ND AND SR ISOTOPIC DATA FROM AN ARC-ROOT PLUTONIC SUITE AND HOST ROCKS: BEAR MOUNTAIN INTRUSIVE COMPLEX, KLAMATH MOUNTAINS, CALIFORNIA
The BMIC intruded metabasalt, meta-argillite, and metaserpentinite of the Rattlesnake Creek terrane (RCT). Metabasaltic rocks of the inner dynamothermal aureole of the BMIC experienced partial melting synchronous with emplacement of the plutonic suite. Argillitic host rocks of the RCT have initial epsilon Nd from 4.9 to 8.9 and Sr from 0.7095 to 0.7141. Slaty argillitic rocks of the structurally lower Late Jurassic Galice Formation have initial epsilon Nd values of 0.9 to 2.5 and initial Sr values of 0.7066 to 0.7071.
The uniformity of isotopic ratios of the ultramafic and mafic parts of the BMIC argues for the lack of significant contamination by host rocks and for isotopically homogeneous mantle sources. However, the higher delta 18 O of the tonalitic rocks combined with their lower initial Sr and higher epsilon Nd values suggests an origin by partial melting of metabasaltic rocks. The source for the tonalites may be the migmatitic rocks of the inner aureole but alternatively could be structurally lower metabasites of the Josephine ophiolite.