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?

M. Boily; J. N. Ludden

doi:10.1139/e91-003

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?

Canadian Journal of Earth Sciences ◽

10.1139/e91-003 ◽

1991 ◽

Vol 28 (1) ◽

pp. 26-36 ◽

Cited By ~ 12

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.

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

Antarctic Science ◽

10.1017/s0954102095000113 ◽

1995 ◽

Vol 7 (1) ◽

pp. 73-85 ◽

Cited By ~ 11

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.

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An early Proterozoic volcanic arc succession in southeastern Wyoming

Canadian Journal of Earth Sciences ◽

10.1139/e84-045 ◽

1984 ◽

Vol 21 (4) ◽

pp. 415-427 ◽

Cited By ~ 26

Author(s):

Kent C. Condie ◽

Craig A. Shadel

Keyword(s):

Fractional Crystallization ◽

Tectonic Setting ◽

Volcanic Rocks ◽

Geochemical Data ◽

Alkaline Basalt ◽

Calc Alkaline ◽

Early Proterozoic ◽

Enriched Mantle ◽

Sierra Madre ◽

Felsic Volcanic

The Green Mountain Formation of early Proterozoic age in the Sierra Madre Range of southeastern Wyoming comprises a bimodal mafic and felsic volcanic assemblage. The rocks, which are chiefly breccias, agglomerates, flows, and volcaniclastic sediments, represent both subaerial and submarine eruptions and in part were redeposited in fluvial and nearshore marine environments. Volcanic rocks are clearly calc-alkaline in character and share a large number of geochemical features in common with continental-margin arcs or evolved oceanic-arc systems.The low Mg numbers and Ni contents of the basalts require 30–40% olivine fractional crystallization, and the high contents of the most incompatible elements, high (La/Sm)N ratios, and low Zr/Nb ratios require an undepleted or enriched mantle source. Geochemical data are consistent with an origin for the felsic volcanics and associated Encampment River granodiorite by shallow fractional crystallization of calc-alkaline basalt in a tectonic setting similar to modern arc systems. The near absence of andesites may reflect the retention of andesitic magma in crustal reservoirs during fractional cyrstallization.

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Petrogenesis and Lu–Hf Dating of (Ultra)Mafic Rocks from the Kutná Hora Crystalline Complex: Implications for the Devonian Evolution of the Bohemian Massif

Journal of Petrology ◽

10.1093/petrology/egaa075 ◽

2020 ◽

Vol 61 (8) ◽

Author(s):

Lukáš Ackerman ◽

Jana Kotková ◽

Renata Čopjaková ◽

Jiří Sláma ◽

Jakub Trubač ◽

...

Keyword(s):

Trace Element ◽

Bohemian Massif ◽

Lithospheric Mantle ◽

Granulite Facies ◽

Ultrahigh Pressure ◽

Garnet Growth ◽

Crystalline Complex ◽

Crustal Rocks ◽

Asthenospheric Mantle ◽

Oceanic Slab

Abstract The Lu–Hf isotope system and Sr–Nd–Hf–Os isotope systematics of mantle rocks are capable of unravelling the early processes in collision belts, especially in a hot subduction context where the Sm–Nd and U–Pb systems in crustal rocks are prone to resetting owing to high temperatures and interaction with melts during exhumation. To improve models of the Devonian–Carboniferous evolution of the Bohemian Massif, we investigated in detail mafic and ultramafic rocks (eclogite, pyroxenite, and peridotite) from the ultrahigh-pressure and ultrahigh-temperature Kutná Hora Crystalline Complex (KHCC: Úhrov, Bečváry, Doubrava, and Spačice localities). Petrography, multiphase solid inclusions, major and trace element compositions of rocks and minerals, and radiogenic isotopic data document contrasting sources and protoliths as well as effects of subduction-related processes for these rocks. The Úhrov peridotite has a depleted composition corresponding to the suboceanic asthenospheric mantle, whereas Bečváry and Doubrava peridotites represent lithospheric mantle that underwent melt refertilization by basaltic and SiO2-undersaturated melts, respectively. Multiphase solid inclusions enclosed in garnet from Úhrov and Bečváry peridotites represent trapped H2O ± CO2-bearing metasomatizing agents and Fe–Ti-rich melts. The KHCC eclogites either formed by high-pressure crystal accumulation from mantle-derived basaltic melts (Úhrov) or represent a fragment of mid-ocean ridge basalt-like gabbroic cumulate (Spačice) and crustal-derived material (Doubrava) both metamorphosed at high P–T conditions. The Lu–Hf age of 395 ± 23 Ma obtained for the Úhrov peridotite reflects garnet growth related to burial of the asthenospheric mantle during subduction of the oceanic slab. By contrast, Spačice and Doubrava eclogites yield younger Lu–Hf ages of ∼350 and 330 Ma, respectively, representing mixed ages as demonstrated by the strong granulite-facies overprint and trace element zoning in garnet grains. We propose a refined model for the Early Variscan evolution of the Bohemian Massif starting with the subduction of the oceanic crust (Saxothuringian ocean) and associated oceanic asthenospheric mantle (Úhrov) beneath the Teplá–Barrandian at ≥380 Ma, which was responsible for melt refertilization of the associated mantle wedge (Bečváry, Doubrava). This was followed by continental subduction (∼370–360 Ma?) accompanied by the oceanic slab break-off and incorporation of the upwelling asthenospheric mantle into the Moldanubian lithospheric mantle and subsequent coeval exhumation of mantle and crustal rocks at ∼350–330 Ma.

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Open-system evolution versus source control in basaltic magmas: Matachewan–Hearst dike swarm, Superior Province, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e90-078 ◽

1990 ◽

Vol 27 (6) ◽

pp. 767-783 ◽

Cited By ~ 18

Author(s):

Dennis O. Nelson ◽

Donald A. Morrison ◽

William C. Phinney

Keyword(s):

Trace Element ◽

Fractional Crystallization ◽

Incompatible Trace Element ◽

Source Control ◽

Superior Province ◽

Crustal Rock ◽

Dike Swarm ◽

Element Abundances ◽

Field Evidence ◽

Element Enrichment

The 2.45 Ga Matachewan–Hearst dike swarm was emplaced over 250 000 km2 in diverse granitoid–greenstone and metasedimentary terranes of the Superior Province of Canada. The Fe-rich tholeiitic dikes host large, uniform plagioclase megacrysts and display significant trace-element variations, e.g., (La/Sm)N = 0.62–2.23, not correlated to terrane lithologies.Fractional crystallization alone cannot produce these variations or simultaneously account for both major- and trace-element abundances. Combined periodic replenishment–fractional crystallization (RFC) in shallow magma chambers is consistent with major- and trace-element concentrations and with field evidence for periodic magma injection within the dikes. RFC cannot, however, produce the observed variation in incompatible-trace-element ratios, e.g., (La/Sm)N. Models invoking mixed mantle sources are unsuccessful at reproducing trace-element trends. Combined assimilation–fractional crystallization (AFC) models, assuming depleted parental magmas and using crustal rock data from xenoliths and from the Kapuskasing Structural Zone, can accommodate the trace-element variations, including the light-rare-earth-element enrichment and the observed relative depletions of the high-field-strength elements. The AFC process apparently took place in the lower crustal regions from where evolved magmas were periodically transported to shallow chambers dominated by RFC.

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Late Triassic porphyries in the Zhongdian arc, eastern Tibet: origin and implications for Cu mineralization

Geological Magazine ◽

10.1017/s0016756819000700 ◽

2019 ◽

Vol 157 (2) ◽

pp. 275-288

Author(s):

Pengsheng Dong ◽

Guochen Dong ◽

Zhuanrong Sun ◽

Huawei Li ◽

Jiahui Tang ◽

...

Keyword(s):

Partial Melting ◽

Water Content ◽

Fractional Crystallization ◽

Lower Crust ◽

Late Triassic ◽

Magma Source ◽

High Water Content ◽

Asthenospheric Mantle ◽

Low Degree ◽

Eastern Tibet

AbstractWhole-rock and Sr–Nd–Pb isotopic composition data, zircon Hf isotopic data and zircon U–Pb ages were obtained for the Late Triassic porphyries in the Zhongdian arc, eastern Tibet. These porphyries are intermediate and metaluminous and are enriched in large ion lithophile elements and depleted in high field strength elements. Moreover, they have weak negative Eu anomalies, high Sr and Ba contents, and high Sr/Y ratios. Different mineral geothermobarometers suggest that the porphyries in the Zhongdian arc crystallized at c. 640–829 °C and pressures of 2.1–2.8 kbar at depths shallower than 8 km. The porphyries have a calculated water content of 4.47–4.94 wt % and a relatively high magmatic oxygen fugacity. These porphyries were emplaced mainly at 230–203 Ma with a peak at 218–215 Ma. The Sr–Nd–Pb–Hf isotope data suggest that the porphyries in the Zhongdian arc were derived from a mixed melt of 50–65 % asthenospheric mantle and 35–50 % eclogite from the western Yangtze lower crust that experienced low-degree partial melting of 2–10 %. Subsequent fractional crystallization resulted in the decreasing trends of the major- and trace-element contents. The high Sr/Y and La/Yb values are the result of the low degree of partial melting of the western Yangtze lower crust rather than fractional crystallization, because no linear relationship was noted between Sr/Y or La/Yb and SiO2. The mixed melts from the lower crust and asthenospheric mantle provided a fertile magma source, and subsequent fractional crystallization under the favourable magmatic conditions of high water content and high oxidation state resulted in the formation of the porphyry Cu–Au deposits.

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Trace Element and Isotope Geochemistry of Gabbro-Derived and Felsic Granulites from the Northern Apennines (Italy): Evidence for Assimilation/Fractional Crystallization in the Lower Crust

Mineralogical Magazine ◽

10.1180/minmag.1998.62a.2.199 ◽

1998 ◽

Vol 62A (2) ◽

pp. 1017-1018

Author(s):

A. Montanini

Keyword(s):

Trace Element ◽

Fractional Crystallization ◽

Lower Crust ◽

Isotope Geochemistry ◽

Northern Apennines

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Petrogenesis and Lu–Hf dating of (ultra)mafic rocks from the Kutná Hora Crystalline Complex: implications for the Devonian evolution of the Bohemian Massif

10.5194/egusphere-egu2020-7983 ◽

2020 ◽

Author(s):

Jana Kotková ◽

Lukáš Ackerman ◽

Renata Čopjaková ◽

Jiří Sláma ◽

Jakub Trubač ◽

...

Keyword(s):

Trace Element ◽

Oceanic Crust ◽

Bohemian Massif ◽

Lithospheric Mantle ◽

Mantle Wedge ◽

Mantle Melting ◽

Crystalline Complex ◽

Crustal Rocks ◽

Asthenospheric Mantle ◽

Basaltic Melts

Orogenic garnet peridotites with associated garnet pyroxenites and eclogites in the (U)HP-(U)HT terranes provide insight into mantle melting and subduction-related metamorphism in collisional orogenic belts. Here we demonstrate that they also represent unique tracers of early subduction processes in the internal part of the European Variscan Belt, where subsequent high-temperature processes affect thermochronometers in crustal rocks. Our study focused on several localities within the Kutn&#225; Hora Crystalline Complex (KHCC), a key area for the evolution of the Variscan Bohemian Massif due to its position, evidence for a deep crustal subduction (diamond in granulites) and complete geochronological record.The mantle rocks show highly variable petrographical and geochemical characteristics reflecting derivation from contrasting mantle sources which have undergone both mantle melting and enrichment due to subduction-related metasomatism.&#160; While the &#218;hrov lherzolite has trace element and Sr&#8211;Nd&#8211;Hf composition similar to depleted oceanic asthenospheric mantle, the composition of the Be&#269;v&#225;ry lherzolite reflects extensive refertilization by basaltic melts associated with Grt&#177;Cpx precipitation. Multiple solid inclusions (MSI) trapped in garnet, dominated by Ti and Fe-Ti oxides (rutile, ilmenite), represent relics of Ti-rich low-degree basaltic partial melt. Minor hornblende/phlogopite and carbonate reflect mantle metasomatism by H2O&#177;CO2-bearing fluids. Highly to mildly radiogenic Sr&#8211;Nd&#8211;Hf&#8211;Os isotopic compositions along with negative HFSE anomalies in clinopyroxene indicate only a very small contribution of recycled crustal component. The Doubrava peridotites exhibit marked petrographic variability ranging from harzburgite to composite dunite-wehrlite/olivine-bearing pyroxenite assemblage and contrasting geochemical patterns. This can be best explained by interaction between depleted protolith and SiO2-undersaturated melt with small proportion of recycled crust (~5 % when subducted oceanic crust is considered). The KHCC eclogites show diverse origins, involving products of high-pressure crystal accumulation from mantle-derived basaltic melts, or a fragment of MORB-like gabbroic cumulate and crustal-derived material both metamorphosed at HT&#8211;HP conditions.The &#218;hrov peridotite yields Lu&#8211;Hf age of 395 &#177; 23 Ma, interpreted as dating garnet growth based on detailed examination of trace element garnet zoning. By contrast, eclogites yield younger Lu&#8211;Hf ages of ~350 and 330 Ma, respectively, representing mixed ages as demonstrated by garnet trace element zoning and a strong granulite-facies overprint.We propose a refined model for Devonian&#8211;Carboniferous evolution of the Bohemian Massif, &#160;&#160;with the subduction of the oceanic crust and associated oceanic asthenospheric mantle beneath the Tepl&#225;&#8211;Barrandian at ~400 Ma related to closure of the Saxothuringian ocean between Gondwana-derived microcontinents. The overlaying lithospheric mantle wedge was refertilized by fluids/melts. Oceanic subduction passed to continental subduction of the Saxothuringian crust (~370&#8211;360 Ma?) accompanied by the break-off &#160;of the eclogitized oceanic crust facilitating incorporation of the upwelling asthenospheric mantle into the Moldanubian lithospheric mantle wedge. Subsequent collision and coeval exhumation of mantle and crustal rocks occurred at ~350&#8211;330 Ma and might be associated with mixing/mingling of crustal-derived melts and mafic lithologies producing the observed geochemical and geochronological signatures.

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