GEOCHEMISTRY OF MIGMATITES AND DIKES FROM THE CENTRAL BLUE RIDGE PROVINCE: CONSTRAINTS ON PARTIAL MELTING IN THE CRUST
Bulk rock chemical analysis shows that the leucosomes, whether stromatic metatexites or dikes, classify mainly as peraluminous diorites to monzonites, and have similar trace and RE element compositions. Almost all stromatic metatexites and leucocratic dikes are more enriched in LREE and show a positive Eu anomaly compared to corresponding melanosomes. Isocon diagrams for related leucosome/melanosome pairs show that Na, Ca, Sr ± Si are always preferentially incorporated in the melt, whereas Ti, Mg, Fe, Mn, and Y are retained by the pelitic melanosome. Leucosomes with semipelitic/ Hb – bearing melanosomes concentrate Na, Ba, Sr, and Si relative to the melanosome. Zr saturation temperatures for stromatic leucosomes and dikes are similar within error (790 ± 50°C), and slightly lower than peak temperatures (850 ± 30°C at 9 ± 1 kbar) calculated for WSG1,2. These results suggest that the stromatic metatexites and dikes developed by peritectic melting at similar conditions. Whereas stromatic leucosomes formed by partial melting of pelitic and Hb-bearing semipelitic rocks, the dikes most likely represent melt extracted from pelitic rocks from the deeper parts of the section. On the other hand, the quartzofeldspathic gneisses do not appear to have produced significant melt.
1 El-Shazly et al. (2011). JMG 29, 753 – 780.
2 Moecher et al. (2004). J. Geol., 112, 289 – 304.