Eu anomaly- reliability of the proxy in inferring source composition of clastic Sedimentary rocks: A case study from western Dharwar craton, Karnataka, India

2020 ◽  
Author(s):  
Anirban Mitra ◽  
Sukanta Dey
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Earth Element ◽  
Sedimentary Rocks ◽  
Dharwar Craton ◽  
Source Rocks ◽  
Granitic Rocks ◽  
Negative Anomaly ◽  
Eu Anomaly ◽  
Ree Pattern

<p>Use of trace and rare earth element concentration of terrigenous sedimentary rocks to deduce the composition of their source rocks in the hinterland is a very common and efficient practice. The results of geochemical analysis of the metaquartzarenites located at the basal part of Bababudan and Sigegudda belt, late Archean greenstone sequences of western Dharwar craton show that the sediments were most possibly supplied from Paleo to Mesoarchean granitoids of western Dharwar Craton. Rare earth element patterns of these basal quartzites display fractionated REE pattern in variable degree (La<sub>N</sub>/Yb<sub>N</sub> =1.47-10.63) with moderate to highly fractionated LREE (La<sub>N</sub>/Sm<sub>N</sub>=2.67-8.93) and nearly flat to slighly elevated HREE (Gd<sub>N</sub>/ Yb<sub>N</sub>=0.62-1.29) and a significant Eu negative anomaly (avg. Eu/Eu*=0.67). In general, presence of negative Eu anomaly in clastic rocks reflect the widespread occurrence of granitic rocks in the source area, which possess negative Eu anomaly. On the other hand, mechanical enrichment of zircon (having negative Eu anomaly, high HREE concentration and low La<sub>N</sub>/Yb<sub>N</sub>), if present, will hamper the whole REE pattern of the sediments and necessarily, do not actually mimic the source composition. Here, in our study, the Th/Sc vs Zr/Sc diagram show mineral Zircon has been concentrated by mechanical concentration in the sedimentary rocks. Few quartzite samples which have high Zr content typically exhibit low La<sub>N</sub>/Yb<sub>N</sub> values, reflecting pivotal role of mineral zircon in controlling the REE pattern of the sediments. Hence, in this case, we should be cautious in interpreting of the Eu negative anomaly of the basal quartzites for meticulously identifying their source rock composition. More geochemical and other analytical approaches are required in this regard.</p>

Geology and geochemistry of Huronian rhyolites and low-Ti continental tholeiites from the Thessalon region, central Ontario

1987 ◽  
Vol 24 (7) ◽  
pp. 1360-1385 ◽  
Author(s):  
Wayne T. Jolly
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Earth Element ◽  
Magma Mixing ◽  
Mantle Metasomatism ◽  
Granitic Rocks ◽  
Heavy Rare Earth Element ◽  
Tonalitic Gneiss ◽  
Oceanic Basalts ◽  
Low K

Bimodal volcanism associated with early phases of Huronian rifting in central Ontario, dated about 2450 Ma, produced low-Ti tholeiitic basalts and two varieties of crustally derived calc-alkaline rhyolite. Early tholeiites are characteristically highly evolved, have Mg* values from 30 to 50, and display pronounced enrichment in large-ion lithophile elements (LILE) and light rare-earth element (LREE) in comparison with modern oceanic basalts, fractionated heavy rare-earth element (HREE) patterns, and low Ti, Zr, P, Nb, Ba, and K abundances. Ti/Zr ratios rise progressively in early basalts and associated basaltic andesite fractionates from about 35 in early flows to 55 in central units. Late basalts also carry enriched LILE and LREE, but, in contrast to early types, have average Mg* values greater than 50 and lower rare-earth element (REE) abundances with flat HREE patterns. They also display negative Ba, Nb, and P anomalies on chondrite-normalized distribution diagrams, but lack low K, Zr, and Ti contents. Their Ti/Zr ratios of about 80 approach chondritic levels. Melting models suggest the differences are explained by lower degrees of fusion (as low as 10%) in a hydrated, LILE- and LREE-enriched peridotite during generation of the early basalts, leaving a residue containing appreciable garnet, amphibole, Ti oxides, zircon, and apatite.Erupted simultaneously with the basalts were two distinctive rhyolite types: (1) a low-LILE, high-LREE group (25% of analysed specimens), derived by −20% melting of granulitic siliceous tonalitic gneiss, presumably at deep crustal levels, and (2) a high-LILE, low-LREE group (75%), derived, probably at shallower levels, by ≤ 30% melting in granitic rocks with pegmatitic or leucogranitic compositions. Mutual magma mixing of basalts and rhyolites during early stages of volcanism produced abundant hybrid andesites, but the frequency of contamination is much lower in later units.Hypothetical subcontinental source compositions, calculated from the Raleigh equation, suggest that the Huronian mantle had already undergone a complex history. Low Ba, Nb, P, Ti, and depleted HREE abundances compared with abundances for modern oceanic basalts suggest that a basaltic melt had already been withdrawn from this source during Archean time. Subsequently, an episode of hydrous metasomatism enriched the source in LILE and LREE. The latter event resulted from (1) subcontinental mantle metasomatism by previous Archean subduction, (2) mantle metasomatism during the terminal Archean Kenoran Orogeny, or (3) a wave of hydrous metasomatism accompanying Huronian mantle convection immediately preceding volcanism.

Rare earth element patterns of carbonado and yakutite: evidence for their crustal origin

1993 ◽  
Vol 57 (389) ◽  
pp. 607-611 ◽  
Author(s):  
Ken Shibata ◽  
Hikari Kamioka ◽  
Felix V. Kaminsky ◽  
Vassili I. Koptil ◽  
Darcy P. Svisero
Keyword(s):  
Trace Elements ◽  
Rare Earth ◽  
Neutron Activation ◽  
Rare Earth Element ◽  
Earth Element ◽  
Meteorite Impact ◽  
Abundance Patterns ◽  
Eu Anomaly ◽  
Crustal Origin ◽  
Monocrystalline Diamond

AbstractCarbonado and yakutite are both porous aggregates of polycrystalline micrometre-size diamond, with very different characters from those of monocrystalline diamond. The genesis of carbonado is very controversial, whereas yakutite is thought to have been formed by meteorite impact. Neutron activation analyses of trace elements in carbonado and yakutite indicate that their rare earth element (REE) abundance patterns have common characteristics: heavy REEs are not much depleted and a negative Eu anomaly is observed. These patterns are quite different from those of kimberlite and monocrystalline diamond and are similar to those of crustal materials such as shale, supporting the hypothesis of a crustal origin for carbonado and yakutite.

Petrological, geochronological, and geochemical potential accounting for continental subduction and exhumation: A case study of felsic granulites from South Altyn Tagh, northwestern China

2020 ◽  
Vol 132 (11-12) ◽  
pp. 2611-2630
Author(s):  
Yunshuai Li ◽  
Jianxin Zhang ◽  
Shengyao Yu ◽  
Yanguang Li ◽  
Hu Guo ◽  
...  
Keyword(s):  
High Pressure ◽  
Rare Earth ◽  
Rare Earth Element ◽  
Earth Element ◽  
Granitic Rocks ◽  
Geodynamic Evolution ◽  
Altyn Tagh ◽  
Rare Earth Element Distribution ◽  
Ultrahigh Temperature

Abstract Deciphering the formation and geodynamic evolution of high-pressure (HP) granulites in a collisional orogeny can provide crucial constraints on the geodynamic evolution of subduction-exhumation. To fully exploit the geodynamic potential of metamorphic rocks, it is necessary to constrain the metamorphic ages, although it is difficult to link zircon and monazite ages to metamorphic evolution. A good case study for understanding these geodynamic processes is felsic granulites in the Bashiwake area, South Altyn Tagh. Petrographic observations suggest that the studied felsic granulites have suffered multi-stage metamorphism, and the distinct metamorphic events were documented by compositional zoning and high Y + heavy rare earth element (HREE) concentrations in the large garnet porphyroblast. Zircon U-Pb dating yielded two major age clusters: one age cluster at ca. 900 Ma represents the age of the protolith for the felsic granulite, and another age cluster at ca. 500 Ma represents the post-UHT (ultrahigh temperature) stage based on the rare earth element distribution coefficients between zircon and garnet. Meanwhile, in situ monazites U-Pb dating yielded a weighted mean 206Pb/238U age of 482 ± 3.5 Ma, and the monazite U-Pb age was interpreted to be in agreement with the metamorphic zircon rims data, which together with zircon recorded the cooling time after the UHT stage. Whole-rock major and trace elements as well as Sr-Nd isotopes suggest that the protolith of the felsic granulite derived from partial melting of ancient crustal materials with the addition of mantle materials. Integrating these results along with previous studies, we propose that the felsic granulites metamorphosed from the Neoproterozoic granitic rocks, and the granitic rocks with associated mafic-ultramafic rocks suffered a common high-pressure–ultrahigh temperature (HP-UHT) metamorphism and subsequent granulite-facies metamorphism. A tentative model of subduction-relamination was proposed for the geodynamic evolution of the Bashiwake unit, South Altyn Tagh.

Rare earth element geochemistry of petroleum source rocks from northwestern Niger Delta

2016 ◽  
Vol 77 ◽  
pp. 409-417 ◽  
Author(s):  
A. Akinlua ◽  
F.S. Olise ◽  
A.O. Akomolafe ◽  
R.I. McCrindle
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Niger Delta ◽  
Earth Element ◽  
Source Rocks ◽  
Element Geochemistry

scholarly journals SHRIMP U–Pb and REE data pertaining to the origins of xenotime in Belt Supergroup rocks: evidence for ages of deposition, hydrothermal alteration, and metamorphism

2015 ◽  
Vol 52 (9) ◽  
pp. 722-745 ◽  
Author(s):  
John N. Aleinikoff ◽  
Karen Lund ◽  
C. Mark Fanning
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Detrital Zircon ◽  
Earth Element ◽  
Greenschist Facies ◽  
Eastern United States ◽  
Burial Diagenesis ◽  
Heavy Rare Earth Element ◽  
Eu Anomaly ◽  
Belt Supergroup

The Belt–Purcell Supergroup, northern Idaho, western Montana, and southern British Columbia, is a thick succession of Mesoproterozoic sedimentary rocks with an age range of about 1470–1400 Ma. Stratigraphic layers within several sedimentary units were sampled to apply the new technique of U–Pb dating of xenotime that sometimes forms as rims on detrital zircon during burial diagenesis; xenotime also can form epitaxial overgrowths on zircon during hydrothermal and metamorphic events. Belt Supergroup units sampled are the Prichard and Revett Formations in the lower Belt, and the McNamara and Garnet Range Formations and Pilcher Quartzite in the upper Belt. Additionally, all samples that yielded xenotime were also processed for detrital zircon to provide maximum age constraints for the time of deposition and information about provenances; the sample of Prichard Formation yielded monazite that was also analyzed. Ten xenotime overgrowths from the Prichard Formation yielded a U–Pb age of 1458 ± 4 Ma. However, because scanning electron microscope – backscattered electrons (SEM–BSE) imagery suggests complications due to possible analysis of multiple age zones, we prefer a slightly older age of 1462 ± 6 Ma derived from the three oldest samples, within error of a previous U–Pb zircon age on the syn-sedimentary Plains sill. We interpret the Prichard xenotime as diagenetic in origin. Monazite from the Prichard Formation, originally thought to be detrital, yielded Cretaceous metamorphic ages. Xenotime from the McNamara and Garnet Range Formations and Pilcher Quartzite formed at about 1160–1050 Ma, several hundred million years after deposition, and probably also experienced Early Cretaceous growth. These xenotime overgrowths are interpreted as metamorphic–diagenetic in origin (i.e., derived during greenschist facies metamorphism elsewhere in the basin, but deposited in sub-greenschist facies rocks). Several xenotime grains are older detrital grains of igneous derivation. A previous study on the Revett Formation at the Spar Lake Ag–Cu deposit provides data for xenotime overgrowths in several ore zones formed by hydrothermal processes; herein, those results are compared with data from newly analyzed diagenetic, metamorphic, and magmatic xenotime overgrowths. The origin of a xenotime overgrowth is reflected in its rare-earth element (REE) pattern. Detrital (i.e., igneous) xenotime has a large negative Eu anomaly and is heavy rare-earth element (HREE)-enriched (similar to REE in igneous zircon). Diagenetic xenotime has a small negative Eu anomaly and flat HREE (Tb to Lu). Hydrothermal xenotime is depleted in light rare-earth element (LREE), has a small negative Eu anomaly, and decreasing HREE. Metamorphic xenotime is very LREE-depleted, has a very small negative Eu anomaly, and is strongly depleted in HREE (from Gd to Lu). Because these characteristics seem to be process related, they may be useful for interpretation of xenotime of unknown origin. The occurrence of 1.16–1.05 Ga metamorphic xenotime, in the apparent absence of pervasive deformation structures, suggests that the heating may be related to poorly understood regional heating due to broad regional underplating of mafic magma. These results may be additional evidence (together with published ages from metamorphic titanite, zircon, monazite, and garnet) for an enigmatic, Grenville-age metamorphic event that is more widely recognized in the southwestern and eastern United States.

scholarly journals Geochemistry of Recent Brahmaputra River Sediments: Provenance, Tectonics, Source Area Weathering and Depositional Environment

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 813
Author(s):  
Md Aminur Rahman ◽  
Sudeb Chandra Das ◽  
Mark I. Pownceby ◽  
James Tardio ◽  
Md Sha Alam ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Chemical Weathering ◽  
Earth Element ◽  
Tectonic Setting ◽  
River Sediments ◽  
Source Area ◽  
Source Rocks ◽  
Heavy Minerals ◽  
Brahmaputra River

Sediments from stable sand bars along a 40 km section of the Brahmaputra River in northern Bangladesh were analyzed for their major, trace and rare earth element contents to determine their provenance, compositional maturity, source area weathering and tectonic setting. Geochemically, the sediments were classified as litharenites and the Index of Compositional Variability (ICV) varied between 1.4 and 2.0, indicating low compositional and mineralogical maturity. A high mean SiO2 concentration (72.9 wt.%) and low Al2O3 (11.1 wt.%) were consistent with a low abundance of shale and clay components. The depletion of the oxide components Na2O, CaO and K2O relative to average upper crustal compositions (UCC) reflected loss of feldspar during chemical weathering in the source region. Average TiO2 values for most samples were higher than average crustal levels, consistent with the northern section of the Brahmaputra River being a potential resource for valuable Fe-Ti oxide heavy minerals. Major and trace element ratios indicated the sediments represented erosional products from typical felsic upper continental crustal materials with contamination (30%–40%) from more intermediate/mafic compositions. The rare earth element patterns showed negative Eu anomalies (0.57–0.71), indicating they were derived mainly from fractionated felsic rocks. Resemblance of the sediment compositions to mean compositions from Higher Himalaya crystalline rocks pointed to these being potential source rocks but with components from a mafic source also present. Major element chemistries and low to intermediate weathering indices for all sediments indicated a lack of substantial chemical weathering. Evidence from tectonic discrimination diagrams suggested the Brahmaputra River sediments were derived from rock types that formed in a transitional tectonic setting ranging from an ancient passive margin to an active continental margin. Deposition occurred under cool to semi-arid climatic conditions in an oxic environment.

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