Stratigraphic section of the metasedimentary rocks of the Winchester-Hemet area: Supplement 3 from "I. Geology of the Winchester-Hemet area, Riverside County, California. II. Geochemical investigations of an arkosic quartzite of the Winchester-Hemet area, California" (Thesis)

I. An area of about 100 square miles located 20 miles southeast of Riverside, California, has been geologically mapped. The oldest rocks of the area are phyllites and quartzites correlated with the Bedford Canyon formation (Triassic). Conformably overlying these rocks is a 13,000 foot thick section of quartzite, schist and rare amphibolite, here named the French Valley formation. The metasedimentary rocks were formed from a series of shales, shale-clast conglomerates, poorly sorted feldspathic, calcareous and arkosic sandstones and rare basalt flows or tuffs. Relict sedimentary structures and textures are locally well preserved. The sedimentary rocks were intruded with a series of basic and ultrabasic magmas and were tightly folded prior to late Cretaceous time. Late in the period of folding they were metamorphosed to the hornblende-hornfels facies (200°-600°C, 3-5 kilobars), producing andalusite, cordierite, sillimanite and garnet in the schists and hornblende-plagioclase (-diopside, -garnet) assemblages in the amphibolites. Zones of progressive metamorphism are mapped trending N-S and cutting the NW-SE structural trend of the folded rocks. In the late Cretaceous these rocks were intruded by basic to intermediate plutonic igneous rocks of the southern California batholith, with no appreciable contact metamorphism. II: A series of seven samples of arkosic quartzite from a single homogeneous member of the French Valley formation has been collected along a profile of increasing metamorphic rank. The component minerals and aliquots of the total rocks have been analysed by X-ray fluorescence, emission spectrographic and wet chemical procedures. For most elements studied, concentrations in the total rock, biotite and ilmenite appear to be constant through the series. These elements either did not vary beyond the experimental uncertainty or they varied without apparent trend over a small range slightly exceeding the uncertainty. With increasing degree of metamorphism the following changes were suggested but fell within or only slightly exceeded the assigned limits of error: a) the total rock gained CaO, Mn, Sr, Co, La, Y, and Ti(?) and lost K2O, Na2O, and V; b) the biotite gained Mn, Ti, Ba, and possibly Co, Cr, V, and La and lost CaO; c) ilmenite gained Mn and Ni and lost Cr, Ba, Zr(?), Y, and Pb. Other changes observed with increasing metamorphic rank were: a) coarsening and homogenization of the rock texture; b) decrease in the ratio Fe+++/Fe++ in both rock and biotite; c) decrease in 2V and basal spacing of the biotite; and d) variations in albite content of plagioclase and potash feldspar that suggest loss of Na2O from rock. For most elements fractionations between biotite and rock appear to vary directly with the concentration in biotite. Fractionations between ilmenite and biotite are shown to be related to ionic size and charge. The composition of the rock is such that partial fusion would yield a liquid with a composition close to that of the total rock. This may be the cause of the small variations in major element composition with metamorphic grade