The Michael Gabbro and other Mesoproterozoic lithospheric probes in southern and central Labrador

1997 ◽  
Vol 34 (12) ◽  
pp. 1566-1580 ◽  
Author(s):  
Ronald F. Emslie ◽  
Michael A. Hamilton ◽  
Charles F. Gower
Keyword(s):  
Crustal Contamination ◽  
Isotopic Signature ◽  
Geochemical Data ◽  
Magmatic Activity ◽  
Flood Basalts ◽  
Grenville Province ◽  
Continental Flood Basalts ◽  
The North ◽  
Basement Rocks ◽  
Northwestern Margin

The Michael Gabbro (1426 Ma) and the Shabogamo Gabbro (1459 Ma) represent two large diabase intrusive episodes that affected the northwestern margin of the northeastern Grenville Province. Both have sustained variable effects of subsequent Grenvillian metamorphism. Other broadly contemporaneous magmatic activity in the region includes the formation of Elsonian anorthosite–granitoid complexes (1.46–1.29 Ga) that intruded Churchill Province and Nain Province rocks to the north, the Harp dykes (1.27 Ga), and Mealy dykes (~1.25 Ga). Petrologic and geochemical data show that the Michael Gabbro and Shabogamo Gabbro are similar, with the latter displaying more cumulate rock characteristics, and the former having compositions closer to those of rapidly cooled magma. Both have compositions comparable to those of other continental diabases and to some continental flood basalts. Sr and Nd initial isotopic compositions of Michael Gabbro (εNd(1426 Ma) = −4.7 to −6.0, ISr(1426 Ma) = 0.7032–0.7044) and Shabogamo Gabbro (εNd(1459 Ma) = −4.0 to −5.5, ISr(1459 Ma) = 0.7020–0.7060) are alike and overlap, suggesting similar sources and processes of development. Comparisons with other nearly contemporary mafic suites in central and southern Labrador show that only the Mealy dykes have a distinctly more radiogenic isotopic signature. Paradoxically, other mafic suites that intrude older basement rocks north of the Grenville Front have less enriched Nd signatures than do those that intrude younger basement rocks south of the front. The argument is made that the subcontinental lithospheric mantle, and not crustal contamination, played the most influential role in evolution of the magmas.

Cyclical variation in composition in continental tholeiites of East Greenland

1989 ◽  
Vol 26 (3) ◽  
pp. 534-543 ◽  
Author(s):  
A. J. Hogg ◽  
J. J. Fawcett ◽  
J. Gittins ◽  
M. P. Gorton
Keyword(s):  
North Atlantic Ocean ◽  
Tholeiitic Basalt ◽  
Primitive Mantle ◽  
Magma Chambers ◽  
Flood Basalts ◽  
East Greenland ◽  
Continental Flood Basalts ◽  
Tholeiitic Magma ◽  
Small Reservoirs ◽  
The North

The Prinsen of Wales Bjerge (PWB), part of the Tertiary volcanic province of East Greenland, consists of tholeiitic basalts overlain by alkalic basalts that were erupted 100–150 km west of the original axis of continental rifting and active ocean-floor development during the creation of the North Atlantic Ocean. They have many features of continental flood basalts but are somewhat enriched in Fe and in Ti relative to Fe and have slightly lower Al2O3. They have slight enrichments in the light rare-earth elements (La/Yb = 3–4). A nunatak within the PWB displays four cycles of tholeiitic basalt, each about 50 m thick, which are defined by trace-element variations (Ni, Cr, Sr, Zr, and Zr/Y). In three of the four cycles the lowermost flows are the most highly differentiated, and successive flows are increasingly primitive. These changes are thought to be the result of frequent injection of primitive, mantle-derived tholeiitic magma into small crustal magma chambers that contain evolved tholeiitic magma. The resultant mixing and expulsion of hybrid magma produce flows of small volume (0.01–0.03 km3) that display increasingly primitive character upward within each cycle (increasing Mg# and decreasing content of incompatible elements). This process is expected to be more efficient in small reservoirs than in the very large magma chambers that have been invoked by previous exponents of the differentiation–replenishment hypothesis. We suggest that cyclical volcanism in areas well back from the line of active rifting may be more common than is realized and is controlled by the fractionation–magma-replenishment process operating in numerous small reservoirs in an extensively fractured continental crust.

scholarly journals NORTH-WESTERN-KORYAK VOLCANIC BELT AND ITS ORE-BEARING VOLCANOGENES

2018 ◽  
Author(s):  
Г.П. Яроцкий
Keyword(s):  
Volcanic Belt ◽  
Magmatic Activity ◽  
Northern Margin ◽  
North West ◽  
The North ◽  
Basement Rocks ◽  
Deep Faults ◽  
Gold Silver ◽  
Metallogenic Zone ◽  
North Western

Обосновано выделение орогенного Северо-Западно-Корякского вулканического пояса. В методологии авторской глыбово-клавишной структуры литосферы определён на границе регионального прогиба и северной активной окраины Корякского микроконтинента механизм образования вулканогенов пояса. На пересечении поперечными межглыбовыми глубинными разломами литосферы границы регионального прогиба и северной окраины микроконтинента образовались локальные впадины вулканогенов. В них в эпоху олигоценовой тектоно-магматической активизации внедрились породы гранитно-метаморфического слоя коры, в которых образовались рудные столбы с золотом, ртутью, ураганным серебром, сопутствующими месторождениями  олова в породах фундамента. Обосновано выделение олово-золото-серебряных рудных районов вулканогенов пояса. Простирание пояса в пределы и Чукотки дает основание определить Северо-Западно-Корякскую металлогеническую зону. We managed to reveal the North-Western-Koryak orogenic volcanic belt. Using the authors'methodology of block and key structure of lithosphere at the boundary of the regional downfold and the northern active margin of the continent we defined the mechanism of the belt volcanogenes formation. The local regional downfolds were formed at the intersection of the transverse intra-block deep faults of regional downfold lithospheric boundary and the Koryak microcontinent's northern margin. During Oligocene tectonic-magmatic activity rocks from the crustal granitic-metamorphic layer with ore columns of gold, mercury, hurricane silver, associated with Sn deposits in basement rocks were introduced in them. The allocation of the tin-gold-silver ore regions in volcanogenic belts is proved. The trend of the belt within the margins and Chukotka gives the basis to determine the North-West Koryak metallogenic zone.

The Hudesheng mafic–ultramafic intrusions in the Oulongbuluke Block, Qinghai Province, NW China: chronology, geochemistry, isotopic systematics and tectonic implications

2018 ◽  
Vol 156 (9) ◽  
pp. 1527-1546 ◽  
Author(s):  
Haoran Li ◽  
Fengyue Sun ◽  
Liang Li ◽  
Jiaming Yan
Keyword(s):  
Crustal Contamination ◽  
Geochemical Data ◽  
Trace Element Geochemistry ◽  
Field Observations ◽  
Element Geochemistry ◽  
Qinghai Province ◽  
Nw China ◽  
The North ◽  
Depleted Mantle ◽  
Regional Tectonic

AbstractThe Hudesheng mafic–ultramafic intrusions are located in the Oulongbuluke Block, north of the Qaidam Block in Qinghai Province, NW China. We carried out a detailed study of the intrusions, including field observations, petrology, zircon U–Pb geochronology, Lu–Hf isotopes, bulk-rock major- and trace-element geochemistry, and mineral compositions, to provide a better understanding of their properties and the regional tectonic evolution. Zircon U–Pb dating on gabbro and pyroxenite samples yielded ages of 465 and 455 Ma, respectively. Geochemical data, in conjunction with the field observations and petrological features, suggest that the complex is Alaskan-type and the magma was derived from a depleted mantle source that was hydrous picritic basalt in composition and influenced by crustal contamination and slab-derived fluid metasomatism. Based on all the chronological, petrological, mineralogical and geochemical and regional geological data, we conclude that the palaeo-ocean closed diachronously from west to east between the Qaidam and Oulongbuluke blocks, and that the ocean in the east of the North Qaidam region closed after ∼455 Ma.

The Mugford Group Volcanics of Labrador: Age, Geochemistry, and Tectonic Setting

1975 ◽  
Vol 12 (7) ◽  
pp. 1196-1208 ◽  
Author(s):  
Jackson M. Barton Jr.
Keyword(s):  
Tectonic Setting ◽  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
Phosphorus Fractionation ◽  
Flood Basalts ◽  
Continental Flood Basalts ◽  
The North ◽  
Isotopic Analyses ◽  
Igneous Activity ◽  
North Atlantic Craton

The Mugford Group is a sequence of volcanic and sedimentary rocks exposed within the Khaumayät (Kaumajet) Mountains of Labrador. Separated from an intensely deformed and deeply eroded Archean basement complex by an angular unconformity, these rocks are nearly everywhere flat-lying and only locally altered. The volcanic rocks within the Mugford Group are of three types: tholeiitic basalts, komatiitic basalts and greenstones. A phosphorus fractionation diagram indicates that the tholeiitic and komatiitic basalts may be differentiates of a common magma. The greenstones, however, have undergone a separate crystallization history, but plot within the field of tholeiitic basalts on a FMA diagram, suggesting they were originally tholeiites. K–Ar whole-rock ages show that the Mugford volcanics are at least 1490 m.y. old. Rb–Sr whole-rock isotopic analyses of the tholeiitic and komatiitic basalts and the greenstones define an isochron of 2369 ± 55 m.y. with an initial 87Sr/86Sr ratio of 0.7033 ± 0.0002. This age is interpreted as approximating the time of extrusion of the Mugford volcanics. The low initial 87Sr/86Sr ratio indicates that the magmas giving rise to these rocks were not appreciably contaminated with older crustal material.The Mugford volcanics are presently the oldest recognized continental flood basalts. Their extrusion apparently occurred contemporaneously with the intrusion of the Okhakh granite at Okhakh (Okak) Harbour, 25 km to the south. This suggests that while no regional metamorphism accompanied extrusion of these volcanics, some local igneous activity did occur at that time. The Mugford volcanics may represent the extrusive equivalents of numerous basic dikes that were intruded during the final stages of stabilization of the North Atlantic craton.

Geochemistry of the Panjal Traps basalts (NW Himalaya): records of the Pangea Permian break-up

2008 ◽  
Vol 179 (4) ◽  
pp. 383-395 ◽  
Author(s):  
François Chauvet ◽  
Henriette Lapierre ◽  
Delphine Bosch ◽  
Stéphane Guillot ◽  
Georges Mascle ◽  
...  
Keyword(s):  
Isotopic Signature ◽  
Middle Permian ◽  
Flood Basalts ◽  
Nw Himalaya ◽  
Continental Flood Basalts ◽  
Enriched Mantle ◽  
Isotopic Analyses ◽  
Compositional Variations ◽  
Geochemical Constraints ◽  
Arabian Platform

AbstractThe late Lower to Middle Permian Panjal Traps (NW Himalaya, India-Pakistan) represent the greatest magmatic province erupted on the northern Indian platform during the Neotethys opening. New geochemical and isotopic analyses were performed on basalts from the eastern borders of the traps (SE Zanskar-NW Spiti area) in order to characterize this volcanism, to discuss its compositional variations in comparison to Panjal counterparts and its relationships with the opening of Neotethys. Lavas show features of tholeiitic low-Ti (< 1.6%) continental flood basalts with LREE, Th enrichments and Nb-Ta negative anomalies. Trace element ratios combined with εNdi values (−3.6 to +0.9) and high Pb isotopic ratios suggest that these tholeiitic basalts were derived from an OIB-like mantle contaminated at various degrees by a continental crust component. Previous geochemical features are broadly similar to those of the coeval Panjal volcanic sequences identified westwards (Ladakh, Kashmir and Pakistan). Present geochemical constraints obtained for the Panjal Traps basalts suggest they originated from rapid effusion of tholeiitic melts during opening of the Neotethys Ocean. Similar magmatism implying an OIB-type reservoir is contemporaneously recognized on and along the adjacent Arabian platform. Both Indian and Arabian Permian volcanics were emplaced during coeval syn-rift to post rift transition. These Lower to Middle Permian south Neotethyan continental flood magmatism are regarded as associated to a passive rifting. In this scheme, OIB-type isotopic signature would be related either to a melting episode of syn-rift up-welling mantle plumes or to a melting of a regional abnormally hot and enriched mantle.

scholarly journals A Comparison of Major and Trace Element Compositions of Chromites from the Stillwater, Bushveld and Great Dyke Layered Intrusions with Chromites from Komatiites, Boninites and Large Igneous Provinces.

2020 ◽  
Author(s):  
Sarah-Jane Barnes ◽  
Eduardo Mansur ◽  
Philippe Pagé ◽  
Julien Meric ◽  
Jean-Philippe Arguin
Keyword(s):  
Minor Element ◽  
Major And Trace Elements ◽  
Layered Intrusions ◽  
Flood Basalts ◽  
Continental Flood Basalts ◽  
Great Dyke ◽  
Minor Elements ◽  
The North ◽  
Igneous Provinces ◽  
Icp Ms

<p>The composition of the magmas from which the chromites that form the massive chromite layers of the Stillwater, Great Dyke and Bushveld Complexes are of interest both to understand the economic importance of the resources in the layers (Cr and PGE), but also in understanding how these layers form.  Magmas that have been suggested as parental to the intrusions are boninites or crustally contaminated komatiites.  Another magma that could be considered in recognition of the continental setting of the Bushveld and Great Dyke is picrite associated with continental flood basalts. In order to investigate whether any of these magmas are suitable parental magmas for the chromites we have determined major and trace elements in komatiites of low metamorphic grade, boninites and chromites from low-Ti and high-Ti picrites of the Emeishan Provence.</p><p>In order to test whether the chromites are in equilibrium with volcanic magmas we first modelled the major and minor element composition of the chromites that should have crystallized from the komatiite, boninites and picrite liquids using SpinMelt v2.  The compositions are approximately correct.  In terms of major and minor elements none of the chromites from the layered intrusions match boninite chromites.  The Great Dyke chromites are similar to chromites from komatiites.  The chromites the Bushveld are slightly more evolved with higher Ti contents and lower Cr# and resemble the chromites from the low-Ti picrites of Emeishan.  The Stillwater chromites have similar Ti contents to the Emeishan low-Ti picrites, but have lower Cr#.  Their compositions resemble chromite compositions reported from the North Atlantic Igneous Provence.</p><p>Hafnium, Ta, Cu, Sn, Sc, Ti, Mn, Ni, Co, Mn, Ga, V and Zn were determined by LA-ICP-MS.  To compare the composition of the chromites an estimate of their partition coefficients into chromite was made based on the concentrations of elements in komatiite chromite divided by element in komatiite.  The elements were then arranged in order of compatibility and the chromites normalized to the median komatiite chromite.  Podiform chromites from boninites are depleted in most elements and none of the layered intrusions chromites resemble them.  The chromites from the Great Dyke have essentially flat patterns close to 1 times komatiite, but with negative Cu anomaly and a slight positive Sn anomaly.  The Bushveld and Stillwater chromites are richer in Al, Ga, V and Ti than the komatiite chromite and are depleted in Cu.  The patterns resemble the chromites form the low Ti-picrites form Sn to Zn, but differ from picrites from Hf to Cu.  The picrites are enriched in Hf, Ta and Cu.</p><p>The chromite compositions suggest that boninite magmas are not involved in forming the chromites from layered intrusions.  The Great Dyke chromites appear to have a komatiitic affinity.  The Bushveld and Stillwater chromites appear to have a low-Ti picrite affinity.</p>

scholarly journals Lead isotope constraints on the mantle sources involved in the genesis of Mesozoic high-Ti tholeiite dykes (Urubici type) from the São Francisco Craton (Southern Espinhaço, Brazil)

2016 ◽  
Vol 46 (suppl 1) ◽  
pp. 105-122 ◽  
Author(s):  
Leila Soares Marques ◽  
Eduardo Reis Viana Rocha-Júnior ◽  
Marly Babinski ◽  
Karine Zuccolan Carvas ◽  
Liliane Aparecida Petronilho ◽  
...  
Keyword(s):  
Mantle Source ◽  
Crustal Contamination ◽  
Experimental Tests ◽  
Pb Isotope ◽  
Flood Basalts ◽  
Nd Isotope ◽  
Continental Flood Basalts ◽  
Rock Fragments ◽  
Mantle Sources ◽  
First Results

ABSTRACT: The first results of Pb isotope compositions of the high-Ti Mesozoic dykes of the Southern Espinhaço are presented. The results do not show large variations and are significantly more radiogenic than the Pb isotope compositions of the high-Ti tholeiites from the Paraná Continental Flood Basalts. The data combined with published geochemical and Sr-Nd isotope results rule out crustal contamination processes in the genesis of the dykes, requiring magma generation in metasomatized subcontinental lithospheric mantle with the involvement of HIMU-type and carbonatite components. The magmas may have been also derived from a mantle source containing ~4 - 5% of pyroxenite and ~1% of carbonatite melts, agreeing with published Os isotope compositions of high-Ti rocks from the Paraná Continental Flood Basalts. These metasomatizing agents could be responsible for mantle source refertilization, as was also proposed in the literature to explain the characteristics of xenoliths of the Goiás Alkaline Province, which also occurs in the border of the São Francisco Craton. Additionally, to evaluate the risks of Pb contamination during sample preparation for analysis, several experimental tests were accomplished, which indicate the need of sawed surface removal and a careful washing of small-sized rock fragments before powdering, especially for rocks with [Pb] < 7 µg/g.

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