TECTONIC ERRATICS - REMARKABLE EXOTIC BLOCKS EMPLACED BY THE HENDERSON THRUST, EUREKA COUNTY, NEVADA

Throughout north-central Nevada, Cambrian-Devonian, largely siliciclastic strata of the Roberts Mountains allochthon (RMA) overlie an autochthon of coeval largely carbonate strata. In Eureka County, masses of the carbonate strata also form topographic highs above the RMA, and on the east side of the Roberts Mountains they occur along a thrust fault that duplicates the RMA. We propose that the Henderson thrust, generated during the Sonoma orogeny, developed initially along the Roberts Mountains thrust at the base of the RMA and then ramped upwards and eastwards duplicating the RMA. In the process, carbonate blocks were plucked from the lower plate of the Roberts Mountains thrust and incorporated and transported in the upper plate of the Henderson thrust. Over large areas, the siliciclastic strata of the RMA in the upper plate of the Henderson thrust has been removed by erosion, but the carbonate blocks carried in the upper plate remain as topographic highs structurally overlying the siliciclastic strata of the RMA in the lower plate of the Henderson thrust. Those forming Lone Mountain and Devils Gate are several kilometers long and up to 300 m thick. By their size, number, distribution, and nature, the exotic blocks in the Roberts Mountains region are remarkable and warrant a specific term. In both process and product, they bear an analogy to glacial erratics and are termed tectonic erratics. With consideration, examples elsewhere can be recognized. Recognition of the tectonic erratics and Henderson thrust has significant implications for understanding the geology of north-central Nevada and for oil, gas, and mineral exploration strategies in the region.