Trace element geochemistry of the Sokoman Iron Formation

1977 ◽  
Vol 14 (7) ◽  
pp. 1598-1610 ◽  
Author(s):  
B. J. Fryer
Keyword(s):  
Trace Element ◽  
Sea Water ◽  
Iron Formation ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Element Abundances ◽  
Rock Types ◽  
Show Evidence ◽  
Trace Element Contents ◽  
Element Contents

Rare earth and other trace element data are presented for samples of the Sokoman Iron Formation, Labrador, and its associated sediments. The results show that the slates associated with the iron formation are typical in trace element contents compared to other argillaceous sediments except for the large Eu depletion characteristic of slates of their age. The iron formation, however, is fundamentally different in its trace element concentrations and patterns from those of the associated rocks. It is relatively enriched in the heavy REE and Eu and both the REE and Co, Cr, Sc, and Th concentrations bear no relationship to those of the slates and the dolomite.Trace element analyses of the various textural and mineralogic rock types in all cases substantiate the genetic conclusions of earlier workers based on field and petrographic observations. Silicate–carbonate facies samples show constant REE, Co, Sc, and Th distributions which are compatible with an origin as crystalline precipitates in equilibrium with sea water. Riebeckite-bearing iron formation is distinctive in that it reflects contamination by ordinary clastic material and (or) metamorphic solutions. Oxide facies rocks exhibit widely variable trace element abundances as is to be expected for rocks whose original trace element contents were controlled by adsorption processes. A group of iron-enriched oxide facies rocks show evidence of important heavy REE complexing associated with the migration of iron during diagenesis. Minor Ce anomalies in all facies of Sokoman Iron Formation indicate that oxidation of Ce to the +4 state was taking place at the time of iron deposition but probably not in close proximity to it.

Magmatic and Tectonic Setting of Archean Granitoids in the Southeastern Singhbhum Craton, India: Developing constraints with major and trace element geochemistry and geochronology

2020 ◽  
Vol 22 ◽  
Author(s):  
Claudia Banks
Keyword(s):  
Trace Element ◽  
Genetic Relationships ◽  
Tectonic Setting ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Peninsular India ◽  
Singhbhum Craton ◽  
Rock Types ◽  
Granite Emplacement ◽  
Singhbhum Granite

The Singhbhum craton is one of five Archean nuclei comprising Peninsular India. It is a composite Archean block that includes the Older Metamorphic Group, the Older Metamorphic Tonalite Gneisses, the Singhbhum Granite, and the Iron Ore Group as its major units. The ages of these components range from ~3.5 to ~3.1 Ga, although overlapping ages and similar rock types confound their genetic relationships. Plutonic felsic rocks from the southeastern Singhbhum craton (BK1: a foliated tonalite, KP1: a non-foliated granite, and SG14: a non-foliated granite) yield U-Pb (zircon) ages of 3321 ± 2 Ma (BK1), 3301 ± 1 Ma (KP1), and  3261 ± 1 Ma (SG14) that coincide with a pulse of Singhbhum Granite emplacement at 3.27 to 3.33 Ga. REE patterns and tectonic discrimination diagrams based on major and trace element ratios suggest a subduction zone setting for these rocks. We report major and trace element data for and compare them to previous works in order to characterize the Archean felsic plutonic history of the craton.

scholarly journals Geomorphology and Geochemistry of Back Arc Basins in the Havre Trough, Southwest Pacific

2021 ◽  
Author(s):  
◽  
Vanisha Pullan
Keyword(s):  
Trace Element ◽  
Aqueous Fluid ◽  
Trace Element Geochemistry ◽  
Magmatic Activity ◽  
Element Geochemistry ◽  
Southwest Pacific ◽  
Digital Terrain ◽  
Show Evidence ◽  
Back Arc ◽  
Subduction System

<p>The Havre Trough back arc system located behind the Kermadec Arc, in the southwest Pacific, is a classic example of an intra-oceanic back arc system. Subduction driven magmatism is focused at the arc front, and melting in the back arc is accompanied by back arc rifting. This study examines the deep back arc basins of the southern Havre Trough. Compared to the well-studied Kermadec Arc front volcanoes, the back arc basins remain poorly explored, yet are important features in understanding key structural and geochemical dynamics of the subduction system.  The back arc is characterised by areas of deeper basins and constructional cross-arc volcanic edifices, which had previously been attributed to ‘rift regime’ and ‘arc regime’, respectively. In this study, recently acquired multibeam data was used to produce digital terrain maps that show individual basins within the Havre Trough that host a range of different morphological features, such as elongated ridges, nearly-flat basin floors, and small volcanic cones. Lavas dredged from the 10 basins were analysed, eight of which sample the rift regime and two sample the arc regime.  The back arc basin lavas are basalts to basaltic-andesites and show fractionation of olivine + pyroxene ± plagioclase mineral assemblages. Olivine phenocrysts were tested for chemical equilibrium and predominantly show that crystallisation occurred in equilibrium with host melts. However, petrographic features such as dissolution and zoning within plagioclase show evidence of multistage magmatic evolution.  Whole rock trace element geochemistry reveals trace element characteristics typical of volcanic arc lavas, such as enrichments in large ion lithophile elements (LILE) and Pb relative to high field strength elements (HFSE). From west to east, the back arc basin lavas show a decrease in NbN/YbN, consistent with trench perpendicular flow and progressive melt extraction towards the volcanic front. There is also a broad correlation between NbN/YbN and distance along the strike of the subduction zone. This may suggest a component of trench parallel flow of the mantle wedge, with increasing depletion northwards, although further evidence is needed to rule out pre-existing mantle heterogeneity.  Ba/Th values, which trace the addition of slab-derived aqueous fluids, decrease with distance from the arc front. This indicates that the aqueous fluid component becomes less prominent with increasing distance from the arc front. Conversely, the basin lavas exhibit broadly increasing LaN/SmN values with distance from the arc front. As LaN/SmN can be used to trace the deep subduction component, i.e. sediment melt contribution, greater LaN/SmN suggests increasing contribution of a sediment signature away from the arc front. The parameters that measure recycled component flux are comparable between rift and arc regimes, so it is unlikely that increased volatile fluxing leads to the larger concentrations of magmatic activity displayed in arc regimes. Gill volcano (arc regime) has similar to higher NbN/YbN than lavas from adjacent basins, suggesting increased magmatic activity may in part relate to pockets of more fertile mantle. This study shows that back arcs and associated volcanism can be complicated, further research is integral in determining mechanisms for voluminous magmatic activity spread throughout the back arc.</p>

Trace element geochemistry of parts of the Closepet granite, Mysore State, India

1972 ◽  
Vol 38 (298) ◽  
pp. 678-686 ◽  
Author(s):  
V. Divakara Rao ◽  
U. Aswathanarayana ◽  
M. N. Qureshy
Keyword(s):  
Trace Element ◽  
Emission Spectroscopy ◽  
Vapour Phase ◽  
Trace Element Geochemistry ◽  
Initial Ratio ◽  
Element Geochemistry ◽  
Granite Magma ◽  
Peninsular Gneiss ◽  
Mysore State ◽  
Trace Element Contents

SummaryTrace elements in twenty samples of the Closepet granite (grey and pink varieties) and the related rocks have been determined by neutron activation analysis (Th, Rb, and Cs), fluorometry (U), flame-photometry (K), and emission spectroscopy (Pb, Sr). The trace element contents of the grey and pink varieties are generally similar. An analysis of the magnitudes of the trace element and other ratios (K/Rb, 235; Th/U, 6·4; U/K (× 104), 0·7; K/Cs (× 10−4), 3·6; Th/K (× 104), 5·3; Fe2O3/(FeO+Fe2O3), 0·27) as well as 87Sr/86Sr initial ratio (0·705; Crawford, 1969) of the Closepet granite indicate two possible modes of genesis: Either the granite magma was not highly differentiated and the vapour phase was relatively insignificant; the crystallization of the magma took place under essentially non-oxidizing conditions; the pink variety, which followed the grey variety, crystallized under essentially the same conditions as the grey variety. Or the Closepet granite had a two-stage history—palingenesis (starting from the Peninsular gneiss) and metasomatism involving the enrichment in K, Rb, Pb, and Th and depletion of Sr and Cs, among others.

Geochemical investigations of basalts and associated rocks from the ocean floor and their implications

1971 ◽  
Vol 268 (1192) ◽  
pp. 469-486 ◽  
Keyword(s):  
Trace Element ◽  
Deep Sea ◽  
Major Element ◽  
Sea Water ◽  
Ocean Floor ◽  
Low Grade ◽  
Basaltic Magmas ◽  
Trace Element Contents ◽  
Element Contents ◽  
Possible Cause

Variations in trace element contents and inter-element ratios of deep-sea basalts are much more marked than variations in major element contents. This paper explores possible reasons for the variations which have been discovered. Inadequacy of sampling techniques may be responsible for some reported differences, but variations due to this cause are unlikely to approach the magnitude of reported variations. Some variation in samples from restricted areas of the ocean floor can be correlated with variation in the degree of silica saturation of the basalts. Submarine alteration of lavas by reaction with sea water is another possible cause of variation. Studies of metamorphosed deep-sea basalts suggest that very low-grade metamorphism may cause some, though slight, elemental migration. Studies on ultrabasic rocks show variations in trace element contents which, to some degree, appear to complement the variations encountered in basalts, suggesting that the extent of partial melting in the mantle during basaltic genesis influences the trace element contents of the products of melting. However, when such possible explanations have been considered, there remain variations in trace element contents of otherwise comparable basalts from different parts of the ocean floor, which appear to represent real variations in the trace element contents of the erupted basaltic magmas. In view of the difficulty of explaining such differences by contamination of magmas on their way to the surface, it is suggested that variations exist in the trace element contents of mantle material at the levels of basaltic genesis. Geochemical provinces exist in oceanic areas just as they do in continental regions.

scholarly journals Geomorphology and Geochemistry of Back Arc Basins in the Havre Trough, Southwest Pacific

2021 ◽  
Author(s):  
◽  
Vanisha Pullan
Keyword(s):  
Trace Element ◽  
Aqueous Fluid ◽  
Trace Element Geochemistry ◽  
Magmatic Activity ◽  
Element Geochemistry ◽  
Southwest Pacific ◽  
Digital Terrain ◽  
Show Evidence ◽  
Back Arc ◽  
Subduction System

<p>The Havre Trough back arc system located behind the Kermadec Arc, in the southwest Pacific, is a classic example of an intra-oceanic back arc system. Subduction driven magmatism is focused at the arc front, and melting in the back arc is accompanied by back arc rifting. This study examines the deep back arc basins of the southern Havre Trough. Compared to the well-studied Kermadec Arc front volcanoes, the back arc basins remain poorly explored, yet are important features in understanding key structural and geochemical dynamics of the subduction system.  The back arc is characterised by areas of deeper basins and constructional cross-arc volcanic edifices, which had previously been attributed to ‘rift regime’ and ‘arc regime’, respectively. In this study, recently acquired multibeam data was used to produce digital terrain maps that show individual basins within the Havre Trough that host a range of different morphological features, such as elongated ridges, nearly-flat basin floors, and small volcanic cones. Lavas dredged from the 10 basins were analysed, eight of which sample the rift regime and two sample the arc regime.  The back arc basin lavas are basalts to basaltic-andesites and show fractionation of olivine + pyroxene ± plagioclase mineral assemblages. Olivine phenocrysts were tested for chemical equilibrium and predominantly show that crystallisation occurred in equilibrium with host melts. However, petrographic features such as dissolution and zoning within plagioclase show evidence of multistage magmatic evolution.  Whole rock trace element geochemistry reveals trace element characteristics typical of volcanic arc lavas, such as enrichments in large ion lithophile elements (LILE) and Pb relative to high field strength elements (HFSE). From west to east, the back arc basin lavas show a decrease in NbN/YbN, consistent with trench perpendicular flow and progressive melt extraction towards the volcanic front. There is also a broad correlation between NbN/YbN and distance along the strike of the subduction zone. This may suggest a component of trench parallel flow of the mantle wedge, with increasing depletion northwards, although further evidence is needed to rule out pre-existing mantle heterogeneity.  Ba/Th values, which trace the addition of slab-derived aqueous fluids, decrease with distance from the arc front. This indicates that the aqueous fluid component becomes less prominent with increasing distance from the arc front. Conversely, the basin lavas exhibit broadly increasing LaN/SmN values with distance from the arc front. As LaN/SmN can be used to trace the deep subduction component, i.e. sediment melt contribution, greater LaN/SmN suggests increasing contribution of a sediment signature away from the arc front. The parameters that measure recycled component flux are comparable between rift and arc regimes, so it is unlikely that increased volatile fluxing leads to the larger concentrations of magmatic activity displayed in arc regimes. Gill volcano (arc regime) has similar to higher NbN/YbN than lavas from adjacent basins, suggesting increased magmatic activity may in part relate to pockets of more fertile mantle. This study shows that back arcs and associated volcanism can be complicated, further research is integral in determining mechanisms for voluminous magmatic activity spread throughout the back arc.</p>

Major and trace element geochemistry of the Neoproterozoic syn-glacial Fulu iron formation, South China

2016 ◽  
Vol 154 (6) ◽  
pp. 1371-1380 ◽  
Author(s):  
LIANJUN FENG ◽  
JING HUANG ◽  
DINGBIAO LU ◽  
QIRUI ZHANG
Keyword(s):  
High Temperature ◽  
Trace Element ◽  
South China ◽  
Major Element ◽  
Deep Ocean ◽  
Iron Formation ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Surface Ocean ◽  
Binary Mixing

AbstractThe Fulu iron formation (IF) is an iron-rich unit in the Neoproterozoic glacial successions, South China. The major element data suggest that the iron sources of the Fulu IF are derived from binary mixing from hydrothermal and detrital loads. The Fulu IF is characterized by slightly positive Eu anomalies similar to other Neoproterozoic IFs, indicating that a high-temperature hydrothermal input may contribute little to Neoproterozoic IFs. A shift from non-existent to slightly negative Ce anomalies of the Fulu IF indicates that the IF precipitated across an iron chemocline separating a weakly oxic surface ocean from an oxygen-depleted deep ocean.

Fe isotope and trace element geochemistry of the Neoproterozoic syn-glacial Rapitan iron formation

2011 ◽  
Vol 309 (1-2) ◽  
pp. 100-112 ◽  
Author(s):  
Galen P. Halverson ◽  
Franck Poitrasson ◽  
Paul F. Hoffman ◽  
Anne Nédélec ◽  
Jean-Marc Montel ◽  
...  
Keyword(s):  
Trace Element ◽  
Iron Formation ◽  
Trace Element Geochemistry ◽  
Element Geochemistry
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