Paleozoic-Mesozoic (Central Asian and Tethyan) collisional orogens. This association is believed to be not just temporal and structural but also genetic due to the hydrous (common presence of amphibole and biotite), highly oxidized (>ΔFMQ > +2) and S-rich (anhydrite in modern Pinatubo and El Chichon adakite eruptions) nature of adakite magmas. Cretaceous adakites from the Stanovoy Suture Zone in Far East Russia contain Cu–Ag–Au and Cu–Zn–Mo–Ag alloys, native Au and Pt, cupriferous Ag in association witn barite and Ag-chloride. Stanovoy adakites also have systematically higher Au contents in comparison with volcanic arc magmas, suggesting that ore-forming hydrothermal fluids responsible for Cu–Au(Mo–Ag) porphyry and epithermal mineralization in upper crustal environments could have been exsolved from metal-saturated, H2O–S–Cl-rich adakite magmas. The interaction between depleted mantle peridotites and metal-rich adakites appears to be capable of producing (under a certain set of conditions) fertile sources for HNB melts connected with some epithermal Au (Porgera) and porphyry Cu–Au–Mo (Tibet, Iran) mineralized systems in modern and ancient subduction zones.

scholarly journals Potential influence of a planned landfill on a high karst plateau in Southwestern Montenegro to nearby karstic springs

2021 ◽  
Vol 50 (2-3) ◽  
Author(s):  
Micha Horacek ◽  
Milan Radulovic ◽  
Dejan Jancic ◽  
Stefan Wyhlidal ◽  
Golub Culafic
Keyword(s):  
Drinking Water ◽  
Water Supply ◽  
Water Samples ◽  
Catchment Area ◽  
Winter Precipitation ◽  
Potential Influence ◽  
Potential Threat ◽  
Isotope Data ◽  
O Isotope ◽  
Good Agreement

The potential threat of a landfill projected on a high karst plateau in southwest Montenegro is investigated with respect to the subjacent nearby springs. The locality is called Duboki do. As the springs are used for drinking water supply this investigation is urgently needed. For the springs exist two hypotheses concerning their catchment area: I) from the high karst plateau, or II) from a topographically lower area. The stable H- and O-isotope ratios of water samples from the springs are compared with precipitation isotope data, to reveal the catchment area of the springs. The isotope results indicate that the catchment area of the springs is at higher altitude fitting to, and in good agreement with, winter precipitation from the high karst plateau of the planned land-fill locality.

Sign in / Sign up

Export Citation Format

Share Document