Trachyandesite of Kennedy Table, its vent complex, and post–9.3 Ma uplift of the central Sierra Nevada: Comment

Emmanuel Gabet

doi:10.1130/b36296.1

Abstract

Hildreth et al. (2021) analyzed a set of table mountains near the San Joaquin River that are capped by a 9.3 Ma trachyandesite lava flow and concluded that, since the deposition of the volcanic rocks, the table mountains have been tilted 1.07° due to uplift of the central Sierra Nevada. While Gabet (2014) suggested that, under a limited set of conditions, the size of fluvial gravels under the table mountains would support the hypothesis of postdepositional uplift, the authors claimed that their evidence is more definitive. In addition, the authors proposed that the central Sierra Nevada tilted as a rigid block. However, their analyses rely on inferences and assumptions that are not supported by field evidence.

Highlights

Hildreth et al (2021) analyzed a set of table mountains near the San Joaquin River that are capped by a 9.3 Ma trachyandesite lava flow and concluded that, since the deposition of the volcanic rocks, the table mountains have been tilted 1.07° due to uplift of the central Sierra Nevada
As Hildreth et al (2021) noted, the tilt estimate determined from the slope-azimuth relationship of the trachyandesitecapped surfaces of McKenzie Table and Table Mountain is only valid in the case where the lava flow followed a meandering channel (Fig. 1)
Perhaps a thin bedrock fin jutted up? If so, how could this bedrock fin have resisted erosion over a long period of time before the lava flow, only to be completely eroded away despite being protected by the trachyandesite deposits? The simplest explanation is that McKenzie Table and Table Mountain are remnants of a broader lava flow that buried a patchwork surface of gravels and bedrock, and erosion has since removed the trachyandesite that once filled the gap

Summary

INTRODUCTION

Hildreth et al (2021) analyzed a set of table mountains near the San Joaquin River that are capped by a 9.3 Ma trachyandesite lava flow and concluded that, since the deposition of the volcanic rocks, the table mountains have been tilted 1.07° due to uplift of the central Sierra Nevada. While Gabet (2014) suggested that, under a limited set of conditions, the size of fluvial gravels under the table mountains would support the hypothesis of postdepositional uplift, the authors claimed that their evidence is more definitive. The authors proposed that the central Sierra Nevada tilted as a rigid block. Their analyses rely on inferences and assumptions that are not supported by field evidence

TILT CALCULATIONS

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EVIDENCE FOR A RIGID BLOCK