Description
The Morena Reservoir roof pendant is located on the western slope of the Laguna Mountains about 60 km east of San Diego. It is surrounded by the typical plutonic rocks of the Peninsular Ranges batholith. The metasediments consist of calc-silicate bearing quartzites and conglomerates, and pelitic schists and quartzites. The calc-silicate bearing rocks are non-foliated whereas the pelitic rocks are moderately to strongly foliated. Assemblages in the calc-silicate bearing rocks include quartz, plagioclase (An50 to An70), diopside, actinolitic amphibole, clinozoisite, grossularite, calcite, wollastonite, apatite, sphene, and graphite. Assemblages in the pelitic rocks include quartz, plagioclase (An28 to An40), potassium feldspar, cordierite, biotite, muscovite, sillimanite, andalusite, and graphite. The major structure of the pendant is a northwest plunging, antiformal fold. Erosion below the hinge has exposed complex folding in the axial region. A series of northwest trending faults cut both the pendant and the surrounding plutonics. Mineral parageneses in the metasediments indicate low-pressure, moderate-temperature conditions of metamorphism, approximately 2 kb and 600 to 650 degrees C. These conditions are best illustrated in the pelitic parageneses. These metamorphic conditions and the parageneses present are similar to many found in the Buchan rocks of Scotland and in the Abukuma Plateau of Japan. A plate tectonics model for the roof pendant suggests that it is miogeosynclinal in nature and that it was metamorphosed and deformed prior to the emplacement of the surrounding Peninsular Ranges batholith.
