Mafic enclaves within the Alpine tonalite have been observed for many years. A geochemical study was undertaken to compare different appearing enclaves found in the same outcrop and compare them to that of the host rock. The study area is approximately 30 kilometers east of San Diego, California. Enclave samples were selected based on differences in size, grain size, mafic percentage, and relative contrast to the surrounding host rock. Most of the enclaves have a bimodal distribution of mafic minerals. The mafic content varied from 28 to 30 percent. The Si02 content of the enclaves varied from 54.7 to 59.3 percent, and the Si02 content of the host rock is 61.3 percent. Some enclaves were rimmed with a mafic depleted margin in the surrounding host rock. The enclave chemistry compared with the host rock suggests that the enclaves were derived from a mafic relative of the host rock and vary by progressive interaction of that mafic rock with the magma which was the parent to the host rock.
