Description
The Duncan Peak chert and Lang sequence have been recognized as the two lower tectonostratigraphic units in the Shoo Fly Complex. However, detailed mapping in the Shoo Fly Complex in the area of Lake Spaulding indicates that these units can be subdivided into, from east to west, the Zion Hill sequence, the Fuller Lake sequence, the Black Oak Springs sequence, and the Lang sequence. Contacts between these units are poorly exposed, but are inferred to be depositional with the exception of the contact between the Fuller Lake and Black Oak Springs sequences. This latter contact is an overturned thrust fault. Well bedded sandstone turbidites and argillites make up the Zion Hill sequence. The latter unit overlies the Fuller Lake sequence which is composed of complexly folded bedded chert and argillite with lesser amounts of sandstone and siltstone. The Black Oak Springs sequence contains discontinuous lenses of limestone, and abundant sandstone turbidites, bedded chert, and argillite. The Lang sequence is composed of a thick succession of sandstone turbidites. Sedimentary facies in the Zion Hill, Black Oak Springs, and Lang sequences suggest that deposition occurred in the middle to outer fan parts of a submarine fan system. Petrologic analysis of sandstones suggest a continental source. U-Pb detrital zircon analysis indicate that some source rocks for sandstones in the Zion Hill sequence were Proterozoic in age. Between Fall Creek Mountain and Zion Hill, the Shoo Fly Complex is unconformably overlain by the Upper Devonian Grizzly Formation which is a conglomerate-breccia. Truncating the Grizzly Formation and the Shoo Fly Complex along the eastern side of the study area is the 165 +/- 2m.y. Emigrant Gap pluton; a hornblende-biotite diorite. Based on preliminary XRF data the Emigrant Gap pluton appears uniform in composition. Bounding the west side of the study area is the 375 +/- 10 m.y. Bowman Lake batholith. In the area of Fall Creek Mountain, the Sierra Buttes and Grizzly Formations are stratigraphically upright and dip to the east. Further to the south, in the area of Blue Lake, these formations are overturned and dip to the west. A tear fault is inferred to separate the eastward dipping units from the westward dipping units, and may be the result of the intrusion of the Emigrant Gap pluton. Two phases of deformation in the SFC, D-1 and D-2, are recognized in the study area. D-1 structures are suggested to be the result of accretion in an early Paleozoic subduction complex that developed along a continental margin. D-2 structures are attributed to the emplacement of the Emigrant Gap pluton. Data from this study are consistent with models which portray the Shoo Fly Complex as part of an accretionary system that developed close enough to a continental landmass to have received detritus derived from it. The continental landmass may have been located in North America; however, data presented here do not uniquely constrain the source of continental detritus in the Shoo Fly Complex.
