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  • 1
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    An ancient depleted mantle source for Archean crust in Rajasthan, India (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Data from an initial set of Banded Gneiss Complex (BGC) east of the city of Udaipur are given. In this region the BGC comprises typical grey gneiss with variably abundant granitic and mafic components. Efforts to date were concentrated on the mafic components which, based on chemical data, appear to be metavolcanic. All samples examined were recrystallized under amphibolite or upper amphibolite facies conditions. Pertinent chemical data for a small number of amphibolites analyzed so far are: SiO2: 49-53%; MgO: 5.7-7.3%; K2O: 0.24-0.50%; Ni: 106-140 ppm; Zr: 37-159 ppm. From Sm/Nd data, all amphibolites show small to moderate LREE enrichments.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst. Workshop on a Cross Section of Archean Crust; p 55-56
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Crustal influence in the generation of continental flood basalts (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The suggestion that primordial undifferentiated material may exist in the earth's mantle has recently been revived on the strength of Nd isotope data for two types of young continental rocks - flood basalts and kimberlites. The limited published data show a clustering of Nd isotopic compositions close to those for meteorites with chondritic relative rare-earth (REE) abundance. In contrast, data are presented for samples from the Columbia flood basalt province of the northwestern United States which show large isotopic variability suggestive of mixing processes acting after the separation of the primary magmas from their mantle source.
    Keywords: GEOPHYSICS
    Type: Nature; 289; Jan. 15
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Episodic mantle differentiation - Nd and Sr isotopic evidence (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A study of Nd and Sr isotopic composition of clinopyroxenes separated from two hydrous and four anhydrous ultramafic nodules is presented. Correlation of Nd-143/Nd-144 with Sm/Nd suggests that a second partial melting occurred about 560 m.y. ago resulting in LREE enrichment of a part of the anhydrous mantle. The isotopic data for anhydrous nodules show that oceanic type mantle underlies at some continental areas. It is concluded that the separation of subcontinental mantle regions from an initially chondritic reservoir may occur in discrete episodes, and that different histories of depletion and/or enrichment will produce isotopically distinct mantle reservoirs.
    Keywords: GEOPHYSICS
    Type: Earth and Planetary Science Letters; 47; 2, Ap; Apr. 198
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Columbia River volcanism - The question of mantle heterogeneity or crustal contamination (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is found that, although crystal fractionation played an important role in producing the chemical characteristics of Columbia River Province basalts displaying a wide range of chemical and isotopic compositions, the isotopic variability calls for the involvement of at least two isotopically distinct components. The major and trace element characteristics of the main volume of the basalts are not consistent with a metasomatized mantle source region, and the presence of a primordial mantel component is not supported by the chemical data. Models of simple binary mixing between a primary magma and Precambrian sialic crustal materials, while satisfying the observed Nd and Sr isotopic variations, fail to account for major trace element abundances. The combination of crustal assimilation and fractional crystalization is found to give a superior fit to the compositional data.
    Keywords: GEOPHYSICS
    Type: Geochimica et Cosmochimica Acta; 45; Dec. 198
    Format: text
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