The Val Verde tunnel of the Metropolitan Water District of Southern California, located thirteen miles south of Riverside, California, passes through 27,000 feet of a single tonalite intrusive and across the intrusive contact into a body of quartz-biotite schist.
Micrometric analyses of the tonalite along the line of the tunnel have shown no progressive variation in the percentage of minerals present; but the albite content of the plagioclase increases toward the contact with the schist, and this correlates directly with the radioactivity and zircon content of the tonalite. The more acid border of the intrusive is believed to be due to assimilation of the quartz-biotite schist.
On the basis of mineralogic and radioactivity determinations, dark fine grained inclusions in the tonalite are believed to be xenoliths of schist and gabbro.
Petrofabric diagrams obtained from the plagioclase, biotite, and quartz of the tonalite indicate that the gneiss planes of the tonalite developed as a result of a combination of now of the partially crystallized magma and post-magmatic deformation. The present linear direction in the rock may or may not represent the original direction of flow of the magma.
