EVALUATING THE SPATIAL EXTENT OF ANOMALOUS UPPER-CRUSTAL HEATING IN THE NEVADAPLANO: INSIGHTS FROM RSCM THERMOMETRY IN THE FISH CREEK RANGE IN EAST-CENTRAL NEVADA

The thermal conditions of orogenic crust can exert a 1^st-order control on the style and magnitude of contractional strain accommodation. During the Late Cretaceous (~70-90 Ma), the hinterland plateau of the Cordilleran orogen in eastern Nevada (the ‘Nevadaplano’) experienced a punctuated tectonothermal event that locally resulted in greenschist- and amphibolite-facies metamorphism at upper-crustal levels. This event produced paleo-peak thermal field gradients as high as 50-60 °C/km, and has been interpreted as the shallow thermal expression of lower-crustal anatexis triggered by delamination of mantle lithosphere. However, the temperature conditions and spatial extent of anomalous upper-crustal heating, which are both fundamental parameters for understanding the thermal evolution of the Nevadaplano, are poorly constrained. The goal of this study is to quantify the peak temperatures attained by rocks in the Fish Creek Range in east-central Nevada, to evaluate the western extent of anomalous upper-crustal heating. The Fish Creek Range exposes Cambrian to Permian sedimentary rocks that restore to pre-deformational depths up to 7 km. We collected 7 samples of limestone and dolostone from Cambrian and Ordovician units in the Fish Creek Range, which span paleo-depths of ~7-4 km. Peak metamorphic temperatures were collected from each sample utilizing the Raman spectroscopy of carbonaceous material (RSCM) thermometer. The structurally lowest four samples, which span between 6.9 and 5.8 km paleo-depths, yielded temperatures that decrease upward from 217 ± 28 °C to 178 ± 28 °C. The highest three samples, which span between 6.6 and 4.3 km paleodepths, yielded temperatures between 210 ± 30 °C and 234 ± 28 °C. The lowest 4 samples are best-fit by a peak thermal field gradient of ~30 °C/km. The highest 3 samples fall above this gradient, which is interpreted as the result of hydrothermal fluids associated with the mineralized Hoosac normal fault system. The 30 °C/km gradient obtained for the deepest crustal levels indicates that the Fish Creek Range did not experience the anomalous upper-crustal heating documented in ranges further to the east in Nevada, and therefore may constrain the western extent of the Late Cretaceous tectonothermal event. This data will guide further research on the thermal history of the Nevadaplano.