COMPILATION OF NEW AND EXISTING AGE DATA INDICATES LARGE SCALE STRUCTURAL IMBRICATION IN THE MINERAL KING PENDANT, SOUTHERN SIERRA NEVADA, CALIFORNIA

The Mineral King pendant is an elongate, northwest-striking, steeply dipping assemblage of Late Tr to Cretaceous metavolcanic and metasedimentary rocks surrounded by massive granitic plutons of the Cretaceous Sierra Nevada batholith. Pendant rocks have well developed bedding-parallel foliation and steeply plunging stretching lineation. Lithologic units are interleaved and discontinuous in map view, due to some combination of original facies changes and superimposed structural imbrication.

We compile new and existing U-Pb age data from SHRIMP-RG analyses at Stanford University/USGS SUMAC lab and LA-ICP-MS analyses from Michigan State University for the Mineral King pendant on a modified geologic map to highlight related units, as well as stratigraphic and structural discontinuities between these units. The age data suggest the presence of two distinct stratigraphic assemblages: (1) a Late Tr to Jr assemblage of predominantly marine sedimentary rocks and andesitic to dacitic volcanic rocks ranging from 236 Ma to 184 Ma; and (2) a mid- to Late Cretaceous assemblage of rhyolitic ash flow tuffs interlayered with shallow marine sedimentary rocks ranging from 136 Ma to ~100 Ma.

The map pattern and age data indicate a combination of original stratigraphic discontinuities and structural imbrication. Interleaving of units may have transpired by (1) strike-slip faulting of vertically dipping units in a broad shear zone, displacing lensoidal blocks; (2) fold-thrust deformation followed by ductile flattening; (3) isoclinal folding and bedding transposition. Strike-slip faulting has little supporting evidence because there are no visible shear indicators. Fold-thrust imbrication and ductile flattening could have occurred during emplacement of granitic plutons, although no evidence for thrust faulting has been observed. Isoclinal folding and bedding transposition driven by pluton inflation and downward return flow of surrounding country rock, is supported by the common presence of map and outcrop-scale folding in pendant rocks. We conclude that in the Mineral King pendant structural imbrication by a combination of fold-thrust deformation followed by ductile flattening, and/or isoclinal folding and bedding transposition interleaved the pendant rocks resulting in an incoherent stratigraphic package.