Abstract

The Sierra City mélange between Bowman Lake and East Fork Creek contains abundant feldspar-poor and feldspar-rich sandstone inclusions. A petrologic study of samples from these inclusions indicates that the average feldspar-poor sandstone is composed of 69% Q, 4% F, and 27% L. In contrast, the average feldspar-rich sandstone is composed of 34% Q, 46% F, and 20% L. On the QFL provenance-discrimination diagram of Dickinson and others, the feldspar-rich sandstones plot in the dissected magmatic-arc field, and the feldspar-poor sandstones plot in the recycled-orogen field. Previous work indicates that detrital zircons in the plagioclase-rich sandstones were derived from a source that probably included Upper Cambrian/Lower Ordovician rocks and that feldspar-poor sandstones contain round to subround Precambrian detrital zircons. These data indicate that feldspar-rich sandstones were derived from lower Paleozoic volcanic/plutonic rocks and that feldspar-poor sandstones probably were derived from associated metasedimentary, sedimentary, and volcanic rocks. The location of the source of the sand-sized feldspathic and volcanic detritus in the Sierra City mélange is problematical. The source may be an unidentified magmatic-arc terrane located somewhere along the Pacific rim.

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