Autori: Zeng, L., Saleeby, J.,, and Ducea, M.N.

Editorial: Contributions to Mineralogy and Petrology, 150 (4), p.386-402, 2005.

Rezumat:

We provide data on the geochemical and isotopic consequences of non- modal partial
melting of a thick Jurassic pelite unit at mid-crustal levels which produced a migmatite
complex in conjunction with the intrusion of part of the southern Sierra Nevada Batholith
at ca. 100 Ma. Field relations suggest that this pelitic migmatite formed and then abruptly
solidified prior to substantial mobilization and escape of its melt products. Hence this
area yields insights into potential mid-crustal level contributions of crustal components
into Cordilleran-type batholiths. Major and trace element analysis in addition to field and
petrographic data demonstrate that leucosomes are products from partial melting of the
pelitic protolith host. Compared with the metapelites, leucosomes have higher Sr and
lower Sm concentrations and lower Rb/Sr ratios. The initial 87Sr/86Sr ratios of leucosomes
range from 0.7124 to 0.7247, and are similar to those of the metapelite protoliths (0.7125
to 0.7221). However, the leucosomes have a much wider range of initial eNd values which
range from -6.0 to -11.0, as compared to -8.7 to -11.3 for the metapelites. Sr and Nd
isotopic compositions of the leucosomes, migmatites and metapelites suggest a
disequilibrium partial melting of the metapelite protolith. Based on their Sr, Nd and other
trace element characteristics, two groups of leucosomes have been identified. Group A
leucosomes show distinct positive Eu anomalies, relatively high Rb, Pb, Ba and K2O
contents, and low Rb/Sr ratios (0.15

Cuvinte cheie: partial melting, granitoids, arcs