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The key magmatic processes that lead to the formation of large magmatic-hydrothermal porphyry copper mineral deposits remain uncertain, and a particular question is why a few of these deposits, such as the Pebble porphyry Cu-Au-Mo deposit, are strongly enriched in both gold and molybdenum. This study investigated the igneous rocks of the Pebble district and obtained major and trace element compositions, Sr and Nd isotopic compositions, and zircon age and trace element data to model the origin of the ore-forming magmas.The Pebble porphyry Cu-Au-Mo deposit, one of the world's largest Cu-Au resources, formed during the final stages of regional Late Cretaceous arc magmatism (101-88 Ma) in the Southwest Alaska Range. Local pre-mineral intrusions (99-95 Ma) are dominated by alkaline compositions including monzodiorite stocks, shoshonite dikes, and monzonite porphyries, but also include lesser volumes of high-K calc-alkaline diorite and granodiorite sills. The occurrence of early alkaline magmas has been noted at other gold-rich porphyry systems, including Bingham and Kerr-Sulfurets-Mitchell. Mineralization at Pebble is associated with granodiorite to granite porphyry dikes related to the >165 km2 high-K calc-alkaline Kaskanak granodiorite batholith (91-89 Ma). Over a period of 10 m.y., Late Cretaceous melts evolved from high temperatures (930-730 °C) and modestly hydrous and oxidized conditions to relatively low temperatures (760-680 °C) and very hydrous and oxidized conditions. Collectively, all Late Cretaceous igneous rocks at Pebble contain magnetite and little or no ilmenite, are metaluminous to weakly peraluminous, and have typical arc trace element enrichments and depletions. They have moderate Sr/Y ratios (20-55) and gently sloped REE profiles (La/Yb = 5-20) that are not adakitic, which supports a source area lacking garnet that is consistent with a thin crust in southwest Alaska. Radiogenic isotopes for Late Cretaceous intrusions at Pebble have a restricted range of primitive Sr and Nd isotopic compositions (87Sr/86Sri = 0.70329-0.70424; εNdi = 4.9-6.1), which overlap with volcanic and plutonic basement rocks of the Jurassic Talkeetna Arc along the Alaska Peninsula. The Kaskanak batholith intrudes the Late Jurassic-Early Cretaceous Kahiltna flysch, and mixing models using Sr and Nd isotopes indicate that the Kaskanak batholith assimilated ≤10 wt% Kahiltna flysch in amounts that did not likely affect magma fertility. Xenocrystic zircon samples are abundant in Cretaceous pre-mineral intrusions and have U-Pb ages similar to detrital zircon samples in the Kahiltna flysch. These data support some assimilation of upper crustal Kahiltna flysch, but the dominance of Devonian-Mississippian xenocrystic zircon populations in some intrusions suggests derivation from unexposed older basement. The extraordinary endowment of Cu and Au at Pebble is inferred to result from primitive calc-alkaline and alkaline arc magmas and the hydrous and strongly oxidized conditions that suppressed the formation and fractionation of Cu- and Au-enriched sulfide melts. Furthermore, differentiation to silicic compositions was a product of extensive crystal fractionation of parental melts accompanied by minor crustal assimilation. The trace element content of the intermediate composition intrusions indicates that both hornblende and titanite fractionation processes in the mid- to shallow-crust were both required to produce the more evolved granodiorite and granite porphyry compositions. Despite the apparent lack of Mo-enriched continental crust in the region, primitive hydrous melts were produced by protracted arc magmatism and were modified by minor crustal assimilation including early alkaline magmatism, periodic recharge of mafic hydrous basalts and hybrid andesites, and fractional crystallization, which was apparently sufficient to enrich Mo in late stage felsic melts.

Tucked away in the northeastern corner of Alaska is one of the most contested landscapes in all of North America: the Arctic National Wildlife Refuge. Considered sacred by Indigenous peoples in Alaska and Canada and treasured by environmentalists, the refuge provides life-sustaining habitat for caribou, polar bears, migratory birds, and other species. For decades, though, the fossil fuel industry and powerful politicians have sought to turn this unique ecosystem into an oil field. Defending the Arctic Refuge tells the improbable story of how the people fought back. At the center of the story is the unlikely figure of Lenny Kohm (1939-2014), a former jazz drummer and aspiring photographer who passionately committed himself to Arctic Refuge activism. With the aid of a trusty slide show, Kohm and representatives of the Gwich'in Nation traveled across the United States to mobilize grassroots opposition to oil drilling. From Indigenous villages north of the Arctic Circle to Capitol Hill and many places in between, this book shows how Kohm and Gwich'in leaders and environmental activists helped build a political movement that transformed the debate into a struggle for environmental justice. In its final weeks, the Trump administration fulfilled a long-sought dream of drilling proponents: leasing much of the Arctic Refuge coastal plain for fossil fuel development. Yet the fight to protect this place is certainly not over. Defending the Arctic Refuge traces the history of a movement that is alive today-and that will continue to galvanize diverse groups to safeguard this threatened land.

Walter Harper, Alaska Native Sonilluminates the life of the remarkable Irish-Athabascan man who was the first person to summit Mount Denali, North America's tallest mountain. Born in 1893, Walter Harper was the youngest child of Jenny Albert and the legendary gold prospector Arthur Harper. His parents separated shortly after his birth, and his mother raised Walter in the Athabascan tradition, speaking her Koyukon-Athabascan language. When Walter was seventeen years old, Episcopal archdeacon Hudson Stuck hired the skilled and charismatic youth as his riverboat pilot and winter trail guide. During the following years, as the two traveled among Interior Alaska's Episcopal missions, they developed a father-son-like bond and summited Denali together in 1913.Walter's strong Athabascan identity allowed him to remain grounded in his birth culture as his Western education expanded, and he became a leader and a bridge between Alaska Native peoples and Westerners in the Alaska territory. He planned to become a medical missionary in Interior Alaska, but his life was cut short at the age of twenty-five, in thePrincess Sophiadisaster of 1918 near Skagway, Alaska.Harper exemplified resilience during an era when rapid socioeconomic and cultural change was wreaking havoc in Alaska Native villages. Today he stands equally as an exemplar of Athabascan manhood and healthy acculturation to Western lifeways whose life will resonate with today's readers.

The geologic mosaic of continental and oceanic terranes, displaced and deformed by multiple plate reorganization episodes, rapid lateral topographic variations, and heterogeneous distribution of strain throughout Alaska, all predict strong variability of crustal architecture. We present the first wide-scale model of crustal thickness based on broadband seismic data across the region that is constrained where seismic instrumentation has been deployed; dense coverage in the south-central region and more sparse coverage in the western and Arctic regions as the USArray Transportable Array (TA) is installed. Analyses of P receiver functions (PRFs) provide the first detailed look at crustal structure across all of Alaska. The variable thickness reflects inherited structure from Mesozoic to early Cenozoic convergent and extension events that in some regions is being extensively modified by ongoing convergence and collision, particularly along the active southern margin. Beneath the southern Alaska forearc to the central Alaska Range, the Yakutat slab Moho is also observed, illustrating the most recent ongoing accretionary event resulting from the collision of the Yakutat microplate. Combining three different receiver function methodologies, i.e., common conversion point stacking, receiver function stacks, and receiver gathers, for viewing and imaging P receiver functions allows for an interpretation of Alaskan crustal structure that spans multiple scales. The four-dimensional interpretation of the Alaskan crust will continue to evolve as the full TA is deployed and geologic studies are combined with the interpretations from this extensive seismic experiment.

Global warming has accelerated glacial retreat in high-elevation and high-latitude ecosystems, exposing new terrain that can undergo predictable patterns of ecosystem succession, especially in coastal areas with relatively mild climates. However, little work has been done in harsher high-elevation and inland areas where the rate of plant and microbial succession may be greatly slowed by dryness and low temperatures. The present study is the first to address microbial succession at a major glacial foreland (the Middle Fork Toklat Glacier) in the interior of Alaska. We used a spatially nested sampling regime to reveal the landscape patterns in microbial activity and biogeochemical pools during the pre-plant stage of primary succession along this high-elevation and high-latitude chronosequence. Recently deglaciated soils (0–10 years) were colonized by a diverse microbial community that included many chemoautotrophs that likely subsist on high levels of un-weathered minerals (for example, pyrite) found at this site. Rates of N-fixation and extracellular enzyme activities were very low in the youngest soils sampled, but increased during the first 20 years of succession coinciding with a decrease in TOC and C:N levels. In older soils (20–54 years), TOC and TON increased and IN became undetectable perhaps indicating N limitation. Indicators of microbial activity stopped increasing 20 years post de-glaciation and remained at levels well below those seen at lower elevation and lower latitude sites, perhaps indicating severe nutrient limitations. Stoichiometric analyses also indicated phosphorus and nitrogen limitation across the entire chronosequence, with no indication of carbon limitation of microbial activity. These results indicate that nutrient limitation, rather than the constraints of a severe climate, may be the dominant factor slowing the rate of succession at high-latitude and high-altitude glacial forelands.

Changing Paths: Travels and Meditations in Alaska 's Arctic Wilderness is an autobiographical exploration of author Bill Sherwonit's relationship with the Alaska wilderness. Written in three parts, it first describes Sherwonit's introduction to the Brooks Range and his years as an exploration geologist. Taking a step back, the author then takes us into the past to explore his childhood roots in rural Connecticut and his recognition of wild nature as a refuge. He concludes with his emergence as a nature writer and wilderness advocate. An engrossing, fascinating, and eye-opening tale of one man's life and of wilderness conceptions, this vivid description of an area of Alaska that few people get to experience is authentic and enlightening. It is an extraordinary contribution to the literature of place from one of Alaska's most accomplished nature writers.

Increment cores from the boreal forest have long been used to reconstruct past climates. However, in recent years, numerous studies have revealed a deterioration of the correlation between temperature and tree growth that is commonly referred to as divergence. In the Brooks Range of northern Alaska, USA, studies of white spruce (Picea glauca) revealed that trees in the west generally showed positive growth trends, while trees in the central and eastern Brooks Range showed mixed and negative trends during late 20th century warming. The growing season climate of the eastern Brooks Range is thought to be drier than the west. On this basis, divergent tree growth in the eastern Brooks Range has been attributed to drought stress. To investigate the hypothesis that drought‐induced stomatal closure can explain divergence in the Brooks Range, we synthesized all of the Brooks Range white spruce data available in the International Tree Ring Data Bank (ITRDB) and collected increment cores from our primary sites in each of four watersheds along a west‐to‐east gradient near the Arctic treeline. For cores from our sites, we measured ring widths and calculated carbon isotope discrimination (δ¹³C), intrinsic water‐use efficiency (iWUE), and needle intercellular CO₂ concentration (Cᵢ) from δ¹³C in tree‐ring alpha‐cellulose. We hypothesized that trees exhibiting divergence would show a corresponding decline in δ¹³C, a decline in Cᵢ, and a strong increase in iWUE. Consistent with the ITRDB data, trees at our western and central sites generally showed an increase in the strength of the temperature–growth correlation during late 20th century warming, while trees at our eastern site showed strong divergence. Divergent tree growth was not, however, associated with declining δ¹³C. Meanwhile, estimates of Cᵢ showed a strong increase at all of our study sites, indicating that more substrate was available for photosynthesis in the early 21st than in the early 20th century. Our results, which are corroborated by measurements of xylem sap flux density, needle gas exchange, and measurements of growth and δ¹³C along moisture gradients within each watershed, suggest that drought‐induced stomatal closure is probably not the cause of 20th century divergence in the Brooks Range.

We report on a paired set of manus and pes tracks from the lower part of the Upper Cretaceous Cantwell Formation in Denali National Park, Alaska, USA. The tridactyl track is bi-lobed in the ‘heel' and the morphology allows attribution to a hadrosaurid. While adult hadrosaurs typically reached body lengths of 1200 cm, the length of this Alaskan pes impression is approximately 11 cm, which provides a hip height estimate of approximately 44–45 cm for this trackmaker. The manus impression is approximately 3.6 cm wide and 2.75 cm long. While hypothesized through studies of skeletal anatomy, given the small body size of the hadrosaur that made these tracks, this paired set of impressions indicates that at least some juvenile hadrosaurs were facultative quadrupeds rather than obligatory bipeds.