Geochemistry of peridotite xenoliths in basalt from Hannuoba, eastern China: Implications for subcontinental mantle heterogeneity

Journal Article · Sun Jan 01 00:00:00 EST 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90276-7· OSTI ID:7243013

Song, Yan; Frey, F A ^[1]

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1. Massachusetts Institute of Technology, Cambridge (USA)

Based on geochemical studies of six anhydrous spinel peridotite xenoliths in basanite, the upper mantle beneath Hannuoba, eastern China is compositionally heterogeneous. These samples range in Sr and Nd isotopic ratios from MORB-like to near bulk-earth estimates. The low {sup 87}Sr/{sup 86}Sr and high {sup 143}Nd/{sup 144}Nd samples contain the largest amount of a basaltic component, but they are relatively depleted in light rare earth elements compared to chondrites. Other samples have U-shaped chondrite-normalized REE patterns. Trace element and radiogenic isotopic data require enrichment processes acting on depleted mantle. Constraints on these processes are: (a) inverse correlations between basaltic constituents, such as CaO and Al{sub 2}O{sub 3}, and La/Sm; and, (b) samples most depleted in CaO and Al{sub 2}O{sub 3} have the highest {sup 87}Sr/{sup 86}Sr and lowest {sup 143}Nd/{sup 144}Nd. These trends can be explained by a model whereby garnet peridotite zoned in isotopic composition undergoes partial melting. Because of a gradient in degree of melting, e.g., from the wall-rock contact to hotter interior, or as a function of depth in a diapir, melts initially segregate from regions where the degree of melting is high. Subsequently, the recently created residues are infiltrated by slower segregating incipient melts. Preferential mixing of these incipient melts with residues from high degrees of melting can explain the observed complex geochemical trends seen in Hannuoba and many other peridotite xenolith suites. Clinopyroxene-rich veins in some of the peridotites may reflect pathways of ascending melt.

• OSTI ID: 7243013
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 53:1; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
BASALT
PERIDOTITES
PETROGENESIS
PETROGRAPHY
CHINA
QUANTITATIVE CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHONDRITES
EARTH MANTLE
GEOCHEMISTRY
GEOLOGIC HISTORY
GEOLOGIC MODELS
ISOTOPE RATIO
MELTING
MINERALOGY
NEODYMIUM ISOTOPES
RARE EARTHS
SPINELS
STRONTIUM ISOTOPES
TRACE AMOUNTS
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
ASIA
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMISTRY
ELEMENTS
IGNEOUS ROCKS
ISOTOPES
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
METALS
METEORITES
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
ROCKS
STONE METEORITES
VOLCANIC ROCKS
580000* - Geosciences