Other
Scientific paper
Jan 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53...97s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 53, Issue 1, pp.97-113
Other
26
Scientific paper
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 87 Sr / 86 Sr and high 143 Nd / 144 Nd samples contain the largest amount of a basaltic component ( e.g. , CaO and Al 2 O 3 ), 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 2 O 3 , and La / Sm ; and, (b) samples most depleted in CaO and Al 2 O 3 have the highest 87 Sr / 86 Sr and lowest 143 Nd / 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.
Frey Frederick A.
Song Yan
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