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.

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.

Caledonian magmatism record within Hebridean Terrane? Loch Roag dyke (Lewis Island, northern Scotland) non-peridotitic xenoliths and megacrysts as messengers from deep lithosphere.

2020 ◽  
Author(s):  
Daniel Buczko ◽  
Magdalena Matusiak-Małek ◽  
Brian J. G. Upton ◽  
Theodoros Ntaflos ◽  
Sonja Aulbach ◽  
...  
Keyword(s):  
North Atlantic ◽  
Parental Magma ◽  
Geological Structure ◽  
Trace Element Composition ◽  
Isotopic Ratios ◽  
The North ◽  
Source Regions ◽  
Mantle Sources ◽  
History Of ◽  
North Atlantic Craton

<p>The northernmost part of Scotland – the Hebridean Terrane – is formed of Archean rocks originally being part of the Laurentian North Atlantic Craton. The geological history of the terrane is well recognised, however details of its internal structure remain unknown. The Eocene (Faithfull et al. 2012, JGS) Loch Roag monchiquite (Lewis Island) sampled deep-seated lithologies, providing insight on evolution and geological structure of the deeper lithosphere of the Hebridean terrane. The monchiquite comprises abundant xenoliths of ultramafic, mafic and felsic rocks. The peridotitic xenoliths represent pieces of Archean mantle underlying marginal parts of the North Atlantic Craton, whereas the origin of non-peridotitic lithologies is uncertain.</p><p>The studied suite of samples comprises two groups: 1) “xenoliths” of diorites (plagioclase, clinopyroxene, orthopyroxene, apatite, opaques) and biotite clinopyroxenites (+apatite), 2) “megacrysts” of clinopyroxene and K-feldspar, both with inclusions of clinopyroxene, biotite and apatite. Megacrysts of alkali-rich feldspar associated with corundum and HFSE-bearing minerals, and composite xenoliths formed of pyroxenite and K-feldspar-rich lithology have also been described from this locality (Menzies et al., 1986, Geol. Soc. Australia Spec. Pub.; Upton et al., 2009, Mineral. Mag.).</p><p>We interpret the “xenoliths” as products of crystallization of fractionated mafic melt(s). The primary character of Sr isotopic ratios in plagioclase (<sup>87</sup>Sr/<sup>86</sup>Sr <0.702) suggests that parental melt of those lithologies originated from melting of depleted lithospheric mantle sources. The “megacrysts” represent fragments of disintegrated alkaline pegmatite(s) formed from melt of plausible mantle origin, possibly enriched (<sup>87</sup>Sr/<sup>86</sup>Sr in feldspar >0.704).</p><p>Trace element composition, similar Sr isotopic ratios of minerals and textural features of “xenoliths” and “megacrysts” groups suggest their close genetic relationship. This geochemical resemblance may reflect crystallisation from primarily similar melt(s) and source regions affected by similar metasomatism. Petrographic features observed in rocks described by Upton et al., (2009) imply that the parental magma of megacrysts might have intruded the rocks forming the xenoliths group. Moreover, the Rb-Sr ages of xenoliths (Der-Chuen et al., 1993, GCA) indicate crystallisation during (or shortly after) Caledonian orogeny. Preliminary age relationship between groups will be determined by on-going Rb-Sr dating of megacrysts.</p><p>Xenoliths similar to diorites from Loch Roag were reported by Badenszki et al. (2019, JoP) from the Midland Valley terrane (“metadiorites” of protolith ages ca. 415 Ma). They were interpreted as products of alkaline syn-/post-collisional Caledonian magmatism. Our study shows that non-peridotitic xenoliths from Loch Roag dyke might represent a record of similar (or the same) magmatism in the northernmost, “Laurentian” part of Scotland. This study presents the first report of such Caledonian magmatism record within the Hebridean Terrane.</p><p>Founded by Polish National Science Centre grant no. UMO-2016/23/B/ST10/01905, part of the data was obtained thanks to the Polish-Austrian project no. WTZ PL 08/2018.</p>

scholarly journals Petrology, Trace Element and Sr, Nd, Hf Isotope Geochemistry of the North Lanzo Peridotite Massif (Western Alps, Italy)

2012 ◽  
Vol 53 (11) ◽  
pp. 2259-2306 ◽  
Author(s):  
Luisa Guarnieri ◽  
Eizo Nakamura ◽  
Giovanni B. Piccardo ◽  
Chie Sakaguchi ◽  
Nobumichi Shimizu ◽  
...  
Keyword(s):  
Trace Element ◽  
Isotope Geochemistry ◽  
Western Alps ◽  
Hf Isotope ◽  
The North

Temporal evolution of a deeply eroded orogen: the Nagssugtoqidian Orogen, West Greenland

2000 ◽  
Vol 37 (8) ◽  
pp. 1121-1142 ◽  
Author(s):  
James N Connelly ◽  
Jeroen AM van Gool ◽  
Flemming C Mengel
Keyword(s):  
Elevated Temperatures ◽  
Time Frame ◽  
Slow Cooling ◽  
West Greenland ◽  
Temporal Correlations ◽  
The North ◽  
Tectonic Events ◽  
Deep Crust ◽  
North Atlantic Craton ◽  
Precise Time

The east-northeast-trending Paleoproterozoic Nagssugtoqidian Orogen of West Greenland records the response of deep crust to collision of the North Atlantic craton and a lesser known cratonic mass to the north. This paper presents conventional U–Pb ages of documented magmatic and thermotectonic events within this orogen, thus providing a precise time frame for its development and offering a test of previous spatial and temporal correlations with segments of the Trans-Hudson Orogen of northern Labrador and Quebec. Convergence of the two cratons culminated in a collision that commenced after 1873+7–4 Ma, the crystallization age of the youngest known pre-Nagssugtoqidian, subduction-related intrusion. Earliest collisional deformation was thrust dominated (west-northwest vergent) and caused thickening and consequent heating to peak temperatures by ca. 1850 Ma. Subsequent north-south shortening at elevated temperatures was accommodated by a fold-dominated style of deformation dated at 1825 ± 1 Ma. Between 1821 and 1778 Ma, temperatures remained sufficiently high to generate pegmatites, metamorphic zircon, and titanite, but no major, penetrative structures are known to have formed in this interval. Further shortening between 1779 ± 6 and 1774 ± 6 Ma exploited preexisting fabrics in steep F3 fold limbs to form discrete, east-northeast – west-southwest-oriented, sinistral steep belts that are not important crustal boundaries. One of these late, steep belts is cut by 1772–1761 Ma pegmatites, indicating that deformation was waning by this time. Slow cooling followed the late shearing, with rutile closing in the central Nagssugtoqidian Orogen as late as 1676 ± 10 Ma. The timing of tectonic events in the Nagssugtoqidian Orogen is indistinguishable from that of the Quebec–Baffin and Torngat segments of the Trans-Hudson Orogen of northeastern Laurentia. Accepting an intercratonic setting for the Nagssugtoqidian Orogen, this new data require that the Quebec–Baffin, Torngat, and Nagssugtoqidian orogens meet in a triple junction offshore. This geometry implies a genetic link between the Rinkian and Nagssugtoqidian belts of West Greenland, thereby defining a middle- to deep-crustal collisional belt more than 900 km wide.

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