A small 33±0.8 Ma lamproite pluton is exposed in the midst of a 23-26 Ma basalt-rhyolite province in Middle Park, NW Colorado. It contains abundant phlogopite phenocrysts in a fine-grained groundmass ...of analcime pseudomorphs after leucite, biotite, potassic richterite, apatite, ilmenite and accessory diopside. The phlogopite phenocryst cores contain ∼4 wt.% TiO2, 1% Cr2O3 and 0.2% BaO. The smallest groundmass biotites have normal pleochroism but compositions unlike any previously reported, with ∼2% Al2O3, ∼8% TiO2 and F<1.5%. Apart from those elements affected by leucite alteration, both the elemental and isotopic composition of this lamproite are close to those of the Leucite Hills, Wyoming. Its Nd-isotopic model age (TDM = 1.6 Ga) is outside the Leucite Hills range but within that of other Tertiary strongly potassic magmatism in the region underlain by the Wyoming craton. Evidence from both teleseismic tomography and the mantle xenoliths within other western USA mafic ultrapotassic igneous suites shows that the total lithospheric thickness beneath NW Colorado was probably ∼150-200 km at 33 Ma, when the Middle Park lamproite was emplaced. This is an important constraint on tectonomagmatic models for the Cenozoic evolution of this northernmost part of the Rio Grande rift system.
The isotopic difference between modern Indian Ocean and Pacific or North Atlantic Ocean ridge mantle (e.g. variably lower 206Pb/204Pb for a given εNd and 208Pb/204Pb) could reflect processes that ...occurred within a few tens of millions of years preceding the initial breakup of Gondwana. Alternatively, the Indian Ocean isotopic signature could be a much more ancient upper-mantle feature inherited from the asthenosphere of the eastern Tethyan Ocean, which formerly occupied much of the present Indian Ocean region. Age-corrected Nd, Pb, and Sr isotopic data for 46–150 Ma seafloor lavas from sites in the western Indian Ocean and ocean-ridge-type Tethyan ophiolites (Masirah, Yarlung–Zangpo) reveal the presence of both Indian-Ocean-type compositions and essentially Pacific–North Atlantic-type signatures. In comparison, Jurassic South Pacific ridge basalts from Alexander Island, Antarctica, possess normal Pacific–North Atlantic-type isotopic ratios. Despite the very sparse sampling of old seafloor, the age-corrected εNd(t) values of the old Indian Ocean basalts cover a greater range than seen for the much more thoroughly sampled present-day spreading axes and islands within the Indian Ocean (e.g. 18 εNd units for basalts in the 60–80 Ma range vs 15 εNd units for 0–10 Ma ones). The implications of these results are that the upper mantle in the Indian Ocean region is becoming increasingly well mixed through time, and that the Indian Ocean mantle domain may not greatly pre-date the age of earliest spreading in the Indian Ocean.
For ground penetrating radar (GPR), smaller antennas would provide considerable practical advantages. Some of which are: portability; ease of use; and higher spatial sampling. A theoretical ...comparison of
the fundamental limits of a small electric field antenna and a small magnetic field antenna shows that the minimum Q constraints are identical. Furthermore, it is shown that only the small magnetic
loop antenna can be constructed to approach, arbitrarily closely, the fundamental minimum Q limit. This is achieved with the addition of a high permeability material which reduces energy stored in
the magnetic fields. This is of special interest to some GPR applications. For example, applications requiring synthetic aperture data collection would benefit from the increased spatial sampling offered
by electrically smaller antennas. Low frequency applications may also benefit, in terms of reduced antenna dimensions, by the use of electrically small antennas. Under these circumstances, a magnetic type
antenna should be considered in preference to the typical electric field antenna. Numerical modeling data supports this assertion.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Knowing the spatial scales at which effective management can be implemented is fundamental for conservation planning. This is especially important for mobile species, which can be exposed to threats ...across large areas, but the space use requirements of different species can vary to an extent that might render some management approaches inefficient. Here the space use patterns of seabirds were examined to provide guidance on whether conservation management approaches should be tailored for taxonomic groups with different movement characteristics. Seabird tracking data were synthesised from 5419 adult breeding individuals of 52 species in ten families that were collected in the Atlantic Ocean basin between 1998 and 2017. Two key aspects of spatial distribution were quantified, namely how far seabirds ranged from their colony, and to what extent individuals from the same colony used the same areas at sea. There was evidence for substantial differences in patterns of space-use among the ten studied seabird families, indicating that several alternative conservation management approaches are needed. Several species exhibited large foraging ranges and little aggregation at sea, indicating that area-based conservation solutions would have to be extremely large to adequately protect such species. The results highlight that short-ranging and aggregating species such as cormorants, auks, some penguins, and gulls would benefit from conservation approaches at relatively small spatial scales during their breeding season. However, improved regulation of fisheries, bycatch, pollution and other threats over large spatial scales will be needed for wide-ranging and dispersed species such as albatrosses, petrels, storm petrels and frigatebirds.
The Menengai volcano is composed almost entirely of strongly peralkaline, Si‐oversaturated trachytes. No mafic or intermediate products have yet been identified. The volcano has had a complex ...geochemical evolution, resulting from the interplay of magma mixing, crystal fractionation and liquid state differentiation. The controlling mechanism at any time was related to the growth stage of the complex, the presence of volatile gradients in the chamber, and the distribution of magma densities in the chamber. Prior to a major ash flow eruption, the magma reservoir was growing by the addition and mixing of two or more trachytic melts, only slightly different in composition. A volatile‐rich cap eventually separated from the lava‐forming zone and became compositionalIy zoned by liquid state processes. In late pfecaldera times, trachyte magma was able to penetrate into the cap zone, resulting in the eruption of mixed magma. The first Menengai ash flow tuff was erupted from a compositionally zoned magma chamber which showed strong roofward enrichment in Fe, Mn, Cs, Hf, Nb, Ni, Pb, Rb, Ta, Th, U, Y, Zn, Zr, and the REE (including Eu) and probably also Na, Cl, and F, and roofward depletion in Al, Mg, Ca, K, Ti, P, Ba, and Sc. Observed enrichment factors of up to 5 make this one of the most strongly zoned ash flow units yet recorded. Zonation was achieved by liquid state differentiation, probably involving volatile transfer and thermodiffusion, and minor crystal fractionation. After a period of rehomogenization of the magma remaining in the upper parts of the chamber, the second Menengai ash flow tuff was erupted, with formation of the present caldera. This unit is also compositionalIy zoned, although with lower observed enrichment factors than the first sheet. Caldera collapse was followed by convective overturn within the magma chamber and the rise to the roof zone of a Ba‐rich magma from a level not tapped by the as flow. Enrichment of volatiles in this zone resulted in the establishment of a stable density interface between an upper, tuff‐producing zone and the lower, lava‐forming zone. In the latter, 25% crystallization of syenite took place against the side walls. Crystallization in the tuff‐forming zone was more extensive (75%) and produced a series of chemically evolved tuffs. At some critical stage, liquid state processes became dominant in both zones and compositional variations comparable to those in the ash flow sheets were established. Some mixing of the upper and lower zone magmas may have occurred relatively recently. The Menengai volcano provides evidence of the development by liquid state mechanisms of extensive compositional zonations through thicknesses in excess of 102 m in times of 102–103 years. It also gives unique information on the senses and amounts of elemental enrichments and depletions during liquid state differentiation of trachytic magma.
ABSTRACT
Compositions and distributions of mafic dykes in the Antarctic Peninsula continental arc show that tapping of several mantle sources was tectonically controlled. In the Cretaceous to ...Tertiary, between 135 Ma and 55 Ma, calc‐alkaline dykes intruded the arc. In the late Cretaceous, however, between 95 Ma and 65 Ma, there was a pulse of compositionally diverse magmatism. This change resulted from collision of an ocean spreading centre with the trench. As a consequence, non‐partitioned dextral transtensional shear in the overriding plate became partitioned into strike‐slip and extensional domains. Calc‐alkaline magmatism was, therefore, replaced by strike‐slip‐related shoshonitic magmatism towards the rear‐arc and extensionrelated tholeiitic magmatism towards the fore‐arc. OIB‐like dykes were emplaced because of the break in otherwise continuous subduction. During the early Tertiary subduction continued but ceased after a late Tertiary ridge‐trench collision.
Seabirds are among the most threatened birds as a result of acute exposure to many anthropogenic threats. Their effective conservation requires a detailed understanding of how seabirds use marine ...habitats. Recently, one of the largest no-take marine reserves in the Atlantic was designated in tropical waters surrounding Ascension Island, on which the largest Atlantic population of sooty terns (
Onychoprion fuscatus
) breeds. Although they are the most abundant tropical seabird, they appear to have suffered marked population declines on Ascension Island as they have elsewhere. Here, we describe year-round movements and habitat use of male and female sooty terns between 2011 and 2015. On average, birds traveled 47,000 km during their 8 months of migration, during which they remained within 2,900 km of the island. They spent most of the day and night in flight, only touching down briefly on the ocean most likely to feed. Habitat suitability models successfully predicted foraging ranges of birds and their at-sea distributions varied considerably between seasons, years and sexes. Considerable variation in range overlap between birds and the new marine protected area (MPA) suggests that similar such studies of other marine taxa are urgently needed. The range of sooty terns mainly falls in the high seas outside of the new MPA, highlighting the very large areas that many oceanic seabirds forage across and the challenges their conservation present.
Abstract
The rock association of minette with silicic lavas and intrusions (granites, syenites, dacites) is a common geologic feature in both collisional and extensional tectonic settings. ...Considerable doubt exists as to whether a genetic link exists between these mafic and silicic rocks. We describe a Miocene sill from NW Colorado which is a clear example of a mixed magma consisting of originally-liquid inclusions of minette in a silicic trachydacite host. Chemical and Sr, Nd and Pb isotopic data are consistent with derivation of the silicic host magma of the sill dominantly by fractional crystallization of the minette magma. Correlations between the elemental compositions of the rock types and their Sr and Nd isotopic ratios imply minor assimilation of continental crust with relatively low values of both
87
Sr/
86
Sr and
143
Nd/
144
Nd, concomitantly with fractional crystallization. The parental minette magma was probably derived by partial melting of subcontinental lithospheric mantle. While the sill was emplaced in a rift-like tectonic setting, the chemical and isotopic composition of the lithosphere-derived minette magmas (and hence the silicic fractionates) was largely independent of this setting, but dependent upon the composition and age of the lithospheric mantle and crust.
The lower Miocene lavas (23–20 Ma) of the Flat Tops volcanic field, NW Colorado, are one of the earliest and most voluminous phases of magmatic activity associated with the development of the Rio ...Grande rift. Flow‐by‐flow collections of the lavas at Flander, Trappers Lake, provide evidence for complex open‐system magma chamber processes. Geochemically, the lavas range from basalts to shoshonites and have concentrations of major and compatible trace elements that are buffered at higher levels than expected for simple fractional crystallisation, cyclic repetitions (at least five) in the geochemical stratigraphy of the Flander lavas suggest that they are the result of replenishment fractional crystallization (RFC). Variations in some incompatible trace element ratios, such as Ta/Yb and LaN /YbN, and radiogenic isotopes (87Sr/86Sr= 0.70458–0.70607 143Nd/ 144Nd= 0.51226–0.51241) suggest that the lavas have also been contaminated by approximately 10% of Proterozoic 87Sr‐rich upper‐crust. In addition, anomalously K‐rich lava flows with low 87Sr/86Sr occur close to the base and at the top of the succession. It is argued that these are the products of mixing between magmas within the Flat Tops reservoir system and an influx of strongly potassic melt from lithospheric mantle; without subsequent geochemical overprint by the effects of crustal contamination and RFC. All of the lavas have incompatible trace element ratios that mostly resemble those of calc‐alkaline basalts; e.g., their chondrite‐normalized patterns have troughs at Nb and Ta. These features could result from several alternative processes, such as melting within convecting mantle above a low‐angle subducted slab; reaction between various asthenospheric melts and overlying lithospheric mantle; and fusion of metasomatized lithospheric mantle as a result of decompression during regional extension.
To investigate the frequency of both actual and missed transportation among lower-income older adults within the context of physical health status.
This study utilizes an ecological momentary ...assessment (EMA) design. EMA occurs in real world settings, using real-time data collection with repeated assessments. Ten adults (70% female, 50% African American, mean age = 69.56, SD = 3.75) logged trips completed and trips missed, including destinations and impact on perceived well-being in a custom-designed app, MyAmble, for 14 days. Results: Participants logged an average of about 5 trips, the plurality to grocery stores. The ten participants logged a total of 95 daily trip plans throughout the two-week study period. Of those trips, more than half were planned (n = 54, 56.8%%), and most were reported as very important to participants (n = 59, 71.1%). Trip destinations most often included the grocery store (n = 28, 29.5%), medical appointments (n = 11, 11.6%), social visits (n = 10, 10.5%), and the bank (n = 12, 12.6%). Nearly half of grocery store trips were unplanned, and a fourth of planned grocery store trips were missed. The pattern was similar for doctor appointment destinations.
Findings show that older adults were unable to complete nearly 16% of the trips that they planned during the two-week study period, or nearly one in five trips. This rate of missing desired transportation is troubling given the destinations and the self-reported importance of the planned trips and suggests that individuals may be missing out on opportunities that directly relate to their health. Findings imply that healthy, livable communities must offer access to equitable, quality transportation. Future research ought to also investigate the link between transportation mobility, access to nutritious food, and its impact on health promotion and disease management.
•The field test of MyAmble reveals that it can capture data related to completed and missed trips and latent demand.•The preponderance of grocery store trips underscores the critical role that transportation may play in and food security.•Individuals are missing out on opportunities that directly relate to their health.•Results suggest that missing out on planned activities may be detrimental to one’s quality of life.•Public partnerships and/or subsidization of ride-hailing or micro transit services represent possible solutions that merit additional study.
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