New Timing and Depth Constraints for the Catalina Metamorphic Core Complex, Southeast Arizona

The Santa Catalina-Tortolita-Rincon Mountains of Southeast Arizona are a classic metamorphic core complex (MCC) and represent footwall exposures of crustal rocks exhumed by a detachment system. This study presents new evidence for the formation of the majority of ductile deformation during the Eocene (similar to 46 Ma), synchronous with the emplacement of the regionally significant Wilderness Sills Suite (57-45 Ma). The evidence is provided by Eocene U-Pb ages of syn- to late kinematic dikes emplaced in the principal ductile mylonitic fabric of the Catalina forerange, earlier than the brittle normal fault system and the formation of Tucson basin beginning with the latest Oligocene. Well-documented shear sense indicators may not reflect extension at that time (Eocene), but more likely the direction of crustal flow now rotated during later extension. Muscovite-plagioclase Rb-Sr isochron ages of three mylonitic rocks are all clustered around 34 Ma, which is inferred to be the last age when these rocks were being deformed under ductile conditions following the emplacement of the Wilderness Sills Suite and various related dikes. Biotite-plagioclase Rb-Sr ages on the same rocks demonstrate that the section cooled below similar to 300 degrees C at 25-26 Ma during the development of normal faulting. Normal faulting was synchronous with the emplacement of the Catalina Intrusive Suite. New U-Pb age results for Catalina Intrusive Suite indicate a combined mean age of 24.9 Ma. Chemical compositions of hornblende-plagioclase pairs were obtained on six Catalina Intrusive Suite samples; depth estimates for the emplacement of the Catalina Intrusive Suite average of about 6 km. These results suggest that the exposed Catalina ductile detachment system was at about 5 km beneath the surface at 25 Ma. These new data bring new light into the development of this core complex and suggest that the similarity in orientations ofprincipalductile and brittle fabrics at the Catalina MCC locality are coincidental. Neither was the principal ductile fabric developed during the low-angle normal faulting of the latest Oligocene nor was this exposed section a midcrustal one at that time. Transient, pluton emplacement-enhanced, and extension-related ductile deformation at shallow crustal levels operated locally at similar to 25 Ma but that does not account for the development of the majority of the Catalina MCC mylonites.6 month embargo; first published online 15 August 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Colorado geoid computation experiment: overview and summary

The primary objective of the 1-cm geoid experiment in Colorado (USA) is to compare the numerous geoid computation methods used by different groups around the world. This is intended to lay the foundations for tuning computation methods to achieve the sought after 1-cm accuracy, and also evaluate how this accuracy may be robustly assessed. In this experiment, (quasi)geoid models were computed using the same input data provided by the US National Geodetic Survey (NGS), but using different methodologies. The rugged mountainous study area (730 km × 560 km) in Colorado was chosen so as to accentuate any differences between the methodologies, and to take advantage of newly collected GPS/leveling data of the Geoid Slope Validation Survey 2017 (GSVS17) which are now available to be used as an accurate and independent test dataset. Fourteen groups from fourteen countries submitted a gravimetric geoid and a quasigeoid model in a 1′× 1′ grid for the study area, as well as geoid heights, height anomalies, and geopotential values at the 223 GSVS17 marks. This paper concentrates on the quasigeoid model comparison and evaluation, while the geopotential value investigations are presented as a separate paper (Sánchez et al. in J Geodesy 95(3):1. https://doi.org/10.1007/s00190-021-01481-0, 2021). Three comparisons are performed: the area comparison to show the model precision, the comparison with the GSVS17 data to estimate the relative accuracy of the models, and the differential quasigeoid (slope) comparison with GSVS17 to assess the relative accuracy of the height anomalies at different baseline lengths. The results show that the precision of the 1′ × 1′ models over the complete area is about 2 cm, while the accuracy estimates along the GSVS17 profile range from 1.2 cm to 3.4 cm. Considering that the GSVS17 does not pass the roughest terrain, we estimate that the quasigeoid can be computed with an accuracy of ~ 2 cm in Colorado. The slope comparisons show that RMS values of the differences vary from 2 to 8 cm in all baseline lengths. Although the 2-cm precision and 2-cm relative accuracy have been estimated in such a rugged region, the experiment has not reached the 1-cm accuracy goal. At this point, the different accuracy estimates are not a proof of the superiority of one methodology over another because the model precision and accuracy of the GSVS17-derived height anomalies are at a similar level. It appears that the differences are not primarily caused by differences in theory, but that they originate mostly from numerical computations and/or data processing techniques. Consequently, recommendations to improve the model precision toward the 1-cm accuracy are also given in this paper

The International Criminal Court and the rebels’ commitment problem

This article argues against the common view that the International Criminal Court (ICC) prevents peace since rebels will not accept accountability. In the presence of an international criminal authority, accountability may be unavoidable. This is true for rebels, but also for state agents. Should the government renege on agreed provisions, it risks ICC attention on its own actors, including into the future. In this way, the ICC functions as a permanent third-party guarantor of the provisions and reduces the commitment problem for the rebels, conditional on certain circumstances. A case study of Colombia finds support for the theoretical proposals.This work was supported by the AXA Research Fund [2016-SE-POSTDOC] and Agència de Gestió d’Ajuts Universitaris i de Recerca [2014-ICIP

Colorado geoid computation experiment: overview and summary

The primary objective of the 1-cm geoid experiment in Colorado (USA) is to compare the numerous geoid computation methods used by different groups around the world. This is intended to lay the foundations for tuning computation methods to achieve the sought after 1-cm accuracy, and also evaluate how this accuracy may be robustly assessed. In this experiment, (quasi)geoid models were computed using the same input data provided by the US National Geodetic Survey (NGS), but using different methodologies. The rugged mountainous study area (730 km × 560 km) in Colorado was chosen so as to accentuate any differences between the methodologies, and to take advantage of newly collected GPS/leveling data of the Geoid Slope Validation Survey 2017 (GSVS17) which are now available to be used as an accurate and independent test dataset. Fourteen groups from fourteen countries submitted a gravimetric geoid and a quasigeoid model in a 1′× 1′ grid for the study area, as well as geoid heights, height anomalies, and geopotential values at the 223 GSVS17 marks. This paper concentrates on the quasigeoid model comparison and evaluation, while the geopotential value investigations are presented as a separate paper (Sánchez et al. in J Geodesy 95(3):1. https://doi.org/10.1007/s00190-021-01481-0, 2021). Three comparisons are performed: the area comparison to show the model precision, the comparison with the GSVS17 data to estimate the relative accuracy of the models, and the differential quasigeoid (slope) comparison with GSVS17 to assess the relative accuracy of the height anomalies at different baseline lengths. The results show that the precision of the 1′ × 1′ models over the complete area is about 2 cm, while the accuracy estimates along the GSVS17 profile range from 1.2 cm to 3.4 cm. Considering that the GSVS17 does not pass the roughest terrain, we estimate that the quasigeoid can be computed with an accuracy of ~ 2 cm in Colorado. The slope comparisons show that RMS values of the differences vary from 2 to 8 cm in all baseline lengths. Although the 2-cm precision and 2-cm relative accuracy have been estimated in such a rugged region, the experiment has not reached the 1-cm accuracy goal. At this point, the different accuracy estimates are not a proof of the superiority of one methodology over another because the model precision and accuracy of the GSVS17-derived height anomalies are at a similar level. It appears that the differences are not primarily caused by differences in theory, but that they originate mostly from numerical computations and/or data processing techniques. Consequently, recommendations to improve the model precision toward the 1-cm accuracy are also given in this paper