Serpentinite weathering and implications for Mars

In the search for life on Mars near-surface soil environments may be important habitats for life accessible to future missions. Serpentinite rocks have been documented on Mars, as well as other clay minerals including smectite and kaolinites. Previous studies of soils formed on serpentinites on Earth have documented the formation of extensive clays. Serpentinites are additionally of interest as habitats for life such as methanogens. Here we examine weathering of serpentinites from bedrock to soil surface, as a potential route for the formation of clay minerals on Mars from abundant ultramafic minerals. We additionally test for the presence of Fe-oxidizing bacteria in weathered serpentinite rocks. Fe-oxidizing bacteria have been previously demonstrated to affect dissolution rates of ultramafic minerals, and may produce important biosignatures

Proton Spin-Lattice Relaxation of Water Molecules in Ferrous-Ferric/Agarose Gel System

Proton spin-lattice relaxation time (T1) of water in aqueous solutions of ferrous and ferric ions and in the corresponding agarose gel systems have been studied in the light of NMR relaxation theory. The theoretical analysis of 1/T1\u27s has revealed that, at the microscopic level, changes in the solvation states of paramagnetic ions in aqueous or gel environment are greater than difference in the paramagnetism between ferric and ferrous ions. The former change is the primary factor for the exhibition of radiation effect. At the phenomenological level, we have confirmed and demonstrated that: (1) Radiation effect is almost exclusively exhibited through changes in 1/T1 caused by the interactions between water proton and ferrous or ferric ions; and (2) fraction of conversion of ferrous to ferric ions induced by radiation is the “true” representation of the spatial distribution of radiation dose

Water-soluble organic aerosol in the Los Angeles Basin and outflow regions: Airborne and ground measurements during the 2010 CalNex field campaign

A particle-into-liquid sampler coupled to a total organic carbon analyzer (PILS-TOC) quantified particulate water-soluble organic carbon (WSOC) mass concentrations during the May 2010 deployment of the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter in the CalNex field study. WSOC data collected during 16 flights provide the first spatiotemporal maps of WSOC in the San Joaquin Valley, Los Angeles Basin, and outflow regions of the Basin. WSOC was consistently higher in concentration within the Los Angeles Basin, where sea breeze transport and Basin topography strongly influence the spatial distribution of WSOC. The highest WSOC levels were associated with fire plumes, highlighting the importance of both primary and secondary sources for WSOC in the region. Residual pollution layers enriched with WSOC are observed aloft up to an altitude of 3.2 km and the highest WSOC levels for each flight were typically observed above 500 m. Simultaneous ground WSOC measurements during aircraft overpasses in Pasadena and Riverside typically exhibit lower levels, especially when relative humidity (RH) was higher aloft suggestive of the influence of aerosol-phase water. This points to the underestimation of the radiative effects of WSOC when using only surface measurements. Reduced aerosol-phase water in the eastern desert outflow region likely promotes the re-partitioning of WSOC to the gas phase and suppression of processes to produce these species (partitioning, multiphase chemistry, photolytic production); as a result, WSOC is reduced relative to sulfate (but not as much as nitrate) as aerosol is advected from the Basin to the outflows

Timescale of Petrogenetic Processes Recorded in the Mount Perkins Magma System, Northern Colorado River Extension Corridor, Arizona

The Miocene Mt. Perkins Pluton is a small composite intrusive body emplaced in the shallow crust as four separate phases during the earliest stages of crustal extension. Phase 1 (oldest) consists of isotropic hornblende gabbro and a layered cumulate sequence. Phase 2 consists of quartz monzonite to quartz monzodiorite hosting mafic microgranitoid enclaves. Phase 3 is composed of quartz monzonite and is subdivided into mafic enclave-rich zones and enclave-free zones. Phase 4 consists of aphanitic dikes of mafic, intermediate and felsic compositions hosting mafic enclaves. Phases 2-4 enclaves record significant isotopic disequilibrium with surrounding granitoid host rocks, but collectively enclaves and host rocks form a cogenetic suite exhibiting systematic variations in Nd-Sr-Pb isotopes that correlate with major and trace elements. Phases 2-4 record multiple episodes of magma mingling among cogenetic hybrid magmas that formed via magma mixing and fractional crystallization at a deeper crustal. The mafic end-member was alkali basalt similar to nearby 6-4 Ma basalt with enriched OIB-like trace elements and Nd-Sr-Pb isotopes. The felsic end-member was a subalkaline crustal-derived magma. Phase 1 isotropic gabbro exhibits elemental and isotopic compositional variations at relatively constant SiO2, suggesting generation of isotropic gabbro by an open-system process involving two mafic end-members. One end-member is similar in composition to the OIB-like mafic end-member for phases 2-4; the second is similar to nearby 11-8 Ma tholeiite basalt exhibiting low epsilon (sub Nd), and depleted incompatible trace elements. Phase 1 cumulates record in situ fractional crystallization of an OIB-like mafic magma with isotopic evidence of crustal contamination by partial melts generated in adjacent Proterozoic gneiss. The Mt Perkins pluton records a complex history in a lithospheric scale magma system involving two distinct mantle-derived mafic magmas and felsic magma sourced in the crust. Mixing and fractional crystallization of these magmas at various levels in the crust generated a suite of intermediate composition magmas. U-Pb zircon SHRIMP ages of phase 1 (15.7 +/- 0.2 Ma), phase 3 (15.8 +/- 0.2 Ma) and phase 4 (15.4 +/- 0.3 Ma) document a 100-300k year timescale for petrogenetic processes recorded in the Mt Perkins magma system

The Mount Perkins block, northwestern Arizona: An exposed cross section of an evolving, preextensional to synextensional magmatic system

This is the published version. Reuse is subject to Society of Exploration Geophysicists terms of use and conditions.The steeply tilted Mount Perkins block, northwestern Arizona, exposes a cross section of a magmatic system that evolved through the onset of regional extension. New 40Ar/39Ar ages of variably tilted (0–90°) volcanic strata bracket extension between 15.7 and 11.3 Ma. Preextensional intrusive activity included emplacement of a composite Miocene laccolith and stock, trachydacite dome complex, and east striking rhyolite dikes. Related volcanic activity produced an ∼18–16 Ma stratovolcano, cored by trachydacite domes and flanked by trachydacite-trachyandesite flows, and ∼16 Ma rhyolite flows. Similar compositions indicate a genetic link between the stratovolcano and granodioritic phase of the laccolith. Magmatic activity synchronous with early regional extension (15.7–14.5 Ma) generated a thick, felsic volcanic sequence, a swarm of northerly striking subvertical rhyolite dikes, and rhyolite domes. Field relations and compositions indicate that the dike swarm and felsic volcanic sequence are cogenetic. Modes of magma emplacement changed during the onset of extension from subhorizontal sheets, east striking dikes, and stocks to northerly striking, subvertical dike swarms, as the regional stress field shifted from nearly isotropic to decidedly anisotropic with an east-west trending, horizontal least principal stress. Preextensional trachydacitic and preextensional to synextensional rhyolitic magmas were part of an evolving system, which involved the ponding of mantle-derived basaltic magmas and ensuing crustal melting and assimilation at progressively shallower levels. Major extension halted this system by generating abundant pathways to the surface (fractures), which flushed out preexisting crustal melts and hybrid magmas. Remaining silicic melts were quenched by rapid, upper crustal cooling induced by tectonic denudation. These processes facilitated eruption of mafic magmas. Accordingly, silicic magmatism at Mount Perkins ended abruptly during peak extension ∼14.5 Ma and gave way to mafic magmatism, which continued until extension ceased

Duas novas espécies de Dasmeusa Melichar (Hemiptera, Auchenorrhyncha, Cicadellidae) Two new species of the Dasmeusa Melichar (Hemiptera, Auchenorrhyncha, Cicadellidae)

<abstract language="eng">Two new species of Dasmeusa Melichar, 1926 are descri bed and illustrated: D. basseti sp.n. from Guyana and D. isabellina sp.n. from Brazil, Pará

Naturally Occurring Asbestos: Potential for Human Exposure, Southern Nevada, USA

Amphibole asbestos minerals are known human carcinogens, and many regulations have been developed to limit occupational exposure. These minerals can also occur in the natural environment, where they may be more difficult to control. We applied a diverse set of analytical methods including scanning electron microscopy/energy dispersive spectroscopy, electron probe analysis, x-ray diffraction, and field-emission scanning electron microscopy to rock, soil, and dust samples and to particles attached to lothing samples and cars. We found naturally occurring fibrous actinolite, a regulated amphibole asbestos mineral, in rock, soil, and dust that can be transported by wind, water, cars, or on clothing after outdoor recreational activities. Sources of these fibrous amphiboles are several plutons in southern Nevada and Arizona and alluvial fans emanating from asbestos-containing bedrock. The morphology of the amphibole fibers is similar to amphibole fibers found in the USEPA Superfund site at Libby, MT. We found that the morphometry of the fibrous particles in the study area did not substantially change when the original bedrock weathered into soil, and particles were eroded and transported through wind and/or water and finally settled and accumulated on natural or other surfaces. Because large populations in Boulder City, Henderson, and Las Vegas are located only a few kilometers, sometimes even only a few tens of meters, downwind from the sources, and because most of the particles are transported in suspension after they are emitted, potentially large populations in Boulder City, Henderson, and perhaps Las Vegas could be exposed. This study demonstrates a potential public health risk to several large population areas.status: publishe