What Makes The Ree Spike For Plagioclase Positive

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Lecture 38 - SOEST

The positive Eu spike for plagioclase results from Eu+2 +2for Ca substitution in crystal lattices. Rocks that have accumulate plagioclase or have had plagioclase removed show positive or negative Eu anomalies (peaks or troughs in REE patterns), respectively. Mathematically, the Eu anomaly (Eu*) is: Eu* = Eu meas /Eu expected = Eu meas


the presence of a minor REE-rich phase. The bulk rock and mineral compositions show depletion in LREE with an increasing slope from LREE to MREE and a near flat pattern from the MREE to HREE. A positive Eu anomaly is observed in plagioclase, whereas oli-vine, pyroxene and bulk rock have small negative Eu anomalies. Figure 1.

Geochemistry of the Lanthanide Elements

Figure 7. Chondrite-normalized REE patterns of low-pressure (blue) and high-pressure (green) garnets. The Gd/Dy ratio may be used as a geobarometer (Bea et al., 1997). The feldspars are enriched in the lightest REE and Sr, thus showing a marked de-crease from La onwards and a strong Eu positive anomaly (Fig. 6). The HREE are