Ben A. van der Pluijm

Dating brittle faults by the growth of authigenic illite in fault gouge allows for direct testing of kinematic models of orogenic evolution, such as in‐sequence versus out‐of‐sequence thrusting, and the presence of orogenic “pulses” of deformation on multiple thrusts simultaneously. We present illite gouge ages from five thrust faults along the Ter and Freser rivers in the south‐eastern Pyrenees fold‐and‐thrust belt dated by Ar‐Ar methods. The ages show in‐sequence thrusting for the south‐eastern Pyrenees fold‐thrust belt during the Eocene and early Oligocene, ranging from 49.5 + 4.4 Ma for the inboard Freser Antiformal Stack to 31.9 ± 3.9 Ma for the frontal L’Escala Thrust. Foreland progression of ages is preserved, although overlapping of ages of the frontal thrusts permits the interpretation of a period of more rapid fault displacement around 35 Ma. Shortening rates for the Ter‐Freser section range from 1.2–2.7 km/my, with strain rates ranging from 7.0 × 10⁻¹⁶ s⁻¹ to 1.6 × 10⁻¹⁵ s⁻¹ The latest Paleozoic ages of the cataclastically derived component inferred from the gouge dating methodology are shown to be pooled 2M₁ illite/mica ages of wall rock sediments and have geological meaning. These inferred mica ages of the thrust wallrocks in the southeastern Pyrenees indicate Hercynian‐age micas were deposited in the Southern Pyrenean foreland basin as early as the late Cretaceous. Previous thermochronometer and Δ₄₇ temperatures from syn‐faulting calcite veins constrain temperature of clay gouge formation in the Ter‐Freser section at 50–210°C, with most likely temperatures of 50–160°C, consistent with previous studies.

Isotopic studies of Canadian Rocky Mountain thrust faults preserve the timing and identity of orogenic fluids and their fault zone pathways. Using previously dated samples, we measure the O‐ and H‐isotopic compositions of fault gouge. These nearly 100% neomineralized gouges and their associated damage zones act as primary orogenic fluid pathways. As such, they provide a specific and local look into the nature of the Late Jurassic to Early Eocene orogenic plumbing system in the Alberta Rockies. Considering clay polytype stability and regional temperature conditions, we obtain a range of geofluid isotopic compositions during Jurassic‐Eocene thrust faulting: δ¹⁸O_fluid ranged from ∼−3.3 to 9.2 ± 3.2‰; δD_fluid ranged from −119 to −46 ± 13‰ VSMOW. The range of O‐ and H‐isotopic compositions reflects mixing of fluid sources, including the pervasive presence of surface‐sourced fluids (up to ∼90%). The interpreted prevalence of a surface fluid source in fault rocks is in agreement with regional isotopic trends previously observed in undated veins of fractured host rock. Our results confirm that thrust faults of the Alberta Rocky Mountains acted as major fluid‐focusing conduits during orogenic activity. We further show that these faults incorporated both deeply sourced and surface‐sourced fluids into zones of enhanced and dynamic permeability, heterogeneously distributing fluids along fault planes across the fold‐thrust belt, promoting the growth of fault‐zone weakening clay minerals.

The configuration of continents and oceans of our tectonically active planet is ever changing. Using new, high‐resolution paleogeographic base maps, we created a set of animations that examine key elements of plate tectonics. These time‐ and space‐based paleoglobe reconstructions illustrate continental rifting, continental breakup, ocean ridges and fracture zones, hot spot tracks, arc‐backarc systems, continental collision, terrane accretion, opening‐closing of ocean basins, supercontinent formation, plate velocities, and future Earth. Each animation is supported by a narrative that offers a brief topical overview, some observations to guide a user's exploration, and key references that formulated the main ideas and concepts that became the foundations of modern plate tectonics.

Seismic background noise dramatically decreased as a result of lockdown measures in place for mitigating the spread of COVID-19.

Isotopic and geochronologic investigation of authigenic, K‐bearing clays in the Appalachian Plateau of the northeastern U.S. Midcontinent yields new insights about the tectonic and diagenetic history of the North American sedimentary cover sequence. In situ texture analysis by High Resolution X‐ray Texture Goniometry indicates preservation of bedding‐parallel diagenetic fabrics with burial depths of 2–5 km, and illite mineralization temperatures are spatially variable, ranging from 80 to 190 °C, correlating to similar depths of 3–6 km. The mineralizing geofluid is surface derived, with δD values ranging from −48‰ to −72‰ (in the range of predicted Pangea meteoric fluid). In addition, we find that mineralizing fluid δD values increase away from the orogenic front, consistent with a rain shadow effect from the high elevation Appalachian orogen. The age of authigenic illite is constrained by ⁴⁰Ar/³⁹Ar geochronology to 308–318 Ma, reflecting Upper Carboniferous diagenesis. We postulate that far‐field stress transmission from continent‐continent collision created regional permeability pathways for surface fluids, altering the hydrologic architecture of the brittle crust and allowing meteoric fluid infiltration into upper crustal rocks. This interpretation challenges the popular view of tectonically forced, lateral fluid flow from the Appalachian orogen (squeegee hypothesis).

AGU's open‐access transdisciplinary science journal Earth's Future continued to grow in size and stature in 2019, with ~40% acceptance rate for ~280 new submissions that were evaluated by a similar number of external reviewers; their names are listed here.

The outgoing Editor in Chief of Earth’s Future reflects on the first 6 years of the open-access journal and the factors that have contributed to its growth and success.

Society's progress along the four corners of prepare, absorb, respond and adapt resilience square is uneven, in spite of our understanding of the foundational science and a growing sense that urgent action is needed. The resilience vignettes describe the meaning and impact of current and near‐term change in four major domains: human health impacts from air pollution, coastal inundation from sea‐level rise, damaging earthquakes in populated areas, and impacts from extreme precipitation. Given our understanding of the scientific principles, societal action, from preparation to adaption, will be critical in minimizing the negative impacts of change. The unprecedented rates of change in today's Earth system argue for urgent action in support of a resilient global society.

Peer review is one of the most important professional activities for scientists, because it ensures the quality of science that is shared with colleagues and with the world. Reviewers generously donate their time and effort with the knowledge that are key to sustaining scientific rigor. Earth's Future is fortunate to engage excellent reviewers that support the growth and reputation of our young journal as it receives and publishes high‐quality, high‐impact articles. We recognize the time, effort, and dedication that each review requires and extend a heartfelt thank you to all of our reviewers. Last year, Earth's Future received 395 peer reviews from 297 individuals that are listed below; reviewers who contributed three or more reviews are recognized in italics. Our acceptance rate remains steady at ~40%, while the number of submissions continue to increase at a healthy pace (269 in 2018).Thank you all for your important and valued contributions to our science in 2018.