Noble Gas Geochemistry Minoru Ozima, Frank A. PodosekNoble Gas Geochemistry discusses the fundamental concepts of using noble gases to solve problems in the earth and planetary sciences. The discipline offers a powerful and unique tool in resolving problems such as the origin of the solar system, evolution of the planets, earth formation, mantle evolution and dynamics, atmospheric degassing and evolution, ocean circulation, dynamics of aquifer systems, and numerous applications to other geological problems. This book gives a comprehensive description of the physical chemistry and cosmochemistry of noble gases, before leading on to applications for problem-solving in the earth and planetary sciences. There have been many developments in the use of the noble gases since publication of the first edition of this book in 1983. This second edition has been fully revised and updated. The book will be invaluable to graduate students and researchers in the earth and planetary sciences who use noble gas geochemistry techniques.

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Upper Cenozoic terrestrial basin-fill sedimentary and basic volcanic rocks are common in the 20,700 km 2 Basalt area, which includes parts of the Gore, Sawatch, and southern Park Ranges, Elk Mountains, Grand Mesa, and White River Plateau. Principally on the basis of whole-rock K-Ar ages from basalt flows, the rocks can be placed in four groups. Group 1 rocks attain a thickness of 210 m and range in age from 24 to 20 m.y. (early Miocene). They consist primarily of flows of alkali-olivine basalt or of basalt flows interlayered with cross-bedded sandstone of the Browns Park Formation. Group 2 rocks, 14 to 9 m.y. old (late Miocene and perhaps early Pliocene), attain a maximum thickness of 180 m and are composed largely of basalt, basaltic andesite, and fine-grained tuffaceous fluvial, lacustrine, and eolian sedimentary rocks containing a rich vertebrate fauna indicative of a semiarid climate and a steppe vegetation. Toward the end stages of the accumulation 155 on July 6, 2015 memoirs.gsapubs.org Downloaded from 156 LARSON AND OTHERSof group 2 rocks, about 10 m.y. ago, the region was subjected to major tectonism, including uplift, reactivation of some Laramide (Late Cretaceous-early Tertiary) structural features, and creation of new warps, folds, and faults. The initiation of the Colorado River system apparently occurred at that time in response to increased precipitation stemming from an increase in elevation and relief. Downcutting began at this time and has continued intermittently to the present. By about 8 m.y. ago (late Miocene or early Pliocene, depending on boundary interpretation), the Roaring Fork River had downcut 600 m and had formed a broad flood plain, upon which thin alkali-olivine basalt flow units (group 3 rocks) were erupted. Downcutting appears to have been slow between about 8 and 1.5 m.y. ago; since then, an additional 300 m of valley deepening has occurred. Sporadic volcanism since 1.5 m.y. has accounted for several small cinder cones and flows of nephelinenormative alkali basalt (group 4 rocks); the last eruption occurred about 4,000 yr ago. on July 6, 2015 memoirs.gsapubs.org Downloaded from LATE CENOZOIC BASIC VOLCANISM, NORTHWESTERN COLORADO 167structural and physiographic development of this region during the latter half of Cenozoic time. The area under discussion covers approximately 20,700 km 2 and includes the White River Plateau, parts of the Park, Gore, and Sawatch Ranges, the Elk Mountains, and Grand Mesa (see Fig. 1 for pertinent geographic names). For simplification, this area is hereafter termed the Basalt area, in reference to the centrally located town of Basalt. The name is particularly appropriate because most of the conclusions in this paper have resulted from investigation of basic lava flows.A generalized geologic map of the Basalt area is shown in Figure 2. Because the scale is small, many geologic elements have been eliminated or minimized: faults and fold axes have been omitted, and pre volcanic rocks are simply designated as Precambrian, Paleozoic, Mesozoic, and Tertiary...

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The nitrogen in lunar soils is correlated to the surface and therefore clearly implanted from outside. The straightforward interpretation is that the nitrogen is implanted by the solar wind, but this explanation has difficulties accounting for both the abundance of nitrogen and a variation of the order of 30 per cent in the 15N/14N ratio. Here we propose that most of the nitrogen and some of the other volatile elements in lunar soils may actually have come from the Earth's atmosphere rather than the solar wind. We infer that this hypothesis is quantitatively reasonable if the escape of atmospheric gases, and implantation into lunar soil grains, occurred at a time when the Earth had essentially no geomagnetic field. Thus, evidence preserved in lunar soils might be useful in constraining when the geomagnetic field first appeared. This hypothesis could be tested by examination of lunar farside soils, which should lack the terrestrial component.

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Re‐examination of the sintering process of Akimoto, Katsura, and Yoshida indicates that titanomagnetite made according to this process does not undergo low‐temperature oxidation to a single‐phase cation‐deficient spinel (γ‐titanomaghemite) but instead oxidizes and unmixes to Mtss and Ilss at about 350–400°C, and Mtss, Ht, rutile, and pseudobrookite at about 600°C. Since this unmixing (high‐temperature oxidation) reduces the Ti content in the spinel phase, the saturation magnetization Js and Curie point increase up to 4 μB (Bohr magnetons at 0°K) and 580°C, respectively, and the lattice parameter decreases down to 8.39 A. From experimental results on synthesized titanomagnetite and titanomaghemite, we conclude that the irreversible increase in Js and Curie point of some submarine basalts during heating in air or in vacuo is the result of unmixing of Ti‐rich titanomagnetite and/or breakdown of γ‐titanomaghemite into Mtss, Ht, pseudobrookite, and rutile. This conclusion is supported by microscopic obervation and chemical and X‐ray analysis.

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