Search for: All records

During plate convergence, shallow subduction or underthrusting of the lower-plate lithosphere beneath an overriding plate often results in far-field intraplate deformation, as observed in the Late Cretaceous–Paleogene North American Laramide or Cenozoic Himalayan-Tibetan orogen. Perplexingly, during this shallow-slab process, wide expanses of crust between the plate boundary and intraplate orogen do not experience significant synchronous deformation. These apparently undeformed crustal regions may reflect (1) a strong, rigid plate, (2) increased gravitational potential energy (GPE) to resist shortening and uplift, or (3) decoupling of the upper-plate lithosphere from any basal tractions. Here we review the geology of three orogens that formed due to flat slab subduction or underthrusting: the Himalayan-Tibetan, Mesozoic southeast China, and Laramide orogens. These orogens all involved intraplate deformation >1000-km from the plate boundary, large regions of negligible crustal shortening between the plate-boundary and intra-plate thrust belts, hot crustal conditions within the hinterland regions, and extensive upper-plate porphyry copper mineralization. A hot and weak hinterland is inconsistent with it persisting as an undeformed rigid block. GPE analysis suggests that hinterland quiescence is not uniquely due to thickened crust and elevated GPE, as exemplified by shallow marine sedimentation with low surface elevations in SE China. Comparison of these intracontinental orogens allows us to advance a general model, where hot orogenic hinterlands with a weak, mobile lower crust allow decoupling from underlying basal tractions exerted from flat-slab or underthrusting events. This hypothesis suggests that basal tractions locally drive intraplate orogens, at least partially controlled by the strength of the upper-plate lithosphere. 

There is a variety of published sample preparation and data acquisition techniques for Raman spectroscopy of carbonaceous material (RSCM) thermometry, which complicates systematic evaluation, assessment, and comparison of RSCM thermometry datasets. In particular, many modern studies are applying large-n RSCM analyses, acquiring high numbers of RSCM temperature estimates, often systematically distributed along transects, to quantify regional thermal structure or spatial temperature gradients associated with geologic structures. Given the significance of RSCM analyses to address numerous geologic questions in a variety of tectonic settings, it becomes imperative to develop a reproducible, standardized, and optimized workflow for RSCM analyses. Here, we introduce and test protocols for RSCM analyses using samples from the Papoose Flat pluton contact aureole, eastern California, western United States, to determine the reproducibility of automated peak-fitting and RSCM temperature estimation programs. Our RSCM results align with previously estimated temperatures derived from calcite-dolomite isotope exchange thermometry, phase equilibria temperature estimates, and quartz c-axis fabric opening-angle thermometry. Temperature estimates derived from two automated peak-fitting programs (i.e., Iterative Fitting of Raman Spectra software [IFORS] and AutoRaman_K2024) are comparable within analytical error. The RSCM temperature estimates were further validated with simple thermal modeling of pluton heat diffusion. Based on these data, we tested sample preparation and data acquisition parameters to optimize large-n workflows. Coupling large datasets at multiple structural levels with supplementary thermal models of varying complexity allows RSCM thermometry to serve as a robust method for tectonic studies.