We provide data on the geochemical and iso- topic consequences of nonmodal partial melting of a thick Jurassic pelite unit at mid-crustal levels that pro- duced a migmatite complex in conjunction with the intrusion of part of the southern Sierra Nevada batho- lith 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 Cordil- leran-type batholiths. Major and trace-element analyses in addition to field and petrographic data demonstrate that leucosomes are products of 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 87 Sr/ 86 Sr ratios of leucosomes range from 0.7124 to 0.7247, similar to those of the metapelite protoliths (0.7125-0.7221). 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 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 have rela- tively high Rb, Pb, Ba, and K2O contents, Rb/Sr ratios (0.15<Rb/Sr<1.0), and initial eNd values . Group B leucosomes have relatively low Rb, Pb, Ba, and K2O contents, Rb/Sr ratios (<0.15), and initial eNd values. The low Rb concentrations and Rb/Sr ratios of the group B leucosomes together suggest that partial melting was dominated by water-saturated or H2O-fluxed melt- ing of quartz + feldspar assemblage with minor involvement of muscovite. Breakdown of quartz and plagioclase with minor contributions from muscovite resulted in low Rb/Sr ratios characterizing both group A and group B leucosomes. In contrast, group A leuco- somes have greater contributions from K-feldspar, which is suggested by: (1) their relatively high K con- centrations, (2) positive or slightly negative Eu anoma- lies, and (3) correlation of their Pb and Ba concentrations with K2O contents. It is also shown that accessory minerals have played a critical role in regu- lating the partitioning of key trace elements such as Sm, Nd, Nb, and V between melt products and residues during migmatization. The various degrees of parent/ daughter fractionations in the Rb-Sr and Sm-Nd iso- topic systems as a consequence of nonmodal crustal anatexis would render melt products with distinct iso- topic signatures, which could profoundly influence the products of subsequent mixing events. This is not only important for geochemical patterns of intracrustal dif- ferentiation, but also a potentially important process in generating crustal-scale as well as individual pluton- scale isotopic heterogeneities.